Efficacy of permethrin-impregnated bed nets on malaria control in a hyperendemic area in Irian Jaya, Indonesia: influence of seasonal rainfall fluctuations.

A malaria intervention study was carried out using permethrin impregnated bed nets in the south-central part of Irian Jaya with perennial transmission, from April 1993 to April 1995. Malariometric surveys were carried out periodically for parasite prevalence by species and for spleen rates. Prior to intervention, the percentage of Plasmodium falciparum infected inhabitants was significantly higher in Hiripau, where permethrin-impregnated bed nets were used during the study, than in the placebo-treated control village, Kaugapu. After two years of intervention the situation was reversed and figures higher in the control village (RR 0.19, 95% CI 0.10-0.36, p < 0.0001). Similarly, P. vivax infection rates, 12.4% in Hiripau vs 5.7% in Kaugapu in April 1993. were reversed in April 1995 (3.6% in Hiripau and 11.3% in Kaugapu, p < 0.001). In the treated village, pre-control hyperendemicity was reduced to a low mesoendemic level (spleen rate 12.5%) during two years of intervention, whereas the level was mesoendemic (spleen rate 35.2%) in the control village. Impregnated bed nets were found an effective intervention both in moderate (April 1993 through April 1994, 1,626 mm rainfall) and high (April 1994 through April 1995/1995, 3,321 mm) transmission seasons.

Efficacy of permethrin-impregnated bed nets on malaria control in a hyperendemic area in Irian Jaya, Indonesia: differentiation between two age groups.

A malaria intervention trial was conducted for two years to evaluate the efficacy of permethrin-impregnated bed nets in reducing malaria infection and splenomegaly in two different age groups, ie below and over age of ten, in a hyperendemic area in Irian Jaya, Indonesia. Permethrin-impregnated or placebo-treated bed nets were provided to a treated and a control village, respectively. Immediately after periods with moderate rainfall in the first year, treated bed nets decreased P. falciparum and P. vivax density in the blood of children <10 years (group 1) but did not reduce the percentage of infection with either species. Children >10 and adults (group 2) showed significant reduction only in P. falciparum infection rates and density, whereas P. vivax was not influenced. After an excessive rainfall season in the second year, the risk for P. falciparum infections in both age groups using treated nets was less than half of that in the control village. P. vivax infection rates were significantly lower in the treated village at the beginning of and after these heavy rainfalls. In the treated village, spleen enlargement was markedly reduced in the younger age group during the second year.

Malaria situation in several villages around Timika, south central Irian Jaya, Indonesia.

Malaria in Timika area, south central Irian Jaya, is a public health problem causing morbidity and mortality, particularly to the vulnerable age group. In August/September 1992 malariometric surveys were conducted simultaneously with sensitivity studies of Plasmodium falciparum to antimalarials, and bionomics of vectors in six villages around Timika (Mwapi, Kaugapu, Hiripau, Pomako, Mapurujaya, Kwamki Lama). The average overall spleen rate was 44.0%, the highest rate observed in Kwamki Lama (68.3%) and the lowest in Mapurujaya (13.7%). The average parasite rate in children aged 2-9 years was 60.6%. The highest rate was found in Mwapi (92.0%) and the lowest rate in Mapurujaya (4.8%). In the study area the dominant species was P. falciparum, (except in Kaugapu), followed by P. vivax. P. malariae and P. ovale were not observed. In vivo sensitivity studies done in 7 villages showed P. falciparum was resistant to chloroquine [51.3% S/R I (sensitive or 1st grade resistant), 43.6% R II and 5.1% R III] in Kwamki Lama, SP I and SP II (transmigrant settlements) and Timika health service center. In vitro sensitivity test in Kwamki Lama, SP I, SP II and Timika health service center showed 64.4% resistant to chloroquine, and remain sensitive to sulfadoxine-pyrimethamine, quinine and mefloquine. Vector studies revealed that Anophelese punctulatus and An. koliensis were the potential vectors as was confirmed by ELISA positive test with a sporozoite rate of 1.43% and 0.33% respectively. The vectors were indoor and outdoor resting.

Correlation of population indices of female Culex tritaeniorhynchus with Japanese encephalitis viral activity in Kapuk, Indonesia.

Nineteen consecutive monthly light trap collections of mosquitoes were made between October 1978 and April 1980 in Kapuk, Indonesia. Kapuk is a small suburb of Jakarta where pigs are raised in close proximity to rice paddies which are breeding sites for Culex tritaeniorhynchus. Japanese encephalitis (JE) virus is believed to be endemic and has been recovered from mosquitoes and pigs in the area on several occasions. A total of 18,435 female Cx. tritaeniorhynchus were allocated to 359 pools of approximately 50 per pool. Virus isolations were attempted in both Vero and BHK-21 cells and agents producing cytopathic effect were identified in a micro-neutralization test. Nineteen strains of JE were recovered from the 359 pools of Cx. tritaeniorhynchus tested. The light trap index of female Cx. tritaeniorhynchus (X) and the relative frequency of pools positive for JE (Y) for each month of the study were plotted and correlation coefficients (r) calculated after transforming the mosquito population data logarithmically and the relative frequencies of isolation by arcsine square root. The close fit of the data (p less than 0.001) to an inverse linear model (1/y = a + b log10X) suggests a close dependence of JE viral activity on the population dynamics of Cx. tritaeniorhynchus. Three additional strains of JE were recovered from other Culex spp. at the same study site. One strain each was isolated from individual pools of Cx. gelidus, Cx. vishnui and Cx. fuscocephala. Cx. tritaeniorhynchus was more frequently infected with JE than the other species tested.

