Biomedical subjects
Publications and source records attributed to I Vythilingam.
Four species of malaria parasites are known to infect humans. A fifth species, Plasmodium knowlesi, has been reported to infect humans in Malaysian Borneo. Here we report for the first time the incrimination of Anopheles latens as the vector of P. knowlesi among humans and monkeys in Sarawak, Malaysia.
A study was carried out from July 2001 until January 2003 in the Kinabatangan area of Sabah, part of Borneo island, where malaria used to be mesoendemic. Vector surveys determined that Plasmodium falciparum was the predominant species and Anopheles balabacensis the primary vector. Malaria cases have dropped drastically over the years but P. falciparum is still predominant. In the present study, Anopheles donaldi was the predominant species and was positive for sporozoites. Although An. balabacensis was present, none were infective. An. donaldi bite more outdoors than indoors and have a peak biting time from 18:00 to 19:00 h when most people are still out of their homes. An integrated malaria control programme along with area development has helped in the control of malaria and its vector.
Surveys were conducted in malaria-endemic villages in the southern province of Attapeu, Lao PDR during various seasons over a 3-year period. All-night mosquito landing collections, blood surveys and a case-control study were conducted. Plasmodium falciparum was the predominant species, and slide positivity rates were higher during the transition/dry season compared with the wet season. Anopheles dirus A was found to be the primary vector, and sporozoite rates were highest during the transition/dry season. Anopheles dirus was found to be endophagic and endophilic. Not using insecticide-treated bed nets, houses close to breeding sites and sleeping away from home were risk factors associated with malaria.
Laboratory strain of the Malaysian Culex quinquefasciatus was susceptible to Wuchereria bancrofti. Thirty three percent of the Cx. quinquefasciatus that fed on W. bancrofti patient were infective after 12-14 days. There is a possibility for W. bancrofti to occur in the urban areas of the Malaysia in the near future.
Adult mosquito collections were conducted for 12 weeks in two residential areas in Kuala Lumpur. The CDC light traps were compared using dry ice and yeast as sources of carbon dioxide attractants for mosquitoes. The efficacy of the dry ice baited trap was significant over yeast generated CO2 trap. The predominant species obtained were Culex quinquefasciatus, Stegomyia albopicta and Armigeres subalbatus.
A study was conducted in four villages in Attapeu Province, Lao PDR in 2002 to determine malaria endemicity. The study villages were Mixay, Beng Phoukham, Phou Vong and Pier Geo. Mass blood surveys were conducted in May, August, and October. Finger prick blood was collected for thick and thin blood film as well as for dipstick. The slide positivity rate was highest in Phou Hom in October (41.7%). Plasmodium falciparum was the dominant species comprising more than 80% of the cases. As a whole, the distribution of malaria was similar among males and females. Children below 15 years accounted for a large percentage of the cases. The sensitivity of the optimal dipstick was 62.36 and the specificity was 61.7. Microscopy was taken as the gold standard. Anopheles dirus was found to be the main vector and the vectorial capacity correlated well with the cases.
A study was carried out in four malaria-endemic villages in Attapeu Province, in the southern region of Lao PDR. All-night human landing collections were carried out in May, August, and October 2002, to determine malaria vectors. At the same time, mass blood surveys were also carried out in the same villages. Anopheles dirus was the predominant species in three of the study villages. Sporozoites were found only in An. drius from Phou Hom. However, in Beng Phoukham, An. dirus was positive for oocysts. The distribution of malaria cases was highest in Phou Hom and this correlated well with the vectorial capacity of An. dirus. The risk for infection from An. dirus was also high, at 0.99.
A longitudinal study was conducted on the prevalence of Anopheles in three malaria endemic villages in Sekong province, in the southern region of Lao PDR, from August 2000 to October 2001. All night, human landing collections took place in August and October 2000 and April and October 2001, and blood smears were taken for malaria parasites during the same period. Mosquitoes were tested for sporozoite antigen using enzyme-linked immunosorbent assay. In August 2000 (wet season) and April 2001 (dry season) the ovaries of the mosquitoes were examined for parity. A total of 16 species of Anopheles were caught in the study sites of which An. dirus A, An. maculatus sl and An. jeyporiensis were positive for sporozoites. The entomological inoculation rate (EIR) ranged from 0.06 to 0.25. There was a good correlation between EIR and vectorial capacity in the wet season, especially in Pai Mai where the prevalence of malaria was also high during the wet seasons (11.8 and 10.53). An. dirus A showed ambivalence in their choice of feeding as approximately 50% attacked man indoors and an equal proportion outdoors. An dirus A was the main vector in Pai Mai. The parous rate did not significantly differ between the wet and dry season, although it was higher in the dry season. In Takaio the parasite prevalence ranged from 8.7% (dry season) to 37.1% (wet season) and An. jeyporiensis was the vector, and the risk of infection was 0.85 in the dry season while 0.99 in the wet season. In Toumgno An. maculatus sl was the vector and infection was found only in August and October 2000. However, malaria prevalence ranged from 9.69 to 20.4% and was equally high in the dry season. Cattle were also present close to the houses in all the villages and this might be a contributory factor in the prevalence of malaria.
