Study shows that Mexican free-tailed bats do not carry the parasite responsible for Chagas disease

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Researchers from the Texas A&M College of Veterinary Medicine and Biomedical Sciences (VMBS) have found 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.¹ The disease, which is most often spread by triatomine bugs—commonly called “kissing bugs” because they drink the blood of people and animals—causes a number of symptoms that are commonly mistaken for other health conditions, including heart failure and cardiac arrest. Chagas disease infections affect domestic animals, including horses, pigs, cats, and dogs, along with humans. Texans can rest assured, though, that any Mexican free-tailed bats roosting near their homes are unlikely to be carriers of the Chagas disease-causing parasite.^1,2

“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,” Ilana Mosley, a doctoral student in the VMBS’ Department of Veterinary Integrative Biosciences (VIBS) said in a university release.¹ “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.”

The study tested a total of 283 local Mexican free-tailed bats that had died as a result of Winter Storm Uri in Brazos County, Texas, in February 2021.² The group conducted bat necropsies in biosafety cabinets, recording species, weight, sex, and presence of ectoparasites. None of the bat hearts or kidneys tested positive for T cruzi.² Based on an assumed roost size in February of 1000 bats, researchers were able to conclude with 95% confidence that the true prevalence of T cruzi in the population does not exceed 1%.²

One possible explanation for why Mexican free-tailed bats have low observed T cruzi prevalence could be a result of infrequent encounters with triatomines. Although, as Mosely points out, “Since bats are insectivores, it seems very likely that they would have contact with kissing bugs and become infected. 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.”¹

T cruzi is commonly found in vectors and wildlife reservoirs throughout the southern half of the United States down to Argentina. Cases of Chagas disease are typically found in rural, impoverished areas of South and Central American countries.^1,3 A majority of United States cases were brought into the country, although there are a small number of autochthonous cases as well. According to the CDC, roughly 8 million people globally, 280,000 in the United States, have the disease, often without knowing it.³

“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,” Mosely said.¹ “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.”

Dogs often lick the bite wounds left by the kissing bugs, thereby ingesting the feces left behind by the insects. They can also become infected by eating infected insects or rodents that carry the parasite, or through canine blood transfusions if a donor dog is infected.⁴ Once ingested, the T cruzi parasite invades several cells within a dog’s body, including the cells lining the blood vessels, the muscle cells of the heart, and other cells, including those in the liver, spleen, kidneys, skeletal muscle, and the central nervous system. Once in the cells, the parasites reproduce, eventually causing cell rupture, releasing large numbers of the parasite into the bloodstream, and causing effects seen with Chagas disease.⁴

“Shortly after infection, T cruzi is known to sequester itself in different tissues where it will replicate before going back into the bloodstream,” Mosely said.¹ “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.”

Most infected dogs will demonstrate signs from lethargy, decreased appetite, and weight loss to fainting, exercise intolerance, vomiting, and diarrhea. On examination, signs of heart failure, fluid in the abdomen, and enlarged lymph nodes may be observed.⁴ The infection can be divided into a 3-stage process for most dogs, classified as acute, latent, and chronic phases. The infection may be detected in the blood stream or lymph nodes during the acute phase of infection, though this can be difficult during the acute phase. Antibody levels may be detectable on lab tests 3 weeks after infection, though false positives are possible. Most dogs are diagnosed based on clinical signs during the chronic phase of the infection, or through examination of tissue samples, postmortem.⁴

There are no current vaccinations or consensus methods of treatment for Chagas disease in dogs. Medications including Benznidazole, Ravuconazole, and Albaconazole have been used during the acute phase, though they have minimal effect in later phases.⁴

The researchers emphasized the importance of further research in this area, gathering samples to allow future research to continue studies on the same group of bats. “Responsibly installing specimens into natural history collections is vitally important for ongoing and future research,” Jessica Light, PhD, the curator of mammals at the Texas A&M Biodiversity Research and Teaching Collections, said.¹ “The specimens that [Mosely] and [the lab of Sarah Hamer, DVM, DACVPM (Epidemiology), PhD, MS] collected are now available for study for countless additional research projects.”

References

1. Mexican Free-Tailed Bats in Texas Do Not Carry the Chagas Disease Parasite, Texas A&M Researchers Find. News release. October 1, 2024. Accessed October 1, 2024. https://vetmed.tamu.edu/news/press-releases/bats-and-chagas-disease/
2. Mosley I., Auckland L., Light J., Hamer S. Apparent absence of Trypanosoma cruzi in Mexican free-tailed bats (Tadarida brasiliensis) from Texas, USA. Vet Parasitol Reg Stud Reports. 2024;51. https://doi.org/10.1016/j.vprsr.2024.101031
3. American Trypanosomiasis, DPDx ­– Laboratory Identification of Parasites of Public Health Concern. US Centers for Disease Control and Prevention. Accessed October 3, 2024. https://www.cdc.gov/dpdx/trypanosomiasisamerican/index.html
4. About Chagas Disease. US Centers for Disease Control and Prevention. September 4, 2024. Accessed October 3, 2024. https://www.cdc.gov/chagas/about/index.html#:~:text=About%208%20million%20people%20globally,where%20we%20find%20Chagas%20disease
5. Weir M., Barnette C. Chagas Disease in Dogs. VCA Animal Hospitals. Accessed October 3, 2024. https://vcahospitals.com/know-your-pet/chagas-disease-in-dogs