Efficacy assessment of a novel and two licensed Leishmania vaccines intended for dogs in an experimental hamster challenge model.

Abstract

INTRODUCTION AND AIM: Visceral leishmaniasis is the most severe form of leishmaniasis affecting humans and canine species. Vaccination is the most cost-effective approach to disease control. Our aim is to compare an experimental vaccine candidate and two marketed vaccines (CaniLeish® and LetiFend®) with a control group using a hamster model. METHODS: The vaccine candidate formulation was based on two parasite antigenic components. The first is a purified fraction isolated from Leishmania donovani named fucose mannose ligand (FML) and the second is excretory/secretory protein (E/S) derived from a L. donovani culture. The proteins are formulated in a novel adjuvant system composed of three different adjuvants (CPG, Quil A and Cholesterol/Ethanol solution). The primary efficacy variables were parasitemia and clinical observations of skin lesions. The secondary efficacy variables were changes in body weight, parasite load and histopathology in target tissues. RESULTS: Compared to the control group, the novel vaccine candidate was superior to the other two vaccines in terms of efficacy based on lower parasitemia, parasite load in target tissues, less presence of amastigotes in the histopathology samples, fewer skin lesions and less bodyweight loss. These differences were statistically significant in the case of parasite load in blood (parasitemia), and target tissues (liver, skin, and spleen). CONCLUSION: The novel vaccine candidate may have a higher efficacy benefit in the hamster model than CaniLeish® or Letifend® when compared to the control group. These results confirm the vaccine candidate as a potentially more efficacious alternative to the current commercially available vaccines against canine leishmaniasis.