Browsing tag: leptospirosis

Ask a vet online – is there a test for Leptospirosis?

Berry Wilkinson asked:

I was wondering if you can titre test for leptospirosis? Or is it only useful when you are testing sick dogs? Thanks.

Answer:

Hi Berry, thanks for your question about testing for Leptospirosis. To answer it, I’ll briefly discuss Leptospirosis as a disease, then talk about the different diagnostic techniques available. Finally, I’ll discuss vaccination and the implications for diagnosis.

What is Leptospirosis?

Leptospirosis (“Lepto”) is a disease caused by bacteria of the genus Leptospira. There are more than 300 strains (technically called serovars) of the bacteria. In the UK, Leptospira icterohaemorrhagiae and L. canicola used to be the most common, but since widespread vaccination against these has started, it is now thought that L. interrogans and L. kirschneri may be more important.

The disease is transmitted by body fluids of infected animals, including rats. The symptoms of Leptospirosis in dogs include:

  • Fever and sore muscles.
  • Loss of appetite, vomiting, diarrhoea and dehydration.
  • It may cause kidney or liver failure
  • Sometimes the only symptom is sudden death.
  • Infected dogs may shed the bacteria in their urine for months or years without showing any clinical signs.
  • Leptospirosis is highly zoonotic – i.e. it is a high risk pathogen for infecting humans.

How is Leptospirosis diagnosed?

There are four methods to test for Leptospira in clinical samples, of which two are clinically useful. They are:

  • Darkfield microscopy – looking for the bacteria themselves. This is very siple, but is notoriously unreliable, unfortunately!
  • Bacterial culture – attempting to grow the bacteria; however, in many cases the bacteria are very hard to culture, so even in confirmed infections, this test may come back negative.
  • Serology – looking for antibodies produced by the immune system in response to the presence of the bacteria. However, vaccination will often lead to a positive response, and low-positive titres (levels of antibody) may persist for a prolonged period. In addition, the levels of antibodies often won’t be significant in the first week of infection.
  • PCR – testing blood (early infection) or urine (later stages of infection or carrier status) for genetic material from the Leptospira bacteria; this is a very sensitive and specific test. However, a negative PCR result doesn’t rule out carrier status because the bacteria are only shed intermittently in the urine, and will not be present in the bloodstream; and it can also appear negative in some milder infections.

So how is serology interpreted?

  • The normal screening test for Lepto is an antibody test (“ELISA testing“) that gives a simple positive or negative result.
    • If this is negative, then in general either:
      • The dog doesn’t have Lepto, or
      • The dog has only been infected in the last week or so.
    • If the result is positive, then:
      • The dog has Lepto, or
      • The dog has had Lepto in the past, or
      • The dog has been vaccinated and still has high levels of circulating antibody.
  • If the ELISA-test is positive; or if the symptoms are suspicious but PCR (genetic) testing is negative, the next phase is to use a different type of antibody testing (“MAT serology“) to determine the level of antibodies in the blood (the titre).
    • On a single test:
      • Low titres are most likely to represent vaccination or past infection.
      • Moderate titres may indicate vaccination or infection.
      • High titres usually represent acute infection.
    • However, it is far more useful to carry out paired serology – 2 tests 7-10 days apart:
      • In a genuine infection, the titre would normally be expected to rise by at least four-fold.
      • In chronic infection, or asymptomatic shedding, diagnosis can be really difficult, but a persistent moderate titre that doesn’t decay over time is highly suggestive of chronic infection; however, demonstration of the organism’s genetic material by PCR in repeated urine samples is often more practical.

What about vaccination?              

There are a number of different Leptospirosis vaccines available; most of them cover 2 strains (“bivalent vaccines”), although some now cover 4 (“quadrivalent vaccines”). They are aimed at covering the most common types that cause disease, and there is relatively little cross-protection between strains (so immunity to one strain or serovar won’t usually protect against another).

The vaccine doesn’t necessarily prevent infection, but it should reduce the risk of infection, and it does reduce the severity of clinical disease and shedding (for whichever strains or serovars are covered by that vaccine).

There are some commercial tests that claim to determine whether a dog requires vaccination against Leptospira by testing circulating antibodies. This may work in some cases, but it is very limited. There are a number of problems with this approach:

  • The serological titre (level of antibodies in the blood) can only tell you how much antibody there is in the bloodstream at the specific time the test is done – it cannot tell you whether the levels will remain high for the following 12 months.
  • The link between antibody levels and protection isn’t consistent – some dogs appear to utilise other parts of the immune system (cell mediated immunity) and are protected against Lepto even in the absence of significant circulating antibody titres.
  • After vaccination, titres normally drop off over 4-5 months, but protection lasts for 12 months.

As a result, it is wisest to maintain annual vaccination against Leptospirosis, to reduce the risk of infection to your dog and to you.

I hope that helps!

David Harris BVSc MRCVS

Dog Vaccinations: are they really necessary?

Tomorrow is World Veterinary Day (WVD), an annual event that highlights the role of veterinary profession around the world. This year’s theme is the importance of vaccination to animal health. Over the past two hundred years, scientists have created vaccines that have prevented – and, in some cases, eradicated – diseases in humans and animals.

