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A Description Of Bird Flu And The Possible Pandemic

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There is a good post about bird flu by Ayu up at Blogcritics, and I though I’d add some information to educate readers about bird flu.

A primary fear is that should bird flu successfully mutate to a pathogen transmitted from human to human, an influenza pandemic may result. Most people are aware of the most famous of flu pandemics, the 1918 Spanish Flu pandemic, which “caused the highest number of known flu deaths: more than 500,000 people died in the United States, and 20 million to 50 million people may have died worldwide. Many people died within the first few days after infection and others died of complications soon after. Nearly half of those who died were young, healthy adults.”

Influenza viruses are found in pigs, ducks, horses, whales, seals, and other birds. However, “certain subtypes of influenza A virus are specific to certain species, except for birds which are hosts to all subtypes of influenza A. Subtypes that have caused widespread illness in people either in the past or the current period are H3N2, H2N2, H1N1, and H1N2. H1N1 and H3N2 subtypes have caused outbreaks in pigs and H7N7 and H3N8 viruses have caused outbreaks in horses.”

According to one news report, the CDC says “there is a high chance that the avian flu will mutate into a form than can transfer from human to human. It is currently the right season for the flu virus to spread in Asia, so the CDC expects to see more cases in the next few weeks. Although few deaths have been reported so far, it is very likely that the numbers will increase.” The symptoms of avian influenza in humans includes “typical influenza-like symptoms (e.g., fever, cough, sore throat, and muscle aches) to eye infections (conjunctivitis), pneumonia, acute respiratory distress, viral pneumonia, and other severe and life-threatening complications.” Influenza drugs such as amantadine, rimantadine, oseltamivir, and zanamivir have worked, but influenza strains may become resistant to drug treatment so these drugs may not always be effective.

The CDC’s web site describes transmission of influenza from birds to humans in this manner:

Most cases of avian influenza infection in humans are thought to have resulted from contact with infected poultry or contaminated surfaces. However, there is still a lot to learn about how different subtypes and strains of avian influenza virus might affect humans. For example, it is not known how the distinction between low pathogenic and highly pathogenic strains might impact the health risk to humans. Of the documented cases of human infection with avian influenza viruses, illnesses caused by highly pathogenic viruses appear to be more severe.

Public health authorities currently closely monitor human influenza outbreaks associated with avian influenza. A fear is that a pandemic may result should avian influenze successfully mutate and transmit from human to human. That said, since 1997, humans infected with avian influenza viruses have not resulted in human-to-human transmission.

The following are incidences since 1997 of avian-to-human influenza outbreaks:

H5N1, Hong Kong, 1997 : Avian influenza A (H5N1) infections occurred in both poultry and humans. This was the first time an avian influenza virus had ever been found to transmit directly from birds to humans. During this outbreak, 18 people were hospitalized and six of them died. To control the outbreak, authorities killed about 1.5 million chickens to remove the source of the virus. Scientists determined that the virus spread primarily from birds to humans, though rare person-to-person infection was noted.

* H9N2, China and Hong Kong, 1999 : Avian influenza A H9N2 illness was confirmed in two children. Both patients recovered, and no additional cases were confirmed. The evidence suggested that poultry was the source of infection and the main mode of transmission was from bird to human. However, the possibility of person-to-person transmission could not be ruled out. Several additional human H9N2 infections were reported from mainland China in 1998-99.

* H7N2, Virginia, 2002: Following an outbreak of H7N2 among poultry in the Shenandoah Valley poultry production area, one person was found to have serologic evidence of infection with H7N2.

* H5N1, China and Hong Kong, 2003 : Two cases of avian influenza A (H5N1) infection occurred among members of a Hong Kong family that had traveled to China. One person recovered, the other died. How or where these two family members were infected was not determined. Another family member died of a respiratory illness in China, but no testing was done.

* H7N7, Netherlands, 2003 : The Netherlands reported outbreaks of influenza A (H7N7) in poultry on several farms. Later, infections were reported among pigs and humans. In total, 89 people were confirmed to have H7N7 influenza virus infection associated with this poultry outbreak. These cases occurred mostly among poultry workers. H7N7-associated illness included 78 cases of conjunctivitis (eye infections) only; 5 cases of conjunctivitis and influenza-like illnesses with cough, fever, and muscle aches; 2 cases of influenza-like illness only; and 4 cases that were classified as “other.” There was one death among the 89 total cases The death occurred in a veterinarian who visited one of the affected farms and developed acute respiratory distress syndrome and complications related to H7N7 infection. The majority of these cases occurred as a result of direct contact with infected poultry; however, Dutch authorities reported three possible instances of transmission from poultry workers to family members. Since that time, no other instances of H7N7 infection among humans have been reported.

