Detection of Bonamia exitiosa (Haplosporidia) in European flat oysters Ostrea edulis cultivated in mainland Britain

Abstract

Following a reported mortality event of European flat oysters Ostrea edulis in southwestern England in December 2010, a sample of 30 oysters was examined using histology and molecular techniques. Histological examination of the oysters revealed the presence of microcell stages in the haemocytes and connective tissues of 3 out of the 30 animals examined. One animal showing marked haemocyte infiltration of the connective tissues was considered to be infected with Bonamia ostreae based on the presence of small uninucleate microcells measuring approximately 1 to 1.5 µm in diameter. Two other oysters were considered by histology to be infected with B. exitiosa. Infected haemocytes contained up to 5 microcells, measuring approximately 2 to 3 µm in diameter with a central or subcentral nucleus. Rarely, larger plasmodia-like multinucleated stages were noted in the haemocyte cytoplasm characterised by its irregular shape and increased eosinophilic cytoplasm. Haemocyte infiltration of the connective tissues surrounding the digestive gland and the mantle was noted along with necrosis of the tissues associated with the infection. Molecular analysis of the infected animals confirmed the presence of B. exitiosa in the sample. This study describes the parasite from flat oysters cultured in the UK; subsequent targeted sampling has not detected the parasite in flat oyster populations at this or other sites within the UK.

Microbial Diseases of Bivalve Mollusks: Infections, Immunology and Antimicrobial Defense

“…Since 2003, the parasite has been observed in both the Atlantic and Pacific coasts of the USA [49], including California [50]; B. exitiosa was also detected in O. edulis from the Galician coast (Spain) and the Manfredonia Gulf, Italy (Adriatic Sea), including concurrent infections with B. ostreae [51] and in Ostrea stentina in Tunisia [52]. B. exitiosa was found, as well, on the Spanish Mediterranean coast [53], in southwestern England [54] and in southern Portugal [55]. Others species, Bonamia perspora and Bonamia roughleyi , have been found on the east coast of the USA [56] and in southeastern Australia [57].…”

Bonamia ostreae in the New Zealand oyster Ostrea chilensis: a new host and geographic record for this haplosporidian parasite

“…However, the discovery of a Bonamia-like parasite in Crassostrea ariakensis in North Carolina, USA (Burreson et al 2004), and the description of another parasite as B. perspora from O. stentina from the same area , in combination with the discovery of B. exitiosa and B. exitiosa-like parasites in O. stentina from the Mediterranean (Hill et al 2010), O. chilensis from Chile (Campalans et al 2000, Lohrmann et al 2009, O. puelchana from Argentina (Kroeck & Montes 2005), O. angasi from Australia, and O. edulis from Europe (Abollo et al 2008, Longshaw et al 2013) have initiated a change in perception of the distribution of Bonamia (Engelsma et al 2014). Some Bonamia species are now reported with overlapping geographic ranges (Abollo et al 2008, Narcisi et al 2010, Carrasco et al 2012, Longshaw et al 2013) and in one case to the point of a concurrent infection of B. exitiosa and B. ostreae within the same O. edulis host (Abollo et al 2008).…”

Moving from Histopathology to Molecular Tools in the Diagnosis of Molluscs Diseases of Concern under EU Legislation

“…However, molecular analyses have led to detection of B. exitiosa naturally infecting the European flat oyster O. edulis in Galician (NW Spain) coastal waters (Abollo et al, 2008) for the first time. Since this detection, the parasite has also been reported from different European countries infecting O. edulis (Narcisi et al, 2010; Arzul et al, 2012; Carrasco et al, 2012a; Longshaw et al, 2013; Batista et al, 2016). …”