Check out our vet-approved guide to leptospirosis in dogs, including what it is, why vaccination is important and how to pick the best vaccination for your dog.
Leptospirosis is a potentially life-threatening bacterial infection that can affect dogs, humans and a range of other species. Regular leptospirosis vaccines for dogs can prevent most cases, but variation in the vaccines used can affect your dog’s level of protection.
In this article we’ll discuss what leptospirosis is, why vaccination is important, which vaccines are available and what to consider when choosing between them.
TL;DR
Leptospirosis is an infection caused by various strains of Leptospira bacteria. These bacteria circulate in wildlife and are found across the UK and around the world. In humans, leptospirosis is often referred to as Weil’s disease.
In both humans and dogs, leptospirosis can cause severe illness and lead to multi-organ failure, internal bleeding and death.
Since the introduction of canine leptospirosis vaccines several decades ago, the incidence of leptospirosis in dogs has dropped dramatically.1 Leptospirosis in dogs is now much less common than it once was, although it’s suspected that cases are underreported, as diagnosis can be challenging.2
The reduction in cases of leptospirosis has unfortunately led some individuals to underestimate the value of leptospirosis vaccination. However, the risk of leptospirosis remains high, as the bacteria responsible are still widely present in the environment.
Various species can host Leptospira, including wild rodents, cattle, horses, pigs and dogs. The bacteria is often shed in the urine, and can survive for weeks to months in saturated soil.3
Unfortunately, there’s no easy way to predict a dog’s risk of leptospirosis - traditionally, farm animals, dogs in rural environments and those that roam near water sources have been considered at higher risk, but leptospirosis is increasingly identified in dogs living in urban and suburban environments.4
While the incidence of leptospirosis is currently low, it still poses a real threat to dogs, and especially those that aren’t fully vaccinated.
Leptospirosis in dogs can cause severe and often life-threatening disease.
It most commonly causes acute damage to the kidneys and/or the liver.5 Signs of leptospirosis in dogs include vomiting, lethargy, anorexia, changes in thirst and urination and in some cases jaundice. Leptospirosis may also cause septicaemia and internal bleeding.
The signs of leptospirosis in dogs can be vague, especially in the early stages, and there’s no simple test for it. Lab tests take time in which affected dogs may be deteriorating rapidly, making diagnosis challenging.
Treatment typically requires intensive care alongside a long course of antibiotics. While dogs can recover well with early treatment, leptospirosis is often fatal in more severe cases. Some dogs are left with long-term health issues despite successful treatment.
Leptospirosis is zoonotic and may also pose a risk to human health, causing Weil’s disease. Cases of dog-to-human transmission are relatively rare, but vaccinating your dog can help to minimise the risk both to them and to their human friends and family.
Canine leptospirosis vaccines, more often referred to as ‘lepto’ vaccines in the UK, form part of your dog’s core vaccinations.
They contain inactivated Leptospira bacteria, alongside adjuvants which help to stimulate the immune response. If a dog is subsequently exposed to Leptospira bacteria of the strains against which they have been vaccinated, their immune system can recognise and fight off the bacteria.
Lepto vaccines for dogs are very effective, but unfortunately can’t eliminate the risk of leptospirosis. Dogs can still be infected by other strains of Leptospira that aren’t included in the vaccine, and in rare cases may be infected despite vaccination. However, being fully vaccinated significantly reduces the likelihood of your dog catching leptospirosis, and the likelihood of them developing severe disease.
Lepto vaccines for dogs are inactivated and non-infectious, meaning that they require two doses several weeks apart to stimulate a good immune response. The lepto vaccine for puppies is usually given from 6-8 weeks, with the second dose given 2-4 weeks later, depending on the vaccine being used.
While some canine vaccines are able to stimulate long-lasting immunity, the lepto vaccine requires a yearly booster to maintain effective immunity.6
Studies of dogs’ immunity following the lepto vaccine indicate that immunity lasts for 12 months, with some studies demonstrating immunity against particular strains at 15 months after vaccination.7 However, immunity has not been reliably demonstrated to last for longer than 12 months. Anecdotally, cases of leptospirosis have been identified in dogs that missed their booster within a few months of their vaccination due date.
