Comparison of the infectivity of Trypanosoma cruzi insect-derived metacyclic trypomastigotes after mucosal and cutaneous contaminative challenges

The importance of estimating the burden of disease from foodborne transmission of Trypanosoma cruzi

Chagas disease (ChD), caused by infection with the flagellated protozoan, Trypanosoma cruzi, has a complicated transmission cycle with many infection routes. These include vector-borne (via the triatomine (reduviid bug) vector defecating into a skin abrasion, usually following a blood meal), transplacental transmission, blood transfusion, organ transplant, laboratory accident, and foodborne transmission. Foodborne transmission may occur due to ingestion of meat or blood from infected animals or from ingestion of other foods (often fruit juice) contaminated by infected vectors or secretions from reservoir hosts. Despite the high disease burden associated with ChD, it was omitted from the original World Health Organization estimates of foodborne disease burden that were published in 2015. As these estimates are currently being updated, this review presents arguments for including ChD in new estimates of the global burden of foodborne disease. Preliminary calculations suggest a burden of at least 137,000 Disability Adjusted Life Years, but this does not take into account the greater symptom severity associated with foodborne transmission. Thus, we also provide information regarding the greater health burden in endemic areas associated with foodborne infection compared with vector-borne infection, with higher mortality and more severe symptoms. We therefore suggest that it is insufficient to use source attribution alone to determine the foodborne proportion of current burden estimates, as this may underestimate the higher disability and mortality associated with the foodborne infection route.

"Natural infections" with Trypanosoma cruzi via the skin of mice: size of mouthparts of vectors and numbers of invading parasites

Investigating parameters influencing natural infections with Trypanosoma cruzi via the skin, the diameters of mouthparts of different stages of triatomines vectors were measured to determine the size of the channel accessible for T. cruzi during cutaneous infection. The mean diameters of the skin-penetrating mandibles of first to fifth instar nymphs of the vector Triatoma infestans increased from 18 to 65 µm. The mean diameter in fourth instar nymphs of Dipetalogaster maxima was 86 µm. Different numbers of isolated vector-derived metacyclic trypomastigotes (10–10,000) were injected intradermally into mice. Prepatent periods, parasitemia and mortality rates were compared with those of mice obtaining 10,000 metacyclic trypomastigotes that are usually present in the first drop of faeces onto the feeding wounds of fifth and fourth instar nymphs of T. infestans and D. maxima, respectively. After injection of 50–10,000 T. cruzi, in all 42 mice the infection developed. An injection of 10 parasites induced an infection in 8 out of 15 mice. With increasing doses of parasites, prepatent periods tended to decrease. The level of parasitemia was higher after injection of the lowest dose. Except for one mouse all infected mice died. After placement of 10,000 metacyclic trypomastigotes onto the feeding wound of fifth or fourth instar nymphs of T. infestans and D. maxima, respectively, the infection rates of the groups, prepatent periods and the levels of parasitemia of T. cruzi in mice indicated that about 10–1,000 metacyclic trypomastigotes entered the skin via this route. For the first time, the present data emphasise the risk of an infection by infectious excreta of triatomines deposited near the feeding wound and the low number of invading parasites.

Histopathological changes in the gastrointestinal tract and systemic alterations triggered by experimental oral infection with Trypanosoma cruzi

Chagas disease, caused by the protozoan Trypanosoma cruzi, is endemic in almost all countries of Latin America. In Brazil, oral infection is becoming the most important mechanism of transmission of the disease in several regions of the country. The gastrointestinal tract is the gateway for the parasite through this route of infection, however, little is known about the involvement of these organs related to oral route. In this sense, the present study evaluated the impact of oral infection on the digestive tract in mice infected by Berenice-78 (Be-78) T. cruzi strain, in comparison with the intraperitoneal route of infection. In this work, the intraperitoneal route group showed a peak of parasitemia similar to the oral route group, however the mortality rate among the orally infected animals was higher when compared to intraperitoneal route. By analyzing the frequency of blood cell populations, differences were mainly observed in CD4⁺ T lymphocytes, and not in CD8^+, presenting an earlier reduction in the number of CD4⁺ T cells, which persisted for a longer period, in the animals of the oral group when compared with the intraperitoneal group. Animals infected by oral route presented a higher tissue parasitism and inflammatory infiltrate in stomach, duodenum and colon on the 28th day after infection. Therefore, these data suggest that oral infection has a different profile of parasitological and immune responses compared to intraperitoneal route, being the oral route more virulent and with greater tissue parasitism in organs of the gastrointestinal tract evaluated during the acute phase.

