Why Are There Malaria Cases in the U.S.? Here’s What Your Public Health Organization Needs to Know

Sep 5

Why Are There Now New Cases in the United States?

This year, nine locally acquired cases of malaria have been identified in the U.S., with seven cases reported in Florida, one case in Texas, and another case in Maryland. Domestically contracted mosquito-borne malaria had not previously occurred within the U.S. since 2003. In all these cases, the individuals did not travel outside of the United States to countries where they could have been infected by malaria. This means the transmission of malaria occurred locally. This is most likely by the bite of a mosquito species capable of carrying malaria in the U.S. having bit an individual who returned from abroad with an imported malaria infection, and then that same mosquito having bit another individual, then transmitting the parasite. In the U.S., there are at least nine species capable of malaria transmission, including: Anopheles quadrimaculatus, An. freeborni, An. punctipennis, An. albimanus, An. pseudopunctipennis, An. diluvialis, An. inundatus, An. smaragdinus, and An. walkeri.

These cases have contributed to a growing concern about the possibility of an increase in imported malaria cases linked to elevated international travel during the summer of 2023. Prior to the COVID-19 pandemic, the United States used to report around 2,000 cases of malaria annually, with nearly all being linked to travel.²

With climate change being of growing concern, experts have cautioned that rising temperatures could lead to an increased prevalence of mosquitoes capable of malaria transmission within the United States. Mosquitoes are highly sensitive to changes in temperature and humidity. As temperatures rise, it can create more favorable conditions for the growth and survival of mosquitoes that carry the malaria parasite. This, in turn, could potentially expand the geographic range of these disease-carrying mosquitoes, allowing them to thrive in regions where they were previously less common. The National Institutes of Health also notes that the increased temperature allows them to breed quicker. Mosquitoes may breed all-year-round in warm areas. Warm climates facilitate the increase in hatching and reproduction rates of mosquitoes”.⁴

This, in combination with an increase in imported malaria cases, mean a greater likelihood a mosquito in the United States might bite an individual who has returned from travel with a malaria infection, and that mosquito may transmit it to other individuals who have not traveled.

What is Malaria?

Malaria is a serious and sometimes life-threatening disease caused by a mosquito-borne parasite. Female mosquitoes of the genus Anopheles which become infected with any of five species of protozoan parasite of the genus Plasmodium, then transmit it to humans through their subsequent bites. The protozoan parasites of the genus Plasmodium that have been detected in the U.S. cases include: P. falciparum, P. vivax, P. malariae, P. ovale, and P. knowlesi. Usually, signs and symptoms of malaria start appearing 7-10 days following a bite by an infected mosquito. Certain species of malaria parasites can remain inactive in the body for as long as several years. Watch out for symptoms such as recurring fever, chills, headache, fatigue, muscle pain, and more, which could indicate a possible case of malaria, as outlined by the Mayo Clinic. Talk to your physician if you develop a fever while residing in or after visiting a malaria-prone area. In case of severe symptoms, promptly seek urgent medical care.¹

What is the history of Malaria in the United States?

In 1951, the National Malaria Society outlined eradication criteria stating that an area can be considered non-endemic for malaria if there's been no primary indigenous case for three years. Over time, this definition has evolved. "Elimination" now denotes the absence of malaria transmission in a specific geographic region, while "eradication" signifies the complete cessation of malaria transmission globally.⁶ This historical achievement aimed to halt the indigenous transmission of malaria. Malaria was eliminated in the 50's following a massive effort by the health authorities, mostly in the south where malaria was rampant. The Centers for Disease Control and Prevention (CDC) website provides information on the National Malaria Eradication Program, which was a cooperative undertaking by state and local health agencies of 13 southeastern states and the Communicable Disease Center of the U.S. Public Health Service. The program commenced operations on July 1, 1947, and consisted primarily of DDT application to the interior surfaces of rural homes or entire premises in counties where malaria was reported to have been prevalent in recent years. By 1951, the country was declared free of malaria as a significant public health problem, and the CDC gradually withdrew from active participation in the program.

However, the recent emergence of new cases of locally-acquired malaria in the U.S. raises concerns about potential shifts in disease dynamics. While these cases remain relatively rare, they highlight the need for effective mosquito control measures and public health interventions to prevent further resurgence of malaria transmission in the U.S.

According to the CDC, the possibility of malaria being locally acquired in the United States remains extremely minimal, and there is no indication of any connection between the cases in Florida and Texas.² However, while the risk of the locally acquired malaria in the U.S. is considered low, the shifting climate and malaria’s potential spread highlight the need for preventative actions like mosquito surveillance and control, and health measures.

How can Vectech help public health programs reduce the risk of future locally-acquired malaria cases?

Mosquito control interventions, when utilized judiciously and based on data, are an effective tool that can prevent transmission of mosquito-borne diseases like malaria. Mosquito surveillance is an important component of effective mosquito control programs. Information on where mosquitoes are most abundant, the diversity of species, and distribution of the mosquito population help mosquito control programs target interventions to the areas of highest risk. Risk for local transmission of malaria requires at least two elements: an individual infected with malaria and mosquito species capable of malaria transmission. While many local health departments receive reporting when a clinical case of malaria is diagnosed in their community, few have the capability to track and monitor the local mosquito population, and distinguish potential malaria vectors from other mosquito species. Vectech’s team of scientists are experienced in building effective vector surveillance programs. We offer a range of solutions, from on-the-ground support, to the latest AI technology in the IDX system that empowers environmental health teams and other public health professionals to collect vector surveillance data with the capabilities of a medical entomologist.

Contact us to work together.

Addressing the potential impact of climate change on malaria requires a collaborative effort involving scientists, public health agencies, policymakers, and communities. By understanding and mitigating the factors that contribute to the increased prevalence of malaria, we can work together to minimize the potential health risks associated with vector-borne diseases.