FLU: As birds ready for trans-border migration beginning November, chances are that the avian flu virus too flies into new areas. Is this the beginning of pandemic? Nations are in a state of fear as the virus threatens to melt borders and spread the wings of death.

WITH the bird flu outbreak in Asia spreading to Europe, alarm bells have started ringing with the UN also asking for action. Tens of thousands of ducks and chickens have been culled to curtail the disease’s spread. As the human death toll continues to grow, many are concerned that the virus will mutate and trigger a human pandemic.

October to February is also a crucial period for the Indian authorities as this is the season when migratory birds visit the subcontinent. Many have already started arriving. Health has prepared a fact file on the flu’s spread.

What is avian influenza (Bird flu)?

Bird flu is an infection caused by avian (bird) influenza (flu) viruses. Theses flu viruses occur naturally among birds. Wild birds worldwide carry the viruses in their intestines, but usually do not get sick from them. However, bird flu is very contagious among birds and can make some domesticated birds, including chickens, ducks, and turkeys, very sick and kill them.

Bird flu and humans

There are many different subtypes of type A influenza viruses. These subtypes differ because of certain proteins on the surface of the influenza A virus (hemagglutinin{HA} and neuraminidase {NA} proteins). There are 16 different HA subtypes and 9 different NA subtypes of flu A viruses. Many different combinations of HA and NA proteins are possible. Each combination is a different subtype. All known subtypes of flu A viruses can be found in birds. However, when we talk about bird flu viruses, we are referring to influenza A subtypes chiefly found in birds. They do not usually infect humans, even though we know they can. When we talk about human flu viruses we are referring to those subtypes that occur widely in humans. There are only three known A subtypes of human flu viruses (H1N1, H1N2 and H3N2); it is likely that some genetic parts of current human influenza A viruses came from birds originally. Influenza A viruses are constantly changing, and they might adapt over time to infect and spread among humans. Bird flu viruses do not usually infect humans, but several cases of human infection with bird flu viruses have occurred since 1997.

Human Symptoms

Symptoms of bird flu in humans have ranged from typical flu-like symptoms (fever, cough, sore throat and muscle aches) to eye infections, pneumonia, severe respiratory diseases (such as acute respiratory distress), and other severe and life-threatening complications. The symptoms of bird flu may depend on which virus caused the infection
The Spread

Infected Birds shed flu virus in their saliva, nasal secretions, and feces. Susceptible birds become infected when they have contact with contaminated excretions or surfaces that are contaminated with excretions. It is believed that most cases of bird flu infection in humans have resulted from contact with infected poultry or contaminated surfaces. The spread of avian influenza viruses from one ill person to another has been reported very rarely, and transmission has not been observed to continue beyond one person.

Treatment

Studies done in laboratories suggest that the prescription medicines approved for human flu viruses should work in preventing bird flu infection in humans.

However, flu viruses can become resistant to these drugs, so these medications may not always work. Additional studies are needed to prove the effectiveness of these medicines. People should avoid contact with infected birds or contaminated surfaces, and should be careful when handling and cooking poultry.

Avian influenza A (H5N1) virus

Influenza A (H5N1) virus also called H5N1 virus is an influenza A virus subtype that occurs mainly in birds. Outbreaks of influenza H5N1 occurred among poultry in eight countries in Asia during late 2003 and early 2004. It is believed that these outbreaks are ongoing. Most recently, influenza H5N1 has been reported among poultry in Turkey and Romania. Human infections of influenza A (H5N1) have been reported in Cambodia, Indonesia, Thailand, and Vietnam. In Hong Kong the virus caused severe respiratory illness in 18 people, 6 of whom died. Since that time, there have been other cases of H5N1 infection among humans. Recent human cases of H5N1 infection that have occurred in Cambodia, Thailand, and Vietnam have coincided with large H5N1 outbreaks in poultry. The World Health Organization (WHO) also has reported human cases in Indonesia. Most of these cases have occurred from contact with infected poultry or contaminated surfaces; however, it is though that a few cases of human-to-human spread of H5N1 have occurred.

So far, spread of H5N1 virus from person to person has been rare and has not continued beyond one person. However, because all influenza viruses have the ability to change, scientists are concerned that the H5N1 virus one day could be able to infect humans and spread easily from one person to another. Because these viruses do not commonly infect humans, there is little or no immune protection against them in the human population.

If the H5N1 virus were able to infect people and spread easily from person to person, an influenza pandemic (worldwide outbreak of disease) could begin. No one can predict when a pandemic might occur.

However, experts from around the world are watching the H5N1 situation in Asia very closely and are preparing for the possibility that the virus may begin to spread more easily and widely from person to person.

H5N1 virus treatment

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, but additional studies still need to be done to prove their effectiveness.

Courtesy: CDC
The New Indian Express, Health Supplement, 8th November 2005