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Canine leishmaniasis is an important zoonosis caused by uncontrolled infection with Leishmania infantum, where an inappropriate immune response is not only responsible for permitting this intracellular parasite to multiply, but is also responsible for several of the pathological processes seen in this disease. Effective canine vaccines are therefore a highly desirable prevention tool. In this randomised, double-blinded, controlled trial, the efficacy of the LiESP/QA-21 vaccine (CaniLeish, Virbac, France) was assessed by exposing 90 naïve dogs to natural L. infantum infection during 2 consecutive transmission seasons, in two highly endemic areas of the Mediterranean basin. Regular PCR, culture, serological and clinical examinations were performed, and the infection/disease status of the dogs was classified at each examination. The vaccine was well-tolerated, and provided a significant reduction in the risk of progressing to uncontrolled active infection (p = 0.025) or symptomatic disease (p = 0.046), with an efficacy of 68.4% and a protection rate of 92.7%. The probability of becoming PCR positive was similar between groups, but the probability of returning to a PCR negative condition was higher in the vaccinated group (p = 0.04). In conclusion, we confirmed the interest of using this vaccine as part of a comprehensive control program for canine leishmaniasis, and validated the use of a protocol based on regular in-depth assessments over time to assess the efficacy of a canine leishmaniasis vaccine.

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The incidence of clinical and clinicopathological signs associated with the progression of infection was evaluated prospectively in 329 naïve young dogs exposed to Leishmania infantum transmission and examined periodically during 22 months (M). The dogs were part of Leishmania vaccine investigations performed under natural conditions. Vaccinated groups were considered in the evaluation when the vaccine resulted non-protective and the appearance and progression of signs did not differ statistically from controls at each time point, otherwise only control groups were included. 115 beagles were part of 3 studies (A to C) performed in the same kennel; 214 owned dogs (29 breeds, 2.3% beagles) were included in a study (D) performed in 45 endemic sites. At M22 the prevalence of any Leishmania infection stage classified as subpatent, active asymptomatic, or symptomatic was 59.8% in studies A–C and 29.2% in study D. Despite different breed composition and infection incidence, the relative proportion of active infections and the progression and type of clinical and clinicopathological signs have been similar in both study sets. All asymptomatic active infections recorded have invariably progressed to full-blown disease, resulting in 56 sick dogs at M22. In these dogs, lymph nodes enlargement and weight loss — recorded from M12 — were the most common signs. Cutaneous signs were seen late (M18) and less frequently. Ocular signs appeared even later, being sporadically recorded at M22. Most clinicopathological alterations became evident from M12, although a few cases of thrombocytopenia or mild non-regenerative anemia were already observed at M6. Albumin/globulin inversions were recorded from M12 and urea/creatinine increase appeared mostly from M18. Altogether our findings indicate that any susceptible young dogs naturally infected by L. infantum present a common pattern of progression of signs during 2 years post infection, providing clues for medical and epidemiological applied aspects.

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Ten Beagle dogs at different stages of Leishmania infantum infection, among which 6 had received a full course of LiESP/QA-21 (CaniLeish(®); Virbac) vaccination, were exposed to the bites of reared Phlebotomus perniciosus to assesses their infectiousness potential. This was found to be negligible/nil in 2 seronegative dogs with subpatent infection. Among the 8 dogs with active infection (=positive serology, bone-marrow qualitative PCR and lymph node culture), 2/5 vaccinated (40.0%) and 2/3 nonvaccinated dogs (66.7%) were infectious to the sand flies (p=0.5). However significantly fewer of the sand flies which fed on the vaccinated dogs were infected when compared to those which fed on the control dogs (10/82 compared to 30/49) (chi-squared test, p<0.0001; mixed binomial model with the dog identity included as a random effect, p=0.03). Furthermore, there was a significant difference in the proportion of sand flies with >500 parasites in their gut (i.e. a higher risk for subsequent transmission): 3.7% for vaccinated dogs compared with 28.6% for nonvaccinated dogs (Fisher's exact test, p<0.0001; binomial mixed model, p=0.006). Although preliminary, these results suggest value in further investigations on L. infantum transmissibility parameters in LiESP/QA-21 vaccinated dogs.