Differential mucosal infectivity of different life stages of Trypanosoma cruzi

Mucosal invasion is an important method of vector-borne transmission of Trypanosoma cruzi to human hosts. We previously have shown that low numbers of virulent insect-derived metacyclic trypomastigotes (IMT) collected from the excreta of reduviid bugs were highly efficient in infecting mice through gastrointestinal and conjunctival mucosa. However, we have recently found that blood-form trypomastigotes (BFT) of T. cruzi cannot efficiently initiate mucosal infection after an oral challenge of the gastrointestinal tract. Evidence for systemic infection after oral challenge with BFT was sought by microscopic parasitemia examinations of fresh blood, polymerase chain reaction analyses with DNA extracted from mouse blood using primers specific for a nuclear repeat present in the T. cruzi genome, and by Western blots of parasite lysates probed with individual mouse serum. Oral challenge doses of 1,000-10,000 BFT were found to rarely initiate mucosal infection. In contrast, 1,000 IMT delivered orally was a sufficient challenge for the consistent infection of 100% of control BALB/c mice. The exceptions infected mucosally by BFT involved animals with mucosal defects due to trauma or ulcerative/periodontal diseases. These data suggest that IMT have uniquely specialized functions for mucosal invasion that are not normally present in BFT.