Study finds Mexican free-tailed bats unlikely to spread Chagas disease In Texas

Bats are widely known around the world for their role in the spread of a number of zoonotic diseases — illnesses that can spread between humans and animals.

But a recent study by scientists at the Texas A&M College of Veterinary Medicine and Biomedical Sciences (VMBS) has revealed that Mexican free-tailed bats do not play a major role in the transmission of Trypanosoma cruzi (T. cruzi), the parasite responsible for Chagas disease. 

“Bats are thought to be the original hosts for T. cruzi, and they frequently roost near or even in people’s homes here in Central Texas,” said Ilana Mosley, a doctoral student in the VMBS’ Department of Veterinary Integrative Biosciences (VIBS). “They have relatively close proximity to humans, which is one reason why we conducted this study. There is also a critical gap in our understanding of the role that bats play in pathogen spread here in North America.”

Chagas disease is a tropical illness that causes many symptoms commonly mistaken for other health conditions, including heart failure and cardiac arrest. It is most often spread by triatomine bugs, commonly called “kissing bugs” because they drink the blood of people and animals to feed. 

“Kissing bugs often pick up the parasite T. cruzi while feeding. They then spread it to the next person or animal they feed on through their feces, which they typically leave near the bite,” Mosley said.

“It’s easy to assume that Mexican free-tailed bats are an important part of Chagas disease spread because bats are often pathogen hosts. But our results were negative, suggesting that these bats are not highly involved in Chagas disease spread.”

According to the World Health Organization, 6 million to 7 million people worldwide, mostly in Latin America, are estimated to be infected with T. cruzi, which also affects domestic animals, including horses, pigs, cats and dogs.

“For Texans, these results mean that Mexican free-tailed bats roosting in or near your home are unlikely to be carriers of the Chagas disease-causing parasite,” said Dr. Sarah Hamer, a professor in VIBS and the Department of Veterinary Pathobiology and Mosley’s lab supervisor. “It’s one less thing to worry about, though it is important to watch out for the main vectors that spread Chagas disease, like kissing bugs, and be aware that bats can still spread other diseases, including rabies.”

Surprising Results

Mosley’s surprise came after she tested about 300 local Mexican free-tailed bats for T. cruzi but found nothing.

“It’s always possible that the parasite was there and we just didn’t find it, which is why we need to continue doing more research,” she said. “But with such a large sample size, that seems unlikely.”

The absence of T. cruzi in this population of bats also creates new questions for researchers.

“Since bats are insectivores, it seems very likely that they would have contact with kissing bugs and become infected,” Mosley said. “So now we have to ask, are they not eating kissing bugs? Is there a reason why? There are many new directions to pursue in future studies.”

An Unexpected Opportunity

While Hamer’s lab has been studying Chagas disease for years, this recent study came as an unexpected opportunity during Winter Storm Uri, a severe storm that struck Texas in February 2021. 

During the storm, which caused millions of Texans to lose power, local wildlife also struggled to endure the harsh conditions. This included hundreds of Mexican free-tailed bats that perished due to the cold temperatures and lack of available food resources. 

“It was really very sad,” Hamer said. “No one planned for it to happen, but when it did, we saw an opportunity to collect data from these bats that could be put toward a greater purpose.”

Being able to salvage so many bat specimens meant that the researchers were able to conduct a thorough investigation of T. cruzi’s presence in the local Mexican free-tailed bat population.

“Over the years, our lab has done plenty of live-capture studies, where we take very small samples from bats and then release them,” Hamer said. “It’s very time-intensive, and in the end, we only take about 10 microliters of blood before setting the bats free. What happened during Winter Storm Uri presented us with the ability to collect blood samples in much larger volumes, as well as complete organs.” 

Having larger samples is important for accurate detection of T. cruzi, which has a complex pattern of behavior.

“Shortly after infection, T. cruzi is known to sequester itself in different tissues where it will replicate before going back into the bloodstream,” Mosley said. “In theory, there are several organs where it can be detected, so it’s possible to miss the infection if, for example, it’s located in the kidneys and you choose to sample the heart.”

But the researchers didn’t just make use of these samples for their project — they also took samples so that future researchers can continue to study the same group of bats.

“We were very careful to take many different kinds of samples that would be useful for a wide range of research,” Mosley said. “We even took samples of the fleas and ticks that were on the bats, and we donated the rest of the remains to the natural history collection here at Texas A&M.” 

“Responsibly installing specimens into natural history collections is vitally important for ongoing and future research,” said Dr. Jessica Light, the curator of mammals at the Texas A&M Biodiversity Research and Teaching Collections. “The specimens that Ilana and the Hamer lab collected are now available for study for countless additional research projects.”

By Courtney Price and Sanjida Akter, Texas A&M University College of Veterinary Medicine and Biomedical Sciences