Basic Facts

The Basic Facts and FAQs presented here are in line with FAO and WHO's guidance.
All Basic Facts and FAQs are in the process of being consolidated at the UN System level, and will be posted on this page as soon as they become available.

• What is avian influenza?
• How does avian influenza virus spread?
• Why so much concern about the current outbreaks?
• Which countries are affected by avian influenza virus?
• Is there evidence of efficient human-to-human transmission now?
• How often does human infection with H5N1 happen?
• What is a pandemic? Where can I get more information?
• Which are the stages of a pandemic?
• What are symptoms of the avian influenza in human?
• Are there drugs available for treatment?
• Is there a human vaccine available against this disease?
• How can I get prepared at home?
• Where else I can get information on avian influenza?

What is avian influenza?

Avian influenza, or "bird flu", is a contagious disease of animals caused by viruses that normally infect only birds. While all bird species are thought to be susceptible to infection, domestic poultry flocks are especially vulnerable to infections that can rapidly reach epidemic proportions.

The disease in birds has two forms. The first causes mild illness, sometimes expressed only as ruffled feathers or reduced egg production. Of greater concern is the second form, known as “highly pathogenic avian influenza”. This form, which was first recognized in Italy in 1878, is extremely contagious in birds and rapidly fatal, with a mortality approaching 100%. Birds can die on the same day that symptoms first appear.

How does avian influenza virus spread?

All birds are thought to be susceptible to infection with avian influenza, though some species are more resistant to infection than others. Fifteen subtypes of influenza virus are known to infect birds, thus providing an extensive reservoir of influenza viruses potentially circulating in bird populations.

Apart from being highly contagious among poultry, avian influenza viruses are readily transmitted from farm to farm by the movement of live birds, people (especially when shoes and other clothing are contaminated), and contaminated vehicles, equipment, feed, and cages. Highly pathogenic viruses can survive for long periods in the environment, especially when temperatures are low. For example, the highly pathogenic H5N1 virus can survive in bird faeces for at least 35 days at low temperature (4°C). At a much higher temperature (37°C), H5N1 viruses have been shown to survive, in faecal samples, for six days.

For highly pathogenic disease, the most important control measures are rapid culling of all infected or exposed birds, proper disposal of carcasses, the quarantining and rigorous disinfection of farms, and the implementation of strict sanitary, or “biosecurity”, measures. Restrictions on the movement of live poultry, both within and between countries, are another important control measure. The logistics of recommended control measures are most straightforward when applied to large commercial farms, where birds are housed indoors, usually under strictly controlled sanitary conditions, in large numbers. Control is far more difficult under poultry production systems in which most birds are raised.

During 2005, an additional and significant source of international spread of the virus in birds became apparent for the first time, but remains poorly understood. Scientists are increasingly convinced that at least some migratory waterfowl are now carrying the H5N1 virus in its highly pathogenic form, sometimes over long distances, and introducing the virus to poultry flocks in areas that lie along their migratory routes. Should this new role of migratory birds be scientifically confirmed, it will mark a change in a long-standing stable relationship between the H5N1 virus and its natural wild-bird reservoir.

Evidence supporting this altered role began to emerge in mid-2005 and has since been strengthened. The die-off of more than 6000 migratory birds, infected with the highly pathogenic H5N1 virus, that began at the Qinghai Lake nature reserve in central China in late April 2005, was highly unusual and probably unprecedented. Prior to that event, wild bird deaths from highly pathogenic avian influenza viruses were rare, usually occurring as isolated cases found within the flight distance of a poultry outbreak. Scientific studies comparing viruses from different outbreaks in birds have found that viruses from the most recently affected countries, all of which lie along migratory routes, are almost identical to viruses recovered from dead migratory birds at Qinghai Lake. Viruses from Turkey’s first two human cases, which were fatal, were also virtually identical to viruses from Qinghai Lake (Source: WHO).

Why so much concern about the current outbreaks?

