Bilharzia or Schistosomiasis is a parasitic infection of man and is caused by blood flukes of the genus Schistosoma. The parasite is transmitted through specific aquatic intermediate hosts in various freshwater habitats. In terms of socioeconomic and public health importance it is regarded second to malaria among the parasitic diseases affecting man in tropical and some sub-tropical countries of the world. To understand the disease transmission patterns better; a study was carried out on the population dynamics of the snail types (Biomphalaria species) that are responsible for the transmission of the disease. This paper discusses the results of the study that was carried out at Lake Albert, which is one of the most affected areas by Bilharzia disease in the country. The growth, reproduction and survival of two Biomphalaria species at Lake Albert were monitored in the field and laboratory for thirteen and fourteen weeks respectively. Field and laboratory growth curves were constructed for the two Biomphalaria species, Biomphalaria stanleyi and Biomphalaria sudanica. The snails from the natural environment for both species showed a rapid and steady increase in size until they reached maximum growth at about the fourteenth week. As the snails matured, maximum egg production capacity was achieved from the tenth week onwards. The growth of snails in the laboratory was much slower especially for B. sudanica, and the snails never attained the shell diameter levels of the snails in the natural environment within the same period. It took an extra week for snails in the laboratory to reach maturity and to start egg production. By the end of the fourteenth week, the laboratory snails did not appear to have achieved a level of maximum egg production. There was a negative correlation between the mean generation time and the intrinsic rate of natural increase. These observations stress the importance and requirement of optimum conditions in the habitat of snails for them to maintain their numbers. With global warming and the attendant floods, occurring in many areas of the tropics including Uganda, fertile ground for multiplication of the snails with eventual possibility of spread of bilharzia, can be a big threat. There is a need to be vigilant and identify possible resurgence in snail population that may lead to the spread of bilharzia.
Prof. Dr. Bilal BİLGİN