Leptospirosis is a widespread bacterial disease that affects cattle globally, often leading to substantial economic consequences for livestock producers. The infection is primarily known for its negative impact on reproductive health, causing significant losses through infertility and late-term pregnancy failures. The disease can range from a subclinical carrier state to a severe, life-threatening illness in both dairy and beef operations. Understanding the organism and its transmission pathways is fundamental to controlling its spread within a herd.
The Bacterial Agent and Modes of Transmission
Leptospirosis is caused by spirochete bacteria belonging to the genus Leptospira. These bacteria are categorized into numerous serovars; two of the most significant for cattle are Leptospira hardjo and Leptospira pomona. L. hardjo is host-adapted, meaning cattle are the primary maintenance host and often become long-term carriers. L. pomona and others are incidental serovars, typically causing more acute disease outbreaks.
The bacteria thrive in warm, moist environments like stagnant water, mud, and wet soil, surviving for weeks or months. Transmission occurs when cattle contact contaminated water, feed, or soil via the urine of an infected animal. The organisms enter the body through mucous membranes or breaks in the skin.
Once inside, the bacteria migrate to specific organs, including the kidneys, uterus, and udder. Infected cattle develop a persistent kidney infection, allowing them to continuously shed the organism via urine. Direct transmission also occurs through contact with placental fluids, milk, aborted fetuses, or during breeding. Wildlife, such as raccoons and opossums, can serve as reservoir hosts, introducing the infection to cattle herds.
Recognizing Clinical Signs and Production Losses
The manifestation of leptospirosis varies significantly depending on the infecting serovar, the animal’s age, and its immune status. In calves, infection with incidental serovars like L. pomona often results in a severe, acute presentation. Clinical signs include high fever, lethargy, anemia, and jaundice. A specific sign is hemoglobinuria (bloody urine), caused by the destruction of red blood cells.
In adult cows, the disease commonly presents as a chronic or subclinical infection, primarily impacting reproductive function and milk production. Dairy cows may experience a sudden drop in milk yield, sometimes called “flabby bag” syndrome, where the udder becomes soft and the milk may appear thick, yellow, or blood-tinged. Reproductive losses are often associated with host-adapted serovars, causing infertility, embryonic death, and repeat breeding.
The most recognizable sign of reproductive failure is an abortion storm, typically occurring in the last trimester of pregnancy. Cows may also give birth to stillborn or weak calves. These failures result in major economic losses due to fewer calves, decreased milk production, and the costs associated with replacement animals.
Treatment Protocols and Herd Management
Veterinary intervention focuses on treating the clinical illness and eliminating the renal carrier state to stop bacterial spread. Antibiotics are the primary treatment, with long-acting formulations of oxytetracycline preferred for both acute cases and clearing chronic renal infection. Repeat treatments may be necessary to address the carrier state.
Dihydrostreptomycin is highly effective for eliminating the bacteria from the kidneys, preventing continued shedding in the urine. Other antibiotics, such as penicillin and amoxicillin, are also utilized, often for supportive treatment of acutely ill animals.
Supportive care, including fluid therapy and blood transfusions, is important for cattle with severe symptoms like hemolytic anemia. Immediate segregation of sick or recently aborted animals is a crucial herd management step to minimize contamination and reduce transmission. All antibiotic use must strictly adhere to mandated milk and meat withdrawal times.
Prevention Strategies and Zoonotic Considerations
Proactive prevention relies on vaccination, biosecurity, and environmental management. Vaccination is a foundational control measure, utilizing bacterins that contain killed Leptospira organisms. Commercial vaccines are polyvalent, targeting common serovars like L. hardjo and L. pomona.
Vaccination is typically administered in a primary course of two injections followed by annual boosting, often timed before the breeding season. While vaccines prevent clinical disease and reproductive loss, their efficacy in preventing renal colonization and bacterial shedding can vary. Environmental control involves restricting cattle access to contamination sources, such as stagnant ponds and shared watercourses.
Leptospirosis is a zoonotic disease, transmissible from animals to humans, sometimes referred to as Weil’s disease. Humans usually contract the infection through direct contact with the urine, blood, or tissues of infected animals, or indirectly from contaminated water or soil. Symptoms in humans range from mild, flu-like illness to severe conditions involving kidney failure or jaundice. Farm workers and veterinarians are at heightened risk of exposure. Safety precautions include wearing appropriate personal protective equipment (PPE) when handling aborted fetuses or cleaning contaminated areas, and maintaining good personal hygiene.