Influenza A(H5N1) infection in mammals: Updated suspect case definition

25 March 2025

The suspect case definition for Influenza of avian origin in kept mammals (pets) has been updated. This is following the detection of influenza of avian origin confirmed in a sheep in England (Influenza of avian origin confirmed in a sheep in Yorkshire – GOV.UK). Updates to the suspect case definition and also, diagnostic testing criteria, highlights that this definition also applies to lactating animals, even if not in the commercial dairy sector.

The specific suspect case definition for pets relates to ‘suspect case definition 1’ as follows:

The animal is a domestic cat, dog or ferret presenting to a private veterinary surgeon and meets all of the following three criteria:

  1. It is (or had been prior to sudden death) exhibiting a combination of clinical signs which could be indicative of a viral infection as determined by a veterinary surgeon, including either:
  • Signs of respiratory disease or
  • Signs of neurological disease.
  1. Other common differential diagnoses have been considered and discounted as determined by a veterinary surgeon.
  2. The animal has either:
    1. Had confirmed or highly probable contact with an infected dead or sick wild bird;
    2. Been in close proximity to a wild bird mass die-off area within 3 weeks of developing its clinical signs;
    3. Been present on a dairy farm (dairy cattle, sheep or goats) where mammals fulfil case definition 3;
    4. Consumed raw milk or imported raw pet food containing poultry.

Confirmed or highly probable contact in this case relates to consumption, killing, or attacking a bird and may include being fed raw wild bird meat.

If you examine a kept or wild mammal or a test a sample from any kept or wild mammal and suspect or detect the presence of avian influenza virus or antibodies to avian influenza virus, you must report it immediately by calling:  03000 200 301 if you’re in England; 03003 038 268 if you’re in Wales; your local Field Services Office if you’re in Scotland. Please be aware that if you don’t report it, you’re breaking the law.

Access further information here: Influenza A (H5N1) infection in mammals: suspect case definition and diagnostic testing criteria – GOV.UK