* H9N2, Hong Kong, 2003 : H9N2 infection was confirmed in a child in Hong Kong. The child was hospitalized but recovered.

* H7N2, New York, 2003: In November 2003, a patient with serious underlying medical conditions was admitted to a hospital in New York with respiratory symptoms. One of the initial laboratory tests identified an influenza A virus that was thought to be H1N1. The patient recovered and went home after a few weeks. Subsequent confirmatory tests conducted in March 2004 showed that the patient had been infected with an H7N2 avian influenza virus. An investigation to determine the source of infection is ongoing.

* H5N1, Thailand and Vietnam, 2004: In January 2003, outbreaks of highly pathogenic influenza A (H5N1) in Asia were first reported by the World Health Organization. From December 30, 2003, to March 17, 2004, 12 confirmed human cases of avian influenza A (H5N1) were reported in Thailand and 23 in Vietnam, resulting in a total of 23 deaths. Visit www.cdc.gov/flu/avian/outbreaks/asia.htm, http://www.oie.int and http://www.who.int/en/ for more information.

* H7N3 in Canada , 2004: In February 2004, human infections of H7N3 among poultry workers were associated with an H7N3 outbreak among poultry. The H7N3-associated illnesses consisted of eye infections.

* H5N1, Thailand and Vietnam, 2004: Beginning in late June 2004, new lethal outbreaks of H5N1 among poultry were reported by several countries in Asia. The new outbreaks of H5N1 in poultry in Asia were followed by renewed sporadic reporting of human cases of H5N1 infection in Vietnam and Thailand beginning in August and continuing into 2005. Of particular note is one isolated instance of probable limited human-to-human transmission occurring in Thailand in September.

The following information about influenza subtypes, transmission, and antigen shift is from the CDC web site:

Influenza viruses have eight separate gene segments. The segmented genome allows viruses from different species to mix and create a new influenza A virus if viruses from two different species infect the same person or animal. For example, if a pig were infected with a human influenza virus and an avian influenza virus at the same time, the viruses could reassort and produce a new virus that had most of the genes from the human virus, but a hemagglutinin and/or neuraminidase from the avian virus. The resulting new virus might then be able to infect humans and spread from person to person, but it would have surface proteins (hemagglutinin and/or neuraminidase) not previously seen in influenza viruses that infect humans.

This type of major change in the influenza A viruses is known as antigenic shift. Antigenic shift results when a new influenza A subtype to which most people have little or no immune protection infects humans. If this new virus causes illness in people and can be transmitted easily from person to person, an influenza pandemic can occur.

It also is possible that the process of reassortment could occur in a human. For example, a person could be infected with avian influenza and a human strain of influenza at the same time. These viruses could reassort to create a new virus that had a hemagglutinin from the avian virus and other genes from the human virus. Theoretically, influenza A viruses with a hemagglutinin against which humans have little or no immunity that have reassorted with a human influenza virus are more likely to result in sustained human-to-human transmission and pandemic influenza. Thus, careful evaluation of influenza viruses recovered from humans who are infected with avian influenza is very important to identify reassortment if it occurs.

While it is unusual for people to get influenza infections directly from animals, sporadic human infections and outbreaks caused by certain avian influenza A viruses and pig influenza viruses have been reported. (For more information see Avian Influenza Infections in Humans.) These sporadic human infections and outbreaks, however, rarely result in sustained transmission among humans.

The health community is quite right to be concerned that avian flu will eventually transmit from human-to-human. Thankfully the CDC and other health organizations are keeping an eye on avian flu, as it should.

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About Trish Wilson

  • we

    good

  • http://www.templestark.com/blog Temple A. Stark

    Trish, This post was chosen by the section editor as a BC pick of the week. Go HERE (link) to find out why.

    And thank you
    – Temple

  • v.prashanth

    good

  • http://ruvysroost.blogspot.com Ruvy in Jerusalem

    Very well done article, if a bit dated. The threats we face from bird flu are far more widespread than they were at the time this article was published. Just today, one Egyptian has died from bird flu, and the Jordanians are preparing to fight the problem. The stock of fowl in Israel will undergo a severe culling as the bird flu spreads through the flocks here.

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