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M J Bockarie

Publications and source records attributed to M J Bockarie.

At least 19 recordsLinked to original sources
PubMed2006

Transmission dynamics of lymphatic filariasis: vector-specific density dependence in the development of Wuchereria bancrofti infective larvae in mosquitoes.

The principles of meta-analysis developed in a previous study were extended to investigate the process of Wuchereria bancrofti (Cobbold) (Filarioidea: Onchocercidae) infection in mosquito (Diptera: Culicidae) hosts, focusing specifically on the functional forms and strength of density dependence in the development of ingested microfilariae (mf) to infective (third instar) larvae (L3). Mathematical models describing observed mf-L3 functional responses for each of the major three parasite-transmitting vector genera, Aedes, Culex and Anopheles mosquitoes, were fitted to paired mf-L3 data collated from all available studies in the published literature. Model parameters were estimated and compared by deriving and applying a data synthetic framework, based on applying a non-linear weighted regression model for fitting mathematical models to multistudy data. The results confirm previous findings of the existence of significant between-genera differences in the mf-L3 development relationship, particularly with regard to the occurrence of limitation in Culex mosquitoes and facilitation in Aedes and Anopheles mosquitoes. New and unexpected findings regarding L3 development from ingested mf were discovered as follows: (1) for Culex, overcompensation in L3 development at higher intensities of mf (or a peaked mf-L3 functional response) was detected; (2) for Aedes mosquitoes, facilitation (with an apparent asymptotic constraint on L3 development at high mf densities) was shown to be the major process governing L3 development, and (3) for Anopheles, a stronger facilitation type of response with no apparent saturation in L3 development appears to govern L3 output from ingested mf. These results yield major new insights regarding filarial vector infection dynamics and their potential impacts on parasite control, and demonstrate the efficacy of employing a data synthetic approach to reveal and estimate parasitic infection processes in host populations.

Aedes↗
PubMed2003

Polymorphisms of innate immunity genes and susceptibility to lymphatic filariasis.

We examined 906 residents of an area of Papua New Guinea where bancroftian filariasis is endemic for genetic polymorphisms in three innate immunity genes suspected of contributing to susceptibility to infection and lymphatic pathology. Active infection was confirmed by the presence of blood-borne microfilariae and circulating filarial antigen in plasma. Disease was ascertained by physical examination for the presence of overt lymphedema (severe swelling of an arm or leg) or hydrocele. There was no association of infection status, lymphedema of an extremity, or hydrocele with chitotriosidase genotype (CHIT1). Polymorphisms of toll-like receptor-2 and toll-like receptor-4 genes (TLR4 A896G; TLR2 T2178A, G2258A) were not detected (N=200-625 individuals genotyped) except for two individuals heterozygous for a TLR2 mutation (C2029 T). These results indicate that a CHIT1 genotype associated previously with susceptibility to filariasis in residents of southern India and TLR2 and TLR4 polymorphisms do not correlate with infection status or disease phenotype in this Melanesian population.

Animals↗
PubMed2002

Impact of untreated bednets on prevalence of Wuchereria bancrofti transmitted by Anopheles farauti in Papua New Guinea.

Despite the growing evidence that insecticide-treated mosquito nets reduce malaria morbidity and mortality in a variety of epidemiological conditions, their value against lymphatic filariasis infection and disease is yet to be established. The impact of untreated bednets on the prevalence of Wuchereria bancrofti (Cobbold) (Nematoda: Filarioidea) infection and disease was investigated on Bagabag island in Papua New Guinea, where both malaria and filariasis are transmitted by the same vector mosquitoes of the Anopheles punctulatus Dönitz group (Diptera: Culicidae). Community-wide surveys were conducted recording demographic characteristics including bednet usage. Physical examinations for hydrocoele and lymphoedema were performed and blood samples assessed for filarial and malaria parasites. Mosquitoes were sampled using the all-night landing catch method and individually dissected to determine W. bancrofti infection and infective rates. Bednet usage among residents was 61% and the mean age of users (25.6 years) was similar to non-users (22.5 years). Anopheles farauti Laveran was the only species were found to contain filarial larvae: 2.7% infected (all stages), 0.5% infective (L3). The overall W. bancrofti microfilaraemia and antigenaemia rates were 28.5% and 53.1%, respectively. Bednet users had lower prevalence of W. bancrofti microfilaraemia, antigenaemia and hydrocoele rates than non-users. In comparison, untreated bednets had no effect on the prevalence and intensity of Plasmodium falciparum and P. vivax infections. The impact of bednet usage on rates of microfilaraemia and antigenaemia remained significant even when confounding factors such as age, location and sex were taken into account, suggesting that untreated bednets protect against W. bancrofti infection.

