By Joseph Choi

The Centers for Disease Control and Prevention (CDC) has issued a health advisory over the spread of a few malaria cases in Florida and Texas, marking the first time locally acquired infections of the disease have been detected in the U.S. in 20 years.

Five cases of malaria caught by people in the U.S. have been identified so far, four in Florida and one in Texas, in the past two months. The fact these individuals were infected in the U.S. is what is causing concern among health officials as infections like these haven’t been seen since 2003.

As the CDC noted in its alert, malaria infections in the U.S. aren’t unheard of. The country saw about 2,000 annual malaria cases every year before the COVID-19 pandemic.

However, cases in the U.S. are almost always found in people who travelled outside of the country to regions where malaria transmission is more common. The five infections in Florida and Texas being caught locally indicates indicate mosquitoes acquired the parasite and spread them to

Effective treatments and mitigation strategies against malaria are available in the U.S, though treatment for the disease can be unpleasant. One expert worries these cases are indicative of a larger problem.

Malaria was once extremely common in the U.S., but its status as an endemic disease in the country was ended after the National Malaria Eradication Program that took place during the 40’s and 50’s.

Malaria is considered a “medical emergency” by the CDC that can be fatal, particularly among children under five and pregnant women. Symptoms can range from mild to life-threatening. Symptoms can be flu-like and also include an enlarged spleen, enlarged liver or mild jaundice.

One of the hallmark symptoms of malaria is what’s called a “malaria attack” in which an infected individual experiences a distinct period of illness that lasts six to 10 hours.

These attacks are defined by three stages: a cold stage of chills and shivering; a hot phase of fever, headaches, vomiting and potentially seizures in children; and a sweating stage in which they return to a normal temperature. Patients cycle through these attacks over the course of their infection.

There are four kinds of malaria and the cases detected in the U.S. have been caused by the parasite P. vivax. Of the more 200 species of mosquitoes in the continental U.S. and territories, there are two that can carry and spread P. vivax.

“It can get out of control really quickly if these cases go undetected for long periods of time. And vivax, some strains can be very non-virulent, so people can be infected and not really realize they’re infected,” said John Adams, professor at the University of South Florida College of Public Health.

The P. vivax parasite takes about 10 to 15 days to develop inside of a mosquito and become transmissible, meaning the potential spread of malaria may not be immediately noticeable, especially if the symptoms are ignored.

The anti-malaria drug chloroquine is effective against infections caused by P. vivax, but cases associated with this parasite will likely require additional treatment.

P. vivax is also one of two forms of malaria that can remain dormant in the liver, potentially causing recurring illness for months or years. Nearly all malaria cases will require medical intervention to be resolved and P. vivax cases will require treatment by another drug — such as one called primaquine — to target the dormant parasite in the liver.

This course of treatment has issues associated with it as well.

Adams noted that primaquine “has a lot of toxicity associated with it.” Side effects can include fatigue; a weak pulse; discoloration of the skin and eyes; seizures; confusion; and blurred vision.

Primaquine also shouldn’t be administered to people who have a genetic condition called G6PD deficiency. The drug can damage red cells in people with this condition, leading to anemia. Many people aren’t aware they have G6PD deficiency until they start a treatment like primaquine.

The CDC has attributed the recent infections to increased international travel brought on by the summer. Hurricane season may have also contributed to these infections as more standing water gives mosquitoes more opportunity to breed.

Speaking on the potential for widespread transmission, Adams said a bigger concern is that these malaria infection could indicate the spread of other mosquito-borne diseases like dengue, the Zika virus, West Nile virus and the Chikungunya virus.

West Nile virus has already been detected in several states as summer sets in. Louisiana has seen an earlier than usual onset of cases this year.

Malaria can be combated with helicopters and airplanes spraying insecticides to kill adult mosquitoes and larva. Adams noted every county in Florida has a mosquito abatement district, a program tasked with controlling mosquito populations and preventing disease.

To reduce the chance of becoming infected, individuals can buy clothing that already contains a synthetic repellent and insecticide called permethrin as well as spray themselves with standard mosquito repellent.

The CDC has advised clinicians to consider malaria when treating patients with fever of unknown origin, regardless of whether they’ve recently traveled international. Clinicians should also obtain a travel history of their patients.