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Facts on avian flu

Considering the current scare, read on

AFFECTED BY FLU? Birds at a poultry market

Here is an updated fact file on H5N1 avian influenza.

What is bird flu? Bird flu is also called avian influenza. There are 15 strains of flu that affect birds, but the one behind the global health scare is the sub-type known as H5N1. The first known cases of bird flu were detected in Hong Kong in 1997.

How it spreads to humans: Almost all the human cases of bird flu have been people who were directly exposed to infected fowl. They made contact with the virus through the birds' saliva, nasal secretions and faeces, which become dry, pulverised and are then inhaled.

Symptoms: Bird flu in humans causes symptoms that are like human flu, such as fever, cough, sore throat and muscle aches, conjunctivitis, pneumonia and other severe respiratory diseases.

Is chicken safe? Avian flu is not a food-borne virus, so the risk from eating properly cooked poultry is considered negligible.

The risk: At present, H5N1 is not easily transmitted from bird to human. In other words, a person would have to pick up a lot of virus in order to be infected. Nor is it easily passed from human to human. The big worry is that H5N1 could pick up genes from conventional human flu viruses, mutating into a form both highly lethal and infectious. As it would be a radically new pathogen, no one would have any immunity to it. The mutation could occur if H5N1 co-infects a human who already has ordinary flu or the agent is picked up from poultry by an animal such as a pig that can carry both bird and regular flu strains.

Economic cost: A global pandemic of any scale would cost hundreds of billions of dollars because of the disruption to economic life. The Asian Development Bank (ADB) estimates costs for Asia ranging from $99 billion to $283 billion. As a comparison, Severe Acute Respiratory Syndrome (SARS), which killed fewer than 800 people in its 2003 outbreak, cost more than 30 billion dollars.

Veterinary controls: There is the time-honoured first line of defence in any outbreak of animal disease. The task is to identify farms where there is an outbreak, quarantine the area, kill all fowl suspected to be in contact with it, disinfect machinery, vehicles and clothing, and bar sales of poultry products from the affected region. But these controls are only really dependable if a country has a good surveillance network and responds quickly and effectively to an outbreak. Adequate compensation, too, is essential for encouraging honest reporting by farmers.

Counter-measures: Greater veterinary surveillance to detect outbreaks, preventative vaccination of poultry, culling of infected flocks and compensation for farmers. The other focus is on strengthening health monitoring systems, stockpiling of antiviral drugs to dampen the spread of an outbreak and exercises to train medical personnel and the public.

Vaccine: No definitive vaccine against the viral threat is available as no one knows the precise shape the virus would take after mutating. Several prototypes are being explored. But the risk is that they could be only partially effective or even useless because the genetic shape of the virus will have changed and thus will not be recognised by antibodies. If a pandemic does occur, the big concern is about the delay. It could take up to six months to formulate and test the right vaccine, which will only be available in limited quantities immediately thereafter.

Drug arsenal: The range of antiviral drugs is small, especially so when it comes to bird flu. Only two are considered effective against H5N1: zanamivir (commercialised as Relenza) and oseltamivir (Tamiflu). These medications are called neuraminidase inhibitors, which block the virus from replicating. If taken within a couple of days of the onset of illness, they can ease the severity of some symptoms and reduce the duration of sickness. The WHO recommends that countries stockpile anti-virals, but does not give a figure as to how big that stockpile should be. A looming worry is whether the shifting virus might become resistant to Tamiflu. — AFP

Sources: WHO, U.S. Centers for Disease Control and Prevention (CDC), US National Institutes of Health (NIH), World Organisation for Animal Health (OIE), Nature, British Medical Journal (BMJ), The Lancet, New England Journal of Medicine (NEJM), U.S. Department of Health and Human Resources, news reports.

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