Amplification of Trypanosoma cruzi-specific DNA sequences in formalin-fixed raccoon tissues using polymerase chain reaction

Trypanosoma cruzi infections and associated pathology in urban-dwelling Virginia opossums (Didelphis virginiana)

Trypanosoma cruzi, a zoonotic protozoan parasite, infects a wide range of mammals. The southern United States has endemic sylvatic transmission cycles maintained by several species of wildlife and domestic dogs. We hypothesized that urban-dwelling opossums (Didelphis virginiana) in South Texas are infected with T. cruzi, and that tissue pathology would be associated with infection. In 2017, we collected blood, heart tissue and anal gland secretions from 100 wild opossums across three seasons that were trapped by animal control in South Texas. In addition, anal gland tissue and intercostal muscle were collected from 43 of the 100 opossums for which time allowed the extra tissue collection. All blood, tissue, and secretion samples were screened for T. cruzi DNA using qPCR with confirmation of positive status achieved through one or more additional PCR assays, including a qPCR to determine the parasite discrete typing unit (DTU). T. cruzi DNA was detected in at least one tissue of 15% of the opossums sampled: blood clot (9%), heart tissue (10%), anal gland secretions (12%), intercostal muscle (16.3%), and anal gland tissue (11.6%). Infection was detected in two or more different tissue types in nine of the opossums. The 35 tissues for which parasite DTU was determined were exclusively 'Tcl'- a DTU previously associated with locally-acquired human disease in the United States. T. cruzi-positive opossums were nearly 14 times more likely to exhibit significant heart lesions on histopathology (lympoplasmacytic inflammation±fibrosis) when compared to negative opossums (OR = 13.56, CI = 1.23-751.28, p-value = 0.03). Three triatomines were opportunistically collected from the study site, of which two were infected (66.7%), and bloodmeal analysis revealed canine, opossum, and human bloodmeals. Given the presence of parasite in opossum blood, unique potential for shedding of parasite in anal glad secretions, and evidence of vectors feeding on opossums, it is likely that opossums serve as wild reservoirs around urban dwellings in South Texas.

Susceptibility Testing of Medically Important Parasites

In the last 2 decades, renewed attention to neglected tropical diseases (NTDs) has spurred the development of antiparasitic agents, especially in light of emerging drug resistance. The need for new drugs has required in vitro screening methods using parasite culture. Furthermore, clinical laboratories sought to correlate in vitro susceptibility methods with treatment outcomes, most notably with malaria. Parasites with their various life cycles present greater complexity than bacteria, for which standardized susceptibility methods exist. This review catalogs the state-of-the-art methodologies used to evaluate the effects of drugs on key human parasites from the point of view of drug discovery as well as the need for laboratory methods that correlate with clinical outcomes.

High Trypanosoma cruzi infection prevalence associated with minimal cardiac pathology among wild carnivores in central Texas

Infection with the zoonotic vector-borne protozoal parasite Trypanosoma cruzi causes Chagas disease in humans and dogs throughout the Americas. Despite the recognized importance of various wildlife species for perpetuating Trypanosoma cruzi in nature, relatively little is known about the development of cardiac disease in infected wildlife. Using a cross-sectional study design, we collected cardiac tissue and blood from hunter-donated wildlife carcasses- including raccoon (Procyon lotor), coyote (Canis latrans), gray fox (Urocyon cinereoargenteus), and bobcat (Lynx rufus) - from central Texas, a region with established populations of infected triatomine vectors and increasing diagnoses of Chagas disease in domestic dogs. Based on PCR analysis, we found that 2 bobcats (14.3%), 12 coyotes (14.3%), 8 foxes (13.8%), and 49 raccoons (70.0%) were positive for T. cruzi in at least one sample (right ventricle, apex, and/or blood clot). Although a histologic survey of right ventricles showed that 21.1% of 19 PCR-positive hearts were characterized by mild lymphoplasmocytic infiltration, no other lesions and no amastigotes were observed in any histologic section. DNA sequencing of the TcSC5D gene revealed that raccoons were infected with T. cruzi strain TcIV, and a single racoon harbored a TcI/TcIV mixed infection. Relative to other wildlife species tested here, our data suggest that raccoons may be important reservoirs of TcIV in Texas and a source of infection for indigenous triatomine bugs. The overall high level of infection in this wildlife community likely reflects high levels of vector contact, including ingestion of bugs. Although the relationship between the sylvatic cycle of T. cruzi transmission and human disease risk in the United States has yet to be defined, our data suggest that hunters and wildlife professionals should take precautions to avoid direct contact with potentially infected wildlife tissues.

Evaluation of the Chagas Stat-Pak assay for detection of Trypanosoma cruzi antibodies in wildlife reservoirs

An immunochromatographic assay (Chagas Stat-Pak) was evaluated for the detection of Trypanosoma cruzi antibodies in 4 species of wildlife reservoirs. Antibodies to T. cruzi were detected in raccoons (Procyon lotor) (naturally and experimentally infected) and degus (Octodon degu) (experimentally-infected) using the Chagas Stat-Pak. In naturally exposed wild raccoons, the Chagas Stat-Pak had a sensitivity and specificity of 66.7-80.0% and 96.3%, respectively. Compared with indirect immunofluorescent antibody assay results, seroconversion as determined by Chagas Stat-Pak was delayed for experimentally infected raccoons, but occurred sooner in experimentally infected degus. The Chagas Stat-Pak did not detect antibodies in naturally or experimentally infected Virginia opossums (Didelphis virginiana) or in experimentally infected short-tailed opossums (Monodelphis domestica). These data suggest that the Chagas Stat-Pak might be useful in field studies of raccoons and degus when samples would not be available for more-conventional serologic assays. Because this assay did not work on either species of marsupial, the applicability of the assay should be examined before it is used in other wild species.

Bioluminescent imaging of Trypanosoma cruzi infection

Chagas disease, caused by infection with the protozoan parasite Trypanosoma cruzi, is a major public health problem in Central and South America. The pathogenesis of Chagas disease is complex and the natural course of infection is not completely understood. The recent development of bioluminescence imaging technology has facilitated studies of a number of infectious and non-infectious diseases. We developed luminescent T. cruzi to facilitate similar studies of Chagas disease pathogenesis. Luminescent T. cruzi trypomastigotes and amastigotes were imaged in infections of rat myoblast cultures, which demonstrated a clear correlation of photon emission signal strength to the number of parasites used. This was also observed in mice infected with different numbers of luminescent parasites, where a stringent correlation of photon emission to parasite number was observed early at the site of inoculation, followed by dissemination of parasites to different sites over the course of a 25-day infection. Whole animal imaging from ventral, dorsal and lateral perspectives provided clear evidence of parasite dissemination. The tissue distribution of T. cruzi was further determined by imaging heart, spleen, skeletal muscle, lungs, kidneys, liver and intestines ex vivo. These results illustrate the natural dissemination of T. cruzi during infection and unveil a new tool for studying a number of aspects of Chagas disease, including rapid in vitro screening of potential therapeutical agents, roles of parasite and host factors in the outcome of infection, and analysis of differential tissue tropism in various parasite-host strain combinations.