Detection and control of brucellosis in reindeer vaccinated with Brucella suis biovar 3

Abstract

The objective of this research was to provide a vaccine for the control of brucellosis in reindeer, that allows serologic discrimination between vaccinated and infected animals. Three vaccines were tested: (1) Brucella suis 1, (2) B. suis 3, and (3) A rough mutant of the infective strain, B. suis 4. All were heat-killed and prepared in Freund's incomplete adjuvant. Each vaccine was administered to four animals. All vaccines stimulated the production of high levels of antibody in Rangifer that were maintained for the 483-day experiment. Significant delayed-type hypersensitivity reactions were seen in all vaccinated Rangifer. Both B. suis 1 and B. suis 3 vaccines allowed serologic discrimination between vaccinated and infected Rangifer. This was accomplished by means of an indirect ELISA (enzyme-linked immunosorbent assay). This test used whole cell B. melitensis and B. abortus as A and M-dominant antigens. Distinction could be made between vaccinated and infected reindeer based on a percentage difference in spectrophotometric abosorbance values obtained with these antigens. The B. suis 3 vaccine provided the best discrimination. Eighty-nine percent of 117 reindeer were correctly classified as either B. suis 3-vaccinated or B. suis 4-infected. Discrimination between vaccinated and infected reindeer was sufficient to allow assessment of the prevelance of brucellosis and vaccinated herds. In addition, the ELISA was more sensitive than standard agglutination tests in identifying reindeer with exposure to B. suis. The B. suis 3 vaccine was further evaluated in a challenge of 7 vaccinated reindeer. The vaccinated group consisted of 5 pregnant adults and 2 8-month-old female calves. These reindeer were challenged with $3.16\times10\sp7$ colony forming units of B. suis 4 at 63 days post-vaccination. Five pregnant adults and 1 female calf served as experimental controls. B. suis 4 was isolated from 3 of 7 vaccinated reindeer (43%) at the time of necropsy. B. suis 4 was isolated from the aborted fetus of 1 of the infected vaccinates. Another infected vaccinate bore a healthy calf for which B. suis 4 could not be isolated. All control reindeer were infected and all 5 adults aborted. B. suis 4 was isolated from all 5 fetuses. The B. suis 3 vaccine provided significant protection against infection and abortion in reindeer challenged with B. suis 4.