Cellular response to Schistosoma mansoni infection in Biomphalaria alexandrina strains selected for susceptibility and resistance.

Exposure of juvenile and adult Biomphalaria alexandrina to Schistosoma mansoni miracidia resulted, typically, in three susceptibility patterns: a) non-infected snails; b) normal infections, and c) retarded infections. Under laboratory conditions, a vigorous resistant-type cellular response to invading miracidia was seen in the histological sections of non-susceptible snails. Accordingly, they were classified as resistant snails. Data pertaining to the influence of host size on suceptibility to S. mansoni indicates that adult snails (i.e. 10-20 mm shell diameter) were significantly less likely to harbour sporocysts than juvenile ones (i.e. 5-10 mm shell diameter). Cellular reaction to the infection varied with sporocysts location and length of infection. At 2 days post-exposure (DPE), most sporocysts were viable. Approximately 8-12% of the sporocysts had elongated shaped transverse constriction and were categorized "normal", while those showing no elongation were categorized "retarded". All remaining sporocysts at 4 DPE were categorized "dead", while at 30 DPE, most sporocysts were "amorphous" with eosinophilic masses. Although encapsulation of sporocysts never occurred in susceptible snails, haemocyte aggregations could sometimes be observed in the proximity of well developed sporocysts. In resistant snails, this cellular response continued to increase and resulted in the encapsulation of the sporocysts. In susceptible snails, the nucleus of secretory cells of the albumen cytoplasm were different in susceptible and resistant snails.

Susceptibility of three successive snail generations from positive and negative laboratory bred Biomphalaria alexandrina from different localities in Egypt to infection with Schistosoma mansoni from Giza.

Susceptibility of snail vectors to schistosome infection varies between geographical areas, populations in the same area and among individuals in the same population. It is also affected by biological factors of which are snail size (age), number and age of miracidia exposed to water, temperature, illumination and darkness. Our preview studies indicated that snails 4-6 mm in diameter exposed to 5 freshly hatched miracidia under light and in water at 25 degrees C are optimum conditions for infection of Biomphalaria alexandria from various localities in Egypt with Schistosoma mansoni (TBRI strain maintained in hamsters). In the present study, groups of 16 snails from three successive generations from positive and negative laboratory bred B. alexandrina from Giza, Alexandria, Menoufia, Cairo and Minia were exposed to S. mansoni miracidia (TBRI Strain) from Giza under the above mentioned optimum conditions. From the 20th day infection snails were checked from cercariae shedding to estimate the prepatent period and their number from each snail light for one hour. B. alexandrina from the various localities in Egypt were susceptible to S. mansoni (TBRI strain) infection. Snails from Alexandria were the most susceptible, followed by those from Cairo, Giza, Menoufia and Minia. Snails from positive generations were more susceptible to infection than those from negative ones. However, there has been a decline in the susceptibility of snails from one generation to the next. The prepatent period for shedding of cercariae was 27 days in case of snails from positive generations and it was extended to 38 days among snails from negative ones. It can be concluded that: (1) There are different levels of susceptibility between B. alexandrina from the various localities in Egypt and infection with S. mansoni from Giza. (2) Unsusceptibility (refractory character) of B. alexandrina to S. mansoni infection could be a heritable character like susceptibility. Consequently, it would be beneficial to select actively resistant snails and mass culture them to increase the proportion of alleles for insusceptibility as a possible mean for biological control of schistosomiasis in natural population.

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.

Fine structure studies of microgametogenesis of Eimeria adenoeides (Eimeriidae, Sporozoa) infecting turkeys in Egypt.

The Ultrastructure of microgametogenesis of Eimeria adenoeides was studied in the intestinal epithelium of experimentally infected turkeys' Meleagris gallopavo gallopavo. Microgamonts were recognizable by the presence of peripherally arranged nuclei and the presence of two centrioles between each nucleus and the limiting membrane of the gamont. A nuclear spindle apparatus and an intranuclear centrocone directed toward the centriole were observed. Each young microgamont was surrounded by a very narrow parasitophorous vacuole which widened during development and contained a few intravacuolar folds. Differentiation of the microgamete began when elevations of the limiting membrane appeared above the centrioles. This event was accompanied by the segregation of nuclear content into a dense osmiophilic portion and an electron-pale portion. A gradual protrusion of the dense portion of the nucleus and developing flagella into the parasitophorous vacuole was proceeded. Microgametes had an anterior perforatorium, a dense elongate nucleus, with an anteriorly positioned mitochondrion in a small groove of the nucleus. Usually two flagella could be detected per each mature microgamete.

Three Egyptian trematodes of fish-eating mammals of family Cyathocotylidae (Poche, 1926).

Fifty-eight specimens of cyathocotylid flukes were collected from dogs fed on the fish Clarias lazera: 10 Duboisia, 27 Mesostephanus appendiculatus; and 21 Prosostephanus industrius. This is the first time that these genera have been identified as parasites of C. lazera. The danger of human infection with these trematodes by means of C. lazera and other commercially important fish is stressed.

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.