# Dengue pandemic in Sri Lanka

The dengue pandemic in Sri Lanka is part of the tropical disease dengue fever pandemic. Dengue fever is caused by Dengue virus, first recorded in the 1960s. It is not a native disease in this island. Present-day dengue has become a major public health problem. Aedes aegypti and Aedes albopictus are both mosquito species native to Sri Lanka. However, the disease did not emerge until the early 1960s. Dengue was first serologically confirmed in the country in 1962. A Chikungunya outbreak followed in 1965. In the early 1970s two type of dengue dominated in Sri Lanka: DENV-1 type1 and DENV-2 type 2. A total of 51 cases and 15 deaths were reported in 1965–1968. From 1989 onward, dengue fever has become endemic in Sri Lanka.

## Status of outbreak

Dengue cases by month and year :
| Month | 2021 | 2020 | 2019 | 2018 | 2017 | 2016 | 2015 | 2014 | 2013 | 2012 |
| January | 1,496 | 11,608 | 5,580 | 7,278 | 10,927 | 6,694 | 6,345 | 3,610 | 3,462 | 3,986 |
| February | 1,794 | 5,368 | 3,736 | 4,490 | 8,724 | 4,439 | 3,731 | 2,011 | 3,258 | 3,145 |
| March | 849 | 1,683 | 3,832 | 3,380 | 13,540 | 2,696 | 1,962 | 1,648 | 2,996 | 2,628 |
| April | 1,702 | 511 | 2,970 | 2,618 | 12,510 | 2,832 | 1,293 | 1,682 | 2,109 | 2,028 |
| May | 137 | 1,548 | 4,260 | 3,560 | 15,936 | 2,422 | 1,625 | 4,292 | 2,614 | 2,550 |
| June | | 2,252 | 6,019 | 5,513 | 25,319 | 4,731 | 1,477 | 6,736 | 2,427 | 5,955 |
| July | | 2,288 | 8,897 | 6,455 | 41,121 | 10,715 | 2,125 | 5,721 | 2,924 | 5,193 |
| August | | 1,559 | 9,546 | 4,293 | 22,270 | 4,873 | 1,604 | 4,022 | 3,282 | 5,266 |
| September | | 1,209 | 7,307 | 2,049 | 9,519 | 3,629 | 1,099 | 2,640 | 1,912 | 2,857 |
| October | | 1,028 | 11,573 | 1,905 | 6,614 | 2,185 | 2,066 | 4,297 | 1,636 | 3,181 |
| November | | 779 | 21,769 | 4,537 | 8,868 | 2,257 | 2,762 | 5,452 | 2,611 | 4,034 |
| December | | 1,318 | 19,560 | 5,581 | 10,753 | 7,677 | 3,688 | 5,91 | 2,832 | 3,638 |
| Total | 6,389 | 31,162 | 105,049 | 51,659 | 186,101 | 55,150 | 29,777 | 47,502 | 32,063 | 44,461 |
Dengue cases by region :
| Region | Region | Cases | Cases |
| Provinces | Districts | 2021 | 2020 |
| Western | Colombo | 1,027 | 4,257 |
| Western | Gampaha | 525 | 2,666 |
| Western | Kalutara | 346 | 1,810 |
| Western | Total | 1,898 | 8,733 |
| Central | Kandy | 252 | 3,443 |
| Central | Matale | 34 | 595 |
| Central | Nuwara Eliya | 23 | 168 |
| Central | Total | 309 | 4,206 |
| Southern | Galle | 90 | 1,671 |
| Southern | Matara | 147 | 545 |
| Southern | Hambantota | 126 | 368 |
| Southern | Total | 363 | 2,584 |
| North Western | Kurunegala | 382 | 969 |
| North Western | Puttalam | 165 | 500 |
| North Western | Total | 547 | 1,469 |
| Sabaragamuwa | Kegalle | 173 | 865 |
| Sabaragamuwa | Ratnapura | 211 | 2,014 |
| Sabaragamuwa | Total | 384 | 2,879 |
| Eastern | Trincomalee | 80 | 2,296 |
| Eastern | Batticaloa | 2,818 | 3,717 |
| Eastern | Ampara | 134 | 1,298 |
| Eastern | Total | 3,032 | 5,015 |
| North Central | Anuradhapura | 55 | 433 |
| North Central | Polonnaruwa | 23 | 251 |
| North Central | Total | 78 | 684 |
| Northern | Jaffna | 94 | 2,157 |
| Northern | Kilinochchi | 20 | 135 |
| Northern | Mannar | 19 | 137 |
| Northern | Mullaitivu | 3 | 90 |
| Northern | Vavuniya | 24 | 252 |
| Northern | Total | 160 | 2,771 |
| Uva | Badulla | 31 | 525 |
| Uva | Monaragala | 39 | 0 |
| Uva | Total | 70 | 525 |

## History

Dengue outbreaks started to emerge in Sri Lanka in the 1960s, with the Ministry of Health first serologically confirming the disease in Sri Lanka in 1962. However, unofficial British Ceylon clinical studies recorded dengue-like cases in Sri Lanka in the early 20th century. The first outbreak was confirmed in 1965 and was associated with DEN types 1 and 2, with 51 cases of 15 deaths between 1965 and 1968. Since 1989 dengue has become a major problem in Sri Lanka. From 1970 to 1990, multiple outbreaks with endemic were reported in Western Province urban areas. In 1990 dengue cases rose 1,350 of 54 deaths. In the early 1990s, annual dengue cases were reported as being up to 1,000. In 2002 the largest outbreak in recent years was recorded, with 8,931 cases and 64 deaths. The following year, 2003, was one of relatively low endemicity, with only 4,749 suspected cases and 32 deaths reported. In 2004 there were 15,463 suspected cases and 88 deaths reported to the Epidemiological Unit of the Ministry of Health. During the year 2005, 5,211 cases of suspected cases of DF/DHF and 26 deaths were reported to the Epidemiological Unit.
Most dengue cases reported dominated in Western Province. Outbreaks from 2005 to 2008 were attributed to a new mutation DEN type 3. Almost all the districts in Sri Lanka have reported cases and posed a threat to the health of the people. Colombo, Gampaha, Kalutara and Kandy districts have recorded highest number of cases.

## Background

Sri Lanka is a tropical and warm country. Mean temperatures range from 28 °C. The rainfall pattern is influenced by monsoon winds from the Indian Ocean and Bay of Bengal. Average rain at 800 to 1,200 mm per year. Average humidity from 75% during different seasons and in the different regions of the country. Tropical region humidity ranges from 75% to 90%. Sri Lanka is a tropical country with two monsoons: the northeast monsoon (December to March) and the southwest monsoon (May to September). Two annual peaks have been identified in the occurrence of dengue cases in the country in association with the monsoon rain.