Update on Leptospira hardjo-bovis Control in Beef Herds

Abstract

Leptospira hardjo bovis has emerged as the most common leptospiral infection of cattle in the United States and Canada. Its new name is Leptospira borgpetersenii serovar Hardjo (hardjo bovis), referred to as 'hardjo-bovis'. The main reason for the widespread prevalence of hardjo-bovis is that it is very efficiently transmitted by a chronic renal carrier/shedder state lasting a year or more. Also, traditionaJ 5-way leptospira vaccines have provided poor protection against hardjobovis because they contain a different hardjo organism, L. hardjo prajitno, which is not found in North America.

Experimental and natural infections of cattle with hardjo-bovis result in reproductive losses including embryonic death, abortion, stillbirths and weak calves. In addition, involvement of the mammary glands in hardjobovis infections can result in the "mastitis/flabby bag syndrome" of beef cattle. In the field, it has been extremely difficult to diagnose hardjo-bovis because traditional use of serology to diagnose leptospiral infections works very poorly for diagnosis of hardjo-bovis. As the maintenance host for hardjo-bovis, cattle mount a weak and transitory antibody response to infection. Identification of leptospires in urine correlated with antibody titers to hardjo-bovis and several other serovars of leptospira can overcome that obstacle to diagnosis. The combination of losses typically not noticed by ranchers, such as embryonic deaths, and the difficulties in diagnosing hardjo-bovis as the cause of obvious losses like abortions have made hardjo-bovis a "hidden disease".

Programs to control hardjo-bovis in beef herds are now possible because of the identification of two antibiotics that can clear the renal carrier state of hardjo-bovis and the availability of new leptospira vaccines that contain hardjo-bovis. Hardjo-bovis control programs have four parts: 1) enhancement of general herd resistance; 2) biosecurity; 3) antibiotic treatment to eliminate the renal carrier state; and 4) vaccination. The primary consideration in the decision on whether to implement a control program for hardjo-bovis in a beef herd is how great is the disease threat?

There are still gaps in our understanding of hardjo-bovis infection of beef herds. Diagnostic testing is still cumbersome. Hardjo-bovis-specific polymerase chain reaction (PCR) tests now being perfected will make possible accurate, fast diagnoses of hardjobovis in urine or tissue samples. That will greatly aid in identification of problem herds and in monitoring the success of control programs. Like most infectious diseases of cattle, clinical trials are needed in United States beef cow/calf operations to determine the herd-level economic impact of hardjo-bovis infection and efficacy of control programs.