Global Courant
Florida health officials reported two additional cases of malaria on Thursday.
Both were identified last week and neither were linked to travel outside the country. That brings the total number of locally contracted malaria infections in the US since May to seven. All but one of the cases were in Sarasota County, Florida. The other case, unrelated to the Florida one, was a Texas man who worked for the National Guard along the Rio Grande.
The cases are the first in 20 years to be acquired in the US
The Centers for Disease Control and Prevention issued a health alert on June 26 asking hospitals to be on the lookout for patients with malaria symptoms and to prepare to diagnose quickly and begin administering anti-malarial drugs within 24 hours.
Dr. Manuel Gordillo, an infectious disease specialist at Sarasota Memorial Hospital, said his hospital has treated four malaria cases in Florida this year, including the first patient found to have the infection and the two most recent cases.
All were diagnosed shortly after being hospitalized, Gordillo said — unlike the Texas patient, who said he was initially misdiagnosed with a viral infection. A few of the patients were homeless, Gordillo said, and arrived with a fever and dehydration.
“Some of the cases were kind of a neglect of the symptoms and they came on much late with other complications,” he said.
As far as he knows, Gordillo said, public health officials are not actively looking for new cases unless they show up at a clinic or hospital. The Florida Department of Health did not respond to a request for information on how it monitors new cases.
Dyann Wirth, an infectious disease professor at the Harvard T.H. Chan School of Public Health, said the new cases are somewhat surprising, but not unheard of.
“This isn’t panic, but it’s also not something we should say, ‘Well, it’s so unusual, we shouldn’t worry about it.’ It’s a warning to monitor,” Wirth said.
Malaria is a serious, sometimes deadly, disease that is usually transmitted by mosquitoes, which transmit a parasite to humans through bites.
Typical symptoms are fever, chills, headache, muscle aches and fatigue. Some patients also experience nausea, vomiting and diarrhea, according to the CDC. Symptoms usually appear 10 days to four weeks after being bitten by a mosquito.
Before the Covid pandemic, the US saw about 2,000 cases of malaria each year, although almost all of them were people who had traveled to other countries.
How do doctors treat malaria patients?
The recent US cases were caused by a parasite called P. vivax, the dominant malaria parasite outside Africa. P. vivax is not as deadly as some other parasites that cause malaria, but it can lie dormant in the liver and cause chronic infections months to years after an initial illness.
Gordillo said doctors typically prescribe two treatments for P. vivax: one to kill the parasite in the blood and another to kill the parasite in the liver.
The antimalarials chloroquine or hydroxychloroquine are usually the first line of treatment, he said. But Gordillo said his hospital has been dealing with supply issues with those drugs, so it’s prescribing Coartem — a drug that’s more effective but costs more and isn’t available through pharmacies.
Gordillo said Coartem is a three-day treatment. Then, he said, patients are given a two-week treatment with a drug called primaquine, which can be taken at home. However, some patients have required longer hospital stays, he said.
“They’re dehydrated, some of them. They have low blood cell counts, especially platelets, which puts them at risk for bleeding. Some of them have had kidney failure, which is one of the complications of malaria,” Gordillo said.
Why are locally acquired cases appearing now?
Malaria was considered eliminated in the US in 1951. The most likely explanation for the new cases in Florida, Wirth said, is that a person with malaria traveled to the US and was then bitten by a local mosquito, which then spread the disease to other people. without travel history.
“Everything has to be right for handover to happen,” Wirth said. “An infected person must have the transmissible form in their bloodstream. The right kind of mosquito has to sting, and then that mosquito has to live long enough to bite someone else.”
The average female Anopheles mosquito — the most common malaria transmitter — lives about two to three weeks, and it takes about seven to 10 days for a parasite to develop in the mosquito, Wirth said. The insects travel up to 2 miles, According to the CDC.
Gordillo said all six Florida cases are from a northern region of Sarasota County, which has forested areas and has had rain recently. Mosquito populations are usually highest in the summer, and Florida’s humidity is ideal for reproduction.
Both Gordillo and Wirth said there may be more cases that have gone undiagnosed.
“We don’t know how long this is going to take because of the nature of this particular species. It can hide in people’s bodies, the incubation period can be long, so it can stick around a bit,” Gordillo said.
Wirth said malaria “can be explosive” because one mosquito can infect many people. That’s why it’s important to screen for new infections through routine blood samples, she said.
In some previous outbreaks in other countries, Wirth said, screening programs ended too early after case numbers dropped.
“Whoever was in charge thought, ‘Well, we’ve largely solved this problem. It’s expensive to keep all this oversight,’ and there were huge rebounds,” she said.
The Florida Department of Health said last month that it sprays insecticides to kill mosquitoes and advised residents to use bug spray, wear long sleeves and pants, and drain standing water.
