Before you start looking around for mosquitoes, take a deep breath. The malaria found by the San Francisco State University study is found only in birds and cannot be transmitted to people.
Still, one of the study’s co-authors said the spread of the disease is an example of another way Alaska is changing as the Earth warms. “These parasites, since they’re cold-sensitive, they may be moving north with climate change,” associate professor Ravinder Sehgal said.
For two years, Sehgal’s team captured and tested more than 600 birds from Anchorage to Coldfoot on the Arctic Circle. Birds tested positive from Anchorage north to about 64 degrees north latitude, as far north as Fairbanks.
Climate modeling applied to the test results shows that in the next 50 years, avian malaria may spread north of the Arctic Circle but not north of the Brooks Range. That’s a concern for bird species in the north that haven’t been previously exposed to malaria.
Penguins infected with malaria in warm-weather zoos die at a rate much more frequently than other birds infected with malaria, Sehgal said. How susceptible northern birds will be to malaria remains unknown. “This is something we don’t know,” he said.
Robin Corcoran, the avian biologist with the Kodiak National Wildlife Refuge, said she was surprised by the results. To date, most research in Alaska has focused on avian influenza (bird flu) and West Nile virus. “Purely from a public health standpoint, avian influenza’s been the one that’s been on everybody’s watchlist,” she said.
On Kodiak Island, where the Kittlitz’s Murrelet is a candidate for the Endangered Species List, dead Kittlitz chicks have been tested for diseases, but never for avian malaria.
Corcoran said she was unaware of other avian malaria testing but believes it may be needed because Alaska sees so many migratory species that come from malaria-infected regions of the world. “The mobility of birds probably helps them,” she said. “It’s more similar to how the disease would spread in humans, when you think about it.”
In Alaska, and especially in Kodiak, human malaria is almost unheard of because the most common varieties require weeks at temperatures of 68 degrees or greater in order to spread. Malaria spreads through mosquitoes that bite infected people or animals, but though the state is notorious for mosquitoes, most of the state’s breeds can’t carry the malaria parasite even if it were present and warm enough to spread.
Still, the state’s latest annual report on epidemic diseases shows five cases of malaria among Alaskans.
Louisa Castrodale, an epidemiologist with the state of Alaska, said those reports come from Alaskans who traveled overseas, became infected, then came home. “The convention by reporting is by state of residence,” she said.
Castrodale said she believes that human malaria is a distant threat for Alaskans because it simply isn’t warm enough. “There’s definitely some temperature factors for both survival of the mosquito and the ability of a parasite or a virus to incubate in a mosquito,” she said. “It’s also unlikely we’ll see West Nile up here because of sustained high temperatures.”
Sehgal’s next study will try to determine if those temperature factors hold true, even in a warmer Alaska. As the latest study was written and edited, he returned to Alaska to collect mosquitoes and birds for testing in the lab. The testing will narrow down what species of Alaska mosquitoes can carry malaria and if so, what temperature ranges keep the parasite alive.