[Focusing of Schistosoma haematobium transmission in irrigated perimeters of the Niger valley (Niger): importance of malacological factors].
BACKGROUND
Currently, the control of urinary schistosomiasis is mostly based on mass treatment. Characterization of Schistosoma haematobium transmission could lead to adding new methods to the control strategy.


METHODS
We carried out malacological and cercariometrical surveys in irrigated perimeters of the Niger River valley. A semi-monthly follow-up was performed in three main sites of human-water contact in a village located at the border of the irrigated perimeter. Bulinids were collected during 20 min; after identification based on the shell morphology, their parasites were characterized by isoelectrofocalisation. The cercariometrical technique by differential filtration was used to evaluate the density of cercariae in every site with two 20-litre samples of water collected at various periods of the day (9, 12, 15 and 18 h).


RESULTS
In the arm of the river, the cercariometry never showed cercariae whereas only some Bulinus truncatus, all negative, were collected. In the channels, B. truncatus and B. globosus were observed and highest density was found during the dry season. Only B. truncatus was naturally infested. Homozygote BB phenotype (characteristic of S. haematobium) was observed in all positive molluscs. Using cercariometry, more than two third of cercariae were collected at 3:00 PM.


CONCLUSIONS
Transmission of S. haematobium was primarily focused in the irrigating channels during the dry hot season at the beginning of afternoon. These results should lead to improve the output of S. haematobium control methods within irrigated areas.
Labbo
R
R
Laboratoire de parasitologie, centre de recherche médicale et sanitaire (Cermes), ministère de la Santé publique et de la lutte contre les endémies, Niamey, Niger.
Ernould
J-C
JC
Djibrilla
A
A
Garba
A
A
Chippaux
J-P
JP
D000383:Agriculture; D000818:Animals; D006801:Humans; D009548:Niger; D045483:Rivers / Q000469:parasitology*; D012548:Schistosoma haematobium / Q000302:isolation & purification*; D012553:Schistosomiasis haematobia / Q000635:transmission*; D014881:Water Supply