N Z Vet J. 2026 Aug 16:1-12. doi: 10.1080/00480169.2026.2708016. Online ahead of print.
ABSTRACT
AIM: To evaluate the efficacy of an inactivated, whole-cell Leptospira borgpetersenii serovar Tarassovi vaccine for prevention of urinary shedding of L. borgpetersenii strain Pacifica, in naturally challenged cattle.
METHODS: Three dairy farms in Northland, NZ, endemically infected with Pacifica, participated in a randomised controlled trial. Female calves (n = 291), aged 3-7 weeks, were randomly allocated in equal proportion to vaccinated and control groups. Two doses of test vaccine or saline were administered 4 weeks apart, then booster doses at 6 and 18 months. Blood and urine samples were collected once or twice between weeks 71 and 93, for determination of Tarassovi serology and shedding of pathogenic Leptospira by urine PCR, with subsequent amplicon sequencing of PCR-positive samples. For each farm separately, and pooled results from Farms 1 and 2, the proportion of animals shedding Leptospira in each group was compared statistically, and vaccine efficacy (VE) calculated.
RESULTS: A strong serological response to Tarassovi was demonstrated following two vaccine doses. Between weeks 81 and 93, when study heifers were 17-20 months old, a high proportion of unvaccinated controls were seropositive to Tarassovi (100%, 89% and 83% on Farms 1-3, respectively), consistent with exposure to Pacifica on each farm. On Farm 1, 13/30 (43%) controls and 0/29 vaccinates were shedding pathogenic Leptospira in urine, representing VE of 100% (95% CI = 73-100%; p < 0.001); Pacifica was confirmed in eight control animals, also representing efficacy of 100% (95% CI = 49-100%; p = 0.005). On Farm 2, 6/73 (8%) controls and 1/72 (1%) vaccinates were shedding pathogenic Leptospira; however, the difference was not significant (p = 0.116). On Farms 1 and 2 combined, 19/103 (18%) controls and 1/101 (1%) vaccinates were shedding pathogenic Leptospira, representing VE of 95% (95% CI = 70-100%; p < 0.001). On Farm 3, one unvaccinated control was found to be shedding, and no vaccinates. No other serovars of Leptospira were identified on any farm by urine PCR.
CONCLUSIONS: The Tarassovi vaccine conferred a very high level of protection (95-100% efficacy) against urinary shedding of L. borgpetersenii strain Pacifica in cattle, following two doses in calves and booster vaccinations at 6 and 18 months.
CLINICAL RELEVANCE: Given the serious zoonotic risk of leptospirosis, and the emergence of Pacifica as an important strain in NZ cattle, incorporation of an effective Tarassovi vaccine in standard leptospiral vaccination programmes is highly recommended.
PMID:42604856 | DOI:10.1080/00480169.2026.2708016
