Malaria No More Japan
2022 repor t

Food Security and Human Health:the Link Between Rice and Malaria in Sub-Saharan Africa

For ward
We are pleased to bring you this report on the link between rice cultivation andmalaria risk in sub-Saharan Africa and the relation between food security and risks ofWhat is Malaria?
Mosquitoes kill more people than any other animal.
An African child dies of malaria every minute.

infectious diseases.This publication was written at the request of The RBM (Roll Back
Malaria) Partnership to End Malaria, a global platform of more than 500 partners, in-Malaria is the most serious mosquito-borne disease. Malaria is one ofcluding private sector, NGOs, community organizations, foundations, research andthe three major infectious diseases, along with HIV/AIDS and tuberculosis.

academic institutions, to coordinate zero malaria activities, and with funding from theUnited Nations Foundation.Climate change and increasing economic activities with a

It is caused by a parasite called Plasmodium falciparum, and is trans-

growing population are causing ecological changes that are affecting our life andmitted by the bite of a mosquito infected with the malaria parasite. The

social infrastructure. In particular, it has long been pointed out that environmental

disease is transmitted when the Plasmodium falciparum enters the humanchanges can affect ecosystems and increase infectious disease risks. This reportbloodstream through the mosquito's salivary glands during the blood-suck-focuses on a literature review of the relation between ecosystem changes associateding process necessary for the female anopheline mosquito to raise its

with the development of paddy rice cultivation in sub-Saharan Africa and the poten-

eggs. The four endemic protozoa that cause malaria in humans are Tropi-

tial for increased infectious disease risks it poses.

cal malaria (Plasmodium falciparum malaria), Tertian malaria (P. vivax malaria), Quartan malaria (P. malariae malaria) and Ovale malaria (P. ovale

Seven years after the United Nations General Assembly unanimously adopted

malaria), although several other types of Plasmodium falciparum such as"Transforming Our World: The 2030 Agenda for Sustainable Development" in 2015,

Simian malaria (P. knowlesi malaria) have been reported to infect humans.

we are witnessing a growing awareness of the Sustainable Development Goals(SDGs), as well as the importance of solving problems from a multidimensional per-According to the World Malaria Report 2021 published by the World

spective, in which the environment, economy, and society are inseparable parts ofHealth Organization (WHO) in December 2021, there were an estimatedone another. The SDGs are also being recognized as an integral part of the environ-

241 million malaria cases and 627,000 malaria deaths worldwide in 2020.

ment, economy, and society. This report discusses the expansion of malaria risk from

About 95% of malaria cases and 96% of deaths were concentrated in

the perspective of both agriculture and infectious disease research. However, further

sub-Saharan African countries, and about 80% of deaths were children

detailed surveys, including field surveys, will be necessary in the future. As a prelimi-

under 5 years old. This means that approximately one child dies from ma-nary study, this report suggests the importance of considering the risk of infectious

laria every minute somewhere in the world.

diseases in agricultural and rural development projects and calls for further studies in
the future. We hope you will read it.

Japan's Contribution to Zero Malaria

Last but not least, the report was written in cooperation with many people, including Dr. Jo Lines, Professor of Vector Biology and Malaria Control of the London

It was at the G8 Kyushu-Okinawa Summit held by Japan in 2000 that

School of Hygiene & Tropical Medicine (LSHTM). We would like to express our sin-

infectious disease control came to the fore as a diplomatic issue. At Ja-

cere appreciation to Dr. Jo Lines, Ms. Kallista Chan, Research Uptake Manager, RAFT

pan's initiative, the "Okinawa Infectious Disease Initiative" was compiled

Consortium, LSHTM, Dr.Ali Ibrahim, Systems Agronomist at Africa Rice Center, andand led to the establishment of the Global Fund (The Global Fund to Fight

Dr. Kazuki Saito, Principal Scientist at Africa Rice Center.

AIDS, Tuberculosis and Malaria) in 2002, to which major countries andothers contributed funds. To achieve zero malaria, policies must be inplace to ensure that all people have access to quality health services, in-June 2022

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cluding malaria prevention, diagnosis, and treatment. Immediate access
Malaria No More Japan

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to malaria diagnosis when there is a fever can be a matter of life anddeath. This calls for malaria control measures that ensure that no one isleft behind, along with the strengthening of health systems. At the sametime, it is important to apply the lessons learned from malaria control todate, such as prevention, multi-sectoral approaches, and new innova-

Food Security and Human Health:the Link Between Rice and Malaria in Sub-Saharan Africa
Suggested citation:Lines, J., Chan, K., Saito, K., Ibrahim, A. 2022. Food security and human health:the link between rice and malaria in sub-Saharan Africa. Malaria No More Japan, Japan 34p.

tions, to achieving Universal Health Coverage (UHC).
Over the last 20 years, the burden of malaria in Africa has been greatly reduced by modern malaria interventions. Most of this reduction is attributable to the technology of long-lasting insecticidal nets (LLINs), which
was first developed in Japan. Sumitomo Chemical's Olyset® net was thefirst LLIN to be developed and one of the first to be recommended by

Abstract5

1 History and progress in rice production in sub-Saharan Africa

6WHO. Since then, hundreds of millions of Olyset nets have distributeda) Current and future trend in demand for rice in sub-Saharan Africa

6

and used in endemic areas around the world. Later Sumitomo introducedb) Trends in rice production: area expansion and yield increase7

the Olyset®Plus, a second generation mosquito net for resistance con-c) Characteristics of rice cultivation in SSA and constraints to rice production

8

trol, which was recommended by WHO’s prequalification (PQ) scheme ind) Current focus in rice sector development in sub-Saharan Africa

8

2018. The company's indoor residual spray, SUMISHIELDTM 50WG, which

2 Trends in malaria infection and its control in sub-Saharan Africa

9

was launched under WHO PQ in 2017, is a residual-spray insecticide thatis highly effective against mosquito populations that have evolved resistance to existing insecticides.
Meanwhile, as part of Japan's efforts to promote R&D for infectiousa) Malaria in sub-Saharan Africa

9b) Trends in malaria infection in sub-Saharan Africa

9c) Current malaria control strategies

10

3 The impact of rice cultivation on malaria risk

11a) The relationship between rice and malaria vectors

11b) Pre-2005 and the paddies paradox

11

vested approximately 12.3 billion yen, or about 44% of the cumulativec) Post-2005 and the re-assessment

13

total of 27.6 billion yen invested since 2013 (as of March 31, 2022), in thed) Summary of this section15

diseases including malaria, the Global Health Innovative Technology Fund
(GHIT Fund), Japan's first international public-private partnership, has in-joint participation of domestic and foreign companies and research insti-

4 Potential interventions to control malaria vector breeding in rice fields

17

tutions in the development of malaria medicines and vaccines, etc. Witha) The need to produce rice without producing malaria vectors

17

the support of the GHIT Fund, exploratory research and pre-clinical trialsb) Control of mosquitoes in rice fields

18c) Potential vector control within rice cultivation practices

20d) Summary of this section

22of candidate anti-malarial drugs and vaccines are underway by research
institutions and private companies, and the movement toward malaria-related R&D is expanding.

