Serological Profile of a Nelore Herd Presenting Endemic Leptospirosis and Submitted to Vaccination

Abstract

The effect of vaccination on the serological profile of a closed Nelore beef cattle herd, endemically infected by leptospirosis was studied. Serum samples of 100% of the females (= 12 months to 8 years) were collected in Oct/1998 and examined by Microscopic Agglutination test (MAT) using 6 serovars of Leptospira spp.: icterohaemorrhagiae, canicola, pomona, grippotyphosa, hardjo and wolffi. After MAT, the animals were vaccinated and divided in 4 groups: I) hardjo/ wolffi MAT positive and vaccinated; II) hardjo/wolffi MAT positive and non-vaccinated; III) MAT negative and vaccinated and IV) MAT negative and non-vaccinated. The first vaccination was in Dec/1999 with reinforcement in Jan/2000; and revaccination in Out/2000. The 3 mL dose of a commercial vaccine containing the same 6 serovars was given subcutaneously. Serum samples were taken in Mar/2000 and Nov/2000 and examined the same way by MAT. The proportion of reagents in the 3 collections was: 62.5% (120/192), 77.4% (106/137) and 74% (91/123). Geometrical means titers were equal to 2.59, 2.34 and 2.15, respectively. Serological profile considering reagents frequency and pre-vaccination titers showed a bimodal distribution with 39.6% of negative results. After vaccination, there was an increase in the frequency of reactors, probably due to the seroconversion of negative heifers and cows, however, the vaccination did not elicit significant increase in the magnitude of the Hardjo or Wolffi titers. Instead, the geometric means in the whole herd, vaccinated and unvaccinated groups, showed a decreasing tendency. In postvaccination serological monitoring the progressive titer decrease would represent vaccine efficiency.