Forecast: Pathogens find new habitats

There is a link between climate change and the global health crisis. In Africa and Asia, global warming is driving pathogens into new habitats and facilitating the outbreak of exotic and often deadly diseases.

LAGOS, Nigeria — I caught malaria twice here.

I cured it early both times, before it had time to gather strength. Nonetheless, it knocked me down.

Walking to the clinic for a blood sample during the second attack, I vomited on the road. That night, on a friend’s couch, my bones ran cold, my skin shivered, my shirt changed color with sweat. It was two days before I was ready to work again.

As temperatures increase, regions that once were free of disease-carrying mosquitoes will become suitable for the insects.

“We’re seeing changes in the range of mosquitoes and the diseases they carry,” said Paul Epstein, associate director of the Center for Health and the Global Environment at Harvard Medical School.

“That’s going to be an issue increasingly in terms of latitude and on the margins, both in terms of extensions of the range and in terms of seasonality,” he said.

Mosquito larvae mature more rapidly when the water in which they grow is warm. Female mosquitoes digest blood faster and bite more frequently as the mercury rises.

The cycle begins when mosquitoes ingest malaria parasites — the parasites split into males and females, reproduce in the mosquito’s gut, and release snake-shaped sporozoites that migrate to its salivary gland, ready to be injected when the insect bites a new human. Malaria transmission begins when a mosquito feeds on an infected person. 

A malaria mosquito will only live a few weeks.

The parasite’s survival depends on it reaching maturity while its host is still alive to bite.

The strain of malaria I caught is called Plasmodium falciparum. In temperatures of 68 degrees Fahrenheit, the parasite takes 26 days to complete its reproductive cycle. At 77 degrees Fahrenheit, it’s ready to reinfect after just 13 days.

Climate change is also accelerating the spread of dengue, a primarily urban, tropical disease that causes fevers and aching. The disease has reemerged in Brazil and climbed up the American coast. In Mexico, the number of cases has risen 600 percent since 2001. Outbreaks have reached the formerly dengue-free state of Chihuahua, on the border with Texas.

The Intergovernmental Panel on Climate Change estimates that by 2080 an extra 2 billion people will live in areas that are hospitable for the virus.

Scientists studying the Ebola virus in Gabon say that outbreaks erupt after wet weather breaks a long, dry spell. In North America, the spread of the West Nile virus accelerated when warm temperatures and drought in 1999 favored the carrier mosquito and the disease within it.

That same year, a new virus emerged in Malaysia. Deforestation and drought-driven forest fires drove jungle bats to feed in orchards near where farmers kept their pigs. The animals fed on the bat droppings, picked up the Nipah virus, and passed it on to their keepers. One hundred and one people died, and nearly a million pigs were culled, but the virus still escaped to Indonesia, Australia, the Philippines and Bangladesh.

In August 2007, an epidemic swept through Castiglione di Cervia, a small village in northern Italy. More than 100 of the town’s 2,000 residents came down with high fever, rashes and crushing pain in their bones and joints. An unusually mild winter had allowed Asian tiger mosquitoes to start breeding early, and their population had soared.

When an Italian tourist returned from India with chikungunya, a relative of dengue, the insects provided the perfect vector. It was the first time the disease had broken out in Europe. “By the time we got back the name and surname of the virus, our outbreak was over,” Rafaella Angelini, director of the regional public health department in Ravenna, told The New York Times.

“When they told us it was chikungunya, it was not a problem for Ravenna anymore. But I thought: This is a big problem for Europe.” According to officials at the World Health Organization, the epidemic was the first European outbreak of a tropical disease caused by climate change.

“This is all part of a pattern of emergence of new diseases and of the resurgence and redistribution of old diseases,” Epstein said. “It’s occurring globally for many reasons: deforestation, changing habitats, chemical use that affects predators, our own use of antibiotics, and then climate.”

Disruptions in normal weather patterns favor opportunistic pests and parasites. Climate change has the potential to unsettle ecosystems and bring humans, animals, and pathogens together in new and unexpected ways. Since 1976, the World Health Organization has identified 39 previously unknown diseases, including Ebola, the New Mexican hantavirus, and Lyme disease— an eruption of pathogens on par with those that occurred during the invention of agriculture and the Industrial Revolution.

“As the climate becomes more unstable, it will have an increasing impact,” Epstein said.
“We’re going to see things shift.”  

Introduction
Forecast: The global consequences of climate change

Part 1: Why America Should Care
The Florida Keys are sinking
Can insurance cover the costs of climate change?
Who will be able to afford to live on the coast?

Part 2: The Spread of Disease
Pathogens find new habitats
Countries could backslide into poverty
How disease relates to carbon dioxide

Part 3: The Arctic Melt
Easier passage through the Arctic
A scramble for control of the Arctic
Opening the Arctic to damage

(Stephan Faris is the GlobalPost environment correspondent. His new book is "Forecast: The Consequences of Climate Change, from the Amazon to the Arctic, from Darfur to Napa Valley.")