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Biomedical subjects

M J Bockarie

Publications and source records attributed to M J Bockarie.

32 records · Page 2Linked to original sources
PubMed1993

Malaria in a rural area of Sierra Leone. II. Parasitological and related results from pre- and post-rains clinical surveys.

The prevalence of Plasmodium falciparum in a cohort of over 900 nought to seven-year-old children living in a rural area of Sierra Leone was found to be approximately 61%, both before and after the rainy season. Plasmodium malariae rates measured in the same children were approximately 12%, and P. ovale rates averaged about 1%. Spleen rates averaged 44% for the two surveys; the age prevalence spleen profiles closely matched those for P. falciparum. The overall gametocyte rates for both P. falciparum and P. malariae were roughly one fifth of the prevalence rates for the asexual parasites. However, whilst there was no difference between the P. falciparum gametocyte rates at the two surveys, the P. malariae rate was significantly higher post-rains when compared with the pre-rains result. Spleen size did not increase with increased parasite density. There was a statistically significant difference between the geometric mean P. falciparum trophozoite densities of febrile and afebrile children both before and after the rainy season, but there was little seasonal difference in the means for the febrile children or in those for the afebrile children. Antimalaria antibody levels, measured by ELISA and IFAT, showed no significant differences at either survey. The levels found were high for all age groups, indicating that exposure to malaria begins at birth. Our results indicate that, in the area studied, malaria is hyperendemic and is probably transmitted perennially.

Animals↗
PubMed1993

The epidemiology of malaria in southern Sierra Leone.

The epidemiology of malaria was investigated in a high rainfall, forested area of southern Sierra Leone. The prevalence rates of P. falciparum, P. malariae and P. ovale in 0-7 year old children, during two surveys conducted over a 12-month period, averaged 61%, 12% and 1% respectively. Groups of febrile children had higher prevalence rates than afebrile groups. Overall, gametocyte rates were approximately one fifth of the trophozoite rates. Malaria accounted for 27% of deaths, as did malnutrition, although no malaria associated deaths occurred in 0-12 month olds. Spleen rates were similar to P. falciparum prevalence rates, and the size did not appear to be related to parasite load at the time of the surveys. Packed cell volumes had normal distributions, with a lower mode after the peak prevalence period. Chloroquine usage increased during the post-rains period compared to the pre-rains period.

Child↗
PubMed1993

The ecology and behaviour of the forest form of Anopheles gambiae s.s.

Studies on the ecology of Anopheles gambiae s.s. and the transmission of malaria were undertaken in a high rainfall forested area in southern Sierra Leone. Anopheles gambiae s.s., identified by chromosomal techniques as the Forest form, was the only malaria vector in the study village. Surprisingly, rice fields or swamps were not favoured breeding places for this species; breeding mainly occurred in temporary pools. The mean annual sporozoite rate of An. gambiae s.s. determined by ELISA was 3.9%. Pyrethrum spray, human bait, and exit trap collections, as well as identification of mosquito blood-meals using the ELISA method, showed that the forest chromosomal form of An. gambiae s.s. was highly anthropophagic and exophilic.

Animals↗
PubMed1990

The transmission of onchocerciasis at a forest village in Sierra Leone. I. Simulium damnosum s.l. biting densities and infection with Onchocerca volvulus at five representative sites.

Previous studies in the forest area of Sierra Leone have shown that transmission of Onchocerca volvulus takes place many kilometers away from large breeding rivers and sometimes in open farmland. To determine where and when people in a forest village were most likely to be infected, catches of Simulium damnosum s.l. were carried out every week for 12 months, at five sites in and near a village where onchocerciasis was mesoendemic. The number of flies caught per man a day at open farm sites was significantly higher than the number caught at riverside sites. Infective flies were caught only in farmland and only during the early rainy season. The combined Annual Transmission Potential for the five sites was 129 larvae per man per year. Isoenzyme electrophoresis and morphology of biting flies identified the S. sanctipauli/soubrense subcomplex as the most common vector species. Simulium yahense and S. squamosum were sometimes present. It was concluded that the classical riverside monitoring sites do not represent high risk areas for the transmission of onchocerciasis in a forest village sited well away from the main S. damnosum s.l. breeding sites. The highest risk areas are in open farmland.

