When the Europeans conquered the New World, they also brought in new infectious diseases and thus killed millions of indigenous people. But the transatlantic slave trade also contributed to the spread of new viruses on the American continent, as is now shown by DNA analyzes of dead people from Mexico in the 16th century. They carried genetic material from hepatitis and parvoviruses, which at that time only occurred in Africa.
Shortly after the start of the European colonization of the New World, dramatic epidemics and a collapse of Indian populations occurred almost everywhere on the American continent. Millions of indigenous people died of pathogens that were completely new to them and their immune systems and which were introduced by the Europeans. However, to this day hardly any known bacterial or viral pathogens were specifically responsible for these epidemics. Among other things, widespread infections such as measles, mumps and smallpox are suspected in Europe at the time.
Genetic tracing of early disease victims in Mexico
In what is now Mexico, historical reports show that the first epidemics broke out shortly after the arrival of the Spaniards. There were particularly many deaths in the 16th century after Mexico became a Spanish colony. “Millions of the indigenous populations were swept away by this plague known as Cocolitzli – the plague on Nahuatl -” explains Axel Guzmán-Solís from the Autonomous National University of Mexico. “But which pathogens were responsible for these outbreaks is unknown.” To gain more clarity, Guzmán-Solís and his colleagues went on a genetic search.
For their study, the research team analyzed 21 DNA samples from the several hundred dead who were buried in the vicinity of the Hospital Real de San José de los Naturales (HSJN) in the 15th and 16th centuries. This colonial hospital in what is now Mexico City was the first in Mexico to also treat the indigenous population. Five more DNA samples came from the cemetery of the “La Concepcion” chapel a few kilometers away. Guzmán-Solís and his team looked specifically for the genetic traces that viruses might have left on them in the course of an infection in the genome of these dead people.
Hepatitis and Parvoviruses from Africa
In fact, the scientists found what they were looking for: They were able to detect the gene signatures of viruses in 17 DNA samples, including hepatitis B viruses, which cause jaundice and liver damage, as well as genes of the parvovirus B19, a pathogen that causes the childhood disease ring rubella, but also severe anemia can cause. The interesting thing about it: The strains of these viruses detected in the dead were not found in Europe or America at the time, but almost exclusively in Africa. Closer analyzes showed that the carriers of these infections and many more of the dead buried at the hospital at the time were of African origin – they were apparently slaves or their descendants.
It is known from historical documents that shortly after the conquest of Central America, the Spaniards began to bring slaves from Africa to their new colonies. “Millions of people were kidnapped from Africa under inhumane conditions and brought to America – 250,000 of them to New Spain alone,” the researchers report. On the crossing, the slaves were crammed into the overcrowded holds of the ships and had to stay there for weeks under the most unhygienic conditions. According to Guzmán-Solís and his team, this not only meant that many of the slaves fell ill with infections on the crossing and afterwards, they could also have transmitted the pathogen to the indigenous population of Mexico after their arrival.
The slave trade encouraged the spread of the disease
“Our results suggest that the Spanish colonists not only brought pathogens with them to the New World, but also promoted the spread of new viruses through their slave trade,” says co-author Daniel Blanco-Melo from the Icahn School of Medicine at Mount Sinai in New York. “The dire living conditions under which the enslaved Africans and Native Americans had to live, especially in the early days of Spanish colonization, then promoted the transmission and spread of the new pathogens.”
The team assumes that in this way not only the two DNA viruses that have now been detected reached Central America, but also presumably other, previously undetectable pathogens whose genetic material consists of RNA. “Our results suggest that several newly introduced viruses were circulating at the same time,” says Guzmán-Solís’ colleague Maria Ávila-Arcos. The indigenous population, whose immune system had never come into contact with these viruses, could not counter these new infections and became seriously ill. “That could explain why the epidemics were so deadly for the indigenous communities,” says Ávila-Arcos.
Source: eLife, doi: 10.7554 / eLife.68612