By Carla L Davis

The Center for Disease Control (CDC) has issued a Health Alert Network Health Advisory in response to the recent cases of locally acquired mosquito-transmitted malaria diagnosed in the United States. In a recent panel discussion, members of the 2023 Malaria Response Team for the CDC, Dr. Alison Ridpath M.D. MPH, Dr. Erika Wallender, M.D. MPH and Dr. Adam Rowe, M.D. reviewed Malaria Diagnosis and Treatment in the United States.  

Between May and July of 2023, eight cases of mosquito-transmitted malaria, Plasmodium Vivax (p.vivax), have been reported in Florida and Texas. Seven of the eight infected individuals were from Sarasota County in Southwest Florida and the eighth was from Cameron County, near the Brownsville- Harlingen metropolitan area in South Texas. None of the cases were interrelated and none of the patients reported having been to an endemic area outside of the U.S.  Seven of the eight adult individuals were hospitalized; all were treated with an oral anti-malarial drug and reported to be recovering well.

Malaria is a very serious and sometimes fatal disease caused by a parasite that breeds in a certain type of mosquito. The female Anopheles mosquito is the transmitter of the p.vivx strain that is most prevalent of all cases in the United States the CDC reports. This type of mosquito is common in the United States and is most present during late evenings and nights. Currently, the CDC is working with the health departments in the recently affected counties to prevent the further transmission of malaria and bring further awareness to the communities. County mosquito control is conducting aerial and truck sprayings,  around the vicinities of those who contracted the disease,  in an effort to track and kill the adult-infected mosquito and larval habitats. 

According to CDC reports, over 99% of malaria patients contract the disease by traveling to endemic regions within 1 yr. of exposure. Symptoms can occur within a few months to a year after returning from an endemic region. The most alarming and common symptom of malaria is that it causes fever.  In less acute or uncomplicated malaria cases, other symptoms can include headache, myalgias, nausea, vomiting, fatigue, cough, abdominal pain, diarrhea, and other non-specific symptoms. 

US residents are at a higher risk of progressing to severe malaria so hospitalization is highly recommended even with the mildest of symptoms present. The treatment regimen for each case is dictated by several factors: severity of the disease, species determination, drug availability, age, and pregnancy status. Those most susceptible to a mild case progressing into severe illness is more commonly diagnosed among older adults and pregnant women. 

There are five species of malaria that cause human disease. Of the five only two can have relapsing effects. Plasmodium Vivax (p.vivax) and Plasmodium Ovale (p.ovale).  These strains have the potential for relapse years after the initial exposure if treatment is inadequate.

  In addition to the anti-malarial treatment drugs, all of the recent patients received additional treatment to prevent relapses. The p. vivax strain of mosquito-transmitted malaria is known for its risks for relapse. In acute cases, drugs such as Chloroquine, Hydroxychloroquine are used.     For less or acute infections, a 14-day dose of Primaquine or a single dose of Tafenoquine is used and Coratem is recommended for all trimesters of pregnancy and for children

The most recent and complete data on Malaria was compiled in 2018. The majority of these cases were the results of travelers coming back from endemic areas where there was a high concentration of the infection. Texas has been very limited in the number of outbreaks compared to other states during this same time period. Data showed one case in 1985, three cases in 1994, and the most recent in 2023. These are the first cases of mosquito-transmitted malaria in 20 years.  The last documented case of this variant of malaria was reported in Florida in 2003

During the Covid-19 pandemic, the number of reported Malaria cases reduced significantly to just 28 cases, primarily due to reduced international travel.  During the time period 2018 thru 2020, preliminary data shows there were between six and seven Malaria related deaths per year. 

As Covid restrictions on travel have been lifted and more people will be traveling outside of the United States to endemic countries; the CDC recommends several lines of defense against mosquito bites. The number one preventive recommendation is to take a full course of prophylaxis medicines before traveling to endemic countries. use strong mosquito repellant, cover windows and doors with insecticide-treated nets, and wear clothing that is loose-fitting and long-sleeved. (An up-to-date list of malarial prophylaxis recommendations by country is available on the website), Based on CDC preliminary data, projections show that the U.S. rebounded in 2022 and expectations are that malaria will return to pre-pandemic levels in 2023.