Should you worry about malaria in South Florida?
Despite a malaria alert across the state, the number of mosquitoes buzzing around South Florida is down slightly this season compared to this time last year, say the officials who handle the biting bugs.
And, so far, the type of mosquitoes that can spread malaria have not been found in significant numbers in the region, according to the officials and a leading infectious disease expert.
But like with an encephalitis scare in the 1990s and Zika virus cases seven years ago, we’re keeping an eye on the reported cases of malaria on Florida’s Gulf Coast.
Although Miami-Dade, Broward and the Keys remain free of reported cases of malaria, mosquito monitors in South Florida also are watching the situation since the six locally acquired cases of the mosquito-borne parasitic illness were reported in Sarasota County earlier this year — the two most recent cases in late June.
Monitoring the mosquito
Mosquito control officials have been on high alert since spring, with indications this mosquito season could be heavier than normal due to heavy rainfall in May.
Typically, South Florida starts a period of daily downpours beginning in late spring, creating fertile breeding grounds for the biting insects. This year’s rainy season arrived a few weeks sooner than expected, meaning swarms of mosquitoes hatched earlier, prompting ramped-up targeting of larvae, aerial spraying and fog spraying by trucks in May, practices that usually begin closer to June.
“Any summer in the Keys contains its share of highs and lows when it comes to mosquito population, and this one is no different,” said Chad Huff, public information officer with the Florida Keys Mosquito Control District. “What has been unusual is the speed in which high season arrived, especially in the Upper Keys.”
But summer ushered in a much drier period of weather, resulting in a drop-off in mosquitoes in South Florida in late June and early July, said Michael Mut, a spokesman for Miami-Dade mosquito control.
“Comparatively speaking, the mosquito numbers for the last quarter are down from the same period last year,” Mut said this week. “Requests for inspections and spraying spiked in mid-April with the first spate of heavy rains, and remained pretty high in May and June, but have tapered off slightly.”
Drier weather to stick around
The drier weather is expected to continue, said Jonathan Rizzo, warning coordination meteorologist with the National Weather Service in Key West.
That’s because a high-pressure system normally located above northern Florida this time of year is instead sitting over the southern part of the state. This, coupled with the Saharan dust coming off Africa that arrived later than usual this year and is still over the area, means heavy rains likely won’t return anytime soon.
“Until we get to a pattern to where say tropical waves start to move across our area, it is going to remain ... drier than normal,” Rizzo said.
Occasional rain is expected, but that’s from the hotter than usual summer, with high temperatures on land and in nearshore waters “literally heating the islands” and creating precipitation overhead, Rizzo said.
Mosquitoes don’t travel far
Fortunately, the type of mosquito that spreads malaria, Anopheles quadrimaculatus, although present in South Florida, has not been found in numbers that alarm South Florida health officials, Mut said.
“Therefore we are not doing anything different as of yet, but we are ready to scale up control measures if necessary,” Mut said.
Dr. Aileen Marty, an infectious disease expert and professor at Florida International University’s Herbert Wertheim College of Medicine, said eight species of Anopheles mosquitoes that live in Florida are capable of spreading the plasmodium parasites that can produce malaria.
The good news for Broward, Miami-Dade and the Keys: Anopheles mosquitoes typically don’t travel farther than a mile and a half from where they hatch, so it’s not likely that the mosquitoes born in across-the-state Sarasota would fly to the region, Marty said.
This doesn’t rule out infections spreading to South Florida, however, because larvae can travel in cars and trucks.
“Adults can travel inside a vehicle, and larvae can travel in larval-contaminated water in vehicles. Thus, we humans can bring infected Anopheles mosquitoes to South Florida,” Marty said. “What we do can affect our risk. Also, blood transfusion and contaminated needles may transmit the parasites that cause malaria.”
What is malaria?
Symptoms of malaria can be mild or life-threatening, Marty said, and are similar to the flu — periodic fever, chills and body and headaches.
“Sometimes it starts with mild symptoms that mimic many other febrile illnesses and then progresses to more serious diseases,” she said. “When it is mild, it can be difficult to recognize as malaria, and healthcare providers need to have a high index of suspicion to run the tests to detect the parasites.”
Severe symptoms can include fatigue, confusion, seizures and trouble breathing.
The species currently causing malaria in Florida is known as Plasmodium vivax, which Marty said is the second-worst form transmitted.
People most at risk are infants and children under 5, pregnant women and those with compromised immune systems, including those with HIV and AIDS, Marty said.
Malaria treatment
Treatment for malaria varies, depending on the species of parasite, the severity of the symptoms and the age and underlying conditions of the infected person, Marty said.
With the current species in Florida, drugs are used to kill parasites not only in the blood, but also dormant parasites living in the person’s liver, she said.
The latter is important because people can carry smaller amounts of the parasite in their liver and not have symptoms of malaria because their immune systems prevent them from manifesting the clinical disease. Without killing those dormant parasites, however, they’re not in the clear.
“But if at any time the number of parasites overwhelms their immune system, the symptoms can reappear,” Marty said.
Most common South Florida mosquito
The bug we do have plenty of is the Aedes taeniorhynchus, or salt marsh mosquito, due to the Keys’ Upper close proximity to the Everglades, said Huff, the Florida Keys mosquito district spokesman.
“The salt marsh mosquito is far and away the most common nuisance species in the Florida Keys and has been very prevalent in summer 2023,” Huff said.
Along with the Anopheles mosquitoes, the Keys mosquito control district also keeps an eye out for Aedes aegypti, a type that spreads dangerous viruses like dengue fever, yellow fever, chikungunya and Zika.
“The district maintains a sophisticated mosquito surveillance program via dozens of traps up and down the Keys,” Huff said. “The contents of those traps are continually analyzed by trained staff. If that situation were to change, [the district] will be aware of it quickly.”
Huff said Aedes aegypti levels are about the same as they were last summer, “but always a concern due to their ability to vector diseases such as dengue fever.”
How can you take steps against mosquitoes?
Everyone can help reduce their chances of getting bitten by mosquitoes, but also to help reduce their breeding environments, Huff said.
Among the advice:
•Drain standing water around your home
•Dressin long sleeves and long pants
•Use an EPA-approved insect repellent with DEET, picaridin, oil of lemon eucalyptus, or IR3535
•Avoid being outdoors when mosquitoes are most active, at dusk and dawn.
