Tuesday, July 6, 2010

Disease Growth: as we alter the environment, watch out for the microbes

Increased levels of CO2 emissions, ocean acidification, melting polar ice - these are some of the major impacts of global warming, ones that have been brought up time and time again to warn us all of worldwide changes that need immediate corrective measures. But there are some very subtle changes also occurring; subtle and yet, if ignored, capable of delivering a measurable blow to terrestrial and marine life alike.

A recently published study highlighted one such change: expansion of fungal-based diseases in mammals. Now I know this sounds pretty obscure at first read and it certainly doesn't appear to have the attention-grabbing sensationalism of rising sea levels and increased hurricanes or tornadoes, but it does represent a real threat to many species including man.

Fungi can be a major pathogen for diseases in plants, insects, and amphibians. It does not usually pose a threat to mammals because of the complex immune systems and higher body temperature that all mammals regulate. In fact, in humans, fungi-borne diseases were not an issue until the late 20th century as a consequence of impaired immunity through medical intervention or HIV infection (in tropical Africa, there is a higher incidence of fungi-transmitted pathogens among AIDS patients because the warmer climate generates a greater variety of fungal carriers).

But the temperature gradient between most of the environment and a mammal's internal temperature acts as a protective barrier. With global warming that could all change. In the study by Monica Garcia-Solache and Arturo Casadevall in mBio magazine, the authors hypothesize that global warming will increase the geographical range of many fungi species and that these unique multi-celled organisms also have the potential for developing higher temperature tolerances, thereby thinning out the protective temperature gradient barrier between themselves and mammals.

And while we're on the subject of man-made environmental changes and disease, scientists are also looking at the ramifications to the environment from the use of phosphorous and nitrogen. There is a proper, ecologically-balanced level for these nutrients, but when it is artificially thrown out of whack, through fertilizing or waste pollution as examples, then the potential for emerging pathogens and/or diseases - including the West Nile virus, malaria, harmful algal blooms, coral reef diseases, and amphibian malformations - is magnified.

In a study published in Ecological Applications (Pieter T.J. Johnson, et al), the authors suggest that, "Interactions between nutrient enrichment and disease will become increasingly important in tropical and subtropical regions, where forecasted increases in nutrient application will occur in an environment rich with infections pathogens." They emphasize the importance of careful disease management in conjunction with anticipated continued global nutrient enrichment.

As we tamper with the earth, watch out for the big changes - but keep an eye on the little guys too.

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