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Leptospirosis Vaccine: A Silent Killer?

Updated: Jun 28, 2023

A blizzard of misinformation about leptospirosis is putting animals and human health at risk



Leptospirosis is a disease spread via a bacteria called Leptospira. Leptospirosis has been classified by the BSAVA (British Small Animal Veterinary Association) as a core vaccine – one that all dogs should receive, regardless of circumstances or geographical location.

The purpose of vaccination is to protect individual animals and populations of animals from lethal or disease-producing infections. Some infections are zoonotic e.g humans can contract it from animals/ shared with humans

Leptospirosis carries a zoonotic risk and control of the disease in the animal population is a means of limiting human infection.


Veterinary professionals encounter misinformation about leptospirosis vaccination that can be worrying given the potential for both animal and human health implications

here is a series of posts to help ease the minds of owners who may have come across misinformation online and want to know more.


Myth: The Leptospirosis vaccination, particularly the quadrivalent version (L4), has a high rate of serious side effects



There have been concerns raised about reactions to quadrivalent vaccines (L4) and about reactions to leptospirosis vaccination, particularly in small dogs. But these are unsubstantiated. The overall incidence of suspected adverse reactions for both L2 and L4 vaccine products is considered to be RARE.


The Veterinary Medicines Directorate has received fewer than 2 adverse reactions for L2, and fewer than 7 for L4, for every 10,000 doses sold.


'This is a similar risk to you developing anaphylactic shock, an asthma attack, or a bleed on the brain after taking an aspirin tablet– it can happen, but it probably won’t.' (Harris 2018)

These statistics includes every suspected adverse event reported, even cases that were considered unclassifiable or were later found to be unrelated to the vaccine.


One member of Veterinary Voices stated:


We had a 14 week old puppy found dead in its crate less than 24hrs after second L4 vaccine. The vaccine company paid for a Post Mortem (PM) which found it choked on some kibble. Without the PM though it’s one of those stories that would have been all over social media.

When polled Veterinary Voices UK found:

  • 92% Had never seen a serious adverse effects of the vaccination

  • 6% Had seen a case that happened shortly afterwards but was never attributed to the vaccine. Remember correlation doesn't always mean causation.

  • 2% Had seen a adverse effect


Remember correlation doesn't equal causation. One member stated:


One of my dogs with a history of severe immune mediated disease was due a DHP/L4 booster on a Friday.
The following Tuesday she had a severe relapse and ended up at a referral centre.
....Only thing was, I was so busy on the Friday that she never got her booster…
If I had given it, it would be extremely likely I would have thought the vaccination was the cause when this simply wasn't the case.


Myth: After the primary course, other core vaccinations don’t always need to be given yearly. Why are we giving Leptospirosis yearly? You are 'over vaccinating'!



Some vaccines have been very successful in achieving their goal of inducing protection and a long-lived memory immune response. Other vaccines, because of their nature, induce only short-lived immunity or may simply reduce the clinical signs of disease rather than preventing actual infections (e.g. canine leptospirosis). These vaccines must be given more frequently in adult animals as ‘booster vaccines’ in order to retain the immune response because memory persists for months rather than years. Leptospirosis is classed as a core vaccination by the BSAVA. Initially it requires two doses administered because it is a non-infectious (killed/inactivated) vaccine; after that it requires yearly boosters.


In contrast to the other core vaccines, which have a long duration of immunity, this vaccines must be given annually to maintain its efficacy. Given that the disease has serious implications for both human and animal health it's important that we attend these and also allows a full health check where worries or concerns can be discussed and your Veterinary Surgeon can pick up any issues you perhaps hadn't noted.


Why can't we just titre test?

With Leptospirosis, antibodies in the blood are less important in the body’s response to the disease. Research shows that high antibody counts are seen in animals that do not have good protection, and low counts are seen in animals that are protected. The studies that are done therefore have to be carried out using more complex methods to assess immunity, but it is clear from all the research that the immunity from both vaccines and from infection is short lived.


When polled 99.6% of veterinary professionals on Veterinary Voices UK believed that the Leptospirosis vaccination was required yearly. The other 0.4%? They believed that depending on risk and geographical location some may even require twice yearly.


Myth: Leptospirosis is not a dangerous life threatening disease



Canine leptospirosis is a bacterial zoonotic disease with worldwide distribution. The term zoonotic (also known as zoonoses) are caused by germs/ viruses/ bacteria that spread between animals and people. As mentioned above Leptospirosis is Zoonotic meaning it puts ourselves, our children, our relatives and veterinary professionals at serious risk.


