Leptospirosis – caused by infection with the spiral shaped bacteria Leptospira – can affect virtually all mammals, including humans and is found worldwide. It represents a One Health issue, in which the health of humans, animals and the environment are intricately linked.
In UK livestock, leptospirosis can result in significant economic losses due to reduced fertility, abortion, and reduced milk yields, but the significance to human health is often overlooked.
Worldwide, Leptospirosis is considered the most common zoonotic infection (spread from animals to humans) with an estimated 1million cases and around 60,000 deaths annually. In developing countries, the most severe form of the disease (Weil’s disease) carries a mortality (death) rate of around 22%.
In the UK, human infection is uncommon with around 60 confirmed and up to 90 suspected cases annually in England, Whilst deaths in the UK are rare (around 5% of severely affected cases), the death of Olympic rower Andy Holmes brought leptospirosis into sharp focus once again.
Leptospirosis in the environment
Transmission of leptospirosis in all species occurs through contact with urine of infected animals, both directly and indirectly (i.e. through urine contaminated water or soil).
Bacteria enter the body through damaged skin or via intact mucous membranes – the moist tissues that lines body cavities such as the mouth, nose, airways, eyelids, stomach, urinary and reproductive tracts. Bacteria then spread to multiple organs including the kidneys from where they are shed intermittently in the urine, continuing the cycle.
There are different classification systems and many different strains of leptospirosis. Depending on the strain, infected mammals may act as;
Reservoir hosts
Including rodents (especially rats), livestock (cattle and pigs), and in some cases dogs. Reservoir hosts often show few symptoms but shed leptospira into the environment in large amounts over long periods.
Incidental hosts
Including humans, dogs (in some cases) and other farm animals e.g. sheep. They may be severely affected by leptospirosis but do not shed large amounts into the environment.
Leptospirosis in Cattle
Lepto in cattle is widespread, affecting both beef and dairy animals, with an estimated 65-70% of the UK herd being exposed at some point during their lifetime. Cattle are reservoir hosts so purchased (or borrowed) cattle who may be carriers (reservoirs) are the main source of introducing infection into cattle herds. Carrier sheep and contaminated water sources also pose a risk.
Leptospira hardjo is the strain predominantly affecting cattle. Symptoms include:
- Suddenly reduced milk yield
- Lethargy, stiffness
- Abortions
- Weak, premature calves
- Infertility – associated with early pregnancy failure meaning cows return to breeding
The disease spreads within the herd via urine and aborted materials (foetus, fluids and membranes).
In all species, diagnosis of leptospirosis is tricky.
- Intermittent shedding in urine makes identifying lepto under the microscope or by urine culture unreliable.
- Leptospira levels in the blood vary during the disease.
- Culture of blood/urine can take many weeks.
- Previous infection or vaccination makes it difficult to determine if infection is current based on blood samples.
- In cattle and pigs, paired blood samples taken 3-4 weeks apart, may help. In dogs, this also works, but many affected animals do not survive that long.
- Where abortions occur in animals, very prompt lab submission of fresh material may allow identification of leptospiral bacteria in the tissues.
During a herd outbreak, treatment with antibiotic (e.g. streptomycin) may help reduce shedding and minimise environmental contamination.
Vaccination is available for cattle. Vaccination lowers risk of infection and reduces shedding from infected animals which, in turn, minimises the risk of zoonotic spread (to humans).
Leptospirosis in Pigs
Pigs contract leptospirosis primarily from other pigs, but dogs, rats and wildlife may also spread disease. Although adult pigs may not become unwell, leptospirosis causes reproductive damage including abortions, birth of weak or stillborn piglets, and reduced fertility in sows, including repeat breeders due to early pregnancy failure.
Treatment with antibiotics may be indicated in certain circumstances under guidance from your vet. At the time of writing, no UK vaccine is available. European vaccines can be imported by a veterinary surgeon under Special Import Certification if required.
Leptospirosis in Dogs
Dogs are susceptible to many strains of lepto, transmitted from other mammals directly or through contaminated water or environments. At least four of these are present in the UK, and several more are widespread in Europe. Symptoms may include:
- Gut upsets – vomiting, diarrhoea, inappetance
- Weight loss
- Lethargy, dullness, fever
- Abortion
- Jaundice (yellowing of skin, gums or eyes)
- Increased thirst and frequency of urination, leading to kidney failure
- Coughing or difficulty breathing
Dogs with suspected leptospirosis must be nursed in isolation to prevent spread to other animals and humans.
Treatment varies according to symptoms, but despite treatment, severely affected patients may die. Others survive initially but develop kidney failure and are euthanased. Those that recover may become chronic shedders, posing a risk to humans and other animals.
