Oyster Mortality Studies In Virginia .V. Epizootiology Of MSX A Protistan Pathogen Of Oysters

MSX, a pathogen of oysters (Crassostrea virginica), produced a drastic epizootic in high-salinity areas of Chesapeake Bay from 1959 to 1963. The patterns of infection and mortality were determined by imports from disease-free seed-oyster areas. Winter and spring imports became infected in early summer and began dying in late summer. Late-summer imports apparently became infected promptly but infections remained subclinical until the following May. Death rates were highest during warm months but losses occurred throughout the year. MSX was assigned as the cause of a high percentage of deaths by sampling live and dead oysters. Mortality for the first and second years after import was usually 50 to 60% annually. A fungus disease caused by Dermocystidium marinum was also prevalent in some areas. Prevalence of MSX did not decline as oyster populations were decimated; hence nearly half of Virginia\u27s private beds have been forced out of productio

Notes on Fungus Parasites of Bivalve Molluscs in Chesapeake Bay

My hobby is collecting the mollusks of Chesapeake Bay.. Having placed a few specimens in museums, and having made a check list · (no new species yet) with appended distribution records, I found my hobby less stimulating than rily research .. , But then my research had. taken a turn which opened up new and inviting fields of discovery. First came a devastating mortality of oysters in the Rappahannock River, for which no explanation has been found. Then Mackin et~ .. l. (\u27]_950) discovered the fungus disease of oysters, Dermocystidium marinum ... But not until Ray (1952) developed the thioglycollate culture technique for .easy detection of the fungus did we seriously begin to study oyster mortalities and their causes in Virginia (Hewatt and Andrews,. 1954) .. For some time Ray and Mackin searched among the invertebrate associates of oysters for alternate hosts, only to find that infection was easily accomplished directly from one oyster to another through water-borne spores (J. G. Mackin, Personal Communication). Since other bivalve mollusks would not be suspected as alternate hosts for an oyster disease, little effort was made ,to check them. With this background, we at the Virginia Fisheries Laboratory were surprised in August, 1953, to find the meat of a dead clam, Venus mercenaria, infected with a D. marinum-like fungus. During the fall and winter of 1953-54, 12 of-16 species of bivalve mollusks collected near Gloucester Point, Virginia, were found infected with similar fungi (Table I). None of the fungus parasites has been identified except the one causing a mycosis in oysters. How many species of fungi are involved? Can spores from one host species infect individuals of other species? And of most immediate importance, how many bivalve species will serve as host to the oyster parasite

Oyster Diseases In Chesapeake Bay

Three major diseases of oysters have been monitored in Virginia estuaries for 2-3 decades. Dermocystidium marinum, causing a warm-season wasting disease, was discovered in Virginia in 1950 and continues actively to kill oysters where beds or populations are found in high salinity waters ( \u3e15%). This disease spreads by close proximity of dying oysters to other oysters, hence each isolated bed must be sampled in early fall annually to document activity of the pathogen. Control involves avoiding infected seed oysters, cleaning beds of all oysters after harvest, and isolation of new beds. A new pathogen, Minchinia nelsoni (MSX), caused catastrophic oyster mortalities in 1959-60, and oyster planting ceased thereafter in a large area of high salinity ( \u3e15%o) waters in lower Chesapeake Bay. A third pathogen, Minchinia costalis (Sea Side Organism or SSO), was found almost simultaneously on Seaside of Virginia in high-salinity waters ( \u3e30 %o). Both these haplosporidan parasites kill native susceptible oysters at rates of 20-50 percent annually. Strains resistant to MSX were selected from survivors by laboratory breeding. SSO appears to be an endemic pathogen that causes confined periods of infection and mortality. Sporulation and infection occur regularly each May-June associated with oyster deaths. A long incubation period of 8 months with hidden or subclinical infections characterizes the disease. SSO is confined to high-salinity waters along the seacoast from Cape Henry to Long Island Sound. MSX is a highly infectious pathogen that appears to be new by importation or advent of a virulent strain. Infections occur during 5 warm months (June-October) and deaths occur throughout the year. Direct transmission has not been achieved in the laboratory for either haplosporidan. Transmission of the diseases and life cycles are still important objectives after 18 years of studies

Summaries of twenty-five years of MSX studies in Chesapeake Bay, 1959 to 1983

Accounts written for the report published in Special Publications of the American Fisheries Society [i.e., Disease processes in marine bivalve molluscs] by Haskin and Andrews in 1987-88

Russian roulette with oysters : a review of exotic introductions and information needed for planning new ones

Importation and transplantation of exotic oysters has probably resulted in introduction of more marine invertebrate species than any other of man\u27s activities. Unintentional introductions have resulted from careless movements of oysters without planning or consideration of consequences. Diseases and parasites are often unknown and oysters cannot be adequately diagnosed or inspected for problems by biologists. (...

