Malaria Infections in Florida and Texas: Will They Spread?

A century ago, malaria was endemic in the United States, especially in the South, but thanks to a vigorous public health response, the disease was considered eliminated in this country by 1951, according to the Centers for Disease Control and Prevention (CDC).

In recent weeks, however, 4 cases of malaria in Florida and 1 in Texas have been reported. All 5 patients have been treated, and all are recovering. So why all the brouhaha over just 5 cases? Because they’re unusual and unexpected, says Dr. Melanie Dubois, a specialist in pediatric infectious diseases and an Assistant Professor in Pediatric Infectious Diseases at Weill Cornell Medicine.

“Given that these cases were locally acquired—i.e., not travel-related—it’s important for public health officials to monitor for any additional cases of malaria in the U.S.

“That having been said,” she continues, “the risk of contracting locally acquired malaria in this country remains very low.”

How is malaria transmitted?

Transmission depends on three “players”: a tiny parasite, a mosquito and a human host.

• The parasite: Malaria parasites belong to the genus Plasmodium, and five species infect humans. P. falciparum is known to cause severe malaria mainly in Africa and Southeast Asia, but the 5 American patients who came down with the disease were infected by P. vivax, which typically causes a milder version of disease.
• The mosquito: The parasite takes up residence and reproduces in the body of a female Anopheles mosquito. And the mosquito, requiring a blood “meal” for its own reproductive purposes, bites one of us. Per the CDC’s malaria advisory, the Anopheles mosquito vector is found in many regions of the U.S. and can transmit malaria if they feed on a malaria-infected person.
• The human host: Through its bite, the mosquito transmits the malaria parasite to a human. Technically, it’s the parasite that makes us sick, not the self-interested mosquito.

The mosquito must bite two people to spread malaria: It picks up the parasite from human number-one and, when the time is right, transmits it to human number-two.

Can malaria be transmitted by means other than mosquitoes?

Malaria is almost always spread via mosquitoes, but it can also be transmitted during pregnancy from mother to fetus or through transfusions, organ transplantation, or contaminated needles or syringes.

Who is at risk for contracting malaria?

“The most vulnerable groups,” says Dr. Dubois, “are those with little to no immunity against the disease, including:

• young children
• pregnant women
• world travelers who come from areas with little or no malaria transmission (like the U.S.)

What is causing the uptick of malaria cases in the United States?

Three factors may be at play:

Climate change

Climate change is already affecting the epidemiology of vector-borne illnesses, such as West Nile virus, Zika virus, dengue and malaria. Warmer weather can lead to more mosquitoes, given that they thrive in warm and humid conditions. Additionally, climate change is driving human migration and associated disease transmission. Climate change is also increasing the length of “mosquito season” and encouraging both insects and ticks to make themselves at home in previously inhospitable areas.

Urbanization

We have been modifying the landscape in such a way as to increase interactions between humans and mosquitoes. In general, urbanization offers more opportunities for the spread of disease and both local and global transmission of malaria.

Globalization

Most U.S. cases of malaria occur in people traveling from countries with high rates of malaria transmission—mainly sub-Saharan Africa and South Asia. Given the rise in international travel worldwide, we may experience more and more travel-related cases of malaria.

What are its symptoms?

“The symptoms of malaria depend largely on the species of parasite with which a patient is infected,” Dr. Dubois says. “The disease is generally categorized either as uncomplicated or severe. Clinical symptoms for uncomplicated malaria include fever, chills, sweats, body aches and headaches. Patients with severe malaria may experience organ failure, with seizures, severe anemia or acute respiratory distress syndrome. Severe malaria is a medical emergency.

How can people protect themselves from mosquito-borne diseases, both outdoors and indoors?

Outdoors, people can avoid getting bitten by mosquitoes by using insect repellent containing DEET or picaridin and wearing long-sleeved clothing, especially at night.

Individuals and communities should drain stagnant water from bird baths, buckets and trash bins, where mosquitoes are known to breed.

Indoors, use screens on windows and doors. And when traveling to areas with a high incidence of malaria, experts recommend sleeping under insecticide-treated bed nets.

What precautions should people take when they're planning to travel?

Dr. Dubois suggests that travelers from the U.S. take the following measures:

• Know the epidemiology and health risks in the countries where you are traveling. See the CDC’s website for travelers.
• Take prophylactic medication if traveling to endemic regions. See a health-care provider before traveling to a high-risk area, and visit the CDC’s website for information about malaria drugs.
• Seek medical care if you experience symptoms of malaria during your travels or if you’ve recently traveled to an area with high malaria incidence.

Make an appointment with an infectious disease specialist at Weill Cornell Medicine if you’re planning a future international trip.