In Peru, guinea pigs are raised for food. Unfortunately, these little mammals also provide sustenance for bloodsucking insects that carry Trypanosoma cruzi, the agent of Chagas disease. And annual guinea pig roasts may have led to the emergence and reemergence of the deadly parasite. The findings were published this week in Proceedings of the Royal Society B.
Up to seven million people are infected with Chagas disease worldwide, though most cases occur in Latin America. It starts with skin lesions, swelling eyelids, and fever and it can lead to cardiac disorders. The potentially life-threatening disease is transmitted specifically through the feces of infected “kissing bugs,” or Triatoma infestans, which carry the T. cruzi parasite. Infected insects are often found living in the cracks of rural houses and at night they feed on the blood of sleeping humans and defecate close to the bite. The protozoan parasites can enter the body when they’re smeared across the bite, the eyes or mouth, or any break in the skin. But the process is so inefficient, Science explains, that only one human becomes infected for every 1,700 kissing bug bites.
Despite the inefficiency, the infection prevalence in humans exceeds 40% in some communities. To investigate this unresolved paradox, an international team led by University of Pennsylvania’s Michael Levy studied T. cruzi transmission in the lab and in the field around Arequipa, Peru. They allowed the bugs to feed on infected guinea pigs and they also documented all the repeat occurrences of large colonies of triatomine bugs with high infection prevalence. They found that a subset of guinea pigs remains highly infectious to the vectors for many months. But it’s not just that...
Because of the seasonal rains, the area sees huge fluctuations in the price of alfalfa, or guinea pig food. So, during the drier months of May, June, and July – when prices for the notoriously water-dependent crop triple – residents kill most of their guinea pigs. They keep a few around in order to replenish the population when alfalfa prices drop.
However, this concentrates the insect vector on the small subgroup of guinea pigs maintained for reproduction. And T. cruzi powers through these bug populations, creating a considerable force of infection, the team concludes. The result is the emergence of a parasite whose transmission probably would have fizzled out otherwise. More than 80% of the kissing bugs taken from two guinea pig pens were infected with T. cruzi, Science reports, while only about 6% of bugs sampled away from the rodent enclosures were infected.