Influenza A virus subtype H5N8

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This family of influenza viruses belong to the Orthomyxoviruses. They all range in severity, but cause respiratory infection in the host animals.

Several subtypes of the influenza A virus exist. This virus is more commonly known as the "bird flu" in that it infects mostly avian species, although some have been found in mammals, as well. These viruses range in the level of pathogenicity. H5N8 is one of the many subtypes. One of the main reasons for concern is these viruses undergo constant change, which makes vaccine manufacturing almost impossible. By the time a vaccine is distributed, the virus may have already mutated. Although H5N8 is considered one of the lower pathenogenic subtypes, it is beginning to become more so. Many times, H5N8 is used as an incubator for the highly pathogenic H1N1. [1]

H and N designation[edit]

The types of viruses are designated by molecules found on the virus. The H is for the type of hemaglutanin (the substance that allows the virus to bind to a specific cell). Hemagglutinin (influenza) is a glycoprotein that attaches the virus to the host cell (agglutinate). Many different types of H antigens are found; each of these is specific to the subtype of the virus to which it belongs.

They are designated with the N for the enzyme neuraminidase (the substance that allows them to exit the cell and spread the virus.) As with hemaglutin, the several types of neuraminidase are specific to influenza. These are most frequently found in fowl.

Antigenic shift vs. antigenic drift[edit]

One of the main reasons that any influenza A virus is so deadly is because of antigenic shift. If a host cell is infected by two different viruses at the same time, the viruses can rearrange their RNA to produce a new strain. These new strains will be completely different from either of the parent cells. This will bypass any immunity that the host has built up to the original virus.

Antigenic drifts are the less significant changes that happen to a virus over time. This is why one flu vaccine does not prevent all cases of the flu and also why one may get the flu more than once per season. At times, antigenic drift is the cause of a last-minute scramble for a flu vaccine. Pharmaceutical companies may have a vaccine ready to be distributed, but find that the particular strain is not the one that is cause for alarm that particular year.[2]

Symptoms[edit]

For the most part, symptoms of the H5N8 virus are respiratory. The common symptoms are "flu-like": fever, chills, headache, coughing, and weakness. Conjunctivitis reportedly has been associated with the virus, as well. When farmed poultry are confirmed as having the virus, the farm will cull the birds. This way, the virus will hopefully not be passed along to the public. However, neighboring farms and area wildlife must be tested, also.

Outbreaks[edit]

Perhaps the most known outbreak of H5N8 occurred in Ireland in 1983. Poultry on two farms showed the usual symptoms, plus diarrhea, nervousness, and depression. Poultry farms within close proximity soon began to show signs of infection, as well, but no contact between the farms could be established. In the end, 8,000 turkeys, 28,020 chickens, and 270,000 ducks were slaughtered. When investigated in the lab, clinical findings demonstrated that turkeys were the most susceptible to infection. The virus could not be clinically reproduced in ducks.[3]

Several pandemics involving other flu strains have occurred over the last century. After World War I, soldiers brought back the "Spanish flu" from Europe. This virus was responsible killing hundreds of thousands around the world. In the late 1950s, the "Asian flu" was brought into the US on naval ships. Widespread deaths were experienced with this virus, but it did give the opportunity for the spread of viruses to be studied more closely. Within the last 20 years, H5N1 (avian influenza virus) has made an impact in Asia. This is a large concern because close contact with fowl in day-to-day activities happens. However, a few cases in which this virus underwent human-to-human transmission are known. If human-to-human transmission became commonplace among any virulent avian virus, the results could be disastrous.[4][5][6]

Sources[edit]

  1. ^ "RCI Inactivation of Avian Influenza". http://www.activtek.eu. 
  2. ^ Todar, Kenneth. "The Microbial World". Retrieved 2012. 
  3. ^ Swain, David. "Avian Influenza". 
  4. ^ Todar, Kenneth. "The Microbial World". Retrieved 2012. 
  5. ^ "Avian influenza A(H5N1)- update 31: Situation (poultry) in Asia: need for a long-term response, comparison with previous outbreaks". Epidemic and Pandemic Alert and Response. World Health Organization. 2004-03-02. Retrieved 2007-11-04. 
  6. ^ Scientific Committee on Animal Health and Animal Welfare (2006-06-27). "The Definition of Avian Influenza : The use of Vaccination against Avian Influenza" (pdf). European Commission, Health & Consumer Protection Directorate-General. Retrieved 2007-11-04. 

Further reading[edit]

  • Walker JA, Kawaoka Y (1993). "Importance of conserved amino acids at the cleavage site of the haemagglutinin of a virulent avian influenza A virus". J. Gen. Virol. 74. ( Pt 2) (2): 311–4. doi:10.1099/0022-1317-74-2-311. PMID 8429306.