Borrelia burgdorferi infection in dairy cows, rodents, and birds from four Wisconsin dairy farms.

A combination of culture and subsequent spirochete identification with the polymerase chain reaction technique was used to identify cows, rodents, and birds infected with Borrelia burgdorferi. Animals were trapped on four Wisconsin dairy farms during the summer of 1990. Farms 1 and 2 were located in counties nonendemic for Lyme disease and Farms 3 and 4 were located in counties endemic for Lyme disease. The results of the rodent and bird samples were as follows given as the number yielding organisms number tested: Farm 1, 1/17 Mus musculus and 2/52 Peromyscus domesticus; Farm 2, 4/49 M. musculus, 1/2 P. maniculatus, 1/1 P. leucopus, and 1/35 P. domesticus; Farm 3, 0/27 M. musculus, 0/5 P. leucopus, 0/12 P. maniculatus and, 3/58 P. domesticus; and Farm 4, 1/24 M. musculus, 2/19 P. leucopus, 1/12 Microtus pennsylvanicus, and 0/17 P. domesticus. One P. leucopus and one M. musculus from Farm 2 were pregnant and fetal tissues from both were positive. Cow blood sample results were as follows: Farm 1, 7/47 in July, and 2/45 in August; Farm 2, 0/28 in August and 0/23 in October; Farm 3, 0/13 in July and 1/18 in August 29; and Farm 4, 3/45 in August. Ticks were found on rodents on Farm 4 and on one bird on Farm 3. Spirochetemic cows, rodents, and birds were found in non-Lyme endemic counties suggesting that alternate modes of transmission other than by ticks may be important. Transplacental transmission was shown in M. musculus and P. leucopus.