Herd prevalence and risk factors of Leptospira infection in beef cow/calf operations in the United States
Leptospira borgpetersenii Serovar Hardjo
Keywords:bovine, beef, hardjo-bovis, leptospirosis, antibodies, bacterial diseases, beef cows, calves, cows, disease prevalence, epidemiology, infections, risk factors, serovars
The herd prevalence of Leptospira borgpetersenii serovar hardjo infection and associated risk factors were determined for beef cow/calf operations in California, Florida, Mississippi, Missouri, South Dakota and Texas, USA. Three veterinary practitioners randomly selected in each state completed a questionnaire on herd management practices, and collected blood and urine from 10 to 15 cows in four randomly selected herds. Serum samples were tested for antibodies against Leptospira borgpetersenii serovars grippotyphosa, hardjo, icterohaemorrhagiae and pomona using the microscopic agglutination test. Urine sediments were stained with a non-serovar specific fluorescein-labeled anti-Leptospira antibody conjugate. Herd infection with L. borgpetersenii serovar hardjo was inferred if one or more cows had leptospires in their urine accompanied by either high antibody titres to the organism, or low titres to it and low titres against L. borgpetersenii serovars grippotyphosa, icterohaemorrhagiae and pomona. 28 (42%) of the 67 herds had results compatible with infection with L. borgpetersenii serovar hardjo. Herds in South Dakota had a significantly lower prevalence than herds in other states (P=0.01). A greater likelihood of infection with L. borgpetersenii serovar hardjo was found in herds with higher mean annual temperatures (P=0.02) and longer breeding seasons (P=0.02). It is recommended that altering risk factors that predispose herds to infection, such as shortening length of breeding season will increase the effectiveness of programmes to control this disease.