Field randomized trial to evaluate the efficacy of the Leish-Tec® vaccine against canine visceral leishmaniasis in an endemic area of Brazil. Issue 19 (27th April 2016)

• Record Type: Journal Article
• Authors: Regina-Silva, Shara; Feres, Ana Maria Leonardi Tibúrcio; França-Silva, João Carlos; Dias, Edelberto Santos; Michalsky, Érika Monteiro; de Andrade, Hélida Monteiro; Coelho, Eduardo Antonio Ferraz; Ribeiro, Gustavo Meirelles; Fernandes, Ana Paula; Machado-Coelho, George Luiz Lins
• Is Part Of: Vaccine. Volume 34:Issue 19(2016)
• Page Start: 2233
• Page End: 2239
• Publication Date: 2016-04-27
• Subjects: Randomized field trial -- Canine visceral leishmaniasis -- Vaccine -- A2 antigen -- Leish-Tec® -- Efficacy; Vaccines -- Periodicals; 615.372
• DOI: 10.1016/j.vaccine.2016.03.019
• Languages: English
• ISSNs: 0264-410X

Abstract

Highlights: Randomized field trial (RTF) to demonstrate Leish-Tec ® vaccine efficacy against canine visceral leishmaniasis. A high transmission pressure and parasite challenge was assured for demonstrating vaccine efficacy. Leish-Tec ® vaccination was significant effective (71%) for prophylaxis of CVL. Efficacy was higher among animals presenting with increased levels of anti-A2 antibodies (81%). A tendency to reduced transmission of parasites to sand fly vectors was also observed among vaccinated animals. Abstract: Background: A canine vaccine remains a promising approach for effective control of visceral leishmaniasis (VL), given its complex epidemiology in areas where zoonotic VL is prevalent. Leish-Tec ® is a recombinant vaccine, based on the Leishmania A2 antigen, against canine VL (CVL). It is, since 2014, the single commercial vaccine licensed in Brazil. Here, Leish-Tec ® efficacy was estimated through a randomized field trial (RFT), in a highly VL endemic area. Methods: The RFT was conducted from 2008 to 2010 in an endemic area of southeastern Brazil, presenting a CVL seroprevalence of 41.9%. Eight hundred forty-seven seronegative dogs were randomly selected to receive Leish-Tec ® ( n = 429) or placebo ( n = 418). Animals were followed up by clinical, serological, and parasitological exams for 18 months. The CVL incidence in both groups was compared through proportion analysis. Results: A significant reduction in the number of cases of CVL was observed in the vaccine group, as compared with the placebo group, whether efficacy was estimated according to parasitological results (71.4%; 95% CI: 34.9–87.3%; p = 0.001; risk ratio = 0.287), by adding results of xenodiagnosis and parasitological exams (58.1%; 95% CI: 26.0–76.3%; p = 0.002; risk ratio = 0.419). Among the animals that converted to a positive anti-A2 serology, efficacy reached 80.8% (95% CI: 37.6–94.1%, p = 0.001; risk ratio = 0.192). Xenodiagnosis has detected a reduction of 46.6% ( p = 0.05) in transmission to sand flies from vaccinated animals presenting anti-A2 positive serology. Conclusion: The Leish-Tec ® vaccine proved significantly effective for prophylaxis of CVL, after natural challenge assured by transmission of Leishmania parasites, in a highly endemic area. Noteworthy, this report has unveiled the complexity of performing a RFT for anti-CVL vaccines in Brazil, which may be helpful for designing of future studies.