• Question: What alters the fact that a virus/disease is contagious or not?

    Asked by anon-256593 on 24 Jun 2020.
    • Photo: Cameron Stockwell

      Cameron Stockwell answered on 24 Jun 2020:

      Some diseases are caused by genetics and cannot be passed from person to person.Most non-communicable diseases, such as cancer, are caused by other factors such as smoking, alcohol intake, exercise and genetic pre-disposition, these are more lifestyle dependant than pathogen dependant

    • Photo: Alex Holmes

      Alex Holmes answered on 24 Jun 2020:

      So a disease that can be passed between people is called a “communicable disease” or contagious. They’re usually caused by bacteria, viruses, fungi and parasites (think any kind of organism that isn’t part of you already!). Because a person ill with this infection is basically stocked full of this invading organism, they can pass it onto other people – either directly through coughing out the virus and having other people breathe it in, or it being in their vomit if they have a tummy bug and other people coming in contact with it.

      Diseases that aren’t caused by these things is usually a non-communicable diease. Like if I have cancer, there’s no way for it to get into you from my breathing or if I vomit. I do say “usually” however, because there are some really bizarre but important experiments that have been done by scientists where these diseases have passed from one animal to another. Usually by injecting a mouse with cancer cells to see if they can treat the new tumour, or a study where mice’s blood streams were joined to each other and it was seen that alzheimers disease passed between them. Of course, these aren’t exactly normal situations at all.

    • Photo: Rachel Tanner

      Rachel Tanner answered on 25 Jun 2020: last edited 25 Jun 2020 12:15 pm

      Cameron and Alex have done a great job of answering what makes a disease contagious or not, so I’ll focus more on what determines HOW contagious a virus is. That depends on several factors:
      – How it’s transmitted (eg. something like HIV requires close contact with bodily fluids, so is harder to spread than something like the novel coronavirus, which can be spread by coughing or even just breathing near someone).
      – How long someone who’s infected stays contagious for
      – How many people contagious people come into contact with (this will be higher in big cities for example or in a densely packed community like a prison)
      – How many people are already immune to the virus – this will be higher if people can generate immunity after a first infection, or if there’s an effective vaccine and a high enough proportion of people get vaccinated

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