Survey to estimate prevalence of Leptospira interrogans infection in mature cattle in the United States.

A total of 5,142 kidney tissue samples and 5,111 serum samples from mature cattle in 49 states and Puerto Rico were collected at slaughter. Age of cattle ranged from 1 to 16 years (mean, 6.6 years). Leptospires were isolated from 88 (1.7%) kidney tissues, and 2,493 (49%) sera contained antibodies against 1 or more of 12 Leptospira interrogans serovars. Leptospires were observed by immunofluorescence in 41 (0.8%) kidney tissues. Using agglutinin-absorption tests, 73 (83%) isolates were identified as serovar hardjo, 11 (12.5%) as serovar pomona, and 4 (4.5%) as serovar grippotyphosa. By use of restriction endonuclease analysis studies of chromosomal DNA, all isolates differed from reference serovars but were identical to strains previously isolated from cattle or swine in the United States. Of the serovar hardjo isolates, 85% were identical to restriction endonuclease analysis type (genotype) hardjo-bovis A and 11 (15%) were identical to genotype hardjo-bovis B. Serovar pomona isolates were identical to genotypes kennewicki A (64%) or kennewicki B (36%), and serovar grippotyphosa isolates were identical to the RM 52 strain. Isolation rates were significantly (P less than 0.001) higher for beef cattle than for dairy cattle and were higher (P less than 0.001) for bulls than for cows. Combined culture and immunofluorescence results indicated that 2% of mature cattle were renal carriers of leptospires.