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PubMed1984

The prevalence of onchocerciasis on selected divisions of the Firestone Rubber Plantation, Harbel, Liberia.

A survey for the prevalence of onchocerciasis was conducted on selected divisions of the Firestone Rubber Plantation, Harbel , Liberia, in November 1980. Divisions 19, 22, 23, and 36 are located in the north-central portion of the plantation, and were selected to complement transmission studies which were performed there in 1979 and 1980. Biopsy of the calf, iliac crest, and shoulder was done on a total of 583 individuals. No lateral difference in microfilarial density was observed. A prevalence of 80.8% was found. Prevalence appeared to be equal between the sexes, and to plateau above 35 years of age. Of those presenting positive skin biopsies, 20.2% had palpable onchocercomata . The geometric mean wet weight microfilarial density/mg of skin for the population sampled was 19. Onchocerciasis is considered hyperendemic in the Harbel area. Further investigations are warranted to define its dimensions in relation to clinical sequelae on the plantation.

Adolescent↗
PubMed1984

Transmission of onchocerciasis by local black flies on the Firestone Rubber Plantation, Harbel, Liberia.

A quantitative description of the transmission dynamics of onchocerciasis on the Firestone Rubber Plantation, Harbel, Liberia is presented. The putative vector, Simulium yahense, comprised 98.5% of the flies examined. Diurnal vector-host contact was unimodal, expressing a distinct peak between 0800 and 1100 hours, particularly during the wet season. Perennial breeding occurs in the Firestone biotope, and is manifested by a mean annual daily landing rate of 75 flies per person per day. S. yahense is considered an efficient vector by nature of its anthropophily, moderate infective worm burden (4.3 infective larvae per infective fly) and its spatial and temporal ubiquitousness. Onchocerciasis transmission peaked during the dry season, when 73.5% of the annual transmission occurred. The mean annual transmission potential for the study area was estimated to be 1,425 infective larvae per person. The significance of onchocerciasis as a public health problem on the Plantation is discussed, and the potential for limiting transmission is considered.

Animals↗
PubMed1985

Swamp rice farming: possible effects on endemicity of schistosomiasis mansoni and haematobia in a population in Liberia.

To obtain a better understanding of the possible influence of swamp rice farming on the patterns of Schistosoma mansoni and Schistosoma haematobium infections, the populations of two communities in rural liberia were studied. In one village, Balama (population of 435), swamp rice farms were initiated six years before the survey; in the other nearby community, Gbarta (population of 216), swamp rice farms had not yet been initiated. The prevalence of S. mansoni infection in Balama was 87% vs. 9% in Gbarta (P less than 0.01). The geometric and arithmetic mean egg counts for all infected subjects in Balama were respectively 263 and 671/g feces. in Gbarta, the geometric and arithmetic mean egg counts were 150 and 129/g feces. S. haematobium eggs were detected in 42% of subjects in Balama vs. 11% in Gbarta (P less than 0.01). Hematuria correlated with the presence of S. haematobium eggs in urine. These data indicate that there is a significantly higher prevalence and intensity of schistosomiasis mansoni and haematobia in a community where swamp rice farming has been utilized for 6 years compared to a nearby village where this water irrigation and drainage practice has not yet been implemented.

Adult↗
PubMed1986

Identification of larval and adult Simulium yahense and Simulium sanctipauli based on species-specific enzyme markers and their distribution at different breeding habitats in Central Liberia.

Human-biting adults and late instar larvae of the Simulium damnosum complex from four ecologically different simuliid breeding habitats in the Firestone Rubber Plantation at Harbel, Liberia, were identified morphologically and the monthly species composition of each site was recorded. Samples of the predominant species found at each site were assayed electrophoretically for species-specific variants of phosphoglucomutase (PGM) and trehalase (TRE). Enzyme identifications of flies and larvae were compared with morphological identifications to determine the accuracy of field identifications relying upon morphological characters. Enzyme identifications confirmed the accuracy of over 98% of the adult female identifications. S. yahense was found to be the predominant human-biting species at each site over the 10 months of sampling, with S. sanctipauli comprising a small percentage of the biting fly population. Species-specific larval enzymes confirmed the accuracy of more than 96% of the larval identifications. S. yahense was the predominant larval species found in smaller, more shaded, cooler breeding waters, while S. sanctipauli predominated in the single large watercourse that was sampled. Normally allopatric, mixed populations of these two larval species were found to exist at all sites, but sympatry occurred primarily during the wet season months of May-October. Biting activity of S. sanctipauli was found to be greatest during wet season months, and generally reflected the increase of S. sanctipauli in the larval populations of habitats dominated by S. yahense. The low human-biting activity of S. sanctipauli at all sites and during times which fostered large populations of S. sanctipauli larvae may be an indication of this specie's zoophilic tendency. Circumstantial evidence of hybridization, the expression of PGM and TRE species-specific variants for both species, was found in adults and larvae morphologically identified as S. yahense. The frequency of this "hybrid" condition, based upon PGM and TRE, was calculated to be comparable to the frequency of hybridization as determined by larval chromosome inversions.

