Ancient hunter-gatherers, by way of their dietary habits, altered the ancient landscape. That's what Karl Reinhard identifies as the key finding in his latest paper, "Prehistoric Earth Oven Facilities and the Pathoecology of Chagas Disease in the Lower Pecos Canyonlands."
"Therefore, ancient humans created a web of potential infection within their territory," said Reinhard, professor and environmental archaeologist in UNL's School of Natural Resources.
Reinhard's paper is shedding new light on the pathology of Chagas disease, a tropical disease caused by the parasite Trypanosoma cruzi. It has recently been identified as an emergent disease in North America.
"Chagas is turning up in the United States," Reinhard said. "Up until a few years ago, people thought that the disease was emergent due to immigration. We can now show that it was always in parts of the U.S. where it cycles among wild animals."
Up to 10 million people in Latin American countries are infected and another 300,000 are infected in nonendemic countries including the United States, he said.
Symptoms of Chagas disease change over the course of infection. Early on, symptoms may include fever, swollen lymph modes, headaches and swelling at the site of the bite. In its chronic state, the disease can lead to an enlarged esophagus, an enlarged colon and heart failure.
"The number of deaths from Chagas has increased over the past few decades," Reinhard said.
Reinhard first became interested in Chagas disease while working in Texas in the late 1980s. In 1990, he began studying mummies in southern Peru, where he encountered pathology from the disease in mummies that were 1,200 to 800 years old.
Since then, Reinhard and his co-author, Adauto Araújo from the Brazilian School of Public Health in Rio de Janeiro, have been exploring other archaeological regions and sites for evidence of the disease.
"We both have an intense interest in archaeology and parasitology," Reinhard said. "Naturally, we are drawn to archaeological sites to find the clues that show when and where parasites infections emerged and whether those infections led to disease."
In 2002, they continued their search for evidence of the transmission of T. cruzi in the Lower Pecos Canyonlands, located in southwest Texas.
“The most interesting aspect was the discovery by molecular biologists that a wild animal-based variant of T. cruzi in North America is domiciled in South America," Reinhard said. "Those authors developed a hypothesis that this variant migrated with ancient humans from North to South America. Adauto and I have found evidence that supports this hypothesis – this shows that the interaction between humans and infected animals over time was dynamic."
In the years since, a deeper understanding of the evolution of Chagas disease began to unfold.
"Over the past two years, all the pieces of this puzzle fell nicely into place," Reinhard said. "The molecular identification of the Chagas variant of interest, the archaeological GIS spatial analysis of ancient sites, publication of ancient subsistence details and the documentation of the disease in several west Texas mammals all appeared."
Then came the tough part: putting it all together.
"This was the most difficult piece of writing I have of the 100 or so journal articles I have seen published in my career," Reinhard said. "The challenge was weaving these very different elements into a comprehensible reconstruction of the pathoecology of Chagas transmission."
Reinhard and Araújo's paper reiterates the importance of understanding a parasite’s endemic region to further develop a concept of that parasite’s natural history.
"This, in turn, is essential in determining whether or not humans could have been infected in both ancient and modern times," Reinhard said.
Moreover, since humans in both ancient and modern times altered the natural environment, knowing the environments of intermediate and definitive hosts is central to estimating whether or not human alteration of the environment expanded the opportunities of the parasite to infect humans.
"This is especially valuable for zoonotic parasites that normally cycle between wild animals but have an ability to infect humans," Reinhard said. "Archaeology provides the opportunity to add time depth to the geographic knowledge of the parasite's distribution. Understanding the time depth of infection in a region elucidates the evolutionary relationship between the parasite, the normal non-human hosts and humans."