Seven villages in Banggi Island, Sabah, Malaysia, were surveyed four times to evaluate the roles of local mosquitoes as vectors of malaria and Bancroftian filariasis. 11 species of Anopheles were found biting man. 53.9% of the anophelines caught were An. flavirostris, 27.1% An. balabacensis, 6% An. donaldi and 4.2% An. subpictus. Infective malaria sporozoites, probably of human origin, were found in two of 336 An. flavirostris and 12 of 308 An. balabacensis. Sporozoites, probably of a non-human Plasmodium, were found in An. umbrosus. Nine of 1001 An. flavirostris and four of 365 An. balabacensis harboured L2 or L3 filarial larvae identified as those of Wuchereria bancrofti. This is the first record of An. flavirostris as a natural vector of malaria and W. bancrofti in Sabah.
Studies were carried out to observe the species composition of mosquitos and to determine the vectors responsible for the transmission of filariasis in Grik, Perak, Malaysia. A total of 2,155 mosquitos belonging to 7 genera and 30 species were collected. Anopheles donaldi comprised 24.1% of the collection. Twelve out of 519 An. donaldi were infected with L3 larvae of Brugia malayi. The peak biting time was around 23.00-24.00 hours. The infective bites per month ranged from 0 to 6.3.
Comparative studies of vector efficiency were done with the Liverpool and Malaysian strains of Aedes (Finlaya) togoi for subperiodic Brugia malayi and Brugia pahangi. The Malaysian strain of A. togoi was found to take in fewer microfilariae under the same experimental conditions than the Liverpool strain. Also, for various microfilarial densities in the host's peripheral blood, the Malaysian strain had less mean infective larvae per fed mosquito than the Liverpool strain. The microfilarial intake of A. togoi was not affected by the site of feeding on the host affected by the site of feeding on the host. Most of the mosquitoes took in fewer microfilariae than expected. It is concluded from these studies that the Malaysian strain of A. togoi is a susceptible and reasonably good vector for subperiodic B. malayi and B. pahangi. Further field studies should be carried out to determine its importance as a natural vector of Brugian filariasis.
Surveillance methods for Coquillettidia crassipes were studied in an open housing estate near Kuala Lumpur using three types of traps Trinidad 10 trap, modified Lard can trap and IMR trap, each baited with chicken or pigeon. All traps attracted Cq. crassipes. There was no significant difference in the catches in the three traps. There was also no significant difference between chicken and pigeon as bait. Catches at heights of 1.5, 3, 4.5 and 6 m did not show any significant difference in density. Cq. crassipes was active at night with an early peak during the first hour of the night and a minor peak between 0100 and 0200 hours. The activity of the parous and nulliparous sections of the population was similar, except that a higher proportion of the parous females was active during the second peak compared with the nulliparous females. The parous rate was 22.3%, and the probability of survival through one day for two gonotrophic cycles was 0.711 and 0.650. The infection rate for Cardiofilaria was 29 out of 1052 (2.76%) and the infective rate (L3 larvae) was 13 out of 1052 (1.24%). 48.3% of the infected Cq. crassipes had a worm burden of more than ten larvae. One of the chickens in the traps was positive for microfilariae of Cardiofilaria four weeks after exposure as bait. Laboratory bred Cq. crassipes fed on this chicken produced infective larvae in ten days, and these were inoculated into clean chickens and pigeons. Microfilariae appeared in the chickens but not in pigeons. The adult worms recovered await identification.
Using seven methods of surveillance, 58 species of mosquitoes from nine genera were in Pantai and the two neighbouring villages during two visits in 1982. Ma. bonneae was the most prevalent species attracted to man. In the forest shade Ma. bonneae and Ma. dives showed activity throughout the 24 hours with peak biting during 1900-2100 hours. An. balabacensis exhibited peak activity shortly after midnight. Inside and outside house, Ma. bonneae showed similar activity except that it ceased during the day. Mansonia was only mildly zoophilic. CDC light traps gave poor yields of mosquitoes. Pyrethrum spray catch inside houses early morning did not include any Mansonia. Outdoor day resting catch included Ma. bonneae fed on man. Transmission of Brugia, probably human filariasis, by Ma. bonneae occurred in Pantai and in the two neighbouring villages. One infection in Ma. dives was found in Pantai. The monthly infective biting rate and monthly transmission potential for Ma. bonneae were estimated at the forest shade and outside the house in Pantai.
The dynamics of the transmission of subperiodic Brugia malayi in a typical endemic area in Malaysia was studied over a period of 4 years. Mass chemotherapeutic control with diethylcarbamazine citrate was found to be inefficient, new cases being detected even after the fifth treatment cycle of 6 mg/kg X 6 days per cycle. This is in marked contrast to the situation in periodic b. malayi areas where mass treatment efficiently controlled the infection. The disparity in results in these two areas is attributed to zoonotic transmission of subperiodic B. malayi from non-human primates where a mean infection rate of 76.3% was found.
