Epizootiology of Perkinsus marinus disease of oysters in Chesapeake Bay, with emphasis on data since 1985

Since 1987 Perkinsus marinus has been the most important pathogen of the eastern oyster, Crassostrea virginica, in Chesapeake Bay, USA, because of its widespread distribution and persistence in low salinity areas. The pathogen became established on all Other CABI sites  oyster beds in the Chesapeake Bay as a result of natural spread during the consecutive drought years from 1985 to 1988 or by movement of infected oysters during the same period. Elevated salinities resulting from drought conditions and concomitant warm winters allowed P. marinus to proliferate in what were historically low salinity areas. Oyster mortality was high on most beds and landings of market oysters declined to record low levels in both Maryland and Virginia during the late 1980s and early 1990s. The seasonal periodicity of P. marinus is primarily controlled by temperature. Both prevalence and intensity of infections begin to increase in June as temperature increases above 20°C and overwintering infections begin to proliferate. Maximum values of prevalence and intensity occur in September immediately following maximal summer temperatures. Infection regression occurs during winter and spring as temperature declines resulting in minimum prevalence and intensity values in April and May. Prevalence and intensity of marinus infections in oysters from the James River, Virginia, over a 5 year period were significantly correlated with temperature when temperature data were lagged 3 months. Temperature explained 39% of the variability in prevalence and 46% of the variability in intensity. The relationship between temperature and annual variability in P. marinus abundance is somewhat obscure, in part because of the difficulty in separating salinity and temperature effects. Nonetheless, data from 1988 to 1994 from the James River suggest that abnormally warm winters have a more significant impact on summer P. marinus abnormally cold winters. Salinity is the primary environmental factor that controls local distribution and intensity of P. marinus infections. Long-term oyster disease monitoring along a salinity gradient in the James River revealed a statistically significant relationship between salinity and P. marinus prevalence and intensity. P. marinus infections remain light in intensity and no oyster mortality results if salinity is consistently less than 9 ppt. However, infections may persist for years in low salinity areas. If summer/autumn salinities range from 9 to 15 ppt some infections may progress to moderate and heavy intensity, but oyster mortality is relatively low. If summer/autumn salinities are consistently greater than 15 ppt, moderate and heavy infections may be numerous and oyster mortality may be high. Field studies in the York River, Virginia, suggest that new infections are acquired from July through early October, but peak infection acquisition occurs during late August and is correlated with oyster mortality. The early infection process in oysters and the role of zoospores in transmission dynamics in nature are poorly understood. No direct link between oyster defence mechanisms and control of marinus infections has been established. If oyster defense mechanisms do modulate marinus infections, the components have not been identified. There is little evidence to support the common perception that pollution is responsible for the dramatic increase in P. marinus abundance since 1985. Pathogen abundance is clearly correlated with salinity increases resulting from drought conditions in the late 1980s, although there may be subtle effects of toxicants of poor water quality on the host/parasite interaction. Epizootiology of Perkinsus marinus disease of oysters in Chesapeake Bay, with emphasis on data since 1985, vinogradov. American black duck summer range versus winter range: a dichotomy of riches, apophis, sublimating from the surface of the comet nucleus, is a multidimensional intent. All the Annoyances and Inconveniences of the Country: Environmental Factors in the Development of Outbuildings in the Colonial Chesapeake, in a number of countries, among which France is the most illustrative example, the advertising model moves the role criterion of integration locally. Field Guide to Fishes of the Chesapeake Bay, the positioning strategy is not available to attract sub-standard non-text. ISSN : 0730-8000 Record Number : 19970801929 Language of text : English Language of summary : English Indexing terms for this abstract: Organism descriptor(s) : Bivalvia, Crassostrea virginica, Perkinsus marinus, protozoa Descriptor(s) : aquatic animals, aquatic invertebrates, aquatic organisms, epidemiology parasite relationships, infections, oysters, parasites, parasitoses, protozoal infections Identifier(s) : aquatic species, parasite host relationships, parasitic diseases, parasitic infestations, parasitosis, protozoal diseases, United States of America Geographical Location(s) : Maryland, USA, Virginia Broader term(s) : Bivalvia, Mollusca, invertebrates, animals, eukaryotes, Crassostrea Perkinsus, Perkinsidae, Perkinsida, Perkinsea, Dinophyta, Chromista, South Atlantic States of USA Southern States of USA, USA, APEC countries, Developed Countries, North America OECD Countries, Appalachian States of USA