• Question: where is an epidemic most likely to occur? how do you find patient 0? do some epidemics share characteristics?

    Asked by Ama to , Kevin, Liz, Beccy, Rosie on 14 Jun 2017.
    • Photo:

      answered on 14 Jun 2017:


      A lot of pathogens (viruses, bacteria, parasites) initially get into humans with a transmission from animals.

      It is transmission of Ebola virus in a bat to a little boy in West Africa that led to the Ebola epidemic that infected more than 20,000 people. Researchers look at reports of all the earliest cases and then follow these clues back to try to identify the first case. Here is some more information about that work:
      http://www.who.int/csr/disease/ebola/one-year-report/virus-origin/en/

      Some pathogens spread in similar ways. Mosquitoes of various sorts spread malaria, dengue virus and Zika virus. Ebola is spread through bodily fluids. Influenza is spread through virus in droplets that are breathed out of one person and into another. These mechanisms are very important to understand. Some diseases spread mostly when those infected are showing symptoms of disease – harder is when a lot of people don’t show signs of infection but still spread the infection on to others. We try our best to use equations that take into account these important differences.

    • Photo: Rosie Fok

      Rosie Fok answered on 14 Jun 2017:


      Epidemics often start when a pathogen (an infectious microorganism that causes disease) crosses from infecting animals to first infecting humans. Because humans haven’t met that pathogen before, and noone in the population is immune, it can cause disease in lots of people.

      Conditions that help diseases to spread – overcrowding, poor sanitation, lack of clean drinking water, lack of access to medical care – are often the result of conflict, or populations being displaced by war or natural disaster. So, epidemics can start in these situations.

      After the earthquake in Haiti in 2010, there was an epidemic of cholera (a bacterial infection of the intestines that can cause people to lose so much fluid that they die).

    • Photo: Liz Buckingham-Jeffery

      Liz Buckingham-Jeffery answered on 22 Jun 2017:


      Good question! And there have been some great answers so far. I thought I’d add more about your question on how to find patient 0.

      When we are trying to control an epidemic, a thing called contract tracing is really important. This is when field epidemiologists try to identify the people who have had contact with an infected person so they can be perhaps treated more quickly or isolated to stop further spread. This was very important during the Ebola outbreak in West Africa, and I had friends who went to Sierra Leone to help with this as part of their jobs.

      Looking for patient 0 can sometime be like doing this, but backwards. Trying to workout from travel history and peoples locations and interactions who they have been infected by.

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