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Friday, 05 October 2018 16:48

A new type of malaria vaccine utilizing the mosquito immune system with Carolina Barillas-Mury

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To eliminate malaria, you have to stop transmission, and that’s what Carolina Barillas-Mury hopes to do. Her work on the interaction of the malaria parasite Plasmodium falciparum may lead to a transmission-blocking vaccine. She explains how, and discusses the co-evolution of malaria, mosquitos, and man.

Host: Julie Wolf Carolina Barillas-Mury

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Julie’s Biggest Takeaways:

When born, babies carry antibodies from their mothers, which may protect them through passive immunity; additionally, babies are more easily protected from mosquito exposure by placing them under bed netting. As they grow, children become more active, and their passive immunity concurrently wanes. They may be exposed to mosquitoes carrying malaria parasites and their still-developing immune systems aren’t able to keep the parasites from replicating, leading to more severe disease, including cerebral malaria.

The Culicines and Anopholines are two major groups of mosquitoes that carry disease. The Culicines have recently spread around the world, but the Anopholines species moved from Africa into South America 100 million years ago, while malaria only moved into the New World a few hundred years ago with the slave trade. The relationship between the mosquitoes and malaria parasites has thus been evolving much longer in Africa than it has been with the specific population of mosquitoes in South America - one of the reasons why the disease is less devastating in South America.

The ‘invisibility gene,’ pfs47, is expressed in the banana-shaped ookinete and helps the malaria parasite to avoid detection by the mosquito immune system. The pfs47 malarial gene is adapted for the localized mosquito populations from the same region as the parasite; if an African mosquito is infected with a South American parasite, the parasite is more likely to be recognized and killed than if the African mosquito is infected with an African parasite.

The most immunogenic proteins in parasites may produce an immune response, but this immune response may not block infection. New vaccines are concentrating on where antibodies bind, to ensure there is a biological effect of the immune response, and this is why Barillas-Mury has used a modified Pfs47 protein to generate immune responses, rather than its native form.

Featured Quotes:

“It’s not clear why some mosquitoes transmit one disease but not another, but it’s clear that they are specific in the diseases for which they are vectors.”

“When you take parasites from different continents, mosquitoes from the same continent tend to get infected better than when you infect with a parasite from a different continent.”

“Melanization [as a part of the mosquito immune system] is not the way the mosquitos kill the parasite, it’s the way you dispose of the dead body.”

“The concept of a transmission-blocking vaccine is a little bit different. You’re trying to prevent mosquitos from becoming infected, with the idea that if the mosquitoes aren’t infected, then they won’t spread disease.”

“Malaria transmission is so effective, that in endemic areas of malaria, the rate of transmission is 300% every year. Basically, everyone gets 3 rounds of infection every year. If you don’t stop the transmission, you don’t stop the disease.”

“I know mosquitos are nasty, but they are beautiful from the biological perspective. They are like little drones that are very effective at what they need to accomplish.”

Links for This Episode:

History of Microbiology tidbit:

The classic children's book Little House on the Prairie and its series featured a case of the Ingalls family contracting fever and ague, which young Laura Ingalls Wilder thought was due to bad watermelon, if I recall correctly - excuse me but it’s been a few decades since I read these books. The true cause of disease is thought to have been malaria, which would have been established by the late 1800s time period of the books, since the disease was introduced to the new world with the slave trade, likely in the 1600s and possibly even the late 1500s.

The history of malaria is an area rife with stories like these, since the disease has been a part of human societies for millenia. Malaria was discovered to have a protozoal cause in the 1880s and by the late 1890s was understood to be transmitted by mosquitoes. The early decades of the 1900s were full of discoveries, as scientists uncovered the complex lifecycle in and outside of humans. In trying to decide which major discovery to highlight, I would actually like to feature research that was going on to find the cause of a different disease, a cattle pathogen called Babesia bigemina, by Theobald Smith and Frederick Kilborne. I found a very readable history of malaria article that lays out the chronology of major discoveries, and in this account, I found this passage particularly striking.

One surprising aspect of this whole story is that some of the clues about arthropod-transmission of blood-inhabiting protozoa were available several years before Ross and the Italian scientists began their investigations. In 1890 the American microbiologists Theobald Smith and Frederick Kilborne had observed that young ticks taken from cattle infected with the piroplasm Babesia bigemina, an intraerythrocytic protozoan resembling a malaria parasite, could infect susceptible animals and this was confirmed in a series of meticulously controlled experiments over the next two years [42]. It is strange that none of the participants in the malaria story seemed to be aware of these discoveries, probably because they were published in an American Government Agricultural document. How differently things might have turned out if they had been aware of these discoveries is a matter of speculation.

Just imagine how history could have changed if the dots had been connected even a few years earlier! What a great illustration of the importance of being broadly read. What great discoveries could we be missing today because there just isn’t enough time to read every study? Let us know by tweeting at us @ASMicrobiology or leaving a comment on facebook.com/asmfan.

 

Send your stories about our guests and/or your comments to jwolf@asmusa.org.

Last modified on Monday, 08 October 2018 10:48
Julie Wolf

Julie Wolf is the ASM Science Communications Specialist. She contributes to the ASM social media and blog network and hosts the Meet the Microbiologist podcast. She also runs workshops at ASM conferences to help scientists improve their own communication skills. Follow Julie on Twitter for more ASM and microbiology highlights at @JulieMarieWolf.

Julie earned her Ph.D. from the University of Minnesota, focusing on medical mycology and infectious disease. Outside of her work at ASM, she maintains a strong commitment to scientific education and teaches molecular biology at the community biolab, Genspace. She lives in beautiful New York City.

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