The rapid spread of bird flu, which is not uncommon among chickens and other fowl, has caught the attention of global health authorities.  There are at least 15 different types of avian influenza that routinely infect birds around the world. The current outbreak is caused by a strain known as H5N1, which is highly contagious among birds and rapidly fatal. Unlike many other strains of avian influenza, it can be transmitted to humans, causing severe illness and death.

Bird flu is not the same as SARS (severe acute respiratory syndrome). Although their symptoms are similar, SARS is caused by completely different viruses. Influenza viruses also are more contagious and cannot be as readily contained as SARS by isolating people who have the infection.

Influenza viruses are highly unstable and have the ability to mutate rapidly, potentially jumping from one animal species to another. Scientists fear the bird flu virus could evolve into a form that is easily spread between people, resulting in an extremely contagious and lethal disease. This could happen if someone already infected with the human flu virus catches the bird flu. The two viruses could recombine inside the victim’s body, producing a hybrid that could readily spread from person to person.

The resulting virus likely would be something humans have never been exposed to before. With no immune defenses, the infection could cause devastating illness, such as occurred in the 1918-19 Spanish flu pandemic, which killed an estimated 40 million to 50 million worldwide.

In rural areas, the H5N1 virus is easily spread from farm to farm among domestic poultry through the feces of wild birds. The virus can survive for up to four days at 71 F (22 C) and more than 30 days at 32 F (0 C). If frozen, it can survive indefinitely.

So far in this outbreak, human cases have been blamed on direct contact with infected chickens and their droppings. People who catch the virus from birds can pass it on to other humans, although the disease is generally milder in those who caught it from an infected person rather than from birds.

If the virus mutates and combines with a human influenza virus, it could be spread through person-to-person transmission in the same way the ordinary human flu virus is spread.

The current outbreak of bird flu is different from earlier ones in that officials have been unable to contain its spread. An outbreak in 1997 in Hong Kong was the first time the virus had spread to people, but it was much more quickly contained. A total of 18 people were hospitalized with six reported deaths. About 1.5 million chickens were killed in an effort to remove the source of the virus.

Unlike the 1997 scare, this outbreak has spread more rapidly to other countries, increasing its exposure to people in varied locations and raising the likelihood that the strain will combine with a human influenza virus.

Bird flu can cause a range of symptoms in humans. Some patients report fever, cough, sore throat and muscle aches. Others suffer from eye infections, pneumonia, acute respiratory distress and other severe and life-threatening complications.

Flu drugs exist that may be used both to prevent people from catching bird flu and to treat those who have it. The virus appears to be resistant to two older generic flu drugs, amantadine and rimantadine. However, the newer flu drugs Tamiflu and Relenza are expected to work – though supplies could run out quickly if an outbreak occurs.

Currently there is no vaccine, although scientists are working to develop one. It probably will take several months to complete and may not be ready in time to stop a widespread human outbreak, if one occurs.

Rapid elimination of the H5N1 virus among infected birds and other animals is essential to preventing a major outbreak. The World Health Organization recommends that infected or exposed flocks of chickens and other birds be killed in order to help prevent further spread of the virus and reduce opportunities for human infection. However, the agency warns that safety measures must be taken to prevent exposure to the virus among workers involved in culling.

Sources: AP, CDC & WHO  

 

Timeline Bird flu

Common in birds, avian influenza usually does not spread to people, but several instances of human infections have been reported since 1997.

Dec. 1997 An outbreak of bird flu in Hong Kong kills six people and sickens another 12. To remove the source of the virus, authorities destroy about 1.5 million chickens. The outbreak is caused by the avian influenza strain known as H5N1, the same virus behind the current crisis in Asia. March 1999 Two children in Hong Kong are diagnosed with avian influenza caused by the strain H9N2, a milder strain than H5N1. Both patients recover and no other cases in Hong Kong are confirmed. Mainland China reports several additional cases caused by H9N2 during the same time frame. Feb. 2003 Two cases of bird flu caused by H5N1 are reported among members of a family in Hong Kong who had recently traveled to China. One person recovers, while the other dies. Another family member dies after contracting a respiratory illness in China, but no testing is done to confirm the cause of death. No additional cases of bird flu are reported. March 2003 An outbreak of bird flu in the Netherlands kills a veterinarian and sickens more than 80 other people, mostly poultry workers and their families. The illnesses are caused by another strain of the avian influenza virus, known as H7N7, which results in mostly eye infections and some respiratory symptoms. Dec. 2003 A child in Hong Kong is diagnosed with bird flu caused by the H9N2 strain. The child is hospitalized and later recovers. Meanwhile, South Korea confirms an outbreak of the H5N1 virus at a chicken farm near Seoul and begins a mass cull of poultry as the virus rapidly spreads across the country. Jan. 8 2004 Vietnam announces that bird flu caused by the H5N1 strain has been found on many of its poultry farms. Jan. 11 Japan says 6,000 chickens have died of avian influenza on a farm, and says it is the first time the disease has been confirmed in the country. Jan. 13 The World Health Organization confirms that the deaths of three people in Vietnam are linked to bird flu caused by H5N1. Jan. 20 Brazil, the world’s No.2 poultry exporter, bans imports of poultry and poultry products from countries afflicted with bird flu. Jan. 23 Cambodia confirms an outbreak of bird flu at a farm on the outskirts of Phnom Penh. Switzerland and the European Union impose a ban on imports of Thai poultry meat and products after two human cases are confirmed in Thailand. Hong Kong, Bangladesh, Japan and Russia have already banned or impounded Thai poultry imports. Jan. 25 Indonesia discovers an outbreak of avian influenza among chickens but has no evidence that the disease has spread to humans. Pakistan says two million chickens have died of a mild form of bird flu, caused by the H7N7 and H9N2 strains. Jan. 26 Thailand confirms the death of a six-year-old boy, the nation’s first human death from bird flu. Jan. 27 The bird flu virus kills ducks in southern parts of China, which begins a cull of 14,000 birds. The agriculture ministry in Laos confirms bird flu in the area around Vientiane. Jan. 29 Afghanistan bans the import of chickens from neighboring Pakistan while Saudi Arabia imposes a temporary ban on chicken exports from seven countries with bird flu. Indonesia bows to international pressure, announcing it will cull chickens instead of vaccinating them. Jan. 30 Hong Kong bans imports of live birds and poultry meat. China says tests confirm the H5N1 virus in Hubei and Hunan provinces as well as the southern region of Guanxi Feb. 1 China’s state television reports five more areas with suspected cases of bird flu in poultry, bringing to 11 the total number of such outbreaks. The WHO says two sisters have died in Vietnam after contracting bird flu and they may have caught the virus from their brother, who had also died. Feb. 2 An 18-year-old dies of bird flu in Ho Chi Minh City, bringing to nine the fatalities in Vietnam. A Thai woman dies of bird flu, raising that country’s toll from the virus to three. The total number of fatalities stands at 12. Feb. 3 Indonesia finds the H5N1 strain of bird flu in its poultry flocks. A seven-year-old Thai boy dies, becoming the country’s fourth confirmed death from the disease. The total number of fatalities stands at 13.