Wednesday, January 16, 2008

Avian Flu Continues to Cause Disease and Deaths

Today, the New England Journal of Medicine released updates regarding Avian Flu, or the H5N1 virus. The review contains updates from a 2005 report, along with World Health Organization recommendations.

What do we really need to know about this potential pandemic. What about vaccines and what are the current predictions?

According to the update, the Avian flu virus has evolved into distinct groups since it was first identified. This makes vaccine choices difficult, even though vaccine is plentiful and available. The necessary antibody levels required for protection have not been established. Studies have shown that antibody response may be age related and vaccination guidelines are simply not yet established.

The virus group (or clade), varies by geographic location. Not all of the virus groups have produced disease in humans. Exposure to poultry infected with Avian flu has been seen widely, yet human infection continues to be rare. Success toward prevention with Avian flu vaccine remains undefined as well as costly even though it has been produced.

It is not certain if migratory birds should be viewed as a potential source of Influenza A, or H5N1 virus, but it is felt that the risk of spread to North American from this source is low. The chance of Avian flu transmission from other domesticated animals to humans remain theoretical.

The incidence of the virus has increased since 2005, and the spread is recognized as being group specific; cited as clade (group) 2.2. The number of confirmed cases as of December 2007 is 340. The increase is believed to be the result of virus proliferation in Eurasia and Africa.

The least amount of deaths from Avian flu (HN51 virus, Influenza A) occurs in people over age 50, with the highest incidence in persons aged 40 or younger. The disease is worse in cooler months when poultry outbreaks are more common.

Avian flu outbreaks continue to occur in clusters, the largest being eight persons. More than ninety percent of those infected have been family members, making genetic predisposition to avian flu a possibility. Since this is only speculative, it is recommended that all body fluids be treated as infectious in anyone who has contacted H5N1 or Influenza A. We cannot make assumptions about genetic predisposition.

Physicians are being urged to suspect avian flu in travelers, though no cases have yet been reported as the result of short term visits to affected countries.

The main method of transmission is still identified as bird to human. Questions remain about how the virus enters the respiratory tract, but it's suggested that it may be through inhalation of aerosolized excrement. It's not known if the virus can enter the gastrointestinal tract, though it has been detected in the feces of infected persons before respiratory symptoms of viral pneumonia were manifested.

Specific inflammatory changes have been detected on autopsy. These markers provide differentiation from human influenza A, but lack of knowledge about the mechanism that produces the inflammation makes it impossible to guide treatment. The amount of time it will take for the avian flu to progress to death has remained the same (9-10 days after onset).

Recommendations for identifying Influenza A include a very close look at anyone who rapidly develops pneumonia. Healthcare providers are being urged to include H5N1 infection when differentiating causes of pneumonia in high risk populations and in those whose illness follows an abnormal course.

Early treatment with the antiviral agent oseltamavir has been shown to improve survival rate, but no optimal dose or length of time for administration has been absolutely determined. In spite of this fact, recommendations are being provided to physicians regarding dosing. The mainstream recommendation for H5N1 treatment is to provide support - oxygen administration, fluids, and prevention of opportunistic infections.

The World Health Organization has stockpiled antiviral agents in case of a predicted widespread outbreak. A current model predicts spread of the disease in rural Asia. The plan is to provide antiviral agents for prophylaxis. Included in this plan are "social distancing" measures to curb spread of the disease.

The CDC and WHO have published guidelines designed to prevent infection, such as using soaps, disinfectants, chlorination and alcohols. The guidelines are available from the U.S. Centers for Disease Control and Prevention and the WHO. It has been established that avian influenza A can be readily deactivated by a variety of chemical agents.

The above information doesn't seem earth shattering, but one thing is very striking to me. Prevention is key. It is the most clearly defined, understood and attainable recommendation regarding the control of Avian flu.

It's obvious - the future of Avian flu appears to lie solely in the hands of conscientious poultry handlers.