Temperature influence on pathogen transmission and subsequent mortalities in juvenile Pacific oysters Crassostrea gigas

Abstract

International audienceSince 2008, mass mortalities of 1-yr-old Crassostrea gigas associated with the ostreid herpesvirus OsHV-1 μVar have occurred along all the coasts of France when seawater temperature reaches 16 to 17°C. The present study aimed to characterize the effect of temperature on oyster survival in combination with OsHV-1 DNA quantification by standard real-time PCR and total vibrio population levels in oyster tissues. To examine the effect of seawater temperature on disease transmission and related mortality of oysters, cohabitation experiments were conducted between healthy naïve oysters and oysters previously exposed to field conditions in areas where mortalities were occurring. Oysters initially maintained in controlled conditions (free of mortality and negative for OsHV-1), and then transferred to an area where high mortalities were occurring among farmed stocks, became infected with OsHV-1 and exhibited high loads of vibrios followed by significant mortalities. When previously exposed oysters were maintained indoors at 13.0°C for 40 d and then at 20.6°C, they exhibited no mortality, were negative for OsHV-1 detection, and did not transmit the disease to healthy oysters. Survival of previously exposed oysters maintained indoors at 8 temperatures ranging from 13.4 to 29.0°C varied from 25 to 48% and was negatively correlated with holding temperature. Concomitantly, survival of naïve cohabiting animals (62 to 98%) decreased with increasing seawater temperature until a plateau was reached between 16.2 and 21.9°C, and increased at higher temperatures. Therefore, the optimal temperature range for disease transmission from field-exposed to naïve animals was between 16.2 and 21.9°C. Our results suggest that a long-term period (40 d) at low temperature (13°C) may offer a method of mitigating mortalities in oysters that have been exposed to an infective environment

Salinity influences disease-induced mortality of the oyster Crassostrea gigas and infectivity of the ostreid herpesvirus 1 (OsHV-1)

“…After a week of exposure to field conditions, few dead oysters were observed, and the remaining live individuals were moved back to the Ifremer facilities in Argenton. These oysters tested positive for the OsHV-1 μVar strain, and the level of virus DNA was 1.9 × 10 9 ± 1.6 ×10 9 copies mg −1 fresh weight (mean ± SD; n = 3 pools of 15 oysters); they were therefore considered useful as OsHV-1 donors and placed in 45 l flow-through tanks at 35 ‰ and 21°C (Petton et al 2013). The seawater surrounding the donors was used as the SI.…”

“…Alive recipient oysters (15 for Expts 1 and 10 for Expt 2) were sampled in each tank on Days 0, 2 and 4 before the onset of mortality (Petton et al 2013(Petton et al , 2015a. Whole tissues were removed from the shells, pooled together, flash frozen in liquid nitrogen and stored at −80°C.…”

“…The SI was then (1) directed towards recipient oysters held at 4 salinities with or without prior acclimation or (2) brought to a salinity of 10 or 25 ‰ and directed towards recipient oysters maintained at 25 ‰. Overall, this method, which has been used in many previous studies (Petton et al 2013, 2015a,b, Tamayo et al 2014, Lassudrie et al 2015, Lemire et al 2015, Pernet et al 2015, reproduces the natural infection process and takes into account the fact that OsHV-1 triggers oyster mortality, although other microorganisms can also play a role (Saulnier et al 2010, Lemire et al 2015, Petton et al 2015b.…”

Antiviral immunity in marine molluscs

“…Water temperature is also a factor in the expression of disease caused by OsHV-1 infection. The water temperatures must exceed 16 uC for OsHV-1 to cause mortality of juvenile Crassostrea gigas (Petton et al, 2013) and mortality of Chlamys farreri to AVNV occurs in late summer (Fu et al, 2005). It is unknown how host physiology and the environment influences disease expression of abalone to AbHV.…”

Pacific oyster mortality syndrome: a marine herpesvirus active in Australia

“…POMS occurs in Sydney estuaries when water temperature is~22À268C 1,2 ; this is~5 o C higher than in France 19,20 . An experimental infection model has been developed and used in Australia to confirm these field observations on water temperature; it revealed an important interaction between water temperature and infectious dose 21,22 .…”