University of Khartoum

Ecological and Experimental Studies on Schistosomes and Their Intermediate Hosts in the Gezira Area of the Sudan

Ecological and Experimental Studies on Schistosomes and Their Intermediate Hosts in the Gezira Area of the Sudan

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Title: Ecological and Experimental Studies on Schistosomes and Their Intermediate Hosts in the Gezira Area of the Sudan
Author: Ghandour, Ahmed Mohamed Ali
Abstract: The first part of the thesis is concerned with ecological studies on the schistosomes and their intermediate hosts of the Gezira area. A general description of the Gezira area and the irrigation systems employed there is followed by an account of the climate and a general review of Schistosomiasis It was originally intended to study seasonal fluctuations in the densities of the snail populations and the effects of ecological factors on such fluctuations. Due to the lack of cooperation with the agricultural and irrigation authorities, however, most of the snail habitats were disturbed during the period of investigation. It was therefore decided to determine the effect of such disturbances on the seasonal fluctuations of snail populations. Sampling techniques employed in the study of aquatic snails are reviewed, and the technique used in the present study was described. This was the fractional method of sampling by a dip-scoop. Seasonal fluctuations in the densities of the Snails B. pfeifferi and Bulinus truncatus showed the same trend. There was an increase in absolute number from January to May, a decline from June to November and a slight increase from October to December. Increased numbers of Bulinus forskali, however, were probably associated with precipitation, since this species appeared in abundance after the annual rains in July. The effects of disturbance on snail populations were also investigated. Natural infection rates were shown to be very low in the case of B. pfeiffeti. No Bulinus spp. were found to be naturally infected. Ecological factors in the habitats of snails are outlined. Seasonal fluctuations in the densities of snail populations, the effects of ecological factors and disturbances (weed clearance, desiccation, dredging and the application of Bayer 73) on such fluctuations are discussed in details. The last part of the thesis is devoted to some experimental studies on schistosomes and their intermediate hosts. The sources of the snails and of the parasites are described, and methods of maintaining them in the laboratory are outlined. The effects of salinity and temperature on the hatching of the ova of the local Schistsoma spp. are described. The effects of salinity and temperature on the miracidia and cercariae of schistosomes are also established. It was found that local species of Biomphalaria are highly susceptible to the local strain of S. mansoni. Tests on the susceptibility of Puerto Rican B. glabrata indicate that there may be more than one strain of S. mansoni in the Sudan. There is a definite pattern in the shedding of cercariae of S. mansoni with a peak towards midday. The ability of Biompbalaria spp. and of Bulinus spp. to survive out of water in the laboratory depends on the moisture of the air, the diameter of their shells and whether they have been acclimatized to desiccation. Bulinus truncatus is more resistant to drying in mud under out doors experimental conditions than is B. pfeifferi. The eggs of B. pfeifferi and Bulinus truncatus are tolerant to desiccation. They were not affected by desiccation for 20 minutes at 30-40 per cent relative humidity, 45 minutes at 70-80 per cent relative humidity and four hours at 90-100 per cent relative humidity. The results of all these experiments are discussed finally in relation to one another
URI: http://khartoumspace.uofk.edu/123456789/16912
Date: 2015-11-04


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