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Africa, the infectious continent

While outbreaks of new, exotic infectious diseases — as well as the resurgence of old killers — have surfaced all over the globe in the past decade, no continent has been harder hit than Africa.
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While outbreaks of new, exotic infectious diseases — as well as the resurgence of old killers — have surfaced all over the globe in the past decade, no continent has been harder hit than Africa. But with international travelers flying viruses across time zones in a matter of hours, experts have no doubt that the emergence of menacing microbes in one locale could bring about a worldwide pandemic. Are infectious diseases the new Armageddon?

Africa's tropical climate makes it a hot zone in the most literal sense. The continent is, to put it simply, a breeding ground for emerging pathogens.

Add to that environmental changes - such as global warming and destruction of the rain forests - rapid population growth and haphazard development, and the scene is set for microbes to thrive, international experts have warned.

Since the mid-1970s, the world has seen the emergence of 30 new infectious diseases and the return of such killers as malaria and cholera - many of them originating in the African continent, said Paul Epstein, associate director of the Center for Health and Global Environment at Harvard Medical School.

And in the past few years, floods and droughts brought on by global warming have exacerbated the situation, he said.

“Extreme weather creates conditions conducive to outbreaks of infectious diseases,” Epstein said. Heavy rains, for example, provide new breeding sites for the mosquitoes that carry malaria, dengue fever and other disease, while contaminating drinking water. Drought, on the other hand, fuels fires that, in turn, spark respiratory ills, even meningitis.

When illness does strike Africa, a poor infrastructure - marked by poverty, malnutrition, crowded living conditions, limited health care and an unstable political climate - permits disease to spread undaunted.

Manmade problem
It’s the manmade aspect of the problem that so perturbs the experts.

“These new pathogens didn’t come in on a tail of a comet,” said Dr. David Heymann, executive director of the World Health Organization’s Program on Communicable Diseases in Geneva, Switzerland. “They’re lurking in animals. But by disrupting nature, we have unleashed them onto ourselves.”

The destruction of the rain forests, for example, may be partly to blame for clusters of killer outbreaks - ranging from feverish malaria to hemorrhagic Ebola.

When trees are cut down, pools of infested water are left exposed in the forest, Heymann said. “What we have done is set up new breeding grounds for mosquitoes that can carry disease such as malaria.”

Dr. Anne Marie Kimball, an expert in infectious disease epidemiology at the University of Washington in Seattle, blames deforestation for recent Ebola outbreaks. As people penetrate the forest in search of firewood, they can be exposed to the virus, which might otherwise have been relatively contained, she said.

Destroying the rain forests also has led to a loss of wildlife that protects against infectious diseases, said Epstein. “As coyotes, snakes and other predators that normally prey upon disease-carrying rodents and mosquitoes are killed off by man in his hunt for more wood, for example, so is our natural buffer against plague and malaria,” he said.

“A hearty forest stocked with birds and a healthy lake stocked with fish are important in controlling mosquitoes,” he said, which may in part explain the resurgence of such diseases as yellow fever and malaria - the latter all but wiped out several decades ago.

Cutting down the forest can sometimes change the mice population from forest to field mice, Epstein added, which can bring about new viruses such as one responsible for a deadly fever in Bolivia.

“While this has yet to happen in Africa, there is every reason to believe it can - and will - if steps are not taken,” he said.

Global warming
Several aspects of climate change, all related to global warming, are contributing the emergence of new diseases and the resurgence of others, the experts say.

Warming itself is allowing malaria to spread to higher altitudes, Kimball said, noting that the mosquitoes that carry the disease to humans can survive only at milder temperatures. Once confined to lower areas, the skin-piercing insects are now able to flourish in the African highlands of Kenya.

The outbreaks have been devastating, Epstein said. With poor access to health care, many residents were sickened and killed as malaria swept through several villages.

El Nino-related extreme weather events also brought flooding to the Horn of Africa,

chiefly Kenya and Tanzania, he said, adding that in 1997-1998, the area was besieged with four times as much flooding as normal. The results: huge clusters of mosquito-borne malaria and Rift Valley fever as well as an epidemic of the water-borne disease cholera.

The big surprise, Epstein said, are the fires brought about by recent droughts - “something we weren’t even thinking about a year ago.”

The fires bring haze, choking, air particulates and respiratory ills. Membranes dry, making residents susceptible to deadly meningitis.

There’s also the impact on an already shattered economy. Due to Rift Valley fever, which strikes cattle as well as humans for example, Africans couldn’t export livestock, Epstein said. Cholera-infested waters limited the sale of fish.

“We knew of the link between climate and infectious disease as early as the 1920s,” Epstein said, “but people put blinders on. And now we are paying the price.”

A global problem
While the term Hot Zone may conjure up images of suited-up medical detectives working in containment zones to stop a deadly virus at its source, nothing could be further from reality, the experts say. Each killer microbe has the potential to make a lethal journey across the globe, carried by migratory birds, international travelers or traded goods.

“Africa’ problem is not its own,” Epstein said, the West Nile-like virus’ recent debut in New York being an important case in point.

While scientists are still mystified as to exactly how the microbe made its way halfway across the world, he said, “What we can be sure of is that the environmental and social conditions in Africa affect emerging diseases throughout the globe.”

Like West Nile-like fever, mosquito-borne dengue fever had been confined to the tropical zones for years, Kimball said, making “an outbreak in Texas earlier this year as scary as it is intriguing.”

It appears “we’re seeing a harbinger of what you can get as vectors move worldwide,” she said.

Other unexplained outbreaks of infectious disease may be due to mosquitoes hitching a ride on a plane, Kimball said. The insects can survive in the wheel wells of aircraft, even at 40,000 feet. So if mosquitoes set up shop while a plane is grounded in Africa, they’ll land overseas with the baggage and passengers, causing previously unseen disease, such as recently happened in Belgium.

Travel also allows the mixing of different microbial strains when people come together, Kimball said. The new strains are often not just deadlier, but also may be resistant to the drugs usually used to eradicate them.

“The world is so intertwined that a problem in one place today will be a problem in another place tomorrow,” she said. “Infectious diseases are giving us a wake-up call to create a global community.”

If we don’t, the experts say, we may indeed be facing the new Armageddon.