Tag Archives: ebola

“Endemicity and the Environment”

MDR Tuberculosis is highly prevalent in countries such as India, South Africa and Ukraine, but virtually non-existent in others.

Metallo-beta-lactamases, such NDM1, are imported into New Zealand, but so far have not become endemic.

Measles is a major killer in sub-Saharan Africa but reduced to the odd sporadic case in other parts of the world.

Just because a micro-organism is successful in one environment, it does not mean it will thrive in another. Like everything else in life, they look for niches.

…and when I talk about environment, I am thinking about everything from Infection Control, Antibiotic Stewardship, Public Health infrastructure, vaccination coverage, even population density.

I think as a microbiologist, using the expertise and experience that has been acquired, you get a feel about how an emerging disease would “cope” in your local environment.

Which leads us onto the major topic of the moment, Ebola. Ebola transmission is currently intense in Liberia, Sierra Leone & Guinea, but struggles to gain a foothold in other countries, despite the importation of sporadic cases.

I think NZ has an environment that Ebola would struggle to become endemic in, although as with other countries, we are always at risk of imported cases and even secondary infections, as experienced in the USA.

However that is not the whole story. Zoonotic micro-organisms, and particularly those ones that are relatively naive in the human host (such as Ebola), have the ability to adapt and change, and make fools of us all….


“Be careful of what you wish for…”

The sustained transmission of Ebola Virus within urban centres in Sierra Leone, Liberia and Guinea is unprecedented, and the consistent mortality rate of greater than 50% is frightening.

It would be great if that mortality rate fell to 10-20%, right?

From a purely scientific viewpoint, not necessarily so….

Ebola is certainly very transmissable, but not as transmissable as other viruses we encounter, such as measles. So far it has failed to cause a large outbreak in a country with a well developed and well financed Public Healthcare system. That is encouraging to some extent but we should not get complacent. I believe the virus in its current form is probably incapable of causing a true worldwide pandemic but….

This is the first time we have seen a period of sustained and intense transmission in the human population. You can be sure that the virus will be mutating and adapting to its new host (the human species) in order that it can attempt to maintain its long term survival within that species. To do this the virus needs to facilitate its transmission within the human host, and decrease it’s virulence. By decreasing its virulence the virus would then have the potential to be transmissable to other potential contacts for a longer period.  Decreased virulence would also give rise to the possibility of sub-clinical cases thus facilitating cross border spread.

So from a humanitarian point of view, it would be great to see the mortality from Ebola virus decreasing. However from a scientific view this would raise the alarm bells that the virus has adapted to the human host to the extent that it is much more capable of causing a true pandemic. (There could of course be other reasons why the mortality rate might decrease, e.g. better treatment…)

The longer the outbreak continues, the longer the Ebola virus has to mutate and adapt and cause exactly this sort of scenario. This is why the governments of developed countries should be pouring resources into controlling the Ebola epidemic in West Africa, because a few months down the line we may be dealing with a quite different virus than the one we have at the moment….


Keep up to date with what is happening with Ebola on an international scale by reading the WHO Ebola situation updates. Click here for the link.