Viral Diseases Avian Influenza

Avian influenza A (H5N1) first infected humans in 1997, in Hong Kong. The virus was transmitted directly from birds to humans. Eighteen people were admitted to hospitals, and 6 died. In 2003, 2 cases of avian influenza A (H5N1) infection occurred among members of a Hong Kong family, 3 of whom had traveled to mainland China. One person died. How or where these 2 people became infected was not determined.

Influenza A has the potential to cross species and has been implicated in the 3 flu pandemics in the 20th century (1918, 1957 and 1968). Pandemics occur when 3 conditions are met:

1. The emergence of influenza A virus with a hemagglutinin subtype is completely different from that of strains circulating in humans for many preceding years.

2. There is a high proportion of susceptible people in the community (i.e., a population with low antibody titers to the new strain).

3. Efficient person-to-person transmissibility of the new virus is possible with accompanying human disease (25-27).

The reported signs and symptoms of avian influenza in humans include:

1. Typical flu-like symptoms such as fever, cough, sore throat, and muscle aches

2. Eye infections

3. Pneumonia

4. Acute respiratory distress syndrome (ARDS)

5. Multiple organ failure

6. Lymphopenia

7. Elevated liver enzyme levels

8. Abnormal clotting profiles.

Physicians are advised to isolate the patient, initiate droplet precautions, and contact their local medical officer for further discussions if an epidemiological link is suspected.

The World Health Organization (WHO) is moving to rapidly produce a new influenza vaccine capable of protecting people against the H5N1 strain of avian influenza A. Preliminary genetic tests conducted in CDC laboratories in Atlanta, London, and Hong Kong suggest that the H5N1 strain is resistant to amantadine and rimantadine but is believed to be susceptible to neuraminidase inhibitors.

The WHO has recommended urgent, rapid culling of infected and exposed bird populations to eliminate the reservoir of the H5N1 strain. In addition, WHO has discouraged the practice of marketing live poultry directly to consumers in areas currently experiencing outbreaks of avian influenza A (H5N1). Some countries have introduced trade restrictions to protect animal health. However, available data do not suggest that processed poultry products (i.e., refrigerated or frozen carcasses and products derived from them) or eggs from affected areas pose a public health risk. The virus is killed by cooking (25-27).

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