A Review Of Introductions Of Exotic Oysters And Biological Planning For New Importations

Importation and transplantation of exotic oysters has probably resulted in the introduction into new areas of more marine invertebrate species than any other of man\u27s activities. Unintentional introductions have resulted from careless movements of oysters without planning or consideration of consequences

Studies on the relation between black mud and mortalities in the Rappahannock River, Virginia, in 1953

Following the reappearance of black mud in May 1953, a meeting was held at Tappahannock to diacuss possible causes of the condition and the steps which might be taken if there was a recurrence of mortality such as followed the black mud in 1949. Lacking any clear cut evidence that pollution or physical factors caused the mortality, we suggested that a newly discovered fungus disease called Dermocystidium marinum be studied as a possible causal factor. A study has been made of this disease in the Rappahannock River in the past year

Oyster mortality studies in Virginia IV. MSX in James River public seed beds

MSX, an unnamed pathogen of oysters, caused an epizootic in Chesapeake Bay which removed from production nearly half of Virginia\u27s private oyster-planting acreage between 1959 and 1961. The organism did not appear in James River seed beds .until fall of 1960. A tongueshaped distribution of MSX was apparently related to influx of salt water along the channel. In 1960-61 and 1961-62, infections of MSX appeared at Wreck Shoal in the middle of the seed area in October, and disappeared the following April coincident with lowest salinities. Infection levels were approximately 30 to 35% each year in populations adjacent to the channel. No appreciable cold-season mortality occurred at Wreck Shoal. MSX was nearly absent from Wreck Shoal oysters during the warm season in summer salinities of about 15 ppt, but at Brown Shoals, with salinities 2 or 3 ppt higher, it persisted through spring freshets and caused summer deaths. From observations for three rather wet years, it is concluded that persistence of MSX infections in the James River seed area depends upon importation of infective material from the saltier waters of Lower James River and Hampton Roads. Also, damage to the seed area will probably be reflected in quality of seed rather than direct mortality. Planting infected seed in high-salinity waters leads to serious losses

MSX disease in Virginia, 1959 to 1965

Compilation of 20 unpublished reports and notes on the oyster disease MSX, arranged in chronological order from 1959-1965. Notes on oyster mortality -- Status of Delaware Bay disease of oysters in Chesapeake Bay area -- Epidemiology - general -- Status of epidemic diseases of oysters in Virginia-- Summary of oyster mortality and disease work at the Virginia Fisheries Laboratory for 1960 -- Notes from talks with Haskin and Carriker at Shallow Water Conference -- Brief summary of disease studies in Virginia for 1961 -- Status of diseases of oysters in Chesapeake Bay -- Table 1: Samples of Incidence data for MSX-- Table 3: Synopsis of SSO occurrence on Eastern Shore, 1960 -- Notes on Mortality Conference, Solomons, Maryland -- Fifth Annual Mortality Conference, Oxford, Md: Notes on disease studies in Virginia-- Marine scientist indicates decline in oyster deaths due to MSX-- Thumb-nail sketch of seasonal MSX activityin Virginia-- Notes on oyster mortality studies in Virginia (prepared for Sixth Annual Mortality Conference, New Brunswick, N.J.) -- Seventh Annual Mortality (Pathology) Conference: The life cycle of MSX-unknown -- Seventh Annual Mortality (Pathology) Conference: Some thoughts on significance of MSX to Virginia oyster industry -- Notes on life cycle of MSX-- [List of publications, reports and handouts] Listed in table of contents but not included in volume: The shellfisheries of Virginiain flux; Graphs showing Distribution of MSX, Seasonal mortalities and prevalences in annual cycles, Monthly mortalities in tray-grown susceptible oysters at Gloucester Point, and Occurrence of MSX and mortalities from early-summer and late-summer importations of disease-free James River oysters