Public health officials are alarmed by the unprecedented outbreaks in poultry for several reasons. First, most – but not all – of the major outbreaks recently reported in Asia have been caused by the highly pathogenic H5N1 strain. There is mounting evidence that this strain has a unique capacity to jump the species barrier and cause severe disease, with high mortality, in humans.

A second and even greater concern is the possibility that the present situation could give rise to another influenza pandemic in humans. Scientists know that avian and human influenza viruses can exchange genes when a person is simultaneously infected with viruses from both species. This process of gene swapping inside the human body can give rise to a completely new subtype of the influenza virus to which few, if any, humans would have natural immunity. Moreover, existing vaccines, which are developed each year to match presently circulating strains and protect humans during seasonal epidemics, would not be effective against a completely new influenza virus.

If the new virus contains sufficient human genes, transmission directly from one person to another (instead of from birds to humans only) can occur. When this happens, the conditions for the start of a new influenza pandemic will have been met. Most alarming would be a situation in which person-to-person transmission resulted in successive generations of severe disease with high mortality.

This was the situation during the great influenza pandemic of 1918–1919, when a completely new influenza virus subtype emerged and spread around the globe, in around 4 to 6 months. Several waves of infection occurred over 2 years, killing an estimated 40–50 million persons.

Which countries are affected by avian influenza virus?

Outbreak in birds: The outbreaks of highly pathogenic H5N1 avian influenza that began in south-east Asia in mid-2003 and have now spread to Europe (France, Germany, Italy and Switzerland), are the largest and most severe on record. To date, nine Asian countries have reported outbreaks (listed in order of reporting): the Republic of Korea, Viet Nam, Japan, Thailand, Cambodia, the Lao People’s Democratic Republic, Indonesia, China, and Malaysia. Of these, Japan, the Republic of Korea, and Malaysia have controlled their outbreaks and are now considered free of the disease. Elsewhere in Asia, the virus has become endemic in several of the initially affected countries.

In late July 2005, the virus spread geographically beyond its original focus in Asia to affect poultry and wild birds in the Russian Federation and adjacent parts of Kazakhstan. Almost simultaneously, Mongolia reported detection of the highly pathogenic virus in wild birds. In October 2005, the virus was reported in Turkey, Romania, and Croatia. In early December 2005, Ukraine reported its first outbreak in domestic birds. Most of these newer outbreaks were detected and reported quickly. Further spread of the virus along the migratory routes of wild waterfowl is, however, anticipated. Moreover, bird migration is a recurring event. Countries that lie along the flight pathways of birds migrating from central Asia may face a persistent risk of introduction or re-introduction of the virus to domestic poultry flocks (Source: WHO).

Outbreak in humans: To date, human cases have been reported in six countries, most of which are in Asia: Cambodia, China, Indonesia, Thailand, Turkey, and Viet Nam. The first patients in the current outbreak, which were reported from Viet Nam, developed symptoms in December 2003 but were not confirmed as H5N1 infection until 11 January 2004. Thailand reported its first cases on 23 January 2004. The first case in Cambodia was reported on 2 February 2005. The next country to report cases was Indonesia, which confirmed its first infection on 21 July. China’s first two cases were reported on 16 November 2005. Confirmation of the first cases in Turkey came on 5 January 2006, followed by the first reported case in Iraq on 30 January 2006. All human cases have coincided with outbreaks of highly pathogenic H5N1 avian influenza in poultry. To date, Viet Nam has been the most severely affected country, with more than 90 cases.

Is there evidence of efficient human-to-human transmission now?

