Histological analysis of an outbreak of QPX disease in wild hard clams Mercenaria mercenaria in New York

Over 600 hard clams Mercenaria mercenaria from a wild population in Raritan Bay, New York, were examined histologically to assess the extent and intensity of quahog parasite X (QPX) disease in the fishery area. The overall rate of positive samples was 5.8%. A further 5.1% of clams had inflamed lesions suggestive of QPX infection but no QPX organisms were observed. In over half of the QPX-positive cases, infections of the viscera were involved. The significant proportion of visceral infections and the appearance of the pathogen in the gonads of clams are previously unreported presentations of QPX disease. Visceral infections are of concern for fisheries because they involve significantly larger numbers of parasites and higher biomass than mantle-only infections.