A highly infectious strain of avian influenza virus (H5N1) has caused multiple outbreaks in domestic poultry and wild birds across Scotland, in other parts of the UK, and internationally. Symptoms vary between bird species, but the infection can cause severe disease and can cause high mortality rates.
The risk to human health is currently very low, and to date, there has been no poultry farm-to-farm spread in the UK this season. Control measures and biosecurity guidance remain in force and must be followed by humans who keep poultry or have close contact with sick or dead birds.
Avian influenza (bird flu) is a viral disease, and the high pathogenic strains can cause severe disease or death in some poultry and wild bird species. As a Notifiable Animal Disease, it must be reported immediately to authorities.
The highly pathogenic virus strain (H5N1) that has been circulating in birds across Europe, Asia, Africa, and North America has been unusually widespread and severe this year, with the outbreak occurring over a lot longer period than usually expected with increased numbers of cases observed in both domestic and wild bird populations. Since October 2021, thousands of outbreaks across the globe have been detected. According to the European Food Safety Authority, 2,398 outbreaks in poultry, 46 million birds culled to curb the spread of the virus, and around 2,733 HPAI events in wild birds have been detected in Europe alone (as of June 30, 2022).
With so many outbreaks occurring in both wild and domesticated birds, the spread of this highly pathogenic strain is raising concerns. Above the usual measures put in place for the prevention, surveillance, and reporting of avian influenza, additional investigations are being conducted in wild and domestic bird populations to identify why this outbreak has been more severe than previous outbreaks.
HUMAN HEALTH IMPLICATIONS
The risk to human health from the virus is currently very low. Birds are the natural hosts for avian influenza viruses therefore infections in humans are uncommon. However, avian influenza viruses may occasionally infect humans: two human cases have been reported since October 2021, one in the United Kingdom and one in the United States. Although evidence of infection was found, there were minimal or no associated illness symptoms.
Those who have close contact with sick birds are at risk of infection with bird flu and should follow public health guidance.
AVIAN INFLUENZA VIRUSES
Influenza viruses are RNA viruses that evolve rapidly, hence the existence of various subtypes and strains. They can affect birds, humans/swine, or other mammals. However, it is rare for strains of avian flu to be transmitted to mammals from birds.
For instance, circulating human seasonal influenza virus strains include two types A’s (H3N2 and H1N1) and type B whereas the circulating strains of avian influenza (bird flu) are predominantly other type A subtypes.
Influenza viruses have two types of surface proteins: Hemagglutinin and Neuraminidase. The current avian influenza H5N1 strain has Hemagglutinin subtype 5 and Neuraminidase subtype 1.
The majority of known subtypes of avian influenza (H1-H16 + N1-N9) are of low pathogenicity to birds. However, a few of these subtypes, specifically those with surface protein Hemagglutinin H5 or H7, can carry a mutation making the strain highly pathogenic to chickens. These so-called ‘high pathogenic’ strains can lead to up to 100% mortality in a chicken's flock within a few days of infection. However, the same strains may be of low clinical impact in other species so facilitating silent spread (e.g. in ducks and geese).
AVIAN INFLUENZA ORIGINS AND SPREAD
The highly pathogenic H5N1 strain emerged in East Asia several years ago, and from the same lineage, it has continued to spread and evolve in poultry and wild birds. It caused the 2014/2015 H5N8 outbreaks in Europe, Asia, and North America, the 2016/2017 H5N8 outbreaks in Europe and Asia, and the 2020/21 H5N8/H5N1 outbreaks.
The current 2021/22 season highly pathogenic avian influenza strain detected is known as H5NX (specifically clade 22.214.171.124.b). It is called H5NX because it has been swapping its N (Neuraminidase) for other N-subtypes from circulating low pathogenicity strains over the past few years.
