Leptospirosis is an infectious disease transmitted from animals to humans (a zoonosis), and from animal to animal, through cuts or cracks in the skin or through the mucous membranes of the eyes, nose or mouth. It is present in almost all warm-blooded mammals, including farm, domestic and feral animals. Leptospirosis spreads easily, and is caused by bacteria known as leptospires that multiply in the kidneys of animals and are shed in the urine. The bacteria thrive in moist or wet conditions and can survive for months.
Two different leptospiral species (L. borgpetersenii and L. interrogans) have been isolated from NZ animals. Leptospira are also commonly classified by their serological characteristics (serovars). In this country these are L. borgpetersenii serovars Hardjobovis, Ballum, Balcanica and Tarassovi and L. interrogans serovars Pomona and Copenhageni. In NZ serovars Hardjobovis, Pomona, Ballum and Tarassovi are currently those most commonly identified with disease in humans whilst Hardjo bovis and Pomona are the types most significant in livestock.
Cattle are infected by grazing pasture or drinking water contaminated with infected animal urine. Cattle may be at risk of the Pomona serovar when there are unvaccinated pigs on the dairy farm, and are more likely to be cross-infected with Hardjo or Pomona from sheep through farm management practices like rotational grazing of different stock.
Introduced animals like dairy heifers or a new stud bull may bring infection if not previously vaccinated.
Cattle are primary hosts of the Hardjo serovar, which causes minor health effects. They appear to be secondary hosts for Copenhageni, carried by rats, which has the most health impact on calves. They are secondary hosts of Pomona which can cause severe illness, including: mastitis and loss of milk production, abortion storms, and death (especially in calves). Acute leptospirosis occurs mainly in calves. Clinical signs may include: fever, anorexia or loss of appetite, and conjunctivitis. In adult cattle the first signs of illness in many cases are: reproductive losses (stillbirth or neonatal death, early foetal loss or abortion), sudden decrease in milk production, and jaundice (in severe cases).
Humans can catch leptospirosis from infected animal urine. Even a splash or fine spray of urine or indirect contact with urine-contaminated water can spread large numbers of leptospires. Cuts, sores and skin grazes increase the risk of infection, as does licking your lips and eating or smoking before washing and drying your hands. People at higher risk are those working near the rear of the animal, such as:
Humans affected by leptospirosis, either mildly or severely, may not show symptoms. Infection may just feel like a bad case of the flu, with headaches and fever. Severe cases can result in permanent complications, usually kidney or liver damage. Some people may not be able to work for months and, in severe cases, be unable to return to running their farm.
The best option for managing risk is via a vaccination programme with a product such as Lepto 3-Way®, as leptospirosis is difficult to eliminate. At least 90% of New Zealand dairy farmers already vaccinate their breeding stocks to protect themselves and their workers from infection, however vaccinated herds may keep shedding if vaccination isn’t carried out regularly or is left too late.
For more information on leptospirosis, talk to your vet and visit saferfarms.org.nz