Trypanosoma cruzi infection follow-up in a sylvatic vector of Chagas disease: Comparing early and late stage nymphs.

Chagas disease is caused by Trypanosoma cruzi and transmitted by the triatomine Mepraia spinolai in the southwest of South America. Here, we examined the T. cruzi-infection dynamics of field-caught M. spinolai after laboratory feeding, with a follow-up procedure on bug populations collected in winter and spring of 2017 and 2018. Bugs were analyzed twice to evaluate T. cruzi-infection by PCR assays of urine/fecal samples, the first evaluation right after collection and the second 40 days after the first feeding. We detected bugs with: the first sample positive and second negative (+/-), the first sample negative and second positive (-/+), and with both samples positive or negative (+/+; -/-). Bugs that resulted positive on both occasions were the most frequent, with the exception of those collected in winter 2018. Infection rate in spring was higher than winter only in 2018. Early and late stage nymphs presented similar T. cruzi-infection rates except for winter 2017; therefore, all nymphs may contribute to T. cruzi-transmission to humans. Assessment of infection using two samples represents a realistic way to determine the infection a triatomine can harbor. The underlying mechanism may be that some bugs do not excrete parasites unless they are fed and maintained for some time under environmentally controlled conditions before releasing T. cruzi, which persists in the vector hindgut. We suggest that T. cruzi-infection dynamics regarding the three types of positive-PCR results detected by follow-up represent: residual T. cruzi in the rectal lumen (+/-), colonization of parasites attached to the rectal wall (-/+), and presence of both kinds of flagellates in the hindgut of triatomines (+/+). We suggest residual T. cruzi-infections are released after feeding, and result 60–90 days after infection persisting in the rectal lumen after a fasting event, a phenomenon that might vary between contrasting seasons and years. Author summary: In the vector-borne transmission of Chagas disease, approximately 150 species of triatomine bugs are potential vectors for the parasite Trypanosoma cruzi. A competent vector must fulfill several features such as the ability to host, amplify, and differentiate the parasite, allowing T. cruzi persistence within the insect vector. Our aim was to describe the dynamics of T. cruzi infection in a competent triatomine species collected in two contrasting seasons—with different environmental temperatures—of 2017 and 2018. We used a follow-up procedure including T. cruzi detection right after collection and 40 days later; both detections were performed after laboratory feeding. Most infected bugs were T. cruzi positive on both occasions. However, infected bugs from winter 2018 presented switches from T. cruzi negative at collection to T. cruzi positive 40 days later. The results suggest infections with T. cruzi attached to the hindgut wall as the colonization site, caused by infections that persist there after a fasting event, are released after a second feeding. [ABSTRACT FROM AUTHOR]