الفهرس 
AcknowledgementOnly 14 pages are availabe for public view
 |  | from | 281 |  |  |
| | | from | 281 | | |
Abstract
Bilharziasis or schistosomiasis is one of the most important public health diseases. In Egypt, B. alexandrina and B.truncatus snails are the intermediate hosts of S.mansoni and£. haematobium respectively. The irrigation waters are tae main sites for the spread of bilharziasis and their host sna ils . Lake Maryut is a brackish shallow lake whose salinity is decreasing by time due to the discharge of agriculture and domestic waste waters into the lake. This situation resulted in the introduction and existence of the bilharziasis vector snails and the disease began to appear among the fishermen of the lake. The aim of this investigation is to study some of ~he ecological i.e. biotic and abiotic conditions affecting the prevalence of vector snails in t he area. This will help to explain the prevalence of the disease among the fishermen. This investigation was performed to study the snail pop i lulation, aquatic vegetations, water quality and pollution. To accomplish this work a map for the area wgs drawn and fifteen I 1 stations were chosen with five linear meters for every station. The choice of stations :was based on the effect o.f water sources, . pollution out falls and the frequence of human contact activit ies around and in the lake . The research was run through a year by IOnthly snail surveillance and water sampling to determine the leasonal differences and changes in the lake. In the field, inails were sampled by the dip net of 1/) meter and so 15 dips III performed for every station. Snails were identified, ~ounted and recorded according to their charact ers, spec ies and The vegetations were identified and recorded accord to their characters, species and densities. At each station, water sample was collecte d for analys is to det e.r””,ine, t he pH, , total hardness, MgH, CaH, B.O.D., D.O. and NH) ’according to the Standard Methods for the Examination of Water and Wastewater (APHA, 1971). Water temp~rature was recorded in the field and host sna.ils were examined in the laboratory, [0 detect their infection. It was concluded that Lake Maryut contained only ~ alexandrina the host snails of §. mansoni -as they are ea.sily transmitted by water movement, tolerant to salinity, pollution and water stagnancy. B. truncatu.’3, the intermediate host of h haematobium showed a limiting distribution in the fresh water canal which was found accidentally infected with S.haematobium cercariae during snail. abundance and t he season of more human activi ties arouild or in t he canal, in sunnner. This situatiop. explains the more. prevalence of S. mansoni than .§.. haematobium among the fishermen of Lake Maryut. ~. alexandrina in Lake Maryut was found allover the year ’-tt varied seasonally. The snails were infected with §. manson~ I~ercariae during the different seasons. Sites subjected to lIi1j1rect and heavy pollution were free from host snails in the louth shore of the main basin. While sites of heavy pollution La the north of this basin showed infestation with B.alexandrina Jbien was affected more by the degree of P911ut iOll rather than Ihe degree of salinity. Such snails collected from the site of 1:’18hermen settlements showed -infection with §.. mansoni cercariae lauring snails abundance in winter. . The basin of 160 feddans ,1 has unsuitable for host snails establishment and colonization j . ’me to its steepy east si(ie, gravelled south shore and the ,other sandy shores, so the vegetat ions were sparce. The basin of 306 feddans was more favourable for B. alexandrina establish ment due to pouring of freshwaters from the fresh waters .canal .; ~d polluted waters from Qalaa Drain. This situation led to salinity dilut ion, beneficial pollution besides the presence of the preferable E. crassipes plant. These are suitable condit~ ions for vector snails abundance and infection with the cercaria especially because of the presence of scattered settlements near this basin. The basin of 1000 feddans showed accidental and temporary infestat ion wit h ~. alexandrina and snails collect ed from the south shore, was infected with cercariae due to their long persis tence and proximity to Abees Village. In the north west basin, B. alexandrina snails were present and showed infection with cercariae during spring due to high snails density and proxim1tJ’ ;t;o fishermen collections. The south west basin was ”,infested with B. alexandrina at higher numbers during winter ~Iand spring, but less during summer due to increased chlorides. This basin was preferred by the fishermen for fishing activities pecause it is away from pollution sources and their belief that 1 fish collected from this basin is healthy. This situation led to the frequency of vector snails infection with .§.. mansoni , cercariae during the different seasons. , It was found in Lake Maryut that the more associated plants with B.. alexandrina- collection were E. crassipes and h demersum. The dense vegetations were unfavourable for host snails especially in periods of their decompos it ion in sunnner. Th.e fresh water canal showed low densities of vector snails, , this may be related to water level fluctuations, continuous water flow and vegetation removal, Abees Drain was free from host snails due to the washing action of the swift water flow and the steepy shores. On the other hand. Umoum Drain with banks containing stagnant overflooded waters had both abundant vegetat ions and vector snails. B. alexandrina collected from Umoum Drain was infected with cercariae mainly during winter. The removal of aquatic weeds and :bed bank clearance during summer resul ted.in vector snails absence from this drain.