The susceptibility of Culex sitiens to Japanese Encephalitis (JE) virus was examined in the laboratory. Cx. sitiens became infected with JE virus on day 8 and subsequently it is able to transmit the virus when it takes a blood meal. Both parts of the experiment were carried out using artificial membrane feeding technique.
Malaria vector surveys were carried out in 8 provinces in Lao PDR in 1999. The surveys were conducted in 4 provinces - Savannakhet, Champasak, Luang Perbang and Sayaboury in May and in another 4 provinces - Bolikhamsay, Sarvan, Sekong and Vientiane in December 1999. Bare leg collection were carried out indoors and outdoors from 6 pm to 5 am. All anopheline mosquitos were identified, dissected and the gut, gland and ovaries were examined. A total of 438 Anopheles mosquitos belonging to 19 species were obtained. Of these only 3 species were found to be infected with oocysts - An. maculatus, An. dirus and An. minimus. All these species were found biting both indoors and outdoors. An. aconitus was the predominant species obtained in the December collection but its vectorial status remains unknown.
Two formulations of lambda-cyhalothrin (EC-Emulsion concentrate and MC-Microencapsulated) were impregnated into bednets made of polyethylene and polyester. The nets were treated at a dosage of 15 mg/m2. For bioassay of insecticidal efficacy, female Anopheles maculatus and Aedes aegypti were exposed to the nets for two minutes and mortality was scored 24 hours later. The nets were also tested after repeated washings with water and with soap and water. Microencapsulated (2.5CS) formulation was more effective than emulsion concentrate (2.5EC) formulation on both net materials--polyethylene and polyester. Repeated washing with water and soap reduces the efficacy of all bednet treatment combinations. Microencapsulated formulation on polyethylene gave best results; it could sustain up to five washes with water and two with soap and water.
Dried Anopheles farauti mosquitos caught in Solomon Islands in 1990 were examined for malaria sporozoites by ELISA and nested polymerase chain reaction (PCR). Only heads and thoraces were used. Plasmodium genus-specific nested PCR amplifications were carried out on all samples. Of the 402 pools of mosquitos that were processed, 30 were positive for malaria. Nest 1 products of positive samples were subjected to further PCR amplifications with species-specific primers for P. falciparum and P. vivax. Twenty pools were positive for P. vivax by PCR while only 7 were positive by ELISA. For P. falciparum 2 pools were positive by both ELISA and PCR, and one of these was a pool which was positive for P. vivax by PCR and ELISA. Thus the sensitivity of PCR for P. vivax was 100% while the specificity was 96.7%. For P. falciparum the sensitivity and specificity were 100%. The PCR technique is highly sensitive and can be used on dried mosquitos which makes it a valuable tool for determining sporozoite rates of mosquitos, even in remote areas.
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.
A 2-yr study of Japanese encephalitis (JE) virus in Sepang District, Selangor, Malaysia, was carried out to identify the mosquito vectors and to determine their seasonal abundance, parity, and infection rates. In total, 81,889 mosquitoes belonging to 9 genera and > 50 species were identified from CDC trap collections augmented with dry ice during 1992 and 1993. Culex tritaeniorhynchus Giles and Culex gelidus Giles were the most abundant species, and both increased in numbers with increases in rainfall. Overall, 45 JE virus isolations were made from 7 species-Cx. tritaeniorhynchus (24), Cx. gelidus (12), Culex fuscocephala Theobald (2), Aedes butleri Theobald (4), Culex quinquefasciatus Say (1), Aedes lineatopennis Ludlow (1), and Aedes (Cancraedes) sp. (1). Based on elevated abundance and JE infection rates, Cx. tritaeniorhynchus appears to be the most important vector of JE virus in Sepang.
Two hundred forty nucleotides from the pre-membrane gene region of 12 Japanese encephalitis virus (JEV) strains isolated from three different regions of Malaysia from 1993 to 1994 were sequenced and compared with each other and with the JEV strains from different geographic areas in Asia. These 12 Malaysian isolates were classified into two genotypes. The four JEV strains isolated from Sarawak in 1994 and the four JEV strains isolated from Sepang, Selangor in 1993 were classified into one genotype that included earlier isolated strains from Malaysia (JE-827 from Sarawak in 1968 and WTP/70/22 from Kuala Lumpur in 1970). The four JEV strains from Ipoh, Perak in 1994 were classified into another genotype that included JEV strains isolated from northern Thailand and Cambodia. In an earlier report, 10 JEV strains from Sabak Bernam, Selangor in 1992 were classified into the largest genotype that included strains isolated in temperate regions such as Japan, China, and Taiwan. The data indicate that at least three genotypes of JEV have been circulating in Malaysia.
A study was carried out to determine the distribution of cockroaches in two different housing areas with central sewerage or individual septic tanks in an urban area in Kuala Lumpur, Malaysia. Six species of cockroaches were present and of these Periplaneta americana and Periplaneta brunnea were found in greater abundance. Seventeen species of bacteria were isolated and of these Escherichia coli and Klebsiella p. pneumoniae were isolated in greatest numbers. Control measures carried out using lambda cyhalothrin showed that there was no significant difference between treated and control sites.
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.
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.