Adult↗
PubMed2001

Evolution of a unique Plasmodium falciparum chloroquine-resistance phenotype in association with pfcrt polymorphism in Papua New Guinea and South America.

The mechanistic basis for chloroquine resistance (CQR) in Plasmodium falciparum recently has been linked to the polymorphic gene pfcrt. Alleles associated with CQR in natural parasite isolates harbor threonine (T), as opposed to lysine (K) at amino acid 76. P. falciparum CQR strains of African and Southeast Asian origin carry pfcrt alleles encoding an amino acid haplotype of CVIET (residues 72-76), whereas most South American CQR strains studied carry an allele encoding an SVMNT haplotype; chloroquine-sensitive strains from malarious regions around the world carry a CVMNK haplotype. Upon investigating the origin of pfcrt alleles in Papua New Guinean (PNG) P. falciparum we found either the chloroquine-sensitive-associated CVMNK or CQR-associated SVMNT haplotypes previously seen in Brazilian isolates. Remarkably we did not find the CVIET haplotype observed in CQR strains from Southeast Asian regions more proximal to PNG. Further we found a previously undescribed CQR phenotype to be associated with the SVMNT haplotype from PNG and South America. This CQR phenotype is significantly less responsive to verapamil chemosensitization compared with the effect associated with the CVIET haplotype. Consistent with this, we observed that verapamil treatment of P. falciparum isolates carrying pfcrt SVMNT is associated with an attenuated increase in digestive vacuole pH relative to CVIET pfcrt-carrying isolates. These data suggest a key role for pH-dependent changes in hematin receptor concentration in the P. falciparum CQR mechanism. Our findings also suggest that P. falciparum CQR has arisen through multiple evolutionary pathways associated with pfcrt K76T.

ATP-Binding Cassette Transporters↗
PubMed2001

Ecologic and biologic determinants of filarial antigenemia in bancroftian filariasis in Papua New Guinea.

The relationship between filarial antigenemia and lymphatic pathology was investigated in residents of 11 villages in an area of Papua New Guinea where Wuchereria bancrofti is endemic. Antigenemia was determined in 1322 persons by means of the Og4C3 antibody capture assay. Prevalence of antigenemia by village ranged from 61.7% to 98.2% and did not vary by sex. Antigen level increased with transmission potential among the 4 villages with measured transmission potential (r(2)=.945; P=.028). Antigenemia was associated positively with age in villages with the lowest annual transmission potentials (45 and 404 infective larvae/year; P<.001), but was distributed evenly across age groups in villages with increased transmission (1485 and 2518 infective larvae/year). These data suggest that children and adults have similar worm burdens in areas of high transmission, whereas worm burdens in areas of lower transmission increase with age. These results may be useful in the design and evaluation of programs aimed at eliminating lymphatic filariasis.

Adolescent↗
PubMed2001

Apparent drug failure following artesunate treatment of Plasmodium falciparum malaria in Freetown, Sierra Leone: four case reports.

Four cases of Plasmodium falciparum malaria who presented in Sierra Leone in November-December 2000 apparently failed to respond to treatment with artesunate. Three (75%) of the cases fulfilled the World Health Organization's criteria for late treatment failure. Although artesunate ranks only sixth as the first-line drug used by clinicians for the treatment of uncomplicated malaria in Sierra Leone, it is widely sold over the counter in pharmacies in the country. The indiscriminate and injudicious use of artesunate among the Sierra Leonean population is likely to increase the level and frequency of resistance among the local strains of P. falciparum. It is recommended that artesunate be reserved for patients who fail to respond to treatment with another of the antimalarial drugs available. Even then, the artesunate should preferably be used in combination with other, longer-acting antimalarial drugs, to slow the development of further resistance.

Adult↗
PubMed2000

Application of a polymerase chain reaction-ELISA to detect Wuchereria bancrofti in pools of wild-caught Anopheles punctulatus in a filariasis control area in Papua New Guinea.

