Geohelminth infection and academic assessment in Jamaican children.
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Adolescent↗
Biomedical subjects
D A Bundy
Publications and source records attributed to D A Bundy.
The epidemiological implications of a multiple-infection approach to the control of human helminth infections.
It has been suggested that there is economic advantage in using a single community therapy programme to deliver multiple treatments against several parasitic infections. This preliminary study estimates the occurrence of concurrent helminth infection in Africa and Brazil to determine whether such an approach is justified epidemiologically. The results indicate that the occurrence of geohelminthiasis with schistosomiasis is sufficiently frequent in some areas of both Africa and Brazil for a combined approach to control to be appropriate, but that the relatively low frequency of occurrence of onchocerciasis with other infections would justify a multi-infection approach to control at specific foci only.
Africa↗
The rate of ingestion of Ascaris lumbricoides and Trichuris trichiura eggs in soil and its relationship to infection in two children's homes in Jamaica.
The rate of exposure to geohelminth infection of children living in 2 institutions in Jamaica, West Indies, was estimated from the product of their rates of ingestion of soil and the density of parasite eggs in the environment. The estimated mean rate of egg ingestion was 9-20 Ascaris lumbricoides eggs and 6-60 Trichuris trichiura eggs per year, although the distribution was highly overdispersed so that some individuals had an estimated annual exposure of several hundred eggs. The estimated individual rates of exposure correlated significantly with the observed worm burdens in children at one of the homes, but not at the other. It is suggested that the susceptibility of the children and the distribution of infective stages in the environment may be important in determining the relationship between exposure and the rate of acquisition of infection.
Adolescent↗
Estimating prevalence of community morbidity due to intestinal helminths: prevalence of infection as an indicator of the prevalence of disease.
The rational design of helminth control programmes for endemic areas requires that the limited resources be focused on the communities in greatest need. The process of locality-targetting would be facilitated by a simple, inexpensive method of assessing morbidity at the community level. This paper describes how a simple model of the distribution of infection in human populations can use infection prevalence data to predict the proportion of heavy, and potentially clinically significant, infections in a community. Analysis of observed data for Ascaris lumbricoides indicates that the risk of clinical ascariasis increases non-linearly with the prevalence of infection. The predicted prevalence of morbidity is low up to approximately 60% prevalence of infection, but increases very rapidly thereafter. Analyses of data for Trichuris trichiura, Schistosoma mansoni, S. haematobium and the hookworms suggests qualitatively similar patterns. The application of the model in predicting resource requirements for control is illustrated using infection prevalence data for A. lumbricoides in Brazil.
Ascariasis↗
Cost analysis of schistosomiasis.
Cost analysis of schistosomiasis is important both in assessing the economic impact of the disease and in identifying the most cost-effective approaches to control. Economic impact has been examined both within and without the health sector, but there is a lack of measurement of the effects of disease, or the threat of disease, on patterns of production and community development. The cost-effectiveness of control approaches has been examined empirically and by using static models. Future analyses require a stronger epidemiological basis incorporating realistic demography and the temporal dynamics of reinfection, and assessment of outcomes in terms of disease rather than infection.
Cost-Benefit Analysis↗
The epidemiology and population biology of Necator americanus infection in a rural community in Zimbabwe.
Baseline data from an epidemiological study of hookworm infection in a rural community in Zimbabwe are presented. The infection status of an age-stratified sample of the community was assessed using anthelmintic expulsion techniques. Necator americanus was the only helminth parasite found to be present. The age-prevalence and intensity profiles rose asymptotically to an adult prevalence of about 80% and adult mean burden of 7.7 worms per host. The overall mean burden was 4.8 worms per host. The frequency distribution of N. americanus was overdispersed and well described by the negative binomial distribution with a value for the aggregation parameter, k, of 0.346. Separate estimates of k were lower in males and older hosts. The distribution patterns were difficult to reconcile with any simple process of age-dependent acquisition of an effective immune response. A significant negative correlation was recorded between per caput fecundity and worm burden, providing evidence for a density-dependent regulation of female worm fecundity. The basic reproductive rate (R0 congruent to 2) was found to be similar to estimates from other geographical areas.
Adolescent↗
A population dynamic approach to the cost-effectiveness analysis of mass anthelmintic treatment: effects of treatment frequency on Ascaris infection.
