Why is the species-diversity of deadly parasites greatest in the tropics? There are so many parasites living in tropical regions of Africa, South America, or Asia, but very few in Europe or North America. Is this due to climate, or are there other reasons? Many of the tropical diseases and parasites are transmitted by insects, such as flies and mosquitoes. Well there are flies and mosquitoes in Europe as well. There might be malaria-transmitting mosquitoes in the very south of Europe, and there is encephalitis transmitted by ticks. But that's it. Why don't the hundreds of different parasitic species from Africa spread to Europe ?

The diversity of parasites shows a gradient with increasing diversity from the poles to the equator. Several reasons have been brought forth to explain the latitude-dependency of parasite diversity:

* An increased diversity overall around the equator; species diversity in general is greater in the rain forests and hence more hosts are available and thus more parasitic species can develop that target specific hosts;
* Larger amounts of precipitation and higher temperatures around the equator may favor the development and transmission) of parasites (Nunn _et al_., 2005);
* Increased available energy overall around the equator (Guernier _et al_., 2004).



**References**
**-** Guernier _et al_., PLOSone (2004): 0020141
**-** Nunn _et al_., _Diversity and Distrib_ (2005); **11** : 249–56