H5N1 Flu

H5N1 is a highly pathogenic strain of avian influenza (bird flu) with the first instance of the flu recorded in Hong Kong in 1997. The infection of humans coincided with an epidemic of avian influenza, caused by the same strain, in Hong Kong's poultry population.

Usually these flu viruses are non lethal and are carried worldwide by wild bird populations in their intestines. However this variant has mutated into the most fatal strain of avian influenza. Normally this virus would not be harmful to humans. Close proximity of humans to live chickens, pigs, and other animals, as may be seen in certain farms or marketplaces could cause the H5N1 virus to exchange genetic material with other viruses that more easily attack humans.

According to the World Health Organization (WHO), there is mounting evidence that the H5N1 strain has a unique capacity to jump the species barrier and cause severe disease, with high mortality, in people. It is feared that the H5N1 subtype of avian influenza A could trigger the next pandemic.

The H5N1 virus could either:

The first documented cases of bird flu infecting people occurred in Hong Kong in 1997 and this was also the H5N1 strain of virus. Investigation showed that close contact with live infected poultry was the source of the infection.

H5N1 is very contagious among birds and often causes severe, even fatal, symptoms. Infected birds pass on the virus through their saliva, nasal secretions, and feces. Other birds may pick up the virus through direct contact with these excretions or when they have contact with surfaces contaminated with this material. The H5N1 virus is likely to spread throughout the world since migratory birds are some of the carriers of the virus.

Past outbreaks of avian flu have often originated in crowded conditions in southeast and east Asia, where humans, pigs, and poultry live in close quarters. The virus is more likely to mutate into one that infects human under such conditions

Avian influenza has been detected in pigs as well increasing fears of the emergence of new variant strains. In February 2004, Avian influenza virus was detected in pigs in Vietnam; in May 2005, the occurrence of Avian influenza in pigs in Indonesia was reported ("swine flu"). The occurrence in swine raises the level of concern about the possible evolution of the virus into a strain capable of causing a global human influenza pandemic.

H5N1 is able to infect people because it is able to cross the species-barrier. In human populations, where domestic pigs and wild and domestic birds live in close proximity with people, the mingling and exchange of human and animal viruses can more easily occur.

In humans, since H5N1 is an influenza virus symptoms can appear like the common flu with fever, cough, sore throat, and sore muscles. However, in more severe cases pneumonia and severe problems with the respiratory system can develop, and can eventually cause death. Patients with H5N1 avian influenza have rarely had conjunctivitis 6, unlike human cases with the H7 virus.

The H5N1 virus currently infecting birds in Asia that has caused human illness and death is resistant to amantadine and rimantadine, two antiviral medications commonly used for influenza. Two other antiviral medications, oseltamavir and zanamavir, would probably work to treat flu caused by the H5N1 virus.