The dynamic of Trypanosoma cruzi transmissibility in field-caught Mepraia spinolai (Hemiptera: Reduviidae) of contrasting seasons: A developmental stage-dependent study.

A competent vector can harbor a pathogen and infect a high number of hosts. Scarce information is available on how triatomine vectors accomplish this task in nature, particularly without knowing the number of parasites they excrete. We study the dynamics of Trypanosoma cruzi transmissibility in the triatomine Mepraia spinolai collected in summer (December 2018) and winter (July 2019) of an austral endemic area. The insects received two feedings in the laboratory, the day after arrival and 45 days after the first feeding. Excreta samples were collected, DNA was extracted, and parasite loads were quantified by qPCR. After feeding, the parasite loads of the first and second excreta samples revealed differences between summer and winter insects. Overall, parasite load reductions and increases were detected in summer (51.2% and 32.5%) and in winter (9.1% and 15.2%) infected insects. The number of times the parasite load was reduced in summer insects revealed that early stage nymphs accomplished it at the highest ratio (× 740), middle stage nymphs (× 14), and late developmental stages with the lowest ratio (× 6.7). Therefore, fifth instar nymphs and adults have the maximal capacity to harbor T. cruzi, and those with the highest competence to transmit it, and early nymphs are the ones with minimal vectorial capacity. About 7% of the winter insects and 58.5% of the summer excreted quantifiable parasite loads right after collection. The amount of T. cruzi excreted in summer by M. spinolai reached medians between 950 and 2597 parasite equivalents/excreta, considering all developmental stages. Finally, molting during processes of T. cruzi load reduction and increase suggests that the exoskeleton shedding does not affect the excretion of T. cruzi.