Some like it hot ... or variable

I have the impression that someone on researchblogging.org has already used a similar title to describe the link between rising temperature and vectors of contagious diseases. But [this article](http://dx.doi.org/10.1073/pnas.0903423106) has pointed out another layer of complexity existing in the temperature-disease connection. Turns out that malaria does not necessarily need hot weather, a reasonably warm mean temperature with high diurnal temperature range (DTR) will do.

The malaria parasites will need to develop to a certain stage before it can actually infect people. And this takes time. Researchers already know that the length of the period depends on the environmental temperature, and accordingly they predict that the risk of malaria epidemics will increase, as the mean temperatures in many areas rise. It takes less time for the parasite to develop, and the carrier -- mosquitoes -- has more time to bite and infect people before it dies. If the period of development is so long that it almost equals or even exceeds the mosquito's life expectancy, very little harm is done.

The authors of the PNAS paper find that the period of development depends not only on daily mean temperature, but also on the temperature range through the day. In areas with relatively low temperature, given the same mean temperature, malaria parasites in areas with higher temperature variation in a day need significantly shorter time to develop. Similarly, high DTR in areas with high temperature may slow down the development. Thus the authors say the picture of malaria and similar epidemic in a global climate change context may be more complex than we previously think.

The immediate lesson is that we may have overestimated the additional risk in some tropical areas, and underestimated that in some temperate regions. But exactly what are these areas asks for studies at local scale.

Paaijmans, K., Read, A., & Thomas, M. (2009). Understanding the link between malaria risk and climate Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.0903423106