Biomedical subjects
D A Bundy
Publications and source records attributed to D A Bundy.
Effect of age and initial infection intensity on the rate of reinfection with Trichuris trichiura after treatment.
The study examines the rate of re-acquisition of Trichuris trichiura infection after treatment in two populations, one of mixed age and the other of children with known pre-intervention infection intensity. A population living in a Caribbean village was treated with mebendazole and the rate of reacquisition of infection of four age classes (2-4, 5-10, 11-30, 30+ years) monitored over a 20-month period. The reinfection rate was higher in the child age-classes indicating either that children are more exposed to infection or that adults slowly develop a partially effective acquired immunity. A cohort of children (mean age 4.5 years) was separated into 3 intensity categories on the basis of expelled worm burdens and their rate of reacquisition of infection monitored over a 12-month period. The rate of reinfection was directly and positively associated with initial infection status. This may indicate that children with low intensity infections are consistently less exposed to infection or that they have effective immune responses. The latter conclusion, however, would imply that they had acquired this immunity early in life, and so appears to contradict the suggestion that resistance is only slowly acquired by adults. Reconciling these two conclusions may require more sophisticated immunological models than have been suggested previously for geohelminthiases.
The evidence for predisposition to trichuriasis in humans: comparison of institutional and community studies.
This article compares the results of two studies of Trichuris trichiura infection, one conducted in a children's home and the other in a village. In both, the intensity of infection of a cohort of children was determined by antihelminthic expulsion initially, and again after a period of re-infection. The cohort of village children showed a predisposition to a particular intensity of infection. An individual with a heavy infection initially was likely to re-acquire a heavier than average worm burden. No such correlation was observed for the cohort of institutionalized children. It is suggested that the causation of predisposition is multifactorial, and that the contrasting results of the two studies may be due in part to differing levels of heterogeneity in exposure to infection, the village children being exposed to dissimilar domestic environments and the institutionalized children to only one.
Antigenic cross-reactivity between the human whipworm, Trichuris trichiura, and the mouse trichuroids Trichuris muris and Trichinella spiralis.
Cross-reactivity was demonstrated between circulating antibodies from Trichuris trichiura-infected humans and T. muris-infected mice for heterologous antigen preparations. Mouse immune sera raised against excretory/secretory (E/S) products and anterior end homogenate from adult T. muris showed marked affinity for T. trichiura adult homogenate in ELISA, and 35S-methionine-labelled adult T. muris E/S products were precipitated by T. trichiura infection sera. Monoclonal antibodies recognizing a 48 kD Trichinella spiralis muscle larval beta-stichocyte granule antigen also showed avidity for T. trichiura adult homogenate in ELISA, as did serum from mice with patent T. muris worm burdens. This cross-reactivity is thought to result from shared stichocyte antigens and the relevance of this observation is discussed.
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.
Epidemiology and population dynamics of Ascaris lumbricoides and Trichuris trichiura infection in the same community.
The gastrointestinal helminth infection status of an age-stratified sample from a single Caribbean community was assessed using anthelmintic expulsion techniques. The same sample was re-assessed in a similar manner after a 17 month period of re-infection. The age-prevalence profile of Ascaris lumbricoides was convex while that of Trichuris trichiura was asymptotic. The age-intensity profiles of both species were convex. These differing patterns are attributed to differences in the absolute worm burdens of the 2 species. The frequency distributions of infection intensity were similar for both species, and largely independent of host age. The basic reproductive rate of A. lumbricoides (Ro = 1-1.8) was similar to that recorded elsewhere and much lower than that of T. trichiura (Ro = 4-6), implying that the latter is intrinsically more resistant to control. Individual hosts were predisposed to high (or low) intensity infection with either species, although predisposition to both species simultaneously was not conclusively demonstrated. Further studies are required to determine the cause of these observations.
Photoreceptor evoked potentials and phototactic behaviour in Cercaria caribbea LXXI cable.
1. Transient potential changes evoked in response to light stimuli, and presumably arising from rhabdomeric eye-spots in the cercarial body, were recorded for the first time, to our knowledge, in helminth parasites. 2. Pigmented Cercaria caribbea LXXI gave a very slowly adapting response to maintained light stimulus, while a non-pigmented variety appeared to emit a stronger, rapidly adapting response to light onset. 3. Swimming towards a directional light source is disrupted by several neuropharmacological agents, which presumably disturb synaptic transmission in the nerve/muscle system. 4. The light evoked potentials were unaffected by these same agents and therefore, appeared to be directly recorded receptor potentials.
The impact of host nutrition on gastrointestinal helminth populations.
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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 initiation 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.
Sigmoidoscopy in children with chronic mucoid diarrhoea in rural St. Lucia.
Sixty-nine per cent of a group of children with chronic mucoid diarrhoea who would not normally be seen in a tertiary health care facility had endoscopically demonstrable abnormality in the distal bowel, especially in the distal rectum. Sigmoidoscopy and punch biopsy of the rectum are safe procedures which can be undertaken in primary health care facilities. The inclusion of such investigations will facilitate the elucidation of the aetiology of chronic mucoid diarrhoea.
Age-relationships of Toxocara canis seropositivity and geohelminth infection prevalence in two communities in St. Lucia, West Indies.
Sera were examined from an age-stratified sample of two Caribbean communities using the Toxocara-ELISA with larval ES antigen. Seropositivity was markedly age dependent, attaining maximal values (40 and 60%) in 5-15 year olds and declining in adults. The rate of acquisition of infection with Toxocara canis and the age-prevalence profile are similar to those of Ascaris lumbricoides and Trichuris trichiura. It is suggested that toxocariasis is likely to be prevalent in tropical areas with endemic geohelminthiasis.
A community-based study of gastrointestinal helminth and protozoan infection in Western Jamaica.
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Chronic dysentery, stunting, and whipworm infestation.
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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.
Epidemiological characteristics of Toxocara canis zoonotic infection of children in a Caribbean community.
The study reports the results of a summary of the prevalence and symptomatology of paediatric toxocariasis in Anse-la-Raye, St. Lucia. The seroprevalence of Toxocara canis among the children, as determined by ELISA, was 86%, the highest level recorded to date. In contrast, the prevalence of infection in dogs was not abnormally high, although the canine population was large and unconstrained compared to that in industrial countries. The presence of infective ova in peridomestic areas and the widespread practice of pica among children in the village probably combine to enhance exposure to infection.
First record of Trichostrongylus axei infection of man in the Caribbean region.
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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.
Rate of expulsion of Trichuris trichiura with multiple and single dose regimens of albendazole.
The efficacy of multiple and single dose regimens of albendazole on Trichuris trichiura infection was evaluated by counting the number of worms expelled/day from two pair-matched groups of children, for nine days following therapy. The temporal patterns of worm expulsion were similar whether the children received a single 400 mg dose or two consecutive doses: no worms were passed before the second day, or after the sixth day, after intervention, and the maximum worm expulsion rate was attained on the fourth day. A second treatment six days after the first expelled no more worms. The results obtained here resemble those obtained previously with a three-day (600 mg) regimen of mebendazole in a study of heavily infected children. We conclude: that irrespective of dose, benzimidazole carbamates require the gut transit time plus 48 hours to immobilize T. trichiura; and that a single dose of albendazole is effective against light infections of T. trichiura but requires further evaluation with high intensity infections.