Leptospirosis in cattle (Proceedings)
Leptospirosis is a broad range of clinical and sub-clinical disease problems caused by a number of Leptospira serovars. The majority of important serovars belong to the Leptospira interrogans group. Leptospira Hardjo is a major serovar associated with bovine abortions. Leptospira interrogans Hardjo is often referred to as type hardjo-prajitno while Leptospira borgpetersenii serovar Hardjo is referred to as hardjo-bovis. Both organisms are thought to be significant causes of bovine abortions and infertility. Additional serovars of L. interrogans of importance for cattle include Pomona, Canicola, Grippotyphosa, and Szwajizak.
Leptospira serovars can be the cause of infertility, early embryonic losses, and abortions in cattle. Abortions can occur from 4 months of gestation to term. Abortion rates are usually less than 10%; but on occasion can reach 50%. Cows can exhibit clinical signs such as hemoglobinuria, anemia, fever, and an atypical mastitis prior to aborting. Calves can rarely exhibit a hemolytic anemia (hemoglobinuria, anemia, and icterus) due to leptospiral infections.Pathogenesis
Leptospira organisms persist in the kidneys and genital tract of cattle and are common in all cattle-producing areas of the world. This allows for spread from carrier animals to susceptible animals. Spread through the urine is thought to be a primary mechanism for new infections. In newly infected cattle the organisms spread hematogenously to the gravid uterus up to 142 after infection. Abortion occurs 1-6 weeks after Leptospira Pomona infection and 1-3 months after Leptospira hardjo-prajitno infection. Leptospira hardjo-prajitno can persist in the reproductive tract for up to 22 days after calving.
Diagnosis is difficult at best. There are a large number of common diseases that result in abortion or infertility in cattle. Some of these conditions are BVD, IBR, Neospora, EBA (foothill abortion), Campylobacter, Trichomonosis, selenium deficiency, just to name some of the more common causes. Additionally, a definitive diagnosis of leptospirosis is difficult due to the fastidious nature of the organism and the fact that the bovine fetus dies well before the time it is expelled during abortion. The aborted fetus is characteristically autolysed, icteric, and edematous at presentation. There is often pneumonia, placentitis, and renal tubular necrosis. Occasionally, the leptospires can be demonstrated in the fetal tissues (kidney) by sliver stains, or fluorescent antibody techniques. Once in a while, the leptospires can be cultured—but this is an unusual situation. Diagnosis is usually based on serologic data and the elimination of other causes. Titers to Leptospira pomona may be greater than 1:12,800 in affected cows; however, titers to Leptospira hardjo-prajitno rarely exceed 1:3200 in cows that have aborted. While acute and convalescent sera are preferable samples, it is often difficult to accomplish in the practical setting.
Treatment and prevention
Oxytetracycline and streptomycin are the most commonly recommended antibiotics for therapy of leptospirosis. Both drugs must be used in an extra-label manner and because of the extended withdrawal time for streptomycin, OTC is usually the recommended product. Isolation of aborting cows is probably warranted in most instances—due to the colonization of the reproductive tract by leptospires.
The practical goal of vaccination is to decrease fetal losses and to minimize urinary shedding in the herd. Vaccination with a commercial 5-way Leptospira vaccine containing hardjo-prajitno did not prevent urinary shedding, renal colonization, or fetal infection after conjunctival instillation of hardjo-bovis. Therefore, cross-protection by vaccination may not be as effective as once thought.
A recent study (Wikse, et al Bov. Pract. 2007 pp. 15-23) shed some light on the prevalence of various leptospires in beef cattle in the U.S. The study examined beef cow/calf operations in 6 states (CA, FL, MS, MO, SD, and TX). The author found 42% of the 67 herds examined had results compatible with infection by L. borgpetersenii serovar Hardjo (hardjo-bovis). The range of prevalence in herds was from 8% (SD) to 58% (MS). In 5 of the states the prevalence ranged from 38% to 58%. These results highlighted the fact that this serovar was more common than expected. Currently, there is only one vaccine in the U.S. that contains this serovar (Spirovac®; Pfizer AH).
Other preventive methods might include rodent control and control of feral populations of swine and canine hosts that might spread their particular serovars to susceptible cattle.