Measles, mumps, and smallpox. These are some of the infectious diseases that the collapse of Indigenous populations in the Americas at the beginning of the 16th century was probably caused by the introduction of these diseases by European colonists. However, the precise viruses that killed millions of people are still unknown.
Daniel Blanco-Melo is trying to figure out that historical conundrum. Working as an evolutionary virologist at the Fred Hutchinson Cancer Center in Seattle, he studies ancient viruses and sheds light on how they have influenced human evolution and history using state-of-the-art techniques. Blanco-Melo and associates have recently recreated two viruses that were prevalent in Mexico during the period of European invasion.
According to Blanco-Melo, “our research on ancient viruses is really appealing to people’s curiosity and how we can study history.” However, as someone who was born and raised in Mexico, Blanco-Melo also finds personal significance in this work. He adds he is able to investigate “something that is very dear in my heart,” namely, “really understanding, with molecular biology, those historical events,” through genetic detective work.
Human evolution is shaped by viruses
After Blanco-Melo happened onto Matt Ridley’s book Genome by accident in high school, his fascination with viruses blossomed. Though Blanco-Melo intended to give it to his father as a Father’s Day present, he ended up reading it himself. Later, he enrolled in a genomics undergraduate program at the National Autonomous University of Mexico, or UNAM, campus in Cuernavaca, encouraged by his biology teacher.
It was while pursuing his doctorate at New York City’s Rockefeller University that he first became aware of ancient viruses. His work concentrated on a specific class of viruses known as endogenous retroviruses, which are essentially the skeletal remains of extant infectious viruses that have merged with the genetic code of their hosts.
Tens of millions of years ago, an ancient retrovirus known as HERV-T propagated among our monkey ancestors, and Blanco-Melo was the first to catalog the genetic remnants of this virus. Subsequent investigation showed that a gene that produced the virus’s outer envelope persisted throughout the history of primates; an inactive form of this gene is still present in modern humans. By interacting with another protein on the cell surface, the envelope protein encoded by this gene facilitates the virus’s entry and infection of a cell.
Blanco-Melo questioned why a viral gene like that would be so well conserved. What possible evolutionary benefit may it have provided? He postulates that, based on investigations of cells cultured in a lab dish, extinct primates had to have appropriated the viral gene and utilized the corresponding protein to eliminate the cell surface protein, thus preventing the virus from infecting cells.
This illustration shows how a virus’s own genetic material might be utilized against it in the course of evolution. “This project not only satiated my curiosity, but we were able to develop it into a comprehensive narrative explaining the evolution, emergence, and eventual extinction of a virus,” explains Blanco-Melo.
Researchers working now could be able to employ similar tactics to fight against retroviruses, with HIV being the main target, according to Blanco-Melo.
defining historical occurrences
In recent times, Blanco-Melo has collaborated with UNAM evolutionary scientist María Ávila-Arcos, an old friend, to investigate viral diseases that primarily destroyed Indigenous populations in the Americas.
Viral DNA was collected and recovered from skeletal remains dating from the 15th to the 17th century by Blanco-Melo, Ávila-Arcos, and their team of researchers. These bones are from mass graves in what is now Mexico City, at a chapel and a colonial hospital. The bodies in the burials appear to have belonged to African slaves and Indigenous people who were enslaved during the 1540s and 1570s epidemics, according to autopsy reports from hospitals and archaeological sites.
The team used those results to reconstruct the genomic instruction manuals of two viruses, human parvovirus B19 and a human hepatitis B virus, which were not previously known to be circulating at the time.
The study, which was not part of this effort but was published in the journal eLife in 2021, may be the first to get ancient viral genomes from the Americas, according to Jesse Bloom, a virologist at the Fred Hutch.
The discovery of the ancient viruses that were afflicting humans hundreds of years ago is, according to Bloom, of significant scientific and historical significance worldwide, but particularly in the Americas.
The researchers discovered that the old viruses resembled modern African variants. Blanco-Melo claims that although they “seem to have arrived in Mexico shortly after the European arrival,” they are not Europeans. They essentially traveled from Africa via the transatlantic slave trade.
Blanco-Melo has taken care throughout the partnership to steer clear of “helicopter research,” in which researchers from elsewhere visit a location, collect data, and then claim ownership of the finished product. “These samples ought to remain in Mexico, where they should be examined by Mexican experts. The communities will undoubtedly be informed of the findings. That’s what we want,” he states.
The two viruses that the team found may not have started widespread epidemics, but they might have made some symptoms of other illnesses worse. Using the same Mexican samples as starting points, further research is searching for more viruses and even peptides to provide a more complete picture of the viruses prevalent at the time and maybe identify major offenders. According to Blanco-Melo, “a lot more research is required in order to capture those other causative agents.”
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