Leptospirosis is a common bacterial disease affecting cattle globally, caused by members of the genus Leptospira. It is a significant concern for the agricultural industry due to its direct impact on herd productivity. Economic losses stem from reproductive failure, including infertility and abortion, and reduced milk yield in dairy herds. This widespread infection often goes undetected until a major outbreak of reproductive issues occurs, necessitating effective management practices to mitigate this threat.
The Bacterial Cause and Transmission Routes
The causative agent is a spirochete bacterium from the genus Leptospira, with multiple variations known as serovars. The most common strain in cattle is the host-adapted Leptospira hardjo (including L. hardjobovis and L. hardjoprajitno). These strains establish a chronic infection within the kidneys and reproductive tract, leading to a long-term carrier state.
Transmission occurs primarily through contact with the urine of infected animals, which can shed the bacteria for months or years. Infected urine contaminates the environment, allowing the bacteria to survive in damp soil and stagnant water sources. Cattle become infected when the bacteria enter the body through breaks in the skin or contact with mucous membranes.
Incidental serovars, such as L. pomona or L. grippotyphosa, are adapted to hosts like rodents or wildlife. Transmission of these strains occurs when cattle access water or pasture contaminated by the urine of alternative hosts. Introducing a persistently infected carrier animal, such as a new purchase or a bull shedding bacteria in its semen, poses a high risk for spreading the infection.
Recognizable Signs in the Herd
The clinical presentation varies significantly depending on the infecting serovar, the animal’s age, and its immune status. Infections caused by the host-adapted L. hardjo strain are typically subclinical, manifesting primarily as chronic reproductive problems in adult cows. The most common sign is reproductive failure, including infertility, increased embryo loss, and stillbirths.
Abortion is a frequent outcome, generally occurring late in gestation, often during the last three months of pregnancy. Calves that survive the infection in utero may be born premature and weak, often failing to thrive. These chronic reproductive issues may be the only noticeable signs of the disease in a mature herd.
Acute disease outbreaks are associated with non-host-adapted serovars, such as L. pomona, or they may affect young calves. In calves, acute signs include high fever, depression, jaundice, and bloody urine, indicating red blood cell destruction. In dairy cows, an acute infection causes a sudden drop in milk production, resulting in a soft, flabby udder. The milk may appear thick, yellow, or blood-tinged.
Control and Prevention Strategies
Control requires a multi-faceted approach combining vaccination, biosecurity, and environmental management. Vaccination prevents new infections and minimizes bacterial shedding. The protocol involves a primary course of two vaccine doses, spaced four to six weeks apart, followed by annual booster shots.
Heifers should complete vaccination before their first breeding. In active herds, revaccination every six months may be necessary to maintain high immunity. Vaccines must cover the specific serovars prevalent locally, especially L. hardjo.
Biosecurity prevents the introduction of bacteria. New animals should be isolated and may require testing or antibiotic treatment before joining the main herd. Using artificial insemination (AI) is often safer than using natural service bulls, as bulls can shed bacteria in semen. Sick or aborting animals must be isolated immediately.
Environmental management focuses on eliminating bacterial survival niches. Fencing off cattle access to shared watercourses or swampy areas is effective, as stagnant water is ideal for bacterial survival. Control of wildlife and rodents is also important, as they introduce incidental serovars. If an acute outbreak occurs, antibiotic treatment can be administered under veterinary direction to clear the renal carrier status.
Human Health Concerns
Leptospirosis is a zoonotic disease, representing a direct public health risk. Agricultural workers, veterinarians, and abattoir employees are at the highest occupational risk due to frequent contact with cattle and contaminated environments. Humans contract the infection through direct contact with infected urine, reproductive fluids, or contaminated soil and water.
The bacteria can enter the human body through breaks in the skin or through the eyes, nose, or mouth. In people, the disease often presents as a mild, flu-like illness with symptoms including fever, headache, and muscle aches. In severe cases, the infection can progress to Weil’s disease, characterized by jaundice, kidney failure, and internal bleeding.
Protective measures are necessary to minimize human exposure. Personnel should use appropriate personal protective equipment (PPE), such as gloves, boots, and eye protection, when handling sick animals or working in contaminated areas. Strict hygiene practices, including thorough handwashing after contact with animals, reduce the risk of human infection.