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Preventing illness is the best way to get health-care costs down. So why aren’t governments doing more to protect the environment? We’ve long known that environmental factors contribute to disease, especially contamination of air, water, and soil. Scientists are now learning the connection is stronger than we realized.

New research shows that 60 percent of emerging infectious diseases affecting humans-those that rapidly increase in incidence or geographic range-start with animals, two-thirds from wild animals. Lyme disease, West Nile virus, Ebola, SARS, AIDS  these are just a few of the hundreds of epidemics that have spread from animals to people. A study by the International Livestock Research Institute concludes that more than two-million people a year are killed by diseases that originated with wild and domestic animals. Many more become ill.

According to an article in the New York Times, “Emerging diseases have quadrupled in the last half-century.” The increase is mainly due to human encroachment into and destruction of wildlife habitat. For example, one study concluded that a four percent increase in Amazon deforestation led to a 50 percent increase in malaria because mosquitoes, which transmit the disease, thrive in the cleared areas.

Another example from the article shows how interconnected life is. Development in North America has destroyed or fragmented forests and chased many predators away. This has led to a huge increase in white-footed mice, which carry Lyme bacteria. The mice are not good at removing ticks and their larvae and so the ticks pick up bacteria from the mice and spread it to other mammals, including humans. Because the number of Lyme-infected ticks has multiplied, more are transferring the disease to humans.