Infection of laboratory bred Biomphalaria alexandrina from Giza and Alexandria governorates with Schistosoma mansoni from Giza in relation to snail size and number of penetrated miracidia.

Snail size and the number of Schistosoma mansoni miracidia penetrated are two important factors among others that might influence Biomphalaria alexandrina infection with S. mansoni. Groups of 16 snails of fixed age but of different size class (2-4 mm), (4-6 mm), (6-8 mm), (8-10 mm) and (10-12 mm) from three successive generations of positive and negative laboratory bred B. alexandrina from Giza and Alexandria governorates were each exposed to five S. mansoni miracidia (TBRI from Giza) under light and in water at 25 degrees C. After 20 days, the snails were examined for cercarial shedding to determine their prepatent periods and to estimate the number of cercariae shed from each snail under light for one hour. Other groups of snails (4-6 mm) from three successive generations of positive and negative laboratory bred B. alexandrina from these two Governorates were each exposed to 3, 5, 10, 15, 20 and 25 miracidia. Snails were checked starting from the 20th day of infection to assess whether or not they had acquired infection. The infection rate of B. alexandrina from Giza and Alexandria governorates and their generations decreased significantly as the snail size increased while it increased significantly as the number of miracidia increased. However, there has been a decline in the susceptibility of snails from one generation to the next. The prepatent period for the shedding of cercariae was long in large sized snails and from those descending from negative snails. It can be concluded that the infection rate of B. alexandriina snails is affected by snail size and the number of miracidia penetrated.

Biological and biochemical comparative studies on Schistosoma mansoni from two localities in Egypt where S. haematobium is endemic.

The changing pattern of Schistosoma mansoni and S. haematobium distribution in Egypt is generally attributed to ecological changes caused by the construction of the Aswan High Dam. Although S. mansoni was previously restricted to Lower Egypt, it is now found at certain foci in Upper Egypt. In areas of Lower Egypt where S. mansoni and S. haematobium are sympatric, S. mansoni eggs are shed almost exclusively in the stools of patients, whereas in Upper Egypt they are more frequently shed in the urine. In spite of this difference, the eggs and adult worms obtained from hamsters infected with S. mansoni strains from each of these areas proved to be morphologically identical. Protein patterns and isoenzyme profiles of male or female adult worms of each of the two isolates, obtained from infected hamsters, also proved virtually identical. In hamsters with mixed infections of S. mansoni and S. haematobium, some S. mansoni females cross-mated with S. haematobium males and they then developed ovaries and laid eggs which were typical of S. mansoni and which were excreted from the urinary bladder. In Upper Egypt, which is predominantly a S. haematobium area, patients with established infections may have a preponderance of S. haematobium males associated with S. mansoni females. These females may then migrate to the vesicular plexus and deposit S. mansoni eggs in the urinary bladder, to be shed subsequently in the urine. The observations appear to be better explained by the phenomenon of parthenogenesis than by the production of true genetic hybrids.

Studies on Eimeria species naturally infecting Gerbillus pyramidum (1) Exogenous stages.

Exogenous stages of two new Eimerian species, naturally infecting the Egyptian gerbil Gerbillus pyramidum were described and diagnosed in the present study. (1) The subspherical type of oocysts was 20 x 17 microns (length x width) in average. These are colourless and enveloped within an even double-layered oocyst wall. Sporulated oocysts containing four sporocysts each averaged in 10 x 8 microns, and a small spherical oocyst residual body was also observed. This type is termed Eimeria pyramidi after the species name of its host. (2) The second type of oocysts was elongated in shape measured congruent to 21 x 16 microns. These are colourless and enclosed within smooth double layered oocyst wall. Sporulated oocysts of this type were lacking oocyst residual bodies. This type is termed Eimeria gerbilli after the generic name of its host. Both types of described oocysts lack micropyle and polar cap.

Comparison of two Egyptian strains of Schistosoma mansoni in hamsters.

In human infection with Schistosoma mansoni from Beni-Suef, the eggs were encountered more frequently in the urine of patients than in infection with S. mansoni from Giza, where eggs were passed into the stool. A comparative study of the two strains of S. mansoni from Beni-Suef and Giza has been carried out in golden hamster. Consistent strain differences were observed. The Beni-Suef strain proved to have lower worm recovery and different egg distribution patterns in tissues of infected hamsters. Worms of both sexes of this strain were larger in size and required a longer period to reach maturity. Hence, the prepatent period was prolonged. Significant differences between the two strains were also noted in the number of eggs per worm. A lower mortality rate and a longer survival time were encountered in hamsters infected with the Beni-Suef strain.

Studies on experimental mixed infections of Schistosoma mansoni and S. haematobium in hamsters.

Golden hamsters were superinfected simultaneously with 100 Schistosoma haematobium cercariae, 1 and 3 weeks after initial infection with 100 S. mansoni cercariae. Results indicate that there was a higher degree of resistance to superinfection with S. haematobium at 1 week following initial infection with S. mansoni than that produced in the other two superinfections. This resistance was evidenced by a reduction in the number and size of worms of both species, decrease in S. haematobium egg extrusion per female and by a striking deviation in the egg distribution pattern of both species. Such an early host resistance was not recorded in previous works. Cross-mating was observed but no hybridization took place and the eggs produced were hatchable and typical of their species.