Malaria is making a comeback in the U.S. What you need to know to stay safe from it—and West Nile Virus—this summer

But it should, with the U.S. Centers for Disease Control and Prevention announcing this week that five malaria cases have been reported in Florida and Texas over the past two months. The cases are not related to travel or each other, according to the federal health agency, meaning that spread of the potentially deadly disease is occurring via mosquitoes—and that prevention is of the utmost importance.

The threat of contracting malaria in the U.S. is low, according to the federal health agency. The sentiment is echoed by Dr. Amesh Adalja, an infectious-disease specialist and senior scholar at the Johns Hopkins Center for Health Security. He tells Fortune that “the average resident of the United States has little to fear from malaria,” because the risk is limited to parts of Florida and Texas.

In the U.S., the risk of contracting West Nile virus is “much higher—and this mosquito-borne virus will kill more Americans than malaria,” he adds.

For Americans unfamiliar with malaria, here’s a primer on the disease—and what you need to know to stay safe from both malaria and West Nile this July 4 holiday and beyond.

What is malaria?

It’s a serious and potentially fatal disease spread by female Anopheles mosquitoes infected with parasites, generally in tropical areas. Globally, more than 240 million cases occur each year. The vast majority of cases—95%—and deaths—96%—occur in Africa. 

Rarely, it can be transmitted from a mother to her fetus, or to her newborn at birth; through blood transfusion or organ transplant; or through unsafe needle-sharing, according to the CDC.

What are the symptoms of malaria?

Unfortunately, they’re not super specific. They include fever, chills, headache, muscle pain, and fatigue. 

“There are no specific symptoms for malaria that reliably distinguish it from other infections,” Adalja says. “Fevers, chills, and muscle aches are common to many infectious diseases.”

There’s usually a considerable delay in symptoms after being bitten by an infected mosquito, from 10 days to up to four weeks, according to the CDC. But a person may start to feel sick as early as a week after the bite and as late as a year after, the agency cautions.

Early, proper care makes malaria a very survivable disease. If not treated in a timely manner, however, it can progress to changes in mental status, seizures, kidney failure, respiratory distress, coma, and death. The disease is especially dangerous for those who are pregnant.

When was malaria last found in the U.S.?

Health officials began efforts to eliminate the disease from the U.S. in 1947, and it was considered eradicated from the country in 1951. About 2,000 cases are diagnosed in the U.S. each year, but they’re virtually all travel-related, with sickened individuals having recently returned from sub-Saharan Africa or South Asia, according to the CDC. 

There hasn’t been a report of malaria acquired in the U.S. since 2003, when eight cases were diagnosed in Palm Beach County, Fla. 

The CDC had anticipated a rise in U.S. malaria cases this summer and early fall, but only because travel is returning to normal after the COVID-19 pandemic.

How high is the risk of getting malaria in the U.S.?

The good news: It’s “extremely low,” according to an alert to medical personnel released this week by the CDC. It is higher, however, in areas where the Anopheles mosquito survives for most of the year, and in areas where people frequently travel to malaria-endemic areas.

Are there other mosquito-borne diseases to worry about?

The best advice is to wear mosquito repellent, avoid mosquito-laden areas, and to clean up standing water, Adalja says. These are the best methods for preventing all mosquito-borne diseases, including West Nile.

What should I do if I suspect I have malaria?

The disease is a medical emergency, according to the CDC, and must be treated as such. Patients suspected of having malaria need to be “urgently evaluated in a facility that is able to provide rapid diagnosis and treatment within 24 hours of presentation,” according to the agency’s recent bulletin on the matter.

Thankfully, medications like chloroquine and hydroxychloroquine exist and are highly successful if treatment begins early, though the exact treatment will depend on the type of malaria one has. 

A vaccine exists, but it’s only recommended for children who live in areas with moderate to high transmission.