Leptospirosis forms part of the annual core vaccination in the UK, reducing the risk of illness as well as minimising shedding if an animal does become infected.
Leptospirosis in Rodents (including pets)
Wild rodents represent a significant source of leptospirosis in the environment, through contamination of livestock areas and water courses to which humans and animals have access.
Pet rodents may also carry infection, which poses risk to humans. Keepers of pet rodents (particularly the young, elderly, pregnant or immune compromised) should take particular care to avoid contracting the disease by;
- Keeping pet rodent environments clean, dry and well ventilated
- Wearing protective clothing e.g. gloves and masks when cleaning out pet housing
- Covering damaged skin before handling rodents
- Thorough hand washing after handling
No rodent vaccination is available.
Leptospirosis in Humans
Leptospira hardjo and Leptospira interrogans are the most common strains to affect humans, and are typically shed by rats, cattle or pigs. Due to the routes of transmission of lepto, human health risk is highest for;
- Occupations with direct animal contact – livestock workers especially dairymen, veterinarians, abattoir staff and pest controllers.
- Occupations with indirect animal contact via environment – sewage/wastewater operatives, construction/demolition workers, military personnel, flood relief workers, canal workers, divers
- Anyone involved in water-based activities e.g. wild swimming, rowing, kayaking/canoeing, caving, fresh-water fishing.
- Visitors to warmer climates and resource-poor regions where contact with contaminated water sources occurs more readily and bacteria survive longer in the environment.
In humans, infection with leptospirosis can result in two syndromes:
- Anicteric leptospirosis – flu-like symptoms e.g. fever, headache, body aches, stomach upset.
- Icteric leptospirosis (Weil’s disease) – may be mild initially but progresses to jaundice (yellowing skin due to liver damage), meningitis, pulmonary haemorrhage (bleeding in the lungs), kidney failure and potentially death due to multiple organ failure.
Diagnosis is challenging as previously discussed, especially in global regions where lepto is most prevalent. Limited access to laboratory equipment and a higher level of previous exposure in the human population, makes it difficult to identify current infection.
Treatment is with antibiotics and support according to symptoms. No vaccine is available for leptospirosis in humans.
Control and prevention on farm
As a One Health issue, control/prevention of leptospirosis involves humans, animals and the environment. Actions taken on farm can protect humans both directly and indirectly.
Blood samples or bulk/pooled milk samples can help determine and monitor herd leptospirosis status. Decisions can then be made on how to protect or improve this status using biosecurity and testing, with or without vaccination.
Biosecurity measures include:
- Keep a closed herd where possible
- Isolate and test added animals before they join the main herd
- Source stock from accredited free herds where possible and avoid borrowing bulls.
- Ensure boundary fencing prevents animals straying on/off the holding
- Avoid co-grazing with sheep, small ruminants e.g. goats, and camelids
- Use mains water supply rather than natural water courses where possible
- Clean and disinfect equipment before use, including housing. Try to avoid sharing equipment
- Keep delivery and pick up points isolated from the main farm
- Control rodent populations
In cattle herds with evidence of leptospirosis exposure, or where human health risk is higher (e.g. dairy herds), vaccination to reduce shedding may be the most appropriate course of action. This is relatively low cost and available in small quantities so accessible to herds of all sizes.
Cattle herds that demonstrate no circulating leptospirosis may become accredited free of the disease through CHeCS health schemes, which also offer various options for monitoring. This can be advantageous when selling animals for breeding but relies on strict biosecurity and does not work alongside vaccination as current tests cannot differentiate between vaccination and natural exposure.
Speak to your vet to determine the best strategy for your holding.
Reducing the zoonotic risk
Cattle Vaccination can reduce the risk to human contacts, especially in the dairy herd where urine splash at milking time is common. Controlling rats on farm also reduces the risk of workers contacting infected urine or rodents themselves. Appropriate protective clothing must be work while handling livestock or rodents (dead or alive) or cleaning equipment or animal housing that may be contaminated. A suitable disinfectant must be used.
Further precautions for humans include;
- Do not drink from natural water sources that may be contaminated
- Avoid swimming in water that may be contaminated (e.g. stagnant water, lakes, canals, ponds)
- Ensure stringent hand washing after contact with animals
- Clean wounds promptly and cover damaged skin
- Wear protective clothing appropriate for your work, e.g. gloves, mask, eye protection and waterproof clothing
- Shower as soon as possible after contact with potentially contaminated water e.g. after watersports
- Maintain annual vaccination for your dog
- Avoid contact with rodents, ensuring pest control is in place if necessary
References and further reading
Leptospirosis in Cattle – NADIS
Leptospirosis Fact Sheet – Cattle Information Service
CHeCS Protocols for Leptospirosis
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