Abstract
Dog vaccination is considered an effective way of reducing Leishmania infantum infection incidence in the canine population, as well as its transmission to humans. However, the use of partially effective vaccines can have the detrimental effect of "masking" vaccinated asymptomatic carriers, capable of harbouring the parasite and transmitting it to naïve individuals. After eight years on the European market, few studies have been released on CaniLeish® vaccine safety and efficacy. The present study, a one-year randomized CaniLeish® vaccine field trial, was performed in a canine leishmaniosis endemic area and included animals selected from a native dog population (n = 168). No severe adverse reactions were observed in vaccinated dogs (n = 85). Cases of active L. infantum infection were detected by serological, molecular and clinical follow-up of dogs. One-year post-vaccination, no differences in number or severity of L. infantum active infections were observed between study groups (n = 4 in each group). Vaccine-induced cellular immunity, assessed through interferon-γ quantification, showed significantly higher levels of this cytokine one-month post-vaccination in the vaccine group (p < 0.001), but no differences were observed after nine months between trial groups (p = 0.078). These results fail to support the reported CaniLeish® efficacy in the prevention of active L. infantum infection in dogs from endemic areas and naturally exposed to the parasite.