Animals↗
PubMed1990

The transmission of onchocerciasis at a forest village in Sierra Leone. II. Man-fly contact, human activity and exposure to transmission.

In the first of these papers we reported on the biting-densities of Simulium damnosum s.l., vector of onchocerciasis, at sites in and near to a village in the forest area of Sierra Leone that was well separated from any large Simulium breeding river. It was found that biting-densities and transmission levels were higher in open farmland than at riverside sites. In this paper we examine the relative time spent by the villagers at the same five sites in and near to the village of Baoma Lungibu, and compare the time spent and activity, with known Simulium biting-densities and transmission indices. It is concluded that, in this situation, the highest risk of infection with onchocerciasis was to persons of either sex in the 20-39 age group who were engaged in farming, or travelling through open farmland, during the months of June to August at the beginning of the wet season. Activities in and close to the village, even by the riverside, where shade cover was heavy, presented little risk of infection.

Adolescent↗
PubMed1989

On the possibility of bovine Onchocerca species infecting Simulium damnosum s.l. in the forest zone of Sierra Leone. II. Biting densities and filarial infections in Simulium spp. and Culicoides spp.

Previous studies of bovine Onchocerca spp. in cattle in Sierra Leone indicated that only O. gutturosa was transmitted in the forest zone at high intensity. To determine its vector(s) and the extent to which Onchocerca-like infections in Simulium damnosum were likely to be of bovine origin, three lines of investigation were pursued. Firstly, a study was made of the biting flies attacking an ox bait animal over a 14-month period at Njala University Campus, near Bo. Secondly, attempts were made to infect the dominant local forest cytospecies of S. damnosum s.l. with O. gutturosa by feeding them on an infected ox under a bed-net. Thirdly, S. damnosum s.l. were infected by intra-thoracic injection of O. gutturosa microfilariae (mff). In 113 collections made at dawn and dusk at weekly intervals from the ox bait, 624 simuliids and 7740 Culicoides spp. were collected. Almost all the simuliids were S. damnosum s.l. which, on the basis of iso-enzyme examination and knowledge of local breeding sites, were identified as S. soubrense 'B'. Although this cytospecies fed readily on the ox at ventral sites where O. gutturosa mff occurred and the bed-net experiments showed that 16.1% of engorged S. soubrense 'B' ingested an average of 3.3 O. gutturosa mff each, no development occurred. The refractoriness of S. damnosum s.l. to O. gutturosa was confirmed by the intra-thoracic injection experiments. The predominant Culicoides spp. attacking the ox bait were C. krameri, C. trifasciellus and C. fulvithorax, with smaller numbers of C. schultzei. In 5803 dissected Culicoides spp., natural infections of Onchocerca-like larvae, presumed to be O. gutturosa, were found in 0.3% of C. fulvithorax, 0.1% of C. trifasciellus and 0.06% of C. krameri. It was concluded that, in the forest zone of Sierra Leone, S. damnosum s.l. is not a vector of O. gutturosa and all Onchocerca-like larvae in S. damnosum are likely to be O. volvulus, while the natural vectors of O. gutturosa are the Culicoides species C. fulvithorax, C. trifasciellus and C. krameri.

Animals↗
PubMedDate not supplied

The late biting habit of parous Anopheles mosquitoes and pre-bedtime exposure of humans to infective female mosquitoes.

Using the all-night landing catch method (18:00-06:00) we showed, for Anopheles gambiae in Sierra Leone and A. punctulatus in Papua New Guinea, that parous females have a tendency to bite later than nulliparous ones. The biting habit of sporozoite-infected A. punctulatus was also investigated. The sporozoite rates for Plasmodium falciparum and P. vivax were 1.8 and 1.4% respectively, but only one (1.3%) of 76 females infected with P. falciparum was caught between 18:00 and 21:00. A significantly higher proportion (11.6%) of mosquitoes infected with P. vivax was caught in the same period. The late biting habit of mosquitoes infected with P. falciparum is discussed in relation to the differential biting habits of parous and nulliparous females. We conclude with a hypothesis that, in areas where Anopheles mosquitoes have a late-biting cycle and low parous rate, exposure to mosquitoes infected with P. falciparum during the pre-bedtime period (18:00-22:00) is very low. This hypothesis could explain why insecticide-treated bed nets protect children better in areas of seasonal transmission, where nulliparous females tend to predominate, than in areas of perennial transmission, where parous females are usually more numerous. The same hypothesis is compatible with the finding in Papua New Guinea that insecticide-impregnated bed nets are more protective against P. falciparum than against P. vivax malaria.

