Healed Lesions of Human Cutaneous Leishmaniasis Caused By Do Not Shelter Persistent Residual Parasites

In human cutaneous leishmaniasis (HCL) caused by () , the cutaneous lesions heal spontaneously and induce a Th1-type immunity that confers solid protection against reinfection. The same holds true for the experimental leishmaniasis induced by in C57BL/6 mice where residual parasites persist after spontaneous clinical cure and induce sustainable memory immune responses and resistance to reinfection. Whether residual parasites also persist in scars of cured HCL caused by is still unknown. Cutaneous scars from 53 volunteers with healed HCL caused by were biopsied and the tissue sample homogenates were analyzed for residual parasites by four methods: i) microscope detection of amastigotes, ii) parasite culture by inoculation on biphasic medium, iii) inoculation of tissue exctracts to the footpad of BALB/c mice, an inbred strain highly susceptible to , and iv) amplification of parasite kDNA by a highly sensitive real-time PCR (RT-PCR). Our results show that the scars of healed lesions of HCL caused by do not contain detectable residual parasites, suggesting that this form likely induces a sterile cure at least within the scars. This feature contrasts with other species causing chronic, diffuse, or recidivating forms of leishmaniasis where parasites do persist in healed lesions. The possibility that alternative mechanisms to parasite persistence are needed to boost and maintain long-term immunity to , should be taken into consideration in vaccine development against infection.