For the first time in 20 years, the United States has reported locally transmitted cases of malaria. Five people in Florida and Texas contracted malaria from infected mosquitoes within the last two months, according to the Centers for Disease Control and Prevention.
Although the United States sees roughly 2,000 cases of malaria a year, they typically occur in people traveling from countries where malaria transmission is more common.
Here is what you need to know about the disease, new cases, and how to stay safe.
What has led to these cases of local transmission?
“The short answer is, we still do not know,” said Prakash Srinivasan, assistant professor at the Johns Hopkins Malaria Research Institute and Bloomberg School of Public Health.
According to the World Health Organization, global malaria rates steadily declined from 2000 to 2015, but the past few years have seen an increase in both cases and deaths, particularly associated with disruptions to services during the COVID-19 pandemic. Srinivasan said it’s unclear whether the new cases are tied to this global trend.
The climate crisis could also play a role. For years, health experts have warned that warming global temperatures and changing rainfall patterns will increase the spread of diseases carried by mosquitoes that thrive in warmer and more humid climates, such as malaria, Zika virus, and dengue fever.
“There’s going to be a greater spread of certain species of mosquitoes in the United States that are going to increase the risk of introduction and spread of diseases like malaria or dengue that we’ve previously eliminated,” according to Dr. David Hamer, professor of global health and medicine at Boston University and director of the travel clinic at Boston Medical Center.
According to the CDC, the four reported cases in Sarasota County, Fla., and one case of a Texas resident who works outdoors in Cameron County do not appear to be related and all patients “have received treatment and are improving.”
What is malaria and how does it spread?
Malaria is a disease caused by parasites spread to humans by the bite of some species of female anopheline mosquitoes. People can also catch malaria from exposure to infected blood, including through organ transplants, blood transfusions, and from mother to fetus.
Classic symptoms include fever, headaches, muscle aches, joint pain, and chills. It can also cause gastrointestinal problems like nausea, vomiting, and diarrhea.
Symptoms typically appear 10 days to four weeks after infection, although some people may feel ill as soon as seven days after exposure or as late as one year.
The illness can be diagnosed by a blood test and is treatable by antimalarial drugs. If not treated promptly, malaria can progress to severe, life-threatening stages and lead to complications such as seizures, respiratory issues, renal failure, and coma. Approximately 300 Americans each year contract severe malaria while traveling, of which five to 10 cases are fatal.
Is it likely that local transmissions will spread to other states like Massachusetts? Should people be taking precautions?
While Anopheles species that spread malaria can be found in New England, they’re not as common here as in southern states like Texas and Florida, said Dr. Louise Ivers, director of the Harvard Global Health Institute and the Massachusetts General Hospital Center for Global Health. She notes that the climate crisis could change this but that there are no current estimates for when or how.
The relatively low number of cases in states so far away are “nothing to get alarmed about,” said Dr. Daniel Kuritzkes, chief of the division of infectious diseases at Brigham and Women’s Hospital.
He encourages residents to take reasonable precautions against mosquito bites, which can cause other illnesses such as West Nile virus and Eastern Equine Encephalitis, like limiting exposed skin by wearing long sleeves and long pants, using insect repellent when outdoors, and spending more time indoors or in screen-protected spaces.
While the mosquitos that cause malaria are more likely to be active during the nighttime, particularly around dawn and dusk, the other species that transmit diseases more commonly found in Massachusetts are more likely to be daytime biters, according to Hamer. “The bottom line for local people is that anti-mosquito measures are really important if you’re going to be outside whether it be in the evening or during the day,” he said.
Should summer travelers take additional precautions against malaria this year?
There’s nothing to suggest this summer is more dangerous than previous ones, according to Srinivasan, who said all travelers visiting countries where malaria is more common should educate themselves about prevention and treatment and take appropriate anti-mosquito measures.
Those traveling to parts of Florida near where the cluster of cases has been found should also consider taking precautions, Hamer said, but, given that Texas has only seen one case so far, he said he does not see any need for immediate concern.
Is there a malaria vaccine?
Yes, and more are on the way. In 2021, the World Health Organization recommended the use of a vaccine called RTS,S to reduce the spread of malaria in countries with “moderate to high” transmission among children. It has a 30 to 40 percent efficacy rate. In April, another vaccine, developed by scientists at the University of Oxford, was approved for use in children aged 5 months to 36 months in Ghana and may soon offer a better alternative.