Last week, I was hiking and birdwatching in Fort Macon State Park in North Carolina. I got a few good bird photos but I got a lot of mosquito bites. In North Carolina, they are a nuisance but in Florida or Texas, they can be deadly. Locally transmitted malaria is now present for the first time in 20 years in the U.S. Many physicians are unfamiliar with its presentation and many hospitals are not prepared to perform diagnostic testing.
Worldwide, malaria affects 241 million people each year and and causes over a half a million deaths per year. It is caused by five species of the protozoan parasite Plasmodium (P. falciparum, P. vivax, P. malariae, P. ovale, and P. knowlesi) which are transmitted by the bite of a female Anopheles mosquito. It primarily occurs in equatorial regions, particularly in central African nations.
In the past, it was also endemic in the United States but was largely eradicated by public health efforts at mosquito control. In 2018, there were 1,823 cases of malaria diagnosed in the U.S., all in foreign travelers who became infected elsewhere. Until this year, the last cases of endemic malaria in the U.S. were in Palm Beach, Florida in 2003 when 8 persons were infected with Plasmodium vivax.
The recent outbreaks occurred in Sarasota County, Florida (4 cases on May 26, 2023) and Cameron County, Texas (1 case on June 23, 2023). In both areas, the species was Plasmodium vivax. Because of rising temperatures from climate change, southern areas of the United States may see more cases of endemic malaria in the future. Because these are locations that many Americans travel to for vacations, physicians in all states need to include malaria not only in the differential diagnosis of patients presenting with fever who have traveled to endemic countries but also in patients traveling to south Texas or south Florida. It has been nearly 3 decades since I last encountered a case of malaria and much has changed in the diagnosis and management since that time. So, this post is to update practitioners and hospitals on what they need to know.
Clinical presentation
After the initial mosquito bite, patients are asymptomatic during the incubation period and symptom onset is generally 1 – 5 weeks after the initial infection. Symptoms are non-specific and most commonly include fever, chills, headache, myalgias, and fatigue. Less commonly, patients can present with GI symptoms such as nausea, vomiting, and diarrhea. If not diagnosed and treated early, patients can become critically ill with mental status changes, seizures, renal failure, acute respiratory distress syndrome, liver failure, and coma. Pregnant women are at particularly high risk for developing severe disease and death. Others at high risk include immunocompromised patients, those with splenectomy, and children less than 5 years of age. Different Plasmodium species cause different severities of infection: P. falciparum and P. knowlesi infections can cause rapidly progressive severe illness or death, whereas P. vivax (the species causing the recent Florida and Texas cases) is less likely to cause severe disease.
Routine laboratory findings are also non-specific and can include anemia, thrombocytopenia, and elevated liver function tests. Patients presenting with thrombocytopenia are more likely to develop severe disease. Because malaria can progress extremely rapidly, it is essential that diagnosis be made immediately. The clinical suspicion of malaria should be considered a medical emergency – this is not a disease that you discharge patients with from the emergency room to follow-up with their PCP the next day.
Diagnosis and treatment
Malaria should be considered in any patient with fever and recent travel to endemic areas (now including the southern most areas of the United States). The diagnosis is confirmed by thin and thick blood smears for visual identification of the Plasmodium parasite. A new rapid diagnostic test for malaria has also been developed. The BinaxNOW Malaria test is approved by the FDA and has a sensitivity of 94% and specificity of 84%. The BinaxNOW Malaria test can be used to make a quick presumptive diagnosis but because both false positive and false negative results can occur, it should always be followed by thin and thick blood smear evaluation. PCR tests for malaria are very sensitive and are available through the CDC but the time required for specimen transport and test completion makes PCR impractical for clinical decision making.
The treatment of malaria depends on the specific species involved, the geographic location of travel, and the severity of infection. A summary table is available on the CDC’s malaria diagnosis and treatment for U.S. clinicians website. Uncomplicated infections with P. vivax, P. ovale, P. malariae, and P. knowlesi are generally treated with either chloroquine or artemisinin combination therapy. Uncomplicated infection with P. falciparum is generally treated with artemisinin combination therapy. Severe malaria infections are treated with intravenous artesunate. Most hospital pharmacies do not stock arteunate but it can be obtained in an emergency by having the pharmacist call 1-855-526-4827 to identify the closest distributor.
What hospitals should do now
With international travel picking up post-COVID and now that P. vivax malaria has been identified in the United States, hospitals should evaluate their malaria preparation. Specific steps include:
- Consider stocking the BinaxNOW Malaria rapid diagnostic test.
- Ensure that laboratory technicians are educated and competent in performing thin and thick blood smears. The CDC has on-line guidelines.
- Ensure that laboratory technicians and pathologists are educated and competent in the microscopic identification of malaria trophozoites. The CDC has an on-line resource for identification of malaria and other parasites that includes photomicrographs of trophozoites of the various Plasmodium species on both thick and thin blood smears.
- Educate medical staff about malaria presentation and diagnosis with particular attention to emergency department providers, hospitalists, critical care practitioners, and primary care providers. Patients with suspected or newly diagnosed malaria should either be admitted or kept overnight in observation status.
- Ensure that the pharmacy has a process in place for obtaining intravenous artesunate in an emergency.
- Educate primary care providers and travel clinics about current malaria prophylaxis measures for patients traveling to high-risk areas.
Mosquito bites can be more than just an itch
A mosquito is like a flying syringe that goes from animal to animal and person to person. Like a contaminated syringe, mosquitos can transmit a wide variety of blood-borne diseases including malaria, yellow fever, dengue fever, chikungunya, filariasis, West Nile virus, various forms of encephalitis, and Zika virus. The best way to prevent these infections is to prevent mosquito bites in the first place. This is particularly true for people traveling to locations where any of these various infections are endemic. Here are recommendations we can give to all of our patients:
- Wear loose-fitting long sleeve clothing. As I learned from my recent outing last week, when shirts get soaked with sweat and stick to the skin, they offer no protection from mosquitos.
- Use effective insect repellant. The most effective is DEET in 25 – 30% concentrations. OLE (oil of lemon eucalyptus) and picaridin are less-effective alternatives to DEET.
- For those who work outside or spend a lot of time outside, treat clothing with permethrin. Some outdoor gear can be purchased already treated with permethrin but you can also buy permethrin spray and treat clothing yourself. Just be sure to follow clothing washing instructions to prevent the permethrin from being washed away.
- Skip the citronella candles, sonic repellant devices, and wearable repellant devices. These are nowhere near as effective as DEET.
- Inspect window screens. Although keeping doors and windows closed is the best way to keep mosquitos from getting into the house, this is not always an option, especially for homes without air conditioning. Be sure that screens fit tightly into window frames and that there are no holes in the screens.
- Eliminate stagnant water. For property owners, eliminating places where water accumulates can prevent mosquitos from laying eggs and prevent eggs from hatching. These can include bird baths, gutters, old tires, toys, and other open containers.
- Where stagnant water cannot be drained, encourage community mosquito control spraying programs.
- When traveling to areas where sleeping outdoors or in unscreened buildings is necessary, mosquito nets can be effective.
It is too early to say whether or not malaria will become regularly transmitted in the United States in the future. But the recent Florida and Texas cases are a reminder that malaria is still with us. International travel makes the world an increasingly small place with endemic areas just a few hours away from every city in the U.S.
June 30, 2023
