Laboratory transmission studies of QPX disease in the hard clam: Interactions between different host strains and pathogen isolates

Dahl, Soren F.; Perrigault, Mickael; Allam, Bassem

doi:10.1016/j.aquaculture.2008.04.026

Cited by 31 publications

(43 citation statements)

References 16 publications

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“…QPX infections are chronic, and QPX is regularly detected in healthy individuals, indicating an opportunistic parasite. In fact, both QPX strains and host genetics are important in the virulence of QPX disease (Dahl et al 2008). This complex interplay of QPX disease in hard clams may provide clues to better understanding the sea fan−Labyrinthulomycetes relationship, as the same factors may be important for disease transmission and host immunity.…”

Section: Discussionmentioning

confidence: 99%

Friend or foe: the association of Labyrinthulomycetes with the Caribbean sea fan Gorgonia ventalina

Burge¹,

Douglas²,

Conti-Jerpe³

et al. 2012

Dis. Aquat. Org.

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A new syndrome in sea fans Gorgonia ventalina consisting of multifocal purple spots (MFPS) has been observed in the Caribbean Sea. Surveys of MFPS on sea fans were conducted from 2006 to 2010 at a shallow and deep site in La Parguera, Puerto Rico (PR). At the shallow site, MFPS increased between 2006 and 2010 (site average ranged from 8 to 23%), with differences found at depths over time using an analysis of covariance (ANCOVA, p < 0.0001). As a potential causative agent we examined a Labyrinthulomycota-like ovoid parasite that was observed to be abundant in MFPS lesions in light micrographs. Labyrinhylomycetes were successfully isolated, cultured and characterized in sea fans from Florida and PR. Sequence information obtained from the small subunit (SSU) rRNA gene indicated that Labyrinthulomycetes in most sea fans (healthy and MFPS sea fans from Florida; MFPS from PR) and the cultured microorganism are in the genus Aplanochytrium, although some healthy sea fans from PR contained members of the genus Thraustochytrium. Both genera fall within the family Thraustochytriidae. Histology confirmed ob servations of thraustochytrids within apparently healthy and MFPS sea fans from PR, and specific staining indicated a host melanization response only in colonies containing Labyrinthulomycetes or fungal infections. Growth trials indicate that the temperature-growth optima for the cultured microorganism is ~30°C. In inoculation experiments, the cultured Aplanochytrium did not induce purple spots, and histology revealed that many of the apparently healthy recipients contained Labyrinthulomycetes prior to inoculation. Taken together, these results indicate that the Labyrinthulomycetes associated with sea fans is likely an opportunistic pathogen. Further studies are needed to understand the pathogenesis of this microorganism in sea fans and its relationship with MFPS.KEY WORDS: Labyrinthulomycota · Caribbean sea fan · Gorgonia ventalina · Multi-focal purple spots · MFPS Resale or republication not permitted without written consent of the publisherDis Aquat Org 101: [1][2][3][4][5][6][7][8][9][10][11][12] 2012 increase in the number of purple sclerites and is a generalized response to invading pathogens or other biotic agents (Petes et al. 2003, Alker et al. 2004, Smith & Weil 2004. Necrotic lesions, surrounded by purple halos in G. ventalina, have been described as aspergillosis (Smith et al. 1996, Nagelkerken et al. 1997, Kim & Harvell 2001. The terrestrial fungus Aspergillus sy dowii was isolated from fans with these signs and Koch's postulates fulfilled in controlled laboratory experiments (Smith et al. 1996, Geiser et al. 1998). More recently, culture-dependent sampling showed that fungal species other than A. sydowii can be associated with lesions (ToledoHernández et al. 2008). During field surveys in Mexico, Florida, and Puerto Rico, a new type of lesion was identified (Weil & Hooten 2009, Weil & Rogers 2011 our Fig. 1) that is characterized by small (1 to 3 mm in diameter), circular to oblong multi-focal...

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Section: Discussionmentioning

confidence: 99%

Friend or foe: the association of Labyrinthulomycetes with the Caribbean sea fan Gorgonia ventalina

Burge¹,

Douglas²,

Conti-Jerpe³

et al. 2012

Dis. Aquat. Org.

