What It Is

Avian influenza, or bird flu, is an extremely common strain of influenza which occurs naturally in bird populations. It is caused by Type A strains of the flu virus, and was identified by Italian scientists over 100 years ago.

It is thought that all birds are susceptible to the more than fifteen varieties of avian influenzas, with some species being particularly vulnerable. While migratory waterfowl often carry and suffer mildly from the disease, domestic poultry are the most susceptible to rapidly contagious, often fatal variations. All known outbreaks of the highly pathogenic influenza disease have originated from this A strain, specifically the H5 and H7 subtypes.

Usually these outbreaks are a result of domestic poultry populations– especially chickens and turkeys – coming into contact with migratory waterfowl like water ducks. Many outbreaks occur because the generally weak pathogen spread from the migratory birds mutates quickly into a more deadly form among the closely quartered domestic flocks.

For example, during an outbreak in 1983-1984 of birds in the United States, the H5N2 type influenza strain was initially a weak form of the flu with a low mortality rate, but within 6 months of the initial spread of the infection, the virus grew into a highly fatal disease with a bird mortality rate of almost 90%. This required the destruction of almost 17 million birds to prevent further occurrence.

When an outbreak occurs or is feared, it is standard to quarantine diseased populations of birds. However, the virus is both highly contagious and long-lived, so it can be transmitted easily from population to population via mechanical means (through contaminated machinery, manure, cages, vehicles or clothing.) Recent studies have shown that “a single gram of contaminated manure can contain enough virus to infect 1 million birds.” (Source: World Health Organization, "Avian influenza frequently asked questions") Thus, containment efforts are not always highly effective.

Bird influenza does not usually infect animals other than birds or pigs, but human infections were first reported in Hong Kong in 1997. Eighteen people became infected with the bird flu and developed severe respiratory distress which led to the deaths of six victims. Investigation into the cases revealed that close contact with live, infected birds, and the ability of the virus to mutate, allowed the influenza to jump directly to humans. Fortunately, though some secondary transmission of the disease occurred from worker to worker, the symptoms were not severe and the victims recovered. Alarmed by this transmission directly from birds to humans, Hong Kong immediately destroyed over 1.5 million birds, which many believe avoided a pandemic, or widespread outbreak.

Since the 1997 Hong Kong deaths, several other cases of bird influenza infections in humans have cropped up in the Netherlands, China, Thailand and Vietnam.

Why the Avian Influenza Might be the Next Pandemic

Scientists believe that parts of the three types of human flu viruses originated from birds. Widespread human influenza outbreaks occur with regularity, on average three to four times a century. It’s estimated that the pandemic of the Spanish flu (H1N1) in 1918-1919 caused an estimated 40 to 50 million deaths worldwide, but killing only about 2.5% of those infected. Scientists say that these pandemics are inevitable, and that the next one might be imminent.

Scientists from the World Heath Organization (WHO) have warned that the bird flu might be the next worldwide influenza pandemic. They are particularly concerned about the H5N1 subtype of virus, the one responsible for the Hong Kong outbreak, for several reasons. First, H5N1 mutates very quickly and can latch onto genes from diseases affecting other animals. Second, it’s already proved highly harmful to humans. (Compare the Spanish flu mortality rate of 2.5% to the H5N1 rate of 70% and you’ll see why scientists are so worried.) Finally, birds that survive the influenza can excrete virus-laden material for up to ten days, increasing the chances of infection among other bird populations.

H5N1 has shown up in bird populations in nine Asian nations - Cambodia, China, Indonesia, Japan, Laos, Malaysia, South Korea, Thailand, and Vietnam. The spread of bird infections to larger geographic areas increases the chances of human infection. Since H5N1 is so easily mutated, scientists worry that an increased number of infections in humans will lead to a virus which transforms into one more easily transmitted from person to person, resulting in a regional or even worldwide pandemic.

In an alarming outbreak in Vietnam, Cambodia and Thailand, H5N1 has resulted in 55 human infections since 2004, of which 42 victims died. To complicate the problem, “a diagnostic test designed by Canadian researchers and used in Vietnam to detect H5N1 avian flu is out of date, scientists from the National Microbiology Laboratory admit — raising the possibility some human cases may have been dismissed in error.” (Source: The Associated Press, May 8, 2005) Additionally, traditional mistrust between Vietnam and the West means that Vietnam has not fully agreed to help from international agencies like the World Health Organization, making quick diagnosis and analysis of new cases much more difficult.

