Life cycle of Bilharziella polonica (Trematoda, Schistosomatidae) parasite of semi-aquatic birds in Uzbekistan

Schistosomatidae are an actively studied ecological group of trematodes. Their ability to cause various parasitic diseases in animals and humans makes them an interesting object of study for a number of research centres worldwide. One of the commonest species in this group is Bilharziella polonica (Kowalewsky, 1895), whose mature stages have been recorded in aquatic and semi-aquatic birds in Uzbekistan. Our research team established that the following birds were infected with mature trematodes B. polonica: Anas platyrhynchos (23%), A. crecca (18%), Podiceps ruficollis (11%), Ardea cinerea (14%) and one individual of Oxyura leucocephala. The highest infection rate was shown by the mallard A. platyrhynchos (23%) and common teal A. crecca (18%). The infection intensity ranged between 2 and 27 individuals. Research into various types of water bodies in Karakalpakstan identified 10 mollusc species – Lymnaeidae (4 species), Planorbidae (4 species) and Physidae (2 species). Cercariae morphologically similar to larvae of B. polonica were found in two species, Planorbis planorbis and P. tangitarensis. 6 chicks of domestic ducks were experimentally infected with those cercariae to track the life cycle of B. polonica in the organism of a definitive host. Helmintholological dissections showed that every duck was infected with B. polonica, which became mature 23–27 days after the infection. Eggs of B. polonica were recorded in the excrement of one of the birds 33–35 days after the infection. Based on field and experimental research, we identify the mollusc P. tangitarensis as a new intermediate host for B. polonica in Uzbekistan.