The Histopathology of Acanthocephalan Infections in the Rainbow Darter, Etheostoma Caeruleum

Responses of naturally infected Etheostoma caeruleum to the presence of the acanthocephalans, Acanthocephalus dirus and Pomphorhynchus bulbocolli, were observed in 10u sections of intestines stained with hematoxylin and eosin. Both parasite species caused tissue damage to the host and elicited host responses. The major difference in parasite destruction was shallow tissue penetration by A. dirus proboscides while the proboscides of P. bulbocolli had deeper penetration and capsule formation. The most common parasite was P. bulbocolli, yet concurrent infections were not uncommon. Effects of concurrent infection were a combination of single species effects on the host. Connective tissue hyperplasia was more evident in intestinal layers, especially the lamina propria, in infections with P. bulbocolli. The proboscides of A. dirus did not penetrate all the intestinal layers of the host. However, the proboscides of P. bulbocolli usually passed through all layers of the intestine. Proboscides of P. bulbocolli were observed penetrating other tissues of the host such as lymphatic, adipose, testicular, and ovarian. Cellular infiltration and connective tissue proliferation were more pronounced in the E. caeruleum infected with P. bulbocolli