Virologists cleaning up after the Ebola epidemic in West Africa say they’ve discovered something surprising and promising: People who had malaria when they caught Ebola were more likely to survive the deadly infection.

People infected with malaria when they caught Ebola were, on average, 20 percent less likely to die from their Ebola infections, the National Institutes of Health team reported.

Researchers are not sure why, but they’re now following up with more studies to see how the malaria parasite affects the immune system, to see if it somehow boosts the body’s ability to fight infection.

Understanding this could help researchers come up with better treatments for the two-year epidemic of Ebola, which infected more than 28,000 people and killed more than 11,000 of them before it stopped spreading in Liberia, Guinea and Sierra Leone earlier this eyar.

Virologists Kyle Rosenke and Emmie de Wit of the National Institute of Allergy and Infectious Diseases, part of the NIH, had both volunteered in Liberia at the height of the epidemic and checking through their records months later.

“The fatality rate was so high at the initial outset,” Rosenke told NBC News. “We wanted to see how it lasted throughout. I was actually going through the database, looking at statistics and the gender effects of different viral loads on fatality rates.”

The team had tested people for malaria and every patient that came through the treatment center was given medications for malaria, which causes symptoms similar to those of Ebola.

“I did the first cross-reference and found the case fatality was much lower in the plasmodium-infected patients,” Rosenke said.

Malaria is caused by the Plasmodium falciparum parasite and transmitted by mosquitoes, and it affects more than 1.2 million people a year in Liberia. Ebola is passed person to person and is caused by a virus, but the symptoms can be similar at first - high fever, headache, sweating and vomiting.

It may be that the parasite infection is priming the immune system, De Wit and Rosenke believe.

“That seems the most likely explanation. The immune system is already finding the Plasmodium parasite and it doesn’t need to start up to fight the Ebola virus,” De Wit said.

The opposite could also be true, she said. Plasmodium might suppress the immune system. That might not sound good, but some of those who died from Ebola appeared to have suffered what’s called a cytokine storm — an overreaction of the immune system that destroys organs.

Overall, 52 percent of the 1,182 patients they tested lived. And 83 percent of those who had the most malaria parasites in their blood survived. Teenagers aged 12 to 18 had a 61 percent survival rate, while just 17 percent of those 65 and older lived, they found. They found 58 percent of people with malaria lived, compared to 46 percent of those who didn’t have malaria.

Writing in the journal Clinical Infectious Diseases, the team also said they’d found that women survived better than men, and people with more virus in their blood - called viral load - were more likely to die.

There’s evidence that malaria affects the immune system. Kids are more likely to die from certain infections if they have malaria, also.

The team, based at NIAID’s Rocky Mountain Laboratories in Montana, will test the theories in mice to see what happens.

They don’t have old blood samples from patients to test. They were working under intense and primitive conditions at Liberia’s ELWA3 Ebola treatment unit in Monrovia, helping out the international aid group Medecins Sans Frontieres (MSF or Doctors Without Borders).

“Very unfortunately, during the outbreak our lab was housed in the part of an a abandoned office building and so we had no good cold chain to keep any samples,” De Wit said.

“During the outbreak we were working 12 hours a day and we didn’t have any extra time to do analysis then.”

Whatever they find, the news doesn’t mean mosquitoes may be helpful after all, says de Wit.

“I wouldn’t say mosquitoes are good for anything,” she said.