With mosquitoes being the primary carrier of malaria, the battle against the disease has been fought at every step of the disease's development: from reducing mosquito populations, to preventing them from biting humans, to dealing with the parasites introduced by the insect after infection occurs. A new vaccine that introduces live malaria parasites into the bloodstream has just undergone clinical trials in humans, and has been shown to provide long-term protection with effectiveness of up to 100 percent.

According to the latest figures from the World Health Organization (WHO), 212 million cases of malaria were reported in 2015, resulting in almost 430,000 deaths, and of those cases, 90 percent occur in Sub-Saharan Africa. The main culprit is the Anopheles mosquito, the bite of which transmits parasites like the Plasmodium falciparum, responsible for the majority of malaria infections and deaths.

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For years, scientists have fought to control the spread of the disease through a variety of means. We've tried to keep mosquitoes from biting humans by altering their sense of smell and making ourselves less tasty. Other studies have tried to turn the bugs' own immune systems against the parasites, or boost our body's response after infection. The new research, from the University of Tübingen and the biotech company Sanaria Inc., focuses on this latter battlefield.

While there are other promising vaccines in the works, including RTS,S/AS01, which is due to be field tested in 2018, this new technique is the first to inject fully viable, live malaria parasites into the human body. The vaccine was tested in 67 adults with no history of malaria. Administered at different intervals, it was found to work best with three high doses of the treatment, four weeks apart. Everyone in the sub-group tested with this treatment reported 100 percent protection from the disease, and the resistance was still present 10 weeks later. Better yet, no adverse side effects were reported.

"That protection was probably caused by specific T-lymphocytes and antibody responses to the parasites in the liver," says Peter Kremsner, an author of the study.

The dark blue spots are the malaria parasite, Plasmodium falciparum, attacking human blood cells under a microscope (Credit: University of Tübingen)

Malaria symptoms usually take about 15 days to show up after first infection, and that's due to the fact that P. falciparum will first migrate to the liver to reproduce. The parasites are vulnerable during this time, but they're careful not to alert the immune system by not yet making the host sick. Once it's ready, the pathogen leaves the liver and enters the bloodstream, where it continues to spread.

The new vaccine skips the incubation period in the liver by introducing the fully developed pathogen into the bloodstream, kickstarting the immune system to fight back. To prevent the disease from actually taking hold, the researchers added chloroquine – a commonly-used treatment for malaria – to the mix.

"By vaccinating with a live, fully active pathogen, it seems clear that we were able to set off a very strong immune response," says Benjamin Mordmüller, lead researcher on the study. "Additionally, all the data we have so far indicate that what we have here is relatively stable, long-lasting protection."

With the success of the clinical trial, the researchers plan to test how effective the vaccine is over the course of several years.

The research was published in the journal Nature.

Source: University of Tübingen

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