Species Composition Of Mosquitoes and The Risk of Dengue Fever in The Batticaloa District

Abstract

Mosquito-borne diseases are a major public health problem in Sri Lanka causing high morbidity and mortality. The parasitic diseases such as Malaria and Filariasis are mainly vectored by Anopheles culicifacies Giles and Culex quinquefasciatus Say respectively. The transmission of viral disease such as Japanese encephalitis is mediated by Culex tritaenorhynchus Giles and Dengue and Chikungunya are transmitted by Aedes aegypti Linnaeus and Aedes albopictus Skuse.Adramatic increase in the reported cases of Dengueand DengueHaemorrhagic Fever (DHF) in Sri Lanka has been observed in recent years. Nearly 23,656 suspected cases with over 237 deathswerereportedduringthe32week periodof theyear2009.(Source:EpidemiologyUnit, SriLanka). In this background, the present study was carried out from June 2008 to end of February 2009 in Urban, Suburban and Paddy field areas in the Batticaloa districts to record the mosquito species and to relate the risk of mosquito borne viral and protozoan diseases. Outdoor Cattle Baited Hut (CBH) and Cattle Baited Net (CBN) collection of adult mosquitoes were made and collected adult mosquitoes were analyzed for their species composition. Out break of Dengue was correlated with the spatial distribution of Aedes aegypti and Aedes albopictus in both indoor and outdoor ovitrap collections in the Batticaloa Urban areas and the Chenkalady Suburban areas. During the study period, five species of Anopheles sp, four Culex sp, one species of Mansonia sp and Armigerous sp and twoAedes sp were identified. In addition, larvivorous predator mosquitoes such as Lutzia sp (subgenus of Culex) and Toxorhynchites sp were also collected. Among these identified mosquitoes, An.subpictus was the predominant species contributing the maximum of 33% in September in Urbanareaswhile 32%and16%in Suburban and Paddyfieldareasrespectively. Aedes aegypti was the predominant species in the outdoor collection in Batticaloa Urban area and in the indoor collection in Chenkalady Suburban area. Statistical analysis indicated that the highest values for Aedes aegypti, with mean value of 157.6± 19(SE), from outdoor collection in Batticaloa Urban areas and from indoor collection in Chenkalady Suburban areas with mean value of191.55±22.70 (SE). The study also revealed a correlation between the Dengue fever records and the presence of Aedes aegypti in the Batticaloa Urban area. The vector management practices should be designed based on the spatio-temporal relationships with vector species with active participation of the public and health education.