Fig 1.
Life cycle and differentiation of Trypanosoma cruzi within kissing bug vectors (Triatominae) and mammalian hosts.
In the anterior midgut of kissing bugs, T. cruzi trypomastigotes transition into amastigotes, which further differentiate into epimastigotes in the posterior midgut. Mature metacyclic trypomastigotes capable of infecting mammalian hosts are excreted with feces. In mammalian hosts, trypomastigotes enter the bloodstream, invade host cells, differentiate into amastigotes, and multiply intracellularly. This cycle illustrates the insect vector-mammalian host interactions critical to T. cruzi transmission and Chagas disease pathogenesis. Note: Modes of T. cruzi transmission other than those illustrated in this figure are also conceivable; see introduction/discussion for details. Graphs were created with GraphPad Prism version 10 (GraphPad Software, San Diego, CA, USA), and illustration components with BioRender.com. Additional artwork was drawn by SM.
Fig 2.
Spatial and temporal distribution of live Trypanosoma cruzi (Y strain) in bed bugs after ingestion of blood infected with live T. cruzi.
Load of live T. cruzi parasites within the anterior midgut (a), posterior midgut/hindgut (b), and feces (c) immediately after feeding (day 0) or 1 to 30 days after oral ingestion. No parasites were observed in the proboscis, salivary glands and hemolymph at any time post-infection. The mean and standard error bars represent data of 10 replicates, with each replicate representing one bed bug (Kruskal-Wallis tests; data with p < 0.05 were considered statistically significant). Note: Very similar results were obtained with two additional cohorts of bed bugs (S1 Data).
Fig 3.
Flagellated forms of Trypanosoma cruzi in the posterior midgut/hindgut of bed bugs after ingestion of blood infected with live T. cruzi.
(a) Single live T. cruzi parasite in a bed bug’s posterior midgut/hindgut. (b) Cluster of live T. cruzi parasites in a bed bug’s posterior midgut/hindgut. Panels a and b show different stages of the parasite. Dots illustrate gut microbiota. Photographs were taken by SM.
Table 1.
Survival of Trypanosoma cruzi in the bed bugs’ hemolymph over 7 days after intrathoracic injection of T. cruzi at 103 or 106 parasites per mL.
Fig 4.
Life cycle of Trypanosoma cruzi in bed bugs and evidence for very low risk of T. cruzi transmission via bed bug feeding and fecal contamination of bite wounds.
During days 1–7 post-ingestion (pi) of T. cruzi-infected blood by bed bugs, T. cruzi counts in the bed bugs’ anterior midgut steadily declined (Fig 2a), suggesting that the bed bugs’ immune response eliminated the parasites. No live T. cruzi parasites were present in the posterior midgut and hindgut on day 1 pi (Fig 2b), but during days 4–7 pi, T. cruzi counts in the posterior midgut and hindgut significantly increased (Fig 2), indicating multiplication of T. cruzi. As T. cruzi parasites were first detected in excreted fecal matter on day 4 pi (Table 2), and bed bugs did not defecate while feeding, and invariably defecated away from their feeding site, transmission of T. cruzi via bed bug feces is not very likely. As T. cruzi parasites were absent at all times from the bed bugs’ proboscis, salivary glands, and hemolymph (as illustrated in this figure), T. cruzi transmission through bed bug feeding on human hosts is highly unlikely. Graphs were created with GraphPad Prism version 10 (GraphPad Software, San Diego, CA, USA), and illustration components with BioRender.com. Additional artwork was drawn and the photographs were taken by SM and Dr. Adam Blake.
Table 2.
Assessment of potential Trypanosoma cruzi transmission by infected bed bugs when feeding on sterile blood on days 1–30 post initial T. cruzi infection.