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Emerging Infectious Diseases
Volume 2, Number 2, April-June 1996
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Dispatches
The Reemergence of Visceral Leishmaniasis in Brazil
Because of a complex array of factors, an increasing number of new and
reemerging infectious diseases are being recognized in both industrialized
and developing countries in the Americas (1,2). The expanding population,
living in overcrowded conditions with inadequate housing and sanitary
facilities, has been exposed to new diseases and human pathogens. For
example, the appearance of the South American arenaviruses (Junin, Machupo,
and Guanarito) illustrates how exploitation of new areas for human
settlement and agriculture increases the likelihood that new infectious
diseases will emerge. Cholera, plague, AIDS, dengue hemorrhagic fever, and
urban/periurban visceral leishmaniasis are examples of new and reemerging
diseases in the region.
In tropical America, zoonotic visceral leishmaniasis caused by Leishmania
chagasi, an intracellular protozoon, is a long-lasting infectious disease
characterized by weight loss, cough, fever, diarrhea, hepatosplenomegaly,
and lethargy. Since not all symptoms appear simultaneously, and many other
conditions manifest the same symptoms, the diagnosis is not always
opportune. This disease is different from the anthroponotic form of
visceral leishmaniasis found in Sudan and India. In the New World this
disease is more common among poor, malnourished children (3) under 15 years
of age who live in semiarid regions. The case-fatality rate is low if
pentavalent antimony therapy is introduced promptly (4). The disease has
also been reported in immunodepressed persons, especially those with HIV
infection.
The domestic dog is the principal animal reservoir of L. chagasi and, as
the constant companion of humans throughout the endemic-disease area,
contributes to the dispersal of diseases during human migrations. The
protozoon is transmitted from one mammalian host to another, including
humans, primarily by the bite of a sand fly who has fed on an infected dog.
In the Americas, the principal sand fly vector is Lutzomyia longipalpis
(5). This 2- to 3-mm long fly has peridomestic and intradomiciliary habits
(6) and avidly bites humans at night, primarily during twilight, while the
host is resting.
Visceral leishmaniasis is usually diagnosed by identifying the parasite in
spleen aspirates; microscope examination of bone marrow aspirates offers a
satisfactory alternative. Specific antibodies may be detected by
immune-enzymatic reactions and immunofluorescence, but these methods lack
specificity and are too complex to be carried out in the field. TRALd, a
recently developed diagnostic test, consists of a 60-second dipstick, based
on a recombinant protein rK39 of a sequence of 298 amino acids and an
improved serologic procedure (7). The procedure is undergoing field testing
and appears to be a promising tool for control programs.
Although visceral leishmaniasis was previously known as a rural disease,
large outbreaks and epidemics of visceral leishmaniasis have been reported
recently in large cities in Brazil because of the favorable epidemiologic
conditions associated with the reduction of the natural ecologic space of
this zoonosis. Waves of droughts, lack of available farm land, and famine
have led to a large migration of the population, to the peripheral suburbs
of large cities, creating densely populated settlements of shanties
(favelas) with minimal infrastructure and sanitation. Most families that
migrate are young, less-established farmers of peak child-bearing age;
children under 15 years of age account for a large percentage of the entire
population. In these communities, the newly introduced disease (parasite)
encounters a vast number of nonimmune hosts who, because of poor living
conditions, are malnourished; malnutrition is one of the prime risk factors
for L. chagasi infection and visceral leishmaniasis (3). The habit of
keeping domestic animals such as dogs, chickens, and horses in the back
yard provides an abundance of blood meals for sand fly vectors and raises
vector population densities dramatically.
Two recent examples of reemerging visceral leishmaniasis in Brazil occurred
in the citiesof Teresina (population = 678,000), the capital of Piau
State, and So Lus (population = 918,000), the capital of Maranho State.
In Teresina, which has the best-documented records, an epidemic of visceral
leishmaniasis occurred from 1981 to 1985; it was initially limited to rural
settings, but later spread to peripheral areas of the city (9) (Figure 1).
Spraying with residual insecticide helped bring the disease under control
during the subsequent 3 years. Since 1989, visceral leishmaniasis has
gradually reemerged; it reached epidemic levels by the end of 1992 and
peaked in 1994. In the State of Maranho, the disease reemerged in 1993,
(Figure 2), 10 years after a previous epidemic (1982 to 1986). In both
Teresina and So Lus, the epidemics were preceded by prolonged, severe
drought. The disease was found predominantly among young people who came
from rural areas and lived in periurban, substandard housing and kept
domestic animals in their back yards. The two states accounted for
approximately 40% to 50% of the number of cases reported in the country
during 1993 to 1994 (3,000/year).
[Image not available in ASCII version]
Figure 1. Number of cases of visceral leishmaniasis from the state of
Pianu, Brazil, 1971 to 1994.
[Image not available in ASCII version]
Figure 2. Number of cases of visceral leishmaniasis from the state of
Maranho, Brazil, 1979 to 1994.
Emergency control plans based on rapid diagnosis, complete treatment of
human patients, spraying of residual insecticide, ultra-low volume
spraying, elimination of infected (seropositive) dogs, and health education
were initiated in these two cities in July 1994 (10). The incidence rate
dropped markedly from January 1995, as expected, since the incubation
period of visceral leishmaniasis is 4 to 6 months (11, 12). The remaining
reported cases include those with longer incubation periods, as well as
others, because of the lack of complete coverage of the control
interventions and reduced sensitivity of the current diagnostic tools.
Technical expertise and effective mechanisms to prevent visceral
leishmaniasis epidemics and urban transmission exist, but they require
social and political commitment as well as the allocation of funds to
provide adequate sanitary and satisfactory housing conditions to the
population at risk. Visceral leishmaniasis in the Americas must be
addressed before it becomes a serious public health problem. Even though it
is a zoonosis, control interventions are available that, when properly
used, can eliminate urban transmission and keep disease incidence in rural
areas at a very low level.
Jorge R. Arias, Ph.D.,* Pedro S. Monteiro, and Fabio Zicker, M.D., Ph.D.
*Pan American Health Organization, Brasilia, Brazil; National Visceral
Leishmaniasis Control Program, Ministry of Health, Brasilia, Brazil; Pan
American Health Organization, Washington, D.C.
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