Is climate change leading to an increase in mosquito-borne illnesses?

While organizations like the World Health Organization have cautioned that climate change could lead to more global cases and deaths from malaria and other mosquito-borne diseases, experts say it's too soon to tell if the local transmission the past two months in Sarasota County has any connection to extreme heat or flooding.

"We don't have any reason to think that climate change has contributed to these particular cases," said Ben Beard, deputy director of the CDC's division of vector-borne diseases and deputy incident manager for this year's local malaria response.

Mosquitoes in the northern part of Sarasota County were likely able to spread malaria to seven people locally because they first bit someone with an undetected travel-related infection, Beard explained.

The U.S. typically sees about 2,000 travel-related cases of malaria a year, caused when people contract the disease in other countries but don’t develop symptoms until after they have returned to the States.

The type of malaria that all the patients in Sarasota had is Plasmodium vivax which, though potentially still fatal if left untreated, usually produces milder symptoms.

It’s possible that someone did not realize they had malaria when they were bit by an Anopheles, the type of mosquito that carries the disease. The infected mosquito could then spread malaria to other Sarasota residents.

A rise in vector-borne diseases

Still, scientists are worried that changing weather patterns could lead to an increased risk of mosquito-borne diseases.

Florida, along with other parts of the country, has been getting hotter and wetter — ideal conditions for mosquitoes to thrive.

"Milder winters; earlier springs; warmer, longer summers — all of those things sort of translate into mosquitoes coming out earlier, getting their replication cycles sooner, going through those cycles faster and being out longer," Beard said. “And so we are concerned about the impact of climate change, and environmental change in general, on what we call vector-borne diseases."

Beard co-authored a 2019 report that highlights a significant increase in diseases spread by ticks and mosquitoes in recent decades.

According to the report, from 2004 to 2017, over 700,000 cases of 16 diseases caused by viral, bacterial or parasitic agents were reported to the CDC. Lyme disease and West Nile virus were among the top five most prevalent.

Researchers identified two trends in the data, including a steady increase in tick-borne illnesses and an increase in intermittent outbreaks of mosquito-borne arboviruses. Those included West Nile, but also diseases like chikungunya and Zika.

Malaria was not accounted for in that research because prior to this year, the last time there was local transmission in the U.S. was in 2003, when eight people contracted the disease in Palm Beach.

Though not the only reason for the uptick in illness, scientists cited climate change as a contributing factor.

"In the big picture, it's (environmental change) a very significant concern that we have," said Beard.

Other mosquito-borne illnesses in Florida

While there have been no malaria cases in Sarasota since the seventh was confirmed in early July, other parts of the state are seeing instances of mosquito-borne disease.

The Florida Department of Health reported two more cases of locally acquired dengue in Miami-Dade in its weekly arbovirus report for July 16-22, bringing the total in that area for this year up to five.

One case of West Nile virus was also recorded in Escambia County. Three sentinel chickens also tested positive for antibodies to West Nile in Orange, Volusia and St. Johns counties.

Health officials confirmed one horse was infected with Eastern Equine Encephalitis virus in Jefferson County, while six chickens tested positive for antibodies to the virus in Leon, Nassau, Orange and Walton counties.

Sarasota, Manatee and Miami-Dade counties remain under a mosquito-borne illness alert.

Escambia, Jefferson, Nassau, Orange, Polk, St. Johns, and Walton counties are under a mosquito-borne illness advisory.

How to stay safe

The best thing residents can do to stay safe is clear their properties of standing water or vegetation that attracts mosquitoes and protect themselves from mosquito bites, experts say.

“Just be aware that mosquitoes are alive and well,” said Beard. “The one thing we can all do is wear repellents, be aware of the risks, [wearing] loose-fitting clothes — all those things can help prevent exposure to the bites of potentially infected mosquitoes.”

Anyone who thinks they may have symptoms of these diseases, such as high fever, should seek medical attention, he said.

The CDC has more information about how to prevent vector-borne diseases on its "Fight the Bite" webpage.

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