Trichobilharzia physellae (DIGENEA: SCHISTOSOMATIDAE) FROM ENDEMIC WATERFOWL ON THE HIGH PLAINS OF TEXAS

Abstract

Adult Trichobilharzia physellae were recovered from the liver and mesenteric veins of green-winged teal, Anas creca, blue-winged teal, A. discors, and pintail, A. acuta, breeding on the High Plains of Texas. Wild ducks naturally-infected with these schistosomes were emaciated with mild to severe atrophy of the breast musculature. The liver was considerably enlarged, pale and somewhat friable. Numerous viable and dead T. physellae were recovered from the cut surface. On histologic examination, viable adult schistosomes were observed in the portal veins and dead, partly calcified T. physellae were found in the interlobular bile ducts. The normal liver architecture was well preserved but there was mild to extensive fibroplasia of most portal triads. An intense inflammatory response consisting mainly of eosinophils and fibroblasts with a few histiocytes, epithelioid cells, plasma cells, and lymphocytes surrounded the infected triads. There was pressure atrophy of adjacent hepatic parenchyma, hyperplasia or atrophy of the bile duct epithelium, bile stasis in smaller interlobular ducts, ectasia of larger portal ducts, focal areas of inflammatory cells throughout the liver, and periphlebitis of portal veins. The basic lesion presented as an obstructive fibrosis of the portal triads. These lesions are compared with those reported in infections by other schistosome species in their respective hosts. The oculate, apharyngeate, furcocercous cercariae of T. physellae were recovered from the snail first intermediate host, Physa anatina. Attempts to infect domestic mallard ducks via skin penetration by these cercariae were unsuccessful. This is the first record of a cercarial dermatitis-producing schistosome species from the Texas Panhandle and the first detailed description of such extensive lesions produced by adult schistosomes in the liver of a vertebrate host.