Guidance

Perkinsus marinus

Updated 11 September 2024

Applies to England and Wales

1. Contents 

Perkinsus marinus is a protozoan parasite infecting Pacific oysters (Magallana [Syn. Crassostrea] gigas) and Eastern oysters (Crassostrea virginica). All life stages are affected. 

Information on susceptible and vector species can be found here: Susceptible and vector species - GOV.UK (www.gov.uk)

Great Britain is free from Perkinsus marinus, and 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) 

There has never been a recorded outbreak of Perkinsus marinus in the UK. 

It does not affect humans. 

2. How to spot Perkinsus marinus 

Signs of the disease can include: 

• Increase of dead and empty shells 
• Gaping shells which don’t close when touched or when exposed to air 
• Thin, watery body  

3. How Perkinsus marinus is spread 

Perkinsus marinus is spread through movements of and contact with infected shellfish and contact with contaminated equipment or water. Transmission is direct between infected animals; parasite life stages are released into the water from the excreted waste of infected animals or when they die and taken up through filter feeding mechanisms. 

4. Preventing and controlling Perkinsus marinus  

There is no treatment for Perkinsus marinus. 

Prevention is the best approach to disease control. You can protect your shellfish by being aware of the signs of Perkinsus marinus 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 are Perkinsus marinus 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 Perkinsus marinus, particularly increased mortality and gaping shells. The FHI will investigate and if required apply disease control measures.   

5. Further information on Perkinsus marinus 

World Organisation for Animal Health (WOAH) Aquatic Manual chapter Perkinsus marinus. 

6. Legislation relating to Perkinsus marinus 

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 Perkinsus marinus  

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 Perkinsus marinus 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 Perkinsus marinus. 

• 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