Biodiversity -- the variety of life, ecosystems, species, populations, and genes -- may at first seem like an issue merely for the environmentalists and hippies, far removed from the medical community. But if you think that the recent flurry of deadly emergent diseases such as SARS, Ebola, bird flu, West Nile, and even AIDS are unrelated to environmental issues -- think again.
The loss of biodiversity changes patterns of infectious disease.
Human activities increasingly threaten biodiversity. The overharvesting of species (either for food or to make way for development), the introduction of species into new environments (for instance, animals for pets or food or plant species for decorative purposes that may prey on or out-compete local species), secondary extinctions (a cascade effect whereby the loss of one species leads to the loss of species that depend on it), and perhaps global climate change (full disclosure: ACSH has no position on this issue) are all ways in which humans can affect biodiversity. These actions have implications for human health whenever they alter (directly or indirectly) the interactions between humans and disease-carrying organisms.
The scourge of Lyme disease in certain states in the U.S., for example, is partially a result of the flourishing of white-footed mice (a reservoir for the disease) in the absence of former predators such as wolves and wild cats, due to deforestation. Outbreaks of leishmaniasis, yellow fever, and sleeping sickness can all result when humans encroach on tropical rainforests through slash-and-burn agriculture or expanding settlements. Finally, the "bushmeat" trade -- the sale of wild, often endangered animals for food -- has been implicated in the spread of HIV-1 from chimpanzees to humans, the spread of SARS from civets to humans, and a cluster of neurodegenerative disease in Guam and Samoa, as well as outbreaks of plague and anthrax in India and Madagascar.
The preservation of biodiversity means the preservation of potential medical treatments.
Preserving biodiversity also means preserving a reservoir of as-yet-undiscovered medical treatments and cures. Consider the cancer drug Taxol, made from the Pacific yew tree; morphine, which was initially derived from poppies; and Artemisia, which yielded treatments for resistant strains of malaria. In addition, microbes -- the most diverse organisms on the planet -- also hold promise: aminoglycosides, a group of antibiotics used in the treatment of severe infections, were derived from a bacterium found in tropical soil. Animal species too are treasure troves of medicines: the cone snail yields a toxin (recently FDA-approved under the name "Prialt") that is a thousand times more potent than morphine as a painkiller but does not lead to tolerance or addiction. That same snail also yields a broad-spectrum anti-epileptic used for the treatment of intractable epilepsy. It should go without saying that the destruction of species such as these means that potential cures are lost forever. Even species that may seem inconsequential to human life (like soil microbes or cone snails) actually have the potential to improve human life greatly -- if they are not driven to extinction.
Conservation of animals and their habitats is a type of preventive medicine.
A severe threat to human health occurs when the loss of species due to human activities results in fewer alternative hosts for pathogens. In other words, some diseases that would usually infect other animals (the "dilution effect") spread to humans when these other animals experience either a severe drop in population or extinction. This effect appears to apply to several diseases found in the United States such as West Nile virus, Lyme disease, and Rocky Mountain spotted fever, as well as the Congolese hemorrhagic fevers. When biodiversity is preserved, there is a lower risk of human exposure to some diseases.
Ecological policies that seek to preserve biodiversity and limit human influences on ecosystem organization may thus be in the best interest of public health, both because biodiversity can yield treatments for existing diseases and provide a buffer against exposure to emergent ones. Of course, some human activities that will effect the environment are necessary, but it is important for us not to carry them out indiscriminately. Conservation makes good sense in just the same way that preventive medicine does. As one expert said ahead of a biodiversity conference set to take place in Oaxaca, Mexico next week, "Preventing emergent disease through biodiversity conservation is far more cost effective than developing vaccines to combat them later."
Mara Burney is a research associate at the American Council on Science and Health (ACSH.org, HealthFactsAndFears.com). This piece drew extensively from "Biodiversity: Its Importance to Human Health," a 2002 report by Harvard Medical School, and was reprinted in the November/December 2005 (No. 213) issue of the Kansas Rural Center's Rural Papers newsletter.