Bird Flu: The Facts

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 and also involved H5N1.

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 feces, which become dry, pulverized and are then inhaled.

The death toll: As of Feb. 9, the World Health Organization (WHO) had confirmed 88 deaths from H5N1 out of 165 cases of human infection. Vietnam has the most fatalities, with 42, followed by Indonesia (16), Thailand (14), China (seven), Cambodia (four), Turkey (four) and Iraq (one). This list does not include an Iraqi Kurd whose death was reported by local authorities on Monday, two Indonesian women who died Thursday and Friday respectively and a woman's death reported by China on Friday.

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: there have been only three suspected cases in which this is believed to have happened. The big worry is that H5N1 could pick up genes from conventional human flu viruses, mutating into a form both highly lethal and highly 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.

Past pandemics: The 20th century saw three flu pandemics, in 1918-19, 1957-58 and 1968-69. The 1918-19 pandemic killed as many as 50 million people -- larger than the death toll from AIDS in more than two decades. Jet travel, the world's huge population today and the larger number of people with compromised immune systems (from HIV and cancer, for instance) compared with 1918 could contribute to a far heavier toll.

Economic cost: A global pandemic of any scale would cost hundreds of billions of dollars because of the disruption to economic life. The World Bank estimates a bill of $550 billion (465 billion euros) for rich countries alone. 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.

Veterinary controls: These are the time-honored first line of defense in any outbreak of animal disease. The task is to identify farms where there is an outbreak of H5N1, 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: An international conference in Beijing drew more than $1.9 billion dollars in pledges to help fight bird flu, after experts estimated that around that amount would be needed over the next three years to help poor countries shore up their defenses. An action plan drawn up in November stresses greater veterinary surveillance to detect outbreaks, preventative vaccination of poultry, culling of infected flocks and compensation for farmers. Its 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 recognized 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. Traditionally, flu vaccines take up to nine months to manufacture, using egg-based technology, although ways of speeding this up using genetic "reverse engineering" are being intensively explored.

Drug arsenal: The range of antiviral drugs is small, but especially so when it comes to bird flu. Only two are considered effective against H5N1: zanamivir (commercialized 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 antivirals, but does not give a figure as to how big that stockpile should be. It hopes to have its own stockpile, sufficient for three million people, by early 2006. A looming worry is whether the shifting virus might become resistant to Tamiflu.

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