MANILA, November 19, 2005
 (STAR) Influenza viruses that primarily affect birds are called "avian influenza viruses" or popularly known as bird flu viruses. Of the three influenza virus types (A, B and C), only influenza A can infect birds.

The virus multiplies in the intestines of certain birds, usually waterfowl, and is later shed. Infected birds, on the other hand, shed the virus from other sites, including saliva, nasal secretions and feces.

Wild birds are the natural hosts of all influenza A subtypes, but they do not get sick when infected.

Certain avian influenza A virus subtypes, however, can cause extensive disease and death among some domesticated birds.

One very pathogenic avian influenza virus is the H5N1 strain, which has been the cause of the reported avian flu outbreaks in Asia.

From 1997 to early 2005, several outbreaks of avian influenza A among humans have been reported in several countries all over Asia.

The most recent outbreak was reported in Vietnam last December 2004 to early January and this was all caused by the avian H5N1 strain.

Outbreaks caused by this particular strain are closely monitored due to its unique capacity to cross species barriers and infect the human population.


Transmission from birds to humans can occur directly from birds or from avian-contaminated environments (bird droppings, contaminated dust and soil, contaminated equipment, feeds, or cages in infected farms) and through an intermediate host like pigs (direct contact and respiratory droplets).

What is significant about this transmission is the gene exchange, which can occur if a human is infected with both avian and human influenza viruses, which may give rise to a completely new subtype to which a few may have any immunity to.

Human-to-human transmission is possible, but there have been no confirmed cases yet. The majority of human cases and deaths are in Vietnam and Thailand, countries with very widespread outbreaks in poultries.


Symptoms of avian influenza among humans may range from fever, cough, sore throat, muscle pains to eye infections.

Complications, however, may be sudden and severe leading to pneumonia, acute respiratory distress, encephalitis and other severe and life-threatening conditions.

Generally, the diagnosis is made on clinical grounds. A thorough history of exposure is sought.

Suspicion of a possible avian flu outbreak is raised when there is an unexplained high number of mortality among domestic fowl.

Prevention tips

The most important precautionary measure for now is prevention of human exposure to the avian flu, hence the need to quickly detect any outbreaks among poultry.

In the Philippines, 14 wetlands and two dams that serve as sanctuaries for migratory birds have been identified as critical areas for surveillance.

Residents and wildlife bureau workers in the perimeter of these areas, together with poultry workers, have also been identified as target risk groups.

Finally, another key preventive measure is frequent hand-washing.

(From the Infection Control Service of St. Luke’s Medical Center)

Chief News Editor: Sol Jose Vanzi

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