Abstract
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.
Highlights
Climatic variation is a major determinant of infectious disease dynamics [1]
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
Summary
Climatic variation is a major determinant of infectious disease dynamics [1]. Insects are ectotherms with a relatively small range of temperatures that can be endured, and in which activity takes place, with variable low thermal limits and narrow upper thermal tolerance [2]. Pathogen transmission in vector-borne diseases can be measured by the basic reproductive number. This epidemiological metric depends on vector and parasite traits including vector competence and density, which can be partitioned as the product of several parameters including development rate, vector survival, feeding, dispersal and reproduction, all dependent on temperature and affecting population abundance [3,4]. Chagas disease, caused by the protozoan parasite Trypanosoma cruzi, is the main neglected vector-borne disease in America [5]. This disease presents at least two phases, acute and chronic. Even though some information has been reported on the effect of temperature on domestic triatomine species, little is known about its effect on infected sylvatic triatomine species with a relevant role in T. cruzi maintenance and interplay between the domestic and sylvatic transmission cycles of Chagas disease
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