The host-parasite relationship between the Saudi Arabian Schistosoma mansoni and its intermediate and definitive hosts. 3. Effects of duration of exposure and cercarial concentration on the infection of mice by S. mansoni cercariae.

The percentage infection rate, worm burden and worm recovery rate in mice increased with an increase in the duration of exposure to cercariae. However, mice exposed to cercariae for 4 min had the same worm burden and worm recovery rates as those exposed for 16 min. Mice exposed to 80 and 160 cercariae each exhibited the highest percentage infection rates. The worm burden was highest in mice exposed to 160 cercariae each, while the worm recovery rate was highest in those exposed to 80 cercariae per mouse.

The host-parasite relationship between the Saudi Arabian Schistosoma mansoni and its intermediate and definitive hosts. 1. S. mansoni and its local snail host Biomphalaria arabica.

The infectivity of miracidia of the Saudi Arabian isolate of S. mansoni in Bi. arabica was found to be influenced by such factors as miracidial dose, water temperature and salinity. The pre-patent period of S. mansoni in Bi. arabica was 30 to 33 days. Miracidial dose had no effect on the mortality of snails during the pre-patent period. The infection rate increased as the miracidial dose was increased. However, cercarial production was highest in snails exposed to 1 miracidium each and decreased as the miracidial dose was increased. Water temperature during exposure had an influence on the mortality, infection rate and cercarial production in Bi. arabica exposed to S. mansoni miracidia. The infection rate was highest in snails exposed at 28 degrees and 34 degrees C. No infection of Bi. arabica occurred at the temperature of 10 degrees C. The number of cercariae per snail per day was highest in snails exposed to miracidia at 34 degrees C. It was demonstrated that salinity had an influence on the infection of Bi. arabica with miracidia of S. mansoni. The infection rate in snails decreased as the salinity increased up to 4,500 mg/l, above which no infection occurred. The daily pattern of cercarial emergence was rhythmic, whereby 94.7% of the total daily production was released within 6 h from infected Bi. arabica, with a peak between 11 a.m. and 1 p.m.

The host-parasite relationship between the Saudi Arabian Schistosoma mansoni and its intermediate and definitive hosts. 2. Effects of temperature, salinity and pH on the infection of mice by S. mansoni cercariae.

The infectivity of cercariae of the Saudi Arabian isolate of S. mansoni was found to be influenced by factors such as water temperature, salinity and pH. The optimum exposure temperature which resulted into the highest worm burdens and worm recovery rates in mice was 28 degrees C. However, the percentage infection rate was highest at a temperature range of 10 degrees to 34 degrees C. Mice were successfully infected with cercariae of S. mansoni at salinities of 0.5 to 6,400 mg/l. The highest worm burden and worm recovery rate occurred in mice infected by cercariae at a salinity of 100 mg/l, while the percentage infection rate was highest at a salinity range of 0.5 to 1,600 mg/l. Mice exposed to cercariae at the pH of 4.4 and 9.4 did not develop any infection. The percentage infection rate was highest in mice exposed to cercariae at a pH range of 6.4 to 8.4. However, both the worm burden and worm recovery rates were highest in mice at pH 5.4.