C57BL/6 α-1,3-Galactosyltransferase Knockout Mouse as an Animal Model for Experimental Chagas Disease

The leading animal model of experimental Chagas disease, the mouse, plays a significant role in studies for vaccine development, diagnosis, and human therapies. Humans, along with Old World primates, alone among mammals, cannot make the terminal carbohydrate linkage of the α-Gal trisaccharide. It has been established that the anti-α-Gal immune response is likely to be a critical factor for protection against Trypanosoma cruzi (T. cruzi) infection in humans. However, the mice customarily employed for the study of T. cruzi infection naturally express the α-Gal epitope and therefore do not produce anti-α-Gal antibodies. Here, we used the C57BL/6 α-1,3-galactosyltransferase knockout (α-GalT-KO) mouse, which does not express the α-Gal epitope as a model for experimental Chagas disease. We found the anti-α-Gal IgG antibody response to an increase in α-GalT-KO mice infected with Arequipa and Colombiana strains of T. cruzi, leading to fewer parasite nests, lower parasitemia, and an increase of INF-γ, TNF-α, and IL-12 cytokines in the heart of α-GalT-KO mice compared with α-GalT-WT mice on days 60 and 120 postinfection. We therefore agree that the C57BL/6 α-GalT-KO mouse represents a useful model for initial testing of therapeutic and immunological approaches against different strains of T. cruzi.

Selected cardiac abnormalities in Trypanosoma cruzi serologically positive, discordant, and negative working dogs along the Texas-Mexico border

BACKGROUND

Chagas disease is increasingly recognized in the southern U.S., where triatomine vectors transmit Trypanosoma cruzi among wildlife and domestic dogs with occasional vector spillover to humans. As in humans, clinical outcome in dogs is variable, ranging from acute death to asymptomatic infections or chronic heart disease. In order to characterize cardiac manifestations of T. cruzi infections, we tracked a cohort of naturally-infected dogs and a matched cohort of uninfected dogs. We hypothesized that selected measures of cardiac disease (abnormal rate, abnormal rhythm, and elevated cardiac troponin I (cTnI; a biomarker of cardiac injury)) would occur more commonly in infected than uninfected dogs matched by age, breed, sex and location. In addition to the clearly positive and negative dogs, we specifically tracked dogs with discordant test results across three independent serological assays to gather clinical data that might elucidate the infection status of these animals and inform the utility of the different testing approaches.

RESULTS

We placed an ambulatory ECG monitor (Holter) on 48 government working dogs and analyzed 39 successful recordings that met length and quality criteria from 17 T. cruzi-infected, 18 uninfected dogs and 4 dogs with discordant results. Overall, 76.5% of positive, 100.0% of discordant, and 11.1% of negative dogs showed > 1 ECG abnormality (p < 0.0001), and positive and discordant dogs had a higher mean number of different types of ECG abnormalities than negative dogs (p < 0.001-0.014). The most common cardiac abnormalities included supraventricular and ventricular arrhythmias and atrioventricular block. Positive dogs had higher serum concentrations of cTnI than both negative dogs (p = 0.044) and discordant dogs (p = 0.06). Based on dog handler reports, nearly all (4/5; 80%) dogs with reported performance decline or fatigue were T. cruzi-infected dogs.

CONCLUSIONS

Further understanding cardiac manifestations in dogs naturally infected with T. cruzi is critical for prognostication, establishing a baseline for drug and vaccine studies, and better understanding of zoonotic risk.

Oral Versus Intragastric Inoculation: Similar Pathways of Trypanosoma cruzi Experimental Infection? From Target Tissues, Parasite Evasion, and Immune Response

Currently, oral infection is the most frequent transmission mechanism of Chagas disease in Brazil and others Latin American countries. This transmission pathway presents increased mortality rate in the first 2 weeks, which is higher than the calculated mortality after the biting of infected insect vectors. Thus, the oral route of Trypanosoma cruzi infection, and the consequences in the host must be taken into account when thinking on the mechanisms underlying the natural history of the disease. Distinct routes of parasite entry may differentially affect immune circuits, stimulating regional immune responses that impact on the overall profile of the host protective immunity. Experimental studies related to oral infection usually comprise inoculation in the mouth (oral infection, OI) or gavage (gastrointestinal infection, GI), being often considered as similar routes of infection. Hence, establishing a relationship between the inoculation site (OI or GI) with disease progression and the mounting of T. cruzi-specific regional immune responses is an important issue to be considered. Here, we provide a discussion on studies performed in OI and GI in experimental models of acute infections, including T. cruzi infection.

