• Question: what is the most harmful known disease?where did it originate?how old is it?

    Asked by henryjones to Clare, Mariana, Pedro, Robert, Susanne on 16 Nov 2012.
    • Photo: Susanne Muekusch

      Susanne Muekusch answered on 16 Nov 2012:

      Hi henry,

      I think the most harmful diseases are infectious diseases where we do not have a vaccine. In the past, the plague killed many many people in Europe. Now we have a real problem with HIV.

      Generally, pathogens and their hosts adapt to each other. Because the pathogen can’t spread very well, if it kills its host immediately. Especially harmful infectious diseases are therefore relatively new to the population they affect.

      Example: HIV is relatively new in humans. It is common in apes, and for some reasons we do not quite understand, the apes can handle it. It probably has been around in apes for a long time. But it has only recently (well, on an evolutionary scale, it was about 30 years ago) been introduced to humans. As you probably know, humans can’t handle HIV at all, because we did not have time to adjust.

      A second example: When america was discovered and the spanish went over, they took some diseases with them. When I remember correctly, it was measles virus. Which is not nice to have, but most of the patients survive it in europe. However, the native americans were never exposed to that virus before. And they dropped like flies.

      A harmful disease, at least an infectious harmful disease, is new to the population it spreads in.

    • Photo: Clare Taylor

      Clare Taylor answered on 17 Nov 2012:

      Hello Henry! I am supposed to be marking some student work but your question is much more interesting, and one of my favourites so far! Good call on the infectious diseases @susanne! There are lots of harmful infectious diseases but it is difficult to say which is the most harmful. It depends on what you mean by ‘harmful.’ Some infectious diseases like are HIV are harmful because they eventually lead to death (people often get AIDS and die of infections as a result) and can’t be treated to get rid of the harmful agent. In fact, since the beginning of the HIV epidemic, more than 60 million people have been infected with HIV virus and approximately 30 million people have died of AIDS. On the other hand, some infections kill people very quickly, like Ebola virus (there’s currently an outbreak in Uganda) and the disease itself is very unpleasant. Other diseases can spread very quickly in the environment like Cholera and Typhoid fever and kills lots of people within a few days. Cholera was a big problem in Haiti following the earthquake there in 2010. Tuberculosis is also a big global problem; in 2011, 8.7 million people became ill with TB and 1.4 million died. TB is a complication that often affects people with AIDS in developing countries, and is why so many people die from it.

      There is evidence from mummified remains that TB was present in ancient Egypt so this disease is very old. The bacterium that causes TB, Mycobacterium tuberculosis hasn’t changed much since then, except recently in the last 20 years it has acquired antibiotic resistance, so now it is even more of a problem.

      Some infectious diseases come from animals like the plague bacteria, while others have evolved from being a harmless bacterium to becoming dangerous. From the point of view of the bacterium or virus, its sole purpose is to replicate itself and ensure its survival, so it is an unfortunate consequence for us that some of the evolutionary adaptations have resulted in the bacterium killing its host.

      Fascinating stuff, eh? This is why I am a microbiologist and that I love studying bacteria!

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