Avian Influenza (Bird Flu)

Spreading
Certain water birds act as hosts of avian influenza virus by carrying the virus in their intestinal tract and shedding it in their feces. Infected birds shed virus in saliva, nasal secretions and feces. Avian influenza viruses are transmitted to susceptible birds through inhalation of influenza particles in nasal, respiratory and fecal material from infected birds; however, fecal-to-oral transmission is the most common mode of spread. Live bird markets have also played an important role in the spread of epidemics.

The avian influenza virus can remain viable for long periods of time at moderate temperatures, and can survive indefinitely in frozen material. As a result, the disease can be spread through improper disposal of infected carcasses, manure, or poultry by-products.

Transmission of Avian influenza A from birds to humans is a rare event; but it may spread to humans, when they come into contact with the droppings of infected birds. Although it was not possible to establish how every case became infected, it is most likely that the individuals who contracted avian flu did so directly through exposure to chickens. However, if the virus were to mutate or combine with a human flu virus, it could start spreading from person to person. The human flu virus can spread more easily than the SARS virus. There is no evidence that the virus can survive in well cooked meat. 

Prevention
Infected birds shed virus in the first two weeks of infection. Four weeks after infection, virus can no longer be detected. Hence, prevention is best accomplished by preventing contact between newly infected and susceptible birds. Preventing direct contact with free-flying birds and protecting domestic poultry from contact with the feces of wild birds is an important way to prevent avian influenza. Countries across Asia are battling to stop the spread of the disease by culling poultry.

The quarantining of infected farms and destruction of infected or potentially exposed flocks are standard control measures aimed at preventing the spread of the virus in a country’s poultry population. Apart from being highly contagious, avian influenza viruses are readily transmitted from farm to farm by mechanical means, such as by contaminated equipment, vehicles, feed, cages, or clothing. Highly pathogenic viruses can survive for long periods in the environment, especially when temperatures are low. In the absence of prompt control measures backed by good surveillance, the epidemic can last for years. Any object located on an infected poultry farm must be considered contaminated and should be completely cleaned and disinfected before it is moved from that premises.

Influenza viruses are very sensitive to most detergents and disinfectants. They are readily inactivated by heating and drying. However, flu viruses are well-protected from inactivation by organic material and infectious virus can be recovered from manure for up to 105 days. Complete removal of all organic material is part of any effective disinfection procedure. All buildings should be cleaned and disinfected after an infected flock is removed. The poultry litter should be composted before being used as manure to cultivated lands.

Contaminated houses are to be  heated for several days to inactivate virus. Organic material should be removed followed by complete cleaning and disinfection of all surfaces. Contaminated litter and manure is problematic and should be composted to ensure that it does not spread infectious virus.

Treatment
There is no effective treatment for avian influenza. Good husbandry, proper nutrition and broad spectrum antibiotics may reduce  secondary infections. It must be remembered that recovered flocks continue to intermittently shed the virus.

Diagnosis of avian influenza may be made on the basis of symptoms and events leading to the disease. However, since the symptoms and course of avian influenza are similar to other diseases, laboratory diagnosis is essential.

Avian influenza in humans can be detected reliably with standard influenza tests. Antiviral drugs are clinically effective in both preventing and treating the disease.

Recently discovered anti-viral drug, Tamiflue is considered as the only possible defense against an outbreak of human to human avian flue. A chemical compound called shikimic acid is the basic material for making Tamiflue drug. The acid is extracted from a spice named star anise, which is harvested in China, North Vietnam and neighbouring countries. The drug has proved effective against the lethal H5N1 strain of the bird flu. The drug will not prevent the Avian flue but it can reduce the severity of the disease.

 Vaccines, however, take at least four months to be made and must be prepared for each subtype. Once the disease has been detected and reported, stringent disease control measures must be taken.