Antibody responses induced by Leish-Tec®, an A2-based vaccine for visceral leishmaniasis, in a heterogeneous canine population

Abstract

Zoonotic visceral leishmaniasis (VL) is a widespread disease, and dogs are the main reservoirs for human parasite transmission. Hence, development of an effective vaccine that prevents disease and reduces the transmission of VL is required. As euthanasia of seropositive dogs is recommended in Brazil for VL epidemiological control, to include anti-VL canine vaccines as a mass control measure it is necessary to characterize the humoral responses induced by vaccination and if they interfere with the reactivity of vaccinated dogs in serological diagnostic tests. Leish-Tec(®) is an amastigote-specific A2 recombinant protein vaccine against canine visceral leishmaniasis (CVL) that is commercially available in Brazil. Here, we tested the immunogenicity of Leish-Tec(®) in a heterogeneous dog population by measuring A2-specific antibody responses. Healthy dogs (n=140) of various breeds were allocated to two groups: one group received Leish-Tec(®) (n=70), and the other group received a placebo (n=70). Anti-A2 or anti-Leishmania promastigote antigen (LPA) antibody levels were measured by ELISA in serum samples collected before and after vaccination. An immunochromatographic test (DPP) based on the recombinant K28 antigen was also used for serodiagnosis of CVL. Vaccinated animals, except one, remained seronegative for anti-LPA total IgG and anti-K28 antibodies. Conversely, seropositivity for anti-A2 total IgG antibodies was found in 98% of animals after vaccination. This value decreased to 81.13% at 6 months before rising again (98%), after the vaccination boost. Anti-A2 IgG2 and IgG1 titers were also increased in vaccinated animals relative to control animals. These data indicate that Leish-Tec(®) is immunogenic for dogs of different genetic backgrounds and that humoral responses induced by vaccination can be detected by A2-ELISA, but do not interfere with the LPA-ELISA and DPP diagnostic tests for CVL.

Epitope mapping of recombinant Leishmania donovani virulence factor A2 (recLdVFA2) and canine leishmaniasis diagnosis using a derived synthetic bi-epitope

“…A recent study has demonstrated that humoral response to rec Ld VFA2 in dogs is associated, presumably, with protective immunity against Leishmania spp . parasites [26], however, B-cell epitope analysis with antibodies elicited in dogs were not conducted. Thus, researches for diagnosis or vaccines applied to dogs could be eventually improved by the identification of B-cell epitope mapping of Ld VFA2, using homologous antibodies.…”

Can vaccines against canine visceral leishmaniasis interfere with the serological diagnostics recommended by the Brazilian Ministry of Health?

“…In studies conducted by the manufacturers of the Leish-Tec ® and Leishmune ® vaccines using the EIE technique for the detection of humoral response to homologous proteins (A2 and FML, respectively), TESTASICCA et al (2014) reported positivity of 98% in animals immunized with Leish-Tec ® ; this value decreased to 81% after six months, and returned to 98% two months after the boosting vaccine dose (14 months after the priming vaccination). Similarly, NOGUEIRA (2005) observed seropositivity of 100% in dogs immunized with Leishmune ® for up to 11 months.…”

“…With respect to the positivity assessment of the tests used by the MH, seroconversion in dogs vaccinated with Leishmune ® was reported in DPP and EIE 6 months after the vaccination protocol (MARCONDES et al, 2013). In contrast, dogs immunized with LeishTec ® , monitored up to 14 months after the priming vaccination, did not present seroconversion in the MH tests (TESTASICCA et al, 2014).…”

“…As DPP utilizes a recombinant antigen different from those that compose both vaccines, this positivity could occur owing to cross-reaction with other trypanosomatids or a natural Leishmania infection in connection with a possible flaw in the immunity induction by the vaccine (TESTASICCA et al, 2014). As the main objective of this study was to assess whether both vaccines would be able to induce an erroneous CVL diagnosis using the diagnostic protocol recommended by the MH, only dogs with positive results in the DPP were also tested in the EIE.…”

Visceral leishmaniasis in Brazil: rationale and concerns related to reservoir control

“…Unfortunately, some of these potential control strategies are not yet available or require additional scientific evidence for proving their effectiveness. 20 There are dog vaccines in Brazil that have shown to be immunogenic and decrease symptoms and mortality of vaccinated dogs; 4 , 7 however, there is no solid evidence that the transmission from vaccinated dogs to sand flies has been decreased to a level that would effectively and significantly protect humans from infection.…”