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Chagas disease is caused by the infection of the parasite Trypanosoma cruzi (Chagas, 1909). Mexico is estimated to be among the countries with the highest rates of human infections. The southernmost region of the Baja California peninsula is home to the endemic, highly aggressive, and largest Triatominae vector, thus far described: Dipetalogaster maxima (Uhler 1894). Previous single-year studies have attempted to estimate the natural infection rate of T. cruzi in this species, none encompassing a multiyear sampling design nor a species-specific diagnostic tool. We report the infection rate based on more than 717 individuals examined via a PCR species-specific diagnosis. The infection rate of T. cruzi was of 4.4% (n = 5/112), 0.9% (n = 4/411), and 4.6% (n = 9/194) for 2016, 2017, and 2018, respectively, resulting in an infection rate of 2% across all sites and years (n = 18/717)., (© The Author(s) 2021. Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Introduction: Updating the distribution and natural infection status of triatomine bugs is critical for planning, prioritizing, and implementing strategies to control Chagas disease (CD), especially after vector reduction programs. After carrying out a control program, the Department of Boyaca contains the highest number of Colombian municipalities certified by PAHO to be free of intradomiciliary transmission of Trypanosoma cruzi by Rhodnius prolixus. The present work describes the spatial distribution, natural infection (NI), and molecular characterization of T. cruzi in synanthropic triatomines from the Department of Boyaca in 2017 and 2018., Materials and Methods: An entomological survey was conducted in 52 municipalities in Boyaca known to have had previous infestations of triatomine bugs. Insects were collected through active searches carried out by technical personnel from the Secretary of Health and community members using Triatomine Collection Stations (PITs-acronym in Spanish). For evaluation of natural infection, triatomines were identified morphologically and grouped in pools of one to five individuals of the same species collected in the same household. DNA derived from the feces of each pool of insects was analyzed by PCR for the presence of T. cruzi using primers flanking the satellite DNA of the parasite. SL-IR primers were used to differentiate TCI from the other DTUs and to identify different genotypes. The distribution of the collected triatomines was analyzed to determine any vector hotspots using spatial recreation., Results: A total of 670 triatomine bugs was collected, belonging to five species: Triatoma dimidiata (73.2%), Triatoma venosa (16.7%), Panstrongylus geniculatus (5.7%), Rhodnius prolixus (4.4%), and Panstrongylus rufotuberculatus (0.4%), from 29 of the 52 municipalities. In total, 71.6% of the bugs were collected within houses (intradomiciliary) and the rest around the houses (peridomiciliary). Triatoma dimidiata was the most widely distributed species and had the highest natural infection index (37.8%), followed by T. venosa and P. geniculatus. TcI was the only DTU found, with the TcI Dom genotype identified in 80% of positive samples and TcI sylvatic in the other insects. Spatial analysis showed clusters of T. dimidiata and T. venosa in the northeast and southwest regions of Boyaca., Conclusions: After some municipalities were certified free of natural transmission within houses (intradomiciliary transmission) of T. cruzi by R. prolixus, T. dimidiata has become the most prevalent vector present, and represents a significant risk of resurgent CD transmission. However, T. venosa, P. geniculatus, and P. rufotuberculatus also contribute to the increased risk of transmission. The presence of residual R. prolixus may undo the successes achieved through vector elimination programs. The molecular and spatial analysis used here allows us to identify areas with an ongoing threat of parasite transmission and improve entomological surveillance strategies., Competing Interests: The authors have declared that no competing interests exist.