Mosquitoes of Bali Island, Indonesia: common species in the village environment.

Routine sampling of mosquito populations in rural villages was carried out during 13 months at 4 locations in southern Bali Island, Indonesia. Sampling was by light trapping and early night resting collections around animal stables. Specimens collected were preserved for assay of arthropod-borne viruses; 104,608 specimens representing 20 species were prepared in 2681 pools for viral assay. Anopheles barbirostris and An. subpictus have been shown to be important vectors of Brugia malayi and B. timori and of malaria and Wuchereria bancrofti in other parts of Indonesia but have not been incriminated in transmission of disease agents in Bali. Anopheles vagus may be involved in filarial transmission in other regions but is not regarded as important in Bali. Culex fuscocephala, Cx. gelidus and Cx. tritaeniorhynchus have been incriminated in the transmission of Japanese encephalitis virus in Indonesia and Cx. vishnui has been similarly implicated in other countries. The populations of these mosquitoes are compared and plotted against rainfall. The potential of the more common species as vector of some human pathogens is discussed.

A study on vectors of Bancroftian filariasis in West Flores, Indonesia.

A brief survey was conducted in a filariaendemic village of Robek, West Flores, Indonesia, to identify the mosquito fauna, to determine the vector of W. bancrofti, and to update information on the bionomics of An. subpictus. A total of 6 genera and 22 species were collected. Five species of culicines collected, have not been previously recorded from Flores. Dissections of wild caught mosquitoes consisted of 592 anophelines, and 70 culicines did not reveal any filarial infection. An. subpictus was a potential vector of bancroftian filariasis in the Robek area, as 11.3% of this species that fed on carriers were found to harbour W. bancrofti larvae. Larvae of An. subpictus were collected in lagoons, rice fields, swamps and ground pools. Breeding sites are exposed to sunlight, contain fresh or brackish water, with or withour vegetation. They have been found primarily associated with An. aconitus, An. annularis, An. barbirostris, Cx. vishnui and Cx. bitaeniorhynchus. The time for a female to become fully engorged with human blood is 3-10 minutes. This species is a night biter, attacking man and animals from twilight to dawn. Its peak of biting activity is between 0100-0300 hrs.

Vector studies and epidemiology of malaria in Irian Jaya, Indonesia.

Human populations in the low-land littoal of southwestern Irian Jaya are exposed to holoendemic malaria, principally caused by P. falciparum. The spleen rate in children of ages 2-9 years, in 4 villages ranged from 78% to 97%, and parasite prevalences were from 21% to 52%. Three known vectors of malaria, An. farauti, An. koliensis and An. punctulatus, were present, the latter two being most abundant. One specimen of each of the latter two species, upon dissection, was found carrying sporozoites in thoracic tissue. Larval habitats were numerous in peridomestic sites, including drainage ditches, natural ground pools and plots of Ipomea reptans; thus the vector populations were always in close contact with the human populations.

Experimental Brugia timori and Wuchereria bancrofti infections in certain species of mosquitoes.

Laboratory reared Aedes aegypti (black eye and Jakarta strains), Aedes togoi, (Taiwan), Aedes albopictus, (Jakarta), wild caught Anopheles barbirostris, (Java) and Mansonia uniformis, (Jakarta) were fed on a carrier with mixed infection of Brugia timori and Wuchereria bancrofti. B. timori and W. bancrofti were able to develop in A. aegypti (black eye) and A. togoi, with development proceeding more rapidly for of B. timori than W. bancrofti. Both species of parasites were readily distinguishable in each of their developmental stages. A. barbirostris from Java was able to support development of B. timori as well as A. barbirostris from Flores. B. timori and W. bancrofti did not develop in M. uniformis, A. aegypti (Jakarta strain) and A. albopictus.

Brugia timori: experimental infection in some laboratory animals.

Experimental infection with Brugia timori of 7 jirds (Merionesunguiculatus), 4 cats and 2 monkeys (Macaca fascicularis) is described. Although no microfilariae were detected by examining 20 microliter samples of tail blood of jirds, adult worms were recovered from 6 of the 7 jirds at autopsy 69-141 days following infection. Some worms were gravid and microfilariae were found in visceral blood of 2 animals. The adult recovery rate in jirds was 16%; the male to female ratio was 1:3. In cats patent infection developed in 95-105 days but microfilaraemias were of low level and transient. No parasites were recovered from monkeys.