Guidance

Bonamia ostreae

Published 22 March 2024

Applies to England and Wales

1. Contents 

Bonamia ostreae is a protozoan parasite infecting oyster species including the native (or flat) oyster (Ostrea edulis).  

Information on susceptible and vector species can be found here: GB Lists of susceptible and vector species. 

Great Britain is free from Bonamia ostreae except in infected zones where the parasite is present in oysters (known as Confirmed designation areas) and which are under disease controls to contain and prevent further spread, more information can be found here: Listed diseases of fish, molluscs and crustacea and their status - GOV.UK (www.gov.uk).  

It is a ‘Listed’ (also referred to as ‘notifiable’) disease which you are legally obligated to report immediately to the Fish Health Inspectorate (FHI), Cefas Fish Health Inspectorate - GOV.UK (www.gov.uk) 

It does not affect humans. 

2. How to spot Bonamia ostreae 

Infections are most likely to been seen from autumn and peaking in the winter and early spring. 

Signs of the disease can include: 

• Increase of dead / empty shells 
• Gaping shells which don’t close when touched or when exposed to air 
• Weak 

3. How Bonamia ostreae is spread 

Bonamia ostreae is spread through movements of and contact with infected shellfish and contact with contaminated equipment or water. The parasite may be spread directly between infected animals, and infected planktonic shellfish larvae may also contribute to the spread of the parasite.    

4. Preventing and controlling Bonamia ostreae  

There is no treatment for Bonamia ostreae. 

Prevention is the best approach to disease control. You can protect your shellfish by being aware of the signs of Bonamia ostreae and other serious diseases and checking stock health regularly. Implement good husbandry and biosecurity practises.  

Further information on biosecurity measures plans, guidance and templates can be found here: Biosecurity Measure Plans - Information and Templates - GOV.UK (www.gov.uk) 

You must be sure any shellfish introduced into disease free areas are Bonamia ostreae free. Do not buy shellfish of unknown origin. Follow the rules on moving aquatic animals: Aquatic animal health and movements guides - GOV.UK (www.gov.uk) 

You must report it to the FHI immediately if you notice or become aware of shellfish showing any of the signs of Bonamia ostreae, particularly increased mortality and gaping shells. The FHI will investigate and if required will apply disease control measures.    

5. Further information on Bonamia ostreae 

World Organisation for Animal Health (WOAH) Aquatic Manual chapter Bonamia ostreae.  

6. Legislation relating to Bonamia ostreae 

The Aquatic Animal Health (England and Wales) Regulations 2009  

The listed diseases are in Regulation 1251/2008 as amended by the Animals, Aquatic Animal Health, Invasive Alien Species, Plant Propagating Material and Seeds (Amendment) (EU Exit) Regulations 2020, at Chapter 2, Annex 1A and Schedule 1 of The Aquatic Animal Health (England and Wales) Regulations 2009. 

7. Who to contact if you suspect Bonamia ostreae  

If you suspect or know of a listed disease of fish and shellfish in England and Wales, you must report it immediately to the Fish Health Inspectorate (FHI), Cefas. You must also tell the FHI immediately if you know or suspect that increased mortality has occurred.  

Under the Aquatic Animal Health (England and Wales) Regulations 2009 it is a legal obligation to report suspicion of Bonamia ostreae in any farmed or wild shellfish to the FHI. It is an offence under the Regulations to fail to inform the FHI of suspicion of Bonamia ostreae. 

• Email: fhi@cefas.gov.uk 
• Telephone: 01305 206700 - Monday to Thursday - 9:00 am to 5:00 pm, Friday 9:00 am to 4:30 pm 
• For emergencies out of hours telephone: 01305 206630 

Fish Health Inspectorate
Centre for Environment, Fisheries and Aquaculture Science (Cefas)
Barrack Road, The Nothe
Weymouth
Dorset
DT4 8UB