Paramoebiasis In The American Lobster, Homarus americanus       Richard A. French1, Salvatore Frasca, Jr.1, K. Spencer Russell1, Tom Mullen Jr.1, and Tom Burrage2   1University of Connecticut, Dept. of Pathobiology. 61 North Eagleville Rd.  U-89, Storrs, CT. 06269; 2U.S. Department of Agriculture; ARS, PIADC, P.O. Box 848, Greenport, NY 11944                 In the spring of 1999 lobsterman reported a mass mortality of lobster in the western Long Island Sound (LIS). Our laboratory initiated a diagnostic investigation in October 1999 and identified a potential cause of the mass mortality, a protozoan parasite. We have identified the protozoan as species Paramoeba.            One prevailing theory, is a cross-species infection, where the lobsters contracted the amoebic infection from other cohabiting crustaceans. These would include Paramoeba perniciosa identified in North American waters in the blue crab, Callinectus sapidus and an amoebae resembling P. perniciosa  (P. invadens) in the sea urchin, Strongylocentrusdroebachiensis. Unlike the disease in blue crab and sea urchin, the agent identified by our laboratory has a distinct pathologic presentation in the lobster. The gross pathology is characterized by variable discoloration (pink/red), coagulopathy, hemocytopenia, excessive coelomic fluid, and microgranulomas. Swelling of the ventral nerve cord is suspected but not defined at this time. The microscopic pathology involves a ganglioneuritis with intralesional protozoa. Additionally, there is ophthalmitis, myositis with myodegeneration/atrophy. The histopathology is consistent with a systemic inflammatory protozoan (paramoebic) disease affecting multiple tissues but primarily the nervous system. The role of environmental factors (anoxia, pesticides and contaminants) is undetermined but may be contributory.  We have initiated studies to characterize the species of the agent isolated from the LIS lobster. This has included culture of the agent for prospective infectivity studies to fulfill Koch’s Postulates. We have performed transmission electron microscopic examination of the agent and associated pathology. The results are consistent with light microscopy and define a parasome (Nebenkörper) in the protozoan, which is indicative of a Paramoeba species. We are in the processes of comparative molecular studies with known agents P. perniciosa, P. invadens, P. pemaquidensis, and P. aestuarina.