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

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.

Natural Trypanosoma cruzi Infection and Climatic Season Influence the Developmental Capacity in Field-Caught Mepraia spinolai Nymphs

“…Interestingly, three out of the five M. spinolai populations showing absence of molting were time-related. Specifically, C3, C4, and W4—all 2018′ populations—presented maximum rates of molting failure in a year with an unusually warm fall [ 48 ]. Therefore, our results of molting failure could be interpreted as diapause by environmental stochasticity, which seems to end after an unknown period of time after failure.…”

“…Fecal samples were individually extracted in a final volume of 200 μL, using conditions already described by manufacturers of the EZNA Blood DNA kit (OMEGA BIO-TEK, Norcross, GA, USA). T. cruzi presence was tested three times by PCR analysis directed to minicircle kDNA with oligos 121 and 122, using different volumes of extracted DNA as templates in a final volume of 50 μL to improve detection [ 47 , 48 ]. A volume of 10 μL of each reaction mixture was run in agarose gel electrophoresis (Lafken, Santiago, Chile) and stained with ethidium bromide (Invitrogen, Waltham, MA, USA).…”