BackgroundCanine Leishmaniasis (CanL) caused by theL.infantumspecies is one of the biggest threats to the health of the South American canine population. Chemotherapeutics currently used for the treatment of CanL fail to induce a total parasite clearance while inducing numerous side effects. As CanL is an immunomodulated disease, the use of immuno-treatments should strengthen the deficient immune response of infected dogs. In this study, we evaluated a nasally administered immunotherapy in dogs naturally infected withL.infantum(stage 2), with both visceral and cutaneous manifestations. Noteworthy, some of them were also infected by other parasites (E.canis,D.immitis,A.platys), what worsen their chance of survival.Methodology/Principal findingsThe treatment was based on 2 intranasal (IN.) administrations of a killedL.infantumparasite loaded into maltodextrin nanoparticles, which treatment was compared with the classical oral administration of Miltefosine (2 mg/kg) for 28 days, as well as a combination of these 2 treatments. The results showed that two IN administrations significantly reduced the serology, and were at least as efficient as the chemotherapy to reduce the skin and bone marrow parasite burden, as well as clinical scores, and that unlike Miltefosine treatments, this nasally administered nanoparticle vaccine was without side effects.ConclusionsThese results confirm the feasibility of a simple therapeutic immuno-treatment againstL.infantuminfected dogs, which is a promising tool for future developments.