Effects of temperature and salinity on the survival of Bonamia ostreae, a parasite infecting flat oysters Ostrea edulis

Abstract

Bonamiosis due to the intrahaemocytic protistan parasite Bonamia ostreae is a European endemic disease affecting the flat oyster Ostrea edulis. The parasite has been described in various ecosystems from estuaries to open sea, but no clear correlation has yet been demonstrated between disease development and environmental parameters. In this study, the effect of temperature and salinity on the survival of purified parasites maintained in vitro in seawater was investigated by flow cytometry. Purified parasites were incubated in various seawater media (artificial seawater, natural seawater, seabed borewater) at various temperatures (4, 15 and 25°C) and subjected to a range of salinities from 5 to 45 g l -1. Parasites were collected after 12, 24 and 48 h of incubation for flow cytometry analyses including estimation of parasite mortality and parasite viability through detection of non-specific esterase activities. Artificial seawater appeared unsuitable for parasite survival, and results for all media showed a significantly lower survival at 25°C compared to 4°C and 15°C. Moreover, high salinities (≥35 g l -1) favoured parasite survival and detection of esterase activities. Flow cytometry appears to be a suitable technique to investigate survival and activities of unicellular parasites like B. ostreae under varied conditions. Although these results contribute to a better understanding of existing interactions between the parasite B. ostreae and its environment, validation through epidemiological surveys in the field is also needed.

Effect of environmental factors on survival and growth of quahog parasite unknown (QPX) in vitro

“…Cold temperatures could decrease the metabolic rates of QPX and therefore delay mortality of the parasite in nutrient-poor seawater whereas in nutrient-rich standard culture medium, higher temperature (23°C) might stimulate parasite's metabolism and growth rates. Similar contradictions were observed between the in vivo and the in vitro performances of the oyster pathogen Bonamia ostreae (Arzul et al, 2009). In that study, the survival of the parasite was higher at low temperature whereas in vivo studies highlighted the importance of warm temperature on seasonal parasite cycling (Carnegie et al, 2008).…”

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

“…Bonamia is directly transmissible between oysters (Elston et al 1987), but an exclusively direct life cycle has not yet been confirmed. Other possible transmission pathways appear more restricted: infective stages are short-lived and appear to be carried passively by water currents (Cranfield et al 2005) or even by oyster larvae (Arzul et al 2009), where they may remain viable in the water column for, at the most, a week (Hollis 1962, Arzul et al 2009), which seems insufficient to explain B. ostreae's arrival in New Zealand. Transmission via other, more resistant, water-borne stages seems unlikely since within the genus Bonamia (with the exception of B. perspora) there is currently no molecular or histological evidence for spore formation .…”

Detection of Bonamia ostreae and B. exitiosa (Haplosporidia) in Ostrea edulis from the Adriatic Sea (Italy)

“…; Bonamia ostreae has been present in Quiberon Bay since 1980, with prevalence usually lower than 0.15% (Arzul et al 2005). A recent study on the influence of environmental factors showed a better survival of purified B. ostreae in hyper-saline (> 35 g l -1…”