Isolation of Japanese encephalitis virus (JEV) from mosquitoes in Sabak Bernam, Selangor, Malaysia, was attempted. An aliquot of homogenate from each pool of mosquitoes, 50 per tube, was inoculated into Aedes albopictus clone C6/36 cells for virus isolation. Each cell culture was tested for the presence of viral antigen by immunoperoxidase staining using an anti-JEV polyclonal antibody. Out of 4 Culex sitiens mosquito pools, 2 pools were positive for JEV by cell culture. Presence of JEV genome in the cell cultures for Cx. sitiens was confirmed by using reverse transcriptase-polymerase chain reaction and JEV-specific primers. This is the first report on the isolation of JEV from Cx. sitiens.
The mosquito Anopheles balabacensis balabacensis has been identified as a natural vector of at least two species of simian malaria in the monsoon forests of the northern Malay States. This mosquito is also a serious vector of human malaria from Viet Nam to northern Malaya. This is the first report of a mosquito which transmits both human and simian malaria in nature.
Systematic surveys of the wild macaques of South Asia by blood culture resulted in the discovery that trypanosomiasis is enzootic in the simians of Indonesia, Malaysia, India, and Thailand. The isolates obtained differ in morphology, metabolism, and ability to multiply in arthropods. Following this discovery, interest focused on possible transmissions of these trypanosomiases. Laboratory-reared and wild-caught insects were studied to determine which are satisfactory intermediate hosts and potential natural vectors. Successful results were obtained with insectary-reared reduviids and Indonesian isolates. In Rhodnius prolixus and Triatoma rubrofasciata the Indonesian trypanosomes multiply for periods which can exceed 40 days. The flagellate infections are in the digestive tract, whereas trypanosomes have never been seen in the salivary glands or in the hemolymph. The feces of trypanosome-carrying reduviids are infective, suggesting a stercoreal method of infection of mammals, and infection was produced in experiments in which feeding by the insects was not possible. The relevance of these findings to natural transmission in Indonesia is not known. Experiments with insects and all other trypanosomal isolates have been negative. The natural transmission mechanism(s) of the simian trypanosomiases in South Asia remains an unsolved problem.
Detection and isolation of Japanese encephalitis (JE) virus were attempted from female mosquitoes collected in Kampong Pasir Panjang, Sabak Bernam, Selangor, from May to November 1992. A total of 7,400 mosquitoes consisting of 12 species in 148 pools were processed and inoculated into Aedes albopictus clone C6/36 cell cultures. Of these, 26 pools showed the presence of viral antigens in the infected C6/36 cells by specific immunoperoxidase staining using an anti-JE virus polyclonal antibody. Presence of JE virus genome was confirmed in the infected culture fluid for 16 pools by using reverse transcriptase-polymerase chain reaction and JE virus-specific primers. Of these, 3 pools were from Culex tritaeniorhynchus, 4 from Culex vishnui, 3 from Culex bitaeniorhynchus, 2 from Culex sitiens, one from Aedes species, and 3 from Culex species. Isolation of JE virus from Cx. sitiens, Cx. bitaeniorhynchus, and Aedes sp. (Aedes butleri and Ae. albopictus) is reported for the first time in Malaysia.
Five mark-release-recapture experiments with wild caught Ma. uniformis were conducted in an open swamp area at Batang Berjuntai in Selangor, 40 km from Kuala Lumpur, Malaysia, between May 1983 and January 1985. A total of 64 (0.14%) from the 45,950 females released were recaptured feeding on humans and cattle and resting in cattle-sheds. Substantially fewer (0.03% to 0.09%) females were recaptured from releases of blood-fed females than from releases of unfed females (0.20% to 0.23%). More than 70% of all recaptures were taken within a radius of 1.5 km around the point of release and the longest detected flight was 3.5 km. The mean dispersal distance for blood-fed and unfed females was 1.445 +/- 1.06 and 1.706 +/- 1.03 km, respectively. However, there was no significant difference in the overall mean dispersal of the two groups of females (p greater than 0.05). The duration of the gonotrophic cycle in the field was between 3 to 4 days. Daily survivorship estimates (0.783-0.867) based on the recapture rates of date specific marked females was comparable to that estimated vertically from the dissection of unmarked females (0.751-0.795). These experiments revealed the remarkable flying ability of Ma. uniformis and the importance of reinvasion must be recognized when control operations are restricted to small areas.