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Is the Lepto4 Vaccine Dangerous for Dogs?

Sophie Jackson is a dog lover and trainer living in the UK. She competes in agility and obedience with her four dogs.

Should You Vaccinate Your Dog for Leptospirosis?

Should You Vaccinate Your Dog for Leptospirosis?

Concerns Over the Safety of Lepto4

You may have heard or read about the scares concerning a vaccine called Lepto4 by Nobivac (Merck). It is designed to protect your dog from acquiring leptospirosis, but many pet owners and vets are expressing concern about the possibly deadly consequences of this vaccine. There has been talk of dogs dying after being given Lepto4, and there is growing pressure to have the vaccine withdrawn from use.

If you are contemplating having your dog vaccinated against leptospirosis, you will want to know all the facts before making a final decision. For this reason, we will address some of the following questions:

  • What is leptospirosis?
  • What is the probability of catching leptospirosis?
  • How dangerous is the disease?
  • What are the risks associated with the Lepto4 vaccine?
Leptospirosis can be picked up from contaminated water.

Leptospirosis can be picked up from contaminated water.

What Is Leptospirosis?

Leptospirosis (sometimes referred to in short as 'lepto') is a bacterial infection that is contracted when pathogenic leptospires enter the body (via the mouth, nose or eyes) or penetrate the skin (through cuts, grazes, etc.) and enter the bloodstream. Leptospirosis is caused by a number of related Leptospira spirochetes much like the human flu (there are numerous strains of the flu).

Where Is It Found?

Leptospira bacteria like wet conditions and can be found in marshy, muddy areas, in pooling water (urban areas included), on decaying animal carcasses (marine mammals), near livestock and also in soil. Areas of exposure are often characterised by long-standing puddles, ditches, rivers and ponds.

Is Stagnant or Fresh Water More Dangerous?

According to the Royal Society for Prevention of Accidents (RoSPA), there is some debate about whether infections are more likely to occur from stagnant or freshwater. RoSPA states that leptospirosis in people is most commonly caught in freshwater. The bacteria spread when infected animals urinate in the water.

In the UK, wild rat and cattle urine is the most common source of lepto, while in other countries, different wildlife species carry the disease. Rodents are a prime source for lepto, which is why dogs on farms or those used for hunting are considered high-risk.

Leptospirosis cannot be acquired from salt water, but it can be acquired from carcasses or stagnant water at the beach.

Leptospirosis cannot be acquired from salt water, but it can be acquired from carcasses or stagnant water at the beach.

What Is the Disease Process of Leptospirosis?

When a dog contracts leptospirosis, it begins to infect the entire body, reproducing in the liver, kidneys, eyes, reproductive organs and the central nervous system. The body reacts by producing antibodies to fight the infection and, in a dog with a healthy immune system, there may be a complete recovery. Some dogs may never even exhibit symptoms; however, the bacteria may remain in the kidneys and can be passed in the dog's urine, putting animals and people at risk. Equally, dogs can appear to recover from leptospirosis and then deteriorate again.

Leptospirosis becomes serious when the infection attacks the kidneys or liver. If untreated, the infection can cause severe damage to these organs and may prove fatal. Younger dogs with a less developed immune system or dogs with compromised immunity are at high risk of developing life-threatening complications.

The Disease Has Zoonotic Potential

Lepto is a disease that affects a range of animals, including humans. You can catch lepto from your pet, as well as from contaminated water, so practice simple hygienic precautions:

  • Wear gloves when cleaning up after your dog.
  • Wear personal protective equipment (goggles and a mask) when washing away urine to prevent exposure from aerosolization.
  • Always wash your hands.
  • Avoid swimming in stagnant water if you or your dog have an open wound.
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After a dog has recovered from leptospirosis, it will have immunity against the specific strain that caused the infection, but it can still contract the disease from another strain of Leptospira.

Will Vaccinating My Dog Protect Them From Infection?

Considering the nasty complications leptospirosis can have, it is natural that people would want to protect their pets from catching it. Vaccination against leptospirosis, Lepto2, has been around for several decades and it provides protection against two strains of leptospirosis. In the last few years, the updated vaccine which covers four strains, Lepto4, was introduced.

Bear in mind that there are around 20 known strains (also called serovars) of lepto; 17 strains are found in Europe, and the vaccine only covers four of these. Therefore, a dog can have the vaccination and still become infected, so the vaccination does not offer complete protection.

