Transmissibility study of two vaccine candidates against bovine tuberculosis

GARCÍA, ELIZABETH ANDREA; ZUMÁRRAGA MJ,; BLANCO, FEDERICO C; CATALDI AA,; FERRARA MUÑIZ X,; BIGI F.; EIRIN ME

Congreso; 3rd International Congress of Asian-African Society of Mycobacteriology; 2021

AASM

INTRODUCTIONVirulence related proteins are attractive molecules to be proven as diagnostic antigens in infectious diseases. Some of them such as ESAT6, CFP10, 3615c have been widely characterized and used as specific antigens in bovine tuberculosis diagnosis. In the present study, rPhoPand rMce2B from M. boviswere assayed showing they induced cell-mediated immune response although with a lower responder frequency than the FP and PPDB in naturally infected cattle. However, this is a preliminary study that should be assayed in a larger sample size to further analyze these two experimental recombinant proteins as diagnostic antigens in the context of the potential use of M. bovisΔmce2 and M. bovisΔmce2ΔphoP vaccine candidates.MATERIALS AND METHODSExperimental design was performed followed a transmission model reported by Marquina-Castillo of active infection of M.tuberculosis and by Marfil et al in which different M.bovis strains were assayed through their capacity for aerosol transmission in mice.Groups of 3 non-inoculated+3subcutaneously inoculated mice with every strain(1.105CFU) were placed in the same cage (in duplicate).Necropsy was performed at 60 and 90 days postinoculation (dpi) in search of visible tuberculosis lesions in lungs and spleens and to determine bacterial load. Ethical approval: CICUAE-INTA-CICVyA:35/2017.RESULTSUnvaccinated group (sentinels): None of the animals presented visible tuberculosis lesions and no M. bovis was detectable neither at 60 nor 90 dpi.Vaccinated animals with M. bovis∆mce2 and M.bovis∆mce2∆phop:M. bovis vaccine candidates were isolated from spleen of all the inoculated mice, although no lesions compatible with tuberculosis were observed during necropsy.In general, the vaccine candidates were not isolated from lungs, except for one mouse inoculated with the M.bovis∆mce2∆phopstrain,exhibited a single CFU isolated at 60dpi.Vaccinated animals with the hipervirulent M.bovis04-303 and the parental strain of mutants M.bovis NCTC10772 (controls): M. bovis control strains were isolated from lungs of all inoculated mice (M. bovis 04-303 exhibited higher bacterial load),although no lesions compatible with tuberculosis were observed during necropsy.CONCLUSIONSThis study suggests the absence of transmissibility of these two experimental vaccine candidates M.bovis ∆mce2 and M.bovis ∆mce2∆phop in the conditions assayed.Recovery of viable control strains M.bovis04-303 and M.bovis NCTC10772 from lungs and spleen of inoculated mice suggests that the administration route would not alter the capacity of virulent strains to colonize organs.Predominantly, the candidate vaccines M.bovis∆mce2 and M.bovis∆mce2∆phop were isolated from spleen, suggesting that they would no have the ability to replicate in lungs in the experimental conditions assayed.Longer periods should be assayed to evaluate transmissibility of these novel experimental vaccine candidates against bovine tuberculosis in the murine model.