3

Contents

5 Overall Summary and Conclusions

24a) New evidence on rice and malaria in Africa (paddies paradox)

24b) The strategic response24c) Priority intervention areas

24

6 References

26

7 Biography

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1 Histor y and progress in rice production in subSaharan Africaa) Current and future trend in demand for rice in sub-Saharan Africa

Abstract

Rice (Oryza spp.) is an important staple food crop and strategic commodity for food security and social stability

in large parts of sub-Saharan Africa (SSA)1. Rice consumption has been increasing more rapidly than any other com-modity and is driven by high population growth, urbanization and changing of consumer behaviour in the region (Figures1, 2). Recently reaching a billion inhabitants, SSA has had the highest population growth rates in the world, where an

Demand for rice is growing rapidly in sub-Saharan Africa

average increase of 2.5% per annum was estimated between 2007 and 20162, During the same period, demand forrice across SSA has also increased, at a rate of 6% per annum. This demand is driven by urbanisation and a rising(SSA), and ministries of agriculture and international donor

middle class with growing income, which have resulted in changes in consumption patterns and preferences away

communities are promoting the expansion and intensifica-

consumption in SSA is expected to continue growing in the foreseeable future because of the continent’s high popu-

tion of rice cultivation for achieving self-sufficiency for rice inthis region. Meanwhile, ministries of health are planning forfrom traditional staple foods (such as millet and sorghum) and toward rice and other commodities2 (Figure 2). Ricelation growth rate and rapid urbanization3.

Since the 1960s, rice consumption in SSA has exceeded its production (Figure 1). This gap between demandand local supply has gradually increased over the past 7 decades. In 2020, rice consumption was estimated to be ap-

the elimination of malaria. Both are desirable in Sustainableproximately 32.2 million tons (MT) of milled rice, which was partially fulfilled by the importation of approximately 15.6

Development Goals (SDGs), but there is a serious concern

ciency rate of only 48%.

MT, an amount equivalent to 33% of that traded in the world market4. This indicates that in 2020, SSA had a self-suffi-

about trade-off, because in SSA, rice fields in wetlands are amajor breeding ground for the mosquitoes that transmit malaria. Our report shows that (i) the area under rice cultivation
has been increasing and is expected to increase in SSA, (ii) a
wide range of development programs have been supporting
rice sector development without any concern about potential
risk for increasing malaria infection, (iii) communities growing
rice in SSA are exposed to greater malaria risk, and (iv) potential interventions exist for growing more rice with fewer
mosquitoes. Based on these observations, the report suggests some future actions for both agriculture and healthsectors.

Figure 1. Trends in rice harvested area, milled rice production, consumption, and paddy rice yield in sub-Saharan Africa4.

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In SSA, rice consumption per capita is around 30 kg/person/year, which is much lower than that of Asia (100 kg/

person/year)5. However, there is large variation across countries. 11 SSA countries including Guinea, Madagascar,

Mali, Côte d’Ivoire, Liberia, Sierra Leone, Benin, Guinea-Bissau, Comoros, Senegal, and Mauritania each consume
more than 50 kg/person/year 4.

c) Characteristics of rice cultivation in SSA and constraints to rice production
In SSA, rice production systems comprise irrigated lowland, rainfed lowland, and rainfed upland, with deep-

water and mangrove rice being of minor overall importance. Irrigated lowland, rainfed lowland, rainfed upland, andb) Trends in rice production: area expansion and yield increase
In response to its growing demand in SSA, rice production has progressively increased (Figure 1). This intensifi-

cation was through enhancing rice yield per unit of land and the expansion of rice harvested area. Between 2000 and

2020, area harvested had increased from 6.9 million ha to 16.6 million ha (Figure 1), whereas rice yield increased from

1.7 tons per ha (t/ha) to 2.1 t/ha. Although rice yield in SSA has gradually improved over the years, recent yield levels
are still much lower than the global average which is around 4.4 t/ha3.

Despite recent increases in rice production, rice production has yet to catch up with consumer demand in SSA(Figure 1). Nevertheless, it is possible to close the gap between demand and supply in the region because of (a) thehigh intrinsic potential for the expansion of rice-growing areas and (b) the large differences between potential yield
and actual yields obtained by farmers6,7. In terms of potential to expand rice cultivated areas, wetlands show great

promise with an estimated total area of 239 million ha in SSA6. Here, wetlands are defined as areas where soil is saturated with water either permanently or seasonally. Furthermore, there is a large untapped potential for irrigation in Afri-ca, extending to about 24 million ha or 1.8 times greater than the existing irrigation area8. On average in selected SSA
9countries, actual yields are only 38% of their potential .

This large gap between demand and supply for rice and substantial potential for rice increase in SSA as well asfears about global food security, which led to a spike in food prices in 2007–2008 gave African governments and theinternational donors’ attention into efforts to strengthen the rice sector to achieve self-sufficiency in SSA1,10. For example, a policy framework known as the “Coalition for African Rice Development (CARD)” was launched in 2008, and inits second phase, the CARD aims to double rice production in SSA countries between 2018 and 20301.

others account for 22%, 40%, 35%, and 4%, respectively, of the total rice area in SSA11. Surface-water regimes andwater sources (e.g., irrigation, rainfall, water table) distinguish the rice-growing environments. Irrigated lowland rice isgrown in bunded fields with assured irrigation for one or more crops per year. Rainfed lowland rice is grown on level toslightly sloping, unbunded or bunded fields in lower parts of the toposequence and in inland valleys. Rainfed upland
rice is generally grown on level or sloping, unbunded fields. Generally, irrigated lowland rice systems have higher

yields than the other environments9,12. For example, on-farm surveys in 19 SSA countries showed that mean rice yields
were 4.0, 2.6, and 1.6 t/ha in irrigated lowland, rainfed lowland, and rainfed upland, respectively. The yield obtainedin irrigated lowland rice is close to the global average which is around 4.4 t/ha. This is against general perceptions of

low rice yield in SSA, which have mainly arisen based on national-level statistics which do not differentiate production
systems and their share of harvested areas. Low national yield level in SSA is attributed to larger area share of rainfed
lowland and upland rice that give lower yields.

Low on-farm yields are caused by a range of biophysical and socioeconomic constraints that impose abiotic andbiotic stress on the rice crop during its growth cycle13. Although the constraints are site- and production system-spe-cific, soil-related constraints including iron toxicity and salinity, extreme temperature, drought (poor water manage-

ment for irrigated lowlands), flooding, weeds, diseases, and suboptimal land and crop management interventions are
the factors causing low yields13–19. For alleviating those constraints and enhancing rice yield in SSA, a wide range oftechnologies including new rice varieties and agronomic practices have been developed over 50 years15,20–23.

d) Current focus in rice sector development in sub-Saharan Africa
As mentioned above, African governments and the international donor community have embarked on ambitious

rice-development programs for rice sector development for achieving self-sufficiency for rice in SSA especially since2008, when the 2007–2008 food crisis occurred. Many programs have focus on increased rice production and farm-ers’ income from rice production, and enhancing competitiveness of locally produced rice (e.g. Coalition for African

Rice Development (CARD24), Competitive African Rice Initiative (CARI25), RIKOLTO26, National Rice Development Strat-egies (NRDS27). In addition to these, a few programs (CARI, RIKOLTO) recently initiated promotion of sustainable riceproduction, aligning with Sustainable Rice Platform (SRP). The SRP is a multi-stakeholder alliance with over 100 institutional members from public, private, research, civil society, and the financial sector, and promotes resource-efficientand sustainable production of rice, at farm to landscape levels. SRP aims to harness innovation to encourage farmers

to adopt climate-smart, sustainable best practices, while enhancing smallholder livelihoods and protecting the environment. The SRP developed “SRP Performance Indicators” for environmental, economic, and social sustainability28.

The indicators include profitability, labour productivity, yield, water productivity & quality, N-use efficiency, P-use effi-

ciency, biodiversity, greenhouse gas emissions, food safety, worker health & safety, child labour & youth engagement,
and women's empowerment. Such indicators help rapid, efficient, and robust monitoring of both development ofagronomic practices and their scaling in agricultural research-for-development programs. However, it is noted that awide range of agricultural development programs have supported rice sector development without any concern about
potential risk for increasing malaria infection.

