Protection of dogs against leptospirosis

Leptospirosis is a potentially serious disease that can affect dogs. It is caused by a type of bacteria called Leptospira. These bacteria are carried by rodents and transmitted to dogs through contact with infected urine, or water or soil contaminated with infected urine. Vaccination of dogs in the UK is recommended to protect them against leptospirosis. By doing this module you will:

  • understand how dogs are affected by Leptospira;
  • be aware of what is known about Leptospira infection in dogs in the UK;
  • know the main features of Leptospira vaccines;
  • know what to advise pet owners who ask about the vaccine.

Leptospira is a type of bacteria. It has a distinctive coiled shape and is widespread throughout the world. It can cause disease in many types of mammal, including dogs and humans. The bacteria can be transmitted from animals to humans (i.e. it is a zoonosis). 

If an animal becomes infected with Leptospira, the bacteria can remain in the kidneys for long periods and be shed via urine, without the animal showing any signs of infection. Under the right environmental conditions the bacteria can survive for several weeks in contaminated water and moist soil. The bacteria are killed by UV radiation, freezing, drying out and by most disinfectants. Climate change and flooding may encourage greater survival and spread of the bacteria. 

In the UK, rodents are the most important carriers of Leptospira. In other countries, other types of mammal, such as pigs or cattle might be a more important source of infection. There are many different types and subtypes of Leptospira bacteria, which all have specific names and some are associated with specific carrier species. In the UK, the types most commonly associated with rodents and infection in dogs are Leptospira Icterohaemorrhagiae and Leptospira Canicola.

Leptospira infection can occur in the dog if there is direct contact of mucous membranes or broken skin with urine from animals infected with Leptospira, or with soil or surface water that is contaminated with infected urine. 

Leptospira infection can cause the disease leptospirosis, which has a wide range of effects. There may be no signs at all, or only mild non-specific signs, whereas some dogs become seriously ill. Signs of infection include vomiting, weakness, lethargy, fever, drinking and/or urinating more than usual, and jaundice. The infection can sometimes cause breathing difficulty or sudden death. Dogs with confirmed leptospirosis are usually treated with antibiotics and with supportive care.

The pattern of signs in an unwell dog might suggest that a dog has leptospirosis. The most reliable way to confirm that a dog is infected with Leptospira would be to take a blood or urine sample and see if the bacteria can be grown in a laboratory. But this is not very practicable for diagnosis because it takes several months to grow Leptospira in a laboratory. Instead, a test (called the Microscopic Agglutination Test or MAT) is used to check if the dog has developed antibodies to the bacteria and confirm the diagnosis. Unfortunately this is not an easy test because of the complex nature of the infection process. It involves taking two blood samples a week or two apart, to detect rising antibody levels. There are some other tests that a vet can do, that together with the signs of infection, can help make a decision about whether to start antibiotic treatment. All in all, testing for leptospirosis is complicated.

As with any vaccine, the decision on whether to vaccinate against Leptospira should be based on an assessment of the likely exposure of the dog to the infecting organism in the environment. In the UK, most dogs are at risk from contact with rodents and potentially contaminated water and so Leptospira vaccine is considered a ‘core’ vaccine, which means that it is recommended for all dogs. 

There are many vaccine products available in the UK to help protect dogs against leptospirosis. All contain killed Leptospira bacteria or purified proteins from the bacteria.

The vaccines that have been around longest contain the two Leptospira subtypes that have been most commonly associated with leptospirosis in dogs: Icterohaemorrhagiae and Canicola. These vaccines are sometime called bivalent or L2 vaccines. 

More recently, new vaccine products have become available that contain three or four Leptospira subtypes. These are the trivalent (L3) and quadrivalent (L4) vaccines. That is, they contain one or two additional Leptospira types in addition to Icterohaemorrhagiae and Canicola. The extra subtypes have been added because there is evidence that these other types are becoming an important cause of infection in dogs in countries in mainland Europe. However, in the UK, it is not very clear yet how important it is to protect against these other types of Leptospira.

Immunity to Leptospira does not last as long as some of the other common infective canine diseases. All the Leptospira vaccines will protect dogs against leptospirosis for 1 year and an annual booster is needed to maintain immunity to Leptospira

The choice of vaccine (whether bivalent, trivalent or quadrivalent) depends on the range of Leptospira types that a dog is likely to encounter. Dog owners should discuss the choice with their vet.

After having a Leptospira vaccine, a dog may have some swelling or pain at the injection site, a short-lived rise in temperature or digestive disorders. In rare cases, a dog might have an allergic reaction, which can occur with all vaccines.  Serious adverse effects (usually allergic reactions) to Leptospira vaccines appear to be rare (i.e. occurring in between 1 in 10,000 and 1 in 1,000 dogs). In 2016, there was high-profile coverage in the media of anecdotal (hearsay) reports of serious adverse effects to quadrivalent vaccines. The medicines regulators are keeping a close eye on reports of adverse effects to these vaccines. So far, there is no conclusive evidence that adverse effects are any more likely with trivalent or quadrivalent vaccines than with the bivalent vaccines, nor that adverse effects are any more likely with Leptospira than other vaccines types.  It is important to be aware that it can be difficult to unpick the cause of a suspected adverse effect, because it is common for several vaccines to be given at once and often parasiticide medicines are started at the same time as vaccinations.

All suspected adverse events to vaccines (including suspected lack of effect) should be reported to the marketing company or the Veterinary Medicines Directorate. Reporting is essential to help identify new adverse effects, and for understanding the frequency of known effects and the need for changes in the composition of vaccines. Anyone can make a report, including pet owners and veterinary professionals.

  • Leptospirosis is a potentially serious disease caused by Leptospira bacteria.
  • Leptospira is carried by rodents. Dogs can become infected through contact with water or soil that is contaminated with infected urine.
  • Leptospira vaccine is recommended for all dogs in the UK.
  • Dogs owners should talk to their vet about vaccination and the choice of vaccine.
  • Annual boosters are needed to maintain protection against Leptospira.


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