Aspirin treatment exacerbates oral infections by Trypanosoma cruzi

Oral transmission of the protozoan parasite Trypanosoma cruzi, the etiological agent of Chagas disease, has been documented in Latin American countries. The reported cases of infection were due to the ingestion of contaminated fresh fruit, juices, or sugar cane juice. There have been few studies on the physiopathology of the disease in oral transmission cases. Gastritis is a common ailment that can be caused by poor dietary habits, intake of alcohol or other gastric irritants, bacterial infection, or by the widespread use of non-steroidal anti-inflammatory drugs (NSAIDs). This study investigated in a mouse model whether gastric mucosal injury, induced by aspirin, would affect the course of disease in animals infected with T. cruzi by the oral route. The CL14 and G strains of T. cruzi, both of low infectivity, were used. To this end, groups of BALB/c mice were treated during 5 days with aspirin (100 mg kg(-1)) before oral infection with T. cruzi metacyclic forms (4 × 10(5) or 5 × 10(7) parasites/mouse). Histological analysis and determination of nitric oxide and TNF-α were performed in gastric samples obtained 5 days after infection. Parasitemia was monitored from the thirteenth day after infection. The results indicate that aspirin treatment of mice injured their gastric mucosa and facilitated invasion by both CL14 and G strains of T. cruzi. Strain CL14 caused more severe infection compared to the G strain, as larger numbers of amastigote nests were found in the stomach and parasitemia levels were higher. Our study is novel in that it shows that gastric mucosal damage caused by aspirin, a commonly used NSAID, facilitates T. cruzi infection by the oral route.

Trypanosoma cruzi Infection through the Oral Route Promotes a Severe Infection in Mice: New Disease Form from an Old Infection?

Oral transmission of Chagas disease has been documented in Latin American countries. Nevertheless, significant studies on the pathophysiology of this form of infection are largely lacking. The few studies investigating oral route infection disregard that inoculation in the oral cavity (Oral infection, OI) or by gavage (Gastrointestinal infection, GI) represent different infection routes, yet both show clear-cut parasitemia and heart parasitism during the acute infection. Herein, BALB/c mice were subjected to acute OI or GI infection using 5x10⁴ culture-derived Trypanosoma cruzi trypomastigotes. OI mice displayed higher parasitemia and mortality rates than their GI counterparts. Heart histopathology showed larger areas of infiltration in the GI mice, whereas liver lesions were more severe in the OI animals, accompanied by higher Alanine Transaminase and Aspartate Transaminase serum contents. A differential cytokine pattern was also observed because OI mice presented higher pro-inflammatory cytokine (IFN-γ, TNF) serum levels than GI animals. Real-time PCR confirmed a higher TNF, IFN-γ, as well as IL-10 expression in the cardiac tissue from the OI group compared with GI. Conversely, TGF-β and IL-17 serum levels were greater in the GI animals. Immunolabeling revealed macrophages as the main tissue source of TNF in infected mice. The high mortality rate observed in the OI mice paralleled the TNF serum rise, with its inhibition by an anti-TNF treatment. Moreover, differences in susceptibility between GIversusOI mice were more clearly related to the host response than to the effect of gastric pH on parasites, since infection in magnesium hydroxide-treated mice showed similar results. Overall, the present study provides conclusive evidence that the initial site of parasite entrance critically affects host immune response and disease outcome. In light of the occurrence of oral Chagas disease outbreaks, our results raise important implications in terms of the current view of the natural disease course and host-parasite relationship.

Chagas disease caused by the protozoan Trypanosoma cruzi is endemic in Latin America and a neglected tropical disease, which affects 6–7 million people worldwide. Currently, oral transmission is the most frequent pathway of infection in Brazil but also occurs in other endemic countries. This important infection route is underestimated and understudied. Here, we demonstrate that the site of parasite entrance, in the oral cavity (OI), as observed in natural infection, or directly to the gastrointestinal tract (GI), differentially affects the host-immune response and mortality. OI promotes a severe acute disease, elevated parasitemia and TNF mediated mortality. OI showed intense hepatitis and mild heart damage. Interestingly, GI mice presented mild disease, along with less circulating TNF and higher TGF-β and IL-17 serum contents. GI animals showed mild liver damage and intense heart inflammation. Our study is a pioneer work that analyzes the features of two distinct routes of oral infection. In addition, it provides new clues for Chagas pathology and stimulates background for the elucidation of disease features in orally exposed populations.

Bed bugs (Cimex lectularius) as vectors of Trypanosoma cruzi

Populations of the common bed bug, Cimex lectularius, have recently undergone explosive growth. Bed bugs share many important traits with triatomine insects, but it remains unclear whether these similarities include the ability to transmit Trypanosoma cruzi, the etiologic agent of Chagas disease. Here, we show efficient and bidirectional transmission of T. cruzi between hosts and bed bugs in a laboratory environment. Most bed bugs that fed on experimentally infected mice acquired the parasite. A majority of previously uninfected mice became infected after a period of cohabitation with exposed bed bugs. T. cruzi was also transmitted to mice after the feces of infected bed bugs were applied directly to broken host skin. Quantitative bed bug defecation measures were similar to those of important triatomine vectors. Our findings suggest that the common bed bug may be a competent vector of T. cruzi and could pose a risk for vector-borne transmission of Chagas disease.