Avian flu

 

What is influenza?

Influenza (most commonly known as ‘flu’) is an acute, usually short-term illness involving mainly the respiratory tract (nose, throat, lungs and breathing tubes) and which also causes generalised symptoms (eg fever, muscle aches and joint pains) throughout the body.  Flu, which occurs throughout the world, is usually not medically serious but on occasions can cause other serious health problems and, in some cases, can be fatal.

Who gets influenza?

Anyone from children to adults can get flu and it does not have serious consequences in most people.  It has been estimated that up to
15 per cent of the population may develop the illness in an average year.  So it is fortunate that, generally speaking, most people recover on their own. However, the problem arises when the elderly or those whose resistance is weakened by other medical conditions (such as emphysema or asthma) catch flu. In these cases it can cause more severe illness. In addition, some strains of flu are more harmful than others and, if a completely new strain of flu develops to which no-one is immune, this has the potential to cause a significant epidemic or pandemic (an epidemic across the world).

 

What is the influenza virus?

In fact there are thousands of different strains of influenza virus, which is why the human body has such difficulty developing resistance to the infection. They can all be grouped into one of three categories (called serotypes): Type A: Influenza A viruses are the most virulent (powerful) and are responsible for most major epidemics or pandemics.Avian flu falls into this type.

Type B: Influenza B is less powerful and usually causes less severe illness although it can still result in widespread or local outbreaks.

Type C: This type of influenza virus usually only causes very mild illnesses, which are very similar to the common cold.

The coating of the flu virus has a number of protein molecules on it, which our body’s immune systems detect and attack. If this coating remained the same, the next time the virus tried to infect the body, it would be immediately recognised by the body's defences as an infection it had dealt with before, and trigger an immune response straight away so that the person would probably not even know they had been exposed to the infection.

The reason why the flu virus is of such concern is because it can easily change its protein makeup, the body's defence mechanisms have to keep learning new variations of the virus against each of which it takes time to mount a fresh defence.  Our immune systems can remember our previous encounters with viruses and we mount rapid vigorous ‘memory-based’ responses when we re-encounter a virus of a type that we have previously repelled but it finds it difficult to cope with an infection, which is forever changing such as the flu virus. This is why a different flu vaccine is administered each year to at-risk groups such as the elderly whereas only one course of vaccine is needed to protect against non-changing viruses such as measles.

So what is avian flu?

In fact there are thousands of different strains of influenza virus, which is why the human body has such difficulty developing resistance to the infection. They can all be grouped into one of three categories (called serotypes): Type A: Influenza A viruses are the most virulent (powerful) and are responsible for most major epidemics or pandemics.Avian flu falls into this type.

Type B: Influenza B is less powerful and usually causes less severe illness although it can still result in widespread or local outbreaks.

Type C: This type of influenza virus usually only causes very mild illnesses, which are very similar to the common cold.

The coating of the flu virus has a number of protein molecules on it, which our body’s immune systems detect and attack. If this coating remained the same, the next time the virus tried to infect the body, it would be immediately recognised by the body's defences as an infection it had dealt with before, and trigger an immune response straight away so that the person would probably not even know they had been exposed to the infection.

The reason why the flu virus is of such concern is because it can easily change its protein makeup, the body's defence mechanisms have to keep learning new variations of the virus against each of which it takes time to mount a fresh defence.  Our immune systems can remember our previous encounters with viruses and we mount rapid vigorous ‘memory-based’ responses when we re-encounter a virus of a type that we have previously repelled but it finds it difficult to cope with an infection, which is forever changing such as the flu virus. This is why a different flu vaccine is administered each year to at-risk groups such as the elderly whereas only one course of vaccine is needed to protect against non-changing viruses such as measles.

 

What is special about the H5N1 strain of avian flu?

Influenza A viruses have many different so-called subtypes which are referred to by different H and N numbers to distinguish one from another. It has been found that the H5 and H7 subtypes frequently cause highly dangerous types of bird flu and what seems to be special about the H5N1 subtype is that it appears to be especially resistant to the usual methods of control. For instance, despite the killing of many millions of birds the virus has still managed to continue to survive and spread throughout many Asian and Indonesian countries.

Why is it a problem for humans?

The reason it is relevant to humans is firstly that when it passes from birds to humans (something that so far has not happened very often) it causes a very serious illness resulting in the death of about one third of those who develop it. In January 2004 the virus was found in people in Vietnam who had died of flu.

