HEALTH: Warmer Climate Gives Malaria New Hunting Grounds

By Stephen Leahy Reprint | | Print |

Stephen Leahy

CHICAGO, U.S., Feb 19 2009 (IPS) - Climate change is bringing malaria to regions of Africa where the disease was previously unknown, researchers report from the conference of the American Association for the Advancement of Science in Chicago this week.

Interestingly, the Arctic, where climate change is happening fastest, is the best place to study how warming temperatures are affecting infectious disease transmission.

Insect-transmitted diseases, primarily malaria, kill 3,000 people in Africa each day, said Andy Dobson of Princeton University in the United States.

Understanding how global warming is altering temperatures and the ecology and ranges of the malaria-transmitting Anopheles mosquito is crucial to understanding the dynamics of how insect-transmitted diseases like malaria will change, Dobson told IPS.

“Ironically, we’re spending huge amounts of money on trying to develop vaccines for malaria but the best possible vaccine we could make wouldn’t last for longer than two years,” he said.

That’s because the natural lifetime of immunity to malaria is perhaps two years and to eradicate malaria using a vaccine would require vaccinating everyone every year because the malaria parasite evolves quickly, he explained.

Instead scientists need to be able to understand and project how and where malaria outbreaks will occur under the altered conditions of climate change. However, there is very little data or research on disease transmission in the field. Rather, the focus has been on developing vaccines and genetic analysis of the malaria parasite and mosquito genome – and that “tells us nothing about transmission”, he said.

“A sad testimony to how the (U.S.) National Institutes of Health and the Gates Foundation spend their money,” Dobson told IPS.

Malaria epidemics will likely be a new threat to tens of millions of Africans in previously malaria-free highland regions of Ethiopia, Kenya and Tanzania, and Rwanda and Burundi, warned Christopher Thomas of Aberystwyth University in Britain.

“This shift is projected to be already underway,” Thomas said, based on new computer models of temperature increases. “Malaria is expected to respond quickly to a changed climate because mosquito populations will increase in regions previously too cold.”

There is little natural immunity to malaria in most of these regions, he added.

That also means that some regions, like the Sahel, will see less malaria as they are projected to become too dry for mosquitoes. Still, it’s hardly good news since drought conditions would undermine local food security, he said.

Warming temperatures can explain the eight-fold increase in malaria in the highlands of western Kenya since the 1970s, said Mercedes Pascual, an ecologist at the University of Michigan, United States.

“Historically, people have settled in these regions to be protected from malaria, but this makes them more sensitive,” said Pascual.

The lack of previous exposure to the disease means local peoples’ resistance is low and mortality is much higher than average. Measured temperature increases in some cases has only been 0.5 C degrees, but in combination with increased resistance to the anti-malaria drug chloroquine, that has been enough to fuel the substantial increases in the disease, she believes.

“Climate change is a concern right now,” Pascual concluded.

The lack of understanding of basic mosquito and parasite biology in the field is a serious knowledge gap in determining when and where malaria will strike in new regions, said Matthew Thomas, an entomologist at Penn State University in the U.S.

The female Anopheles mosquitoes spread malaria by biting infected humans and ingesting the malaria parasites along with the blood. The parasites grow very slowly in cooler temperatures and faster when it is warmer. Climate change is not only raising the average temperatures but making nighttime temperatures even warmer.

According to Thomas’s research, that that can make all the difference because during the first 12 hours of the parasite’s incubation, it is very vulnerable to cooler temperatures. Since most mosquitoes bite in the evening or at night, warmer nights are good news for parasites, bad news for humans.

However, Thomas has also learned that if mosquitoes that feed in the morning face rapidly rising daytime temperatures then the malaria parasite development can be stopped. To project what will happen, “We need to understand the effects of temperature and environmental change through the eyes of the mosquito,” he said.

The best place to understand mosquito biology is the Arctic, suggests Andy Dobson, even if there are no malarial parasites. The primary reason is that climate change is already in fast-forward in the Arctic, well ahead of Africa. The life cycles of local parasites have accelerated with the warming temperatures by a factor of three or four, he said.

“Mosquito populations have boomed and the caribou are getting hammered,” Dobson said.

The Arctic also is simpler ecologically, with far less biodiversity than Africa, making it easier to tease out the details of host-parasite interactions. It is a kind of giant disease-transmission lab that could provide early insights into what may happen in the Mediterranean and tropical regions in the future, he explained.

It is also important to remember that malaria is a disease of the poor. The southeastern U.S. and the northern portions of Australia have perfect conditions for the disease but are malaria-free, noted Matthew Thomas.

“We could make serious inroads in understanding the biology in three to five years, but lack funding,” said Thomas.