This highly pathogenic virus strain has been detected in birds across Europe, Asia, Africa and North America. The hypothesis is that wild bird flyways are contributing to the spread between countries and continents. In fact, the viruses are carried inside the birds’ intestines and are distributed into the environment via bird droppings. There is no evidence that farmed poultry and domestic poultry are driving this current wild bird epidemic.
Some wild bird populations are affected more severely than others, such as barnacle geese (Branta leucopsis) on the Solway Firth in 2021 and the Dalmatian pelicans (Pelecanus crispus) in Greece in early 2022. In Scotland, the main conservation concern is currently for wild great skuas (Stercorarius skua) and northern gannets (Morus bassanus). These seabirds are suffering high mortality at the breeding colonies this year, which is of serious concern because Scotland holds around 60% of the global population of great skuas and around 50% of the global population of northern gannets.
In the wider UK, the strain has caused multiple outbreaks across wild bird species. Migrating wild birds are a probable vector for the spread of avian influenza, with multiple transmission cases to domestic poultry. Thanks to the control measures, to date there has been no farm-to-farm spread in the UK this season
CLINICAL SIGNS: SYMPTOMS AND DIAGNOSIS
Whilst low pathogenic avian influenza (LPAI) is milder, high pathogenicity avian influenza (HPAI) can cause severe disease or be fatal in birds. Clinical signs vary between species of birds but include: sudden death, swollen head, tremors and incoordination, lethargy, blue discoloration of comb and wattles, loss of appetite, respiratory distress, diarrhoea and decrease in egg production.
PREVENTION, SURVEILLANCE AND REPORTING: HOW TO CONTROL AVIAN INFLUENZA
Humans who keep poultry should follow the public health guidance on biosecurity best practices. Those who have 50 or more birds are legally required to register their poultry. All keepers of poultry are encouraged to register their birds so that they receive disease updates rapidly. To minimise disease spread, keep a close watch on poultry for any signs of disease and seek advice from vets. A sudden and rapid increase in the number of birds found dead may indicate an avian influenza infection. To stop the spread of highly pathogenic avian influenza, infected domestic bird populations are culled. Vaccination of poultry against avian influenza is not currently a routine control measure in the UK.
Avian Influenza Prevention Zone (AIPZ) which had been in force across Great Britain since the start of the outbreak in Autumn 2021 was lifted on the 16th August 2022. Bird keepers are encouraged to continue with measures to limit the spread of the disease include appropriate cleansing and disinfection of equipment, clothing and housing, movement restrictions and prevention of poultry to wild bird contact (such as protection of food and bedding stores and making sure that housing is secure against birds and vermin).
Disease control zones including buffer zones around detected cases remain in place across the country as new cases are identified with movement restrictions to minimise disease spread.
Follow the latest updates and find details of current outbreaks and measures in place to prevent the spread of the disease on the government website.
Against a backdrop of an increased risk that wild birds may be arriving in the UK carrying influenza, there are two main reasons for small-scale backyard keepers being asked to house their birds. Housing your birds minimises the risk of your birds coming into contact with infected wild birds or their faeces and so minimises the health risks to your birds. There is also a risk that if your birds become infected then the virus will multiply in your birds and, in the period before the disease is detected, you may unwittingly spread the disease to other domestic birds and in particular other, poultry flocks. So housing is a way to protect your birds and the birds owned by others.
In the UK in recent years there have been a number of outbreaks of AI in commercial flocks associated with exposure to wild birds. Water fowl can carry the disease without showing clinical signs: these birds in particular migrate west from AI hotspots on mainland Europe and beyond, so the risk to birds in the UK increases. Wild birds in which AI has been detected include: Tufted Ducks, Common Pochards, mute swans and various gulls as well as other waterfowl, such as grebes, curlews, herons and coots and some raptor species.
It is recognised that keepers of some small flocks may not be able to house their birds indoors without putting the health and welfare of their birds at risk. Under these circumstances there is a requirement to do what is practicable to minimise the risk to your birds and to those of others. You should consider if you can take steps to keep them separate from wild birds, such as: feeding and watering birds inside, making sure feed stores are protected against wild birds or vermin and removing any wild-bird attractants (removing feeders or filling in puddles) from the area around your birds.
