FUNGAL INFECTIONS Fungi of Bivalvia Linn 1758
The phycomycete fungus, Ostracoblabe implexa, is responsible for severe shell damage in European oysters O. edulis , known as maladie de la charni re 'hinge disease' , maladie du pied 'foot disease' erroneously , shell disease and Dutch shell disease Fig. 20.15 . Less severe infections occur in C. gigas, Fig. 20.15. Opposite a Conchiolin warts in the shell of Ostrea edulis infected by the fungus Ostracoblabe implexa 'shell disease' . Note lesions at the adductor muscle attachment point of the...
Husbandry practices
The principal method of disease control in hatcheries is destruction of the infected shellfish and disinfection of the tanks and equipment with which they were in contact Elston, 1990, 1993 . In some cases, however, early detection and removal of individuals with clinical signs may control pathogen proliferation or enhance effective chemotherapeutant treatment of remaining stocks see 'Treatment and protection' below . All prophylactic measures involve risk benefit examination of production...
BACTERIAL INFECTIONS Bacteria of Bivalvia Linn 1758
Rickettsia-, Chlamydia- and Mycoplasma-like organisms Bacteria belonging to the orders Rickettsiales, Chlamydiales and Mycoplasmatales class Mollicutes infect a wide range of bivalves and crustaceans Table 20.2 . With certain exceptions, described below, Rickettsiaceae are Gram-negative, intracytoplasmic, membrane-bound, oval to rod-shaped bacilli, measuring 0.3-0.6 mm x 0.8-2.0 mm. Chlamydiales are also Gram-negative, but have a complex developmental cycle, multiplying within cytoplasmic...
Fungi of Nephropidae Dana 1852 genera Astacus Pacifastacus Cambarus Cherax
One of the best-known fungal diseases of crustaceans is crayfish plague Krebspest or Kraftpest or la peste or crayfish aphanomyciasis , caused by Aphanomyces astaci Saprolegniales . This fungus is common in North American crayfish Pacifastacus leniusculus and Procambarus clarkh , where it causes superficial lesions, but is not associated with epizootic mortality. In contrast, crayfish in Europe Astacus astacus, A. leptodactylus and A. pallipes have been decimated by A. astaci infections...
Chemotherapy
Chemotherapeutants have long been used in fin-fish aquaculture Meyer and Schnick, 1989 Michel and Alderman, 1992 however, there is increasing awareness of the risks associated with their indiscriminant or continuous application. These risks include drug-resistant pathogens, overdosage and impacts on the environment, consumer health and market perception and aquaculturist handling and economics . Moreover, increased restrictions on aquaculture imports between countries with non-complementary...
Bacteria of Gastropoda Cuvier 1797
Juvenile vibriosis in red abalone, Haliotis rufescens, from a hatchery in California Elston and Lockwood, 1983 and H. kamtschatkana from a hatchery in British Columbia Bower et al., 1994a was responsible for swollen patches of epipodial tissue, which became necrotic and ruptured. Small numbers of bacteria were detected on sloughed-off epithelium Elston and Lockwood, 1983 , as well as from the intramuscular vascular sinuses and along peripheral neurons. Nine isolates from the Californian...
Quarantine and disinfection
Quarantine is commonly used to control disease spread. Types of quarantine range from high-technology facilities, with automated fail-safe containment and treatment equipment, to tanks with disinfected effluent. The first documented quarantine for a shellfish disease was for Malpeque disease in American oysters, C. virginica from PEI, Canada, in 1915 and 1916. Although the cause of the mortalities was not known, oyster transplants out of the Malpeque Bay were prohibited geographical quarantine...
Viruses of uncertain affinities
A virus or group of viruses of undetermined affinity occur s in six penaeid species P. vannamei, P. stylirostris, P. monodon, P. semisulcatus, P. chinensis orientalis and P. japonicus , as well as four experimentally infected species Fig. 20.7. and Opposite a Yellow-head baculovirus YHB in the cytoplasm of an infected lymphoid organ in Penaeus monodon. Photograph courtesy of S. Boonyaratpalin. TEM, x 7700. b Gill lamellae of Penaeus monodon infected by YHB. Note aggregations of viral particles...
Baculoviral and baculoviruslike viruses
The first baculovirus described from shrimp was baculovirus penaei BP in Penaeus duorarum from Florida Couch, 1974a,b . J.-R. Bonami, L.D. Bruce, B.T. Poulos and D.V. Lightner unpublished, cited in Bruce et al., 1993 propose changing BP to 'PvSNPV' 'the most characterised variant, from Penaeus vannamei, in the singly enveloped nuclear polyhedrosis virus group' , in compliance with the guidelines for virus nomenclature designated by the International Committee on Taxonomy of Viruses. For the...
Grampositive bacteria
Relatively few Gram-positive bacterial diseases have been described from bivalves however, Nocardia sp. is a Gram-positive, acid-fast actinomycete, Fig. 20.10. and Opposite a Chlamydia-like inclusion bodies arrows in the digestive tubules of Crassostrea virginica. H amp E, x 160. b Different developmental stages of a filamentous Chlamydia-like infection of the digestive tubules of Crassostrea virginica. Note rupture of the basal membrane, rather than the apical membrane, by one colony. H amp E,...
Histology
The standard disease-screening technique applied to shellfish is histology Howard and Smith, 1983 Bell and Lightner, 1988 Bucke, 1989 . Although frequently insufficient for species identification of microbial pathogens especially those with a non-specific host response , histology provides a useful record of infection foci and host response. The host-parasite interaction at the tissue and cellular level is essential for interpreting pathogenic effects. Furthermore, light microscopy is...
Baculoviruses and baculoviruslike viruses
A non-occluded baculovirus named Tau t , after the lagoon in southern France from which infected Mediterranean shore, Carcinus mediterraneus, were collected Pappalardo and Bonami, 1979 , induced 100 mortality in experimentally inoculated crabs Pappalardo et al., 1986 . Infections developed faster at 23 C than at 18 C and crabs fed infected tissues developed heavier infections than those which were inoculated. Clinical signs of Tau infections were non-specific increased lethargy, decreased...
Herpesviruslike viruses
Farley et al. 1972 found a herpes-like infection in the haemocytes of moribund American oysters, C. virginica, held in thermal effluent 28-30 C, within the temperature tolerance range of C. virginica from a power plant in Maine. Mortalities of 52 were attributed to this infection, which was characterized by Feulgen-positive nuclear inclusions in the haemocytes of all moribund specimens Fig. 20.1 . Similar inclusions were found in wild, apparently healthy, oysters at the site of collection...
Iridoviruslike viruses
The first viral disease recorded from bivalves was 'maladie des branchies' gill disease , which appeared in Portuguese oysters C. angulata in France in 1966 Marteil, 1969 . The disease spread throughout Atlantic populations of Portuguese oysters until stocks reached a non-exploitable level in the early 1970s. The gills of infected oysters demonstrated intense haemocyte infiltration, abscessing and necrosis. Iridovirus-like viral particles, subsequently named gill necrosis virus GNV Comps and...