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

ABSTRACT

Susceptibility of snail vectors to schistosome infection varies between geographical areas, population 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. The previous studies indicated that snails 4 - 6 mm in diameter exposed to 5 freshly hatched miracidia under light and in water at 25C are optimum conditions for infection of Biomphalaria alexandrina from various localities in Egypt with Schistosoma mansoni [TBRI strain maintained in hamsters]. In the present study, groups of 16 snails from 3 successive generations from positive and negative laboratory bred B. Alexandrina from Giza, Alexandria, Monoufia, Cairo and Menia were exposed to S. mansoni miracidia [TBRI strain] from Giza under the abovementioned optimum conditions. From the 20th day of 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, Monoufia and Menia. 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