Monday Micro – World TB Day

By Siouxsie Wiles 25/03/2013

Yesterday, the 24th of March, was World TB Day which aims to build awareness for tuberculosis, a lung disease which kills about 2 million people around the world each year. That’s 3 people a minute. Why the 24th March? This was the day, in 1882, that Dr Robert Koch* announced he had discovered the bacterium that causes TB, Mycobacterium tuberculosis.

TB, or consumption as it was known, had long been thought to be a hereditary disease. In 1869, French physician Jean-Antoine Villemin showed the disease was infectious. He injected rabbits with material taken from people who had died of TB. Not surprisingly, the rabbits became ill. Thirteen years later, Robert Koch, purified the microorganism responsible, for which he won the Nobel Prize in Physiology or Medicine in 1905.

But despite it being over 100 years since M. tuberculosis was discovered, we are a long way from eradicating TB, hence World TB Day. The Global Fund, supported by the Gates Foundation and others, have put together this nice infographic highlighting some facts and figures.


M. tuberculosis is one of the organisms my lab at the University of Auckland are busy working on. If you want to know what we are doing, here’s the little animation I made with graphic artist Luke Harris and his team to show how we are using fireflies to make TB research faster and more humane.

*Koch is best known to microbiologists for what we now refer to as Koch’s Postulates, four criteria he stated needed to be proven to establish a causal relationship between an microorganism and a particular disease. These are:

1. That the microorganism is found in all cases of the disease examined, while absent in healthy organisms
2. That the microorganism be isolated from a diseased host and grown in a pure culture
3. That the microorganism should be capable of producing the original infection when introduced into a healthy host, even after several generations in culture
4. That the microorganism is retrievable from an inoculated/experimental host and cultured again.

As with everything though, it turns out that there are exceptions to every rule, and we now know many microorganisms that fail one or more of Koch’s Postulates but are still clearly the cause of a particular disease. For example, many nasty microorganisms can be carried asymptomatically by healthy people (including Vibrio cholerae, the agent responsible for cholera), while there are a number of microorganisms which we are unable to culture in the laboratory (including Mycobacterium leprae, the agent responsible for leprosy, which can only be grown in the footpad of a mouse, or a nine-banded armadillo).

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