Secondly, so far, the H5N1 flu virus has not developed the ability to transfer itself from one human to another and that this may eventually happen is the main concern. The way this may happen is if someone catches an ordinary type of human flu and, simultaneously, catches avian flu. This person may then become a ‘melting pot’ in which the two viruses may somehow combine to form a completely new flu virus that is as deadly as avian flu and has the ability to spread readily from human to human.
 
Once person-to-person spread occurs, a pandemic could result.

 

How is it caught?

So far all the known cases have been as a result of a person being in direct contact with infected birds or their droppings and, as mentioned, no human to human transmission has so far been reported. The virus is not easy for a human to catch since there have been only a small number of reported cases of the disease in humans compared to the large number of infected birds, many of which live in close contact with their human owners.

Is it possible for avian flu to be caught by eating chicken or eggs?

It is not thought that eating properly cooked chicken or eggs poses any risk since the illness is transmitted via contact with live birds, which have the flu virus or the faeces of infected birds.It is thought that the killing, plucking or preparation of infected birds for eating is a potential source of infection but this tends to occur more in those areas of the world where families live in close contact with their poultry and kill them to sell or to eat for themselves..

What are the symptoms?

The symptoms of avian flu are similar to other forms of severe influenza namely high fevers, sweats, muscle pains, cough, and a runny nose. Avian flu also has a tendency to cause diarrhoea.  It is impossible to distinguish avian flu from other forms of influenza without a specific blood test or by analysing a sample of infected tissue.  It should be remembered that, so far, all cases have related to contact with infected birds in the countries mentioned above; at the time of writing there have been no cases of avian flu in humans in the UK.

The incubation period, the time between the person catching the infection and developing symptoms, is between three and five days. And when the symptoms occur they tend to be severe with rapid worsening of the patient’s condition sometimes leading to pneumonia and the failure of many of their organs with death in about a third of cases.

How is avian flu diagnosed?

There are certain features which would make a doctor consider avian flu such as a person who has a fever of more than 38°centigrade who has symptoms of severe flu and who has recently travelled to an area known to be infected with avian flu or close contact with a person who has suffered from a severe respiratory illness in an area of the world where avian flu is known to occur.

Therefore doctors are aware that if an individual develops severe flu symptoms and has recently been to an area in the previous week where avian flu is known to exist and particularly if they have had contact with live poultry or pigs then bird flu should be suspected.

If avian flu is suspected, the individual will be admitted to hospital and into an isolation unit following which further tests will be done including a chest x ray and blood tests. Throat and nose swabs may also be taken along with blood cultures.

 

Is there a treatment for avian flu?

There are two types of drugs available for prevention and treatment of flu. These types of drugs are called M2 inhibitors (amantadine and rimantadine) and neuraminidase inhibitors (oseltamivir –commercially known as tamiflu and zanimivir).  However, initial analysis of viruses isolated from the recently fatal cases in Vietnam indicates that the viruses are resistant to the M2 inhibitors. Further testing is underway to confirm the resistance of amantadine. 

It is thought that the H5N1 virus may respond to treatment with the neuraminidase inhibitors if given within 48 hours of the start of symptoms and as a result may improve the chances of survival of the individual.

Treatment of avian flu also includes the prevention or treatment of the complications of the illness such as pneumonia by administering antibiotics, if appropriate, and generally providing supportive medical care, which may include admission to an Intensive Care Unit.

Is there a vaccine against avian flu?

At the time of writing, there is no effective vaccine against avian flu. The usual flu vaccine given to certain groups of people in the UK such as the elderly and those with lung and heart conditions does not protect against avian flu. However, it is thought that preventing as many people as possible from developing the usual types of flu may reduce the chances of one person catching both human flu and bird flu simultaneously and therefore make the chances of the emergence of a human form of bird flu less likely.

Work is underway to develop a vaccine against avian flu but it takes time to produce a new flu vaccine, not least because it has to be properly tested before large amounts being licensed for widespread use.

Another reason why a vaccine is not available is that the makeup of the vaccine has to be based on the very particular virus causing the illness and, as yet, the human-to-human form of virus does not exist. To a certain extent the scientists have to wait for the virus to emerge before they can develop a fully effective vaccine against it.

 

Where can I get further information?

For updates on avian flu, you may wish to contact one of the following organisations:

World Health Organisation
Website: www.who.int/en/

Health Protection Agency (Central Office)
7th Floor Holborn Gate
330 High Holborn
London
WC1V 7PP
Tel: 0207 759 2700
Website: www.hpa.org.uk

Or contact the Health at Hand team for more information.
Helpline: 0800 003 004