Richard Jackson BVMS (Hons) MRCVS, St David’s Poultry Team
The winter of 2020/2021 was the worst on record for AI in Europe and the UK with most cases being the Highly Pathogenic Avian Influenza (HPAI) H5N8 strain. Whilst the broiler sector has generally been less affected than other parts of the poultry industry, AI still poses considerable risks both directly and indirectly to the sector.
AI is carried by wild birds (often without making them ill) and typically makes its way around the globe through migratory birds e.g., the pink footed goose. These birds come to our shores in autumn and can infect our native birds (such as mute swans) and potentially our poultry. Most of our migratory birds come from Russia and Kazakhstan, with a minority coming from Africa and Canada. Each strain of AI varies in terms of the species of bird it can affect, along with the severity of infection.
AI is characterised in two ways. Firstly, each strain has a H number and a N number e.g., H5N8. There are lots of different combinations of H and N numbers giving rise to many different strains. For any strains with a H number of 5 or 7 they can be either highly pathogenic AI (HPAI) or low pathogenic AI (LPAI). For strains with all other H numbers, they are always LPAI. Even within a given H and N combination such as H5N8 the individual strain can vary considerably. In 2016/17 we had H5N8 as with 2020/21. However, the H5N8 in 2020/21 was considerably more harmful to poultry than the 2016/17 version.
AI can have an incubation of up to 14 days and as such our short-lived broilers may not have enough time between infection and processing to show clinical signs. Our free range and organic broilers are more at risk due to a high kill age and the fact that they are free ranging. However, many broilers grown for the independent market can live for up to 50 days and as such are at greater risk of developing AI. In 2019, the Belgian poultry sector was hit by H3N1 low pathogenic AI that affected broiler flocks illustrating that broilers are not immune from AI.
There are several potential routes for AI to enter a shed. The most common route is through water ingress (either via leaking rooves or water coming in through leaks in the floor). Contaminated bales can also be a route for incursion. It goes without saying ensuring that PPE is worn by everyone entering the sheds along with having covered foot dips that are replaced twice per week is a must.
Clinical signs of AI include:
- Raised mortality
- Head shaking/sneezing
- Nervous signs
- Swollen heads/blue coloured heads
- Drop in water intake
- Enteritis
Where AI is suspected it is a legal requirement for the farmer/their private vet to notify APHA. They will discuss the case over the phone and will possibly visit the farm to inspect the flock if they think there is a risk of AI. When APHA visit, they may negate AI after examining the birds or they may decide to sample the flock. If the flock are sampled APHA will place restrictions on the farm meaning that a license will be needed to move feed onto the site and a license will be needed for people to enter/leave the farm until the results are known. The birds (including dead birds) will not be permitted to leave the farm without having the test results.
If the results are negative for AI then the restrictions are lifted and other potential causes will need to be looked at with your private vet.
If low pathogenic AI is confirmed the APHA will declare a 1KM zone and technically the birds can go into the food chain, however, most producers/companies choose to depopulate the flock on site to reduce the chances of the LPAI spreading to other sites.
If HPAI is detected then APHA will depopulate the birds on site, remove the litter and will carry out the primary wash and disinfection. APHA will examine the visitors records closely and will contact any people they deem to be at risk of having moved AI from the infected farm to another site.
The farmer then has 2 options:
- Sign a document to say that the farm will not be repopulated for the next 12 months
- Carry out secondary cleaning and disinfection to APHA’s satisfaction
As soon as HPAI is confirmed, APHA declare two zones around the affected site. A 3KM Protection Zone and a 10KM Surveillance zone. Unfortunately for farms in these zones, licenses will be needed to move birds, fallen stock and feed onto and off their farms.
Birds from the 10KM zone can go to an abattoir for processing but with birds from within the 3KM zone, whilst abattoirs can process them, many retailers will not take the chickens as they need to have a special label placed on the chicken in the supermarket. If an abattoir or hatchery finds themselves in the zones, then licenses will be needed for birds moving between them and the farms. Where farms or abattoirs are in the 10KM zone, no chicken from them can be exported (including to NI) for 90 days!
Currently, for farms within the 10KM zone, a license can be applied for to move day old chicks (or hatching eggs at 18 days of incubation) onto the farm. However, there are new EU regulations that will prohibit the restocking of farms in the 10KM zone until the zone is revoked. It is unclear currently whether the EU will mandate that the UK writes this into UK law to facilitate trade with the EU. Were this to happen it would be devastating to farms that were unlucky enough to find themselves within the zone and it would have a massive impact on the hatchery trying to find homes for the chicks.
Revocation of the Zones
The protection zone will last for at least 21 days from the primary cleaning and disinfection of the infected site at which point it will be merged into the surveillance zone. The surveillance zone will last a minimum of 30 days from the primary cleaning and disinfection of the infected premises. During that time APHA will carry out extra checks on flocks within the zones to ensure there are no cases starting.
When AI is found in the UK restrictions on the trade of poultry meat and day-old chicks are imposed by other countries. The UK can declare itself as AI free 28 days from the secondary cleaning and disinfection of the last infected premises. On the 3rd of September 2021 the UK declared itself as AI free following the outbreak of winter 2020/2021.
Take Home Messages
- Broilers are not immune against AI
- Ensure sheds are well maintained (prevent leaking water or wate ingress through the floor
- Ensure bedding is stored in a biosecure manner
- Ensure covered foot dips are present containing a DEFRA approved disinfectant and are changed twice per week
- Ensure site dedicated boots and PPE are present
- Train all staff (including parttime staff) on the importance of biosecurity