Geophagy as a risk factor for geohelminth infections: a longitudinal study of Kenyan primary schoolchildren

Abstract

Geophagy among primary schoolchildren and its impact on geohelminth infection were studied in western Kenya. In a cross-sectional survey, 204 children aged 10-18 years were interviewed about geophagy and examined for helminth infections (Ascaris lumbricoides, Trichuris trichiura, Schistosoma mansoni, hookworm). Children found infected were treated with albendazole (600 mg in a single dose) and/or praziquantel (40 mg/kg in a single dose). The children were re-examined after 4, 8 and 11 months. In the initial cross-sectional survey, 77% of the children ate soil daily and 48% of all soil samples were contaminated with eggs of A. lumbricoides (median egg count in contaminated samples was 3/2 g of soil; range 1-15). Twenty-nine children (14.2%) were infected with A. lumbricoides and 87 (42.6%) with T. trichiura. Significant associations between geophagy and infection intensity with A. lumbricoides and T. trichiura, but not S. mansoni or hookworm, were found. Re-infection with A. lumbricoides was twice as common among geophagous children as among non-geophagous children (27.4% vs. 12.0%; P = 0.030). The intensity of reinfections was higher in geophagous children (median 773 eggs/g vs. 95 eggs/g; P = 0.027). The relative risk for A. lumbricoides reinfection was 2.28 for geophagous children (95% confidence interval [95% CI] 1.02-5.11), and the fraction of reinfection attributable to geophagy was 56.0% (95% CI 1.7%-80.4%). There was a significant difference in T. trichiura infection intensity between geophagous and non-geophagous children (median no. of eggs/g 68 vs. 20; P = 0.049), but not in reinfection rates. No difference between the groups was seen in S. mansoni or hookworm reinfection rate or intensity, or in the families' socioeconomic or educational status. Geophagy was associated with an increased risk of reinfection with A. lumbricoides and possibly with T. trichiura. Neither family background nor infection with non-orally transmitted helminths was associated with geophagy, suggesting that this association was not due to confounding, but causal. Geophagy is therefore likely to be a source of ascariasis and possibly trichiuriasis among primary schoolchildren.

Geophagia is not associated with Trichuris or hookworm transmission in Zanzibar, Tanzania

“…We do not expect it to be less sensitive than previous methods used and it was sensitive enough to be able to detect nematodes in the rejected samples. Finally, the quantity of sample that we analysed for each substance (approximately 15 g) is much greater than the amounts analysed by Geissler et al (1998a) or Wong and Bundy (1990), but the number of samples analysed is much smaller, limiting our interpretation.…”

“…Because the physiological basis for geophagia causing hookworm is not strong (Geissler et al, 1998a;Gelfand, 1945;Saathoff et al, 2002), we looked for other explanations of a relationship. One such explanation comes from the primate world, where parasitic infection stimulates animals to eat earth.…”

“…the substance must contain viable nematode eggs or larvae). An association between earth consumption and increased Trichuris and Ascaris burden in earth consumers has been shown in several (Geissler et al, 1998a;Luoba et al, 2005;Saathoff et al, 2002;Wong et al, 1991) but not all (Vermeer and Frate, 1979) studies. Yet, to date, measurement of the parasite content of the soil has been investigated in only two sites (Geissler et al, 1998a;Wong and Bundy, 1990;Wong et al, 1991), no studies have determined the parasite content of earth consumed by adults and no studies have looked at the parasitic content of non-earth pica substances.…”

“…Whilst there is strong epidemiological and biological evidence that geophagia is not a significant mechanism for hookworm infection (Geissler et al, 1998a;Gelfand, 1945;Saathoff et al, 2002;Vermeer and Frate, 1979), there is insufficient evidence to determine whether there is a relationship between geophagia or the consumption of other non-food substances and non-hookworm nematode infections, namely Trichuris and Ascaris. For causality to be demonstrated, a vector that links pica to nematode infection must first be demonstrated (i.e.…”

“…If pica is indeed a route by which geohelminths establish infection, this would help to explain the frequent association between anaemia and pica (Geissler et al, 1998a(Geissler et al, ,1998bGlickman et al, 1999;Kettaneh et al, 2005;Nchito et al, 2004;Rainville, 1998;Thomson, 1997;Young and Ali, 2005). There are other explanations for a pica-anaemia association, which include replacement of nutritious food in the diet with non-nutritious substances, chelation of dietary iron by the pica substance and reduction of iron absorption by the gut (Arcasoy et al, 1990;Berkel et al, 1970;Danford, 1982;Hooda et al, 2004).…”