Chemotherapy-based eradication programs are aimed at stopping transmission of Wuchereria bancrofti by its obligatory mosquito vector. This study compares one year post-treatment W. bancrofti infection rates of Anopheles punctulatus, the main vector of lymphatic filariasis in Papua New Guinea, using traditional dissection techniques and a polymerase chain reaction (PCR)-based ELISA of a parasite-specific Ssp I repeat. A total of 633 mosquitoes in 35 batches were dissected. Six batches contained W. bancrofti-infected mosquitoes, giving a minimum infection rate of 0.9%. This value was not different than the actual infection rate, which was 9 (1.4%) of 633 mosquitoes (P = 0.48). The DNA was extracted from 47 pools containing a mean of 13.2 mosquitoes per pool. A total of 621 mosquitoes were processed for the PCR-ELISA, including 486 caught by human bait and 135 by light trap, which included both dead and live mosquitoes. Of 23 pools of alcohol-preserved human-bait mosquitoes, seven were positive by the PCR-ELISA, giving an infection rate identical to that obtained by dissection of individual mosquitoes (1.4%). The minimum infection rates for pools of light-trap mosquitoes found dead and alive were 2.7% (2 of 74) and 4.9% (3 of 61), respectively. These values did not differ from each other (P = 0.84), but the overall infection rate of light-trap mosquitoes was greater than that of mosquitoes captured by human bait (3.7% versus 1.4%; P = 0.09). These data indicate that the PCR-ELISA of a W. bancrofti Ssp I repeat using pools of mosquitoes is comparable to traditional dissection techniques for monitoring transmission intensity following introduction of mass chemotherapy. This approach may also be useful for rapid and cost-effective assessment of transmission in endemic areas where the frequency of overt lymphatic pathology is low.

Animals↗
PubMed2000

Isolation of Japanese encephalitis virus from mosquitoes (Diptera: Culicidae) collected in the Western Province of Papua New Guinea, 1997-1998.

After Japanese encephalitis (JE) virus emerged in the Torres Strait in Australia in 1995, investigations were initiated into the origin of the incursion. New Guinea was considered the most likely source, given its proximity to islands of the Torres Strait. Almost 400,000 adult mosquitoes were processed for virus isolation from 26 locations in the Western Province of Papua New Guinea (PNG) between February 1996 and February 1998, yielding three isolates of JE virus. Two isolates of Murray Valley encephalitis, 17 isolates of Sindbis, and 1 each of Sepik and Ross River viruses were also obtained. Nucleic acid sequences of the PNG JE isolates were determined in the prM region, and in a region overlapping a part of the fifth nonstructural protein and the 3' untranslated region. The PNG isolates belonged to genotype II, and shared > 99.2% identity with isolates from humans and mosquitoes from the Torres Strait, suggesting that PNG is the source of incursions of JE virus into Australia.

3' Untranslated Regions↗
PubMed1999

Mass treatment with ivermectin for filariasis control in Papua New Guinea: impact on mosquito survival.

Field studies were carried out to determine the impact of mass human treatment with ivermectin on the survival of anthropophagic mosquitoes of the Anopheles punctulatus complex (Diptera: Culicidae), the vectors of lymphatic filariasis and malaria in Papua New Guinea. In a village where mass treatment had been given, using 400 microg/kg ivermectin plus 6 mg/kg diethylcarbamazine citrate (DEC), we performed pre- and post-treatment collections of freshly blood-engorged mosquitoes from the same nine bedrooms. All blood-fed mosquitoes collected less than 4 days after mass treatment died within 9 days, whereas 67% of those collected before treatment survived for >9 days. Comparison (using the log-rank test) of the survival curves for mosquitoes collected (i) before treatment, (ii)<4 days after treatment, and (iii) 28 days after treatment, showed the survival rate of group (ii) to be significantly lower than the other two (chi2=176, df=2, P<0.0001). Pre- and post-treatment all-night landing catches showed no reduction in human biting rates in the experimental village. In another village, where people were mass treated with ivermectin (400 microg/kg) only, the survival rates of freshly blood-engorged An. punctulatus collected from bedroom resting-sites less than 1 day after treatment, were compared to similar collections carried out at the same time in a nearby village where people were not treated with ivermectin. The 48-h survival rate for the ivermectin-treated village was 31% compared to 94% for the other; this difference was highly significant (chi2=32.42, df=1, P<0.0001). Mosquitoes fed 2 months post-treatment with DEC or collected 38 days post-treatment with ivermectin had normal survival rates. We conclude that the duration of the systemic lethal effect of ivermectin on mosquitoes is insufficient to be of epidemiological significance in filariasis control programmes that are based on biannual and annual single-dose treatments, but might reduce vectorial capacity sufficiently to block epidemics of dengue or even malaria.