Animals↗
PubMed1986

Anti-Plasmodium falciparum antibodies acquired by residents in a holoendemic area of Liberia during development of clinical immunity.

Sera from 48 children and adolescents (2-15 years of age), residing in a malaria holoendemic area of Liberia were investigated for specificities and isotypes of anti-P. falciparum antibodies. No clear-cut relationship to the development of clinical immunity was found when the overall antibody activities to total parasite antigens were determined by enzyme-linked immunosorbent assay (ELISA). Although there was a certain rise of IgM, total IgG- and IgG2 antibody activities, this was most pronounced at ages when a clinical but nonsterile immunity is already present. When the sera were investigated by immunoprecipitation of 35S-methionine labeled parasite polypeptides, the total number of parasite antigens precipitated was similar at all ages. Analysis by indirect immunofluorescence (IFA), registering antibodies to intracellular parasite antigens, revealed no age-dependent changes in antibody titers. In contrast, when the sera were assayed by a novel IFA, specific for a restricted number of parasite antigens in the membrane of infected erythrocytes, the frequency of positive sera as well as the anti-P. falciparum titers rose in parallel with the development of clinical immunity. Thus, these antigens appeared to be important inducers of protective immune responses and may be suitable candidates for a vaccine against the asexual blood stages of P. falciparum.

Adolescent↗
PubMed1987

Quantitative studies of onchocerciasis transmission by Simulium yahense and Simulium sanctipauli in the Firestone Rubber Plantation at Harbel, Liberia.

Black fly vectors of onchocerciasis from three ecologically different Simuliid breeding habitats in the Firestone Rubber Plantation at Harbel, Liberia, were surveyed by human-biting collections conducted at weekly intervals over a 13-month period. Black flies were identified morphologically and the monthly and seasonal contribution of different vector species to the transmission of Onchocerca volvulus at each site was determined. Simulium yahense was identified as the predominant vector species at each site. Greatest populations of this species occurred during wet season (May-Oct), but its impact on transmission of onchocerciasis was most profound during dry season (Nov-Apr) when parity, infection, and infectivity were high. S. sanctipauli was the only other vector species captured, but biting populations of this species were small, and during wet season confined primarily to the vicinity of its breeding site in the Farmington River. Dry season populations of S. sanctipauli were also characterized by lower human-biting rates, and by higher rates of parity, infection, and infectivity. Monthly transmission potentials at each site were attributed primarily to S. yahense, with peak monthly transmission occurring during the dry season months of January-April. Against the WHO standard of 100 as a "tolerable" annual level of onchocerciasis transmission, annual transmission potentials for the three sampling sites were 94, 1,877, and 4,900, with highest values being calculated for S. yahense breeding sites.

Animals↗
PubMed1990

Effect of mass treatment of a human population with ivermectin on transmission of Onchocerca volvulus by Simulium yahense in Liberia, West Africa.

The impact of mass treatment with ivermectin on the intensity of Onchocerca volvulus transmission by the black fly (Simulium yahense) was evaluated on the Liberian Agricultural Company rubber plantation in Liberia, West Africa. The adult pre-treatment prevalence of onchocerciasis was greater than 80%, and the average intensity of infection was 5.35 mf/mg of skin. The drug was administered at 2 annual intervals, reaching 58-60% of the approximately 14,000 people living in 73 camps. Landing/biting catches of black flies made in central and peripheral plantation zones indicated similar fly activity before and after ivermectin treatment (man hr index of 2.1 and 2.4 within the plantation, and 10 and 10.9 outside the plantation, respectively). The number of infected flies with developing larvae (L1, L2, L3 stages) of O. volvulus in treated areas was reduced by 93.4-95%; the number of infective flies with L3 larvae was reduced by 81.7-89.3%. Parasite loads of infected (L1, L2) and infective flies (L3 stages only) outside the plantation also decreased by 86.8% and 80%, respectively. Monthly transmission potential (MTP) showed a similar decrease: from 22.9 to 5.8 (74.6% reduction) in the treated area, and from 210 to 158.8 (24.4% reduction) in untreated areas. Mass treatment with ivermectin efficiently controlled, and at least temporarily interrupted, transmission of Onchocerca volvulus by black fly vectors.

