Schistosoma mansoni cercarial host location and infection under simulated natural conditions in Egypt

This study was performed in water ditches under simulated natural conditions in Egypt to elucidate the effect of various environmental factors on Schistosoma mansoni cercarial host location and infection of the definitive host [using albino mice]. Evaluation of these factors was dependent on both infection rate of exposed mice as well as the schistosome worm load under the same experimental conditions. The seasonal water temperature proved to be a very important factor and this was proven by the infection rate of mice and the worm load recovered were lower in January and April [16°C and 22°C midday water temperature] and much higher in July and October [29°C and 25°C]. The daytime factor is similarly important as temperature illustrated by the schistosome infection of mice groups exposed at 8-10 am was much higher than in groups exposed between 1pm and 3pm [p<0.001]. The greatest infection rate of mice and worm load were obtained when the shedding snails were close to the exposed group of mice. Both criteria increased with the increase of cercarial density in the water. The length of exposure period is also an extremely important factor for schistosome infection, being highest 87.5% [p<0.001] in3 hours exposure period. Infection rate was found to be 88.2% and 55.6% of shedding snails were located at water surface and midway to the bottom, respectively, and no infection occurred when located at the bottom. The schistosome infection of mice decreased in presence of increasing density of the floating plant Eichhornia crassipes in the ditch water, but low condensation of the submersed plant Ceratophyllum demersum appeared to have stimulating effect

Interaction of different load of schistosoma mansoni in mice

The present study proved that all mice could be infected when exposed to 50 cercariae or more per mouse. The number of worms recovered is directly proportional to the exposed cercariae, but the number decreases with the increase of age of infection. The recovery rate is considerably less in mice exposed to high number of cercariae than in those exposed to low number. More than 83% of the worms were found in porto-mesentric viens of mice two months after infection. In lightly infected mice, the worms showed more shift to the liver as the age of infection increased from two to three months. The length of worms increased significantly with the increase of the age of infection from two to three months in group of animal exposed to 25 cercariae / mouse. In groups of mice exposed to 100, 200, and 300 cercariae / mouse, the worms were more or less of the same length. The number of ova retained in the liver and intestine increased with the increase in the number of worm load and the time of patency