The eggs of S .mansoni worms are emitted in the faeces of the final host into the water, the ripe miracidia hatches out of the eggs. The hatching happens in response to temperature, light and dilution of faeces with water. The miracidia search for a suitable freshwater snail Biomphalaria alexandrina to act as an intermediate host and penetrate it. Then, the parasite develops via a so-called mother-sporocyst and
daughter-sporocyst generation to the cercariae. The purpose of the growth in the snail is the numerical multiplication of the parasite. From a single miracidium result a few thousand
cercarie, every one of which is capable of infecting man [3].
One of the environmental modifications for controlling snail vectors is the lining of water canals [4]. In China, reference
[5] stated that Environmental modification was primarily carried out in areas of low endemicity with the aim of permanently interrupting transmission. Environmental modifications included the digging of new ditches and filling
of old ones, lining of irrigation canals with concrete, and the alteration of sluice gates to prevent snails from spreading into other sections of an irrigation system. Reference [6] in Egypt, reported that physical control is achieved through the alteration of the substrata in the snails habitats, causing the death of large numbers and interrupting the propagation of those surviving the new conditions. The concrete lining of canals contributes in controlling snail populations, because higher flow speeds can be maintained and weed growth is minimized and during the periods that irrigation water is not needed, canals can be left to dry, snail populations will diminish and aquatic weeds can be eliminated [7].
The aim of the present study is to evaluate the impact of certain lining materials such as cement and plastic as well as mud substratum of the water bodies on the survival and
infection rates of B. alexandrina snails by Schistosoma
mansoni miracidia as well as the cercarial production from snails was also determined. |
