Trichinella in pig herds

Trichinella testing is a legal requirement for breeding herds – both boars and sows – and pigs that are raised in non-controlled housing. Find out more about preventing the disease and the testing requirements. 

What is trichinella?

Trichinella spiralis is a parasitic (nematode) worm which can infect a wide range of mammals (including humans) and some birds. The parasite is spread by the consumption of meat containing the immature (larval) stage of the worm. Natural infections are most likely in carnivores and omnivores, such as foxes, bears and rats, but infection also occurs in horses.

Trichinosis is one of the most widespread foodborne parasitic diseases and occurs in most countries of the European Union (EU). There have been no human cases acquired from meat produced in the UK for over 30 years. However, there have been occasional cases in the UK of people eating undercooked pig or horse meat sourced from abroad.

What are the clinical signs and how can it be prevented?

Animals infected with trichinella generally show no obvious signs of disease, unless the infestation is very severe. Please consult with your vet in the first instance.

To reduce trichinella infection, ensure there is secure feed storage and pest control in place. Find out more:

Biosecurity; limiting the spread of diseases

What are the trichinella testing requirements?

All pigs going to slaughter must be classified as being from either ‘controlled’ or ‘non-controlled’ housing.

The criteria for controlled housing is set out in EU legislation that defines controlled housing as “a type of animal husbandry where swine are kept at all times under conditions controlled by the food business operator with regard to feeding and housing”.

Where pigs have outdoor access, you must prove that this does not pose a danger of trichinella being introduced to the holding by completing a risk assessment.

For more information on testing, visit the FSA website.

The table below provides some guidance while waiting for the publication of the FSA guidance. It does not replace the FSA’s risk assessment.

The definitions of the production systems aim to help you identify whether you could consider applying controlled-housing conditions.

Production system 1   Definition of production system Subject to meeting the requirement and pending FSA’s risk assessment tool, the view is that the following production systems are very likely to fall under controlled housing

Fully housed

These pigs are born, reared and finished indoors Yes

Outdoor bred 

These pigs are born outside in fields, where they are kept until weaning Yes

Outdoor reared

These pigs are born outside in fields, where they are reared for approximately half their life (defined as at least 30 kg) Likely
Free-range and organic pigs2 

These pigs are born outside in fields and remain outside until they are sent for processing


(this does not rule out that free range could not come under controlled housing conditions)

1 Definitions from:

2 The key difference with organic pigs is that the use of pharmaceuticals is heavily restricted

Risks to be managed (controlled housing)

  • All practical precautions regarding building construction and maintenance, in order to prevent rodents, any other kind of mammals and carnivorous birds from having access to buildings where animals are kept
  • Pest-control programme in place, particularly for rodents, to prevent infestation. Records of the programme must be kept
  • All feed to be obtained from a legitimate facility. Feed must be stored in closed silos or other containers that are impenetrable to rodents
  • Feed supplies must be heat-treated or produced and stored adequately
  • Dead animals are collected, identified and transported without undue delay
  • If a rubbish dump is in the neighbourhood of the holding, the operator must inform the competent authority. Subsequently, the competent authority must assess the risks involved and decide whether the holding is to be recognised as applying controlled-housing conditions
  • Piglets coming onto the holding from outside and pigs purchased are born and bred under controlled-housing conditions
  • Traceability of pigs at all times.

New animals may be introduced onto a holding if they come from holdings also officially recognised as applying controlled-housing conditions.