What is it?
Bonamia exitiosa is a Haplosporidia protozoan parasite infecting haemocytes of several oyster species and
inducing physiological disorders and eventually death of the animal.
Where and when might it occur?
Infection with B. exitiosa is found in O. chilensis in the Foveaux Strait and other locations around South Island, New Zealand; in O. angasi in Australia (Port Philip Bay, Victoria; Georges Bay, Tasmania; and Albany, Western Australia); and in O. edulis in Galicia (Spain).
In O. chilensis, prevalence shows an annual pattern with two peaks reported in April (early autumn) and August (winter).
Clinical signs include dead or gaping oysters, but these clinical signs are not pathognomonic for infection with B. exitiosa and could be indicative of other infections.
Infection is often lethal. In O. chilensis, death usually occurs concurrently to the highest intensity infection level, particularly in association with high intensity apicomplexan infections. The disease seems to kill more than 80 percent of the oysters as the wave of infection passes through an oyster bed over a period of two to three years.
Control and treatment
There is no vaccine currently available.
Development of lighter dredges and less damaging fishing strategies should reduce the chance of disease outbreaks by lowering disturbance.
Avoiding stressors such as exposure to extreme temperatures (below 7˚C or above 26˚C) and salinity (40 percent), starvation, handling, or heavy infection with other parasites, as well as decreasing density, should help to reduce the impact of the disease.