Figure 2. Trends in population growth, milled rice consumption, and per capita rice consumption (FAO, 2021)

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82 Trends in malaria infection and its control in subSaharan Africa

Despite some challenges in this progress, including growing insecticide resistance, constrained funding and,most recently, the COVID-19 pandemic (which has resulted in almost 50,000 additional deaths), WHO still has ambi-

tious goals to reduce malaria case incidence and mortality rates by at least 90% by 2030. These gains have led some

African countries to start to plan their pathway to the goal of malaria elimination29; for example in Nigeria, the “National
Malaria Control Programme” is now the “National Malaria Elimination Programme”.

a) Malaria in sub-Saharan Africa
Malaria, a life-threatening disease caused by Plasmodium parasites, is a major public health problem. In 2020,

there were an estimated 241 million malaria cases and 627,000 deaths worldwide. Thirty-two countries in sub-Saharan
29

Africa (SSA) carry a disproportionately high share of these cases, and harbour 93% of all malaria deaths globally .
In areas of high transmission, the most vulnerable populations are young children, specifically those under 5 years ofage, and pregnant women. The costs of malaria, from individual to national level, are enormous; it is estimated thatthe disease costs Africa US$12 billion per year.

SSA suffers more malaria than other regions because: (1) the predominant parasite species, Plasmodium falci-

parum is the deadliest of the human malaria parasites, (2) health systems are relatively weak compared to other re-gions, and most importantly, (3) the African malaria vector, Anopheles gambiae s.l., is the most efficient vector species
in the world. It is efficient partly because it is very anthropophilic (i.e. high preference for feeding on humans for bloodas opposed to other animals), but mainly because it has a long average lifespan. This allows the parasite to develop

within the mosquito and be transmitted to humans. Anopheles gambiae can make use of a diverse range of breedingsites, including muddy footprints on a roadside, and it is especially well-adapted to ricefield conditions.

c) Current malaria control strategies
The present global malaria control strategy relies primarily on vector control using LLINs and IRS. These are themost powerful and cost-effective currently-available malaria control interventions – in the last two decades they have
prevented more than ten million deaths due to malaria – but they have serious limitations. First, in Africa, they are in-completely effective: they can reduce transmission but not prevent completely, because of variability in the behaviourof the vectors. Second, they are based on chemical insecticides, and therefore subject to challenges such as insec-

ticide resistance, which is currently widespread and rapidly-evolving. For these reasons, alternative control methods
complementary to existing methods have sometimes been deployed, particularly larval source reduction through environmental management. Larval source management (LSM), targeting the aquatic stages of mosquitoes, has histori-

cally been important in some successful malaria elimination campaigns, including some settings where ricefelds were
important breeding sites for the local vector Anopheles species. These include parts of Europe, Central Asia and Chi-na31. In these cases, interventions to prevent mosquito-breeding in rice fields are thought to have played an importantrole not only in the intensive campaigns leading up to elimination, but also and especially post-elimination, during theprolonged stages of ‘consolidation’ and ‘prevention of re-introduction’, when other forms of vector control have been
withdrawn.

b) Trends in malaria infection in sub-Saharan Africa
There has been a general global decline in malaria transmission since the 1950s due to various efforts such as

the Global Malaria Eradication programme (GMEP) in the 1960s. However, the big house-spraying campaigns of the

GMEP were delivered mainly in Asia and Latin America. In most SSA countries, it was not until the early 2000s thatefforts began to provide effective protection against malaria to rural populations at national scale.

Three factors made this feasible. The first was a strong platform of evidence, derived from a series of trials in

the 1990s, that insecticide-treated nets were extremely cost-effective as a child-survival interventions, for all-cause

mortality in young African children. The second was the development, in 2000-4, of long-lasting insecticidal nets

(LLINs). These did not need frequent re-treatment with insecticides. The third was the creation of The Global Fund,in 2002, which enabled international donors to invest directly in the scaling-up of proven life-saving interventions likeantiretrovirals and LLINs. With the combination of these three factors, it became feasible for the first time for African
governments to deliver effective vector control in a sustained manner to the general rural population, even in settings
with poor infrastructure.

Between 2004 and 2012, the delivery of LLINs through national-scale mass-campaigns led to rapid scaling up ofcoverage, and in 2007, the UN Secretary-General announced that the public health community should adopt the goalof “Universal Coverage” with effective anti-malaria interventions. Evaluations showed that the increased coverageachieved by “universal coverage” campaigns was both equitable and effective in reducing child mortality rates even inremote and poor communities.

As a result, in the last two decades, the African population at risk of infection and the age-standardisedprevalence of infection in children under 5 have been greatly reduced. The annual number of deaths due to malaria
has been reduced by about 50% (fig 3)30.

Figure 3. Trends in total estimated malaria deaths, globally and in Africa. Data from WHO29.

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3 The impact of rice cultivation on malaria risk

expanded set of observations followed the same paradoxical pattern: the rice villages had substantially larger mosquitoes
populations but similar or slightly lower indices of malaria49.

Various mechanisms were suggested to explain the paddies paradox, but the main idea was that rice brought nota) The relationship between rice and malaria vectors

only more mosquitoes, but also other beneficial mechanisms that tended to protect against malaria. What mattered was
the balance between the harmful effects of the extra mosquitoes and the beneficial effects of these mechanisms. In mostaThroughout the rice-growing regions in the world, there are local mosquito species that exploit flooded rice

fields as breeding sites. However, in most regions, the species of mosquitoes that predominate in rice fields have little
or no importance as vectors of malaria, while the main local malaria-vector species have other breeding sites.

cases, the balance seemed to be either neutral or slightly beneficial.

This conclusion has been highly influential. Ever since, agencies promoting irrigated lowland rice production in Africa

have used this “paddies paradox” story to provide assurance that despite the mosquitoes, rice development in Africa is not

There are, however, some important exceptions, where rice fields are a primary breeding site for mosquitoesthat are (or used to be) the main local malaria vectors. These places include central China, parts of southeastern
Europe and Central Asia, parts of Colombia and Peru, parts of Indonesia and sub-Saharan Africa32–34. In some ofthese regions, e.g. southeastern Europe and mainland China, malaria has already been eliminated, but it remains amajor problem in sub-Saharan Africa. The main malaria vector in Africa, An. gambiae s.l., is exceptionally efficient attransmitting malaria, and consequently Africa suffers more than 85% of global morbidity and mortality due to malaria.

bad for malaria50.

It is important to look more closely at these proposed underlying mechanisms of the paddies paradox. Three kinds ofmechanisms have been suggested, each with some supporting evidence.

The first and most general is that the introduction of rice-growing brings compensating socio-benefits, that is, a wide

An gambiae s.l. is one of those anopheline species that has a strong preference for breeding in rice fields. Hence,

range of socio-economic and environmental benefits that tend to suppress transmission. These include general benefits

are for regions such as South Asia and the Greater Mekong Region, where there is more rice, but the malaria vectorbought mosquito nets and drugs, and to good-quality health services43,51–55. Note that these various possible mechanismsbfrom an agricultural perspective, the interactions between rice and malaria are more significant for SSA than theysuch as better roads and housing, and also specific anti-malaria defences, including better access to both commercially-mosquitoes (e.g. An. culicifacies, An. dirus, An. minimus) are not so well-adapted to breeding in flooded rice fields.

are all closely correlated with each other, and in practice it is very difficult to disentangle those that were really acting to

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An. gambiae s.l. prefers to breed in shallow sunlit newly-flooded freshwater pools . Hence the aquatic conditionsof rice fields, especially during the early stages of growth, are very suitable for this species

35,36. An. gambiae s.l. is a‘pioneer’ species: it is one of the first insects to colonise a newly-created body of suitable water, such as a rice field
just after transplantation of the young rice37. While the water is still new, and invertebrate aquatic predators have notsuppress malaria from those that were just passively correlated with the process. Note that a key feature of this mechanismis that it depends on inequity: it requires substantial and persistent socio-economic inequalities between rice and non-rice
villages.