Animals↗
PubMed1990

Ultrasonographical investigations of onchocerciasis in Liberia.

The efficiency of ultrasonography (US) for the diagnosis and clinical characterization of onchocerciasis was evaluated. US was performed on 120 probands in Liberia. Ninety-two patients had generalized onchocerciasis, 21 patients suffered from the chronic hyperreactive form of onchocerciasis (sowda), and 7 probands served as controls. Patients were examined by US with linear (7.5 MHz and 5 MHz) and sector (3.5 MHz) scanners. US results were evaluated by examination of extirpated nodules. The US structure of nodules revealed a typical pattern consisting of a homogeneous echogenicity with small echodense particles and a lateral acoustic shadow, and differentiation from lymph nodes, lipoma, or fibroma was achieved. Within the onchocercomata, calcifications or fluid were identified. Regarding the estimation of the worm burden, it is important to note that in 24 patients, additional nodules not previously palpated were found by US. Also, the number of worm centers in palpable conglomerate nodules were determined more exactly by US than by palpation. In 4 of 16 sowda patients, impalpable nodules were found by US. In 13 patients with positive microfilaria counts, no nodules could be detected. The highly characteristic ultrasonographical pattern of onchocercomata may serve as a basis for further US investigations in onchocerciasis.

Adolescent↗
PubMed1991

A longitudinal study of seroreactivities to Plasmodium falciparum antigens in infants and children living in a holoendemic area of Liberia.

Investigators studied 348 children age 0-10 years, living in a holoendemic area of Liberia, for parasitological, serological and clinical parameters. The age-specific parasite rate increased towards the 7-10 year-old age group in which it was 86.8%. The geometrical mean parasite density decreased from the 3-4 year-old age group, in which fewer episodes of clinical malaria were observed. Antibodies to crude Plasmodium falciparum parasite antigens were detected in all children. The (EENV)6 seropositive rate was a maximum of 67.9% in the 3-11 month-old age group. It declined to a minimum of 31.7% in the 5-6 years age group after which it increased slowly in the 7-10 years age group. Antibodies to the synthetic peptide (NANP)6 showed a steady seropositive rate after the age of 3 months, between 30.0% and 39.3% in all the age groups up to 10 years. No statistically significant correlation was found between seropositivity to (EENV)6 and malarial parasitemia. In contrast, a statistically significant positive correlation was found between seropositivity to (NANP)6 and parasite rates. The antibody response for the individual child was transient to both Pf155/RESA, measured by immunofluorescence, and to (EENV)6 and (NANP)6, measured by ELISA, especially in the younger age groups of this study population. Parasitological and clinical immunity developed before a stable antibody response to these defined malaria antigens was established. These antibodies may still contribute to the immune protection against malaria, but they were not reliable parameters for protective immunity in the population we studied.

Amino Acid Sequence↗
PubMed1992

Antibodies to a recombinant glutamate-rich Plasmodium falciparum protein: evidence for protection of individuals living in a holoendemic area of Liberia.

A Plasmodium falciparum antigen gene coding for a 220-kD glutamate-rich protein (GLURP) has been cloned, and the 783 C-terminal amino acids of this protein (GLURP489-1271) have been expressed as a beta-galactosidase fusion protein in Escherichia coli. The encoded 783 amino acid residues contain two areas of repeated amino acid sequences. Antibodies against recombinant GLURP489-1271, as well as against a synthetic peptide corresponding to GLURP899-916, and against a synthetic peptide representing the major glutamate rich repeat sequence from the P. falciparum ring erythrocyte surface antigen (Pf155/RESA) (EENV)6 were examined in 423 individuals (age range 30 days-78 years) living in a malaria holoendemic area of Liberia. In the 5-9-year-old age group, subjects with anti-GLURP489-1271 antibody concentrations greater than the mean value of the group had lower parasite densities than those with low antibody concentrations (P = 0.0151). High levels of anti-GLURP899-916 antibodies did not correlate with low parasite densities. However, high levels of anti-(EENV)6 antibodies were associated with significantly lower parasite densities in the 2-4-year-old age group (P = 0.0189). There was no correlation between the anti-GLURP489-1271 and anti-(EENV)6 antibody responses. The data provide indirect evidence for a protective role of antibodies reacting with recombinant GLURP489-1271 as well as with the synthetic peptide (EENV)6 from the Pf155/RESA.

