A survey of parasites in primary school children in Dominica, West Indies

Estimating occurrence of Strongyloides stercoralis in the Caribbean island countries: Implications for monitoring and control

BACKGROUND

Few data are available for the prevalence of Strongyloides stercoralis in the Caribbean region. This frequently under diagnosed soil-transmitted helminth (STH) can result in long-term low intensity chronic infections that are asymptomatic or can cause varied intestinal disturbances. With autoinfections, infections lasting over 60 years can occur and hyperinfections lead to high morbidity and mortality.

METHODOLOGY/PRINCIPAL FINDINGS

Historical literature was searched to determine the prevalence of S. stercoralis in the Caribbean island countries with some additional countries and islands included for comparative data. A previously published model was used to calculate prevalence taking in to account the sensitivity of the diagnostic methods used. Data for 17 islands/Caribbean countries were found and sufficient data were located to calculate prevalence for 14 locations. Prevalence ranges from <1% to 20.3% and while it has decreased in many islands it has not decreased at the same rate as other STHs in the last 40 years within the Caribbean region.

CONCLUSIONS/SIGNIFICANCE

S. stercoralis continues to be an important STH within the Caribbean. Potential reasons for the current prevalence include: long lasting infections, populations not targeted with mass drug administration (MDA) programs being infected, low efficacy of commonly used drugs in MDA programs, and under-diagnosis resulting in infections not being treated.

Prevalence of Entamoeba histolytica and other intestinal parasites in a community from Maracaibo, Venezuela

The prevalences of Entamoeba histolytica and other intestinal parasites were assessed in a suburban community of Maracaibo, Venezuela, by examination of a stool specimen from each of 342 individuals, using iron-haematoxylin stained faecal smears and formalin-ether concentration. The overall parasitic infection rate was 80.4%, and 65.8% of the population had multiple infections. The overall amoebic infection rate, which was highest in female adults, averaged 39.7%. The E. histolytica infection rate was 8.7% and most of those infected were passing cysts. Entamoeba polecki was observed in two samples. Amongst the protozoa, Entamoeba coli was observed most frequently (24.8%) and Giardia lamblia was the predominant pathogen (13.0%). Trichuris trichiura (71.9%) and Ascaris lumbricoides (54%) were the most common parasites, particularly in school-children. The high rates of parasitic and multiple infections reflect the low socio-economic status of the community studied.

Age-related prevalence and intensity of Trichuris trichiura infection in a St. Lucian community

Age-related changes in the average worm burden and the prevalence of Trichuris trichiura infection, in a village community in St. Lucia, were examined by field studies based on worm expulsion techniques. Horizontal age-intensity profiles were convex in form with peak parasite loads occurring in the 2 to 15-year-old children. Prevalence is shown to be a poor indicator of changes in average worm load with age. Faecal egg counts (epg and epd) provide a qualitative measure of worm burdens since fecundity is shown to be approximately independent of worm load. The parasites were highly aggregated within the study community, with most people harbouring low burdens while a few individuals harboured very heavy burdens. Of the total parasite populations in the study sample, 84% were harboured by the 2 to 15-year-old children. Of those individuals harbouring 100 worms or more, 87% were in the 2 to 10-year-old age range. Crude estimates of population parameters (basic reproductive rate, 4-5; rate of reinfection, 90 year-1) suggest that the rate of reinfection is higher than for other helminth parasites of man. The control of morbidity and parasite transmission is discussed in the context of targeting drug treatment at the child segment of the study population.

Epidemiological aspects of Trichuris and trichuriasis in Caribbean communities

The review argues for a reappraisal of the health significance of the human whipworm, Trichuris trichiura. Infections with this geohelminth are at least as prevalent as Ascaris lumbricoides in many localities, and are associated with significant morbidity. Infection may result in severe trichuriasis syndrome or, more frequently, in a chronic colitis associated with growth stunting. Under-reporting of the chronic manifestations of disease has resulted in a gross under-estimation of the health impact of trichuriasis. Furthermore, estimation of the population dynamical parameters of T. trichiura transmission suggests that whipworm infections are intrinsically more resistant to control than those of other common geohelminths. A major determinant of the transmission dynamics and morbidity characteristics of this helminthiasis is the aggregation of worm burdens in certain predisposed individuals and age groups. It is suggested that improved understanding of the factors generating this distribution of infection intensity is a pre-requisite for effective control of both infection and morbidity.

Population distribution of Trichuris trichiura in a community of Jamaican children

The Trichuris trichiura worm burdens of 23 children living in a Place-of-Safety in Kingston, Jamaica, were assessed by stool collection for more than five days after treatment with mebendazole. This procedure was repeated after a seven-month period of natural re-infection. For both collections the maximum rate of worm expulsion was achieved on the fourth day after starting treatment. The worm population distributions were overdispersed and well described by the negative binomial probability model (k = 0.29) in each case. For any one individual, the number of worms passed on the first expulsion was unrelated, absolutely or relatively, to the number passed on the second. These data suggest that: knowledge of the time dependency of helminth expulsion is essential for the accurate estimation of worm burdens by this method; populations of Trichuris are more highly aggregated than those of Ascaris and may thus be more susceptible to control by selective rather than random chemotherapy; and the inherent predisposition of hosts to infection may be of minor importance in determining the distribution of worms in the population-heavily infected hosts appear no more or less likely to acquire large worm burdens on subsequent exposures.

Population dynamics and chemotherapeutic control of Trichuris trichiura infection of children in Jamaica and St. Lucia

Population dynamical parameters of Trichuris trichiura infections in children were estimated from longitudinal intensity and prevalence data from a population (n = 23) in a children's home in Jamaica. The theoretical predictions of a deterministic model incorporating these parameters were approximated to observed horizontal-age prevalence data from a naturally infected population (n = 203) of children in a St. Lucian village, and a rough estimate of the basic reproductive rate (Ro = 8-10) of T. trichiura obtained. The findings suggest that T. trichiura populations are intrinsically more difficult to control by traditional mass-treatment chemotherapy (eradication requires greater than 91% of the population to be treated every 6 months for greater than 5 years) than are populations of Ascaris, but may be more susceptible to selective chemotherapy programmes which aim to treat only the most heavily infected individuals.