Cercarial density in the river of an endemic area of schistosomiasis haematobia in Kenya.

The cercarial density in natural water and number of infected Bulinus globosus were monitored over a one-year period to identify the transmission foci in an endemic area of schistosomiasis haematobia in Kenya. Overall prevalence and intensity of infection of the study community were 59.2% and 10.9 eggs/10 ml of urine. Cercariometry was carried out on 456 occasions at 20 study sites while snail sampling was done on 465 occasions at the same sites over a one-year period. Cercariometry was exclusively done at flowing water habitats. The results showed the focality and seasonality of transmission. Cercariae were detected on 44 occasions at 11 sites. The detections were made on seven occasions at two study sites, six occasions at one site, four occasions at four sites, three occasions at one site, two occasions at two sites, and one occasion at one site. Densities of 1-4 cercariae/100 liters of water were found on 31 occasions. Five to nine cercariae/100 liters of water were found on seven occasions, 10-19 cercariae/100 liters of water were found on two occasions, and high cercarial densities greater than 20 cercariae/100 liters of water were found on four occasions. The highest count was 52 cercariae/100 liters of water. The presence of cercariae in natural water was shown to depend on the water temperature, but the intensity and duration of sunlight did not affect the presence of cercariae in water. The monthly variability of cercarial density was proportional to the number of infected snails. Cercarial density was highest in March and April, in the middle of the rainy season, whereas no cercariae were detected in cool dry season. The snail population peaked late in March, the beginning of the long rainy season, remained high for two months, and decreased rapidly late in May when heavy rain occurred. The overall infection rate of snails was 7.3% and the majority of infected snails were collected from March to May. There was no definite correlation between the presence or absence of cercariae and infected snails. Cercariae were frequently found where infected snails were absent and cercariae were sometimes absent where infected snails were present. Cercariometry and snail sampling remain quite complementary in identifying the transmission foci of schistosomiasis.

Hourly change in cercarial densities of Schistosoma haematobium and S. bovis at different depths in the water and distances from the shore of a dam in Kwale District, Kenya.

Hourly change in cercarial densities was studied at different depths in the water and distances from the shore at a dam in Kwale District (Kenya), where Schistosoma haematobium is highly endemic, by using a filtration apparatus for detecting cercariae. The peak of cercarial density at the surface of water (2-3 cm deep) was at 11:00 hours. Those at the middle point (25 cm deep) and the bottom (50 cm deep) were at 12:00 and 13:00 hours respectively. In the morning, the majority of cercariae (79% of the total detected) was obtained at the surface of water, but none at the bottom. After midday, 40% of the cercariae were obtained at the bottom. Cercariae seemed to sink with time resulting in a wider distribution in the water. The numbers of cercariae obtained at a sampling point 20 cm from the shore, which was inside the wire-screened snail-free area, were 3.4-23 times more than those obtained at a sampling point 340 cm from the shore, indicating that cercariae were accumulating immediately near the shore. Winds might cause the accumulation.

Effects of Schistosoma haematobium infection on mental test scores of Kenyan school children.

Adverse effects of Schistosoma haematobium infection on mental activities were studied at a primary school in rural Kenya, where the intensity of infection was light (the average egg count: < 50/10 ml of urine). The school children received three kinds of mental tests, which examine attentiveness and concentration, before and a month after treatment with a single dose of praziquantel. A pretreatment analysis showed that test scores became worse as egg counts of children increased. The praziquantel treatment improved the scores of all three tests among children who got high scores in the first tests. The study showed that even the light infection caused adverse effects on mental activities, which were detectable using simple mental tests.

Ecological studies on intestinal microbial flora of Kenyan children with diarrhoea.

The intestinal microflora was analysed together with short-chain fatty acids (SCFA) and bile acids in faeces from nine children with acute diarrhoeal disease in Lari, Kenya. Enteric pathogens such as enteroinvasive E. coli, enteropathogenic E. coli, Yersinia enterocolitica, rotavirus, Giardia lamblia and Entamoeba histolytica were isolated either singly or in combination from diarrhoeal faecal specimens. The most striking finding in these patients was a marked reduction of anaerobes. Analysis of the SCFA revealed a significantly higher quantity of the volatile fatty acids (VFA) such as acetic, propionic, and butyric acid in recovery period faeces in comparison to diarrhoeal faeces, although no significant difference was seen in the quantity of non-volatile fatty acids. On analysing bile acids in faeces, conjugated primary bile acids were detected from all cases in diarrhoea whereas the free form of secondary bile acids was seen only in recovery. The pH of recovery faecal specimens was significantly lower than that in diarrhoeal faecal specimens. There was a parallel between the decrease in number of anaerobes and fluctuation in the amount of SCFA, showing that the drastic reduction of VFA accompanying decrease of anaerobes during the diarrhoeal state, and the rise in pH thought to arise from these facts, result in an increase of water content.