Whether or not you are able to house your birds, you and anyone else in contact with your birds should avoid contact with all other poultry as far as possible.
Poultry like a routine and backyard poultry are used to being able to scavenge for food. Being able to roam means that they can also control their environment, they can avoid, for example getting too hot by moving into shade. If you house your birds, you prevent them scavenging for food, limit their space and their ability to control their temperature. All of these changes can increase stress and lead to undesirable behaviours such as feather pecking and cannibalism. To minimise the risk of stress you need to:
Provide your birds with sufficient food in a sheltered area to prevent attracting wild birds - they will probably eat more than you are used to because they will not be supplementing their diet with vegetation, insects, worms etc that they may eat normally;
Ensure your birds have access to adequate supplies of clean water which cannot be accessed by wild birds– birds will drink up to twice what they will eat.
Provide as much space as possible for your birds. A good way of doing this is to provide sufficient perch space for all of your birds. Properly designed perches enable subservient birds to get away from dominant birds during the day – when on a perch a bird’s ‘flock size’ reduces to three, itself and up to two neighbours. At night birds will want to perch - their feet are designed to lock automatically onto a perch while they sleep – as this is deeply ingrained predator avoidance response. At night you will find the most dominant birds on the highest perches.
Poultry are inquisitive – they need things to occupy them. Normally this need would be fulfilled by ranging around their territory but it your birds are constrained to a small run then you need to think of other things to keep them occupied. There are lots of ways that this can be done but giving the birds something to work at underpins most of them. So for example, put some of their food onto the litter that you should have on the floor of the house – this will encourage them to scavenge in the litter looking for food. Provide greens (cabbages suspended off the floor for example), for the birds to peck at. A full or part bale of straw or hay will give birds something to explore. Always check that anything you are introducing to your housed area hasn’t been in contact with wild birds or their faeces.
Dust bathing is important for the physiological and physiological health of your poultry – provide suitable space and material of dry material for this (e.g. wood shavings, sand or sawdust).
The environment that your birds experience is crucial to their wellbeing. If housed then there is a risk from poor air quality and high temperatures, even in the winter months. Birds are warm blooded animals and produce a considerable amount of heat from the food they consume. In cold weather birds flock together – birds should not be kept on their own - and providing they are not exposed to draughts, even at sub-zero temperatures can keep each other warm. The biggest risk in the UK is overheating – birds are not able to lose heat very efficiently. If the housing is small and poorly ventilated then heat build-up can be a problem. An air temperature of 21oC or below is what you should aim for – an inexpensive maximum/minimum thermometer placed at bird level will enable you to monitor air temperature. You should not be unduly concerned about low temperatures, providing your birds are kept dry and draught free, but high temperatures can be lethal. Do not allow the ammonia concentration to build-up – more frequent than normal replacement of litter material may be required.
If you are struggling to house your birds without a significant risk to their health and welfare, you should discuss this with your local veterinarian and agree preventative steps that you can take to keep them separate from wild birds.
AI strains can be either low or high pathogenicity (ability to cause disease) with low pathogenicity strains having the ability to mutate into high pathogenicity strains. Birds infected by low pathogenicity strains may show no obvious signs of infection or may have mild breathing problems (although a number of conditions can cause this). In contrast high pathogenicity strains can cause sudden and widespread mortality. Birds that have not died may show signs that include: swollen head; blue discoloration of neck and throat; loss of appetite; respiratory distress such as gaping beak; coughing, sneezing or gurgling; diarrhoea and a drop in egg production.
It should be noted that some species of bird (such as ducks, geese and pigeons) display few or no clinical signs of avian influenza (AI).
If you are concerned about the health of your birds, contact your private veterinarian and if you suspect your birds have AI you must contact your local APHA Office.