Leptospirosis in cattle is an economically important disease, and current thoughts are that approximately 75% of the UK cattle population has been exposed. It can also be spread from cattle to people causing severe illness. It is caused by the spirochaete bacteria Leptospira hardjo and in the environment this organism survives well in moist conditions and temperatures of over 10°c for up to 6 months. In the UK this covers from Spring to early December and is when spread of infection is at its highest.
When cattle are infected with Leptospira hardjo the bacteria settles in the cows' reproductive tract and kidneys. Cattle are maintenance hosts of Leptospira hardjo and following infection are capable of spreading the infection for many months or years. The main source of spread is through urine, but spread can also occur venereally through infected semen in bulls and through abortion material in cows. The bacteria enters the animal through mucosal surfaces, including eyes, mouth, nose and genital tract.
Factors which increase the risk of cattle becoming infected with leptospirosis include buying in cattle, using a bull rather than AI, cattle and sheep co-grazing and access to stagnant water and watercourses.
When a cow becomes infected the incubation period of the disease is between 3 and 20 days, and a range of symptoms can be seen. Some may only have a raised temperature and be slightly off colour for a short while, with the disease going unnoticed. In other cattle, symptoms of the disease can be more severe and appear when the bacteria localise in the reproductive tract, kidneys and udder of infected cattle. The effects seen include infertility, abortion and milk drop known as ''flabby bag''. With flabby bag all 4 quarters are affected, the bag becomes soft, and the milk goes yellow taking on a clotty/colostrum consistency. Without treatment recovery does occur, but takes up to 10 days. In some cows, particularly those in late lactation, the cow may just dry off.
The severity of symptoms seen depends on whether the herd is totally naïve or endemically infected. In a totally naïve herd, introduction of the disease will result in severe disease with abortion storms and milk drop potentially affecting over half of the herd within a 2 month period. In an endemically infected herd losses are more insidious, often with lower conception rates and small numbers of abortions, still births, and weak, infected calves being born. Calves infected at birth and apparently healthy can also go on to be infertile due to localisation of the infection in the uterus and oviducts.
When leptospirosis is suspected there are specific tests which can be done to confirm the presence of disease. In beef herds leptospirosis can be diagnosed by taking blood tests from cows, or in dairy herds blood tests can also be used or bulk milk samples can be taken which give an indication as to the level of disease in a herd.
Treatment of cows which are clinically ill with leptospirosis can be under taken. Antibiotics which are of use are either tetracyclines, or dihydrostreptomycin. However on a herd basis this is both expensive, and will not prevent re-infection.
Control of Disease
The disease is best controlled by vaccination. When herds are being vaccinated for the first time, 2 doses of vaccine should be given 4 to 6 weeks apart, and after that cattle should be vaccinated annually. As the disease is most prevalent from Spring to early Winter the best time of year to vaccinate is Spring. Calves born to vaccinated dams will have some protection from maternal antibodies until about 3 to 4 months of age, after which time they will be at risk. Heifer calves should be vaccinated before they are to be bred from for the first time, and for maximum protection they should be vaccinated from 3 months of age and prior to turnout.
Disease control should be considered not only for the beneficial health effects to the herd, but also for the safety of the people who are working with the cattle. This is because leptospirosis can be passed on to people through contact with contaminated urine and abortion material. Milkers, vets and AI technicians are particularly at risk. The infection can cause severe illness in people withs symptoms including flu-like illness with prolonged recovery, raised temperature, headaches, meningitis, severe abdominal pain, jaundice and occasionally renal failure. COSHH regulations state that a risk assessment must be carried on every infected farm to determine the risk of leptospirosis and adequate steps should be taken to control and eliminate the disease if found to be present.