Animals↗
PubMed1999

It all began with Ronald Ross: 100 years of malaria research and control in Sierra Leone (1899-1999).

It was in Sierra Leone, 100 years ago in 1899, that human malarial parasites were first observed in wild-caught Anopheles gambiae and An. funestus, the principal vectors of malaria in Africa. In the same year, Ronald Ross initiated the first antilarval measures for malaria control. This paper reviews 100 years of malaria field research and control in Sierra Leone, which became known as the 'White Man's Grave' in the 19th century largely because of the high malaria-related mortality amongst Europeans living there. The establishment of a field laboratory for the Liverpool School of Tropical Medicine in Freetown in 1920 made Sierra Leone the centre for malaria field research in Africa up to and during the Second World War. Eminent malariologists including Ronald Ross, Samuel Christophers, George Macdonald, Leonard Bruce-Chwatt, Brian Maegraith, Ian Macgregor, Brian Greenwood and Michael Service visited Sierra Leone for malaria-related activities. This review highlights the tremendous efforts made towards defining the epidemiological picture of the disease and the most effective means of combatting it. Malaria control in Sierra Leone, as in many other parts of the world, used to be based largely on mosquito eradication. However, experience gained over the past 100 years has shown that mosquito control is often not cost-effective in areas where the interruption of transmission cannot be sustained. Emphasis should now be on early diagnosis, treatment with effective antimalarials, and the selective use of preventive measures including vector control and insecticide-treated materials where they can be sustained.

History, 19th Century↗
PubMed1998

Randomised community-based trial of annual single-dose diethylcarbamazine with or without ivermectin against Wuchereria bancrofti infection in human beings and mosquitoes.

BACKGROUND: WHO has targeted lymphatic filariasis for elimination. Studies of vector-parasite relations of Wuchereria bancrofti suggest that a reduction in the microfilarial reservoir by mass chemotherapy may interrupt transmission and thereby eliminate infection. However, no field data exist on the impact of chemotherapy alone on vector efficiency and transmission intensity of W bancrofti. We compared the impact of an annual community-wide single-dose treatment with diethylcarbamazine alone or with ivermectin on rate and intensity of microfilaraemia, and transmission intensity in an area of Papua New Guinea endemic for intense W bancrofti transmission. METHODS: We carried out clinical and parasitological surveys in 14 communities in matched pairs. People aged 5 years or older in seven communities received randomly assigned diethylcarbamazine 6 mg/kg and people in the other seven communities received diethylcarbamazine 6 mg/kg plus ivermectin 400 micrograms/kg. We made physical examinations for hydroceles and leg oedema and investigated microfilarial densities by membrane filtration before and after treatment. We selected five communities for monthly entomological surveys between September, 1993, and September, 1995. Mosquitoes were collected in these communities by the all-night landing catch method and were individually dissected to identify rates of infection and infectiveness. FINDINGS: 2219 (87.6%) of 2534 eligible people received treatment. Microfilarial rate and density had decreased 1 year after treatment in all 14 communities; this decrease was significantly higher in communities given combined therapy than in those given diethylcarbamazine alone (mean decreases 57.5% and 30.6%, respectively; p = 0.0013). Greater decreases were also seen in community-specific microfilarial intensity with combined therapy (mean reductions 91.1% and 69.8%, respectively; p = 0.0047). The rate of leg oedema was not altered, but the frequency of advanced hydroceles decreased by 47% with combined therapy and 56% with diethylcarbamazine alone. 26,641 Anopheles punctulatus mosquitoes were caught during 499 person-nights of landing catches. Exposure to infective third-stage larvae decreased in all monitored five communities. Annual transmission potential decreased by between 75.7% and 98.8% in combined-therapy communities and between 75.6% and 79.4% in communities given diethylcarbamazine alone. Transmission was almost interrupted in two communities treated with combined therapy. INTERPRETATION: Annual single-dose community-wide treatment with diethylcarbamazine alone or with ivermectin is effective for the control of lymphatic filariasis in highly endemic areas, but combination therapy brings about greater decreases in rates and intensity of microfilaraemia.

