Two epizootic diseases in Chesapeake Bay commercial clams, Mya arenaria and Tagelus plebeius

Abstract

Declining Chesapeake Bay harvests of softshell clams, together with historical and emerging reports of epizootic diseases in Mya arenaria, prompted a survey in summer 2000 of the health status of selected commercial clam populations. All sampled populations (8 M. arenaria softshell clam, 2 Tagelus plebeius razor clam) were infected by Perkinsus sp. protozoans at prevalences ranging from 30 to 100% of sampled clams. Nucleotide sequences for the internal transcribed spacer (ITS) region of the rRNA gene complex were determined for clonal in vitro Perkinsus sp. isolates propagated from both M. arenaria and T. plebeius. Multiple polymorphic sequences were amplified from each isolate, but phylogenetic analysis placed all sequences into 2 clades of a monophyletic group, which included both recently described clam parasites P. chesapeaki and P. andrewsi. Sequences amplified from each clonal isolate were found in both sister clades, one containing P. andrewsi and the other P. chesapeaki. Most (7 of 8) M. arenaria samples were also affected with disseminated neoplasia (DN), at prevalences of 3 to 37%, but neither T. plebeius sample showed DN disease. Disease mortalities projected for sampled clam populations, especially those affected by both diseases, may further deplete subtidal commercial clam populations in mesohaline portions of Chesapeake Bay. KEY WORDS: Mollusc neoplasia · Disseminated neoplasia · Hemic neoplasia · Dermo disease · Perkinsus chesapeaki · Perkinsus andrewsi · Softshell clam · Razor clam Resale or republication not permitted without written consent of the publisherDis Aquat Org 50: [67][68][69][70][71][72][73][74][75][76][77][78] 2002 circulatory systems of affected clams, displacing normal hemocyte cells and their critical physiological functions. DN disease pathogenesis has been compared to that of vertebrate leukemia (Smolowitz et al. 1989), and it is fatal within 9 mo of experimental transmission (House et al. 1998). With prevalences of up to 58% reported in some Chesapeake Bay clam populations (Farley et al. 1991), mortalities from DN disease are estimated to be significant.Although the etiology and natural transmission mechanisms of DN disease remain unknown, it is mechanically transplantable between affected and healthy Mya arenaria, and is experimentally transmitted through the water column. However, it is not transmitted by injection of healthy clams with cell-free filtrates of affected clam hemolymph, or of filtered hemolymph cell lysates. Despite one report of wholesale DN disease transmission by injection of 0.45 µm-filtered DN cell lysates into healthy clams (Oprandy et al. 1981), consistent failure by later investigators to transmit the disease with cell-free filtrates has been interpreted as refuting the possibility of a viral agent (McLaughlin et al. 1992). Recent detection of retroviral reverse transcriptase activity in filtrates of tissue homogenates only from DN-affected clams suggests that a retroviral agent is present. However, the failure of reverse transcriptase-pos...

Continuous in vitro culture of the carpet shell clam Tapes decussatus protozoan parasite Perkinsus atlanticus

“…17). A recent study, however, has reported that ITS sequences previously thought to distinguish P. chesapeaki and P. andrewsi are really ITS variants that can both be found in a single clonal isolate culture (Dungan et al 2002). This result suggests that P. chesapeaki and P. andrewsi are the same species of Perkinsus.…”

Withdrawn: “A health status survey of clams, Mya arenaria and Ensis siliqua, in the Irish Sea”

“…protozoans, have been documented in this species on the Atlantic west coast (Brousseau & Baglivo, 1991;Dungan et al, 2002;Earle & Crisley, 1975 (Perez, 2011;Ruiz et al, 2013).…”

Comparison of diagnostic techniques to detect the clam pathogen Perkinsus olseni

“…However, Perkinsus spp. can infect several alternate hosts in addition to the type host, and this is especially true for P. olseni (Kotob et al 1999, Dungan et al 2002, Bower & McGladdery 2003.…”

“…P. marinus was the first species of the genus to be described and was reported as the causative agent of mortalities of Crassostrea virginica in the Gulf of Mexico (Mackin et al 1950). Since the synonymy between P. olseni and P. atlanticus (Goggin 1994, Robledo et al 1999a, Murrell et al 2002, Cremonte et al 2005) and between P. chesapeaki and P. andrewsi (Dungan et al 2002, Burreson et al 2005 has been described, the remaining species of the genus are P. qugwadi in Patinopecten yessoensis (Blackbourn et al 1998), Perkinsus mediterraneus in Ostrea edulis (Casas et al 2004), and P. honshuensis in Ruditapes philippinarum (Dungan et al 2006); recently, P. behaensis has been described in oysters from China (Moss et al 2008). However, Perkinsus spp.…”

“…Internal transcribed spacers (ITS-1 and ITS-2) are non-coding regions of the RNA gene cluster that are less conserved than the ribosomal RNA coding genes and are suitable to distinguish among proximal species. They have been used in several studies to distinguish different species of the genus Perkinsus (Kotob et al 1999, Robledo et al 1999b, Casas et al 2002, Dungan et al 2002). Here we compared histopathology, RFTM, and PCR of the rDNA ITS region for the diagnosis of P. olseni in the principal clam species cultured in Galicia (NW Spain).…”