No. Investigations of all the most recently confirmed human cases, in China, Indonesia, and Turkey, have identified direct contact with infected birds as the most likely source of exposure. When assessing possible cases, the level of clinical suspicion should be heightened for persons showing influenza-like illness, especially with fever and symptoms in the lower respiratory tract, who have a history of close contact with birds in an area where confirmed outbreaks of highly pathogenic H5N1 avian influenza are occurring. Exposure to an environment that may have been contaminated by faeces from infected birds is a second, though less common, source of human infection. To date, not all human cases have arisen from exposure to dead or visibly ill domestic birds. Research published in 2005 has shown that domestic ducks can excrete large quantities of highly pathogenic virus without showing signs of illness. A history of poultry consumption in an affected country is not a risk factor, provided the food was thoroughly cooked and the person was not involved in food preparation. As no efficient human-to-human transmission of the virus is known to be occurring anywhere, simply travelling to a country with ongoing outbreaks in poultry or sporadic human cases does not place a traveller at enhanced risk of infection, provided the person did not visit live or “wet” poultry markets, farms, or other environments where exposure to diseased birds may have occurred.

How often does human infection with H5N1 happen?

Since December 2003, a limited number of cases of infection with the H5N1 strain have been reported worldwide. You can find the updated number of cases in http://www.who.int/csr/disease/avian_influenza/country/en/

What is a pandemic? Where can I get more information?

The article Ten things you need to know about pandemic influenza posted by WHO contains very useful information on this subject.

Which are the stages of a pandemic?

Phase 1 and Phase 2: are inter-pandemic phases during which no new Influenza A virus subtypes have been detected in humans but a circulating animal Influenza A virus subtype has been identified which poses a substantial risk of human disease.

Phase 3: human infection with a new Influenza A virus subtype has been identified but there is no spread of the virus from human to human (or most rare instances of spread, and only to a close contact). We are currently in Phase 3.

Phase 4: small cluster(s) are identified with limited human to human transmission, but spread is highly localized suggesting that the virus is not well adapted to humans yet.

Phase 5: large cluster(s) are identified but human to human spread is still localized. This suggests that the virus is increasingly better adapted to humans but not yet fully transmissible. Risk for a pandemic is substantial at this stage.

Phase 6: increased and sustained viral transmission is seen in the general population.

What are symptoms of the avian influenza in human?

The incubation period for H5N1 avian influenza may be longer than that for normal seasonal influenza, which is around two to three days. Current data for H5N1 infection indicate an incubation period ranging from two to eight days and possibly as long as 17 days. Initial symptoms include a high fever, usually with a temperature higher than 38°C, and influenza-like symptoms. Diarrhoea, vomiting, abdominal pain, chest pain, and bleeding from the nose and gums have also been reported as early symptoms in some patients. The spectrum of clinical symptoms may, however, be broader, and not all confirmed patients have presented with respiratory symptoms; it may include neurological symptoms as well.

Many patients have symptoms in the lower respiratory tract when they first seek treatment. On present evidence, difficulty in breathing develops around five days following the first symptoms. Almost all patients develop pneumonia, usually without microbiological evidence of bacterial supra-infection at presentation. Turkish clinicians have also reported pneumonia as a consistent feature in severe cases; as elsewhere, these patients did not respond to treatment with antibiotics.

Are there drugs available for treatment?

Yes. The antiviral medication called oseltamivir (better known as Tamiflu) is thought to be effective regardless of the causative strain, as long as treatment is started within 48 hours since onset of the symptoms. Certain antibiotics may be efficient in treatment of lower respiratory tract infection, which is common in human avian influenza.

Is there a human vaccine available against this disease?

At present, there is no vaccine available.

How can I get prepared at home?

Consider buying:
  - a body thermometer for EACH member of the family
  - a box of surgical masks
  - a box of disposable latex gloves
  - antipyretics such as acetaminophen (Tylenol) and/or ibuprofen (Advil)
  - antiseptic solutions to clean hands and surfaces used by many (such as door handles, keyboards etc).

Where else I can get information on avian influenza?

Following these links, you will find additional information on Avian Influenza:

http://www.who.int/csr/disease/avian_influenza/en/index.html

http://www.fao.org/ag/againfo/subjects/en/health/diseases-cards/special_avian.html

http://www.oie.int/eng/en_index.htm

http://www.cdc.gov/flu/avian/index.htm

http://www.health.state.ny.us/diseases/communicable/influenza/avian/index.htm