Posted: 27 February 2006
Avian Influenza A (H5N1) "Bird Flu" - Frequently Asked Questions
28 February 2006
Professor William Hall and Dr Claire O’Connell
- What is bird flu?
- What animals can bird flu affect?
- What does the name H5N1 mean?
- Which bird flu viruses are the most serious?
- How does bird flu spread around the world?
- Where has the current outbreak of highly pathogenic H5N1 been identified in birds?
- Does the bird flu virus spread easily from birds to humans?
- Where have human cases occurred?
- How do people become infected?
- Should we be concerned about eating poultry and eggs?
- What’s the significance of a human being infected with H5N1?
- What is an influenza pandemic?
- How could the current H5N1 virus mutate so that it moves easily between humans?
- How serious is the current pandemic risk?
- What are the most important warning signals that a pandemic is about to start?
- How quickly will a pandemic spread around the world?
- how will a pandemic affect local services?
- What will determine the number of deaths in a pandemic?
- What can we do now to minimise the death toll from a pandemic?
- Is there a vaccine?
- What drugs can we use against a pandemic virus?
- Can a pandemic be prevented?
- Could a flu pandemic spread to Ireland?
- How has Ireland prepared for the possibility of a pandemic?
- How is the flu virus currently monitored in Ireland?
- Who in Ireland will receive H5N1 vaccine when it becomes available?
- Who in Ireland will receive antiviral medication in the event of a flu pandemic?
1. What is bird flu?
Bird flu, or avian influenza, is a contagious disease caused by a member of a large group of influenza viruses that infect mainly birds.
Avian influenza is not an influenza pandemic, which happens when a new flu virus emerges, adapts to humans and circulates quickly among human populations throughout the world.
2. What animals can bird flu affect?
Bird flu infects a wide range of wild and domestic bird species and, less commonly, pigs.
Bird flu viruses tend to move between animals of the same species. This means they move from bird to bird or from pig to pig. However on rare occasions they have crossed the species barrier to infect humans.
If domestic poultry such as chicken are infected, they can suffer from either a mild or a more serious form of disease. The mild form ("low pathogenic") may cause only ruffled feathers and a drop in egg production. However, the more serious or “highly pathogenic” form affects the bird’s internal organs, frequently causing breathing problems and often killing the animal within 48 hours. This more dramatic form can be highly infectious and spread rapidly through bird flocks.
3. What does the name H5N1 mean?
H5N1 is a code name that scientists use to describe a certain strain of influenza virus.
All influenza viruses are divided into three types – A, B or C – based on their structure.
Type A flu viruses are responsible for our yearly influenza outbreaks but have also been responsible for all lethal flu pandemics so far, and can affect both animals and humans.
Type A viruses are further classified into subtypes based on two proteins on their surface: Hemagglutinin (H) and Neuraminidase (N).
Influenza A viruses has 16 H subtypes and 9 N subtypes. At least 15 flu subtypes affect birds, the most virulent being H5N1.
In terms of a pandemic, the H component of the virus is the most important because it governs the ability of the virus to enter cells where it can multiply.
An infected cell containing influenza virus
Strains of the virus evolve within these subtypes, changing their genetic makeup by swapping genes in an unpredictable manner, a process known as "reassortment". This unpredictable property of the virus is what makes it difficult for scientists to anticipate the makeup of a particular strain of influenza virus in advance of a pandemic.
4. Which bird flu viruses are the most serious?
Only viruses of the H5 and H7 subtypes are known to cause the highly pathogenic form of bird flu. However, not all viruses within these subtypes are highly pathogenic, and not all will cause severe disease in poultry.
Scientists currently believe that when a H5 or H7 virus first infects poultry flocks, it doesn’t cause serious disease in individual animals. However as the virus circulates in poultry populations it can mutate, usually within a few months, into the highly pathogenic form.
This is why scientists carefully monitor any H5 or H7 virus in poultry, even when animal populations are not seriously affected.
5. How does bird flu spread around the world?
Migratory birds can spread highly pathogenic avian influenza virus around the world, but scientists do not fully understand how this happens.
Wild waterfowl appear to be the natural reservoir of all influenza A viruses, including bird flu viruses, which they seem to carry with no apparent harm. Scientists think that migratory birds can introduce low pathogenic H5 and H7 viruses to poultry flocks, which then switch to the highly pathogenic form within the poultry population.
