Bovine tuberculosis in Swedish deer farms: epidemiological investigations and tracing using restriction fragment analysis.

Bovine tuberculosis was eradicated from Sweden after a programme lasting many years. By 1991, no tuberculosis in wildlife had been discovered for 50 years and the last case in cattle had occurred 13 years before. In 1991, the disease was identified in a herd of farmed fallow deer (Dama dama) and over the next three years nine other infected herds were identified. Investigation revealed that all the infected deer were either deer that had been imported into Sweden from the United Kingdom in 1987 or had been in contact with them. Restriction fragment analysis of eight isolates of Mycobacterium bovis from five of the herds showed that the isolates had identical patterns of DNA fragments, which indicated a common source of infection. Among more than 800 isolates of M bovis that have been analysed, these patterns were identical to those of only two previous isolates, both of which came from British deer. These results indicate that the eight Swedish strains of M bovis and the two British strains may have a common source of infection.