Ecological destruction fuels emerging diseases

The destruction of habitat by human activity and the extinction of species around the world is more than a looming environmental catastrophe, warns a Canadian zoologist. This ecological damage also endangers human health by turning parasites into “evolutionary land mines.”

Dr. Daniel (Dan) Brooks, a parasitologist at the University of Toronto, says the decline of global biodiversity is linked to the emergence of new human and wildlife diseases such as West Nile Virus and avian flu.

“The biodiversity crisis is not just about extinctions,” says Dr. Brooks, whose pioneering parasite systematics research is supported by Science and Engineering Research Canada (NSERC). “In the past, when there have been episodes of major climate change or mass extinction, and species have moved out of their areas of origin into other areas, there have been emerging diseases. Parasites have moved into new areas and they’ve jumped ship into new hosts.”

He will present his latest findings on February 21 as part of a panel discussion on environmental systematics at the 2005 meeting of the American Association for the Advancement of Science in Washington D.C.

Dr. Brooks has spent much of the past decade slogging through the dense jungles of Costa Rica tracking down and collecting parasites. Since 1996, he has coordinated the parasite Taxonomic Working Group for the All-Taxa Biodiversity Inventory (ATBI), an international scientific and economic initiative to help developing countries preserve the world’s biodiversity.

In the Guanacaste Conservation Area of northwest Costa Rica, a 1,000 square km (400 square mile) United Nations World Heritage Site that features habitats ranging from rain forests to savannas, the ATBI is documenting an estimated 250,000 species of plants and animals, including everything from viruses to jaguars.

For his part, Dr. Brooks has looked for parasites in more than 4,000 individuals from species ranging from frogs to deer. So far, he has found more than 5,000 different types of these often microscopic hangers-on and created one of the world’s most comprehensive inventories of parasites. And, notably, more than two-thirds of these parasites are new to science.

But Dr. Brooks argues that the real work has only just begun. The researchers still have a very poor to non-existent understanding of the roles these thousands of parasites play in different diseases, something that will require a detailed understanding of their often complex multi-host life cycles. “It’s very difficult to link these things up,” he says. “It’s very time consuming to do that, but without that information we don’t know how these parasites are transmitted.”

And without basic systematics and taxonomic information about parasites, Dr. Brooks points out that we lack the ability to predict and thus prevent emerging parasitic diseases. “Right now, we’re just reacting out of ignorance whenever an unfamiliar disease catches us off guard and we call that management,” says Dr. Brooks. “We’re always behind the curve, because we don’t know where these things are coming from.”

In fact, while parasites like malaria are well known, we may have identified only a fraction of the total number of the world’s parasites, and the prospect of cataloguing them poses a daunting technical challenge. Since the physical characteristics of many parasites are very similar, Dr. Brooks and his colleagues are using the latest molecular taxonomy tools to classify parasites based on genetic characteristics.

“These things are evolutionary accidents waiting to happen,” he warns. “This is not something brand new – it’s something old. But in this case it’s something that human beings are stimulating. These little evolutionary land mines are going to jump up and bite us.”

Dr. Brooks’ AAAS presentation
Systematics: Vanishing Safety Net for Food Security and the Environment