Observations on Ornithobilharzia turkestanicum and Schistosoma bovis in Iran

The geography and freshwater ecology of Khuzestan and those human activities which affect the snail ecology are described. O. turkestanicum, S. bovis and S. haematobium were the only animal and human blood flukes found in Khuzestan. The molluscan hosts of both species of Schistosoma is B. truncatus whereas O. turkestanicum is transmitted by L. gedrosiana. The infection rate of O. turkestanicum in ruminants was high and causes considerable economic loss. The morphology of O. turkestanicum and its distinguishing characteristics from other schistosomes are discussed. The prevalence of O. turkestanicum and S. bovis infection in ruminants in Khuzestan abattoirs was studied. Infection rates of O. turkestanicum in cattle was higher than in sheep and goats. The intensity of O. turkestanicum in in naturally infected cattle and sheep was determined. Sheep suffered More than cattle from the disease. The intensity of O. turkestanicum declined with increasing age in cattle but increased in sheep. Experimental studies were carried out, on, calves, sheep, goats, and buffalo-calf infected with O. turkestanicum and S. bovis. The intensity, pathogenicity and pathology of O. turkestanicum and S. bovis in naturally and experimentally infected ruminants were compared. S. bovis caused more serious damage to ruminants than O. turkestanicum. In O. turkestanicum infections the duodenum was the most intensely involved organ and the liver was less affected and large intestine was free from infection. S. bovis was evenly distributed along the alimentary tract. Susceptibility of different species of rodents, carnivores and birds to O. turkestanicum were tested. Only Tatera indica (a wild local rodent ) was found to be susceptible to O. turkestanicum infection. Carnivores and birds were resistant to infection. In the heterologous immunity experiments mice were immunized with different numbers of O. turkestanicum cercariao and challenged with S. bovis, S. haematobium and S. mansoni. Homologous immunity was also studied in mice with S. bovis. In these experiments mice produced a partial protection against the challenge infections. Reciprocal heterologous immunity experiments were carried out in calves and sheep using S. bovis and O. turkestanicum. Calves showed a high degree of protection but the effect was poor in sheep. Calves immunized with repeated inoculations of S. haematobium cercariae developed some immature worms and produced considerable resistance against challenge infection with O. turkestanicum and S. bovis. Calves also developed a considerable immunity in homologous system with and. O. turkestanicum and S. bovis. Studies were carried out on the distribution and ecology of Lymnaea gedrosiana the intermediate host of O. turkestanicum in Khuzestan. Detailed studies were made on the population dynamics of this snail by fortnightly surveys in different type of habitats over a Period of 12 months. The results showed that peaks of snail population occurred in 2 seasons, spring and autumn. Transmission occurred throughout the year in Canals; in spring, summer and autumn in swamps; in spring and autumn in ponds. Canals and swamps accessibl to livestocks were found to be important transmission sites of O. turkestanicum. Laboratory experiments were carried out to study the develop of larval stages of O. turkestanicum in L. gedrosiana after the snails had been exposed to various number of miracidia. The results showed that the miracidial exposure dosage did not affect the cercarial prepatent period, but the life-span of infected snails was shorter and all the snails exposed to 20 miracidia each shed fewer cercariae than those exposed to 5-20 miracidia.