Recent evidence now suggests that some migratory birds are also involved in spreading the highly pathogenic form of the H5N1 virus into new areas.
We also know that domestic ducks can excrete large quantities of highly pathogenic H5N1 virus without showing signs of disease. These means the virus circulates in duck populations, and uses them as a host reservoir before moving on to other bird species.
6. Where has the current outbreak of highly pathogenic H5N1 been identified in birds?
Since December 2003, avian influenza A (H5N1) infections in poultry or wild birds have been reported in the following countries:
Africa:
- Nigeria
East Asia & the Pacific:
- Cambodia
- China
- Hong Kong (SARPRC)
- Indonesia
- Japan
- Laos
- Malaysia
- Mongolia
- Thailand
- Vietnam
Europe & Eurasia:
- Austria
- Azerbaijan
- Bosnia & Herzegovina
- Bulgaria
- Croatia
- France
- Germany
- Greece
- Italy
- Romania
- Russia
- Slovenia
- Turkey
- Ukraine
Near East:
- Egypt
- Iraq
- Iran
South Asia:
- India
- Kazakhstan
For additional information about these reports, visit the
.
7. Does the bird flu virus spread easily from birds to humans?
No. The best-case scenario is that the current virus, H5N1 Influenza, will not be infectious for humans. H5N1 is spreading in bird populations throughout the world, but to date there have been very few human cases.
Of the 169 documented cases (to February 2006) of the virus among humans, evidence for human-to-human spread is limited.
It’s important to remember that the number of humans infected with the virus in this outbreak is small compared with the hundreds of millions of birds affected and the many opportunities for human exposure, especially in areas where humans are in close contact with domestic poultry.
At present, scientists do not understand why some people and not others become infected following similar exposures.
8. Where have human cases occurred?
Since January, 2004 WHO has reported human cases of avian influenza A (H5N1) in the following countries:
East Asia and the Pacific:
- Cambodia
- China
- Indonesia
- Thailand
- Vietnam
Europe & Eurasia:
- Turkey
Near East:
- Iraq
9. How do people become infected?
It is rare for the current H5N1 virus to infect humans. If that happens, it is generally though direct contact with infected poultry, or with surfaces and objects contaminated by their faeces (droppings), which contain large quantities of the virus.
Scientists consider exposure to be most likely during slaughter, defeathering, butchering and preparation of poultry for cooking, although cooked poultry or eggs do not appear to pose an infection risk.
To date, most human cases have occurred in areas where households share living and playing spaces with small, free-roaming poultry flocks.
There is no significant evidence of human-to-human spread of the virus, despite millions of cases of H5N1 avian flu in birds over several years.
10. Should we be concerned about eating poultry and eggs?
There is no evidence that the virus is transmitted through eating poultry or eggs as long as they are cooked properly.
It is important to remember that there have been very few human infections with the virus, even in individuals who are in constant contact with infected poultry.
Health experts have been monitoring the H5N1 strain for almost eight years. To date [mid-February 2005], the World Health Organisation has reported 91 deaths from a total of 169 cases. You can find up-to-date statistics on infection and mortality on the .
Previously two outbreaks were documented in Hong Kong, where the first case of human infection with H5N1 was recorded in 1997. In that outbreak the virus infected 18 people and six of them died. In second outbreak in 2003, the virus infected two individuals, with one death.
11. What’s the significance of a human being infected with H5N1?
If a human becomes infected with H5N1 through contact with poultry, that person is likely to suffer severe disease. Over half of people infected with the current H5N1 virus have died.
Another risk is that once in a human host, the H5N1 virus could potentially change its genetic makeup or combine with an existing human influenza virus ("re-assortment") to become easily transmissible between humans, sparking a pandemic.
12. What is an influenza pandemic?
An influenza pandemic is a specific and well-defined event that satisfies three criteria:
- a new influenza virus emerges
- it infects humans, causing serious illness
- it spreads easily and sustainably among humans
The H5N1 virus has already met the first two conditions: it is a new virus for humans and it has infected 169 humans to date [mid-February 2006], killing over half of them.
Because H5N1 viruses have never circulated widely among human populations, no-one will have immunity should an H5N1-like virus emerge that can pass easily and sustainably between people.