Adolescent↗
PubMed1993

Health expenditure and household budgets in rural Liberia.

Fieldwork conducted in Kpelle village in north-central Liberia revealed that health-care expenses constitute a major part of domestic spending. The actual transactions for major health-care expenditures are handled by men, typically using income that jointly belongs to the couple in addition to the husband's personal income. Women are likely to spend their personal incomes on minor health expenses for themselves and their children. Women's health expenditure, as well as their income handling arrangements, seem to differ according to the type of conjugal union they are in. Although Kpelle wives have input in most financial decisions, they tend to defer to men on issues which are associated with the Western world, namely Western health care, educational and tax expenditures.

Adolescent↗
PubMed1975

Visual impairment and incidence of blindness in Liberia and their relation to onchocerciasis.

The results of the epidemiological survey of 10,860 inhabitants of 121 Liberian communities from 1969-1971 were analysed on the prevalence, incidence and risk of blindness associated with onchocerciasis infection. The overall prevalence of economic blindness in the population sample was 3.24%, the total rate of measured visual damage in both eyes was 5.37% (impairment of vision etc.). Onchocerciasis was prevalent in a very high proportion of those having visual defects. Causes of blindness as by frequency were cataract in 45%, lesions of the anterior segment, other than onchocerciasis-related in 14%, phthisis bulbi (9%) and optic atrophy (6%). The importance of onchocerciasis as a cause of blindness and as a public health problem in Liberia is examined by the comparison of 5 categories of village populations, classified by their adjusted onchocerciasis prevalence rates. The risk of exposure to onchocerciasis increases gradually from nil to 100%, providing one infection-free control population and increasing degrees of prevalence in the next categories, dependent on duration of exposure and intensity of transmission. The attempt to estimate the risk of blindness attributable to onchocerciasis from this data reveals a 3-fold risk in people exposed to the infection in their habitat, whereas a 2,5-fold risk is found from the evaluation of findings in people classified by mf-prevalence in their skins only. Considering a proportion of at least 65% of the rural population to be living under onchocerciasis exposure, the attributable risk amounts to more than 50%, which suggests that this population suffers from 50% more blindness than would be expected without exposure to onchocerciasis sometime in life.

Adolescent↗
PubMed1985

Male role in fertility decisions in Robertsport, Liberia.

"This paper examines the role of men in family planning among the Vai tribe in Robertsport, Liberia. The data were collected from a sample survey of Vai males in the town in 1982." The author found in a sample of 100 married men aged 15-39 that husbands, generally desiring large numbers of children, are a dominating influence in fertility decisions. In decisions that are reached jointly, educational attainment appears to be a significant factor.

Africa↗
PubMed1986

Male role in fertility decisions in Robertsport, Liberia: an experimental exercise for policy formulation.

There is a tendency to believe that in African societies men are the dominant decision makers in the family. In Robertsport, Liberia, there are indications that, with respect to fertility regulation, the dominance of the husband in fertility decisions exists, but it is also apparent that many of these decisions are made jointly by both husband and wife. Education is particularly influential in the joint fertility decision-making process. The 100 husbands sampled in 1982 desired a large number of children and had experience with infant and child mortality. If family planning programs should attain their goals, men should be more involved, than at present, in every aspect of the programs. Equally important is the urgency for studies related to the role of men in fertility regulation, using adequately large samples.

Africa↗
PubMed2003

Cholera epidemic after increased civil conflict--Monrovia, Liberia, June-September 2003.

