Window of infection study

NSW DPIRD undertook research in Port Stephens over three oyster production seasons to determine the time of year when an oyster can become infected with Marteilia sydneyi due to suitable environmental conditions.

Naïve oysters (n = 30) were deployed every two weeks at the sites hardest hit by QX disease earlier in 2022, in Tilligerry Creek and the Karuah River. Oysters were maintained at these sites for a period of 6 weeks and then retrieved for testing. Testing was undertaken using a new real time polymerase chain reaction (PCR) tool for early M. sydneyi detection as well as cytology to look for sporulating QX disease.

Temperature and salinity measurements collected via dataloggers for each of the window of infection study sites are shown. Daily rainfall was also recorded from the nearest local weather station.

The permissive temperature for infection is believed to be 21.5°C (dashed lines). The orange arrows indicate the window of detection which is defined as the period of time when M. sydneyi is detectable in consecutive oyster batches, as shown through PCR. The red arrows indicate the window of infection which is defined as the period of time when consecutive oyster batches are cytology positive for M. sydneyi.

Decreases in salinity appeared to be important at the beginning of the window of infection, but not at the end of the window, which is consistent with the idea that low salinity impacts the immune status of the oyster rather than the infectivity of the parasite.

Site 1: Karuah River