The second potentially-contributing factor is that in conditions of intense transmission, the prevalence of infection

yet arrived, a large proportion of newly-recruited first-stage mosquito larvae may survive to adulthood (which takes

saturates. In such conditions, most people are infected most of the time, and have high levels of partial immunity. Whenof aquatic predators, so that an increasing proportion of young larvae will be eaten before they mature. Hence, there

Further increases in transmission can happen, but this merely increases the frequency with which already-infected people

about 1 week). But if the water remains more or less stable for a few weeks, it will be gradually colonised by a variety

the prevalence of infection approaches 100%, then most infectious bites are falling on people who are already infected.

is normally a peak in mosquito production in the first 4-5 weeks after transplantation, and the numbers of adults

receive additional super-infecting bites; it can have little effect on prevalence because that is already near-100%. Hence,38

emerging in this first month often comprises more than 50% of the total emerging over the entire growing season .

Irrigation schemes are usually installed in settings that were previously natural freshwater wetlands, with theirown natural mosquito fauna. However, the transformation from natural wetland to irrigated rice alters the mosquito
fauna profoundly, to something close to a monoculture of malaria vectors39–41. For example, one study in Western Kenya sampled a diverse mixture of mainly animal-biting non-vector species emerging from natural wetlands, while thoseemerging from the rice fields were equally numerous but much less diverse, 90% of them being An. gambiae s.l. andprevalence and similar malariological indices become relatively unresponsive to further increases in transmission, while

presumably remaining sensitive to factors such as people frequently treating themselves with anti-malarial drugs. Notably,
several previous reviews have concluded that an association between rice and malaria in Africa is more likely to be seen insettings with unstable rather than stable transmission48,49.

Third and last, entomological mechanisms can also produce “paddies paradox” outcomes, with more mosquitoes but

less transmission. One of these is general, and perhaps common. This is the idea that when mosquito population densities

An. funestus.

are very high, density-dependent mechanisms can reduce (or at least set an upper limit to) the vectorial capacity of theb) Pre-2005 and the paddies paradox

adult lifespan due to increased competition during larval stage development or (2) a reduction in adult feeding success due

population, and hence the ability to transmit the parasite. This could happen through two different ways: (1) a reduction inOver the decades, it has been consistently observed that An. gambiae s.l. adults are especially abundant in villages

near irrigation schemes42–45. There were many expressions of concern about the possibility that these additional mosquitoes

might lead to additional malaria in the nearby human population. On this question, however, the evidence was surprisingly

mixed. In some places with “unstable malaria transmission”, such as Madagascar, a clear and strong association between

to increased mosquito net use (driven by extreme biting nuisance) or, in some places, due to increased cattle numbers nearrice fields.

Given these three possible mechanisms, what are the questions that we should consider when updating and re-appraising the studies comparing malaria transmission in rice and non-rice communities? One key issue is that there may

malaria and rice fields has been reported46,47. Elsewhere, and especially in high-transmission parts of mainland Africa, theassociation between ricefields and malaria was inconsistent and unclear.

For example, in 2001, Ijumba and Lindsay reviewed a set of studies in which malaria outcomes had been measured

a In this section of the report, we use the word “rice” to refer to irrigated and rainfed lowland rice production systems, and we do not consider upland riceproduction systems.

48

in rice and nearby non-rice communities . They found that in areas of stable malaria transmission, rice villages tended tohave more vectors but less malaria. They called this the “paddies paradox” 48. Over the next few years, there was a further
series of such studies in a range of rice settings in West Africa, co-ordinated by the Africa Rice Center (AfricaRice). This11b The most widely distributed members of the An. gambiae s.l. group of species are An. gambiae s.s., An. coluzzii and An. arabiensis; all three of thesebreed prolifically in flooded rice. Adaptation to breeding in irrigated rice systems in West Africa is thought to have driven the divergence of An coluzzi
from An gambiae s.s.

Malaria no more japan ｜ 2022 repor t

12have been many changes in these mechanisms, and their relative importance, over the last 15 to 20 years.
Since the 1990s and early 2000s, when the “paddies paradox” studies were conducted, the malaria picture in Africa

has changed profoundly. There has been massive scaling up of coverage with modern anti-malaria interventions – vector

control, diagnostics and treatment. Coverage has also become much more equitable, within and between communities.

As a result, there has been a concomitant and equally widespread decline in the general intensity of transmission, and in
the prevalence of malaria infection in the general population. This has two implications for our modern view of the “paddies
paradox”.

First, because of the improvements in coverage and equity in coverage, it is no longer safe to assume that non-rice

villages have very poor defences against malaria. Presumably, the magnitude of the change depends on which village
characteristics were previously giving the differential protection between rice and non-rice villages. For example, LLIN

coverage is now remarkably equitable, whereas previously, it was often reported that (untreated) net coverage was very

high in rice villages and much lower in non-rice villages (that is, villages with and without irrigated lowland rice fields)56,57. On

the other hand, there has been no very-large-scale intervention to improve housing quality, and the differentials in housing
between rice and non-rice villages may or may not be as strong now as they were before.

Also, and as a consequence of general decline in transmission, there has been a substantial reduction in the fractionof the population at risk exposed to high intensity transmission. Many of those who were previously intensely exposed are

now exposed only to low levels of transmission30. Hence, if there is a difference in exposure between rice and non-rice vil-lages, we would now expect this to be relatively clearly observable in human malariological indices.

c) Post-2005 and the re-assessment
A systematic review and meta-analysis was conducted to compare the malaria epidemiological andentomological malaria outcomes associated with rice across 53 studies. These studies were conducted from 1971
to 2016, in rural settings in 14 SSA countries in West, Central and East Africa. At the start of this period, coveragewith effective modern anti-malaria interventions (such as LLINs) was very low. Starting in the early 2000s, the Global
Fund supported a programme of “Scaling-Up for Impact” (SUFI). By 2016, coverage was much higher (around 50%)and by the standard of most public health interventions, coverage was remarkably equitable between rich and poor
households. For analysis, these studies were divided into two groups: those carried out before or after 2003, which
was about the time when the period of rapid ‘scaling-up’ was initiated.

Epidemiology
23 studies compared malaria infection prevalence in rice and non-rice growing villages and were included in

the meta-analysis. In the 16 studies carried out before 2003c, the overall crude risk ratiod [RR] was not significantly

different from 1 (crude RR 0.82, 95% confidence interval 0.63–1.06); in other words there was no evidence of an
association between rice and malaria risk. In the 7 studies carried out after 2003, by contrast, pooled analysis

indicated that the risk of malaria infection was substantially and significantly higher in rice villages (crude RR 1.73,
95% CI 1.01–2.96). These two pooled risk ratios were significantly different from each other.

There was some evidence supporting the idea that in the earlier studies, the malariogenic effects of rice might

have been concealed by ceiling effects such as the saturation of prevalence in high-transmission conditions (seeabove). If these studies are ranked by baseline (no-rice) prevalence (Figure 4B), they appear to fall into three groups. In

the few studies with very high (>75%) baseline prevalence, there was almost no difference between rice and non-rice

villages. In studies with medium to high (26 to 75%) prevalence, there was the paddies paradox: rice villages had lessmalaria than non-rice villages. And in most (but not all) of the studies with relatively low (<25%) prevalence, rice villages had more malaria than non-rice villages.

13

Figure 4. Meta-analyses of the association between rice cultivation and malaria epidemiological outcomes.
Crude risk ratios of malaria infection and their 95% CIs 537 (presented as error bars) are plotted according to (A) subgroup (before and after 2003) and (B)underlying malaria intensity. (C) Crude incidence risk ratios of malaria incidence (per 1000 person-day) and their 95% CIs are plotted according to year of
study. Pooled effect estimates of quantitative studies calculated using random-effects models are presented as dark coloured bars at the bottom (of eachsubgroup). Red bars indicate that, compared to control areas, the epidemiological measure was higher in rice-growing areas, whilst blue bars indicate lower measures in rice.
Chan, K., Tusting, L. S., Bottomley, C., Saito, K., Djouaka, R., & Lines, J. (2022). Malaria transmission and prevalence in rice-growing versus non-rice-growing villages in Africa: a systematic review and meta-analysis. The Lancet Planetary Health, 6(3), e257-e269.