Background: Triatomine insects are vectors of Trypanosoma cruzi, the causal agent of Chagas disease. The insect-parasite interaction has been studied in relation to the transmission and prevalence of this disease. For most triatomines, however, several crucial aspects of the insect immune response are still unknown. For example, only for Rhodnius prolixus and Triatoma infestans has the activity of phenoloxidase (PO) and its zymogen prophenoloxidase (proPO) been reported in relation to the hemolymph and anterior midgut (AM). The aim of this study was to gain insight into the immune response to T. cruzi infection of an important triatomine in Mexico, Meccus pallidipennis., Methods: Parasites were quantified in the rectal contents of infected M. pallidipennis groups. We examined some key factors in disease transmission, including the systemic (hemolymph) and local (gut) immune response., Results: Parasites were present in the rectal contents at 4 days post-infection (pi) and reached their maximum density on day 7 pi. At 7 and 9 days pi mainly metacyclic trypomastigotes occurred. Compared to the control, the infected insects exhibited diminished PO activity in the hemolymph on days 9, 16 and 20 pi, and in the AM only on day 9. Additionally, infected insects displayed lower proPO activity in the hemolymph on day 1, but greater activity in the AM on day 28., Conclusions: The parasite strain originating from M. pallidipennis rapidly colonized the rectum of nymphs of this triatomine and developed high numbers of metacyclic trypomastigotes. Neither the changes of concentrations of PO and proPO in the hemolymph nor in the AM correlated with the changes in the population of T. cruzi.

Climate change can influence the geographical range of the ecological niche of pathogens by altering biotic interactions with vectors and reservoirs. The distributions of 20 epidemiologically important triatomine species in North America were modelled, comparing the genetic algorithm for rule-set prediction (GARP) and maximum entropy (MaxEnt), with or without topographical variables. Potential shifts in transmission niche for Trypanosoma cruzi (Trypanosomatida: Trypanosomatidae) (Chagas, 1909) were analysed for 2050 and 2070 in Representative Concentration Pathway (RCP) 4.5 and RCP 8.5. There were no significant quantitative range differences between the GARP and MaxEnt models, but GARP models best represented known distributions for most species [partial-receiver operating characteristic (ROC) > 1]; elevation was an important variable contributing to the ecological niche model (ENM). There was little difference between niche breadth projections for RCP 4.5 and RCP 8.5; the majority of species shifted significantly in both periods. Those species with the greatest current distribution range are expected to have the greatest shifts. Positional changes in the centroid, although reduced for most species, were associated with latitude. A significant increase or decrease in mean niche elevation is expected principally for Neotropical 1 species. The impact of climate change will be specific to each species, its biogeographical region and its latitude. North American triatomines with the greatest current distribution ranges (Nearctic 2 and Nearctic/Neotropical) will have the greatest future distribution shifts. Significant shifts (increases or decreases) in mean elevation over time are projected principally for the Neotropical species with the broadest current distributions. Changes in the vector exposure threat to the human population were significant for both future periods, with a 1.48% increase for urban populations and a 1.76% increase for rural populations in 2050., (© 2017 The Royal Entomological Society.)

Three behaviors of epidemiological importance: the time lapse for the onset of feeding, actual feeding, and defecation time for Meccus phyllosomus pallidipennis (Stål), Meccus phyllosomus longipennis (Usinger), Meccus phyllosomus picturatus (Usinger), and their laboratory hybrids were evaluated in this study. The mean time lapse for the beginning of feeding was between 0.5 and 8.3 min considering all instars in each cohort, with highly significant differences only among fifth-instar nymphs, females, and males of M. p. pallidipennis and M. p. longipennis relative to the hybrid cohorts. Four hybrid (LoPa [M. p. longipennis and M. p. pallidipennis] and LoPi [M. p. longipennis and M. p. picturatus] and their reciprocal experimental crosses) cohorts had similar mean feeding times to one of the parental subspecies, but longer than the other one. The remaining hybrid cohort (PaPi [M. p. pallidipennis and M. p. picturatus]) had longer feeding times than both of its parental subspecies. The specimens of the LoPa and LoPi hybrid cohorts defecated faster than the respective instars of the three parental cohorts. With exception of first- and fifth-instar nymphs, PaPi cohorts defecated faster than the remaining seven cohorts. More than 60% of defecation events occurred during feeding in the six hybrid cohorts. Our results indicate that hybrid cohorts have more potential to acquire infection and transmit Trypanosoma cruzi Chagas than their parental cohorts., (© The Authors 2016. Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

