Bird Flu is a form of influenza, which is caused by a highly pathogenic subtype of the influenza A virus, called H5N1. The name H1N5 is based on two proteins that occur on the surface of the virus particles, hemagglutinin (H) and neuraminidase (N). Avian influenza is a respiratory virus which predominantly causes fever, coughing, sore throat, muscle aches, and in severe cases breathing problems and pneumonia, which can be fatal.
Infection is caused by viruses that occur naturally in birds, and normally only infect them. The H5N1 strain has adapted from birds, and can cause illness in humans and many other animal species including cat, pigs, tigers and leopards. The people who are most at risk from bird flu are those who come into direct with birds, either by handling poultry or wild birds, or by visiting live poultry markets. To try and limit the spread of avian influenza, there is currently a ban on the importation of birds and bird products from countries where the H5N1 strain has been isolated.
Since 2003, avian influenza has spread rapidly in poultry across 17 countries from Asia to Eastern Europe and the Near East. Human cases of bird flu have been reported in Asia, Africa, Europe, the Pacific and the Near East. The highest number of cases have been reported in Indonesia and Vietnam. The bird flu virus does not infect people easily, and infection usually occurs by direct transmission from birds. Transmission from person-to-person is very rare. When humans become infected with bird flu it is very serious, with up to 60% of cases results in death. Avian influenza usually affects previously health children and young adults, with the majority of cases occurring in people between the ages of 10 and 19.
Because avian influenza is a bird virus, people do not have a high natural, or pre-existing, immunity. This makes the threat of a world-wide outbreak (pandemic) very dangerous, because many people could die. A bird flu pandemic could only occur if the H5N1 virus became able to spread easily from person to person, allowing efficient and sustained transmission among humans. Viruses are very efficient at swapping information with each other, which means the H5N1 strain could learn how to infect humans more efficiently from other viruses. While the likelihood of this occurring is low, the risk remains eminent as long as the virus continues to circulate through the avian population, and come into contact with viruses that readily infect humans. Public health authorities closely monitor cases of avian influenza as a means of controlling the risk of pandemic. Authorities are most concerned about cases of human infection and any evidence for increased person-to-person transmission.
Wild birds carry the bird flu virus in their intestines, and infected birds transmit the virus through their saliva, nasal secretions, faeces and blood. Birds that are susceptible to the virus become infected when they come into contact with the secretions of infected birds, or with surfaces that are contaminated with them. Domesticated birds and poultry often become infected through direct contact with infected waterfowl or wild birds, or by contact with material and surfaces that they have infected such as water, feed, dirt or cages. Humans, as well as other animals, become infected with bird flu by coming into direct contact with infected birds, their bodily fluids or things contaminated with them.
During outbreaks of avian influenza in poultry, there is a possible risk to people who have contact with infected birds. Of the human cases associated with outbreaks in poultry and wild birds, more than half of these people infected with the virus have died. To date, people have only contracted bird flu in Africa, Asia, Europe and the Near East. Most of these cases have occurred in previously healthy children and young adults, and have resulted from direct or close contact with infected poultry or contaminated surfaces. In general, H5N1 remains a very rare disease in people. The H5N1 virus does not infect humans easily, and if a person becomes infected, it is very difficult for the virus to spread to another person.
The spread of diseases from animals to people is called zoonosis. The H5N1 virus is not well adapted for transfer between people following a zoonotic event, and there is no evidence that it can be spread in the air by aerosolised droplets containing virus particles. The spread of avian influenza virus from one person to another has been reported very rarely, and in any event, transmission has not occurred beyond one person.
The threat of the H5N1 virus is that it is constantly changing, and may adapt overtime to spread easily between people. Scientists are concerned that the H5N1 virus could one day be able to infect humans more easily and spread easily from one person to the next. Because the incidence of H5N1 infection is rare, many people around the world have not been exposed to the virus. This means that the human population has little to no immune protection against a bird flu pandemic, which could begin if sustained H5N1 virus transmission occurred. No one can predict when a pandemic might occur, which is why public health authorities are monitoring the situation carefully, and preparing for the possibility that the virus may begin to spread more easily and widely from person to person.
The symptoms reported from avian influenza can be very varied. These include:-
Conjunctivitis – involves inflammation of the membrane surrounding the eyelids (conjunctiva). Symptoms include redness, swelling and pain around the eye. Yellow-green fluid can also discharge from the eye area.
Pneumonia – is caused by inflammation of one or both of the lungs due to fluid build-up. Symptoms of pneumonia include chest pain, shortness of breath, chills, fever and the production of phlegm when coughing.
Influenza-like symptoms – are the most common and include the symptoms that are associated with common influenza. These include chills, fever, cough, sore throat or muscle aches.
These symptoms can also by accompanied by nausea and vomiting. Symptoms usually develop within a week of being exposed to the avian influenza virus.
Bird flu viruses cause infection by infiltrating the mucous membrane of the respiratory tract. When this occurs they are able to attach to the cells lining the respiratory tract and replicate. Common influenza viruses replicate throughout the entire respiratory tract, however the H5N1 strain can only replicate in the lower region. This restriction prevents the virus from being highly contagious and spreading between people. If the nature of the virus were to change, to enable it to replicate in the upper respiratory tract, then this could result in the infectivity of the virus dramatically increasing because it could spread easily through sneezing and coughing.
The H5N1 virus hinders immune function, and at the same time, also ‘tricks’ the immune system into overproducing inflammatory molecules called cytokines. These molecules have roles in regulating cell function, and abnormal increases there production induces the ‘flu-like’ symptoms such as fever, chills, vomiting and headache.
Currently, bird flu is diagnosed by taking a blood sample, and testing for the production of antibodies against the H5N1 strain. Antibodies are a large variety of proteins, which are produced in response to disease causing organisms in the body. The body makes specific antibodies against the H1N5 virus, and these can be identified in the blood and be used to diagnose if a person is infected.
Treatment and Prevention
People most at risk of infection are those in close contact with birds. These people can minimise the risk of bird flu by following good infection control practices. These include:-
• Careful attention to hand hygiene – cleaning hands thoroughly after handling birds or their excretions
• Personal protective equipment – wearing protective clothing or masks to avoid infection with the H5N1 virus
For people who think they may be exposed to bird flu, such as those who handle birds, there are two options for minimising the risk of developing the illness. These include:-
• Being vaccinated against seasonal influenza
• Taking influenza antiviral agents.
Anyone who is exposed to bird flu should be monitored carefully for the symptoms associated with H5N1 infection.
For people who are at risk, antiviral medications are recommended for prevention and treatment of avian influenza. Oseltamivir, which is sold under the trade name ‘Tamiflu’, is the recommended prescription antiviral medication. The most common side effects of oseltamivir are nausea and vomiting, and these are usually mild to moderate and happen in the first two days of treatment. A serious side effect to this drug can be confusion, and people, especially children, can be at increased risk of self-injury shortly after taking oseltamivir. After taking this medication, people should be monitored closely for signs of unusual behaviour.
Scientists are currently working on a vaccine against the H5N1 strain that is responsible for avian influenza. As yet, there are no vaccines currently available to protect people from avian influenza