Seroepidemiological study of the transmission of mumps virus in St. Lucia, West Indies

A seroepidemiological study of the prevalence of mumps virus specific antibodies reveals a pattern of endemic persistence on the island of St. Lucia in the West Indies. In the unvaccinated population the proportion seropositive rose rapidly in the child age classes to attain a stable plateau close to unity in value in the teenage and adult age groups. The average age at infection was estimated to be between 3 and 4 years of age and the average duration of detactable levels of maternally derived antibodies was approximately 3 months. Analyses based on mathematical models of the transmission dynamics of the virus suggest that in excess of 75 percent of each cohort of 1-to 2-year-old children must be effectively immunized to eliminate mumps virus transmission. A mumps radial haemolysis test, developed for quantitive measurements of antibody, is discussed. (AU)

Predisposition to Trichuris trichiura infection in humans

The study examines the distribution of Trichuris trichiura infection in a village community in St. Lucia, West Indies. The infection intensity of the same age-stratified population was assessed (by drug expelled worm burden and faecal egg count) at the intiation of the study, and after 17 months of reinfection following treatment. The frequency distribution of worm numbers per person was similar at both periods of sampling. There was a significant correlation between the initial infection intensity of an individual, and the intensity acquired by the same individual following the 17 month period of reinfection. This relationship was observed in a broad range of host age classes. The study provides firm evidence that individuals are predisposed to heavy (or light) T. trichiura infection. (Summary)

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 percent were harboured by the 2 to 15-year-old children. Of those individuals harbouring 100 worms or more, 87 percent 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.(AU)

Horizontal-age prevalence and intensity of trichuris trichiura infection in a rural population in St. Lucia - abstract

The clinical severity of trichuriasis and the rate of production of Trichurius infective stages are dependent upon the size of the worm burden. This study examines the horizontal-age distribution of prevalence and intensity of Trichurius infection in a St. Lucian village, with the twofold aim of identifying the age group which makes the major potential contribution to the transmission of infection and is at its greatest risk of disease. Duplicate faecal specimens from a minimum of 16 individuals in 8 age groups (<0.5->30 years) were examined twice, using the Kato thick-smear technique. A minimum of 16 individuals, infected with Trichuris, from 6 of the age groups (1->30 years) had their worm burdens determined by expulsion with mebendazole (Vermox, Janssen Pharmaceutica). Ovogenic infections occurred in 6 percent of children under 12 months; the youngest case was 5 months. Prevalence increased dramatically after the first year of life, exceeding 90 percent by 3 years of age, and remaining high and constant into adulthood. Intensity rose over a similar time preiod to prevalence but approximately one year later in life. Maximum intensity was attained in the age group 2-10 years old, and thereafter declined with increasing age. These results indicate that the population is exposed and susceptible to trichurius infection before 12 months of age. The decline in worm burden after 10 years of age may reflect age-dependency in the force of infection or the development of an immune response. Children aged 2-10 years have the largest worm burdens and are therefore: (1) the major contributors to the transmission of infection and hence the major focus for targeted chemotherapy; and (2) most likely to develop the clinical manifestations of trichuriasis (AU)

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 observe 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 >91 percent of the population to be treated every 6 months for >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 (AU)

Population distribution of Trichuris trichiura in a community of Jamaican children

The trichuris trichiura worm burdens of 23 children 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 reinfection. For both collections the maximum rate of worm expulsion was achieved on the fourth day after starting treatment. The worm populations 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 determination of worm burdens by this method; populations of Trichuris are more highly aggregated than those of Ascaris and thus may 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. (AU)