Evaluation of the skin test for hookworm as an epidemiological tool.

The usefulness of a skin test with larval Necator americanus antigen for assessment of hookworm prevalence was evaluated in an endemic area of Costa Rica. In comparison with standard coprologic techniques employed to survey the population, the skin test detected 83% of infections, showing a fairly satisfactory sensitivity. The overall specificity of the test was 50%, i.e., random. No correlation was found between skin reactivity and hookworm burden. The sensitivity of the test increased moderately with age, but its specificity decreased significantly at the same time. False positive reactions were more numerous among persons formerly infected with hookworm who had been negative for as long as 5 years. There was an indication of cross reactivity with intestinal nematodes other than hookworm. The test was used to detect hookworm infected persons in the community for selective treatment, in comparison with mass treatment of all the people in another village. The selective administration of an anthelminthic drug to only skin test positive persons did not achieve the same drop in community hookworm prevalence as did the indiscriminate treatment of the whole population.

Hookworm infection in Kweneng District, Botswana, A prevalence survey and a controlled treatment trial.

Stool specimens from a sample of schoolchildren at six schools in Kweneng District were examined for hookworm infection, using the brine flotation method. Necator americanus was the only hookworm identified. The western part of the District forms part of the Kalahari Desert, and in four villages here 90%, 88%, 88% and 86% of the children were infected. In two villages in the eastern non-desert part, only 13% and 9% were infected. Most infections were light. There was no significant correlation between severity of infection and anaemia. In one school (228 pupils; 86% infected with hookworm), half the children were treated with tetrachloroethylene (0.1 ml/kg, maximum 5 ml) and the other half with placebo. Two weeks after treatment the prevalence of infection were 28% and 75% respectively (p less than 0.001), and five months after treatment 51% and 69% (p less than 0.05). Measured over the five-month period there were no significant changes in haemoglobin and nutritional status (weight/height). Based on the results of the survey, a hookworm mass treatment programme was not recommended.

The treatment of Fasciolopsis buski infection in children: a comparison of thiabendazole, mebendazole, levamisole, pyrantel pamoate, hexylresorcinol and tetrachloroethylene.

Four relatively new broad spectrum anthelmintics (thiabendazole, mebendazole, levamisole and pyrantel pamoate) were compared with two older anthelmintics, (tetrachloroethylene and hexylresorcinol) to treat heavy Fasciolopis buski infections in 17 children aged 4-13 years in hospital. Tetrachloroethylene was the most effective drug in these 17 children and another 49. Large numbers of worms were expelled and faecal egg counts were markedly reduced (99%). The mean number of worms per child was 122 with a range of 7 to 818. All the other anthelmintics tested were ineffective; no worms or only a few were expelled after treatment. However, the oral administration of tetrachloroethylene and hexylresorcinol were associated with severe anaphylactic reactions which were prevented by prior treatment with antihistamines.

Hookworm burdens and faecal egg counts: an analysis of the biological basis of variation.

The relationships between various measures of faecal egg output and hookworm burdens were investigated in 84 villagers from West Bengal with mixed Necator americanus and Ancylostoma duodenale infections. The pattern of day to day variability in egg counts from individuals can be characterized by the linear relationship between the logarithms of the variances and means. Egg output is shown to be non-periodic in long runs of day-to-day records. The distribution of worm numbers per host is well described by the negative binomial probability model, and the relationship between per capita egg output and worm burden is non-linear where egg output declines as parasite burden rises. Density-dependent effects on fecundity are shown to act at comparatively low worm burdens in relation to the range of observed parasite loads. Egg output measures are shown to be qualitative as opposed to quantitative measures of worm burdens as a consequence of inherent sampling heterogeneity and variability induced by biological processes, such as density-dependent depression of parasite fecundity. The analyses suggest that it is possible, on the basis of egg counts, to discriminate between individuals with low and high hookworm burdens. The intrinsic per capita fecundities of the two species of hookworms are shown to be similar, but density-dependent constraints on egg production by N. americanus appear to be more severe than those acting on A. duodenale. This observation may help explain why A. duodenale appears to produce larger numbers of eggs per unit of time than N. americanus. The regulatory role of density-dependent fecundity and aggregated distributions of worm numbers per person are discussed in relation to the over-all transmission dynamics of hookworm parasites.

Pediatrics: ridding children of common worm infections.

The most common worm infection in children in the United States is pinworm infection. In second place is roundworm infection. Agents that are effective against these nematodes in a high proportion of cases are available. In hookworm disease, generally seen in older children, tetrachloroethylene treatment is being supplanted by use of drugs less likely to have adverse side effect. Visceral larva migrans is difficult to diagnose and to treat, and our best hope for control lies in prevention.