Avian flu: Some basic information

An outbreak of Bird Flu is affecting bird populations in countries throughout Asia. The outbreak is caused by the subtype H5N1 of influenza A. In birds, outbreaks have been confirmed among poultry in Cambodia, China, South Korea, Hong Kong, Indonesia, Japan, Laos, Vietnam and Thailand. In people, the outbreak has resulted of H5N1 infection in Vietnam and Thailand. Deaths have also been reported. Infected birds usually shed viruses in saliva, nasal secretions and feces. So at this time, it is believed that these cases resulted from contact with infected birds or surfaces contaminated with excretions from infected birds.

The virus was first isolated from birds in South Africa in 1961. The first instance of direct bird-to-human transmission of H5N1 was documented in 1997 during an outbreak of avian influenza among poultry in Hong Kong; the virus caused severe respiratory illness in 18 people, of whom six died.

Bird flu viruses are not easily transmitted to humans, but they can be passed to people through those live in close contact with birds, such as farmers raising chickens. If humans are infected, they become very sick, and it can be fatal. Over the last few years, there have been several outbreaks in Asia and one in the Netherlands in which the viruses caused epidemics among birds, and were then passed to humans.

Since mid-December 2003, the outbreaks reported in the above mentioned countries affecting large numbers of farm birds have caused at least 12 human infections. Millions of domestic poultry have died or been killed, and the human patients quarantined. The WHO has issued a full-scale alert.

The flu viruses that typically infect humans, and that cause epidemics of the regular flu each winter, are very contagious. In contrast, the viruses that cause bird flu, and that on occasion spread from birds to humans, cause disease that is serious but not contagious in humans. In summary, bird flu viruses are very serious but not contagious, while the human flu viruses are less serious but very contagious. But the main concern is that if a human becomes infected with both bird flu virus and a human flu virus at the same time, the two could combine and create a hybrid virus that causes very serious disease and is very contagious. That virus could rapidly spread all over causing serious illness in a huge number of people.

Certain water birds also act as hosts of influenza viruses by carrying the virus in their intestines and shedding it. The viruses spread among susceptible birds and the most common mode of spread is fecal-to-oral transmission. The range of symptoms in birds varies greatly depending on the strain of virus and the type of bird. Infection with certain viruses (some H5 & H7 strains) can cause widespread disease and death among some species of wild and especially domesticated birds such as chickens, ducks and turkeys. The reported symptoms of avian influenza in humans have ranged from typical influenza-like symptoms (e.g. fever, cough, sore throat and muscle pain) to eye infections, pneumonia, acute respiratory distress, viral pneumonia, and other severe life-threatening complications.

Key to containing the outbreak is the killing of sick and exposed birds. This was done in 1997 in Hong Kong. For the current outbreaks in Asia, governments are killing poultry to try to contain the virus. Patients are being treated and isolated, and investigations are underway to determine the source of infection.

The travelers to countries in Asia with documented H5N1 outbreaks should avoid poultry farms, contact with animals in live food markets, and any surfaces that appear to be contaminated with feces from poultry or other animals.

Dr ATM Emdadul Haque is lecturer, Universiti Sains Malaysia, Kelantan, Malaysia.