Increased Virulence in an Introduced Pathogen:Haplosporidium nelsoni(MSX) in the Eastern OysterCrassostrea virginica

Abstract

The protistan parasite Haplosporidium nelsoni has caused extensive mortality in the eastern oyster Crassostrea virginica along the mid-Atlantic coast of the United States since 1957. The origin of H. nelsoni has remained unresolved. Molecular diagnostic tools were used to examine the hypothesis that a haplosporidian parasite in the Pacific oyster C. gigas is H. nelsoni. A DNA probe specific for H. nelsoni reacted positively in in situ hybridizations with haplosporidian plasmodia from C. gigas collected in Korea, Japan, and California. Primers that specifically amplify H. nelsoni DNA in the polymerase chain reaction amplified product from Californian C. gigas infected with the haplosporidian parasite. The DNA sequence of the 565-base pair amplified product was identical to the H. nelsoni sequence except for a single nucleotide transition, a similarity of 99.8%. These results are conclusive evidence that the parasite in C. gigas is H. nelsoni and strongly support previous speculation that the parasite was introduced into Californian populations of C. gigas from Japan. Results also support previous speculation that H. nelsoni was introduced from the Pacific Ocean to C. virginica on the East Coast of the United States, likely with known importations of C. gigas. These results document greatly increased virulence in a naive host-parasite association and reinforce potential dangers of intentional, but improper, introductions of exotic marine organisms for aquaculture or resource restoration.

Comparison of in vitro-cultured and wild-type Perkinsus marinus. II. Dosing methods and host response

“…Thus, a given parasite may appear virulent in one host because that host is susceptible to, and mounts a poor defense against, the parasite, whereas the same parasite appears avirulent in another host that has good defenses or is insusceptible (e.g. Burreson et al 2000). The external environment may also affect apparent virulence.…”

Declining impact of an introduced pathogen: ­Haplosporidium nelsoni in the oyster Crassostrea virginica in Chesapeake Bay

“…The parasite was introduced from Asia (Burreson et al 2000) sometime prior to 1957, when it emerged in Delaware Bay; by 1959, oysters were dying of H. nelsoni parasitism also in Chesapeake Bay (Andrews 1962, Haskin et al 1966). Oyster mortality due to this parasite exceeded 90% on reefs in lower Delaware and Chesapeake Bays during the early years of the epizootic , Haskin & Andrews 1988, an acute impact that presumably reflected a new encounter between an introduced parasite and a naïve host (Burreson et al 2000). H. nel-ABSTRACT: Disease caused by the parasite Haplosporidium nelsoni has devastated Crassostrea virginica in Chesapeake Bay, exacerbating effects of overharvesting and adversely impacting the ecology of the bay.…”

Spore ornamentation of Minchinia occulta n. sp. (Haplosporidia) in rock oysters Saccostrea cuccullata (Born, 1778)

“…The parasites of phylum Haplosporidia Caullery and Mesnil, 1899 can be amongst the most pathogenic of all bivalve parasites (Burreson et al, 2000).…”