The risk that the H5N1 virus will acquire the ability to spread easily between humans although unlikely, will persist as long as the virus continues to circulate in birds, thereby presenting opportunities for human infection. So the risk of an influenza pandemic arising from this source could persist for many years.
13. How could the current H5N1 virus mutate so that it moves easily between humans?
There are two potential scenarios where this could happen: the current H5N1 virus could mutate by itself to become a strain that infects humans easily, or it could combine with another influenza virus ("re-assortment") that can infect humans.
The H5N1 avian influenza virus has already mutated, and has undergone numerous re-assortments with other avian viruses. In fact whereas there was one major type of H5N1 circulating in 1999, there are presently five distinct forms of H5N1. The virus could further mutate its genetic material in a way that allows it to infect humans and facilitate human-to-human spread. This kind of adaptive mutation would be expected to happen relatively slowly initially, resulting in small clusters of human cases and giving the world some time to take defensive action against its spread.
Alternatively, the H5N1 we currently see in birds could infect a human or an animal, such as a pig, that is already infected by another influenza virus. Under these circumstances, the two virus strains could exchange genetic material, reassorting to create an offspring between regular human influenza and bird influenza. This could be an extremely virulent virus which would appear as a sudden surge of human cases with an explosive spread. This type of event was responsible for the 1957 and 1968 pandemics.
We cannot predict if any of these scenarios could happen. The H5N1 virus has been present in Asia at least since 1997, and there have only been a small number of human infections.
14. How serious is the current pandemic risk?
The risk of pandemic influenza is serious, according to the World Health Organisation. The world is currently in a state of pandemic alert.
Thus the occurrence of a future pandemic is not in doubt, but we don’t know when it will arise, how severe it will be or where it will originate.
15. What are the most important warning signals that a pandemic is about to start?
The first warning sign that a pandemic is beginning will be evidence of human-to-human transmission of the virus. This would come to light as clusters of patients in the same area with influenza symptoms at similar times. It could also manifest as cases in health workers who are in close contact with individuals who are infected with influenza.
Early detection of a pandemic is essential to mount appropriate protective strategies, which is why areas with established H5N1 presence are kept under surveillance, and why reference laboratories study viruses to track changes in the virus that could facilitate human-to-human spread.
16. How quickly will a pandemic spread around the world?
The hallmark of an influenza pandemic is that a new virus appears and to which humans have little resistance. The virus is transmitted through coughing and sneezing. However individuals can also carry and shed the virus even before they show symptoms. Modern transport such as air travel would facilitate rapidly spread to almost all countries of the world, possibly leading to significant infections throughout all continents within three months.
17. How will a pandemic affect local services?
The illness caused by a global influenza outbreak will result in increased demand for medical and hospital treatment, placing enormous strain on health services. Other services such as policing, communications, transport and food production could also be severely disrupted.
Scientists cannot accurately predict the number of deaths which might caused by a pandemic. Illness and mortality in previous pandemics has varied. The World Health Organisation predicts that in the best-case scenario for the current outbreak, if the emergent pandemic virus causes mild symptoms, there could be 2 million to 7.4 million deaths worldwide. Estimates are higher for a pandemic strain that would cause more severe symptoms.
18. What will determine the number of deaths in a pandemic?
Death rates from an influenza pandemic are influenced by four major factors:
- The number of people infected
- The virulence of the virus
- The robustness or vulnerability of infected populations
- The effectiveness of preventative measures
19. What can we do now to minimise the death toll from a pandemic?
In August 2005, WHO advised all countries to prepare a strategic plan to respond to the current pandemic threat.
Actions were proposed to strengthen national preparedness, reduce opportunities for a pandemic virus to emerge, improve early warning detection systems, delay global spread, and accelerate vaccine development.
Ireland has its own pandemic plan in place (see below), which is being constantly updated to reflect the dynamic situation of avian flu in Asia and other parts of the world.
20. Is there a vaccine?
At present there is no effective vaccine against a pandemic virus because that virus has not yet emerged in the human population. Every year, vaccines are produced against seasonal influenza, but these vaccines will not protect against pandemic influenza.
Several countries are developing vaccines against the current strain of H5N1. Ireland intends to obtain sufficient stocks to vaccinate 200,000 front-line workers. However if a new influenza virus is involved in a pandemic, a candidate vaccine will have to be identified and be tailored to protect against it.
