High Parasitic Loads Quantified in Sylvatic Triatoma melanica, a Chagas Disease Vector

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 10⁴ 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 10⁷ compared to 10³ 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: Trypanosoma cruzi; blood-feeding behavior; brasiliensis complex; triatomine.

Figure 1

Box plot showing the parasite load in 59 T. melanica specimens collected in the municipalities of Espinosa and Monte Azul. The box illustrates the median and interquartile range, while the whiskers give the “minimum” and “maximum” values, and the open circles represent outliers.

Figure 2

Bar plot comparing estimates of the T. cruzi parasite load (95% C.I.) according to the infecting T. cruzi DTU lineage in 51 T. melanica from the municipalities of Espinosa and Monte Azul. Groups with different letters indicate significant difference (p < 0.05). Groups not sharing any letter are significantly different.

Figure 3

Bar plot comparing estimates of the T. cruzi parasite load (95% C.I.) according to blood meal source in 51 T. melanica from the municipalities of Espinosa and Monte Azul. GC: Galactis cuja; GG: Gallus gallus; KR: Kerodon rupestris; TA: Thrichomys apereoides; WC: Wiedomys cerradensis Groups with different letters indicate significant difference (p < 0.05). Groups not sharing any letter are significantly different.

Figure 4

Bar plot comparing the estimate of the T. cruzi parasite load (95% C.I.) according to the development stages of 51 T. melanica from the municipalities of Espinosa and Monte Azul. Groups with different letters indicate significant difference (p < 0.05). Groups not sharing any letter are significantly different.

Figure 5

Association between T. cruzi diagnosis using optical microscopy (OM) and parasite load. (A) Stacked histogram showing the number of T. melanica specimens diagnosed by OM as either negative or positive for T. cruzi according to their parasite load. (B) Positive diagnosis probability estimate given the parasite load (the grey area gives 95% C.I. of this estimate).