The Nobivac Lepto4 vaccine is designed to protect against the following serovars in the UK:

  • Canicola
  • Copenhageni
  • Bratislava
  • Bananal/Lianguang

Statistics: Exposure, Symptoms and Mortality

The British Small Animal Veterinary Association

Of the four serovars in the UK, only canicola and bratislava are considered common (or most typically seen), according to a recent article by the British Small Animal Veterinary Association. The article noted that canicola, one of the primary strains vaccinated against, is actually very rare in the UK, accounting for less than 19% of cases of the disease. Recently, a strain of leptospirosis known as 'pomona' has been identified in Ireland, but it is not included in the vaccine.

The University of Liverpool

A study on the spread of lepto and vaccination rates in the UK was undertaken by the University of Liverpool, and the results were presented in a thesis by Christopher Ball in 2014. A questionnaire was sent to 472 veterinary practices around the UK which, along with asking about vaccination rates at the clinic, asked about the number of cases of leptospirosis they had seen; 89 of the clinics responded. The results showed that just over 60% of the patients seen at the clinics were vaccinated.

Out of these 89 practices, only 13 (less than 15%) reported suspected cases of infection in the last twelve months, while only five had their cases confirmed via laboratory testing. Of the eight practices with suspected cases, either samples were never sent for confirmation or the samples came back negative. Of the five confirmed cases, one of the dogs, a Springer Spaniel, was vaccinated for lepto. Three of the five dogs recovered (including the vaccinated Springer Spaniel), while two died. Two of the three survivors were not vaccinated.


An additional 29 practices reported seeing lepto cases within the last 15 years. No practice had seen more than a single case within the span of a year. The reported incidences of leptospirosis were, therefore, extremely low, with only five cases being found in the 89 practices that responded over a 12-month period. One of those dogs was vaccinated, so either the vaccine had not been taken up or the dog had come into contact with a strain that the vaccine did not cover.

The findings suggest that contracting leptospirosis is pretty rare. A low contraction rate may be due to vaccination, but also due to low numbers of detection and observable symptoms.

Dogs that love mud are more likely to come into contact with the bacteria.

Dogs that love mud are more likely to come into contact with the bacteria.

What Is the Risk of Catching Leptopirosis?

Surprisingly, there has been limited research done on the actual risks of dogs contracting the disease. A study conducted in the US used data collected by a commercial veterinary diagnostic laboratory for 33,119 dogs. The laboratory had been sent samples from the dogs to examine microscopically for evidence of leptospirosis antibodies between 2000 and 2007. The lab found that 2,680 of the samples contained antibodies (8.1% of the dogs tested).

Variance in Exposure Results

There are additional factors to bear in mind when it comes to these results, the main one being that when a lab tests for lepto antibodies, they cannot differentiate between antibodies produced as a result of infection or antibodies in the sample from the lepto vaccination. That means that a false positive could result.

Reported Vaccinations vs. Detected Antibodies

Additionally, if the lab test picks up the result of the vaccination, why was the sample rate not higher for lepto? Surely if around 50–60% of dogs were being vaccinated, then there should have been a great number testing positive for lepto just because of the vaccine. That suggests that either the majority of the 33,119 dogs were not vaccinated, or the vaccine had failed to produce the results in the body it should have (i.e. antibodies against the disease).

Exposure and Survival Considerations

The next thing to bear in mind is how dangerous lepto is if it is contracted. Now, many dogs who catch lepto show no signs or have a mild response. In dogs that do require veterinary treatment, 90% survive, according to Dr JD Foster at Penn Vet's Ryan Hospital:

'Of all the diseases we do dialysis for, leptospirosis has one of the best outcomes. Dogs that are really sick can turn around and have a remarkable recovery'.

The World Small Animal Veterinary Association also considers the risk of catching lepto depending on where your dog lives:

'Vaccination should be restricted to use in geographical areas where a risk of exposure has been established or for dogs whose lifestyle places them at risk'.

Of course, as low as the risks are, none of us would like to be that person with the dog in the 10% fatalities category. So better safe than sorry, right? Well, that brings us to a new worry: the risk to your dog's health posed by the vaccine.

Water frequented by wildlife, mainly rats, can become contaminated.

Water frequented by wildlife, mainly rats, can become contaminated.

The Risks of the Lepto Vaccine

NC College of Veterinary Medicine: Dr Patricia Jordan, DVM

Dr Patricia Jordan qualified as a veterinarian from the North Carolina College of Veterinary Medicine in 1986, and worked in conventional veterinary medicine for 15 years before moving into holistic medicine. She believes the potential dangers of the lepto vaccine outweigh its benefits:

'If your dog is vaccinated for Lepto, the antigens in the vaccines do the same harm to the immune system as possibly a natural infection. There have been cases of dogs having to go through dialysis also to save them and no Leptospira were found. The reason? The damage from the antigens in the vaccinations are just as capable as causing the disease pathology . . . . Vaccinating your dog can also destroy the kidneys in 48 hours and in some cases, cause untreatable dermatitis. The damage from Lepto vaccination to your dog’s immune system also includes the associated risk of cancer from the adjuvant (chemicals in the vaccine), and the same adjuvant is associated with upregulation of IgE and the consequence includes allergies, asthma, atopy, anaphylaxis and death'.

