Effectiveness of a commercial leptospiral vaccine on urinary shedding in naturally exposed sheep in New Zealand.
L. borgpetersenii serovar Hardjo and L. interrogans serovar Pomona are endemic in New Zealand sheep. An effective vaccine and vaccination strategy would protect both humans and livestock. Four to 12 lambs were selected from each of eight farms (total=84, vaccinated group), while four to 16 lambs (total=98) served as unvaccinated controls. A commercial Hardjo/Pomona vaccine was given at 1-6 weeks of age, 5-11 weeks later and 33-67 weeks later on seven farms and at 18 weeks of age and 5 weeks later on the eighth farm. Vaccinates and controls were grazed together. Blood was regularly collected from the control group to assess flock exposure. Urine was collected from both groups 26-82 weeks after the second vaccination and tested by quantitative PCR. Seroprevalence in controls at the time of urine sampling ranged from 2.7 to 98.2% for Hardjo and from 0 to 54.1% for Pomona with seroconversion occurring 13 to 67 weeks after the second vaccination in all but one farm where exposure had happened by the time of vaccination. The shedding prevalence adjusted for clustering in farms was 45.1% [95% CI 17.6-72.7] (for an observed number of 50/98) in the control animals and 1.8% [95% CI 0.0-10.1] (for an observed number of 5/84) in the vaccinated animals. The vaccine was 100% effective on five farms where animals were vaccinated before 12 weeks of age and before natural exposure occurred, but the effectiveness was 80% [0-97] on one farm where the lambs were exposed before vaccination and 65% [9-87] to 80% [0-97] on one farm where the animals were fully vaccinated by 24 weeks of age. The overall vaccine effectiveness was 86.3% [63.6-94.8%] despite maternal antibodies in some flocks at first vaccination. Vaccination timing seemed to be crucial in achieving optimum reduction in shedding in urine in vaccinated sheep.
Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Private Bag 11222, Palmerston North 4442, New Zealand; EpiCentre, IVABS, Massey University, Private Bag 11222, Palmerston North 4442, New Zealand. Electronic address: E.Vallee@massey.ac.nz.
Emilie
E
Vallée
Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Private Bag 11222, Palmerston North 4442, New Zealand. Electronic address: A.L.Ridler@massey.ac.nz.
Anne L
AL
Ridler
EpiCentre, IVABS, Massey University, Private Bag 11222, Palmerston North 4442, New Zealand. Electronic address: C.Heuer@massey.ac.nz.
Cord
C
Heuer
mEpiLab, Hopkirk Research Institute, Infectious Disease Research Centre (IDReC), IVABS, Massey University, Private Bag 11222, Palmerston North 4442, New Zealand. Electronic address: J.M.Collins-Emerson@massey.ac.nz.
Julie M
JM
Collins-Emerson
mEpiLab, Hopkirk Research Institute, Infectious Disease Research Centre (IDReC), IVABS, Massey University, Private Bag 11222, Palmerston North 4442, New Zealand. Electronic address: J.Benschop@massey.ac.nz.
Jackie
J
Benschop
Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Private Bag 11222, Palmerston North 4442, New Zealand. Electronic address: P.R.Wilson@massey.ac.nz.
Peter R
PR
Wilson
D000818:Animals; D000907:Antibodies, Bacterial / Q000097:blood; D001428:Bacterial Vaccines / Q000008:administration & dosage / Q000276:immunology*; D002417:Cattle; D007919:Leptospira / Q000276:immunology* / Q000302:isolation & purification*; D007922:Leptospirosis / Q000453:epidemiology / Q000276:immunology / Q000517:prevention & control / Q000662:veterinary*; D009520:New Zealand / Q000453:epidemiology; D016036:Seroepidemiologic Studies; D012756:Sheep; D012757:Sheep Diseases / Q000276:immunology / Q000382:microbiology / Q000517:prevention & control; D014556:Urine / Q000382:microbiology*; D014611:Vaccination / Q000662:veterinary; D064166:Vaccine Potency
D000907:Antibodies, Bacterial; D001428:Bacterial Vaccines
Hardjo; Leptospirosis; Pomona; Shedding; Sheep; Vaccine effectiveness