One member of Veterinary Voices UK stated:


An acquaintance of mine is currently in an induced coma in ICU with Leptospirosis. I think the zoonotic potential is often underestimated.

It can cause numerous serious issues such as renal and hepatic disease, coagulopathies and other abnormalities. Case mortality rate ranges in various studies from 10–43.3+%

A UK study noted a 29% mortality rate with clinical signs of the disease including inappetence, vomiting, lethargy, polydipsia and polyuria, abdominal pain with hepatic (liver) and renal (kidney) involvement.


When polled 100% of Veterinary professionals from Veterinary Voices UK believed Leptospirosis to be serious and life threatening. These are professionals who have been the front line in dealing with these cases in practice and have diagnosed, intensively nursed, treated, medicated and fought to keep these Leptospirosis cases alive. Sadly many have to be euthanased due to multiple organ failure and poor prognosis.


Myth: Leptospirosis is easily treated, you don't have to worry about it.



It is often cited that a quick course of antibiotics is enough to treat leptospirosis in dogs.

Although it is true that dogs with leptospirosis are recommended a minimum 14 day course of antibiotic, this is rarely the only treatment these cases receive given the hepatic and renal involvement and severity of the disease.


Dogs commonly require hospitalisation, intravenous fluid therapy, analgesia, intensive nursing care, anti-emetics, anti-hypertensives, and nutritional support. In severe cases with pulmonary injury they may even require oxygen therapy and mechanical ventilation.

Devastatingly dogs are often extremely sick, with multiple organ failure and have to be humanly euthanised. This is extremely upsetting for both the owners and veterinary professionals.


On member on Veterinary Voices reflects on a case:

One case I particularly remember survived but required a feeding tube, a weeks hospitalisation and very intense barrier nursing. After she went home, she had weekly blood tests to monitor kidney and liver parameters for around 8 weeks. Very expensive for the owner, compared to vaccinating. Also, not covered by insurance, as she was not vaccinated and it’s a preventable disease.

Dogs presenting with kidney injury associated with leptospirosis can take months to recover and in approximately 50 per cent of dogs impairment persists for more than one year. This will incur veterinary costs for ongoing treatment and monitoring of the animals renal health.


When polled 100% of veterinary professionals from Veterinary Voices UK agreed that Leptospirosis was not easy to treat and often requires intensive care or euthanasia.


Myth: We don’t need to vaccinate against L4 in UK!



Bivalent vaccines contains the serogroups

-L icterohaemorrhagiae -L canicola


Historically these were the most common types seen – however, in recent years others have been increasingly being seen and in the L4, the manufacturers made two changes.

Changes include:

The manufacturer increased the amount of antigenic compound (i.e. how many dead bacteria were present)


They also added two additional strains, Australis(the group containing the specific strain Bratislava) and Grippotyphosa (reported to be the most common strain in much of Europe).

So now the current L4 vaccine contains four serogroups -L canicola -L icterohaemorrhagiae -L grippotyphosa -L Bratislava


In 1991 a major study was conducted in Edinburgh and Glasgow and found that just over 6% of dogs had been exposed to Bratislava (part of the Australis group) – and of those dogs testing positive for exposure to any Lepto strain, 5% were actively excreting Bratislava bacteria.


Now we may also have an increase in the European serogroup risk because imported dogs are on the increase and a number of dogs travel to Europe for holidays with their owners.

The number of dogs being commercially imported has surged by more than 50% due to lockdown - with imports from Romania leaping by 67% as the demand for puppies soared in the UK. While the number of imports just from Romania increased by 67% from 19,489 to 32,525 and now represent more than half (54%) of all EU imports.


One veterinary surgeon from Veterinary Voices UK stated:

We had 2 confirmed cases in one household earlier this year, all dogs were vaccinated with lepto 2 but the strain affecting them was typed and was in lepto4 not lepto2
Sadly both dogs who were confirmed with Leptospirosis died despite intensive treatment.


Robyn Lowe BSc Hons, Dip AVN (Small Animal), Dip HE CVN is a small animal Registered Veterinary Nurse (RVN) who regularly writes articles for academic journals and publications for animal owners. Robyn has a passion for evidence-based medicine, volunteers for Canine Arthritis Management, runs the Veterinary Voices Public Page, and campaigns on mental health and animal welfare issues.

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