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PubMed1977

Epidemiological investigations of Bancroftian filariasis in the coastal zone Liberia.

A survey in 5 study areas along the Liberian coast was conducted to gain information on the prevalence and importance of bancroftian filariasis. The examination of 2675 persons revealed prevalence rates between 2% and 37%. The median microfilarial densities (MfD50) ranged from 5 to 24 microfilariae in 20 mm3 capillary blood taken between 20.30 hours and midnight. Catalytic curves fitted to age-specific infection rates were used to estimate incidence (1% to 3%) and recovery rates. It was extrapolated from the survey results that in a population of 71,0000 there are 16,0000 to 20,0000 infected with Wuchereria bancrofti. An estimated 2500 to 40000 men suffering from hydroceles and 3700 to 40000 elephantiasis patients demonstrate that bancroftian filariasis has to be regarded a health problem in rural coastal Liberia.

Blood↗
PubMed1987

Infection rates and parasitic loads of Onchocerca volvulus, and other filariae, in Simulium sanctipauli s.l. and S. yahense in a rain-forest area of Liberia.

Simulium sanctipauli s.l. and S. yahense are common and widespread in the rain-forest zone of Liberia, but differ with regard to their biting densities and contribution to the transmission of Onchocerca volvulus. Although, in a study area on the St. Pauli River, S. sanctipauli s.l. (presumably S. soubrense in the sense of Post) was the predominant ma-biting species (74.3% of 30,855 females examined), S. yahense was shown to be the important vector. While 1000 biting females of S. yahense carried 96 3rd stage larvae indistinguishable from O. volvulus, only 14 were found per 1000 females of S. sanctipauli s.l. Of the parous females (3135 S. sanctipauli s.l./1621 S. yahense) 23.8/39.9% harboured 1st and/or 2nd stage filarial larvae and 1.9/9.4% 3rd stage larvae of O. volvulus. Animal filariae of unknown origin, indicative of zoophily, were very common in S. sanctipauli s.l. (13.8%) but practically absent from S. yahense (0.5%). In spite of its poorer vectorial performance S. sanctipauli s.l. cannot be neglected as a vector because it may occur in high biting densities and contribute considerably to the transmission, in particular in the vicinity of the St. Paul River. The interplay of two vector species, which develop in different types of water-courses explains the overall high endemicity of onchocerciasis in the study area.

Animals↗
PubMed1987

Failure of Onchocerca gutturosa to develop in Simulium soubrense and Simulium yahense from Liberia.

Laboratory reared female S. soubrense and S. yahense from Liberia were intrathoracically inoculated with bovine skin dwelling microfilariae of Onchocerca gutturosa. Of a total of 174 flies, each injected with 50 fresh microfilariae, the maximum development was to late first-stage larvae. One S. soubrense also contained two second-stage larvae and a maldeveloped third-stage larvae. No development to normal third-stage larvae was observed in any fly despite maintenance at 28 degrees C for up to 10 days following infection. This contrasts with complete development of O. volvulus in both blackfly species under similar conditions.

Animals↗
PubMed1978

Dynamics and intensity of Wuchereria bancrofti transmission in the savannah and forest regions of Liberia.

In four villages in the savannah and in the rain forest of Liberia, regular assessment of the biting activity and infection rates of anthropophilic mosquitoes have been carried out through full annual cycles. The microfilaremia rates in the localities in the savannah were 18.3% and 20.0% and in those of the forest 10.3% and 12.5%. The all-night catches were performed inside ordinary inhibited houses at monthly or fortnightly intervals. Presence of infective larvae of Wuchereria bancrofti proved Anopheles gambiae, A. funestus and A. nili to be the local vectors. Biting densities were high in the savannah, and low in the forest. From the mosquito catches and the results of their dissections for filarial larvae it could be estimated, that during the observation year a person in the savannah villages would be bitten annually by 18,165 and 36,450 vector mosquitoes respectively, and would receive 236 and 536 infective bites with 570 and 1211 infective larvae. In the two forest villages the number of vector bites per person per year was calculated to be in the order of 6120 and 1102 of which 64 and 8 would be infective bites transmitting 101 and 8 larvae. The findings of considerable differences in transmission intensities between villages of the same bioclimatic zone and of comparable microfilaremia rates indicates instable epidemiological conditions in at least some of the localities investigated.

Animals↗
PubMed1979

Studies on Bancroftian filariasis in Liberia, West Africa. I. Distribution and prevalence in the north-western savanna area.

A nightblood survey was carried out in 17 villages in the savanna area in Upper Lofa in Liberia. A total of 1968 people was examined for the prevalence of microfilariae of Wuchereia bancrofti and for clinical symptoms of filariasis. 279 (14,2%) persons proved to be microfilaria carriers. Men were almost twice (19,0%) as much infected than women (10,4%). Only two cases of leg elephantiasis and one breast elephantiasis were found. Enlargements of scrotum were seen in 60 men (6,9%). The scrotal enlargement rate increased steadily with age.

