Bioluminescence imaging of chronic T rypanosoma cruzi infections reveals tissue‐specific parasite dynamics and heart disease in the absence of locally persistent infection

Abstract

SummaryChronic Trypanosoma cruzi infections lead to cardiomyopathy in 20–30% of cases. A causal link between cardiac infection and pathology has been difficult to establish because of a lack of robust methods to detect scarce, focally distributed parasites within tissues. We developed a highly sensitive bioluminescence imaging system based on T. cruzi expressing a novel luciferase that emits tissue-penetrating orange-red light. This enabled long-term serial evaluation of parasite burdens in individual mice with an in vivo limit of detection of significantly less than 1000 parasites. Parasite distributions during chronic infections were highly focal and spatiotemporally dynamic, but did not localize to the heart. End-point ex vivo bioluminescence imaging allowed tissue-specific quantification of parasite loads with minimal sampling bias. During chronic infections, the gastro-intestinal tract, specifically the colon and stomach, was the only site where T. cruzi infection was consistently observed. Quantitative PCR-inferred parasite loads correlated with ex vivo bioluminescence and confirmed the gut as the parasite reservoir. Chronically infected mice developed myocarditis and cardiac fibrosis, despite the absence of locally persistent parasites. These data identify the gut as a permissive niche for long-term T. cruzi infection and show that canonical features of Chagas disease can occur without continual myocardium-specific infection.

Putting Infection Dynamics at the Heart of Chagas Disease

“…There are a variety of techniques to detect and potentially quantify T. cruzi in tissue samples, each with benefits and drawbacks (Table 1). Detection sensitivity is a marginal concern in analyses of acute or reactivated infections when parasite loads are high, but becomes critical in the chronic phase, when parasite abundance is decreased by several orders of magnitude [16]. For example, extracellular, non-replicating trypomastigotes are routinely detectable in the blood for a period during acute infection and can be observed by light microscopy.…”

“…A key development was the introduction of a firefly luciferase gene engineered to emit longer wavelength light, which has enhanced tissue penetrating capacity [30, 31]. The use of T. cruzi expressing this red-shifted luciferase enabled highly sensitive imaging of chronically infected mice [16, 32-34]. Drawbacks include the high associated costs and, potentially, a reduced ability to detect parasites that are metabolically quiescent.…”

An enhanced chimeric firefly luciferase-inspired enzyme for ATP detection and bioluminescence reporter and imaging applications

“…As a result of the pioneering work of McElroy, White and Seliger [3–5], beetle luciferases, particularly those found in fireflies, are used in numerous applications that include probes for detecting bacteria and fungi [6–9], whole-cell based biosensors [10–15] and gene expression assays [16–19]. Firefly luciferases have also been expressed in live mammals to visualize disease states [20–23], tumor growth and metastasis [24–27], cell trafficking [28, 29] and genetic regulation [30]. Many of these applications can be applied in high-throughput screening format in support of drug development [31–34].…”

Drug Susceptibility of Genetically Engineered Trypanosoma cruzi Strains and Sterile Cure in Animal Models as a Criterion for Potential Clinical Efficacy of Anti-T. cruzi Drugs

“…describes the use of a bioluminescence imaging system (2) to evaluate the efficacy of benznidazole, a 2-nitromididazole, and posaconazole, an antifungal triazole, in murine models of acute and chronic Chagas disease. While the use of bioluminescence in Trypanosoma cruzi research has been reported before (3)(4)(5)(6), the improved sensitivity of the red-shifted reporter facilitates following tissue distribution more accurately (2).…”

“…While the use of bioluminescence in Trypanosoma cruzi research has been reported before (3)(4)(5)(6), the improved sensitivity of the red-shifted reporter facilitates following tissue distribution more accurately (2). However, there are issues concerning the nature and interpretation of the experimental results to consider.…”