Abstract

Caliciviruses are a diverse group of microbial agents, infecting a wide variety of animals. Norwalk-like caliciviruses, or small round structured viruses, are a major cause of epidemic nonbacterial gastroenteritis in adult humans. These outbreaks of food poisoning are often linked to the consumption of raw or undercooked shellfish. Mussels have been shown to act as reservoirs for pinniped caliciviruses, suggesting that caliciviruses important in human disease may have shellfish reservoirs as well. Recreationally and commercially important bivalve mollusks, Eastern Oyster (Crassostrea virginica), Hard Shell Clam (Mercinaria mercinaria), Soft Shell Clam (Mya arenaria), and California mussel (Mytilus californianus), were sampled along the East, Gulf, and West coasts of the United States. Sixty animals were collected from each site, pooled into 12 groups of 5 animals. Most pools were further divided into 5 tissue components: hemolymph, gill, reproductive, intestinal, and mantle. Virus isolation in porcine kidney cells, cDNA dot hybridization, Western and dot immunoblotting, and electron microscopy were performed on the samples. While no viruses could be grown in cell culture, soft shell clams, eastern oysters, and mussels were found to contain calicivirus by cDNA hybridization and immunoblot at sites in Oregon, Maryland, and California, respectively. Virus-like particles with typical calicivirus morphology could be observed in negative stain electron microscopy preparations. These findings suggest that caliciviruses responsible lor gastroenteritis in humans also use ocean reservoirs, such as shellfish, for maintenance and transmission to naive host populations.