France is now the seventh European Union country to confirm a case of the H5N1 strain of avian influenza virus, after Austria, Germany, Greece, Hungary, Italy and Slovenia. Iran, India and Egypt have now also confirmed their first cases of H5N1.
In Asia, tens of millions birds have died as a result of H5N1 infection, which kills 100% of chickens within 48 hours of infection.
To date, the World Health Organization (WHO) has confirmed 146 confirmed cases of the virus being transmitted to humans, leading to 76 deaths in Cambodia, China, Indonesia, Thailand, Turkey and Vietnam.
A person infected with H5N1 experiences classical flu symptoms of coughing, headache, nausea, dizziness, muscle pains and diarrhoea, as well as pneumonia, encephalitis, meningitis, respiratory distress syndrome and internal bleeding and haemorrhage.
The first virulent strain of H5N1 killed 68% of those people who became infected; more recenly, another strain had a mortality rate of 38%; and, in the spring of 2005, three out of seventeen people infected with a third strain H5N1 died.
Thus, there appears to be a pattern emerging, whereby the virus is becoming less deadly but more infectious. Flu experts say that this pattern has been a prelude to every flu pandemic in the past, and there are now growing fears that a strain of H5N1 transmissible from person to person could cause a bird flu pandemic. Such an event could have devastating effects on the global economy.
According to the Centers for Disease Control and Prevention (CDC), the worst-case scenario is a "middle-level pandemic," which could result in up to 80 million infections in the United States with 16 million deaths, a mortality rate of 20%, assuming there is no vaccine available.
The WHO has advised governments to stockpile the anti-flu drug Tamiflu. So far, more than 40 million doses have been ordered by 14 countries, and there is talk of imposing restrictions on the international poultry trade in order to try and contain the virus.
Flu viruses originate in wild aquatic, usually migratory birds, such as ducks and geese, which carry the viruses but are not infected by them. Transmission to, and infection of, domesticated birds (e.g. chickens) causes a genetic mutation which makes the virus capable of infecting pigs and, possibly, humans.
H5N1 appears to have evolved the ability to survive in chicken faeces and dead meat. In the last few years, 147 of the 418 tigers kept in Thai zoos have died after being fed raw chicken meat infected with the virus.
The first outbreak of H5N1 was in Hong Kong in 1997. High population densities and the practice by Chinese farmers of keeping ducks, chickens and pigs penned together makes Southern China particularly prone to outbreaks of avian influenza. China raises 13 billion chickens a year. These factors increase the likelihood of an outbreak of H5N1 and also of genetic mutations, some of which could produce a highly virulent strain capable of being transmitted between people.
Given that approximately 100 million birds have died in Asia from H5N1, while less than 150 human infections have been confirmed, the fears of a pandemic seem somewhat exaggerated. One cannot, however, discount the possibility of the emergence of a virulent strain of H5N1 capable of easily infecting humans.
H5N1: Virology
Viruses consist of nucleic acids (DNA or RNA) enveloped in a protein coat. There are three types of influenza viruses, types A, B and C. Those that infect humans and birds are mostly type A flu viruses.
All flu viruses, including H5N1, are retroviruses. That is, their genetic material is composed of RNA rather than DNA. H5N1 has 8 genes, two of which encode the proteins hemagglutin and neuraminidase, that are recognized by the human immune system. These two genes, called H and N, give bird flu and related viruses their name.

H5N1 viral particles
All viruses have short life cycles, which makes them acquire genetic mutations quickly. Retroviruses, and especially avian influenza viruses, are even more prone to genetic mutation, as they have unstable genes which are prone to reassortment during replication.
Anti-flu drugs and vaccines
The manufacture of vaccines is a complex process. The high mutation rate in influenza viruses means that a flu vaccine must be produced annually. It is also likely that, because of the high mutation rate, flu viruses will quickly become immune to any vaccine that is produced. For these reasons, there is little investment by pharmaceutical companies in vaccines, with vaccines accounting for only $5.4 billion of a global pharmaceutical market valued at $334 billion (i.e. less than 2%).
There are two types of anti-influenza drugs. H5N1 is believed to be immune to M2 inhibitors such as amantadine, but might be susceptible to the newer type, of which oseltamivir phosphate (marketed as Tamiflu) is an example. Currently, the Swiss pharmaceutical giant Roche is the only company to manufacture Tamiflu.
In the event of a pandemic caused by a strain of human-to-human transmissible H5N1, it is generally agreed that the demand for doses of Tamiflu and vaccine would far outweigh the supply. It would be months before adequate numbers of vaccines and Tamiflu doses could be made and distributed. Furthermore, the vast majority of the world's population would not have access to these drugs, and even in developed countries that can afford to stockpile them, public services would be overwhelmed with the scramble for vaccines and anti-virals.