Why it matters: A resurgence in travel could lead to more cases.
The United States eradicated malaria decades ago, but worldwide there were nearly 250 million cases of malaria in 2021, the vast majority in Africa, according to the World Health Organization. Before the Covid-19 pandemic, about 2,000 cases of malaria were reported in the United States each year, almost all of them in people who contracted the disease abroad, the CDC said. (Pregnant women can transmit the parasites to their children, and the disease can also be spread through blood transfusions, though such incidents are rare in the United States, according to the CDC. The country typically sees a transfusion-related case every two years, the agency says.)
But when people infected in other countries return to the United States, local mosquitoes can feed on them and transmit the parasites. “Things like that happen,” said Colin Carlson, a biologist at Georgetown University. “You would expect that in a country that has successfully eliminated the disease: from time to time, you will have reintroductions and a bit of local transmission.”
Dr Carlson said he did not believe the country was on the verge of a major malaria epidemic. But as international travel ramps up this summer, the number of imported malaria cases could rise, the CDC noted.
Background: The role of climate change is unclear.
Malaria is more common in warm climates, and some Anopheles mosquitoes have already expanded their range in ways compatible with climate change, Dr Carlson found in a recent study.
But it’s hard to say whether the new US cases are linked to climate change. It’s possible that the weather in the southern United States had become more conducive to malaria transmission, but the area was already warm enough for the disease to spread, Dr. Carlson noted.
Still, the climate could contribute to these cases in more nuanced ways, he said, perhaps by making the disease more prevalent in the places Americans travel to. This could lead to more imported cases, giving the parasites more opportunities to spread to the United States.
“If travelers are returning from places that are on the front lines of climate impacts, there will simply be a higher chance of malaria transmission taking off,” Dr Carlson said. “We live in a connected world, and the impacts of climate change in other countries can be health issues in our country.”
And then: Officials will monitor other cases.
The CDC is working with state health officials to investigate the new cases. Authorities are actively monitoring other potential cases and working to control local mosquito populations, the agency said.
People can protect themselves by using insect repellent, wearing long pants and long sleeves, and using mosquito nets, among other precautions. Those planning to travel should research the risk of malaria in their destinations and speak to their doctors about preventative measures, the CDC said.