Leptospirosis is endemic in many beef herds and has important public health implications.
There is evidence of the disease in 63% of beef herds, but it is difficult to know if this is increasing, as diagnostic tests can not distinguish between vaccinated herds and infected herds.
The disease was the topic of one of Scarsdale Vets’ recent Beef Talks. Farmers Weekly asked Scarsdale vet Vicki Rhodes about the disease, its control and prevention, and how to minimise risk to human health.
What is leptospirosis?
Leptospirosis is a common bacterial infection in beef and dairy herds, causing infertility and abortion. It is caused by Leptospira hardjo, which is from the family of bacteria called spirochetes.
How is it contracted by cattle?
Cattle are the maintenance host for leptospirosis, which means they can harbour infection in their kidneys for years. Infected cattle then excrete these bacteria in their urine and become a source of infection for other cattle in the same herd and/or pasture.
Infection arises from contact with infected urine, or the products of abortion. Infection occurs when the bacteria comes into contact and crosses mucous membranes, including the eyes, mouth, nose and genital tract.
Open herds, sharing bulls, mixed grazing with sheep (which can carry and excrete Leptospira hardjo) and shared watercourses can all contribute to the spread of leptospirosis. Disease is spread most often during the spring and summer months while cattle are in the pastures.
What are the clinical symptoms in cattle?
Clinical signs depend on where in the cow’s body the bacteria has localised to. These areas typically include the reproductive tract, kidneys and udder. A sudden drop in milk yield occurs two to seven days after infection of susceptible cows.
The udder becomes soft and flabby, with colostrum-like secretions or blood-tinged milk in all quarters. Signs may be mild and go undetected, but some cows become lethargic and stiff with a fever and have a reduced appetite. However these might be only subtle signs which can go unnoticed.
Abortion may occur three to 12 weeks following infection, with most abortions occurring during the final three months of pregnancy. Infection may also produce premature and weak calves.
There is circumstantial evidence of infertility following isolation of Leptospira Hardjo from the reproductive tract of a high percentage of repeat breeder cows.
Infertility symptoms can be seen either with infection being picked up prior to bulling, or from a congenital infection. Leptospira Hardjo may also cause embryonic death.
Venereal (sexual) transmission is possible but may not adversely affect the pregnancy rate because Leptospira Hardjo is killed by uterine defences during oestrus.
Split-herd vaccination trials have shown improved fertility parameters in vaccinated cows in herds with endemic Leptospira Hardjo infection.
What is the broader and economic impact on a herd?
The primary economic impact is through abortion as the main aim of a beef cow is to produce one live calf per year. Late-on abortion will either mean that the cow will remain empty until the next breeding period (while still having to be fed) or will be culled.
How do you test for it?
A blood sample is sent to an external lab to look for antibodies to Leptospira Hardjo; this can either be diagnostic in the case of a cow that has aborted, or we can test a group of youngstock to assess the status of the herd. At Scarsdale Vets we recommend testing six animals aged nine to 12 months from each management group every year – TB testing is the ideal time to do this.
Can it be treated in cattle?
Control of Leptospira hardjo in cattle herds relies on a combination of management decisions to reduce risk of infection, strategic antibiotic treatment, and vaccination.
Antibiotic treatment of milk-drop cases is recommended to reduce excretion of leptospires and zoonotic risk (disease being transmitted between animals and humans).
A single intramuscular injection of tetracyclines/streptomycin will eliminate infection in most cattle. However, vaccination is the better approach, avoiding unnecessary use of antibiotics.
In a closed herd with no evidence of previous infection all replacements including bulls should be isolated for three weeks and treated with antibiotics on two occasions 10-14 days apart before entry into the herd.
For herds experiencing acute Leptospira Hardjo infection for the first time whole herd antibiotic treatment should be considered to reduce the risk of spread of infection. as well as a vaccination programme.
How can you minimise risk or prevent it in cattle?
The important risk factors for leptospirosis are:
- Risk of infection is increased by two-fold in open herds. Buying in infected cattle, particularly from infected unvaccinated herds can infect the herd, especially if it is naïve (have never been exposed to the disease). If buying in, it is important to check for vaccination in endemically infected herds or check stock is from clean sources.
- Using shared bulls increases the risk of infection by four-fold. Using artificial insemination (AI) is the safest method to minimize the spread of disease. If using a bull though, make sure the bull is vaccinated and check that he comes from a known health status herd.
- Mixed grazing with sheep increases the risk of infection by six-fold. Try to avoid sharing land with sheep. However, you can use land that has been rested for two months after sheep have grazed there.
- Shared grazing with common watercourses increases the risk of infection by eight-fold. It’s advisable to provide animals with water troughs to prevent them from drinking in streams and brooks. If possible, fence off these areas, especially if animals graze land upstream to your farm. This also applies to wet and marshy land.
Can you vaccinate against it?
Vaccination will not get rid of any pre-existing infection, but it can prevent new infection occurring by reducing the bacterial shedding (excretion of the bacteria in the urine) from previously infected animals.
The primary course of immunisation consists of two injections four weeks apart, followed by an annual booster.
Vaccination should prevent urine shedding following exposure and will protect against milk drop yield and abortion in the herd.
Herds with evidence of endemic infection indicated by herd screening or abortion serology should be vaccinated with an annual booster. Replacement heifers should have completed their vaccination course before first service.
Can it be passed to humans?
Yes – dairy farmers especially are at a high risk of infection from urine splashing in the face while milking. Pasteurisation destroys all leptospire organisms excreted in milk, so there is no danger of contracting the disease from drinking cow’s milk.
The greatest risk of transmission in the beef herd is during calving so it is advisable to wear gloves to reduce the risk. However, the main way of preventing transmission is to detect the disease early and vaccinate the cows.
How does it affect humans?
Leptospirosis causes influenza-like symptoms combined with severe headaches, but it can be treated effectively, usually with a long course of antibiotics.