Evaluation of the shedding of Sarcocystis falcatula sporocysts in experimentally infected Virginia opossums (Didelphis virginiana)

Five Virginia opossums (Didelphis virginiana) were fed muscles of brown-hea ded cowbirds (Molothrus ater) containing sarcocysts of Sarcocystis falcatul a. Shedding of sporocysts was confirmed in all five opossums by fecal flota tion. Counts were conducted daily for 2 weeks and then biweekly until the a nimals were euthanized and necropsied. The average prepatent period was 9.8 (7-16) days. The number of sporocysts shed varied greatly between the opos sums with maximum mean shedding occurring at 71.6 (26-112) days post-infect ion (DPI). Average sporocyst production was 1480 sporocysts/gram of feces ( SPG). Maximum output was 37,000 SPG. Average fecal yield in captivity was 1 7.5 g of feces/day. Opossums shed 25,900 sporocysts/day (average) and a max imum of 647,500 sporacysts/day. All opossums shed sporocysts until time of euthanasia (46-200 DPI). Histologically, numerous sporocysts were present i n the lamina propria at necropsy, primarily in the proximal half of the sma ll intestine. Sporocysts were generally in clusters within the lamina propr ia of the luminal two-thirds of the villi. Sporocysts were found less frequ ently in the epithelium. No evidence of ongoing gametogony or other develop ment was evident. (C) 2001 Elsevier Science B.V. All rights reserved.