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“…Northern quahogs, Mercenaria mercenaria (L.), from a portion of the east coast of North America (Virginia to Prince Edward Island) have demonstrated variable infection with the protozoan parasite, Quahog Parasite Unknown, QPX, Labyrintohomorpha, Thraustrochytriales (Smolowitz and Leavitt, 1997), in some locations resulting in variable and sometimes high mortalities (Smolowitz et al, 1998;Ford, 2001;Ford et al, 2002;Dahl et al, 2008). Pathogenesis of this disease begins with appearance of parasite cells in mantle and gill tissues, which induces hemocyte migration into the area of infection to isolate and destroy the QPX cells (Smolowitz et al, 1998).…”

Section: Introductionmentioning

confidence: 99%

Combined effects of a parasite, QPX, and the harmful-alga, Prorocentrum minimum on northern quahogs, Mercenaria mercenaria

Hégaret

Smolowitz

Sunila

et al. 2010

Marine Environmental Research

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a b s t r a c tNorthern quahogs, Mercenaria mercenaria (L.), frequently are infected with the parasite Quahog Parasite Unknown (QPX, Labyrintohomorpha, Thraustochytriales), which can cause morbidity and mortality of the quahogs. Possible interactions between this parasitic disease and exposure to the harmful dinoflagellate Prorocentrum minimum in M. mercenaria were studied experimentally. Quahogs from Massachusetts with variable intensity of QPX infection were exposed, under controlled laboratory conditions, to cultured P. minimum added to the natural plankton at a cell density equivalent to a natural bloom. After 5 days of exposure, individual clams were diagnosed histologically to assess prevalence and intensity of parasitic infection, as well as other pathological conditions. Further, cellular defense status of clams was evaluated by analyzing hemocyte parameters (morphological and functional) using flow-cytometry. Exposure of quahogs to P. minimum resulted in: a lower percentage of phagocytic hemocytes, higher production of reactive oxygen species (ROS), larger hemocyte size, more-numerous hemocytic aggregates, and increased numbers of hemocytes in gills accompanied by vacuolation and hyperplasia of the water-tubular epithelial cells of the gills. Quahogs had a low prevalence of QPX; by chance, the parasite was present only in quahogs exposed to P. minimum. Thus, the effect of QPX alone on the hemocyte parameters of quahogs could not be assessed in this experiment, but it was possible to assess different responses of infected versus non-infected quahogs to P. minimum. QPX-infected quahogs exposed to P. minimum had repressed percentage of phagocytic hemocytes, consistent with immuno-modulating effect of P. minimum upon several molluscan species, as well as smaller hemocytes and increased hemocyte infiltration throughout the soft tissues. This experiment demonstrates the importance of considering interactive effects of different factors on the immunology and histopathology of bivalve shellfish, and highlights the importance of considering the presence of parasites when bivalves are subjected to harmful-algal blooms.

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“…Previous studies demonstrated variation in M. mercenaria susceptibility toward QPX among different clam stocks with higher resistance of northern clam broodstocks compared to southern broodstocks [19,23,24,54]. Ragone Calvo [24] suggested that both host genotype and environmental parameters were important determinants in clam susceptibility to QPX disease and the impact of genetic variation on overall performance of geographically different hard clam populations was previously demonstrated [55].…”

Section: Comparison Of Defense and Stress Response Following Qpx Chalmentioning

confidence: 99%

“…We have been successfully using these aquacultured clam lines for comparative studies because of their confirmed differential susceptibility to QPX infections in laboratory settings [23,26] and in the field [30]. A sub-sample (30 clams/stock) was checked for pre-established QPX infections before the initiation of the experiment using standard histopathology techniques [25] and all tested clams were negative.…”

Section: Mercenaria Mercenariamentioning

confidence: 99%

“…This disease has been observed along the eastern coast of North America, from Maritime Canada to Virginia but never south of Virginia [18e22]. This geographic distribution is likely responsible for variations in clam susceptibility toward QPX among different clam stocks with lower resistance of southern (Florida and South Carolina) clam broodstocks, which are not exposed to selective mortality due to parasite pressure, as compared to northern (New Jersey, New York, Massachusetts) broodstocks growing and reproducing in enzootic areas [19,23,24]. The biological bases for the resistance process to QPX in Northern hard clams are not known although the outcome has been described as a granulomatous inflammatory response and encapsulation of parasite cells ultimately leading to the healing of infected individuals [18,20,25].…”

Section: Introductionmentioning

confidence: 98%

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Differential immune response in the hard clam (mercenaria mercenaria) against bacteria and the protistan pathogen QPX (quahog parasite unknown)

Perrigault

Allam

2012

Fish & Shellfish Immunology

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Laboratory transmission studies of QPX disease in the hard clam: Interactions between different host strains and pathogen isolates

Cited by 31 publications

References 16 publications

Friend or foe: the association of Labyrinthulomycetes with the Caribbean sea fan Gorgonia ventalina

Friend or foe: the association of Labyrinthulomycetes with the Caribbean sea fan Gorgonia ventalina

Combined effects of a parasite, QPX, and the harmful-alga, Prorocentrum minimum on northern quahogs, Mercenaria mercenaria

Differential immune response in the hard clam (mercenaria mercenaria) against bacteria and the protistan pathogen QPX (quahog parasite unknown)

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