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Entomology

expansion and intensification of irrigated lowland rice production.

⃝ Malaria remains a major public health problem in Africa: it kills more than 400,000 people every year in Africa; thisrepresents >80% of the world’s malaria burden.

We did a similar summary meta-analysis of the 36 studies that collected entomological outcomes, including

Anopheles human biting rates (HBRs) in rice and non-rice villages. These are summarised in Figure 5.

Overall the abundance of vectors (An gambiae s.l.) was much greater in rice than in non-rice villages: overall

about seven- or eight-fold (95% CI 2-fold to 21-fold) greater.

Infection (sporozoite) rates tended to be somewhat lower in rice-villages, but by a smaller margin: RR 0.29, 95%

B Established ideas about irrigated rice and malaria in Africa: “Paddies Paradox”⃝ In 1995-2005, reviews of the evidence found that irrigated lowland rice is associated with more abundant malaria

vector mosquitoes, but not more malaria. This was called “Paddies Paradox”.

⃝ This was largely because rice brought not only mosquitoes but also economic and infrastructural development: better

housing and health services, more household resources to buy nets and drugs. Thus residents of rice villages were,

CI 0.19–0.46, 17 studies.

Only 3 studies quantitatively reported entomological inoculation rate (EIR) of An. gambiae s.l. and their meta-analysis

at that time, much better able to protect themselves against malaria.

⃝ The idea that rice in Africa brings more mosquitoes but not more malaria has been a critical assumption underpinninginvestments in rice-development in Africa over the last 20 years.

implied that EIR in rice communities was about twice that in non-rice areas (RR 2.03, 95% CI 1.02–4.06, three studies).

Previous reviews have emphasised the idea that at very high population densities, increased competition between

mosquitoes may reduce their longevity and hence their vectorial capacity. However, ours seems to be the first meta-

analysis of this. Our analysis confirms that the vector populations in rice villages tend to be larger but less infectious(lower sporozoite rates) than those in non-rice villages. However, in most cases, the degree of reduction in sporozoite

rates is relatively small, and does not compensate for the major increase in vector numbers. Thus on balance, residents’

C New evidence that irrigated lowland rice does bring more malaria in Africa⃝ Our review of recent studies (since 2003) indicates that residents of flooded-rice villages are exposed to more intense

malaria transmission, and have a higher prevalence of malaria infection than residents of non-rice villages.

⃝ This is probably because, over the last 20 years, there has been massive scaling-up of coverage with effective anti-

malaria interventions.

exposure to biting by infective mosquitoes (EIR) tends to be higher in rice villages (Figure 5).

・ Large-scale surveys show that population coverage with interventions (especially insecticide-treated nets) is
generally much more equitable than before. This presumably reduced differentials between rice and non-rice
villages in the ability of residents to protect themselves against mosquitoes and malaria.

d) Summary of this sectionA・ Twenty years ago, there was very intense malaria transmission in much of the lowlands in Africa. In these conditions,
infection prevalence is not very sensitive to further increases in transmission because most infectious bites fall uponalready-infected people. Because of the general reduction in transmission, many more communities are exposed to

The relationship between rice and malaria in Africa matters because:intermediate levels of transmission, where population prevalence is very sensitive to changes in transmission.

⃝ Consumption and demand for rice are rapidly growing in Africa; there is ongoing and substantial investment in bothD

The rice-attributable burden of malaria⃝ Further work will be needed to estimate the “rice-attributable burden of malaria” in Africa, but we already know that it

must be substantial.

E

This will probably be an emerging problem for malaria in Africa⃝ Our analysis suggests that the additional malaria risk associated with rice depends on baseline levels of malariatransmission. The effects of irrigated lowland rice on malaria tend to be more conspicuous (and probably larger) insettings with lower background levels of transmission.

⃝ Hence, as malaria declines in Africa, the contribution of irrigated lowland rice production is likely to become more

conspicuous and strategically important for national malaria elimination programmes.

⃝ This should not be surprising. Rice fields are an important breeding site for the local malaria vector species inmainland China, parts of Central Asia and southeastern Europe. In these settings, interventions to control vector
breeding in rice fields were considered an essential component of the elimination process, and had to be maintained
after elimination in order to prevent malaria from returning.

Figure 5. Meta-analyses of the association between rice cultivation and entomological outcomes.
Crude ratio of means (HBR and EIR, where the comparator group was non-rice growing communities), risk ratios (sporozoite rate) and their 95% CIs (onlyin quantitative studies, presented as error bars) are plotted according to year of study. Red bars indicate that, compared to control areas, the entomologicalmeasure was higher in rice-growing areas, whilst blue bars indicate lower measures in rice. Whilst light-coloured bars indicate semi-quantitative studies,solid-coloured bars indicate quantitative studies. Pooled effect estimates of quantitative studies calculated using random-effects models are presented as
dark coloured bars at the bottom. Chan, K., Tusting, L. S., Bottomley, C., Saito, K., Djouaka, R., & Lines, J. (2022). Malaria transmission and prevalence inrice-growing versus non-rice-growing villages in Africa: a systematic review and meta-analysis. The Lancet Planetary Health, 6(3), e257-e269.

15c Through a sensitivity analysis, the year 2003 was determined to be a relatively robust year to mark the start of the scale-up of malaria interventions.
d Risk ratio, in this instance, measures the relative risk of malaria (prevalence or incidence) among rice communities relative to the risk of malaria among
non-rice communities. A risk ratio greater than 1 indicates an increased risk in rice-growing communities, whereas a risk ratio less than 1 indicates adecreased risk in rice-growing communities.

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4 Potential inter ventions to control malaria vector
breeding in rice fields

Some interesting and potentially important comparisons are to be made with greenhouse gases. Like themosquitoes, these are harmful emissions produced as a side-effect of irrigation, and in both cases, this happens withlittle or no awareness on the part of the farmers. Rice-development agencies have already acknowledged and started
to address the problem of greenhouse gas (GHG) emissions: they now need to acknowledge and start to address the
problem of malaria mosquitoes in Africa.

a) The need to produce rice without producing malaria vectors
It appears that nowadays, as sub-Saharan Africa is no longer under “saturation” levels of malaria intensity, theintroduction of flooded ricee production can bring increased malaria risk. However, preventing rice expansion is not an

option, because rice cultivation is a necessity for food security. Thus the cultivation of irrigated rice is necessary, but it
currently has an unintended negative side effect: an increase in malaria transmission.

This is clearly an intersectoral problem: a health problem is made worse by an agricultural activity. So which

sector should take responsibility for it, or how should responsibility be divided?

The answer to this question would be clearer if there was a simple and decisive intervention on the health side.

For example, Dengue, Zika virus and Yellow Fever (YF) are all flaviviruses transmitted between humans mainly by
Aedes mosquitoes. Of these three viruses, Yellow Fever is by far the most deadly, and the only one for which we havea vaccine giving 100% life-long immunity. Therefore, for the control of dengue and Zika, public health authorities
must rely on vector control interventions that are expensive and only partially effective. Outbreaks of Yellow Fever, bycontrast, can be quickly and decisively interrupted by emergency vaccination campaigns.

In the case of malaria, a decisive intervention on the health side does not exist. The world spends more thana billion dollars per year on the delivery of vector control and improved diagnosis/treatment interventions. Good

progress has been made, but there is a long way to go. There is a new vaccine, but it gives only partial protection fora number of months; it is unlikely to be a cost-effective way to mitigate the additional malaria transmission caused byirrigated lowland rice.

