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Biomedical subjects

J L Hii

Publications and source records attributed to J L Hii.

31 records · Page 2Linked to original sources
PubMed1987

The influence of permethrin-impregnated bednets and mass drug administration on the incidence of Plasmodium falciparum malaria in children in Sabah, Malaysia.

A small-scale trial was carried out in the Upper Kinabatangan district of Sabah, Malaysia, to determine the effect of using permethrin-impregnated bednets on malaria transmission. A total of 306 nylon bednets with cotton borders, impregnated at a dose estimated to have been 0.062 g permethrin/m2 of nylon netting, were distributed to 139 households in five villages. At the time of distributing bednets, mass drug administration with Fansidar plus primaquine was also administered to the human population to clear all parasitaemias due to Plasmodium falciparum Welch. In another village, for comparison, mass drug administration was the only intervention. After intervention measures in December 1984 and January 1985, the parasite rates in children declined in all villages during the first month, significantly more in the villages with impregnated bednets than in the control, thus proving that the nets had an impact on malaria. However, after about 2 months, parasite rates started to increase again. After 4-6 months, parasite rates in the villages with bednets approached the rate in the control village without nets. The increase in parasite rates was paralleled by a significant deterioration in the quality, physical condition and the degree of non-utilization of bednets. Entomological evaluation proved the efficacy of permethrin-impregnated nets for controlling Anopheles balabacensis Baisas and other anophelines. Bioassays (1 h exposure) of permethrin-impregnated bednets gave 100% mortality initially and 44-61% mortality after 85-106 days. Mosquito collections in treated bednets were significantly reduced for at least 217 days. The project failed to achieve prolonged suppression of malaria transmission for a combination of entomological, sociological and practical reasons which are discussed in relation to the objectives and implementation of future bednet studies.

Animals↗
PubMed1985

Anopheles flavirostris incriminated as a vector of malaria and Bancroftian filariasis in Banggi Island, Sabah, Malaysia.

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.

Anopheles↗
PubMed1985

Evidence for the existence of genetic variability in the tendency of Anopheles balabacensis to rest in houses and to bite man.

Mark-release-recapture experiments were carried out in Sabah, East Malaysia on the malaria and filariasis vector, Anopheles balabacensis. Samples of wild females were marked with different colours of fluorescent pigments, released in man-baited huts fitted with exit traps. Simultaneous collections and releases were also made in night-biting catches on a water buffalo and on four men. All subsequent recaptures were made in the same situation in which the mosquitoes were marked. The same individual mosquitoes were caught biting men and buffalo on different occasions and the numbers caught showed a strong preference for man over buffalo. The length of the oviposition cycle in the field was found to be 3.0 days. After blood-feeding on man in a hut, An. balabacensis were found to exit on the night or early morning. The same individual mosquitoes were found resting in the hut or exit trap on different occasions. The results indicate that there is strong evidence for the existence of genetic variability in the tendency of An. balabacensis to rest in houses and to bite man and buffalo. The obvious existence of this phenomenon is considered discouraging for the prospects of interruption of malaria transmitted by An. balabacensis in nature.

Animals↗
PubMed1984

Insecticide susceptibility studies of three cryptic species of the Anopheles balabacensis complex.

Susceptibilities of two colonies of the taxon An. dirus (one from Perlis and from Thailand) and one colony of An. balabacensis from Sabah to DDT, dieldrin, malathion, fenitrothion and propoxur were determined. DDT and fenitrothion tolerance was found in An. dirus species B and An. balabacensis. No resistant strain was isolated as the two colonies were not either homozygous or nearly so for resistance. Field testing of the susceptibility of the adults of An. balabacensis to DDT was carried out between 1957 to 1976. The results indicated a progressive rise in the LC50 levels greater than 1% in almost all instance. The variation in the number of sprays applied in some districts have resulted in varying sensitivities. Association between the changes in levels of DDT susceptibility and exophilic habit of An. balabacensis has been observed but needs further confirmation. The significance of these findings and the difficulties in distinguishing tolerant from truly resistant individuals are discussed in relation to accurate species identification.

