Diversity & Disease

The spread of potent diseases like West Nile virus and Lyme disease is getting a boost from the loss of biodiversity, concludes a new study. But there is still a lot to be learned about the complex interplay between diversity, disease and habitat change, the researchers say.

In theory, biodiversity could play two roles in the emergence and transmission of infectious diseases, Felicia Keesing of Bard College in Annadale-on-Hudson, New York and colleagues report in the current issue of Nature. On one hand, high biodiversity may provide a big pool of novel pathogens that could infect humans, they note. On the other hand, diverse ecosystems could help block the transmission of both established and emerging diseases by keeping carriers in check.

After reviewing a wide range of cases, however, the researchers concluded that “mounting evidence indicates that biodiversity loss frequently increases disease transmission…  Overall, despite many remaining questions, current evidence indicates that preserving intact ecosystems and their endemic biodiversity should generally reduce the prevalence of infectious diseases.”

In Virginia, for instance, researchers believe the decline of opossum populations in forests is contributing to the spread of Lyme disease. Opossums can kill disease-carrying ticks that latch on to them, helping keep the parasites in check. When opossum populations crash, however, ticks feed off the Virginia white-footed mouse – which reproduces quickly, helping fuel tick numbers.

Other studies have shown a link between diversity and the spread of West Nile virus, a mosquito-transmitted virus hosted by birds. When bird diversity is low, the virus tends to concentrate in species that amplify the virus, increasing the risk that it will jump to humans. Researchers have found a similar trend for hantavirus, which is carried by mice. “Diversity has a similar effect for plant diseases,” the researchers add, citing two fungal rust pathogens that do better when diversity is low.

They conclude that the “connections between biodiversity and disease are now sufficiently clear to increase the urgency of local, regional, and global efforts to preserve natural ecosystems.” David Malakoff | December 7, 2010

Source: Keesing, F., Belden, L., Daszak, P., Dobson, A., Harvell, C., Holt, R., Hudson, P., Jolles, A., Jones, K., Mitchell, C., Myers, S., Bogich, T., & Ostfeld, R. (2010). Impacts of biodiversity on the emergence and transmission of infectious diseases. Nature, 468 (7324), 647-652 DOI: 10.1038/nature09575

Image courtesy Nature