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Biodiversity Decline Can Increase Human Disease

Posted By Prucia Buscell, Thursday, December 23, 2010
Updated: Tuesday, February 15, 2011

The decline and extinction of plant and animal species and their habitats isn’t only a loss of the world’s natural riches. Scientists find it is also increasing the spread of infectious diseases and influencing the emergence of new diseases.

Take the case of the opossum and the white-footed mouse and their surprising role in the spread of Lyme disease among humans. The more white-footed mice there are, the more Lyme disease humans get, while the presence of opossums may actually protect us. Opossum populations are declining as their natural forest habitats are bulldozed for development. White footed- mice, which are less dependent on forests, are flourishing. In several cases, researchers say, the species most likely to decline as biodiversity is lost are the ones most likely to reduce the transmission of pathogens.

The December 2 issue of the journal Naturereports on findings by 13 scientists that robust biodiversity tends to decrease the transmission of infectious diseases, while declining biodiversity increases that danger. They also say that principle seems to hold even if the population of the species hosting the pathogen remains stable: in an environment with a wide variety of species, the spread of disease is less likely. Researchers studied the spread several contagious human illnesses, including Lyme, West Nile virus, schistosomiasis, a parasitic affliction among people in tropical climates, and hantavirus pulmonary syndrome, an often-fatal disease spread by rats. They note that from 1940 to 2004 more than 300 new "emerging disease events” were found in humans, and that many old diseases such as malaria are reasserting themselves with a vengeance. Researchers also found that increased spread of disease in plants, animals and the corals in the sea accompanies biodiversity declines.

Conventional thinking has dictated that human diseases are best understood by looking at humans. "Now there is the beginning of a movement to bring epidemiology and econolgy together,” EPA scientist Montira Pongsiri told ScienceDaily. Pongsiri and Joe Roman, a biologist at the University of Vermont, wrote about biodiversity and global disease ecology in the December issue of BioScience.

Roman explained to ScienceDaily that Lyme disease was probably rare historically, because ticks once fed on a wide range of small mammals in the forests and some of those hosts were poor carriers for the disease, so only a small number of infected ticks reached human populations. The Nature article points outticks that try to bite sharp-clawed opossums are likely to get picked off and killed. White-footed mice thrive in species poor environments, such as small patches of forest on the edge of neighbor hoods, Roman said. They carry Lyme infections without getting sick themselves, and with other small mammals gone, they are a prime host for large numbers of ticks to feed on.

An NPR broadcast on the topic reports there were 30,000 confirmed cases of Lyme disease in the U.S. in 2009, up from 12,000 in 1995. The Nature study reports on land in Virginia where research showed ticks that fed on the mice were highly likely to be infected, and ticks that fed on opossums were not. Low bird diversity increases the numbers of mosquitoes that spread West Nile, The article also reported field studies showing the reservoir of rodent hantavirus increased when rodent diversity declined.

Diverse Voices in Joyful Song

A flash mob has been described as a group of friends and strangers who gather on short notice in some public place to do something spontaneous and entertaining. Enjoy The Philadelphia Opera Company’s "Hallalujah,” a Random Act of Cultureand the exuberant performance of the Christmas Food Court Flash Mob.

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