Context: United States has confirmed the presence of avian influenza strain H5N1 in dairy cattle for the first time. The same strain has also killed thousands of seals and sea lions in coastal stretches from the USA to Chile.
Influenza Virus:
- There are four species of Influenza Virus viz. Influenza-A, Influenza-B, Influenza-C and Influenza-D.
- Influenza A infects birds and mammals. Influenza A and B viruses cause seasonal epidemics of disease in people (known as flu season) almost every winter in the United States. Influenza A viruses are the only influenza viruses known to cause flu pandemics (i.e., global epidemics of flu disease).
- Influenza A viruses are divided into subtypes based on two proteins on the surface of the virus: hemagglutinin (H) and neuraminidase (N). There are 18 different hemagglutinin subtypes and 11 different neuraminidase subtypes (H1 through H18 and N1 through N11, respectively).
- Influenza C Virus: Detected less frequently and usually causes mild infections, thus does not present public health importance.
- Influenza D virus: primarily affects cattle and are not known to infect or cause illness in people.
- It has a very high rate of mutation, and this is the reason that so many different strains of influenza virus are found.
- Various strains of Virus differ in certain proteins on the virus surface — hemagglutinin (HA) and neuraminidase (NA) proteins. This is the basis of naming viruses.
- The common Influenza outbreaks caused by Influenza-A strains include H1N1 (swine flu); H5N1, H5N8, H2N9 (Bird Flu).
About Avian Flu:
- Avian influenza refers to the disease caused by infection with avian (bird) influenza (flu) Type A viruses.
- These viruses occur naturally among wild aquatic birds worldwide and can infect domestic poultry and other bird and animal species. Avian flu viruses do not normally infect humans.
- However, sporadic human infections with avian flu viruses have occurred.
- Influenza A viruses are divided into subtypes based on two proteins on the surface of the virus: hemagglutinin (HA) and neuraminidase (NA).
- There are 18 known HA subtypes and 11 known NA subtypes. Many different combinations of HA and NA proteins are possible.
- For example, an “H7N2 virus” designates an influenza A virus subtype that has an HA 7 protein and an NA 2 protein. Similarly, an “H5N1” virus has an HA 5 protein and an NA 1 protein.
DOES IT SPREAD EASILY TO HUMANS?
- No, it does not. Generally, people coming in close contact with infected alive or dead birds have contracted the H5N1 bird flu, and it does not usually spread from person to person, as per the WHO.
- There is also no evidence, the WHO says, that the disease can be spread to people through properly prepared and cooked poultry food. The virus is sensitive to heat and dies in cooking temperatures.
THEN WHY THE SCARE?
- H5N1 is severe and deadly – around 6 out of 10 confirmed cases in humans have led to deaths (though the actual mortality rate may be lower due to under-reporting of asymptomatic cases).
- If the virus mutates and becomes easily transmissible from person to person, say by altering its shape to grab human cells much more effectively, it can potentially cause a pandemic.
- Also, flu viruses are more prone to mutation because they have a segmented genome. All known strains of flu – including the seasonal flu and the pandemic flu – have jumped from birds to humans in this way.