In other words: when rice experts took on the GHG problem, they developed “win-win-win” solutions: methods

that (a) suppress GHGs, (b) maintain or increase rice yield, and (c) reduce the need for water. Now, perhaps,“suppressing malaria mosquitoes" must be added to that list: the need is for “win-win-win-win” solutions!

If the R&D task is to develop rice-growing methods that maintain or improve yield, save water, minimiseemissions of mosquitoes as well as methane, and (last but not least) will be adopted by farmers, then surely the R&D
process must be led by rice experts with technical input from mosquito experts, not the other way round. Farmers are
not likely to be interested in rice-growing methods developed by mosquito entomologists.

There is good reason to believe that such solutions are possible. The alternative options for rice cultivation

methods are many and diverse, and only a few of them have been studied for their effects on the mosquitoes. Thesestudies, although limited, certainly support the assumption that almost all rice-growing options have more or less sub-stantial effects, positive or negative, on the mosquitoes. We need to study the effects of rice variety (which may affectmosquitoes through effects on shade), methods of levelling and preparation, methods of transplantation, weeding andapplying fertiliser. A great deal of more detailed work is needed, but it does seem likely that a combination of modified
methods, each of which is partially effective, could add up to effective overall control.

b) Control of mosquitoes in rice fields
Because the relationship between rice and malaria vectors is well-established, malariologists have investigatedmany different methods of larval source management (LSM) in rice fields since the 1930s. A detailed narrative review
by Lacey and Lacey (1990) covers a wide range of these studies, except for chemical control69. It also includes studies

So what about the interventions we do have, such as LLINs and IRS? Of course, from an agriculturalof techniques that are built into conventional rice cultivation practices, and which only require slight adjustments tointerventions. At first sight, this is an attractive idea, and could be described as re-establishing the Paddies Paradox:

fied water management methods for suppressing mosquito breeding. For example, Keiser et al (2002) prepared a nar-better protected.

ble of significantly reducing malaria vector densities, as well as reducing methane emissions and water consumption

perspective, it is natural to suggest that the problem could be solved by targeting rice villages with theseeffectively reduce vector proliferation in rice paddies. Substantial research attention has been paid to the use of modi-

villages with rice have more mosquitoes, but those mosquitoes are less able to bite people because the people are

rative review on the potential of intermittent irrigation in rice fields. They concluded that intermittent irrigation is capa-

The problem with this, as an idea, is that its effectiveness depends on inequity: it works only while the non-ricecommunities are deprived of the benefits given to the rice villages. It is hard to reconcile this, as a strategy, with theoverarching principle of equity and the specific policy of universal coverage.

Clearly the problem of malaria is not going to be solved by the agricultural sector. Even the health sector, withremarkably powerful interventions and working at full stretch, can deliver only a partial and not a complete solution.

But at the moment, it does seem that the contribution of agriculture is to make the problem worse. So perhaps therole of agriculture is to simply stop being part of the problem, and start being part of the solution.

Therefore, rice-growing methods need to be developed that are unfavourable to mosquitoes but still favourable

for the rice. This may require extra effort but it can be done: in many previously malarious countries such as Portugal,

Spain, Turkmenistan and China, rice areas were identified as the last hotspots of transmission, and targeted control in
the rice fields was often required to achieve malaria elimination and to prevent resurgence65–68.

whilst maintaining good rice yield70.

As an update to the two reviews written 20-30 years ago, we conducted a systematic review and meta-analysis

to assess whether, by and large, riceland LSM (including chemical and biological control) and rice cultivation practices can reduce malaria vector abundance whilst increasing rice yield and reducing water use. Here, we provide a summary of results and their implications.

Most of the relevant studies were conducted in the 1980s and 90s. Most were conducted in North America, Af-rica, and East and Southeast Asia. There were 16 studies on bacterial larvicides, 10 on chemical larvicides, 8 on fishand 1 each on Azolla, copepods and neem. There were 8 studies on modified irrigation, and 7 on land preparation,
weeding, water height and plant variety, height and spacing.

Larviciding
Monomolecular surface films (MSF) had mixed results: they produced a modest reduction in anopheline larval

numbers in two studies but not in a third.
e In this section of the report, “rice” refers to irrigated and lowland rice production systems and does not consider upland rice

17

Chemical larvicides, such as deltamethrin and temephos, were consistently effective, achieving reductions of 56%

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18

to 93% in 8 studies (Figure 6A).
The performance of bacterial larvicides was more variable (Figure 6B). The pooled estimates of effectivenesswere good (55% - 72%) but there were some cases where the results were disappointing (<20%). The most effective
bacterial larvicides were Bti-based.

(A) Synthetic organic chemicals

The effects of larvicides were highest immediately after application, but the effect did not persist for more than

two weeks. These larvicides mostly had short residual half-lives because they were applied to paddy water which is, inmost cases, completely stagnant.

Normally, there is a small but continuous process of water loss (through drainage,

evapotranspiration and percolation) and replacement through irrigation. In some settings, it is common for each small
plot to have a trickle of water in and a trickle of water out.

This is important because it means that for sustained

control, re-applications have to be repeated at weekly intervals, even with supposedly residual formulations71–74.

Thus, it would be costly and labour-intensive to scale-up a larviciding operation, applying larvicides evenly toevery small plot in an entire irrigation scheme. To do this repeatedly at weekly intervals throughout the five months longrice-growing season per year would be even more logistically challenging75,76. Aerial application (including unmanned
aerial vehicles), although widely used in the US and Europe, is unlikely to be a feasible delivery system for smallholders
in SSA, even in large irrigation schemes72,73,77,78.

Biological control
The simultaneous cultivation of rice and fish was more than 80% effective in reducing the abundance ofanopheline immatures, in five trials. Other forms of biological control, including copepods, Azolla (mosquito fern) andneem, were not associated with lower numbers of anopheline larvae in rice fields.

Biological control using fish was found to be, in general, somewhat more effective than (chemical, bacterialand MSF) larviciding. The degree of effectiveness was dependent on the fish species and their feeding preferences:(B) Biological larvicides

surface-feeding, larvivorous species provided better anopheline control than bottom-feeding selective feeders81,82.
Selecting the most suitable fish for local rice fields is not straightforward; many criteria need to be considered82–84. In

two studies that accounted for its scalability, fish were well-received by farmers. It was reported that farmers regard
fish as contributing to increased yield by reducing weeds and pests and providing fertiliser through excrement81,85.

This was reportedly also observed in Guangxi, China, where a certain proportion of the field had to be deepened

into a side-trench where the fish could take shelter when the fields were drained. Even with this reduction in riceproduction area, carp rearing still reportedly increased yields by 10% and farmer’s income per hectare by 70%84.

In SSA, irrigated lowland rice-fish farming could be scaled up provided that an inventory of fish species suitable

for specific locations is available and that water is consistently available in fields (an important limiting factor in African
irrigation schemes)86. Lessons can be learnt from successful large-scale rice-fish systems in Asia, where they have
served as win-win solutions for sustainable food production and malaria control87,88.

Unfortunately, none of the eligible studies in this review had included yield or water use as an outcome. Future

entomological studies need to measure these critical agronomic variables so that studies of vector control in rice canbe understood by, and transferred to, agronomists.

c) Potential vector control within rice cultivation practices
Intermittent irrigation
Compared to continuously flooded fields, water management techniques involving drying intervals were notconsistently associated with lower densities of anopheline immatures (Figure 7). When separated into subgroups
according to type of drainage, neither active (where water is removed by drainage into canals) nor passive (where
Figure 6. Pooled estimate of the effect of (A) synthetic organic chemicals and (B) bacterial larvicides on Anopheles larval densities in rice fields. Fivecontrolled time series studies on (A) synthetic organic chemicals and eight controlled time series on (B) biological larvicides were included, conducted
between years 1975 and 2004. Squares represent the relative effectiveness of individual studies, where square size represents the weight given to thestudy in the meta-analysis, with error bars representing 95% CIs; diamonds represent the pooled effects from random effects (RE) sub-group andmeta-analyses.
Chan, K., Bottomley, C., Saito, K., Lines, J., & Tusting, L. S. (2022). The control of malaria vectors in rice fields: A systematic review and meta-analysis.
Under review.

