Leptospirosis is a widespread bacterial disease affecting cattle globally. Caused by Leptospira bacteria, it leads to significant health and productivity issues within herds. This infectious condition is zoonotic, meaning it can transmit between animals and humans, posing a public health concern. The disease often results in economic losses for producers, particularly impacting reproductive performance.
Understanding Leptospirosis in Cattle
Leptospirosis in cattle is caused by pathogenic Leptospira bacteria, also known as spirochetes, which are flexible and spiral-shaped. These bacteria can infect a wide range of mammals. Cattle typically become infected through direct contact with urine from infected animals, or indirectly via contaminated water, soil, or feed. The bacteria enter the host through mucous membranes or breaks in the skin.
Once inside the animal, leptospires spread through the bloodstream, localizing in organs like the kidneys, uterus, and udder. Infected animals can shed bacteria in their urine for extended periods, even without showing obvious illness, acting as carriers. Moist environments with a neutral pH, such as damp soil and stagnant water, allow leptospires to survive outside a host for days to weeks. Flooding can also spread the bacteria to uninfected farms.
Specific Leptospira serovars affect cattle, with some being host-adapted and others incidental. Leptospira borgpetersenii serovar Hardjo (hardjo-bovis) is a host-adapted strain for which cattle are maintenance hosts. It colonizes the kidneys and reproductive tract, leading to chronic infections and long-term shedding in urine. Leptospira interrogans serovar Pomona is an incidental serovar, often carried by pigs, and can be introduced to cattle herds through contact with contaminated effluent or infected wildlife.
Recognizing the Signs in Cattle
Leptospirosis in cattle presents with varied clinical signs, from acute illness to chronic or subclinical forms. Signs depend on the infecting Leptospira serovar, animal age, and immune status. With host-adapted strains like L. borgpetersenii serovar Hardjo, infection may go unnoticed, with reproductive problems being the first indication.
Reproductive issues are a primary manifestation, causing economic losses. These include mid to late-term abortions, often in the last trimester, sometimes weeks or months after initial infection. Stillbirths and the birth of weak or premature calves are also common. Herds experiencing their first outbreak might see abortion rates as high as 30%, while endemically infected herds might observe around 5%.
Beyond abortions, reduced fertility, embryonic death, and increased repeat breeding are associated with chronic leptospirosis. In dairy cattle, an acute form can cause a sudden drop in milk production, known as “milk drop syndrome” or “flabby bag.” The udder may feel soft, and the milk might appear thickened, yellowish, or blood-tinged.
Other acute signs, more common in calves or with incidental serovars like L. interrogans serovar Pomona, include high fever, loss of appetite, and lethargy. Jaundice (yellowing of mucous membranes) and hemoglobinuria (reddish-brown urine due to red blood cell breakdown) can occur in severe cases. A combination of these symptoms, especially reproductive failures, indicates a need for investigation.
Management and Prevention Strategies
Diagnosing leptospirosis in cattle involves multiple methods, as clinical signs vary and are often subclinical. Serological tests, such as MAT or ELISA, detect Leptospira antibodies in blood or milk. While a high antibody titer (e.g., ≥1:800 for MAT) suggests recent infection, serology alone may not identify chronically infected animals, as antibody levels can fluctuate or be low in carriers.
To confirm active infection or carrier status, direct bacterial detection is used. PCR tests identify Leptospira DNA in blood (early infection), urine (7-10 days post-onset), or tissue samples, including aborted fetuses and placentas. Bacterial culture, the definitive diagnostic method, is challenging due to slow Leptospira growth, requiring specialized media and prolonged incubation (up to 16-26 weeks).
Treatment involves antibiotics like streptomycin, oxytetracycline, or penicillin, especially when administered early in the acute phase. A single intramuscular injection of streptomycin at 25 mg/kg can eliminate the renal carrier state. Supportive care, including fluid therapy, may also be provided to manage symptoms like dehydration or appetite loss.
Prevention strategies are important for controlling leptospirosis. Vaccination is a primary tool, with multi-valent vaccines available covering common serovars like L. borgpetersenii serovar Hardjo and L. interrogans serovar Pomona. A common protocol involves two doses 4-6 weeks apart, followed by annual boosters, often given one month before breeding. Vaccination reduces disease severity, prevents shedding, and protects against reproductive losses and milk drop.
Biosecurity measures are also important to prevent disease introduction and spread.
Biosecurity Measures
Fencing off natural water sources like ponds and streams, which can be contaminated by wildlife or other livestock, helps limit exposure.
Controlling rodents and other wildlife, which can act as carriers, by repairing buildings, securing feed, and managing waste, reduces environmental contamination.
Isolating newly acquired animals for at least 28-30 days upon arrival, away from the main herd, allows for observation and testing before integration.
Proper disposal of aborted fetuses and placental tissues is important, as these materials are contaminated with bacteria.
Maintaining good hygiene in barns and pens, regularly cleaning and disinfecting equipment, and avoiding overcrowding can minimize bacterial spread within the herd.
These comprehensive measures, in conjunction with veterinary consultation, help defend against leptospirosis.
Zoonotic Risk to Humans
Leptospirosis is a zoonotic disease, meaning it can transmit from infected animals to humans. Humans contract the infection through direct contact with infected animal urine, blood, or tissues, or indirectly through contaminated water, soil, or feed. The bacteria enter the human body through mucous membranes (eyes, nose, mouth) or cuts in the skin.
Occupations with increased exposure risk include farmers, veterinarians, abattoir workers, and those involved in outdoor activities where contaminated water may be present. Human symptoms range from a mild flu-like illness (fever, chills, headaches, muscle aches) to severe forms affecting kidneys, liver, or central nervous system. Severe cases can develop jaundice, kidney failure, liver failure, or meningitis. Protective measures for individuals working with cattle include wearing gloves, boots, and overalls, avoiding contact with urine and birth products, and practicing good personal hygiene, such as thorough handwashing after animal contact.