The Opossum (Didelphis virginiana) as a Host for Sarcocystis debonei from Cowbirds (Molothrus ater) and Grackles (Cassidix mexicanus, Quiscalus quiscula)

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Abstract
Sarcocytis-infected muscles from ducks, cowbirds and grackles were fed to cats, opossums, rats and a dog. Only the opossum (D. virginiana) was a suitable definitive host. All opossums that were fed Sarcocystis-infected cowbirds (M. ater) and grackles (C. mexicanus, Q. quiscula) passed sporocysts in their feces. Opossums that ate the cowbirds had prepatent periods of 5 and 10 days and remained patent for at least 105 days. Opossums that ate the grackles became patent on day 10 after the infective meal and remained patent for over 90 (Quiscalus) and 105 (Cassidix) days. A single opossum fed infected muscle from a pintail duck (Anas acuta) passed sporocysts in the feces from days 13 through 18 after infection. No sporocysts were passed by opossums fed infected muscle from the green-winged teal (Anas carolinensis) and shoveller (Spatula clypeata). Sporocysts of duck, cowbird and grackle origin were structurally similar. Mean dimensions of sporocysts were: duck-origin, 11.2 by 8.2 .mu.m; cowbird-origin, 11.4 by 7.8 .mu.m; Cassidix-origin, 11.2 by 7.8 .mu.m; and Quiscalus-origin, 11.6 by 7.7 .mu.m. The sporocysts of cowbird and grackle origin is designated as S. debonei Vogelsang 1929 (= Isospora boughtoni Volk 1938).