Infection With Bonamia Exitiosa

The outbreak was triggered through a report of poor condition in oysters collected from that area rather than an associated mortality event.

The oysters were reported as weak, losing fluid and not closing. Of the 30 oysters sampled Bonamia like parasites were observed through histology in three of the animals.

nfection with species of Bonamia rarely results in clinical signs of disease in oysters. More often, the only visual cue is increased mortality.

Bonamia exitiosa infects blood cells, destroying the immune system and interfering with other critical physiological processes.

PCR and gene sequencing confirmed the histology findings as: 1) One case of Bonamia ostreae (already present and controlled in this area) 2) One case of Bonamia exitiosa 3) One case inconclusive.

It is unclear whether Bonamia exitiosa can be attributed as a causative agent for the poor health of the oysters. On 21 February 2011 IFREMER (EU-RL) confirmed B. exitiosa in one animal.

B. ostreae was already present in the area. After initial suspicion of the presence of B. exitiosa, movement controls have been applied to all mollusc species and the initial controls extend across the entire River Fal estuary.

The current designation prohibits all movements of molluscan shellfish into, out of or within the control area and stipulate that disposal of dead molluscs must be using an approved method for disposal of Category 2 animal-by-product waste.

This particular population of O. edulis may have been subject to stress due to dredging of the area in summer 2010 to manage a red algae problem. Epidemiological investigations are underway.