Researchers examine role of climate change in disease spread
"GALVESTON, Texas — Ever since scientists first proposed that our planet might be experiencing widespread climate change, concerns have been raised about its implications for the spread of arboviruses – viruses carried by arthropods such as mosquitoes, midges and ticks.
However, while alterations in temperature and rainfall are important factors in making new territory hospitable to an invading arbovirus, many other forces also play significant parts in new patterns of viral emergence.
Those factors include genetic mutation, the introduction of new species of mosquitoes, the presence of an immunologically vulnerable human population and ease of transportation of infected humans (Chikungunya virus); cyclic periods of high rainfall, modern irrigation projects, and livestock trade between Africa and southern Arabia (Rift Valley fever virus); and modern air transport, the availability of compatible mosquito species and large numbers of virus-spreading migratory birds (West Nile virus).
Of the four viruses under review, Higgs said, climate change could probably only be given the lion's share of the credit for the spread of Bluetongue virus. The midge-borne virus can cause fatal disease in sheep, goats and cattle and until about 10 years ago was limited to Africa. Then a warmer climate in Europe made it possible for the cold-sensitive Culex imicola midge species responsible for carrying the virus to move north. Today, borne by other midge species, Bluetongue has spread to 12 European countries.
"There are some confounding factors here, in that infected but asymptomatic livestock are being moved around, and midges can be spread great distances quickly by the wind," Higgs said. "But it seems clear that Bluetongue's dispersal has been driven by the northward expansion of Culex imicola, and that climate change may have contributed to that. If average temperatures increase in certain regions of the world as predicted by some experts, then species of arthropod vectors may disperse beyond their current geographic boundaries, and we need to be ready for the possibility that similar outbreaks could occur.""