Brucellosis in Ontario: a case control study.

Data from cattle herds infected with brucellosis and from control (noninfected) herds were collected and analyzed using case control techniques. It appeared that herds located close to other infected herds and those herds whose owners made frequent purchases of cattle had an increased risk of acquiring brucellosis, particularly those who made purchases from other herds or from cattle dealers. Infected herds had a lower level of vaccination than noninfected herds. However, the percentage vaccinated was highly variable in each group. Vaccination per se did not appear to adversely influence the interpretation of serological test results nor did it appear to protect the individual animal. Once infected, the time required to become free of brucellosis was increased by large herd size and/or loose housing. Closed herds also took longer to become brucellosis free than more open herds. The percentage of animals removed from the herd was increased by active abortion. Those herds with multiple serological reactors (positives and questionables) at the first herd test after the imposition of quarantine had the highest percentage of cattle removed.