Frequently Asked Questions on Avian Influenza
Updated January 13, 2006
1. What is High Pathogenicity Avian Influenza H5N1?
In contrast, some variants of the H5 and H7 ’subtypes’ can cause massive mortality in poultry. These are designated ’High Pathogenicity Avian Influenza‘ (HPAI). HPAI viruses do not normally occur in wild birds. They arise in poultry, where intensive rearing and crowded conditions allow the virus to evolve to a highly pathogenic form. Hence HPAI is also called ‘poultry flu’.
Wild birds can also be infected with, and killed by, HPAI viruses. They appear to acquire the virus through contact with infected poultry or with facilities used by them.
The H5N1 virus currently circulating is a High Pathogenicity Avian Influenza (HPAI). This strain of the virus first appeared in Hong Kong in 1997. It evolved in poultry from Low Pathogenicity Avian Influenza (LPAI) viruses that were robably acquired from wild birds.
Conditions in poultry flocks (such as crowding, especially in mixed species groups, and prolonged contact with faeces, saliva and other bodily secretions) keep the viruses circulating as they evolve. The current series of outbreaks began in 2003 in South-east Asia, where a dramatic increase in intensive poultry production is sometimes combined with poor hygiene and bio-security in small “backyard” enterprises.
2. Why is there so much concern about this virus?
At present, H5N1 is not easily transmitted to humans. Many people have been exposed to infected birds in the present outbreak, but just 147 people (as of 10 January) have caught the disease. Nevertheless, more than half of them (78) have died. If contracted, it is a serious illness.
H5N1 is also not easily transmitted from human to human. However, this may change since the virus is constantly volving. A form of H5N1 that is transmitted easily between people would cause a global influenza pandemic, in which many millions of people might die. Such a virus could arise through ‘reassortment’ (when human and avian influenza viruses exchange genetic material, during co-infection of a human or a pig) or through a more gradual process of adaptive mutation. Continued outbreaks of H5N1 increase the chances of this happening.
3.1 Can wild birds catch H5N1?
3.2 Are migrating wild birds spreading High Pathogenicity Avian Influenza H5N1?
While a few outbreaks are consistent with the direction and timing of wild bird migration, most are not. The 2005 autumn migration came and went without migrating waterbirds spreading H5N1. The virus has not so far been reported from the birds' wintering areas in India, the Philippines, the Pacific and Africa.
The detailed pattern of outbreaks is also inconsistent with what would be expected from the movements of wild birds. All the evidence suggests that H5N1 is highly lethal to migratory wild bird species, and kills them quickly; that infected migrants cannot move long distances; and that the virus is most likely to be contracted locally, close to the site of deaths.
In short, wild birds could possibly have been involved in some H5N1 outbreaks (more likely in none) but other factors appear to be much more important – and should be the first focus of control efforts.
3.3 Can ‘healthy’ wild birds carry the HPAI H5N1 virus?
In currently uninfected areas, many thousands of migratory waterbirds have recently been tested in Korea, New Zealand, Australia, Alaska and Europe. All were found to be negative for HPAI H5N1.
On the other hand, Mallard ducks inoculated in the laboratory with certain high-pathogenicity H5N1 variants showed few clinical symptoms of infection. Tree Sparrows from Henan in China have also been found with a new variant of H5N1 that did not seem to make them ill (but proved lethal to chickens). So, while wild birds do not appear to carry and spread the HPAI H5N1 virus at present, it is possible that they could do so in future.
3.4 Is H5N1 a conservation threat?
3.5 What further research is needed?
We also need better systems of monitoring and surveillance for migrants – both for conservation purposes and to help predict and control the spread of H5N1 should migrant birds be found to carry it in the future.
3.6 Should wild birds be culled to stop the disease spreading?
In the event that wild birds were found to be carrying HPAI H5N1, any attempts at culling would spread the virus more widely, as survivors dispersed to new places, and healthy birds became stressed and more prone to infection.
3.7 Should wetlands be drained to deter waterbirds?
Draining wetlands is not only environmentally disastrous, but also likely to be counterproductive — for the same reasons that culling would be more likely to spread the Avian Influenza virus than control it. Birds would seek alternative staging places on their migration routes, and wildfowl forced to fly further and endure more crowded conditions along their migration route would become stressed and exhausted, and more prone to infection.
4. Can I still go birdwatching? Should I stop feeding wild birds in my garden?
So far there is only one, unconfirmed, report (from Turkey) of a person contracting the virus from a wild bird. All other cases have been linked to intimate exposure to infected poultry.
Most outbreaks in south-east Asia can be linked to movements of poultry and poultry products (or infected material from poultry farms, such as mud on vehicles, or peoples’ shoes). Live animal or ‘wet’ markets have played a major part in spreading the virus in south-east Asia: they were identified as the source of the H5N1 infection in chicken farms in Hong Kong in 1997 when approximately 20% of the chickens in live poultry markets were found to be infected.
There is also a huge international trade in poultry—legal, unregulated or illegal. Recently it was revealed that poultry meat is being illegally imported from Asia into the USA; in October 2005 3,000 chickens were intercepted by Italian customs after being smuggled into the country from China; and in November 2005 the UK authorities revealed that large quantities, possibly hundreds of tonnes, of chicken meat had been illegally imported from China.
The widespread illegal trade in cage birds has been demonstrated to have transported flu-infected birds over large distances. Customs in Taiwan recently intercepted two consignments of infected birds smuggled from mainland China. An outbreak of H5N1 at a bird quarantine station in the UK may also be attributable to smuggled birds ‘laundered’ into a legally imported consignment. The most likely source of infection in captive birds is at live animal ‘wet’ markets, where domestic and wild-caught birds are kept in close proximity, posing a high-risk of bird flu cross-contamination.
The use of untreated chicken, duck and other poultry manure as fertiliser and feed for pigs, fish and other livestock is widespread in Asia and Eastern Europe. Birds infected with the H5N1 virus excrete virus particles in their faeces: putting untreated faeces from infected birds into fish ponds provides a new source of infection. The manure may be transported for long distances before being used or sold, a dangerously effective way of spreading the virus. The United Nation’s Food and Agricultural Organisation recommends that "the feeding of poultry manure/poultry litter should be banned in countries affected by or at risk from avian influenza, even if correctly composted, ensiled or dried with heat treatment."
6. What should be done to prevent the spread of HPAI H5N1? The current focus on migrating wild birds is misplaced and a potentially dangerous diversion of energy, effort and resources. Attempts to cull wild birds are even more misguided—the target is wrong and the approach is completely ineffective.
Rather, preventive measures need to concentrate on better bio-security—surveillance and testing of poultry, controlling the movements and sale of poultry, poultry products and cage birds, ensuring that all poultry manure used in aquaculture and agriculture is properly treated prior to application, and stepping up national and international efforts to control the illegal trade in poultry, poultry products and wild birds.
Some countries are now vaccinating their poultry flocks. Research has shown that vaccines can reduce the infectiousness of chickens with avian flu and the susceptibility of healthy birds to the virus. However, there are no international standards for the minimum amount of antigen contained in poultry vaccines. Birds immunised with poor quality vaccines look healthy, but spread the virus at high concentrations in their faeces for longer, and the virus keeps replicating, spreading and evolving. Bad vaccines may be contributing to antigenic drift, allowing the virus to evolve into new forms.