19

water is lost through evaporation or percolation) intermittent irrigation was associated with reduced larval densities
but one-time drainage was associated with 24% higher densities (2 studies, Figure 7). When immature abundance
was separated into developmental stages, it was revealed that although intermittent irrigation was not associatedwith significant reductions in early instar larvae, it reduced the abundance of late instars by a pooled estimate of

35% in four studies. In one Kenyan study, draining during transplanting followed by active intermittent irrigation was

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associated with a 35% reduction in late stage larvae, but a 770% increase in early stage larvae35.

concentrated in depressions (usually footprints), suggesting that rice operations which leave or remove footprints (e.g.

Overall, there was only limited evidence that intermittent irrigation is effective at reducing late-instar

hand-weeding, drum seeders, levelling) will influence vector breeding82.

anopheline larvae in rice fields. This finding contrasts with prior reviews, which found mixed results (regardless ofd) Summary of this section

criteria of our systematic review. These excluded some older studies that reported successful anopheline control

A The task: to reduce the production of adult mosquitoes over the whole rice-growing season

differentiation between culicines and anophelines87,90–94. It seems, from our review, that intermittent irrigation does

B There are interventions that kill the larvae at the moment of application:

prevent their development into late-stage immatures. This important conclusion is, however, based only on four

⃝ These are mostly chemical or biological insecticides; they have good immediate effectiveness but no residual effect.

with adequate replication, controls and differentiation between larval instars and species.

⃝ In practice, this is not long-term sustainable: it would be too expensive and too demanding in terms of logistical effort

larval stage) but emphasised that success was site-specific70,82,89. This contrast is presumably due to the inclusion
with intermittent irrigation but lacked either a contemporaneous control arm, adequate replication or adequate35

not prevent the recruitment of early instars (and in one case, may have encouraged oviposition ) but tends tostudies; more evidence is urgently needed where future trials should consider the basic principles of modern trials

Generally, it is observed that drainage, passive or active, did not reliably reduce overall numbers of mosquito

immatures. In India and Kenya, closer inspection revealed that soils were not drying sufficiently, so any stranded
larvae were not killed

35,95. Highlighted by van der Hoek et al. (2001) and Keiser et al. (2002), water management inrice fields is very dependent on the physical characteristics of the soil and the climate and is most suited to places

that not only favour rapid drying, but also have a good control of water supply70,89. Moreover, repeated drainage,
although directed against mosquitoes, can also kill their aquatic predators 96. Since mosquitoes can re-establish

themselves in a newly flooded rice field more quickly than their predators, intermittent irrigation with more than aweek between successive drying periods can permit repeated cycles of mosquito breeding without any predationpressure. Its efficacy against malaria vectors is therefore highly reliant on the timing of the wetting and drying

periods. Further site-specific research on timing, especially with regards to predator-prey interactions within therice agroecosystem, is required to find the perfect balance.

Another limitation in intermittent irrigation is that it cannot be applied during the first 2-3 weeks following

transplanting, because rice plants must remain flooded to recover from transplanting shock. Unfortunately, thistime coincides with peak vector breeding. Thus, other methods of larval control would be required to fill this gap.

To agronomists, intermittent irrigation provides benefits to farmers, as it does not penalise yield but significantly
reduces water consumption. Nonetheless, farmer compliance seems to be variable, especially in areas where wa-

ter availability is inconsistent and intermittent irrigation would potentially require more labour 35,97,98. Moreover, rice
farmers doubted their ability to coordinate water distribution evenly amongst themselves, suggesting that there may

be sharing issues, as in the “tragedy of the commons”99. Instead, they said that they preferred to have an agreed

authority to regulate water 95.

Rice cultivation practices other than water management
Studies that examined the effect of rice cultivation practices other than water management methods were

scarce. One study in Japan observed that varying rice plant heights were not associated with larval numbers100. A

study in India showed that plant density, regardless of rice variety, did not affect anopheline larval densities101. It

was also observed that using herbicides for weed control, compared to no weed control, was associated with 77%
102

higher larval numbers . On the other hand, pesticides were associated with a 76% reduction of anopheline larvae
103

in Indonesia . Different processes in land preparation seemed to affect mosquito numbers: whilst levelling had no⃝ Frequent re-application would be needed for longer-term control;and discipline.

C There are interventions that give longer-term suppression: these are not immediately lethal but
reduce the fraction of larvae that survive to adulthood⃝ These tend to be less immediately effective, but their effect lasts longer.

⃝ Most of these interventions take time to be effective; they cannot prevent the peak of mosquito production 1-5

weeks after transplantation, but they might help to reduce breeding later in the rice-growing season, when the rate ofproduction of adult mosquitoes is still going on, albeit at lower levels because of the presence of predators.

D Effective cover for the whole of the season might be possible using a combination of these twoclasses: short-term insecticidal interventions during the initial 4 to 5 weeks post-transplantation, andsuppressive interventions later.
E In any case, it is important that these interventions must not interfere with the growth of predator
populations. (NB note that the control of rice pests also relies on promoting predators and the same
“integrated pest management” principles).

In practice this implies a strong preference for bio-

insecticides that target mosquitoes, such as Bti.
F Other promising ideas include Azolla and rice-fish co-culture⃝ Surprisingly the potential of killifish (Nothobranchius spp, very rapid growth, short life-cycle, can survive in dry mud)does not seem to have been investigated.

⃝ The rice-and-fish co-cultivation methods used in southern China (and elsewhere) should be investigated for theirpotential in Africa

G If the task of controlling mosquito-breeding in rice fields is to be led by the rice experts (whilst being
supported by medical entomologists), then entomologists will need greatly improved methods ofmonitoring mosquitoes, i.e. improved methods of counting larvae.

effect, rice plots that were minimally tilled were associated with a 65% reduction compared to those with deep tillage(one study)104.

No general conclusions could be made on the effect on malaria vectors of other rice cultivation practices (apartfrom water management) because only one study was eligible for each practice. Nevertheless, these experiments on
pesticide application, tillage and weed control, as well as another study on plant spacing (not eligible since glass rods
were used to simulate rice plants), do illustrate that small changes in agronomic inputs and conditions can have con-siderable effects on mosquito densities102,104,105. Moreover, in partially- or shallowly-flooded plots, the larvae are often

21

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22

5 Overall Summar y and Conclusionsa) New evidence on rice and malaria in Africa (paddies paradox)⃝ The relationship between rice and malaria in Africa has changed: nowadays, irrigated lowland rice production iscontributing to the burden of malaria in Africa.
・ In the last 20 years, the massive distribution of effective interventions has reduced malaria transmission, andreduced inequities in intervention coverage.
・ Before this change, the available evidence suggested rice was bringing additional mosquitoes but not moremalaria; this was called “paddies paradox” and was probably correct at the time.
・ More recent evidence implies that currently, irrigated lowland rice brings not only more mosquitoes but also moremalaria.
⃝ Further analysis suggests that in the future as malaria continues to decline, the associations between rice andmalaria will emerge and become stronger. Rice fields are likely to emerge as foci of remnant transmission and
Figure 7. The effect of different intermittent irrigation techniques on larval densities of Anopheles vectors in rice fields. Seven studies were included, conducted between the years 1936 and 2016. Squares represent the relative effectiveness of individual studies, where square size represents the weight given
to the study in the meta-analysis, with error bars representing 95% CIs; diamonds represent the pooled effects from random effects (RE) sub-group andmeta-analyses.
Chan, K., Bottomley, C., Saito, K., Lines, J., & Tusting, L. S. (2022). The control of malaria vectors in rice fields: A systematic review and meta-analysis.
Under review.

become more conspicuous as an obstacle to elimination.

b) The strategic response⃝ These findings should NOT be interpreted as an inevitable trade-off between health and food and nutrition security,

or as a reason to delay the expansion and intensification of rice in Africa.
⃝ In fact the trade-off is not inevitable.