This study examines the cost-effectiveness of different frequencies of mass chemotherapy in reducing helminth infection and morbidity at the community level. The cost-effectiveness framework utilities a dynamic model of helminth transmission which permits the effectiveness of treatment to be expressed as some long-term reduction in infection and disease. Cost analysis is incorporated into this framework using an itemized cost menu and cost data from an actual control programme. The cost-effectiveness of mass treatment is investigated using epidemiological measures considered appropriate to Ascaris lumbricoides infection in both a high and low transmission area. The optimal strategy for control is shown to be dependent on the control objectives, the rate of transmission, and existing budget constraints. The analysis suggests that if the aim of control is to reduce morbidity due to ascariasis and mass treatment is the approach selected, then it is more cost-effective to intervene in a high transmission area than in a low transmission area, and that relatively long intervals between treatments offer the most cost-effective strategy.
Animals↗
The epidemiology and control of hookworm infection in the Burma Valley area of Zimbabwe.
An integrated hookworm control programme, involving mass chemotherapy and improvements in public health, was conducted in the Burma Valley and Vumba areas of Zimbabwe between 1985 and 1990. Three sequential annual mass chemotherapy programmes were implemented. Infection status was monitored annually throughout. Initial observations indicated asymptotic age prevalence and intensity profiles, with peak infection levels in adults. Mass chemotherapy was shown to have immediate and medium term benefits for community health. Reinfection was slow to develop, and average intensity had not returned to pre-intervention levels 39 months after the cessation of chemotherapy. The results support the existence of age-dependency in reinfection. Despite a marked increase in the number of sanitation units, no relationship was found between latrine availability and reinfection intensity on individual farms. This result is consistent with observations that the effect of sanitation is slow to develop, and indicates that repeated anthelmintic intervention should be maintained until sanitation has an impact on transmission.
Adolescent↗
Compliance and absenteeism in school children: implications for helminth control.
The validity of epidemiological surveys and the success of helminth control programmes based on the diagnosis of infection depend upon an accurate screening procedure. The success of all school-based control programmes, whether they involve prior diagnosis or not, depends on the level of school attendance and school enrollment. The degree to which compliance and school absenteeism may affect estimates of helminth infection and the coverage of treatment was investigated using empirical data from a survey conducted in 3 rural schools in Jamaica. Two sequential stool samples were requested from each child aged 9 to 12 years and screened for the presence and intensity of helminth infection using the Kato thick smear technique. Of the 696 children recruited into the study, 94% agreed to participate but only 90% of these children actually provided a stool sample for diagnosis and only 74% returned the second stool. Children infected with moderate to heavy loads of Trichuris trichiura were less likely to comply fully with the protocol than the uninfected children. They also took longer to comply and were absent from school more often than their uninfected counterparts. Increasing the sampling effort increased the compliance of all infected, and heavily infected, children. By giving them the option to comply, heavily infected children were under-represented by the sampling procedure. This has important implications for the design of control programmes and epidemiological surveys.
Absenteeism↗
Immunodiagnosis of Strongyloides stercoralis infection: a method for increasing the specificity of the indirect ELISA.
Indirect enzyme-linked immunosorbent assay (ELISA) allows sensitive detection of serum immunoglobulin (Ig) G against a soluble extract of Strongyloides stercoralis infective larvae. In this study, 40/40 (100%) human strongyloidiasis sera had high levels of anti-S. stercoralis IgG, but 30/40 (75%) filariasis sera, and 12/40 (30%) necatoriasis sera also had higher levels than control sera from UK residents. In attempts to increase the assay specificity by absorption of cross-reactive IgG, the effectiveness of pre-incubation of sera with extracts of different parasitic nematodes was investigated. One hour of incubation with 20 micrograms/ml aqueous extract of Onchocerca gutturosa absorbed cross-reactive IgG in most filariasis and necatoriasis sera, reducing the proportion with IgG levels above the positivity threshold by more than one-half. Preliminary results suggest that absorption with extracts of other filarial nematodes is equally effective, and that some of the cross-reactive IgG is directed against phosphorylcholine. Cross-reactive IgG in most necatoriasis sera was effectively absorbed with 20 micrograms/ml extract of Necator americanus. Cross-reactive IgG was not effectively absorbed with an extract of Ascaris lumbricoides. Absorption of cross-reactive IgG is an effective means of increasing the specificity of the indirect ELISA, for use in the immunodiagnosis and immuno-epidemiology of S. stercoralis infection.
