Widespread survey finds no evidence of Haplosporidium nelsoni (MSX) in Gulf of Mexico oysters

Abstract

The advent of molecular detection assays has provided a set of very sensitive tools for the detection of pathogens in marine organisms, but it has also raised problems of how to interpret positive signals that are not accompanied by visual confirmation. PCR-positive results have recently been reported for Haplosporidium nelsoni (MSX), a pathogen of the oyster Crassostrea virginica in 31 of 40 oysters from 6 sites in the Gulf of Mexico and the Caribbean Sea. Histological confirmation of the PCR results was not undertaken, and no haplosporidian has been reported from the numerous histological studies and surveys of oysters in the region. To further investigate the possibility that H. nelsoni is present in this region, we sampled 210 oysters from 40 sites around the Gulf of Mexico and Puerto Rico using PCR and 180 of these using tissue-section histology also. None of the oysters showed evidence of H. nelsoni by PCR or of any haplosporidian by histology. We cannot, therefore, confirm that H. nelsoni is present and widespread in the Gulf of Mexico and the Caribbean Sea. Our results do not prove that H. nelsoni is absent from the region, but taken together with results from previous histological surveys, they suggest that for the purposes of controlling oyster importation, the region should continue to be considered free of the parasite. KEY WORDS: PCR · Oyster · Crassostrea virginica · Molecular detection · Infection · Shellfish importation · Haplosporidian Resale or republication not permitted without written consent of the publisherDis Aquat Org 93: [251][252][253][254][255][256] 2011 C. virginica from Nova Scotia, Canada, to Biscayne Bay, Florida, USA (Haskin & Andrews 1988, Barber et al. 1997, Stephenson et al. 2003, but none of the several histological studies of oysters in the Gulf of Mexico have reported H. nelsoni or any other haplosporidian (Couch 1985, Gauthier et al. 1990, Fisher et al. 1996, Kim et al. 1998, Winstead et al. 2004, Kim & Powell 2006. The most comprehensive of these is the annual status and trends (S&T) MATERIALS AND METHODSCrassostrea virginica were collected between December 2007 and February 2008 at 32 sites representing 14 bay systems from lower Laguna Madre, Texas, to Florida Bay, Florida, USA, and C. rhizophorae were collected from 2 bays in Puerto Rico (Fig. 1, Table 1). In May and July 2010, C. virginica were sampled from 6 additional sites, representing 2 bay systems in Texas and 1 in Florida (Fig. 1, Table 1). All samples were express shipped directly to HSRL. Upon receipt, 12 oysters from each sample were opened using a shucking knife, which was rinsed in 10% bleach between each oyster. A section of gill about 4 mm wide and encompassing all 4 demibranchs approximately 6 to 7 mm posterior to the gill-palp junction was excised and preserved in 70% ethanol (EtOH) for PCR analysis. Dissecting instruments were scraped clean in a bleach-sand mixture, dipped in EtOH and flamed between each oyster. Between the PCR section and the palps, and adjacent to the piece of gill ta...

Scanning Electron Microscopy and Molecular Characterization of A New Haplosporidium Species (Haplosporidia), A Parasite of the Marine Gastropod Siphonaria pectinata (Mollusca: Gastropoda: Siphonariidae) In the Gulf of Mexico

“…infecting gastropods only form a monophyletic group (H. pickfordi, H. tuxtlensis, H. montforti, and H. lusitanicum) as opposed to the rest of the Haplosporidia occurring in Bivalvia. Ulrich et al (2007) reported H. nelsoni in the Gulf of Mexico, but subsequent studies have cast doubt on the methods used for detection of parasites (Burreson, 2008), and no evidence from further surveys detected H. nelsoni in this area (Ford et al, 2011). Haplosporidium tuxtlensis is, therefore, the first confirmed record of a haplosporidian parasite species in the Gulf.…”

Development of a multiplex qPCR for the quantification of three protozoan parasites of the eastern oyster Crassostrea virginica

“…Distilled water was used to bring the final reaction volume to 20 μl. The thermal cycling protocol consisted of a 95°C hold for 10 min followed by 45 cycles of (Ford et al 2011, OIE 2021.…”

Managing marine mollusc diseases in the context of regional and international commerce: policy issues and emerging concerns

“…Previously, H. nelsoni had been reported only from the Atlantic coast of North America, never in the Gulf of Mexico, so this report created uncertainty about potential movements of shellfish, even shellfish gametes, from the Atlantic to the Gulf coasts of North America. Subsequently, an extensive survey was unable to confirm the presence of H. nelsoni in the Gulf of Mexico [74]. This example points to the need for diligent surveillance.…”