Background & Objectives: Meccus pallidipennis is one of the most epidemiologically important vectors of Trypanosoma cruzi to reservoir hosts in nine states of Mexico. Triatomines occurring in distinct locations normally adapt to local conditions. The aim of this study was to examine the biological attributes of three populations of M. pallidipennis from areas with different environmental characteristics as a factor influencing the triatomine capacity for T. cruzi transmission., Methods: The values of biological parameters related to the life cycle, the number of blood meals to molt to next instar, fecundity and percentage of females after a biological cycle of three populations of M. pallidipennis were evaluated. A cohort of each of the three studied populations from different geographical areas of Mexico was maintained under similar laboratory conditions and then compared with each other., Results: The life cycle was less than six months in all the studied cohorts, with differences among them. The number of blood meals to molt was lower for the cohort from Izϊcar de Matamoros. Laid eggs per day per female was lower for the cohort from Luvianos. In contrast, no important differences were recorded on the percentage of mortality, egg eclosion rate or percentages of obtained females., Interpretation & Conclusion: It was found that an important level of heterogeneity exist between the three studied populations of M. pallidipennis, apparently influenced by the remarkable differences on environmental conditions on the localities where the founders were initially collected, that emphasizes the necessity of studies on local populations of triatomines.

The Southern Pacific Ocean coast has been traditionally considered a non-active transmission area for Chagas disease. In this report, we show evidence of Trypanosoma cruzi infection in the sylvatic kissing bug Mepraia gajardoi from the northern Chilean coast.

Trypanosoma cruzi is the causative agent of Chagas disease, a zoonosis involving domestic and sylvatic mammalian reservoirs. Since scarce information has been published about the susceptibility of T. cruzi lineages to other triatomine species besides Triatoma infestans, we evaluate the susceptibility of T. infestans and Mepraia spinolai to different T. cruzi lineages, originated from naturally infected Octodon degus rodents as mammal host. Xenodiagnosis-PCR methods to detect T. cruzi positive rodents and genotyping to differentiate T. cruzi lineages (TcI, TcIIb, TcIId and TcIIe) identified singly and mixed T. cruzi infections. More infections and nearly all mixed infections were identified using the wild vector M. spinolai than T. infestans.

The morphological identification of Trypanosoma cruzi is currently considered to have a high specificity, but its sensitivity, which depends on the volume of the sample examined, is rather low. Trypanosome developmental stages suspended in blood, reduviid feces, and culture media are routinely searched for by means of fresh film examination (about 2 microL). High speed centrifugation of blood samples separates the buffy coat, where most trypomastigotes concentrate. As the parasites are transparent and colorless, their detection is mostly dependent on their motility. The fluorescent vital stain acridine orange has been used to enhance image contrast, as exemplified by the QBC (Quantitative Buffy Coat) technique. Staining blood, buffy coat, reduviid feces, and culture media samples with methylene blue (also a vital dye) is a means of producing sharp, well contrasted images of motile or non-motile T. cruzi developmental stages, only standard laboratory microscopes being required. Slides previously coated with a thin layer of methylene blue are used to stain fresh blood films. Photomicrographs exemplify the results of methylene blue staining applied to living and fixed parasites.

Molecular evidence showed 46.2% of Trypanosoma cruzi infection in Mepraia spinolai insects from North-Central Chile, which is significantly higher than previous reports of up to 26% by microscopic observation. Our results show similar infection levels among nymphal stages, ranging from 38.3 to 54.1%, indicating that younger nymphs could be as important as older ones in parasite transmission. A cautionary note must be stressed to indicate the potential role of M. spinolai in transmitting T. cruzi in country areas due to the high infection level detected by molecular analysis.

There are two vectors of the Chagas' disease in Chile: Triatoma infestans Klug the domestic vector and Mepraia spinolai Porter the sylvatic vector. The alimentary profile of M. spinolai has been poorly studied. In this work we study the participation of humans, goats, dogs, cats, rodents, rabbits, birds (hens) and reptiles in the diet of M. spinolai by analyzing the intestinal content through immunoradiometric assay. To put our results in a general context, we also compared the diet with that described for T. infestans. In decreasing order, we detected blood of rabbits, dogs, goats, rodents, humans, and birds (hens). There were 12.3% of insects infected with T. cruzi, but this fact was not significant for diet variance. In warm weather there was a larger diversity of alimentary sources than in a cold one. The niche breadth increased from 0.029 in cold weather to 0.464 in warm weather. The niche overlap of T. infestans and M. spinolai was 0.23.