Since 1989, civil war in Liberia has resulted in the displacement of hundreds of thousands of persons. In June 2003, as rebel forces approached the capital city of Monrovia (2003 estimated population: one million), an estimated 300,000 internally displaced persons (IDPs) settled in private homes with family members, public buildings, and other sites. Because of fighting during June-July, the normal collection of health data by the Liberian Ministry of Health (MoH) was interrupted. In June, cases of cholera were confirmed by international nongovernment organizations. To estimate the magnitude of the outbreak, in August, the World Health Organization (WHO) conducted a retrospective review of data collected by health organizations during June--August 2003 but not reported to MoH. Additional data were collected from an emergency surveillance system that began operation on August 25. This report summarizes the results of that analysis, which indicated that as of September 22, a cholera epidemic was ongoing in Monrovia. During the week ending October 20, a total of 1,252 cases of suspected cholera were reported (WHO, MoH, unpublished data, 2003). As of November 12, the epidemic was continuing. The epidemic began in June and was associated temporally with increased fighting and the movement of IDPs. Because cholera transmission was probably attributable to an acute shortage of clean water, poor sanitation, and crowded living conditions, international and Liberian organizations attempted to supply IDP settlements with sufficient potable water and began chlorinating wells. To stop cholera transmission and avoid additional illness and death, further preventive measures are needed.

Cholera↗
PubMed2006

Consequences of vector behavior in epidemiology of onchocerciasis on the Firestone Rubber Plantation in Liberia.

In the current study, we have assessed the distribution of black fly vectors and the occurrence of onchocerciasis among residents of the Firestone Rubber Plantation (FRP) in Liberia. The degree of endemicity of onchocerciasis on the FRP is correlated with the breeding of Simulium yahense on the Du River and Simulium soubrense on the Farmington River, as well as with the feeding behavior of these black fly vectors. S. yahense is highly anthropophilic and highly susceptible to Onchocerca volvulus, thus, it is apparently the primary vector of O. volvulus on the plantation. S. soubrense is predominantly zoophilic; consequently, it has a low capacity for transmitting of O. volvulus to humans. The prevalence of the disease is hyperendemic in the divisional camps near the Du River, affecting 77.6% to 94.4% of males and 64.9% to 88.9% of females. In the camps along the Farmington River, the disease is hypoendemic, affecting 26.1% to 49.2% of males and 25.6% to 35.1% of females. The mean intensity of infection in the camps near the Du River was 14.1 microfilariae (mf)/mg of skin in males and 13.7 mf/mg of skin in females. The density of microfilariae in people in the camps along the Farmington River was 4.8 mf/mg of skin in males and 1.9 mf/mg of skin in females. The age-specific infection in camps along both rivers substantially increased after the ages 21-30, reaching a maximum at ages 41-50. The mean density of mf/mg of skin in three anatomic locations (calf, hip, and shoulder) was 28.0, 24.5, and 14.1 mf/mg of skin, respectively, for those living on the Du River, and 10.2, 7.6, and 5.8 mf/mg of skin, respectively, for those on the Farmington River.

Adolescent↗
PubMed1989

Isolation of microcercous cercariae from snails caught in an endemic focus of Paragonimus uterobilateralis in Liberia, West Africa.

Microcercous cercariae have been recovered from the snail Homorus (Striosubulina) striatella RANG. which were collected in a focus of human lung fluke disease in Liberia, West Africa, and are here described. Metacercariae of Paragonimus uterobilateralis were isolated from freshwater crabs (Liberonautes latidactylus) captured at the same location, and at the same time, as the infected snails. The dimensions of the Liberian cercariae have been found to differ markedly from those of a cercaria from Cameroon previously described as that of Paragonimus africanus. The structure and dimensions of the Liberian cercariae clearly resemble those of the cercariae of other species of Paragonimus from Asia and America.

Animals↗
PubMed1986

Hemorrhagic fever virus infections in an isolated rainforest area of central Liberia. Limitations of the indirect immunofluorescence slide test for antibody screening in Africa.

Serum samples from 119 healthy individuals and 106 epilepsy patients inhabiting Grand Bassa County, Liberia, were tested for antibodies to hemorrhagic fever viruses (HFV) by indirect immunofluorescence. E6 Vero cells infected with Lassa fever virus (LAS), Rift Valley Fever virus (RVF), Congo Hemorrhagic Fever virus (CON), Marburg virus (MBG) and the Ebola (EBO) virus strains Mayinga (May) and Boniface (Bon) were used as antigen. To obtain reproducible and specific test results sera had to be absorbed extensively with uninfected E6 Vero cells, tested for reactivity to both virus infected and uninfected E6 Vero cells and read "blindly" by two independent observers. Antibodies to EBO were shown to be highly prevalent (13.4%) in the population of this rainforest area, while prevalences of antibodies to LAS (1.3%), RVF (0.4%) and MBG (1.3%) were much lower. No correlation between past HFV infection and post-encephalitic epilepsy or other reported febrile illnesses could be established.

Adolescent↗