Absorption↗
Immunoepidemiology of intestinal helminthic infections. 1. The global burden of intestinal nematode disease.
Estimates of the world-wide prevalence of intestinal nematode infections indicate that there are more than 1000 million people infected, and several million cases of clinical helminthiases. Recent studies suggest that the morbidity has been underestimated and that moderate intensities of infection may have important developmental consequences, particularly for children of school age.
Ascariasis↗
Immunoepidemiology of intestinal helminthic infections. 3. Mucosal macrophages and cytokine production in the colon of children with Trichuris trichiura dysentery.
Mucosal macrophages and accessory cells have been studied by immunohistochemistry in the lamina propria of the colon of children with Trichuris trichiura dysentery syndrome (TDS). No difference was found in the numbers of cells recognized by the monoclonal antibodies CD11c, CD68, or RFD7 between TDS children and local controls. However, large numbers of cells were recognized by an antibody against calprotectin (an anti-bacterial glycoprotein found in tissue infiltrating-monocytes) in TDS colonic mucosa, but few in control colon. Large numbers of cells containing tumour necrosis factor alpha (TNF alpha) were also seen in TDS mucosa; cells isolated from TDS mucosa secreted more TNF alpha than cells from control mucosa; and children with TDS had high levels of circulating TNF alpha. Non-specific macrophage-mediated inflammation and local cytokine production may therefore play a role in the pathogenesis of TDS.
Child↗
Serum isotype responses after treatment of human trichuriasis.
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Animals↗
Enzyme polymorphisms in Ascaris lumbricoides in Bangladesh.
Fourteen enzymes of Ascaris lumbricoides were analysed electrophoretically on cellulose acetate plates; 8 stained well and 3 were found to be polymorphic. Allelic and genotypic frequencies at the 3 polymorphic enzyme loci, Mpi, Pgi and 6-Pgd, were determined in a sample of 117 worms from 8 children living in different houses in an urban slum in Bangladesh. Allele frequencies in samples of parasites from the different children were compared to test for the possibility of non-random distribution of parasite genotypes between people. No strong evidence of differences was found. Diploid genotype frequencies did not deviate significantly from those expected from the Hardy-Weinberg equilibrium. Significant linkage disequilibrium was observed in one of 3 pairs of enzyme loci tested, which might suggest that some genetic subdivision exists in the local A. lumbricoides population, although no strong interference should be made from this single result. Overall, the results suggest that the worms sampled formed part of a single population which appears to be randomly mating.
Alleles↗
Aggregation and predisposition to Ascaris lumbricoides and Trichuris trichiura at the familial level.
This study examines the persistence of familial aggregation and familial predisposition to Ascaris lumbricoides and Trichuris trichiura infection over 2 periods of treatment and reinfection, in an urban community in Kuala Lumpur, Malaysia. Both parasite species were shown to be aggregated (assessed by the variance to mean ratio) within families at all 3 interventions, although no consistent trend in aggregation was observed over the period of the study. Associations between mean A. lumbricoides and T. trichiura infection levels of families, at all 3 interventions, were highly significant (P < 0.0001), suggesting persistent predisposition at the family level.
Adolescent↗
Hookworm infection in pregnancy.
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Adolescent↗
'Catch-up' growth velocities after treatment for Trichuris dysentery syndrome.
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Body Height↗
Household aggregation of Strongyloides stercoralis infection in Bangladesh.
Strongyloides stercoralis infections were shown to be aggregated in households in an urban slum community in Dhaka, Bangladesh. Parasitological data on 880 residents living in 280 households were analysed statistically using 3 different tests, each of which yielded significant evidence of household aggregation of S. stercoralis infection. One test was applied to the data after stratification for 4 variables were previously shown to be independently associated with infection. Evidence of household aggregation of infection remained after stratification, suggesting that aggregation is due not only to shared risk factors, but also to either familial genetic predisposition to infection or close contact person to person transmission of infection within households.
Adolescent↗