More dengue fever, less malaria. That may be the future in parts of Africa on a warming planet, depending on where you live.
New research suggests that the only thing that matters is which mosquitoes will thrive. And the methods of controlling one don’t necessarily work on the other.
The mosquito that spreads malaria prefers relatively cool temperatures of 25 degrees Celsius. The dengue mosquito is best at 29 degrees Celsius (84.2 degrees Fahrenheit).
Because of this difference in optimal temperatures, we would actually predict that climate change could have opposite effects [on disease transmission]”Said Erin Mordecai, assistant professor of biology at Stanford University and lead author of the study.” With climate change, transmission of malaria may be less likely, but transmission of dengue fever is more likely. ”
FILE – A doctor tests a child for malaria at Ithani Asheri Hospital in Arusha, Tanzania, on May 11, 2016.
Using data on the optimal temperature of mosquitoes and population density, the researchers forecast the risk of malaria and dengue in Africa under worst-case-business-as-usual climate projections.
The dengue mosquito, which also spreads many viruses that cause diseases like chikungunya, zika and yellow fever, is expected to expand its range and increase the risk of these diseases across sub-Saharan Africa by 2080.
In contrast, the areas at greatest risk of malaria are predicted to shrink and move further south to high-altitude regions.
The researchers say that increasing urbanization in Africa could further increase dengue risk. Malaria is often a bigger problem in rural areas because the mosquito breeds in natural waters such as ponds and streams. But the dengue mosquito prefers to breed in tiny, man-made containers that are “the size of a bottle cap,” as is common in cities, Mordecai said.
FILE – An Indian woman walks with a child along an open drain filled with plastic and stagnant water used as a breeding ground for mosquitoes in New Delhi, India on Sept. 20, 2016.
Urban areas also tend to be warmer than the surrounding rural areas and provide a more suitable habitat for the warmth-loving dengue mosquito.
“We expect dengue to become a much bigger problem in Africa. And I think that in itself is a very big deal because, by and large, Africa is probably not well prepared because it has focused on another very important vector-borne disease – malaria, ”said Desiree LaBeaud, professor of pediatric infectious diseases at Stanford University and co-author of the study.
Public health measures such as insecticide-treated bed nets have helped contain malaria as they protect against the nightly malaria mosquito. But nets are not very helpful against dengue fever, as the mosquito bites during the day.
Rising cases of dengue fever and other viral diseases can pose new challenges for Africa. Mordecai says diagnostic tools for dengue fever are not widely available in many parts of the continent, which can lead to misdiagnosis and inappropriate treatments.
“Generations of scientists and controls have been trained and experienced in the fight against malaria vectors. But for dengue, you have to start by essentially retraining people for an entirely different creature and enemy, ”said Philip McCall, professor of medical entomology at the Liverpool School of Tropical Medicine who was not involved in the study.
According to McCall, other studies have shown links to climate change and dengue fever.
“Dengue fever, or possibly chikungunya and zika, is more likely to increase and become an emerging serious urban phenomenon,” he said. “But I can’t see that malaria, which is so established in Africa, is going away easily. So it could be like double trouble. ”
Experts say this study only shows one possible scenario for mosquito-borne diseases in Africa.
“This study is only looking at the very high emission, very fossil fuel intensive future that some people think is a bit unlikely,” said Joacim Rocklöv, professor of epidemiology at Umeå University, who did not contribute to the research. “I think if you looked at a different scenario that might be more plausible, or if we made changes to emissions control, you could actually see very different results with malaria.”
The best way to combat dengue is to reduce the breeding habitats for the mosquito by removing containers of standing water or making sure they are covered with airtight cover.
However, there is new hope for a different type of dengue control.
A naturally occurring bacterium called Wolbachia blocks dengue virus replication in the mosquito and prevents transmission. Dengue cases were reduced in a study of the release of Wolbachia-infected mosquitoes in Indonesia.
“They cut transmission by 77% in a huge area of Yogyakarta, which is incredible,” said McCall.