Avian Influenza Questions and Answers

Avian influenza is a disease of animals caused by influenza A viruses.  Avian influenza viruses are normally only found in birds, but may affect pigs and have been known to infect sea mammals, mink, horses and other mammals.  On rare occasions some types of avian influenza viruses have infected humans.

Avian Influenza viruses can be classified according to their ability to cause severe disease (pathogenicity) as either highly pathogenic or low pathogenic. Highly pathogenic avian influenza viruses- (HPAI) can cause severe disease in susceptible birds and low pathogenic avian influenza viruses- (LPAI) generally cause mild disease or no disease at all. Avian influenza is one of the most important poultry diseases, and serious outbreaks of disease have been reported in many countries.

Unlike Foot and Mouth disease, AI is not an air-borne disease.  AI is spread by movement of infected birds or contact with their secretions, particularly faeces, either directly or through contaminated objects, clothes or vehicles.

No.  This disease is different from Newcastle disease and is caused by a totally different virus.

Many different subtypes of avian influenza exist. The subtypes are named after the combination of variants of two of the virus proteins. Each influenza A virus has one of 16 H subtypes and one of 9 N subtypes. Only avian viruses which have the combination of H5 and H7 subtypes are known to cause the highly pathogenic form of the disease. However, not all viruses of the H5 and H7 subtypes are highly pathogenic and not all will cause severe disease in poultry.

Low pathogenic avian influenza viruses appear to have the ability to become highly pathogenic by mutation, which appears to occur only after the H5 or H7 viruses have moved from their natural wild bird hosts into domestic poultry. Mutation is a process where there is an alteration in the genes of a cell or virus which is transmitted to the offspring.

The current outbreaks of highly pathogenic avian influenza, which began in south-east Asia in mid-2003, are some of the largest and most severe on record. Never before in the history of this disease have so many countries been simultaneously affected. The disease, and attempts to halt its spread, has   resulted in the death or destruction of an estimated 150 million birds. The H5N1 virus is now considered endemic (regularly found) in many parts of Indonesia and Vietnam and in some parts of Cambodia, China, and Thailand. Establishing control of this disease in poultry is expected to take several years.

Influenza A viruses contain 8 distinct RNA genes and reassortment of these can occur if two different viruses infect the same animal so that viruses emerge with a set of genes made up of some of the genes from one virus and some from the other. In the 20th Century there were 4 pandemics of influenza due to the emergence of new and genetically distinct strains in humans: 1918 (H1N1), 1957 (H2N2), 1968 (H3N2) and 1977 (H1N1). The 1957 and 1968 pandemic viruses differed from the preceding viruses in humans by the substitution of genes that came from avian viruses, suggesting they arose by genetic reassortment of viruses of human and avian origin.

Mutation and re-assortment happen continuously in the family of influenza viruses, but as can be seen pandemics have only occurred four times in 100 years and are unevenly spaced over time

For more information about the human risk to health please refer to the Q&A on human health issues.

No. There have been severe and prolonged outbreaks in birds in South East Asia but only sporadic and isolated occurrences in the rest of the world. The outbreaks cannot be described as a pandemic; there is not a worldwide outbreak of bird flu in birds and animals at this time.

The severity depends upon the strain of virus and the type of bird infected.  Birds infected with HPAI may die suddenly or show a range of clinical signs including respiratory signs, swollen heads, dullness, a drop in egg production, and a loss of appetite. Some birds, especially waterfowl, can be infected with LPAI without showing any signs of disease.

In domestic poultry, infection with avian influenza viruses causes two main forms of disease, distinguished by low and high extremes of virulence (intensity of the disease). The so-called “low pathogenic” form commonly causes only mild symptoms (ruffled feathers, a drop in egg production, respiratory signs) and may go undetected. The highly pathogenic form is far more dramatic. It spreads very rapidly through poultry flocks, causes disease affecting multiple internal organs, and can kill up to 100% of the infected birds, often within 48 hours.

Direct contact with infected poultry, or surfaces and objects contaminated by their faeces, is presently considered the main route of human infection by the avian H5N1 virus. To date, most human cases have occurred in rural or urban fringe areas where many households keep small poultry flocks, which often roam freely, sometimes entering homes or sharing outdoor areas where children play. As infected birds shed large quantities of virus in their faeces, opportunities for exposure to infected droppings or to environments contaminated by the virus are abundant under such conditions. Moreover, because many households in Asia depend on poultry for income and food, many families sell or slaughter and consume birds when signs of illness appear in a flock, rather than disposing of the birds safely, and this practice has proved difficult to change. Exposure is considered most likely during slaughter, defeathering, butchering, and preparation of poultry for cooking. There is no evidence that properly cooked poultry or eggs can be a source of infection.

Poultry keeping practices are very different in the UK and the risks of coming into contact with bird flu very much lower for the general population. There will be some risk for poultry keepers, veterinarians and those who assist them in the advent of an outbreak of H5N1 bird flu in the UK. Dard and other Government Departments and Agencies have contingencies for this event

Yes.  If anyone suspects AI they should immediately report it to the local Divisional Veterinary Office.

The risk of it happening is very low. Because we are aware of the possibility we can look for it happening and deal with it if it does.  It is more likely to happen on premises where there is already infection in poultry.

We know that during the outbreak of AI in 2003 (H7N7) in the Netherlands, seropositive pigs were found on premises where birds had disease.  This means that the pigs on those premises, exposed to presumably large amounts of infected bird faeces, developed antibodies to AI.  In one case the pigs had been fed broken eggs from infected flocks.  However the Dutch found no evidence of clinical disease in those pigs and no evidence of pig-to-pig transmission.  No AI virus was isolated from the pigs, so at the time they were sampled they were not infectious.

Pigs did not appear to play any part in the spread of disease in the Netherlands.  The Dutch, sensibly, did not slaughter the pigs.

There are reports of the H5N1 AI infections in pigs in China and Indonesia.  However these infections, like the Dutch cases do not appear to be significant in the maintenance and spread of disease

In current circumstances the risk to cats and dogs is very low.  We know the cat family can catch avian influenza. We understand avian influenza H5N1 virus was found in a dead cat found on the island of Ruegan (north Germany), where avian influenza was identified in a number of wild birds including swans.

We believe H5N1 infection in cats under natural circumstances is rare as there are few confirmed reports of it occurring. We are awaiting further scientific advice on this.  There have been no cases in dogs.

Current knowledge indicates that no H5N1 infection has ever occurred in humans due to animals other than domestic poultry.  Current knowledge suggests that the disease in carnivores such as cats is a ‘cul de sac’ of the infection that has not lead to an increase in the risk posed by this virus for animal or public health.

We are not currently advising cat owners of any need for precautionary measures at the moment because surveillance of wild birds for H5N1 in NI has shown no evidence of infection.

In the event of an outbreak of H5N1 in wild birds we are likely to follow the procedures agreed at the Standing Committee on Food Chain and Animal Health (SoFACH) on 1 March – that in areas where H5N1 has been confirmed in wild birds, cats should be kept indoors and dogs walked on a lead or kept under close control so that they do not come into contact with wild birds.

If pet owners are concerned about the health of their animals, they should consult their vet.

For further Information please contact DARD Helpline on 028 90 524999 or your local Divisional Veterinary Office (DVO)