War, trade and colonization: how malaria came to us

249 million cases and 608,000 deaths in 2022 alone: ​​these are the figures for the heavy toll of malaria in the world, according to the World Health Organization (WHO, 2023).

If more than nine out of ten cases of malaria – and the same proportion of deaths – today concern Africa, the history of this infectious disease reveals to us that in the past, its distribution was much more widespread. What’s more, it was intertwined with our own travel, well before the rise of international air transport.

Parasitic DNA hidden in patients’ teeth

“Although today it is primarily a tropical disease, only a century ago the pathogen’s range (THE Plasmodiuma single-celled parasite carried by the Anopheles mosquito, Editor’s note) covered half of the globe’s land surface, including parts of the northern United States, southern Canada, Scandinavia, and Siberia.”compares Megan Michel, doctoral student at the Max Planck Institute and Harvard University (press release).

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Because the disease leaves no visible and specific mark on the human remains exhumed by archaeologists, the researcher and her colleagues from around twenty countries tried to detect the tiniest traces. DNA fragments from Plasmodium vivax And P. falciparum – two agents of malaria, responsible for the most serious forms – in fact nestle… in our teeth!

Published in the journal Nature (June 12, 2024), their study reveals the fascinating links between human history and the dissemination of parasites across the globe, thanks to the analysis of the dentition of some 36 individuals found on five continents and who, at the time of their death between now and approximately 5,500 years ago, all bore the Plasmodium in their blood.

The arrival of the parasite in America: mystery solved

One of these sufferers lived near the Laguna de los Cóndores, a high-altitude lake in the heart of the cloud forest of the eastern Peruvian Andes, around the 16th century. His remains made it possible to answer a crucial question: the Plasmodium vivaxadapted to the temperate climate, did it arrive on the American continent via the Bering Strait at the same time as human settlement, or did it travel later, in the wake of colonization by European Empires?

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Genomic analysis revealed a remarkable similarity between the strain of P. vivax from Laguna de los Cóndores and the ancient European strain of the parasite, which confirms with a high degree of certainty that European colonizers spread this species in the Americas during the first century or so after the populations came into contact.

“Amplified by the effects of war, slavery, and population displacement, infectious diseases, including malaria, devastated the indigenous peoples of the Americas during the colonial period, with mortality rates reaching 90 % in some places”notes Dr Evelyn Guevara, of the University of Helsinki and the Max Planck Institute (press release).

Mediterranean soldiers…

Across the Atlantic, the team uncovered another captivating story. Their analysis focused on remains exhumed from the cemetery of Saint-Rombout Cathedral in Mechelen, Belgium. Which was located near the very first permanent military hospital in modern Europe, between 1567 and 1715.

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Within the population buried there before the construction of the military hospital, DNA made it possible to identify the local presence of P. vivax. While the people subsequently buried carried within them P. falciparum, more virulent. Particularly men, who the authors were able to determine were in fact of Mediterranean origin: probably soldiers recruited from northern Italy and Spain to fight in the Habsburg army during the War of Four. twenty years (1568-1648).

“We find that large-scale troop movements played an important role in the spread of malaria during this period, similar to so-called ‘airport’ malaria cases in temperate Europe today.” hui”underlines Alexander Herbig of the Max Planck Institute (press release).

…and a Nepalese trader

Long before this significant episode, another page in the history of malaria was being written in Asia. The team identified the oldest known case of malaria in P. falciparum, at the Himalayan site of Chokhopani, Nepal, occupied around 800 BCE. However, at 2,800 meters above sea level, this valley is well outside the habitat zone of the parasite and the Anopheles mosquito. Odd !

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If the infected individual was indeed a local man, genetically adapted to life at high altitude, the nearby archaeological remains suggest that these Himalayan populations actively participated in long-distance trade. The authors therefore believe that the man went to a lower region, where malaria is endemic, before returning or being brought back to Chokhopani, where he was then buried.

“Today we consider these regions both remote and inaccessible, but in fact the Kali Gandaki River valley served as a sort of trans-Himalayan highway connecting the populations of the Tibetan Plateau to the Indian subcontinent”details Professor Mark Aldenderfer, from the University of California at Merced (press release).

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The intimate details revealed by ancient DNA thus provide clues to the countless ways in which infectious diseases such as malaria spread in the past, painting the current landscape of epidemics. And perhaps constitute an additional tool for understanding – or even combating – this threat to public health, exacerbated by climate change.