Adolescent↗
PubMed1979

Studies on bancroftian filariasis in Liberia, West Africa. II. Changes in microfilaraemia in a rural population some years after first examination.

The population of eleven villages in the savanna area in Upper Lofa in the hinterland of Liberia was investigated in 1973 and 1976/77 for infections with microfilariae of Wucheria bancrofti. From a total of 1255 persons examined in 1973 16,3% were microfilaria carriers and in 1976/77 17,9% out of 1356 inhabitants were microfilaria positive. To obtain informations on the change of microfilaraemia in individuals, emphasis was laid in 1976/77 on the identification of those persons, who had been examined already in 1973. From 477 persons examined in both surveys 78 proved to be infected with microfilariae and 348 were microfilaria negative in both examinations. 35 inhabitants were microfilaria positive only in 1976/77 and 18 persons showed microfilariae in the blood samples only in 1973. The median density of microfilariae of the microfilaria carriers examined in 1973 and 1976/77 increased little but statistically significantly within a period of about three years.

Adolescent↗
PubMed1972

Distribution of Necator americanus and Ancylostoma duodenale in Liberia.

In the first country-wide survey of hookworm infection in Liberia, diagnosis by test-tube filter-paper cultivation revealed a prevalence of more than 90%. This sensitive technique also permitted differential species determination. Necator americanus was found to occur in all regions and in a high proportion of the persons examined. Ancylostoma duodenale was mainly confined to a narrow coastal belt, and usually parasitized individuals harbouring N. americanus as well. The average number of eggs per gram of faeces (EPG) of infected individuals was lowest in the population of the hinterland. During the latter part of the studies a modified test-tube filter-paper cultivation technique was used in combination with dilution counting to obtain data on intensity of infection separately for the 2 species. For N. americanus there was little regional difference in the intensity of infection, but the EPG for A. duodenale was much higher in people living in the coastal area.

Adolescent↗
PubMed1966

Studies on chloroquine-resistance of Plasmodium falciparum in Upper Volta and Liberia, West Africa.

The emergence of strains of Plasmodium falciparum resistant to normal dosages of chloroquine or other 4-aminoquinolines has caused concern in a number of malarious areas. Well-documented reports have confirmed this resistance in wide areas of South-East Asia and in some areas of South America. Occasional reports have been received from parts of West Africa, and the present investigation sought to clarify the situation in two areas, Ouagadougou, Upper Volta, and Kpain, Liberia, from which such reports had emanated. Studies were carried out to determine the sensitivity of local strains of P. falciparum to chloroquine. The results, based on the rapidity of parasite clearance, indicated a normal sensitivity in the cases treated. Although it is concluded that strains of P. falciparum with significant resistance to chloroquine are not at present a problem in the areas concerned, a watch should be kept for the possible future emergence of this problem.

Adolescent↗
PubMed1980

Preliminary epidemiological survey of schistosomiasis in central and southern Liberia.

Some basic epidemiological data on schistosomiasis in central and southern Liberia were collected. A study of snail density fluctuations was carried out in waterbodies bordering the road between Harbel and Gbarnga. Samples from schoolchildren living in ten selected villages were examined for Schistosoma spp. and other helminths. In the coastal region no snail hosts were found, the prevalence rates in schoolchildren were low and the infections were apparently imported. Inland, the intermediate host of Schistosoma haematobium Bulinus globosus was common and the prevalence of urinary schistosomiasis was high. Further inland, around Gbarnga, both Schistosma mansoni and S. haematobium were endemic. The seasonal patterns of patent cercarial infections in Bulinus globosus and Biomphalaria pfeifferi are described. Both snail densities and cercarial infection rates were markedly reduced by heavy rains. The results of the study may contribute to the planning of future integrated control strategy.

Adolescent↗
PubMed1980

Studies on bancroftian filariasis in Liberia, West Africa. V. The influence of treatment with diethylcarbamazine and vector control on the transmission of Wuchereria bancrofti.

The transmission intensity of bancroftian filariasis was investigated during a study on filariasis control carried out in eight villages of the savanna area in the hinterland of Liberia. Although the microfilarial reservoir had been reduced considerably in the human population of two villages by mass treatment with the filaricide drug diethylcarbamazine the transmission of Wuchereria bancrofti was continued without any distinct reduction. The transmission however decreased distinctly or was even interrupted when residual spraying with DDT was used in two other villages for vector control. The combined application of both control measures did not prevent completely that mosquitoes became infected with mature stages of W. bancrofti.

Animals↗
PubMed1983

Studies on the epidemiology of schistosomiasis in Liberia: the prevalence and intensity of schistosomal infections in Bong County and the bionomics of the snail intermediate hosts.

