Citation: Valença-Barbosa, C.; Finamore-Araujo, P.; Moreira, O.C.; Alvarez, M.V.N.; Borges-Veloso, A.; Barbosa, S.E.; Diotaiuti, L.; de Souza, R.d.C.M. High Parasitic Loads Quantified in Sylvatic Triatoma melanica, a Chagas Disease Vector. Pathogens 2022, 11, 1498. https:// doi.org/10.3390/pathogens11121498 Academic Editors: Fernando Villalta, Wanderley De Souza and Carlos Robello Received: 16 November 2022 Accepted: 1 December 2022 Published: 8 December 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). pathogens Article High Parasitic Loads Quantified in Sylvatic Triatoma melanica, a Chagas Disease Vector Carolina Valença-Barbosa 1, *, Paula Finamore-Araujo 2 , Otacílio Cruz Moreira 2 , Marcus Vinicius Niz Alvarez 3 , André Borges-Veloso 1 , Silvia Ermelinda Barbosa 1 , Liléia Diotaiuti 1 and Rita de Cássia Moreira de Souza 1, * 1 Grupo Triatomíneos, Instituto René Rachou-Fiocruz Minas Gerais, Belo Horizonte, Minas Gerais 30190-002, Brazil 2 Plataforma de PCR em Tempo Real RPT09A, Laboratório de Virologia Molecular, Instituto Oswaldo Cruz/Fiocruz, Rio de Janeiro 21040-360, Brazil 3 Instituto de Biotecnologia de Botucatu, Universidade Estadual Paulista, São Paulo 18607-440, Brazil * Correspondence: carolina.valenca@fiocruz.br (C.V.-B.); rita.souza@fiocruz.br (R.d.C.M.d.S.) Abstract: Triatoma melanica is a sylvatic vector species in Brazil. In We aimed to characterize the Trypanosoma cruzi discrete typing units (DTUs), the parasitic loads, and the blood meal sources of insects collected in rocky outcrops in rural areas in the state of Minas Gerais. An optical microscope (OM) and kDNA-PCR were used to examine natural infection by T. cruzi, and positive samples were genotyped by conventional multilocus PCR. Quantification of the T. cruzi load was performed using qPCR, and the blood meal sources were identified by Sanger sequencing the 12S rRNA gene. A total of 141 T. melanica were captured. Of these, ~55% (61/111) and ~91% (63/69) were positive by OM and KDNA-PCR, respectively. We genotyped ~89% (56/63) of the T. cruzi-positive triatomines, with TcI (~55%, 31/56) being the most prevalent DTU, followed by TcIII (~20%, 11/56) and TcII (~7%, 4/56). Only TcI+TcIII mixed infections were detected in 10 (~18%) specimens. A wide range of variation in the parasitic loads of T. melanica was observed, with an overall median value of 10 4 parasites/intestine, with females having higher T. cruzi loads than N2, N4, and N5. TcII showed lower parasitic loads compared to TcI and TcIII. The OM positive diagnosis odds ratio between T. cruzi infection when the parasite load is 10 7 compared to 10 3 was approximately 29.1. The most frequent blood meal source was Kerodon rupestris (~58%), followed by Thrichomys apereoides (~18%), Wiedomys cerradensis (~8%), Galactis cuja (~8%) and Gallus gallus (~8%). Our findings characterize biological and epidemiological aspects of the sylvatic population of T. melanica in the study area, highlighting the need to extend surveillance and control to this vector. Keywords: triatomine; Trypanosoma cruzi; brasiliensis complex; blood-feeding behavior 1. Introduction Chagas disease (ChD) is considered an enzootic disease transmitted by triatomine species and maintained in sylvatic mammals. It became an anthropozoonosis with the entry of humans into sylvatic environments, where Trypanosoma cruzi, the etiological agent of the disease, circulates [1]. Currently, ChD is a neglected disease and affects about 7 million people, with 25 million at risk in American countries [2]. The transmission of T. cruzi is highly complex, involving various species of both wild and domestic mammalian hosts and more than 150 triatomine species occupying different habitats [3–6]. The epidemiological importance of each triatomine species for human public health is related to their degree of involvement in domestic parasite transmission cycles. In Brazil, advances have been made in the control of vector transmission, including the use of insecticide treatment for domiciles. Using such approaches, the elimination of the non-native species Triatoma infestans has been achieved throughout much of this national territory [7]. Although vector control measures have significantly reduced the risk of T. cruzi transmission, the existence of native triatomine species that occur in sylvatic Pathogens 2022, 11, 1498. https://doi.org/10.3390/pathogens11121498 https://www.mdpi.com/journal/pathogens