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U.S. Department of Health and Human Services

Animal & Veterinary

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Federal Government Developing Response to Avian Influenza Concerns

FDA Veterinarian Newsletter September/October 2005 Volume XX, No V

The outbreak of avian influenza (AI) in Asia and reaching west and south is caused by a virus that could mutate and could cause a human influenza epidemic or even pandemic, which is why the Federal Government is heavily engaged in developing a response to this threat.

The virus responsible for the outbreak of AI that started in Asia has shown that it can cause serious illness in humans, even death, but as of mid-February health officials had reported fewer than 200 cases of human infections. The risk to humans is clear, though, especially if the virus becomes highly contagious in humans.

Health officials have identified the strain of AI first reported in Asia as H5N1, and they considered it to be highly pathogenic, or “high-path” (HPAI), in poultry, which means that it usually kills poultry infected by it. It also efficiently transfers between sick and healthy birds, so it is highly contagious among poultry.

But the AI first seen in Asia has not caused many reported human illnesses. The humans who have become ill from the influenza are those who had close contact with infected poultry or, in rare cases, with other individuals, usually relatives, who were infected. So, although the disease can jump the “species barrier” between poultry and people, which concerns scientists and public health officials, at this point it does not appear to do so efficiently, and it does not appear to spread between people efficiently, either. Consequently, the disease is widespread in poultry flocks, but not in the human population.

The HPAI first reported in Asia is caused by a Type A virus. All viruses that can infect poultry are Type A. The category of Type A viruses also includes viruses that infect mammals, including humans, as well as birds. If the HPAI seen in Asia somehow picks up a genetic trait that makes it more contagious among humans – either by mutating or by acquiring genes from another virus – and it is highly pathogenic in humans, then we could face a human influenza pandemic.

President Bush has already responded to the pandemic threat by issuing the “National Strategy for Pandemic Influenza,” which outlines the roles and responsibilities of the Federal, State, and local governments, industry, international partners, and individuals in preparing for and responding to an influenza pandemic. More information about the White House’s response click here.

Health and Human Services Secretary Michael Leavitt in November said that the Department of Health and Human Services (HHS) has developed the HHS Pandemic Influenza Plan, and he directed all operating units of HHS, which includes the Food and Drug Administration, the parent Agency of the Center for Veterinary Medicine, to develop operational plans.

More information about the Federal Government’s preparations is available at http://www.pandemicflu.gov/.

Scientific evaluation

Scientists classify all Type A influenza viruses by subtype based on the characteristics of two proteins on the surface of the virus – hemagglutinin and neuraminidase, which are abbreviated as H and N (as in H5N1).

Most people in the United States have developed immunity to some influenza viruses, but the U.S. population probably does not have much of a natural immunity to H5 viruses.

Bacteria are relatively stable, genetically, compared to viruses. In fact, influenza viruses are significantly more likely than bacteria to incorrectly reproduce themselves. Those mistakes, or mutations, can give the virus new characteristics, possibly including the ability to efficiently infect humans.

Influenza viruses are also capable of acquiring genes from another strain of influenza virus, a process called “re-assortment.” In that process, basically two different viruses occupying the same cell in a host animal (which could be a human) exchange genes. Because Type A influenza viruses can be found in humans as well as other mammals and birds, the avian influenza viruses have opportunity to re-assort genes with viruses that can infect humans, potentially giving the AI virus the ability to infect humans, causing severe illness, and spread efficiently between humans.

However, the fact that AI is present in an area does not mean that humans will become infected. The United States has seen outbreaks of HPAI in birds in previous years. In 1924, an outbreak was recorded in East Coast live bird markets. In 1983-84, an HPAI outbreak in the Northeast was contained, but authorities had to destroy about 17 million chickens, turkeys, and guinea fowl. The most recent HPAI outbreak was in 2004, when the disease was seen in the southern United States. U.S. Department of Agriculture, State, and local authorities were able to quickly contain and eliminate the disease.

Therefore, the mere presence of HPAI in birds does not automatically mean a human influenza epidemic or pandemic. But certain strains of AI carry the risk of a human epidemic, which if not contained could spread and become a pandemic.

Editor’s Note 

The FDA Veterinarian production schedule has been delayed, which is why this issue is dated September-Octo-ber 2005. However, we will publish all of the issues, including the final issue from 2005, as soon as possible.