Urine samples from 3548 individuals residing in six of the eight districts which comprise Bong County, Liberia, the project area of the Bong County Agricultural Development Project (BCADP), and fecal specimens from 3408 of these individuals were examined for schistosome ova. A total of 164 water sites, including rice paddies, were surveyed for schistosome vector snails and monthly changes in snail population density and infection rate were determined in selected water sites. Bulinus globosus was more widely distributed than Biomphalaria pfeifferi but the latter species showed a higher infection prevalence (12.3%) than the former one (10.3%). Snail population density and infection rate fluctuated with season, being higher in the dry season and lower during periods of heavy rainfall. Dessication and/or heat stress may have contributed to the contraction of snail population size at the end of the dry season. More water sites contained infected snails during December through February than at any other time of the year. In selected water sites examined at monthly intervals, mean snail density was higher in rice paddies than in other water contact sites but the latter showed a higher prevalence of infected snails than the former. The overall prevalence of Schistosoma mansoni (24.8%) was significantly higher than that of S. haematobium (22.7%) but the difference in prevalence rates of two species in school children was not statistically significant. The intensity of S. haematobium infection (13.2 means G) was significantly higher than that of S. mansoni (6.3 means G). Mixed infections in school children did not have a significant effect on egg output. The prevalence and intensity of S. haematobium showed a dramatic decline between the age groups 0-15 and 20-50 + years old; the differences between these age groups in S. mansoni infection were unremarkable. In Zota, Jorquelle and Kokoya Districts, prevalence rates of S. haematobium were higher than those of S. mansoni; the reverse was observed in Suakoko and Panta-Kpai Districts but relative prevalence rates varied according to specific locality in each district. A south to north stratification of schistosomal infection prevalence was observed similar to the west to east gradient reported by Saladin et al. (1980). New rice paddies developed during the three year operational period of the BCADP contained little or no vector snails and schistosomal infections in farm families of these paddies reflected the characteristic of the disease in corresponding localities.(ABSTRACT TRUNCATED AT 400 WORDS)

Adolescent↗
PubMed1983

The impact of schistosomiasis among rural populations in Liberia.

Human infection with Schistosoma haematobium and/or Schistosoma mansoni is known to be widespread in central Liberia, but no information is available about its clinical manifestations or its significance for public health. Details of a cross-sectional morbidity study are reported. A sample from hospital out-patients and samples from 3 villages situated in areas with different transmission patterns (lack of transmission, transmission of only S. haematobium and transmission of both S. haematobium and S. mansoni) were examined. All 184 individuals were examined by standardized case history, clinical and parasitological investigations, including a skin snip for onchocerciasis and a count of schistosomal and other intestinal worm eggs from stool and urine. A complete blood count, urine analysis, urine cultures, hepatitis-B surface antigen determination and abdominal X-rays were also carried out. Schistosomal egg counts ranged from 1 to 6200/10 ml urine for S. haematobium and from 1 to 228/g stool for S. mansoni. Difficulties for the definition of accurate morbidity indices are discussed. Except for haematuria and dysuria, the overall morbidity in the study area was not striking, neither for S. haematobium nor for S. mansoni infection. No cumulative pathology was observed in patients with mixed infection. The frequency of hypertension, hepato- and splenomegaly, ascites and bacteriuria was low and no relationship to schistosomiasis could be established. Bladder calcifications were found in 10% of people living in an area of transmission of S. haematobium. Although the intensity of infection is low for both S. haematobium and S. mansoni, long-term follow-up studies are essential for a more accurate assessment of the public health importance of these parasites.

Adolescent↗
PubMed1983

The influence of schistosomiasis on the serum concentrations of retinol and retinol binding protein of a rural population in Liberia.

121 persons from rural areas of central Liberia were examined for possible interactions between helminthic infections and the retinol (vitamin A) and retinol binding protein (= RBP) status. About 2/3 of this mainly adult population had retinol and RBP serum concentrations less than or equal to 400 micrograms/l and less than or equal to 40 micrograms/ml, respectively. Only one person had a serum retinol concentration less than 100 micrograms/l which is critical for the appearance of xerophthalmia. The retinol and RBP concentrations showed a linear, positive correlation. 19 parasitologically helminth free individuals had mean serum retinol and RBP concentrations of 414 micrograms/l and 43 micrograms/ml, respectively, while the corresponding values of 20 individuals with schistosomiasis as the only helminthic infection were 339 micrograms/l and 35 micrograms/ml. 65 other persons with mixed intestinal and/or tissue helminthiases, and 9 persons with pure Onchocerca volvulus infection exhibited intermediate mean concentrations. 32 persons without serological evidence of helminthic infections had higher serum concentrations of retinol and RBP than 32 individuals in whose sera at least one raised antibody titer was found in the enzyme-linked immunosorbent assay with 3 different helminthic test antigens. In addition to age, sex and pregnancy schistosomiasis might be a further risk factor of latent retinol and RBP deficiency among adults and teenagers living in a schistosomiasis endemic area.