Accurate identification of filarial parasites in mosquitoes poses a major problem for the coordination of filariasis control programs. Traditional methods are tedious, and some are not specific enough to give satisfactory results. Amplification of specific gene sequences by primer-directed polymerase chain reaction (PCR) has been increasingly utilized as a diagnostic tool. However, current protocols for the extraction of parasite DNA from mosquito samples are tedious and could lead to failure of PCR amplification. We demonstrate that the use of Chelex is an efficient method for DNA extraction from mosquitoes and the parasite and that PCR amplification with primers specific for Brugia malayi yields a band of the expected size. The PCR products were transferred to a nylon membrane with Southern blotting, and a B. malayi-specific digoxigenin-labeled probe confirmed the sequence similarity of the PCR-amplified fragment and increased the sensitivity of the PCR assay. Use of this probe enabled us to detect PCR-amplified product from B. malayi even when a product was not visible on an ethidium bromide-stained agarose gel. This increased sensitivity allowed us to detect the parasite in the heads of mosquitoes.
Entomological investigations on malaria and bancroftian filariasis transmission were carried out in the endemic area of Baram District, Sarawak. The Anopheles composition, survival and infection rates of malaria and filariasis were compared in the village and 0.5 km from the village ecotype, in forested areas. Anopheles leucosphyrus, An. barbirostris and An. donaldi are the vectors for malaria and bancroftian filariasis in both ecotypes. Biting and infection rates vary, but An. leucosphyrus differed with a peak around midnight in the forested area and soon after dusk in the village setting. The parous rate of An. leucosphyrus was significantly higher in the forest ecotype (P < 0.0001); however, the proportion of 3-parous and older was not overall higher in the forest ecotype (P = 0.68). The entomological inoculation of malaria parasites by An. leucosphyrus was comparatively higher in the forested areas (P > 0.5). The implications of malaria and filariasis transmission in the forested areas in Baram District are discussed.
A total of 37 species of mosquitoes from seven genera were collected in six villages in the Bengkoka Peninsula, Sabah State, during two visits in 1981 in connection with studies on malaria and filariasis. Fifty-five per cent of the total mosquitoes collected were Mansonia. An. collessi constituted a new record of the species from Sabah. An. balabacensis was found to be naturally infected with sporozoites. Ma. bonneae was found to be naturally infected with Brugia, probably B. malayi. Parous rates of An. balabacensis and Ma. bonneae were very high with consequent high probability of survival ideally suiting transmission of malaria and filariasis.
Studies on age groups within activity cycles, age composition and survivorship in natural populations of Mansonia in Kampung Pantai, Bengkoka Peninsula of Sabah state have been described. Early activity of 3-5 parous Ma. bonneae during the first hour after sunset was noted. Age composition of Ma. bonneae at forest shade, indoor and outdoor of house, comparative buffalo vs human bait outdoor in Kampung Pantai showed all round high parous rates ranging from 66.7 to 75.4%. Population 3-parous and older ranged from 18.8 to 26.7%. Nine of the 14 infective Ma. bonneae were 3-parous and this segment of the population was engaged in active transmission. High parous rates were observed in Ma. dives and Ma. uniformis taken in small numbers. Parous rates of Ma. bonneae taken in Kampung Delima and Kampung Taradas were also high. Estimates of daily survivorship of Ma. bonneae and Ma. dives determined by two methods were very high.
A study to identify the knowledge of infected and uninfected respondents on filariasis and epidemiologic factors in one endemic community in Malaysia to determine their role in the transmission and control of filariasis was carried out. The data were collected by non-participant observations and interviews using semi-structured schedules. The majority of respondents in both groups had knowledge of filariasis. There was no marked difference between male and female respondents, and similarly, there was fair distributions of knowledgeable respondents with and without some years of schooling. On filarial transmission, 9.2% of the infected said that filariasis was contacted through mosquito bites, while among the uninfected it was 7.4%. Within the infected, 14.8% thought that filarial worms entered the human body through the consumption of unhygenically prepared foods and drinks while, among the uninfected it was 20.4%. Both groups were aware of the presence of mosquitoes in their village. However, the majority did not associate this factor with host's susceptibility to filarial infections. Rather, they were of the opinion that personal hygiene and proper meals had something to do with filariasis. The findings showed there was general awareness of filariasis in the community which might indicate that the health campaigns had reached various levels of the population. Yet, they still lacked knowledge on disease transmission. Also, they did not make direct association between environment and exposure to mosquitoes bites though they were aware of their presence but which they regarded as not directly harmful to their health.
Filarial infections in 447 cats and 68 dogs from six endemic areas of human filariasis in Peninsular Malaysia were studied as part of the study on the zoonotic transmission of subperiodic Brugia malayi infection. 20.6% of cats and 57.4% of dogs had filarial infections. Cats were infected with subperiodic B. malayi, B. pahangi, Dirofilaria repens and D. immitis. Dogs were infected with B. pahangi and D. immitis. 6.9% of the cats had subperiodic B. malayi infection. The zoonotic implications of these infections and their impact on the filariasis control programme in Peninsular Malaysia were discussed.