Histopathological alterations associated with Perkinsus spp. infection in the softshell clam Mya arenaria

Abstract

Softshell clams (Mya arenaria) collected from the Chester River in the upper Chesapeake Bay showed the presence of Perkinsus spp. in ∼ 12% (28/240) of clams examined. The infection seems to run a mild course with the host prevailing in encapsulating invading parasites. The gills appear to be the major site of infection; however, the parasite was also found in the digestive gland, gonads, and kidneys and occasionally in the tissue and sinuses of adductor muscles. Typically, clusters of protozoal cells were embedded in an amorphous PAS-positive substrate and were surrounded by one or more layers of granulocytes. In heavy infections, both free and encapsulated Perkinsus spp. cells were observed in affected tissue forming aggregations of different sizes. Within the tissues of M. arenaria, the parasite propagated by schizogony. The presence of large encapsulations in vital organs such as the gills and gonads may adversely affect growth and fertility of affected clams.