First report of Perkinsus sp. infecting mangrove oysters Crassostrea rhizophorae from the Brazilian coast

Abstract

Protozoan parasites of the genus Perkinsus are considered important pathogens responsible for mass mortalities in several mollusk species worldwide. In the present study we describe for the first time a parasite of the genus Perkinsus infecting the mangrove oyster Crassostrea rhizophorae from the Brazilian coast. Prevalence of this parasite was low in the Pacoti River estuary (Ceará, northeast Brazil) and absent in oysters from southern Brazil. Oyster gill and rectum tissues incubated in Ray's fluid thioglycollate medium (RFTM) revealed the presence of spherical hypnospores (5 to 55 µm diam.). Histological analysis showed the occurrence of typical signet-ring trophozoites and schizonts (3 to 6 µm diam.) infecting connective tissues of several organs and digestive epithelia. PCR assays specific to the genus Perkinsus, followed by cloning and sequencing of the internal transcribed spacer (ITS) region of the ribosomal ribonucleic acid (rRNA) gene complex, confirmed a close phylogenetic relationship between Brazilian Perkinsus sp. and P. beihaiensis infecting Chinese oysters. KEY WORDS: Crassostrea rhizophorae · Mangrove oyster · Perkinsus sp. · Protozoan parasite · PCR-RFLP · rRNA · RFTM · Sporulation Resale or republication not permitted without written consent of the publisherDis Aquat Org 88: [13][14][15][16][17][18][19][20][21][22][23] 2009 eases affecting edible and cultured bivalve species from 2 Brazilian regions. The project was designed to survey parasites among wild and cultivated populations of oysters Crassostrea rhizophorae and C. gigas from Santa Catarina Island and the Pacoti River estuary (Fortaleza, in the state of Ceará, northeast Brazil). The results provide data on distributions of pathogens and on host susceptibilities to pathogens, which will qualify further monitoring programs, help avoid disease transfers from infected populations, and inform efforts to keep unaffected areas parasite-free.The first described parasite of the genus Perkinsus was P. marinus (Mackin et al. 1950), which was identified as being responsible for mortality outbreaks among Crassostrea virginica oyster stocks from Louisiana, USA. It was first described as Dermocystidium marinum, based partly on characteristics of hypertrophic hypnospores and zoosporangia that enlarge among infected oyster tissues when they are incubated in a high-salt formulation of Ray's fluid thioglycollate medium (RFTM) (Ray 1952). Since that time, diverse Perkinsus spp. have been reported to infect many important commercially cultured mollusk species worldwide.Perkinsus olseni was first described as a pathogen of Australian abalone Haliotis ruber (Lester & Davis 1981). Azevedo (1989) described the species P. atlanticus infecting the carpet shell clam Ruditapes decussatus in Portugal. P. olseni, which is currently synonymous with P. atlanticus, has wide geographic and host ranges. It has subsequently been reported in other bivalve species, such as Pitar rostrata from Uruguay (Cremonte et al. 2005) and R. philippinarum, Venerupis pullast...

Perkinsus sp. infecting the oyster Crassostrea rhizophorae from estuaries of the septentrional Northeast, Brazil

“…The study complements reports published by Sabry et al (2009), Silva et al (2013) and Brandão et al (2013) on the occurrence of this pathogen in the states of Ceará, Paraíba and Bahia, respectively. In addition, the study makes a significant contribution to current knowledge about the distribution of Perkinsus along the Brazilian coast and provides subsidies for the development of sanitary measures to prevent contamination of protozoan-free areas.…”

“…This is consistent with the absence of records of mortality among these oyster populations which might be associated with the parasite. However, the values found were higher than the prevalence of 6.7% recorded by Sabry et al (2009) Only 6 of the 50 cases detected by RFTM assays were confirmed by PCR, probably because most infections were very light and/or because the amount of gill tissue retrieved from each specimen for DNA extraction was too small to ensure the detection of the pathogen. In a discussion on the occurrence of false-negative PCR results in the detection of parasites in bivalves, Burreson (2008) reached the same conclusion.…”

“…Histological sections of oyster tissues contained cells of Perkinsus sp. with a vacuole occupying most of the internal volume of the cytoplasm, an eccentric nucleus and prominent nucleoli, as described by Sabry et al (2009Sabry et al ( , 2013 and Brandão et al (2013). These authors detected changes in oyster tissues and organs infected by Perkinsus sp.…”

“…In a discussion on the occurrence of false-negative PCR results in the detection of parasites in bivalves, Burreson (2008) reached the same conclusion. Other authors have reported discrepancies between RFTM and PCR results (Reece et al, 2008;Sabry et al, 2009), and other causes of sampling errors can compromising the accuracy of PCR assays, including the effects of focal or localized lesions (Burreson, 2008). Histological sections of oyster tissues contained cells of Perkinsus sp.…”

“…Since the first report of Perkinsus marinus infecting the American oyster Crassostrea virginica (Gmelin, 1791) in the Gulf of Mexico (Mackin et al, 1950), other species of the genus Perkinsus have been reported infecting several species of marine mollusks around the world (Lester and Davis, 1981;Azevedo, 1989;Blackbourn et al, 1998;Villalba et al, 2004;Choi and Park, 2010). In Brazil, Sabry et al (2009) recorded the first occurrence of Perkinsus sp. infecting natural populations of the oyster Crassostrea rhizophorae (Guilding, 1828) in the Pacoti river estuary (Ceará, Northeast Brazil).…”