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Microbiome Monday: Of Malaria and Microbes

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It's Microbiome Monday again! Before the Museum’s upcoming exhibition The Secret World Inside You opens November 7, we’re offering weekly primers on the microbiome and the research surrounding it from Curators Rob DeSalle and Susan Perkins, as well as from other scientists who are working in this exciting field.

Today's posts comes from Dr. Perkins, whose lab is exploring the role that animal microbiomes may play in battling malaria infections. Those results may help us understand how microbes that already live inside us can help prepare our immune systems to fight off invading microbes that could cause us harm.

Malaria has been a scourge for centuries. Its name, from the Italian for "bad air," comes from the early idea that it was caused by noxious chemicals emanating from the swamps around Rome. Later, the disease was traced to single-celled Plasmodium parasites that invade the liver and red blood cells of humans. In 1897, Sir Ronald Ross completed the transmission puzzle when he demonstrated that these parasites are transmitted through mosquito bites.

Close-up of an Anopheles mosquito feeding on human skin
A mosquito of the Anopheles genus takes a meal, during which it can transmit diseases including malaria.
© CDC/J. Gathany

Over a century later, malaria remains a massive public health burden. Just one species of malaria parasite, Plasmodium falciparum, is estimated to cause almost a million deaths per year globally. This huge health cost has made malaria parasites a big target, with huge sums of money and time devoted to researching ways to prevent and eliminate infections.

Some of that research is looking into the relationship between malaria parasites and the human microbiome, which we are learning plays a huge role in immune function. The first major study on this relationship, published last year in the journal Cell, showed that gut microbiota in mice play a fundamental role in protecting the animals against infection with Plasmodium.

A sample of blood cells containing Plasmodium falciparum parasites that cause malaria.
Courtesy of CDC/Dr. Mae Melvin Transwiki

This protection seems to stem from the fact that the common gut microbe E. coli produces a carbohydrate that stimulates the immune system to produce antibodies. It turns out that malaria parasites express a very similar carbohydrate to the one on E. coli. In healthy subjects, the antibodies produced by exposure to E. coli also reduced the impact of malarial infections.

The authors also demonstrated that humans under the age of 3 did not have these antibodies present yet. This lack of antibodies could help to explain why malaria is so prevalent among young children, and why these cases are often more severe.

E. coli bacteria
E. coli bacteria like these may play an important role in human health.
Image courtesy of USDA

In a second study, published earlier this year, scientists observed that certain compositions of gut microbes resulted in significantly lower rates of malaria infection during times when transmission was common. While there is work yet to be done—this correlation might be caused by other factors—it points an exciting way to better prevent the occurrence of this disease, suggesting that modifying the microbiome could help to stem the spread of the disease.

Humans are not the only hosts of Plasmodium parasites, however. In my lab, we study the relatives of human pathogens that infect other vertebrates like birds, bats, and lizards. There are approximately 500 of these species found worldwide, all in the family Haemospororida. Although the basic life cycle is much the same across all of these species, they do sometimes use different vectors, infect different tissues, and have very different effects on their hosts.

My students and I are now incorporating studies of the microbiome of these other vertebrate hosts and vectors as a means of understanding how these two very different types of microbial inhabitants interact and how they may have coevolved with their hosts. Stay tuned—we think it's going to be pretty exciting.