Elucidating the life cycle of Marteilia sydneyi, the aetiological agent of QX disease in the Sydney rock oyster (Saccostrea glomerata)

Marteilia spp. parasites in bivalves: A revision of recent studies

“…Studies demonstrated that sporonts are viable for less than two hours if ingested by fish or birds (Roubal et al, 1989) and survive for 9 days in seawater (Wesche et al, 1999). Adlard and Nolan (2015) sampled the macrobenthos of the Hawkesbury River, New South Wales (Australia) and found two different developmental stages of M. sydneyi present in the polychaete worm, Nephtys australiensis, corroborated by qPCR and in-situ hybridization. A primordial cell with a well defined nucleus and little differentiation in the cytoplasm, similar to Carrasco et al (2008) for M. refringens in A. grani, and plasmodial cells with syncytial structure resembling the "thin" stages described by Boyer et al (2013).…”

“…have been observed in different invertebrate hosts in a wide range of geographical locations including Europe, Oceania, Asia and Africa, but with only a single report from the Americas (Grizel et al, 1974;Perking and Wolf, 1976;Comps et al, 1986;Moyer et al, 1993;Elgharsalli et al, 2013;Audemard et al, 2002;Adlard and Nolan, 2015) (Figure 2; Table 1). …”

“…number of zooplanktonic species, including Acartia grani and A. latisetosa, which could potentially act as an alternative host in the life cycle of M. refringens (Audemard Carrasco et al, 2007a, b;Boyer et al, 2013;Arzul et al, 2014). Similarly, the polychaete Nephtys australiensis is being studied as a potential alternative host in the life cycle of M. sydneyi (Adlard and Nolan, 2015). Even with recent advances, many knowledge gaps remain regarding the complex life cycles and transmission of these parasites.…”

“…The PCR assay could detect the DNA equivalent of 0.01 sporonts following agarose gel electrophoresis and the in-situ DNA probe could detect 10 pg of M. sydneyi DNA in a dot-blot assay(Kleemand & Adlard, 2000). These molecular tools were primarily developed to assist in identifying different life stages of M. sydneyi within S. glomerata(Kleeman et al, 2002a) and for alternative host of M. sydneyi(Adlard & Nolan, 2015). Nevertheless, histology and cytology are still routinely used to diagnose farm mortalities of Sydney rock oysters with QX disease.5.1.3.…”

Infectious diseases of marine molluscs and host responses as revealed by genomic tools

“…Marteilia refringens is now found in Europe from Sweden and Britain in the north to Greece and Croatia in the Mediterranean [18] and in Australia, M. sydneyi is now found over 900 km south of where it was first reported [23]. The spread is thought to have occurred via the commercial movements of stocks among growers in different regions; however, neither pathogen is directly transmitted among oysters and potential alternative hosts have been described [19,24], although a complete life cycle has not yet been elucidated. Thus, an alternative host would have had to be already present in the new locations or moved along with the oysters.…”