If a dog’s immunity declines too far before their booster, a single vaccination is less likely to stimulate sufficient immunity, leaving them at risk. This means that if your dog’s booster is significantly overdue, your vet may recommend ‘restarting’ their vaccinations with two doses.
For some vaccines, a blood test can check antibody levels and determine whether a booster vaccination can be delayed if immunity is still present at a good level.
However, antibody levels in the blood are not well correlated with immunity to leptospirosis. The immune response stimulated by lepto vaccines is more complex, relying more on immune cells (which are difficult to measure) rather than antibodies. The antibodies may be high in a dog that doesn’t have good immunity, or low in a dog that does.
This means titre testing cannot reliably predict whether a dog is still immune to leptospirosis and whether their booster can be delayed.
There are several leptospirosis vaccines from different manufacturers licensed in the UK. There is one major factor that divides these vaccines, which is whether they are a ‘lepto 2’ vaccine or a ‘lepto 4’ vaccine. These may also be referred to as L2 and L4 vaccines.
The lepto 2 vaccine is the original leptospirosis vaccine. This vaccine offers protection against the two most common strains of leptospirosis in UK dogs, Leptospira icterohaemorrhagiae and L. canicola.
The lepto 4 vaccine was introduced in 2014 to address the increasing threat from two other strains of leptospirosis: L grippotyphosa and L Bratislava.
The first is the most common strain in Europe, and is believed to be increasing in the UK due to widespread pet travel and the importation of foreign dogs. The latter has also been associated with outbreaks of leptospirosis in the UK, with one study finding that it was as common as L. icterohaemorrhagiae in wild rat populations.8
The lepto 4 vaccine also contains a higher dose of inactivated bacteria to more effectively stimulate immunity.
Cross-protection between strains of leptospirosis is minimal, meaning that dogs vaccinated with a lepto 2 vaccine are not protected against these additional two strains. For dogs vaccinated with only the lepto 2 vaccine, these strains can still cause serious and even life-threatening illness.
Most vaccines specify if they contain the four strains, so a vaccine that offers protection against leptospirosis without specifying will typically be a lepto 2 vaccine.
The majority of UK vet practices offer the lepto 4 vaccine, although they may also stock the lepto 2 vaccine for occasional use. If you have a particular vaccination preference, it’s worth checking with your practice in advance which vaccines they offer.
The lepto 4 vaccine offers greater protection against leptospirosis, and is the most commonly used type of canine leptospirosis vaccine in the UK. However, when the lepto 4 vaccine was released social media reports of suspected side effects were circulated widely, fueling fears over its safety.
With any vaccination - and any medication - there is risk involved. In humans, for example, paracetamol can (rarely) cause anaphylaxis, but the risk is so low most people don’t consider it when they have a headache!
Common side effects of the leptospirosis vaccine in dogs include mild swelling of the injection site, a mild fever, lethargy and reduced appetite. This is similar to other vaccinations and doesn’t usually require any treatment.
However, what caused the most concern about the lepto 4 vaccine - understandably - were reports of more severe side effects.
Very rarely, more severe side effects are observed as a result of any vaccination. These are recorded by both the manufacturers and regulators as suspected adverse reactions (SAR). The latest figures indicate that for the lepto 2 vaccine, it’s expected that 2 dogs will require treatment for a SAR out of every 10,000 dogs that are vaccinated (0.016%). For the lepto 4 vaccine, this figure is 5 dogs per 10,000 vaccinated (0.045%).9
While the risk of the lepto 4 vaccine is higher than the risk of giving lepto 2, severe adverse reactions are rare for both vaccines. The risk of leptospirosis to dogs vaccinated with lepto 2 rather than lepto 4 is believed to be significantly higher than the small increased risk of giving the lepto 4 vaccine. This is why the vast majority of vets recommend the lepto 4 vaccine.
Find out more about your dog’s preventative healthcare with our comprehensive guide to canine vaccinations, or learn more about routine flea and worm treatments for dogs.