Adolescent↗
PubMed1996

Can mosquitoes transmit AIDS?

Surveys to determine knowledge regarding AIDS have shown in many countries, including Papua New Guinea, that a large proportion of the literate population still mistakenly believe that mosquitoes can transmit the AIDS virus from one person to another. In this paper we review the theoretical mechanisms which would allow blood-sucking insects such as mosquitoes to transmit virus and discuss the evidence against transmission of HIV by mosquitoes. AIDS is a sexually transmitted disease with no scientific evidence for arthropod transmission.

Acquired Immunodeficiency Syndrome↗
PubMed1995

Vectorial capacity and entomological inoculation rates of Anopheles gambiae in a high rainfall forested area of southern Sierra Leone.

We report the first study of gonotrophic cycle duration, survival rates, pre-gravid rates, vectorial capacity and chromosomal polymorphism of Anopheles gambiae s.s. in Sierra Leone. In the village of Bayama in the Southern Province, An. gambiae was the only species found to be naturally infected with Plasmodium falciparum and it constituted 99.7% of 22,541 anopheline mosquitoes caught. Chromosomal studies revealed only An. gambiae s.s. out of 66 females examined for chromosomal polymorphism, 61 (92.4%) had the 2LA inversion in the standard arrangement. Other inversions observed in low frequencies included 2Rcu and 2Ru. We estimated a gonotrophic cycle length of three days and survival rate per gonotrophic cycle of 0.59 for this species. The mean daily survival rate of An. gambiae was 0.85 and the entomological inoculation rate was 1,235 infective bites/person/year. Blood-meal ELISA tests showed that the species was very anthropophagic and that there were an estimated 35.4 daily inoculations per infective case. The epidemiological significance of these entomological parameters is discussed in the light of parasitological results for nearby villages.

Animals↗
PubMed1994

Malaria in a rural area of Sierra Leone. III. Vector ecology and disease transmission.

Studies were undertaken on the role of Anopheles gambiae and An. funestus in the transmission of malaria in four villages in a high-rainfall, forested area in the Bo district of southern Sierra Leone. Anopheles gambiae s.s., identified chromosomally as the Forest form, was the most important vector, with a mean annual sporozoite rate, based on ELISA, of 7.4%. Anopheles funestus, which was found in considerably lower numbers, was mainly a dry season vector, with an annual sporozoite rate of 11.4%. Despite these relatively high sporozoite rates, vector populations were at a low level, with approximate mean densities of only 1.0 An. gambiae and 0.1 An. funestus resting females per house room, and average biting rates of just 1.1 and 0.1 bites/person/night by these two species, respectively. In the rainy season, biting rates peaked at 9.5 An. gambiae bites/person/night and 1.0 An. funestus bites/person/night. Annual sporozoite inoculation rates by An. gambiae and An. funestus were 0.088 and 0.007 infective bites/person/night, respectively. ELISA showed that both species were highly anthropophagic. Exit-trap collections and outdoors searches showed that An. gambiae exhibited a considerable degree of exophily. Light traps inside houses caught nine anopheline species, whereas pyrethrum spray collections in houses caught only An. gambiae, An. funestus and An. hancocki.

Animals↗
PubMed1993

Malaria in a rural area of Sierra Leone. I. Initial results.

Malaria surveys to collect base-line data for an intervention study was carried out in a rural, high rainfall area of West Africa. Methods for the different components of the study are described. A mortality survey, using verbal autopsy questionnaires, established an infant mortality rate of 74/1000 live births/year, a child mortality rate of 25/1000/year and a mortality rate for children under five years of 36/1000/year. The most common causes of death were malaria and malnutrition. The results of two clinical surveys showed that the prevalence of illness in nought to seven-year-olds increased from 30% at the pre-rains survey to 58% at the post-rains survey. The most significant increases were a three-fold increase in the prevalence of upper respiratory infections, whilst skin and eye infections and fever rates doubled. A knowledge, attitudes and practice survey of 210 heads of households or women of child-bearing age revealed that 76% had never had any formal education. Eighty-nine per cent recognized that there was a malaria problem in the area, but only 30% knew that mosquitoes were involved in its transmission, and only half of the respondents were aware that malaria was preventable.

Child↗