Scientists are further concerned that traditional antiviral medications may not work on the hardy HSN1 sub-strain of influenza. For example, analysis has shown that the viruses are resistant to two of the medications, antadine and rimantadine. Though they are confident that other common treatments will work and are conducting studies to confirm this, scientists concede that it’s possible the H5N1 could mutate into a form that is resistant to all current antiviral treatments.

Other possibly dangerous strains of the avian influenza have been documented in many regions, including the Netherlands and North America. One recent, highly pathogenic outbreak in Gonzales County, Texas, was a result of the H5N2 subtype, and was reported in a flock of 7,000 chickens. The population of birds was culled, and the disease declared eradicated. It resulted in no human infections, though scientists warn that human infection was a risk during this time.

Iris Evan, a health minister in Alberta, Canada, says “most people don't understand how overwhelmed the health-care system would become if there were a flu pandemic. What worries me most is the ignorance of people in the public who assume that if they get sick there'll be something there for them, and they don't realize the devastation this could be.”

Flu would hit health-care workers as well. As many as a third of Canadians could fall ill at the same time.

There are few warning signs before a pandemic strikes – except a large and rapidly growing number of new and unrelated cases every day. The WHO says in the best-case scenario, two to seven million people will die in the next pandemic and tens of millions will need medical attention. But if the virus is particularly virulent, the number of deaths could be dramatically higher.” (Source: CBC News Online, March 8, 2005)

Why Things Might Not Be as Bad as They Seem

Though still potentially dangerous, H5N1 doesn’t appear, currently, to transmit well from person to person. There have been cases of person-to-person transmission, but only in 2 known cases did such transmission result in a human death, and even then only among those living in the same household as the infected person. Most person-to-person infections currently result in milder symptoms for the recipient than for the vector. Also, analysis of these cases showed that none contained human flu variants, which means that H5N1 does not appear to have melded with current human flu strains.

Another encouraging fact to note: history has shown flu vaccines to have been very accurate and effective in fighting influenza infection, and only require a lead time of about 4 months to develop. These efforts are already underway; research studies to test a vaccine to protect humans against H5N1 virus began in April 2005.

Additionally, because the World Health Organization and other agencies are so worried about the potential dangers of the disease, they’ve stepped up their campaign to educate health departments domestically and abroad on how to detest, diagnose, and prevent the spread of avian influenza A. The U.S. Government has increased spending on flu initiatives by seven times over the past few years. The National Institute of Allergy and Infectious Diseases (NIAID) has developed a device that identifies a particular flu strain in just minutes, simply by taking a throat swab, speeding up the process of developing appropriate treatments.

In the Meantime

As with any disease, its spread is hampered by frequent hand-washing, and avoidance of contaminated surfaces. Normal food preparation precautions are sufficient to rid surfaces of material that could be covered in infectious material. Currently, there is no need to avoid eating chicken or other poultry for two main reasons: first, that the virus is not food-borne; and second, that the U.S. has placed an import embargo on any poultry from countries where the avian flu is considered a risk. As of February 2004, the United States does not accept domestic fowl from the following countries: Cambodia; Indonesia; Japan; Laos; Malaysia; People's Republic of China, including Hong Kong, SAR; South Korea; Thailand; and Vietnam.

The Center for Disease Control (CDC) currently advises that travelers to countries in Asia with known outbreaks of influenza A (H5N1) 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. Also, assemble a travel health kit containing basic first aid and medical supplies. Be sure to include a thermometer and alcohol-based hand rub for hand hygiene. You may wish to check your health insurance plan or get additional insurance that covers medical evacuation in the event of illness. (Source: CDC website)

The Bottom Line

The avian influenza, or bird flu, is a potentially dangerous virus that bears watching. It is currently not a worldwide threat to humans, and measures are being taken to develop treatments and vaccines for the virus should it become an easily transmissible disease. While many experts, and the World Health Organization, caution that the virus could be the next flu pandemic, people should be aware that these dire warnings have also led health agencies to prevent them from becoming a reality.