Adolescent↗
PubMed1983

A pilot control trial of schistosomiasis in central Liberia by mass chemotherapy of target populations, combined with focal application of molluscicide.

In an area of high transmission of Schistosoma haematobium and S. mansoni in Central Liberia, populations of five villages and intermediate host snails were surveyed for two years. In three of these villages focal application of molluscicide (niclosamide) in the main transmission sites was combined with mass chemotherapy of a target population representing 76 to 90% of the contamination index. In the two other villages, which served as control, the prevalence indexes remained stable or increased a little during the period of this study. A three dose metrifonate mass treatment was applied in one village with only S. haematobium infections. The compliance was very poor for the second and third dose but the quantity of eggs eliminated by the whole population present before and after mass treatment was reduced by 50%. No snails were found after molluscicide applications but as the incidence remained unchanged it is suspected that inhabitants have been reinfected by going to their fields. Concurrent metrifonate and niridazole mass treatment in one dose was applied in another village with only S. haematobium infections. Molluscicide applications reduced the snail population by 80% but did not affect the transmission. Prevalence indexes were almost the same before and after this intervention. In the last village, praziquantel (40 mg/kg in 1 dose) was used because both S. haematobium and S. mansoni infections were present. Molluscicide applications reduced the snail population by 99% and 87% for Bulinus globosus and Biomphalaria pfeifferi, respectively. This intervention stopped the transmission of S. haematobium for at least one year and reduced the prevalence from 21% to 4.6%. On the contrary for S. mansoni infections, the incidence remained very high (50%) and the prevalence was unchanged after one year follow-up. This could be explained by lower efficacy of praziquantel against S. mansoni (cure rate: 53%) and of molluscicide application against B. pfeifferi, which are highly susceptible to S. mansoni (infection rate 44%). The importance of migration in these villages is emphasized. Prevalence indexes were largely influenced by the arrival of newcomers who played a more important role in the maintenance of transmission after target mass chemotherapy than the infected persons excluded from this treatment. The costs per capita protected were 3.33 US $ for metrifonate, 1.53 for metrifonate and niridazole combined and 1.67 US$ for praziquantel. These figures do not include costs for parasitological examinations.(ABSTRACT TRUNCATED AT 400 WORDS)

Adolescent↗
PubMed1984

Morphological identification of simulium sanctipauli and S. yahense in Liberia and comparison of results with those of enzyme electrophoresis.

Simulium sanctipauli and S. yahense have been incriminated as the main vectors of Onchocerca volvulus in the rain-forest zone of Liberia. An accurate identification of the females of the two species which breed in different types of water-courses but are morphologically similar is essential for a proper study of their epidemiological importance and the planning of control measures. Various external characters were examined for their diagnostic value by the comparison of identifications using these characters and those based on enzyme electrophoresis (phosphoglucomutase, trehalase). It was shown that the females of the two species can be separated reliably by the use of external morphological characters. The occasional finding in the same fly of phosphoglucomutase variants typical for each species indicated the possible occurrence of natural hybridization between S. sanctipauli and S. yahense.

Animals↗
PubMed1984

Evaluation of immunoassays for diagnosis and management of sleeping sickness in Liberia.

Nineteen parasitologically confirmed Liberian sleeping sickness patients were observed for up to 40 months. Efficacy of suramin therapy was indicated by decrease of serum and CSF immunoglobulins as well as by decreasing IgG and IgM serum antibody levels as determined by ELISA and fluorescence antibody tests. The tendency of serum antibody concentrations to increase again during the second and third years after treatment could be explained in one patient only who experienced relapse or reinfection, confirmed by demonstration of blood trypanosomes. Known endemic and nonendemic areas in Liberia could not be discriminated by the prevalence of Trypanosoma IgG antibodies. Furthermore, IgM antibody was present in 18% of a random sample of sera from non-endemic ares. The possibility of trypanosomes other than T.b. gambiense to stimulate antibody production in man is discussed.

Animals↗
PubMed1984

Identity of Trypanozoon stocks isolated from man and a domestic dog in Liberia.

The isoenzyme patterns (electrophoresis on thin-layer starch gel) and the human serum resistance (blood incubation infectivity test) of a Trypanozoon stock from a dog and 14 stocks from man in Liberia were examined. The complete conformity of criteria for man-infectivity of the dog stock with 5 human stocks and the very close similarity to the 9 remaining stocks from the same epidemiological locality indicates the dog as a reservoir host of gambiense sleeping sickness.

Alanine Transaminase↗