Abstract
This work consists of a review of the avian schistosomes, description of the morphology and life cycles of three new species from ducks, and a survey of anatids and snails to determine the prevalence of infection with nasal and visceral schistosomes in the Townsville district of North Queensland.
The review represents the first such comprehensive account of the avian schistosomes. Out of one hundred avian schistosome species described to date, this number has been reduced to 54 valid species by synonymising and placing the species in inadequate description under species inquirenda. The genus Trichobilharzia, about which the present thesis is primarily concerned, has been extensively revised. Out of 46 species described so far, the number considered valid has been reduced to 26. A key has been proposed for the Trichobilharzia on the basis of characters in adults and cercariae, and their snail and vertebrate hosts.
Because variations caused by differences in technique used by different authors have contributed to the taxonomic confusion in the avian schistosomes, an effort was made to standardise and optimise procedures in the hope that better taxonomic comparisons will be possible in the future due to adoption of these standards by others. Techniques developed were related to collection, fixation, staining and permanent mounting of adult worms and their larval stages; experimental infection of snails with respect to miracidial dose and temperature and methods of infection in birds with cercariae.
The three new schistosomes identified were Trichobilharzia australis and Trichobilharzia arcuata from the nasal blood vessels of black ducks (Anas superciliosa) and water whistle ducks (Dendrocygna arcuata) respectively, and Trichobilharzia parocellata from the portal and mesenteric blood vessels of grey teals (Anas gibberifrons) and black ducks. Separation of these three new species from others described under the genus was based on the characters of their adult and larval stages, and development inside snails and experimental final hosts. T. australis and T. arcuata were distinguished from all other species, except the five African nasal schistosomes, on the basis of the cercarial excretory system. Cercariae of these two species had 16 flame cells with a formula 2[(3) + (4 + 1)] = 16. In contrast, all other species for which information is available had 14 flame cells with the formula 2[(3) + (3 + 1)] = 14, except T. corvi which had 12 flame cells with the formula 2[(3) + (2 + 1)] = 12. Furthermore, T. australis and T. arcuata were found only in the nasal blood vessels whereas visceral schistosomes occurred in portal, mesenteric and renal blood vessels. From the African nasal schistosomes, T. australis and T. arcuata differed with respect to the position of caecal reunion in the male, texture of the tegument, number of testes, spines on the genital papilla and on the ventral tegument over the ovary and seminal receptacle, and shape of the eggs. T. australis and T. arcuata were closer to each other in most characters than to any other species. These similarities and their common geographical range and snail host led to speculation about their common ancestry. Adults differed from each other only in the position of caecal reunion in males, number of testes, spines on the genital papilla and on the ventral tegument over the ovary and seminal receptacle, and shape of the eggs. Their cercariae were similar, but miracidia differed with respect to the patter of germinal cells and the nerve mass. An unusual feature of these two worms was the restricted host range of their adults. T. arcuata was common in water whistle ducks but was not found in black ducks, and T. australis was common in black ducks but did not occur in water whistle ducks, even though both species of ducks shared the same wetlands
The adults of T. parocellata were distinguished from closely related species on the basis of the species of snail hosts, point of caecal reunion in the male, number of testes, and nature of the tegument. Their miracidia were also different from all others under the genus as they had a pair of coarsely granulated compact posterior secretory glands, a pair of apical glands, and a papilla on each side in front of the lateral processes.