Distribution changes of cutaneous leishmaniasis: A postulated risk of disease transmission in Hambantota, Sri Lanka.

BACKGROUND OBJECTIVES: Leishmaniasis is caused by various species of parasite Leishmania. Approximately twenty of them are pathogenic to mammals. In Sri Lanka, cutaneous leishmaniasis (CL) is an established vector-borne disease. CL originates and spreads mainly through sandfly bite in many endemic countries. The aim of the present study was to compare the geographical distribution and demographic features of CL cases in Hambantota district, Sri Lanka in 2014 and 2016. METHODS: The patients who were presented to the Tangalle Base Hospital from June to December in 2014 and 2016 were examined and a descriptive study was carried out using a structured-questionnaire. Slit-skin smears were collected from each patient, Giemsa-stained and examined under the light microscope to identify Leishmania amastigotes. RESULTS: Out of 256 and 314 suspected CL patients, 156 and 155 were identified positive for the year 2014 and 2016, respectively. Out of 12 District Secretary Divisions (DSD) in Hambantota district, the highest number of CL cases, 85 and 86 was reported from Tangalle DSD in 2014 and 2016 respectively. Number of identified CL patients in Beliatta DSD had increased from 50 to 67 during the study period. In both years, majority of CL patients were ≥50 years old with males more infected than females. Although CL association with occupations were insignificant, housewives were the highly (23%) infected occupants in this area. INTERPRETATION CONCLUSION: Based on the present findings, geographical distribution within DSDs in Hambantota district had changed. This emphasizes the importance of CL as a health problem in Hambantota district.

Wolbachia infection is widespread in brackish and fresh water Aedes albopictus (Diptera: Culicidae) in the coastal Jaffna peninsula of northern Sri Lanka.

BACKGROUND & OBJECTIVES: Aedes albopictus and Aedes aegypti are important vectors of dengue and many other arboviral diseases in tropical and sub-tropical locations. Both vectors are tolerant of salinity in the dengue-endemic coastal Jaffna peninsula of northern Sri Lanka. Aedes albopictus pre-imaginal stages are found in field brackish water habitats of up to 14 parts per thousand (ppt, gL-1) salt in the Jaffna peninsula. Salinity-tolerance in Aedes is characterized by significant genetic and physiological changes. Infection with the wMel strain of the endosymbiont bacterium Wolbachia pipientis reduces dengue transmission in the field by Ae. aegypti, and the same approach is also being considered for Ae. albopictus. In this context, we investigated natural Wolbachia infections in brackish and fresh water field isolates of Ae. albopictus in the Jaffna district. METHODS: Aedes albopictus collected as pre-imaginal stages using conventional ovitraps in the Jaffna peninsula and adjacent islands of the Jaffna district were screened by PCR utilizing strain-transcending primers for the presence of Wolbachia. Wolbachia strains were then further identified by PCR using strain-specific primers for the Wolbachia surface protein gene wsp. The Jaffna wsp sequences were compared by phylogenetic analysis with other wsp sequences available in Genbank. RESULTS: Aedes albopictus were found to be widely infected with the wAlbA and wAlbB strains of Wolbachia in Jaffna. The partial wAlbB wsp surface protein gene sequence in Jaffna Ae. albopictus was identical to a corresponding sequence from South India but different from that in mainland Sri Lanka. INTERPRETATION & CONCLUSION: Widespread infection of salinity-tolerant Ae. albopictus with Wolbachia is a factor to be considered when developing Wolbachia-based dengue control in coastal areas like the Jaffna peninsula.

Salinity tolerant Aedes aegypti and Ae. albopictus-Infection with dengue virus and contribution to dengue transmission in a coastal peninsula.

BACKGROUND & OBJECTIVES: Aedes aegypti and Ae. albopictus are major arboviral vectors that are considered to lay eggs, and undergo preimaginal development only in fresh water collections. However, recently they have been also shown to develop in coastal brackish water habitats. The ability of the biologically variant salinity-tolerant Aedes vectors to transmit arboviral diseases is unknown. We therefore, investigated the infection of salinity-tolerant Aedes mosquitoes with dengue virus (DENV) and analysed dengue incidence and rainfall data to assess the contribution of salinity-tolerant Aedes vectors to dengue transmission in the coastal Jaffna peninsula in Sri Lanka. METHODS: Brackish and fresh water developing female Ae. aegypti and Ae. albopictus were tested for their ability to become infected with DENV through in vitro blood feeding and then transmit DENV vertically to their progeny. An immunochromatographic test for the NS1 antigen was used to detect DENV. Temporal variation in dengue incidence in relation to rainfall was analysed for the peninsula and other parts of Sri Lanka. RESULTS: Aedes aegypti and Ae. albopictus developing in brackish water, became infected with DENV through in vitro blood feeding and the infected mosquitoes were able to vertically transmit DENV to their progeny. Monsoonal rainfall was the discernible factor responsible for the seasonal increase in dengue incidence in the peninsula and elsewhere in Sri Lanka. INTERPRETATION & CONCLUSION: Fresh water Aedes vectors are main contributors to the increased dengue incidence that typically follows monsoons in the Jaffna peninsula and elsewhere in Sri Lanka. It is possible however, that brackish water-developing Aedes constitute a perennial reservoir for DENV to maintain a basal level of dengue transmission in coastal areas of the peninsula during the dry season, and this supports increased transmission when monsoonal rains expand populations of fresh water Aedes.