Animals↗
PubMedDate not supplied

Towards eliminating lymphatic filariasis in Papua New Guinea: impact of annual single-dose mass treatment on transmission of Wuchereria bancrofti in East Sepik Province.

The impact of annual single-dose community-wide treatment on the transmission of Wuchereria bancrofti was investigated in 5 villages in the East Sepik Province where pretreatment prevalence of microfilaraemia ranged from 34% to 73%. Anopheles punctulatus and An. koliensis were the only carriers of the parasite. 3 villages received diethylcarbamazine citrate (DEC) in combination with ivermectin (IVR) and 2 received DEC alone. The rate and intensity of microfilaraemia were both reduced in all 5 villages. Reduction in prevalence was between 43% and 67% in the DEC+IVR study villages and between 24% and 27% in the DEC alone villages. Density was reduced by between 81% and 95% in the DEC+IVR villages and between 69% and 74% in the DEC alone villages. Breaks in perennial transmission (failure to detect infective mosquitoes in four or more consecutive monthly collections) occurred in all 3 communities treated with DEC+IVR. Transmission was almost completely interrupted in 2 villages, where infective mosquitoes were not detected during 11 of the 12 months following treatment. We concluded that repeated annual single-dose community-wide treatment with DEC+IVR could lead to complete interruption of transmission and ultimately elimination of lymphatic filariasis.

Animals↗
PubMedDate not supplied

The epidemiology and control of lymphatic filariasis on Lihir Island, New Ireland Province.

Clinical, parasitological and entomological surveys performed in 9 villages on Lihir Island, Papua New Guinea, before mass treatment with diethylcarbamazine (DEC), showed that lymphatic filariasis, caused by nocturnally periodic Wuchereria bancrofti, was endemic in 8 of them. Blood samples from 593 people revealed an overall microfilarial carrier rate of 24%. Amongst endemic villages, microfilarial carrier rates ranged from 5% to 43% and there was no significant difference in parasite prevalence between males and females. Obstructive filarial disease, defined as lymphoedema of the limbs or hydrocele, was observed in only 2% of 262 males examined. None of the 265 females examined had clinical symptoms. Entomological surveys yielded a total of 4095 mosquitoes including 3,692 anophelines and 241 culicines but only Anopheles farauti was found to harbour infective larvae of W. bancrofti. Pretreatment infection and infective rates of An. farauti were 7% and 1% respectively and up to 12 infective larvae were found in a single specimen. The microfilarial carrier rate in a cohort of people who received two DEC treatments dropped from 59% to 32% but the difference was not statistically significant. However, density of microfilaraemia decreased significantly from 170 to 10 mf/ml. Biannual mass treatment with DEC significantly reduced vector infection rates and transmission intensity on Lihir.

Diethylcarbamazine↗
PubMedDate not supplied

Control of lymphatic filariasis in a hunter-gatherer group in Madang Province.

Diethylcarbamazine (DEC) has been successfully administered to millions of people in established villages and towns, but little or no information exists on the use of this drug to control lymphatic filariasis in isolated seminomadic groups. We have studied the impact of biannual single-dose mass treatment to control filariasis in the Hagahai, an isolated hunter-gatherer, shifting horticulturist group in the fringe highlands of Papua New Guinea. Despite low treatment coverage, 6 mass treatment rounds significantly reduced the overall prevalence of infection with Wuchereria bancrofti, by antigen detection assay, from 55% before treatment to 34% after treatment. Obstructive filarial disease in the form of elephantiasis or hydrocele was not observed among the indigenous population. Anopheles species accounted for 91% of human-biting mosquitoes collected in the area. A total of 1126 mosquitoes were caught and dissected individually but none was infected with third-stage larvae (L3). Our findings support the phenomenon of facilitation, which predicts that Anopheles-transmitted lymphatic filariasis can be interrupted by mass chemotherapy alone in areas of low vector density and low transmission intensity as observed in the Hagahai.

Diethylcarbamazine↗