Mortality and hematology of blue crabs, Callinectes sapidus,experimentally infected with the parasitic dinoflagellate Hematodiniumperezi

摘要

On the eastern seaboard of the United States, populations of the blue crab, Callinectes sapidus, experience recurring outbreaks of a parasitic dinoflagellate, Hematodinium perezi. Epizootics fulminate in summer and autumn causing mortalities in high-salinity embayments and estuaries. In laboratory studies, we experimentally investigated host mortality due to the disease, assessed differential hematological changes in infected crabs, and examined proliferation of the parasite. Mature, overwintering, nonovigerous female crabs were injected with 10(3) or 10(5) cells of H. perezi. Mortalities began 14 d after infection, with a median time to death of 30.3 +/-1.5 d (SE). Subsequent mortality rates were greater than 86% in infected crabs. A relative risk model indicated that infected crabs were seven to eight times more likely to die than controls and that decreases in total hemocyte densities covaried significantly with mortality. Hemocyte densities declined precipitously (mean=48%) within 3 d of infection and exhibited differential changes in subpopulations of granulocytes and hyalinocytes that lasted throughout the course of the infection. Crabs that did not present infections after injection (i.e. "immune" hosts) did not show hemocytopenia and exhibited significant long-term (21-27 d;) granulocytemia. Detection of the parasite in the hemolymph of infected crabs increased from approximately 30% after 14 d to 60% after 21 d to 100% after 35 d. Plasmodial stages were, however, detectable in histological preparations of the heart within 3 days of infection and increased in number over 5 and 7 days. Sporulation of the parasite occurred over a short time (at least 4 d, after 43 d of infection) and did not culminate in the immediate death of the host. Hematodinium perezi represents a significant threat to the blue crab fisheries in high-salinity estuaries. Although the parasite infects male and female crabs, it may have a greater impact on mature females as they move to higher salinities to breed.