Malaria mostly spreads to people through the bites of infected female Anopheles mosquitoes. Blood transfusion and contaminated needles can also transmit malaria.1 There are 5 Plasmodium parasite species that cause malaria in humans and 2 of these species, P falciparum and P vivax, pose the greatest threat. P falciparum is the most prevalent on the African continent. P vivax is the dominant malaria parasite in most countries outside of sub-Saharan Africa. The other malaria species which can infect humans are P malariae, P ovale and P knowlesi.1
Malaria’s Human Toll
In 2023, there was an estimated 263 million malaria cases, with 597,000 deaths worldwide, according to the World Health Organization (WHO).1 The African continent experienced a majority of these cases at 94%, and in addition, 95% of the deaths. Children under 5 were 76% of the deaths in the African region.1
In addition to the high mortality, Jane Carlton, PhD, director of the Johns Hopkins Malaria Research Institute, and Bloomberg distinguished professor, says the acute infection is debilitating but people who contract malaria more than once can suffer from very serious ongoing side effects.
“About 40% of the world’s countries have malaria, and that is found mainly in the poorest regions of developing countries where access to health care is limited, is very much a debilitating disease, repeated bouts of fever, resolving to chills and sweats, nausea, vomiting, and there can be severe complications as well, leading to multi organ failure, seizures, coma and eventually death,” Carlton said. “And repeated bouts of malaria, even if they don’t end in death, can lead to cognitive issues, memory impairments, and a real weakening of the body as well.”
At first, malaria symptoms may be mild, similar to different illnesses that begin with a fever, and it may be difficult to identify the fever as one of the symptoms of the vector-borne disease. Left untreated, P falciparum malaria—which carries the deadliest disease parasite—can progress to severe illness and death within 24 hours.1
Utilizing Genomics to Understand the Parasites
The Johns Hopkins Malaria Research Institute is working to develop strategies to prevent the disease through understanding the genomics of the malaria parasite. Carlton has her own lab, and a big part of her team’s research has been looking at trying to genetically modify mosquitos to prevent people from contracting malaria. Specifically, they have been researching different malaria parasite species, utilizing the latest in genomics.
“There’s been a real revolution in genomic sequencing, and now it’s much easier, faster, and cheaper to decode and to sequence the DNA of parasites,” Carlton said. “So genome sequencing enables us to identify, for the first time, every single gene in the genome of the parasite, and then to predict every protein, and to reconstruct the metabolic pathways of the parasites. This will enable us to find chinks in the armor of the parasites that could be developed into new drugs or new vaccines.”
Genetically Modifying Mosquitos
In addition to its work on parasites, the institute is working on modifying mosquitos so they cannot transmit malaria. The institute is hosting its World Malaria Day Symposium today. The symposium will include speakers discussing the work around genetically modified mosquitos.
“We’re bringing a whole host of speakers to talk about how we can engineer mosquitos to either be sterile so they can’t reproduce and the populations of mosquitoes die out or refractory to malaria parasite infection,” Carlton said.
She says the institute is only working on the latter area.
“Research in the institute is geared towards engineering genetically modified mosquitos that are resistant to malaria parasite infection. So these types of mosquitos would not die out, but they would just be made resistant to malaria parasites infecting them,” Carlton said.
Malaria in the US
At one time, the US was a malaria-endemic region, but public health efforts including insecticide spraying, has mostly eradicated the disease.1 Typically, malaria is contracted in the US by travelers who go to regions where malaria is prevalent. Still there was a handful of cases in a few states last year in what was considered locally acquired malaria. This means transmission happened without travel.
“There were about 10 cases of those in Arkansas, Texas, Florida and Maryland, and most of them were one species of malaria parasite, plasmodium vivax. But there was one case of the more virulent, the more deadly, plasmodium falciparum—in fact, that was found in my home state of Maryland. It was a very interesting case; a patient who’d never left the country, had not been on vacation, and who came down with plasmodium falciparum,” Carlton said.
Her lab received a blood sample from this patient from the Maryland Department of Health and they researched where the parasite had originated.
“We put it into culture. We were able to grow it; we extracted the DNA and sequenced it, and by comparing to a database of other malaria parasite genomes, we found that it was from a central African country and that it had resistance to certain antimalarial drugs and not to others,” Carlton said. “So it really shows the power of what we call genomic epidemiology to study these sorts of cases.”
These locally acquired malaria cases beg the question of whether evolving factors like climate change and US regions becoming hotter could potentially lead to increased cases of malaria in the country.
“We do have the vectors for these locally acquired malaria cases,” said Carlton. “The Anopheles [mosquito] vector used to transmit malaria parasites very frequently in the United States during the 1800s. Malaria wasn’t eradicated until the 1950s, so it may well be that regional changes in climate in the US will enable the mosquito vector populations to rise,” Carlton said. “We need more studies to look into this, and this is something that the Johns Hopkins Malaria Research Institute is planning to do in the future.”
This is the second installment of an interview with Carlton. To watch the first part, go here.
References
1. Malaria. WHO. December 11, 2024. Accessed April 25, 2025.
https://www.who.int/news-room/fact-sheets/detail/malaria
2. The History of Malaria in the United States. ASM. September 15, 2023. Accessed April 25, 2025.
https://asm.org/articles/2023/september/the-history-of-malaria-in-the-united-states