The Canine Health Concern: Christopher Day, DVM

An additional study of the risks of vaccination was conducted by Canine Health Concern. In the 1990s, they had been contacted by homeopathic veterinarian, Christopher Day, who often treated referral cases where traditional veterinary medicine had failed. He felt that 80% of the dogs he saw were sick due to a reaction to vaccination. This was a high figure, and the Canine Health Concern decided to investigate and see if this could be verified. A survey was conducted of 3,800 dogs, and the results were worrying:

'In the 1996 Canine Health Concern vaccine survey 100% of dogs with Leptospirosis had been vaccinated within three months prior to infection. This can only be because:

  1. The vaccine caused the disease, or
  2. The vaccine didn’t contain the serovar that caused the illness, or
  3. The vaccine contained a non-local serovar that the dog hadn’t adapted to, or it just didn’t work'.

The Telegraph: Carol Blackburn-Harvey, Owner Account

More recent news reports have raised concerns that pets have suffered fatal reactions to the lepto vaccine. In 2016, Carol Blackburn-Harvey told The Telegraph that her rare Russian Tsvetnaya Bolonka dog had died just weeks after receiving the vaccine. Bridgette Evans, a Kennel Club-accredited breeder of spaniels, told the newspaper that every dog she had taken to be vaccinated with Lepto4 had suffered adverse reactions. One litter of six puppies all developed swollen glands and inflammation around the injection site. One of her dogs died within three weeks of having the vaccine.

The European Medicines Agency

The European Medicines Agency recognises there are risks to the vaccine and states in their guidelines for its use:

'A mild and transient increase in body temperature has been observed very commonly (more than 1 in 10 dogs) in clinical studies for a few days after vaccination, with some pups showing less activity and/or a reduced appetite. A small transient swelling at the site of injection which can occasionally be firm and painful on palpation, has been observed very commonly in clinical studies. Any such swelling will either have disappeared or be clearly diminished by 14 days post-vaccination . . . . In very rare cases, (defined as less than 1 in 10,000 dogs) clinical signs of immune-mediated haemolytic anaemia, immune-mediated thrombocytopenia, or immune-mediated polyarthritis have been reported. In very rare cases a transient acute hypersensitivity reaction may occur. Such reactions may evolve to a more severe condition (anaphylaxis), which may be life-threatening. If such reactions occur appropriate treatment is recommended'.

It is, therefore, recognised that for every 10 puppies vaccinated, at least one or two will suffer a reaction often characterized by a raised temperature, loss of appetite and swelling. But these are just the visible signs of what the vaccine is doing to the body. What about the things we cannot see? What long-term harm has that 'transitory' effect had?

Facebook Group: 'Nobivac Lepto 4 - Our Experiences'

Dog owners are also arguing that the risks of serious adverse effects are far higher than stated. Unfortunately, scientific data to support this is not currently available and it remains a controversial topic.

A Facebook group called 'Nobivac Lepto 4 - Our Experiences' has been set up to record canine deaths and adverse reactions to the vaccine. While this information is sometimes anecdotal, it does reveal a worrying trend. As of April 2019, 103 vaccinated dog deaths have been reported in the group.

Some traditional vets are now reconsidering the use of Lepto4 and do not offer it. They are instead reverting to the Lepto2 vaccine, which is considered far safer.

The potential risks of the vaccine have to be weighed against your dog's lifestyle.

The potential risks of the vaccine have to be weighed against your dog's lifestyle.

Should I Vaccinate My Dog for Lepto?

Ultimately, the decision to vaccinate your dog against leptospirosis is yours and yours alone. This article has hopefully provided you with information about the risks of your dog catching lepto and also the potential risks of the vaccine.

Vaccinations can be beneficial in preventing dogs from contracting fatal illnesses, but when the vaccine itself is causing unnecessary harm, one might consider if the risks outweigh the benefits, especially since lepto vaccines must be given annually.

You are in the best position to decide what is right for your dog, and now you have all the information about the pros and cons of the lepto vaccine. There are never any exact answers in situations like this, you just have to go with what makes the most sense to you.

This article is accurate and true to the best of the author’s knowledge. It is not meant to substitute for diagnosis, prognosis, treatment, prescription, or formal and individualized advice from a veterinary medical professional. Animals exhibiting signs and symptoms of distress should be seen by a veterinarian immediately.

© 2019 Sophie Jackson

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