A once-vanquished disease spread by mosquitoes may be making inroads into the United States. New Jersey officials are now investigating whether a resident’s malaria infection was locally acquired.

The New Jersey Departments of Health (NJDOH) and Environmental Protection reported on the case Monday. The resident hadn’t recently traveled, suggesting they likely caught it from homegrown mosquitoes. If so, this would be the first locally acquired malaria case seen in the state in over three decades, though not the first such case reported in the country this year.

The blood-loving parasite

Malaria is caused by several species of the single-celled parasite Plasmodium. When an infected mosquito transmits the disease to a person, the parasites will first invade certain tissues (usually the liver), reproduce, and then infect red blood cells. A small percentage of the parasites in the bloodstream will develop into a stage of life that can newly infect and grow inside mosquitoes that bite the person, starting the cycle all over again.

The symptoms of malaria, which include fatigue, chills, and other flu-like illnesses, are caused by the damage the infection causes to our blood cells. Though most people survive their bout of malaria, it can also cause life-threatening complications like seizures, kidney failure, and sepsis. Even with available treatments today, malaria still kills roughly 600,000 people worldwide every year—making it one of the deadliest diseases around.

Malaria was once a common threat in the U.S., particularly in warmer areas during the summer. But a dedicated public health campaign, which included mosquito spraying programs and the removal of breeding sites, eradicated the disease by the 1950s. Since then, just about all malaria cases reported in the U.S. are travel-related, originating from places where the disease is endemic. But the potential for malaria to make a comeback remains.

A mosquito mystery

Malaria is spread by the bite of a female Anopheles mosquito, and there are native species in the U.S. that can transmit the disease to humans, including in New Jersey.

Though officials are unsure about the origin of this latest case, it’s possible that a person with travel-related measles arrived in the area and was bitten by a mosquito that may have then bitten someone else. According to health officials, roughly 100 travel-related cases are reported annually in the state. If this new case is confirmed as local, this would be the first homegrown case documented in New Jersey since 1991.

Officials say that malaria’s threat to the greater public is minimal, but other recent cases have been locally acquired. In 2023, for instance, there were three separate clusters in Florida, Texas, and Maryland (at the time, they were the first local U.S. cases documented in two decades). And earlier this month, Washington officials reported their own possible homegrown case of malaria, quite possibly the first ever found in the state.

Low as people’s risk of malaria may be, we should still do our best to prevent mosquito bites. There are other diseases that mosquitoes in the U.S. can spread outside of malaria, including West Nile virus, Eastern Equine Encephalitis (EEE), and even dengue fever. We can personally reduce bites by using insect repellent and wearing long-sleeved clothing. And people should also do their part to clean up areas around their homes that could turn into literal breeding grounds for mosquitoes.

“I urge the public to continue taking steps to eliminate standing water around their properties, which will go a long way to reducing the risk of mosquito breeding,” said Shawn M. LaTourette, NJ Environmental Protection Commissioner, in a statement. “As the summer winds down, taking this simple but necessary step will help ensure quality of life and protect public health.”