Yet if you talk to pet owners online, the question of the need to vaccinate is one that keeps cropping up. People worry that vaccines may even be causing illnesses, and sadly, they sometimes feel that they cannot trust the advice from their vet, because the vet benefits financially from the sale of the vaccine.

There is a danger here that pet owners may stop vaccinating their pets, and if they do, it’s likely that they will get away with doing so for a number of years. Vaccines have caused serious illnesses to become rare, so that there may not be an immediate threat to most pets. The problem is that if people choose not to vaccinate, there will be a growing population of unprotected animals that are vulnerable to viral disease if an epidemic does occur.

It’s useful to compare the situation with measles in humans. Before the introduction of measles vaccination in the UK in 1968, about half a million people caught measles each year of whom about 100 died. The introduction of the MMR vaccine in 1988 led to a dramatic reduction in measles, with only two human deaths from the disease in the past twenty years. False claims in the late 1990′s that MMR could cause autism led many parents to refuse to vaccinate their children. Vaccine rates dropped and there are now up to two million young people who remain unvaccinated: they are at risk of the disease.

This is not just theoretical: an outbreak of measles is currently happening in Wales, with over eight hundred confirmed cases including over eighty patients being treated in hospital. The first death happened last week, when a twenty five year old man passed away. As one official said, “Measles is a serious, horrible disease. We need to get rid of it.” The sad truth is that we know how to get rid of it: vaccinations, which have been proven to be safe and effective. Public health officials are now running large scale measles vaccine clinics to protect people who missed out on childhood vaccination, but there are still worries that the proportion of unvaccinated people may be so high that the current measles outbreak will spread to elsewhere in the UK, with further deaths.

There have been similar false claims about dangers associated with vaccinations in the pet world, and as a result, there is a risk of the gradual development of a large unvaccinated population of pets. This would create the potential for an outbreak of one of the nasty viral diseases of pets in a similar way to the human measles situation.

It is true that there is a low incidence of adverse reactions to vaccines. Like humans who feel a little under the weather after some vaccines, pets can suffer mild signs of illness as their immune system reacts to the vaccine. This is part of the same immune reaction that causes the body to produce antibodies against the virus, so it’s nothing to worry about. More serious adverse reactions, such as allergic or autoimmune diseases, do happen, but they are exceptionally rare. Overall, the reported incidence of any type of problem is less than one in five thousand; the risk of a serious reaction is much lower than this.

The aspect of dog vaccines that seems to worry owners most is the traditional model of “once yearly boosters”. People don’t understand why this is necessary, when in humans, childhood vaccines often confer lifetime immunity. Why do pets need so many vaccines?

The answer to this is complicated: when vaccine regimes were first devised, back in the 1970′s,  there was a high mortality rate from diseases like Parvovirus and Distemper. Duration of immunity after vaccines had not been clearly established, and the safest option was the once yearly booster. In recent years, more studies have been done, with many vaccines now promising immunity for three to five years for some diseases after the annual booster at fifteen months of age.

In the face of this changing information about vaccines, the challenge for vets has been to recommend a reduced vaccine schedule while still ensuring that no vulnerable animals slip through the loop. Much as pet owners may appreciate the opportunity to go to the vet less often, if even one animal died of a preventable viral disease, vets would feel that they had failed.

The veterinary profession has tackled this on a global scale, by setting up expert groups, using independent scientists to assess the evidence and to provide guidelines for the vaccination of pets. A simple set of recommendations have now been issued to vets across the world by the World Small Animal Veterinary Association, and these offer the safest approach to pet owners. You can read them for yourself online by clicking here.

Vaccines are now classified as “core” and “non-core”. Core vaccines include those which all animals need to receive, which means Distemper, Hepatitis and Parvovirus for dogs. Non-core vaccines are those that are required by only those animals whose geographical location, local environment or lifestyle places them at risk. Examples include Leptospirosis, Kennel Cough and Rabies, although the prevalence of rats in many parts of the UK  is so high that many people would regard Leptospirosis as a core vaccine in this country.

The aim of the veterinary profession is to vaccinate every animal with core vaccines and to vaccinate at-risk individuals against non-core vaccines if they are seen to be at risk.

The WSAVA guidelines also address the recommended frequency of vaccination: for the main core vaccines, after puppy shots followed by a booster at fifteen months of age, it’s now regarded as safe to repeat the vaccine every three years. If dogs need to be protected against certain other illnesses- including Leptospirosis and Kennel Cough – immunological studies have demonstrated that once yearly vaccines are still needed.

This can all become over-complicated for the average pet owner, which is why it’s still recommended that the safest answer is a once yearly health check by your vet. The vet will review your pet’s health and lifestyle, and will then only give the vaccines which are judged to be necessary. In the United Kingdom, for most dogs, the recommendation is likely to be a once yearly vaccine against Leptospirosis, with a booster against Distemper, Hepatitis and Parvovirus every three years. Other vaccines, such as Kennel Cough and Rabies, may also need to be given, depending on the dog’s activities.

There is plenty more to discuss on this subject, including widely-disseminated but unproven claims that over-vaccination is the cause of a wide spectrum of illnesses in the dog world. Perhaps that’s a subject for another blog.

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