The global health community has been in a state of alarm due to recent outbreaks of the avian influenza disease in many parts of the world, particularly in Asia. The disease has infected humans, prompting many to believe that a global pandemic will soon occur.

In the past decades, avian influenza has affected only birds and in some cases, pigs. Avian influenza does not normally affect humans but the first human case of avian influenza has been recently documented. Diseases previously known to only affect animals have crossed over to humans - avian influenza being one of these diseases. As a consequence, this crossing over has started many of the health pandemics that the world has suffered from for centuries.

Avian flu virus: constantly mutating

Avian influenza typically affects birds, specifically migratory birds, ducks and chickens. Avian influenza is an infectious viral disease that is similar to human flu. Several subtypes of Type A flu viruses cause avian influenza. Avian influenza differs from human flu in terms of the proteins that reside on the surface areas of the avian influenza virus subtypes.

It is known that there are 16 different HA (hemagglutinin) subtypes and nine NA (neuraminidase) subtypes of the avian influenza virus. These subtypes can combine with each other, producing different subtypes of the disease. Because of these constant combinations of subtypes, producing vaccines becomes even more difficult. One can never know what subtype will emerge next, let alone what its impact will be.

In addition, viruses are known to be constantly evolving. Viruses are constantly "changing their spots." Thus, scientists have to also evolve the medicines and vaccines that are being produced in order to keep up with the viruses' constant evolution.

H5N1: deadly avian flue subtype

So far, only a few subtypes of the avian influenza virus have managed to cross over from the bird species to human species. These subtypes are H9N2, H7N7, H7N3 and H5N1. Of these subtypes, H5N1 has created the biggest alarm within the international health community. Among the subtypes that have been reported to affect humans, the H5N1 subtype appears to be the worst. The H5N1 subtype has caused more than 50 deaths to date.

Bird flu symptoms in humans are dependent on the subtype that caused the infection. Some of the bird flu symptoms in humans are typical flu like symptoms such as fever, cough, sore throat and muscle aches. Bird flu symptoms in humans also include eye infections, pneumonia, and severe respiratory diseases such as acute respiratory distress and other life-threatening complications.

Avian flu: human to human transmission may be possible

The avian influenza virus and its subtypes have the tendency to easily mutate. This may be one reason that the avian flu has managed to cross over from birds to human beings. This mutation may also be the reason that human to human transmission of the disease is a distinct possibility.

The World Health Organization has said that there are three ways for the virus to cross over and become a "human flu", which means that the disease will not only be contracted from birds but also from humans. Humans may contract the virus and mutation occurs while the virus is within the body. The bird flu virus may also combine with ordinary human flu, thereby assimilating the characteristics of the disease, including its ability to infect humans. Mutation through combination with human flu can occur in the body of humans who contract the disease while being sick with human influenza or by being in contact (consumption, for example) with pigs, which serve as carrier of both kinds of flu.