6/27/23, 2:50 PM
Malaria spreading in Texas and Florida; first US-based cases in two decades | Ars Technica
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Malaria spreading in Texas and Florida;
first US-based cases in two decades
Despite cases in Texas and Florida, the overall risk is considered "extremely low."
BETH MOLE - 6/27/2023, 11:56 AM
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The Centers for Disease Control and Prevention is warning doctors to be on the lookout for malaria
cases after five people who had not traveled outside of the country fell ill with locally acquired
infections in Texas and Florida. In a health alert Monday evening, the agency expressed concern that
the country could see a rise in imported cases due to increased international travel this summer.
The Florida and Texas cases are the first locally acquired malaria infections in the US since 2003, the
agency highlighted.
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Malaria spreading in Texas and Florida; first US-based cases in two decades | Ars Technica
So far, there have been four cases in Florida's Sarasota County and one case in Texas' Cameron
County, which sits at the state's far eastern border with Mexico, where malaria is endemic. There is
no indication that the Florida cases and the Texas case are linked in any way. The four infected people
in Florida, who have all since recovered, were in close geographic proximity to each other, and the
Texas case occurred in a person who spent time working outdoors.
Prior to the COVID-19 pandemic, the US typically saw around 2,000 imported malaria cases each year,
with around 300 severe cases and five to 10 deaths. The cases are mostly among people who return
from travel to malaria-endemic regions. The occasional small clusters of locally acquired cases, like
the recent cases in Florida and Texas, are typically thought to be spread from an imported case,
usually in a tight geographic area.
Malaria is caused by an infection with one of five protozoan parasites of the Plasmodium genus. The
parasites are transmitted by the bites of female mosquitoes of the Anopheles genus. There are
multiple species of Anopheles mosquitoes in the US capable of picking up and spreading malaria, and
32 states have reported the presence of at least one potential malaria vector.
Once a person is infected, malaria symptoms begin between 10 days to four weeks later, with nonspecific signs such as fever, chills, headache, myalgias, and fatigue. It can also involve nausea,
vomiting, and diarrhea. If left to progress, it can develop into a severe life-threatening disease, with
symptoms including mental status changes, seizures, renal failure, acute respiratory distress
syndrome, and coma.
Persistent parasites
Two species of malaria parasites can also go dormant in the liver, causing chronic and relapsing
disease that requires additional treatment. The two species capable of doing this are P. ovale, a rare
cause of malaria that's primarily found in sub-Saharan Africa, and P. vivax, one of the two most
common malaria parasites, found mostly in Asia and Latin America. The recent locally acquired cases
in Florida and Texas were caused by P. vivax.
The other top malaria parasite is P. falciparum, which is the deadliest cause of malaria. P. falciparum is
found in dozens of countries but is most concentrated in Africa.
In the last outbreak of locally acquired malaria in the US, which occurred in 2003, at least seven
people in Palm Beach, Florida, fell ill from malaria with a P. vivax infection. The source of the infection
was not identified, but investigators noted that it could have been from international travelers,
people who immigrated, or migrant farm laborers from Mexico or Central or South America.
In 2002, another cluster of locally acquired malaria cases was reported among two teenagers in
Loudon County, Virginia. The cause was again P. vivax. The source of the infection was not
determined, but investigators assumed that a malaria-infected person must have been in the vicinity.
They noted a nearby international airport (Dulles) that receives travelers from P. vivax-endemic areas,
though the teen cases were more than 10 miles from the airport. Interestingly, anopheline
mosquitoes collected and pooled from the area tested positive for P. vivax, marking the first time
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Malaria spreading in Texas and Florida; first US-based cases in two decades | Ars Technica
since 1957 that US mosquitoes linked to locally acquired cases had tested positive for a malaria
parasite.
While the CDC still deems the overall threat of locally acquired malaria in the US to be "extremely
low," these occasional cases are a reminder that reemergence is possible and vigilance is required.
Global travel and climate change will continue to create opportunities for malaria transmission to
increase in endemic and controlled areas, like the US, and even in places that have traditionally been
malaria-free.
Currently, there are more than 240 million malaria cases each year worldwide, and there were over
600,000 deaths in 2021. Ninety-five percent of the case and 96 percent of the deaths are in the
African region, according to the World Health Organization. Eighty percent of the malaria deaths in
Africa are in children under age 5.
Malaria used to be endemic in temperate areas of the US but was considered eliminated from the
country in 1951 after the establishment of the Office of Malaria Control in War Areas—a precursor to
the CDC. The elimination was achieved by improved sanitation, medical care, drainage of mosquito
breeding sites (mosquitoes breed in standing water), and insecticide use.
READER COMMENTS
40
BETH MOLE
Beth is Ars Technica’s Senior Health Reporter. Beth has a Ph.D. in microbiology from the University of
North Carolina at Chapel Hill and attended the Science Communication program at the University of
California, Santa Cruz. She specializes in covering infectious diseases, public health, and microbes.
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