The actual rate of bird flu infection in human might be small, but the threat of avian influenza needs to be taken very seriously. The main source of human infection appears to be from close contact with sick or dead birds infected with H5N1.

Scientists look for patterns

Killing, butchering, and eating infected poultry is the most risky behavior. However, scientists have traced some cases to exposure to chicken feces and swimming in water contaminated by the carcasses of infected birds.

A high percentage of the human bird flu victims have been seemingly healthy children and young adults. Most of the cases have occurred in rural, poverty-stricken areas where people live in close proximity with their livestock.

Strangely, people that would seem to be in high risk groups -- poultry processing workers, veterinarians, and healthcare workers -- have rarely contracted bird flu. These inexplicable patterns puzzle scientists as they try to determine what makes some groups more susceptible to bird flu than others.

H5N1 may mutate

When discussing avian influenza, it must be stressed that it is a relatively rare disease. In fact, when you consider that several hundred thousand people die each year from other forms of human influenza, bird flu seems like a small, isolated problem. So, why are health experts so worried?

The fear is not over the current strain of H5N1, but over the potential for it to mutate. Influenza viruses are constantly changing and merging. If H5N1 were to combine with another virus that is more easily spread among humans, the new mutated virus could create a pandemic, capable of killing an unprecedented number of people.

The perplexing nature of bird flu puts health officials and politicians in a difficult situation. They don’t want to unnecessarily scare people over a disease that may never impact large numbers of humans. Yet, at the same time, the population needs to be educated and prepared for the possibility of a wide-scale outbreak.

Most experts agree that avian influenza is a threat that must be closely monitored.

Hong Kong outbreak monitored

The first documented outbreak of H5N1 in humans was in Hong Kong in 1997. Eighteen cases were linked to an identical virus found in area poultry farms and live markets. Scientists learned that the 18 human cases were the result of direct contact with infected poultry.

They studied family members, friends, and even their healthcare providers, and found virtually no evidence of transmission of the virus from one person to another. Almost all of Hong Kong’s poultry was destroyed within three days and there were no further human infections.

The symptoms

After infecting a person, H5N1 incubates for five to seven days, which is much longer than the normal flu incubation of two or three days. After incubation, the initial symptoms appear, such as:

• High fever
• Diarrhea
• Vomiting
• Abdominal pain
• Chest pain
• Bleeding from the nose or gums

Five days after the initial symptoms appear, people may begin to exhibit respiratory difficulties and show signs of eye infections. Almost everyone will develop pneumonia at this stage. The acute respiratory distress that follows is the main cause of death.

The symptoms may, however, vary from case to case. Sometimes there is no diarrhea and sometimes there are no respiratory symptoms. We still know very little about avian influenza.

Despite attempts by the World Health Organization (WHO) to learn as much as possible, there have been less than 200 bird flu cases in humans to investigate. The small number of incidences considerably limits our knowledge.

See also

• What you need to know
• Bird flu and SARS
• All about virus dispersion
• The latest news