Growth response and shedding of Leptospira spp. in urine following vaccination for leptospirosis in young farmed deer

Abstract

AIM: To investigate the effect of vaccination against Leptospira serovars Hardjo-bovis and Pomona on growth rate and shedding of leptospires in urine in rising 1-year-old farmed red deer. METHODS: In early March 2007, 230 female and 205 male, 3-month-old deer on five farms were treated with streptomycin then were randomly allocated to a control group (n = 218), or were vaccinated (n = 217) with a bivalent whole-cell killed leptospiral vaccine (Leptavoid-2) followed by a booster 4 weeks later. These animals were isolated from other 3-month-old deer on each property until May, when all vaccinated and control deer were combined with deer not treated with streptomycin, for maximum exposure to natural leptospiral challenge. Seroconversion was monitored in control deer against Leptospira borgpetersenii serovar Hardjo-bovis and Leptospira interrogans serovar Pomona using the microscopic agglutination test (MAT). A cut-off of ≥ 1:48 was used to identify a seropositive response to infection, and ≥1:24 to indicate a response to vaccination. Urine was collected from females in all groups and tested for shedding of leptospires using bacterial culture and real-time PCR. Male deer from vaccinated and control groups were weighed every 2–3 months to measure growth rate. RESULTS: In vaccinated female deer, antibody was present to Hardjo-bovis in 39–73% and to Pomona in 78–100% of animals in May, with titres ranging between 1:24–1:96 and 1:24–1:1536, respectively; control female deer were all serologically negative. In November, female control deer were seropositive to Hardjo-bovis on 4/5 farms (seroprevalence range 4–78%) but seronegative to Pomona on all farms. Between March and November mean growth rate was higher in vaccinated than control deer (26 g/day) on one farm (p = 0.049) that had the highest prevalence of seroconversion (78–88%) and urinary shedding (56%). Between August and November on 4/5 farms, when almost all seroconversions occurred, growth rates were higher in vaccinated than control deer (31 g/day; p = 0.011). Urinary shedding of leptospires was detected by culture and/or PCR in 8/34 (24%) unvaccinated control and 20/38 (53%) animals not treated with streptomycin on 2/5 farms; no shedding was detected in vaccinated deer. The average risk difference for shedding between vaccinated and control deer was –11% (95%CI = –18 to –4) (p = 0.001). CONCLUSION: Vaccination against Leptospira serovars Hardjo-bovis and Pomona was associated with higher liveweight gain and reduced urinary shedding of leptospires in young deer naturally challenged by Hardjo-bovis. The association with liveweight gain was evident on some but not all farms.