It is anticipated that 4-6 months will be required to produce the vaccine on a large scale, and at present the world lacks the production facilities to meet the global demand of a pandemic vaccine.
21. What drugs can we use against a pandemic virus?
While vaccines are considered the first line of defence in a pandemic, antiviral drugs may be able to reduce symptoms and reduce the severity of clinical illness. Tamiflu (oseltamavir) and Relenza (zanamivir) belong to a class of drugs called neuraminidase inhibitors. They lessen the severity and duration of seasonal influenza. If such drugs are administered early enough to patients, they may reduce morbidity and mortality, although clinical data are limited.
The main limitation with producing neuraminidase inhibitors, is that the world cannot manufacture enough in time to respond effectively to a pandemic. Present estimates suggest that it would take ten years to produce enough Tamiflu to treat 20% of the world’s population.
It’s unclear if resistance will develop relatively easily to Tamiflu. There has been one report from Viet Nam of Tamiflu resistance in one individual who took suboptimal doses of the medicine.
Members of an older class of antiviral drugs called M2 inhibitors are problematic because viruses can quickly develop resistance. It should be noted that the currently circulating H5N1 is totally resistant to the M2 inhibitors, probably because of their indiscriminate use in treating poultry. However, these drugs might possibly be effective against a new virus.
22. Can a pandemic be prevented?
The ideal way to prevent an H5N1 influenza pandemic would be to eliminate the H5N1 virus from bird populations, but this is unlikely to happen in the short-term.
To date several hundred million birds have been slaughtered and in any new outbreak of disease in bird populations, wholesale culling should help to prevent spread. It is also possible to vaccinate poultry. However it will be extremely difficult to eliminate the virus from wild birds.
It may be possible to use antiviral drugs in areas of emerging human infection to help slow down the spread of a pandemic virus which could provide time to develop more effective vaccines.
23. Could a flu pandemic spread to Ireland?
There is no way of knowing whether the H5N1 avian flu strain or another pandemic strain will ever cause widespread human infection in Ireland. However the country must be prepared as best as possible.
24. How has Ireland prepared for the possibility of a pandemic?
Ireland has its own pandemic plan in place based on WHO recommendations. This has been overseen and prepared by the Influenza Pandemic Expert Group convened by the Department of Health and Children. The plan is constantly being updated to reflect the dynamic situation of avian flu in Asia and other parts of the world.
The Health Services Executive (HSE) is responsible for the implementation of the Irish plan in the event of a pandemic. In 2005, seven HSE subcommittees were established to ensure effective implementation.
As part of the Irish pandemic plan, the Department of Health and Children is procuring 200,000 doses of a candidate H5N1 vaccine for use for front-line workers.
In addition the Department is pre-ordering any future pandemic virus vaccine by putting in place contracts with various vaccine-producing pharmaceutical companies. The intention is to procure enough pandemic vaccine to vaccinate all individuals in Ireland.
The Department of Health is procuring a total of one million doses of Tamiflu, a powerful antiviral drug that can suppress flu infection and currently has a stock of 600,000 doses.
The total amount of one million doses will cover 25 per cent of the population, which modeling predicts will greatly reduce hospitalisation, morbidity and mortality among the population.
The Department of Health is also planning to procure a second antiviral drug, Relenza, which will increase the total anti-viral coverage to some 40% of the population.
25. How is the flu virus currently monitored in Ireland?
At present there is an active surveillance programme for influenza in Ireland. This is a collaboration between the National Virus Reference Laboratory (NVRL) at 51黑料, the Health Protection Surveillance Centre (HPSC) and the Irish College of General Practitioners (ICGP).
Samples collected from all respiratory illnesses in 24 sentinel centres around the country are sent to the NVRL and analysed for the presence of influenza A or influenza B.
The Department of Agriculture also carries out active surveillance of poultry populations.
26. Who in Ireland will receive H5N1 vaccine when it becomes available?
Government departments have determined a priority group of workers who will be the first to receive an appropriate vaccine. These include healthcare workers, emergency service providers and suppliers of food, electricity and water.
27. Who in Ireland will receive antiviral medication in the event of a flu pandemic?
Antiviral medication will primarily be given to people who are symptomatic.
Adapted from material produced by the World Health Organisation (WHO)