Leptospirosis is a bacterial disease caused by spirochetes of the genus Leptospira. It affects a wide range of animals, including cattle, and can have substantial effects on animal health and farm productivity. Common serovars, such as Hardjo and Pomona, establish themselves in the kidneys and reproductive tracts of infected animals. The disease occurs globally, presenting a challenge for livestock management.
Transmission Pathways in Cattle
The primary source of Leptospira infection is contact with urine from an infected animal, either directly or through contaminated environments. Pastures, bedding, and soil can harbor the bacteria for weeks in warm, moist conditions. Contaminated water sources, such as ponds, streams, and areas with poor drainage, are also common reservoirs for transmission.
Chronically infected carrier animals are a major factor in maintaining the disease within a herd, continuously exposing other animals. Bulls can also transmit the bacteria through semen during natural breeding.
Wildlife and other livestock can introduce the infection to a cattle herd. Rodents, deer, raccoons, and pigs act as reservoirs, contaminating feed and water sources. The risk of transmission is heightened by wet weather, flooding, and co-grazing with other livestock like sheep, which can also be carriers.
Clinical Signs in Infected Cows
The clinical signs of leptospirosis in cattle vary depending on the infecting serovar, the animal’s age, and its immune status. Many infections are subclinical, meaning animals appear healthy but suffer from reduced productivity and act as carriers. When symptoms do appear, they often manifest as reproductive problems.
Reproductive failure is a primary indicator of the disease. Signs include:
- Abortions, which occur in the last three months of pregnancy
- Stillbirths and the birth of weak calves
- Infertility and reduced conception rates
- Irregular heat cycles requiring multiple breeding attempts
A sudden drop in milk production, or “milk drop syndrome,” is another sign in lactating cows. The milk may appear yellowish or thickened, but the udder is not hot or swollen as with mastitis. In acute cases, especially in calves or unexposed adults, more severe systemic signs can occur, including fever, lethargy, jaundice, and reddish-brown urine from kidney damage.
Diagnostic Approaches and Treatment Protocols
Veterinarians use several methods to diagnose leptospirosis, as its signs can mimic other diseases. Serological testing, like the Microscopic Agglutination Test (MAT), detects antibodies in blood serum. A diagnosis often requires paired samples taken two to four weeks apart to show a rising antibody level, indicating an active infection.
Direct detection of the bacteria is another option. Polymerase Chain Reaction (PCR) tests can identify Leptospira DNA in urine, milk, or fetal tissues. While bacterial culture can isolate the organism, it is too slow for routine diagnosis. A bulk milk tank can also be tested to screen a dairy herd for exposure.
Treatment focuses on eliminating the infection and stopping bacterial shedding in urine. Antibiotics such as streptomycin, oxytetracycline, ceftiofur, and tulathromycin are effective. For acutely ill animals, early treatment may be combined with supportive care like fluids to improve the outcome and prevent a chronic carrier state.
Strategies for Prevention and Herd Management
A prevention strategy for leptospirosis is centered on vaccination and biosecurity. Vaccination is a primary tool for controlling the disease. Multivalent vaccines protecting against several serovars are available, with programs involving an initial course for young cattle followed by annual boosters before the breeding season.
Biosecurity measures are also necessary to prevent the spread of bacteria. These include:
- Quarantining and testing all new animals before introducing them to the herd
- Controlling wildlife access to feed storage and implementing rodent control
- Preventing co-grazing with other potentially infected livestock like sheep
- Avoiding the use of untested bulls for breeding
Environmental management helps reduce exposure. This involves providing clean water from troughs rather than ponds or streams and improving drainage in pastures to reduce standing water. Fencing off swampy areas also limits exposure.
Economic and Public Health Significance
Leptospirosis in cattle leads to significant economic losses for producers. The most substantial impacts come from reproductive failure, including abortions, stillbirths, and infertility. Decreased milk production in dairy cows further reduces profitability, along with costs from diagnostics, treatments, and culling of chronically infected animals.
Beyond its agricultural impact, leptospirosis is a zoonotic disease, meaning it can be transmitted to humans. Farmers, dairy workers, veterinarians, and slaughterhouse employees are at a higher risk of exposure through contact with infected urine or contaminated environments. The bacteria can enter the human body through breaks in the skin or the mucous membranes of the eyes, nose, or mouth.
In humans, the disease presents as a flu-like illness with fever, severe headaches, and muscle pain. While many cases are mild, some can progress to a more severe condition known as Weil’s syndrome, which affects the kidneys and liver. Using personal protective equipment like gloves and boots, along with diligent hand washing, is recommended when handling potentially infected animals.