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.
Kimura
E
E
Institute of Tropical Medicine, Nagasaki University, Japan.
Uga
S
S
Migwi
D K
DK
Mutua
W R
WR
Kiliku
F M
FM
Muhoho
N D
ND
D000818:Animals; D002033:Bulinus / Q000469:parasitology; D002940:Circadian Rhythm; D006224:Cricetinae; D004199:Disease Vectors; D005618:Fresh Water; D007630:Kenya; D008647:Mesocricetus; D012547:Schistosoma / Q000502:physiology*; D012548:Schistosoma haematobium / Q000502:physiology*