Animals↗
PubMed1978

Co-existence and attempted hybridization between Anopheles litoralis (King) and Anopheles sundaicus (Rodenwaldt) in Sabah, Malaysia.

Anopheles (Cellia) litoralis King and Anopheles (Cellia) sundaicus Rodenwaldt, vectors of malaria, were collected from the same brackis and sea-water habitats in six localities in Sabah. They share the same breeding habitats with predominance of one species over the other. The two species although distinct have small morphological differences and are taxonomically separated by certain wing characters. Hybridization between the two species was successful. Reciprocal crosses produced viable progeny which appeared to develop normally to adults. Hybridized females laid fewer viable eggs in comparison with the parents. The F1 hybrids resembled the litoralis parent in most characters. Backcrosses of both litoralis and sundaicus parents with the F1 hybrids yielded no eggs. F1 male hybrids were thus assumed to be sterile. The results obtained from cross matings between the two species suggested something more than subspecific status.

Animals↗
PubMedDate not supplied

Associations of peak shifts in age--prevalence for human malarias with bednet coverage.

Effects of bednet coverage (C) on prevalence of malaria were analysed using data from 1990-92 from 9 Papua New Guinean villages. Effects of coverage varied by age, resulting in a shift in age of peak prevalence from 4.7 (C = 0%) to 11.6 (C = 100%) years for Plasmodium falciparum, from 3.4 to 4.9 years for P. vivax and from 11.0 to 16.8 years for P. malariae. In small areas with no bednets the age distribution of P. falciparum parasitaemia was like that of a holoendemic area. Where coverage was complete the pattern corresponded to mesoendemicity. Thus, protracted use of bednets can result in profound changes in the endemicity of malaria even when coverage is incomplete and without insecticide treatment. Average entomological inoculation rates (EIRs) estimated from indoor landing rates on individuals without bednets were 35, 12 and 10 infectious bites per person per annum for P. falciparum, P. vivax and P. malariae, respectively. Logistic regression analyses indicated that the EIR estimate for P. falciparum was related to prevalence of this species independently of effects of bednet coverage. However, the recent EIR still accounted for much less variation than did the bednets. A similar pattern was seen for P. malariae, while there were no significant relationships between the recent EIR and the parasite positivity for P. vivax. It is concluded that short-term variations in inoculation rate are not important determinants of parasite prevalence in this population.

Adolescent↗
PubMedDate not supplied

Area effects of bednet use in a malaria-endemic area in Papua New Guinea.

Relationships between area coverage with insecticide-free bednets and prevalence of Plasmodium falciparum were investigated in 7 community-based surveys over a 33-month period in 1990-93 in 6 villages in the Wosera area of Papua New Guinea. Spatial patterns in circumsporozoite rates for P. falciparum, P. vivax isomorphs K210 and K247, and P. malariae, and the proportions of mosquito blood meals positive for specific human, goat, cat, dog and pig antigens were determined using ELISAs. P. falciparum prevalence in humans was better explained by bednet coverage in the immediate vicinity than by personal protection alone. Circumsporozoite rates for both P. falciparum and P. vivax were also inversely related to coverage with bednets. There was some increase in zoophagy in areas with high coverage, but relatively little effect on the human blood index or on overall mosquito densities. In this setting, protracted use of untreated bednets apparently reduces sporozoite rates, and the associated effects on prevalence are greater than can be accounted for by personal protection. Even at high bednet coverage most anophelines feed on human hosts, so the decreased sporozoite rates are likely to be largely due to reduction of mosquito survival. This finding highlights the importance of local vector ecology for outcomes of bednet programmes and suggests that area effects of untreated bednets should be reassessed in other settings.

Adolescent↗