Avian Influenza

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    • Recently, the head of the World Health Organisation, warned that the world had to prepare for a possible bird-flu pandemic.

    About

    • The bird flu outbreak has killed 15 million domestic birds, while 193 million others have been culled since October 2021. It has spread from Europe and Asia to North America, South and Central America.
    • Adaptation in mammals: The US Department of Agriculture has confirmed avian flu cases in mammals such as skunks, a raccoon and a red fox. These mammals were suspected to have consumed infected birds.
      • The mutation is a signal that this virus is trying to cross the barrier between species and adapt to the mammalian population.
    • Outbreak in India:  The latest major avian flu outbreak in 2020-2021 swept through many States causing mass mortality of wild birds

    Avian Influenza

    • Depending on the origin host, influenza A viruses can be classified as avian influenza (bird flu, subtypes A H5N1 and A H9N2), swine influenza (swine flu, subtypes A H1N1 and AH3N2).
    • They are distinct from human influenza viruses and do not easily transmit among humans.

     

    • The “H” and “N” in the name of a flu virus stand for hemagglutinin and neuraminidase, two proteins on the surface of the virus that allow it to enter and exit host cells. 
    • Hemagglutinin and neuraminidase were the first aspects of the flu virus to be identified hence it was named so.
    • Reservoir of Virus: Aquatic birds are the primary natural reservoir, most cause asymptomatic or mild infection in birds.

    Concerns Associated with Avian Influenza in India

    • Lack of active surveillance.
    • In India poultry birds are not vaccinated against flu.
    • The farms with a diversity of animals or in the vicinity of nearby wetlands increases the potential for the viruses to generate more virulent strains which could then infect humans. 

    About Influenza Virus

    • There are four types of influenza viruses: types A, B, C and D.
    • Influenza A viruses infect humans and many different animals.
    • Influenza B viruses circulate among humans and cause seasonal epidemics. Recent data showed seals also can be infected.
    • Influenza C viruses can infect both humans and pigs but infections are generally mild and are rarely reported.
    • Influenza D viruses primarily affect cattle and are not known to infect or cause illness in people.

    Human Infection

    • Humans can be infected with avian , swine  and other zoonotic influenza viruses.
    • Spread in humans: Human infections are primarily acquired through direct contact with infected animals or contaminated environments, these viruses have not acquired the ability of sustained transmission among humans.
    • Severity: It may cause disease ranging from mild upper respiratory tract infection (fever and cough), early sputum production and rapid progression to severe pneumonia, sepsis with shock, acute respiratory distress syndrome and even death. 
      • Conjunctivitis, gastrointestinal symptoms, encephalitis and encephalopathy have also been reported.

    Prevention

    • Controlling the disease in the animal source is critical to decrease risk to humans.
    • Travelers to countries and people living in countries with known outbreaks should avoid poultry farms, entering areas where poultry may be slaughtered, and contact with any surfaces that appear to be contaminated with faeces from poultry or other animals. 
    • To minimize public health risk, quality surveillance in both animal and human populations, thorough investigation of every human infection and risk-based pandemic planning are essential.

    Treatment

    • Some antiviral drugs, notably neuraminidase inhibitor (oseltamivir, zanamivir), can reduce the duration of viral replication and improve prospects of survival.
    • Treatment is recommended for a minimum of 5 days, but can be extended until there is satisfactory clinical improvement.

    Pandemic potential

    • H5N1 is most significant to public health due to its potential to cause an influenza pandemic.
    • An influenza pandemic occurs when a novel influenza virus emerges with the ability to cause sustained human-to-human transmission, and the human population has little to no immunity against the virus. 
    • According to the WHO, there have been a total of 868 cases of H5N1 in humans between January 2003 and November 2022, out of which 457 were fatal.
    • However, as per WHO, there is no evidence of human to human spread of bird flu so far.
    • Whether currently-circulating avian, swine and other zoonotic influenza viruses will result in a future pandemic is unknown. 

    Source: TH