Soil contamination and infections by soil-transmitted helminths in an endemic village in southern Thailand.

The aim of this study was to test the association between soil contamination and infection of the household members by soil-transmitted helminths in dry and rainy seasons. A lake-side community in southern Thailand with a population of 2,340 was studied twice, in the dry season and rainy season of 1995. Fifty households were randomly selected. Soil samples near the latrine, in the yard, at the foot-washing area and under the trees were taken and analysed for presence of helminthic eggs. All members of the selected household were interviewed and stool samples obtained. Age-adjusted odds ratios of presence of Ascaris and Trichuris eggs in the household soil for ascariasis and trichuriasis were 10.5 (95% CI 1.5-77.1) and 5.5 (95% CI 2.4-12.7) in dry season and 10.4 (95% CI 2.5-43.8) and 8.3 (95% CI 3.4-20.0) in rainy season. The levels of hookworm eggs detected in the soil were too low to test the association. Soil analysis for eggs of Ascaris and Trichuris may be used to predict infections among the household members but not that for hookworm.

Contamination of soil with parasite eggs and oocysts in southern Thailand.

Soil contamination with parasite eggs and oocysts was surveyed in southern Thailand in December 1994 and September 1995. The survey areas were Hat Kai Tao Village in Phatthalung Province and a slum area in a city of Songkhla Province. We used a modification of the centrifugal floatation technique with sucrose solution (specific gravity, 1.200) to recover helminth eggs and protozoa oocysts. Overall, 10 genera and 11 species of parasite eggs and oocysts were recovered. They included eight species of nematoda eggs, one species of cestoda eggs, and two species of protozoan oocysts. The definitive hosts of these parasites are dogs, cats, sheep, lizards, humans, etc. The contamination rates in two areas at different occasions varied from 55% to 72% with an average of 64%. Contamination rates of Hat Kai Tao Village in beginning and end of the rainy seasons were 72%, and 55%, respectively. Although the contamination rate in the end of rainy season was higher than that in beginning of the rainy season, the difference was not statistically significant (p > 0.05). Of the 11 parasites recovered, six were infective to humans, of which, Trichuris trichura, Ascaris lumbricoides, and Toxocara species were predominant. The mean numbers of these eggs recovered in each test were more than 10. Therefore, the contamination was estimated to be more than an egg per gram of soil sample based on the recovery efficiency (40%) of this test. These results suggested that the soil in some parts of southern Thailand may be heavily contaminated by both animal and human feces.