New Insights Into the Transmissibility ofLeishmania infantumFrom Dogs to Sand Flies: Experimental Vector-Transmission Reveals Persistent Parasite Depots at Bite Sites

Abstract

Canine leishmaniasis (CanL) is a chronic fatal disease of dogs and a major source of human infection through propagation of parasites in vectors. Here, we infected 8 beagles through multiple experimental vector transmissions with Leishmania infantum–infected Lutzomyia longipalpis. CanL clinical signs varied, although live parasites were recovered from all dog spleens. Splenic parasite burdens correlated positively with Leishmania-specific interleukin 10 levels, negatively with Leishmania-specific interferon γ and interleukin 2 levels, and negatively with Leishmania skin test reactivity. A key finding was parasite persistence for 6 months in lesions observed at the bite sites in all dogs. These recrudesced following a second transmission performed at a distal site. Notably, sand flies efficiently acquired parasites after feeding on lesions at the primary bite site. In this study, controlled vector transmissions identify a potentially unappreciated role for skin at infectious bite sites in dogs with CanL, providing a new perspective regarding the mechanism of Leishmania transmissibility to vector sand flies.

Patchy Parasitized Skin Governs Leishmania donovani Transmission to Sand Flies

“…This means that the infection is always initiated in the skin. Our group has previously reported that a proportion of parasites remains in the skin after transmission by sand flies [8, 9]. These primary skin parasites are present at bite sites of symptomatic and asymptomatic animals, remain viable long term, and can be taken up by sand flies (Figure 1).…”

Toll-Like Receptors 2, 4, and 7, Interferon-Gamma, Interleukin 10, and Programmed Death Ligand 1 Transcripts in Leishmanin Skin Test-Positive Reactions of Ibizan Hound Dogs

“…The Montenegro skin test reaction in human beings has been suggested as a surrogate of the early response to Leishmania infection, based on similarities in cellular immunophenotyping between acute lesions in cutaneous leishmaniosis and Montenegro skin testing of the same patient [20]. Papular dermatitis is a mild cutaneous manifestation of L. infantum infection classically diagnosed in young dogs, generally under one year of age, which has been clinically and experimentally associated with sand fly bite sites [31,32]. It is likely that this is a clinical entity observed after the first contact with L. infantum inoculated by sand flies in an immunocompetent dog.…”

Cutaneous parasitism in patients with American visceral leishmaniasis in an endemic area

“…Recent experiments in L. infantum-infected dogs have demonstrated lasting parasitemia for over six months and the tendency of infections to remain on the skin around the site of the infectious sandfly bite 22 . Further, performing a biopsy in a covered area could result in a lower parasitic load and difficulty in visualization through immunohistochemical staining.…”