By Robert Pore
robert.pore@theindependent.com

Posing the greatest risk to humans are new diseases originating from wild animals in poor nations, according to the researchers.

With shrinking pockets of biodiversity, the researchers said human populations are expanding, resulting in more contact with wildlife.

At the same time, the research shows that richer nations are nursing other outbreaks, including multidrug-resistant pathogen strains, through overuse of antibiotics, centralized food processing and other technologies.

Emerging diseases are defined as newly identified pathogens, or old ones moving to new regions. For example, the HIV/AIDS pandemic, thought to have started from human contact with chimps, has led to more than 65 million infections; recent outbreaks of SARS originating in Chinese bats have cost up to $100 billion. Outbreaks such as the exotic African Ebola virus have been small but deadly.

In the new study, researchers from four institutions analyzed 335 emerging diseases from 1940 to 2004, then converted the results into maps correlated with human population density, population changes, latitude, rainfall and wildlife biodiversity.

What they found is that disease emergence has roughly quadrupled during the past 50 years. Some 60 percent of the diseases traveled from animals to humans (such diseases are called zoonoses) and the majority of those came from wild creatures.

With data corrected for lesser surveillance done in poorer countries, the researchers found that "hot spots" jump out in areas spanning sub-Saharan Africa, India and China; smaller spots appear in Europe, and North America and South America.

"We are crowding wildlife into ever-smaller areas, and human population is increasing," said co-author Marc Levy, a global-change expert at the Center for International Earth Science Information Network (CIESIN), an affiliate of Columbia University's Earth Institute. "The meeting of these two things is a recipe for something crossing over."

The main sources are mammals, Levy said. He said some pathogens may be picked up by hunting or accidental contact; others, such as Malaysia's Nipah virus, go from wildlife to livestock, then to people. Humans have not developed resistance to zoonoses, so the diseases can be extraordinarily lethal.

The scientists said the more wild species in an area, the more pathogen varieties they may harbor.

"It turns out that conservation may be an important means of preventing new diseases," said Kate E. Jones, an evolutionary biologist at the Zoological Society of London and first author of the study.

Another finding by the researchers is that about 20 percent of known disease emergence is multidrug-resistant strains of previously known pathogens, including tuberculosis.

"Richer nations' increasing reliance on modern antibiotics has helped breed such dangerous strains," said Peter Daszak, an emerging-diseases biologist with another Earth Institute affiliate, the Consortium for Conservation Medicine at the Wildlife Trust, which directed the study.

Daszak said some strains, such as lethal variants of the common bacteria E. coli, now spread widely with great speed because products such as raw vegetables are processed in huge, centralized facilities.

"Disease can be a cost of development," he said.

Last year, meat producers had to recall more than 33.3 million pounds of beef products due to E. coli, including 21.7 million pounds from Topps Foods in New Jersey that forced the company into bankruptcy.

The group's analyses showed also that more diseases emerged in the 1980s than any other decade likely due to the HIV/AIDS pandemic, which led to other new diseases in immune-compromised victims. In the 1990s, insect-transmitted diseases saw a peak, possibly in reaction to rapid climate changes that started taking hold then.

Daszak says the study has immediate uses.

"The world's public-health resources are misallocated," he said. "Most are focused on richer countries that can afford surveillance, but most of the hotspots are in developing countries. If you look at the high-impact diseases of the future, we're missing the point."