Credit Martin County Health Department
#18,829
Although roughly 2,000 travel-related cases of Malaria are reported each year in the United States, locally acquired cases have been quite rare in this 21st century. If we go back a hundred or so years, however, Malaria was still fairly widespread.
Fifteen years ago, in Florida: Locally Acquired Malaria Case Suspected, we looked at a rare case in a resident of Jacksonville with no history of international travel. In 1996 (2 cases) and again in 2003 (8 cases) of locally acquired P. vivax malaria were detected in Palm Beach County (see Multifocal Autochthonous Transmission of Malaria --- Florida, 2003).
More recently, in June of 2023 (see CDC HAN: Locally Acquired Malaria Cases Identified in the United States) local transmission of Malaria was reported in 2 different states. Two months later, a 3rd state (Maryland) reported a single case.
While the risks of acquiring Malaria are quite low, they aren't zero.
Most viral (and parasitic) infections have at least a 3 to 15 day incubation period, giving infected travelers a fairly long asymptomatic `window' in which to travel. Should a viremic visitor be bitten by a competent local vector, there is the possibility the disease may be transmitted on to others.
Which is likely how a local resident in Washington State came to be infected with Malaria, as reported in the following press release from the Tacoma-Pierce County Health Department.
First the announcement, after which I'll have a bit more on the importation of vector-borne diseases.
We are investigating possible locally acquired case of malariaAugust 6, 2025
The risk to the public is very low.
An East Pierce County woman who has not traveled recently was diagnosed Aug. 2 with malaria. She is receiving treatment and we continue to monitor her status.
We are working with Washington State Department of Health (DOH) and Centers for Disease Control and Prevention (CDC) to investigate potential sources of infection. It’s possible she was recently infected with malaria in Washington. If confirmed, this would be the first known locally acquired case of malaria in Washington.
The most likely cause of a locally acquired case is a mosquito biting someone infected with a travel-associated case of malaria, then passing the infection on to this patient.
“The risk of getting infected with malaria in Pierce County remains very low,” said Dr. James Miller, Tacoma-Pierce County Health Officer. “Malaria is a rare disease overall in the United States—and the vast majority of cases in the United States occur following exposures in countries with ongoing transmission.”
Malaria is a mosquito-borne disease caused by a parasite. It typically causes fever, chills, body aches, headaches, and fatigue. It can also cause nausea, vomiting, and diarrhea. In most cases, the incubation period—the time between infection and start of symptoms—is 7-30 days. Malaria does not spread directly from one person to another.
Malaria can be cured with prescription antimalarial drugs. It can be life-threatening if is not diagnosed and treated quickly.
The U.S. sees about 2,000–2,500 and Washington sees about 20-70 reports of malaria cases each year linked to travel. In 2023, the United States experienced its first locally acquired mosquito-transmitted malaria case in 20 years. Between May 2023–October 2023, 10 cases were reported across four states.
The Anopheles mosquitoes that transmit malaria live across the U.S. If they bite someone infected with malaria, they may become infectious and could transmit the parasite to people in the area.
As part of the investigation, we are working with DOH to implement mosquito trapping and testing. Fortunately, at this time of year mosquito populations in Pierce County are decreasing.
The best way to prevent malaria is to prevent mosquito bites and ensure early diagnosis and treatment of cases in returning travelers. Use an EPA-registered insect repellent and wear long sleeved clothing when spending time in areas with mosquitoes and use screens on windows and doors. Remove and reduce places where mosquitoes can breed by removing or covering sources of standing water like birdbaths, animal troughs, pools, tires, or other places where water may collect.
Travelers to countries where malaria is more common should take steps to prevent acquiring malaria. That sometimes includes taking medications to prevent malaria. Contact a healthcare provider before traveling to see if you need to take medications to prevent malaria. If you develop symptoms of malaria, contact a healthcare provider right away.
This situation also highlights the importance of a prepared and coordinated public health system that is ready to respond to urgent communicable disease investigations. We are grateful to our partners at DOH and CDC for their assistance with various aspects of this investigation. We also rely on healthcare workers to recognize and report rare diseases to public health and thank the astute clinicians who diagnosed this person.
About Tacoma-Pierce County Health Department: Tacoma-Pierce County Health Department’s mission is to protect and improve the health of all people and places in Pierce County. As part of our mission, the Health Department tackles known and emerging health risks through policy, programs, and treatment to protect public health. Learn more at tpchd.org.
While this is likely an isolated incident, over the past 20 years we've kept watch on the steady spread of vector-borne diseases - like Dengue, Zika, Malaria, and Chikungunya - around the globe.
Nations that were once considered free of these exotic diseases now battle outbreaks on a regular basis.
Before 1999, the United States was free from the West Nile Virus. By 2005, the virus has spread nationwide. In 2009 Dengue returned to Florida (see MMWR: Dengue Fever In Key West) after an absence of roughly 60 years, likely carried in by an infected traveler.
Chikungunya - which is currently sparking a serious epidemic in China (see FluTrackers Thread) - was first introduced to the Caribbean in 2013, and is now a serious concern in South America.
And with recent reports of A Widespread Super–Insecticide-Resistant Aedes aegypti Mosquito in Asia, we'll need to find new and better ways to control these mosquito vectors, if we are to stay ahead of these growing 21st century threats.
While it might not be at the top of your list of stock up items for your Hurricane/Disaster kit, having mosquito repellent for you and your family is highly recommended.
For some earlier mosquito-borne illness blogs, you may wish to revisit:
