Ecoepidemiology of Chagas Disease in a Biological Corridor in Southeastern Mexico: A Promising Approach to Understand the Risk of Chagas Disease.

Ecoepidemiology is an emerging field that attempts to explain how biotic, environmental, and even social factors influence the dynamics of infectious diseases. Particularly in vector-borne diseases, the study under this approach offers us an overview of the pathogens, vectors, and hosts that coexist in a given region and their ecological determinants. As a result of this, risk predictions can be established in a changing environment and how it may impact human populations. This paper is aimed at evaluating some ecoepidemiological characteristics of Chagas disease in a natural reserve in southeastern Mexico that borders human settlements. We carry out a cross-sectional study in 2022 where we search insects manually and with light traps. We set traps for small mammals and bats and conducted interviews with the inhabitants living around the study site. We identified the presence of Triatoma dimidiata and T. huehuetenanguensis species with a percentage of TcI T. cruzi infection of 68.4% (95% CI: 66.9-69.9). Temperature and humidity were not determining factors for the probability of insect capture. Of the 108 wild mammals (Chiroptera, Rodentia, and Didelphimorphia), none was infected with T. cruzi. Knowledge about Chagas disease in nearby inhabitants is poor, and some characteristics were found on the periphery of dwellings that could offer a refuge for insect vectors. With this information, surveillance strategies can be generated in the study area that reduce the risk of transmission of T. cruzi parasite to humans, and it is expected to motivate the use of this field in future research.

A Trypanosoma cruzi strain from southern Mexico is more virulent for male mice in part by blocking the immune response.

INTRODUCTION: Chagas disease is a neglected disease in the American continent. The southern Mexican state of Chiapas has the highest incidence rate of Chagas disease in the country. The disease, mainly caused by Tripanosoma cruzi in Mexico, is more prevalent in males than in females but the scientific basis for the sex-related tropism is not completely understood. The objective of this study was to evaluate the pathogenicity of a T. cruzi strain in mice of both sexes and to assess certain elements of the immune response in the infected animals. METHODOLOGY: Triatomines bugs were searched at Los Mezcales, Chiapas, Mexico and T. cruzi was identified by PCR and sequencing. A T. cruzi strain was isolated from the feces of triatomines bugs. Mice were infected with the strain and the virulence of the T. cruzi strain as well as the immune response against the infection was compared in male versus female mice. RESULTS: T. dimidiata was identified in all dwellings. 42.9% of the bugs were infected with T. cruzi lineage TcI. Male mice exhibited higher parasitemia than females, and developed leukopenia and lower levels of anti-T. cruzi antibodies compared to female mice. CONCLUSIONS: The identification of the T. cruzi strain in this endemic region of Mexico revealed that male mice are prone to this infectious protozoo, in addition to manifesting a deficient immune response against infection. These findings may explain the greater number of cases of Chagas disease among men in this endemic region of Latin America.

Higher temperatures reduce the number of Trypanosoma cruzi parasites in the vector Triatoma pallidipennis.

BACKGROUND: Relatively little is known about how pathogens transmitted by vector insects are affected by changing temperatures analogous to those occurring in the present global warming scenario. One expectation is that, like their ectothermic vectors, an increase in temperature could reduce their fitness. Here, we have investigated the effect of high temperatures on the abundance of Trypanosoma cruzi parasites during infection in the vector Triatoma pallidipennis. METHODS: We exposed T. pallidipennis nymphs to two strains (Morelos and Chilpancingo) of T. cruzi. Once infected, the fifth-instar bugs were distributed among three different temperature groups, i.e. 20, 30, and 34 °C, and the resulting parasites were counted when the bugs reached adulthood. RESULTS: The number of parasites increased linearly with time at 20 °C and, to a lesser extent, at 30 °C, especially in the Chilpancingo compared to the Morelos strain. Conversely, at 34 °C, the number of parasites of both strains decreased significantly compared to the other two temperatures. CONCLUSIONS: These results suggest negative effects on the abundance of T. cruzi in T. pallidipennis at high temperatures. This is the first evidence of the effect of high temperatures on a pathogenic agent transmitted by an insect vector in the context of global warming. Further tests should be done to determine whether this pattern occurs with other triatomine species and T. cruzi strains.

Effects of Trypanosoma cruzi on the phenoloxidase and prophenoloxidase activity in the vector Meccus pallidipennis (Hemiptera: Reduviidae).

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.