Understanding Zoonotic Diseases (Download PDF)

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Understanding Zoonotic Diseases

  • In the last two decades, world has seen many viral outbreaks-

    • Avian influenza

    • Ebola virus disease

    • Zika virus disease

    • Nipah virus disease

    • Severe Acute Respiratory Syndrome (SARS)

    • Middle East Respiratory Syndrome (MERS)

  • Recent viral outbreak has been coronavirus pandemic.

  • SARS, MERS, and COVID-19- these three are caused by the virus belonging to coronavirus family.

Understanding zoonotic diseases

Understanding zoonotic diseases


  • In 2002 - 03, around 8,422 people were infected and 914 were killed by SARS, which was caused by SARS CoV.

  • MERS CoV infected 1,791 people and killed 640 people between 2012 and 2016.

  • SARS CoV -2 is more contagious.

  • SARS CoV-2 has infected more than 3 million people in five months.

  • But it’s less fatal as the mortality rate is 2 - 5 percent in comparison to SARS (9.5%) and MERS (34%).

  • What is common in all the three diseases is that they all are caused by zoonotic viruses that infected the humans.

  • Though viruses are omnipresent, but just a few can mutate and infect us.

  • The studies say that infections do not usually happen in the first exposure.

  • For an infectious disease, three major requirements are there. These are

    • The causative agent

    • The host

    • The environment in which the host and agent are brought together

  • In recent viral outbreaks, it has been observed that causative viruses and their precursor strains were present in the system already through sylvatic cycle/enzootic cycle.

  • Sylvatic/enzootic cycle is the natural transmission cycle of viral pathogens within its natural animal host. E. g.

    • Bats for rabies and Nipah

    • Macaques and rodents for Kyasanur Forest Disease

  • Ebola outbreaks can be traced to 1976 so Ebola is not new to Africa.

  • Though initial individual outbreaks of Ebola were restricted to one or two countries, the 2013 - 14 outbreak in West Africa was not only largest ever recorded, but also differed dramatically from previous outbreaks in

    • its duration

    • number of people affected

    • geographical extent

  • Between 1970 and 2013, a positive correlation has been observed between the outbreak and population and urban growth in these countries.

  • The outbreak depends on mode of transmission also.

  • The pandemic potential of virus drastically increases if it is airborne (i. e. transit through respiratory droplets and aerosol particles).

- Published/Last Modified on: August 9, 2020

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