・Modified methods of rice-cultivation can minimise the number of mosquitoes emerging from rice fields.
・It seems likely that with further research, methods can be developed that will not only reduce mosquitoes but also
improve yield and be attractive to farmers.
・ Achieving such co-benefits should become a prioritised element within rice development research in Africa. Thiscan follow the example of reducing greenhouse gas (GHG) emissions from rice fields; researchers successfully
developed methods to address this challenge. It might even be possible to develop methods that can control
emissions of both GHG and mosquitoes.
⃝ More anti-malaria interventions – more nets and drugs – may be part of a short-term response, but they do not

represent a sustainable long-term solution for the pathway to malaria elimination.
⃝ Using current cultivation methods, the additional vectors from rice fields will always be a harmful unintended side

effect of rice-growing in Africa. Conversely, the suppression of mosquito-breeding using modified rice-cultivation
methods would be a highly beneficial intended side-effect.
⃝ Thus the development of irrigated rice in Africa should continue, but accompanied by a comprehensive programmeof research to develop such anti-mosquito methods of growing rice.

c) Priority intervention areas⃝ The best approach is probably to integrate the objective of mosquito control as fully as possible in the work of rice-

research & development agencies. It means adding the monitoring of mosquito-breeding into every development

23

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24project working for expansion and intensification of rice cultivation.
⃝ This raises a methodological issue: current methods of counting larvae are hopelessly labour-intensive and6 References

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7 Biography

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Name: Jo Lines
Position: Professor of Vector Biology and Malaria Control
Affiliation: the London School of Hygiene & Tropical Medicine.
Profile:I work on practical methods for the control of malaria mosquitoes. After training inevolutionary genetics and then medical entomology, I lived and worked in a small
town in Tanzania, working with colleagues to develop methods for the study ofvector control interventions, especially insecticide-treated nets, and helping tobuild a field research station. Over the years, I’ve been involved in collaborative
research in Southeast Asia, China and Latin America, and I’ve worked as aconsultant in support of national malaria control programmes, and in the designand evaluation of malaria control projects. From 2008 to 2011, I was Coordinatorof the Vector Control Unit of the World Health Organisation’s Global Malaria
Programme in Geneva, where I initiated and led the development of several stillcurrent set of WHO policy recommendations, especially the Global Plan for
Insecticide Resistance Management. Over the years, my research has gradually
become more multi-disciplinary and inter-sectoral. My current research addresses
two main issues: the insecticide resistance arms race with Africa vectors, and thegrowing problem of “man-made malaria” in anthropogenic landscapes.

103. Martono. Direct impact of agricultural insecticide application on anopheline larvae population with special reference to An. aconitus donitz in rice field. Bul. Penelit. Kesehat. 16, (1988).

Name: Kallista Chan

104. Djègbè, I. et al. Minimal tillage and intermittent flooding farming systems show a potential reduction in
the proliferation of Anopheles mosquito larvae in a rice field in Malanville, Northern Benin. Malar. J. 19,
333 (2020).
105. Russell, P. F. & Rao, T. R. On relation of mechanical obstruction and shade to ovipositing of Anopheles
culicifacies. J. Exp. Zool. 91, 303–329 (1942).
106. Chan, K. et al. Rice and Malaria in Africa: A Systematic Review and Meta-Analysis. SSRN Electron. J.
(2021). doi:10.2139/ssrn.3822272

Position: Research Uptake Manager
Affiliation: RAFT Consortium, London School of Hygiene and Tropical Medicine
Profile:With a background in infectious disease epidemiology and medical entomology,
I have a special interest in vector-borne diseases and their control. I am
particularly interested in the multisectoral nature of vector-borne diseases suchas the influence of landscape and agriculture on risk and potential control. I
am currently a PhD candidate at the London School of Hygiene and Tropical
Medicine, where I am exploring methods of growing rice without growing
malaria vectors.
In collaboration with AfricaRice and International Rice Research Institute, thePhD aims to identify potential agriculture and health co-benefits in improved ornovel rice cultivation techniques such as alternate wetting and drying irrigation.

31

Malaria no more japan ｜ 2022 repor t

32About Malaria No More Japan

Name: Kazuki Saito
Position: Principal scientist
Affiliation: Africa Rice Center
Profile:I am an agronomist employed by the Africa Rice Center, based in Côte d'Ivoire.
I have >20 years of research experience in Asia (2000-2005 as part of my MSc
and PhD studies) and sub-Saharan Africa (2006-present). I am also research
fellow in Japan International Research Center for Agricultural Sciences (JIRCAS)(2017-present), and part-time lecturer for Tokyo University of Agriculture andTechnology (2018-present). My works have focused on yield gap assessment,
diagnostic surveys, integrated management practices, decision support tool on

Malaria No More Japan was established in 2012 as the Japanesebranch of the U.S.-based Malaria No More and is the only certified
non-profit organization specializing in malaria in Japan (acquired
non-profit status in 2013, certified as a certified non-profit organization in2015).
Malaria No More group work to achieve our vision, “To be zero-malaria world in our lifetime”. To achieve this vision, Malaria No More Japan
has committed policy advocacy, communication, and promotion of partnerships.

nutrient management practices, farming systems research, and improvementof yield potential and abiotic/biotic stress resistance in rice. I have authoredand co-authored more than 100 scientific papers in peer-reviewed journals. I
received my PhD degree in Agriculture from Kyoto University,
Japan on ‘Description, constraints and improvement of slash-and-burn upland
rice production systems in northern Laos’. I was awarded the Louis Malassis

Official name:Malaria No More Japan (NPO)

Representative: Prof. Dr. Takahiro Shinyo
Dean of the Integrated Center for UN and Foreign Af-International Scientific Prize for Young Promising Scientists in 2015.

fairs Studies, Kwansei Gakuin University, and Trusteeof Kwansei Gakuin. He has served as Director of the
Global Issues Department of the Ministry of Foreign Af-

Name: Ali Ibrahim

fairs, Ambassador Extraordinary and Plenipotentiary at

Position: Systems Agronomist

the Permanent Mission of Japan to the United Nations,

Affiliation: Africa Rice Center

Japan in the Federal Republic of Germany. After serv-

and Ambassador Extraordinary and Plenipotentiary of
ing as Vice President of Kwansei Gakuin University, heProfile:I have been working for Africa Rice Center as Systems Agronomist since2019. My current research focuses on developing, testing, and disseminating
sustainable intensification and diversification options in irrigated rice farming
systems for improving livelihoods, nutrition and resilience of rural communities
and smallholder farmers in sub-Saharan Africa. Prior to joining AfricaRice, I
worked for OCP Africa as agronomist to develop and implement site-specificassumed his current position in June 2018.
Establishment: October 26, 2012
Office address: Chichibuya Bldg. 8F, 3-7-4 Kojimachi, Chiyoda-ku,
Tokyo 102-0083, JapanTEL:+81-3-3230-2553

E-mail:info@malarianomore.jp

nutrient management practices for sustainable crop production. I have authoredand co-authored more than 20 papers in peer-reviewed journals. I received my
PhD degree in Integrated Soil Fertility Management from Kwame University of
Science and Technology, Ghana in 2015. I received the President's International
Fellowship Initiative (PIFI) Postdoctoral Researcher Award from Chinese
Academy of Sciences (CAS) in 2016 and the Emerging Leader for African
Agricultural Transformation (ELAAT) Award in 2021, which was sponsored by
OCP Northern America and the American Society of Agronomy.

33

www.malarianomore.jp
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