University of South Florida researchers are developing a new malaria vaccine that would prevent the return of the disease once a person has already been infected.
Unlike viral mosquito-borne illnesses such as dengue, malaria is caused by parasites in the genus Plasmodium, which are transmitted by infected female Anopheles mosquitoes.
The parasites can primarily be found in tropical climates such as Central and South America and Southeast Asia.
Two malaria vaccines already approved by the World Health Organization work by training the immune system to attack the Plasmodium falciparum parasite before it can infect the liver. That effectively stops someone from contracting malaria.
But USF researchers are developing a vaccine that targets the Plasmodium vivax parasite, which invades liver cells and allows malaria to return months or even years later. By removing this parasite, the vaccine will prevent malaria from remaining dormant in the body and stop it from coming back.
While the P. vivax parasite affects a larger portion of the world, P. falciparum receives much more research focus due to its higher mortality rate.
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Until now, researchers had limited knowledge of the P. vivax parasite, because of its ability to hide in the liver and sit there for decades. Another reason it's harder to study is because the parasite can't be grown in a lab like P. falciparum.
To combat this, Noah Sather, a professor in the USF College of Public Health’s Department of Global, Environmental and Genomic Health Sciences, and his team had to collaborate with two groups in Thailand to fly P. vivax-infected mosquitoes to them.
“We literally would fly mosquitoes by courier from the Thai-Myanmar border all the way into the United States,” Sather said. “And you could only do these inhibitory studies a couple of times a year because our colleagues had to do field trips, driving eight or nine hours by van from Bangkok up to the border, working in their clinic.”
Despite these adversities, the USF-led research team identified a part of the parasite that the vaccine can use to alert the immune system to attack by producing protein. The immune system then neutralizes the parasite.
Sather and fellow USF researcher John Adams had been working on developing this vaccine separately for around five years. However, the two were unaware of the other's study until Sather came to USF on a visit where he was considering joining the College of Public Health malaria research program.
Once Adams and his group started to talk about the developments they were making, Sathers realized they were studying the same problem.
Sathers said it will take a few years to develop the vaccine. But getting there will create milestones that can take place sooner.
For example, researchers are creating laboratory models that mimic the human immune system.
They are doing this to try to understand how this epitope — the vaccine ingredient that helps the immune system identify the parasite — interacts with the human immune system.
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This process would allow scientists to not have to test an experimental vaccine on humans. Instead, they can test the vaccine in the lab and see how the immune system responds in a much more low-stakes environment.
“This kind of combination of trying to design toward the human immune system rather than trying to design a molecule and then shoot it in and see what happens,” Sather said. “It's again part of this rational approach, and so we're hopeful that this will dramatically shorten the iterative cycle time.”
This would also make the need for shipping bugs from Bangkok much less significant.
“It kind of takes it so that the need to go to Thailand to get those bugs is greatly reduced, and we only need the real bugs in the very last steps of validation,” he said.
While there are drugs available to help combat malaria, scientists have lacked the resources to treat everyone because the disease is so widespread.
“You're talking about billions of people that might need drugs in a year, and there's just simply not the resources,” he said. “This is why vaccines are the most effective approach here, because they're the most effective, cheapest medicine you can get.”
In addition, preventive medicine is not enough because P. vivax can stay dormant for years until it gets activated again.
“Let's say somebody gets vivax malaria, and the fever goes away, and they feel pretty OK, they may be carrying any number of dormant parasites that will reactivate completely randomly at any time,” Sather said.
He’s hopeful the advancements they are making will lead to a healthier world.
“I think that there is a future that's not too distant, where hopefully, if you want to go to Southeast Asia or South America,” he said, “you can go down to the pharmacy and you can get a vaccine shot into your arm that will have been developed in your own backyard at USF that will protect you from infection, and that's our goal, both home and abroad.”
