A Blood-Sucking Foe Lurks in Central American Caves

Since the dawn of our species, caves have provided humans with shelter and safe haven. And while caves today are more likely to attract tourists than settlers, Latin America’s extensive cavern systems still frequently harbor weary overnight guests, from hunters to local workers hired to protect the caves against vandals. Some of those visitors, however, pay a steep price for that shelter—their blood and, potentially, their health.

Kissing bugs are blood-sucking nocturnal insects that inhabit Central and South America. The amorous moniker arose because they often bite sleeping victims around the mouth. Even more worrisome is the fact that kissing bugs transmit Trypanosoma cruzi, the parasite that causes Chagas disease. That malady—which can go undetected for years—causes life-threatening heart and digestion problems in at least 30 percent of its victims. It is the most costly parasitic disease in Latin America, where some 9 million people carry the T. cruzi parasite.

Normally, kissing bugs implicated in the disease creep into people’s homes at night or live in thatched walls and roofs. But researchers from the University of Vermont, the University of San Carlos of Guatemala and Loyola University New Orleans wondered whether caves might be another potential site of transmission. In Guatemala, people often use caves for religious ceremonies as well as for shelter, and caves in both Guatemala and Belize are popular tourist attractions. One cave in Belize is even a regular bathing site for both locals and tourists.  

The team visited four caves at three sites in Guatemala and Belize, where—clad in protective clothing—they scoured the walls, ceiling and floor for the bugs. They conducted four 25-minute searches at each cave, as the bloodthirsty insects usually emerge from cracks and crannies within 30 minutes of human arrival, after picking up on the carbon dioxide in their victims’ breath. All together, they scooped up 24 kissing bugs.

Next, they extracted DNA from each of the insects’ abdomens and sequenced it to sort out the genetic traces of each bug’s most recent meals. Reporting in last week’s PLOS Neglected Tropical Diseases, the team says that the bugs had indeed been feasting on humans as well as on animals associated with humans.

Out of all the species they identified, human blood turned up in more than half of the insects they collected. Some of the insects that contained human blood also tested positive for the parasite that causes Chagas disease, they add. Pigs and dogs were other common meals, along with ducks, sheep (or possibly goats) and rodents. This is worrisome, because domesticated animals and animals that live near human homes can increase the likelihood of parasite transmission to a human. Wild animals made up just 20 to 30 percent of the bugs’ blood meals in two of the locations. In one cave, wild animals didn’t factor into the insects’ meals at all.

These findings might change how experts track Chagas disease transmission. “The dogma has been that kissing bugs living in wild or sylvan areas are not a problem for Chagas transmission to humans,” Patricia Dorn, a biologist at Loyola and a coauthor of the paper, said in an email. As such, they were initially quite surprised by their findings. But after they learned about the different cultural practices taking place in these caves, she said that the results made more sense.

The findings indicate that people should avoid caves, if possible. If they must use them, they should take appropriate precautions, like sleeping under bed nets. Additionally, caves might be indicative of a larger problem of previously unknown disease transmission in natural places, the researchers warn: “Just as caves may pose an epidemiological risk, there may be other situations where risk is thought to be minimum, but is not.” 

Rachel Nuwer | | READ MORE

Rachel Nuwer is a freelance science writer based in Brooklyn.