You’ve seen the news headlines – but what’s the deal?

 

What is leptospirosis?

Leptospirosis (or ‘lepto’ for short) is a disease caused by a type of bacteria called Leptospira.

These bacteria live in soil and water all over the world. They can cause disease in most mammals – with dogs currently being the ones featuring in the news. Leptospirosis a zoonotic disease, which means it can be spread from animals to people.

Although the bacteria are widespread, the disease is rare.

Before we get into what the disease looks like and what to do about it, we need to focus some attention on the bacteria.

 

Leptospira bacteria

Leptospira is the genus. Within the genus are different species.

The particular species that causes disease is Leptospira interrogans sensu lato.

Now stay with me. The species is further subdivided into strains (called serovars). There are over 250 of these. Different serovars occur in different locations and produce different types of disease.

Some of the serovars are similar enough (or 'antigenically related') to be grouped together. These are called serogroups.

The reason this all matters is that it impacts vaccination. There is no one 'lepto vaccination'. Vaccinations are specific for the serogroup. We'll get into this later, but for now, just know that message in the media to get your dog vaccinated is oversimplified.

Here are a few (of the many) serogroups.

  • Australis – contains serovars Bratislava, Lora, Jalna and Muenchen (usual hosts* include pig, horse and dog)

  • Autumnalis – contains serovars Autumnalis and Bim (usual host is the mouse)

  • Canicola – contains just itself, Canicola (usual host is the dog)

  • Grippotyphosa – contains just itself, Grippotyphosa (usual hosts are rodents)

  • Icterohaemorrhagiae – contains serovars Copenhageni and Icterohaemorrhagiae (usual host is the rat)

  • Pomona – contains serovars Mozdok and Pomona (usual hosts include small rodents, cattle, sheep and pigs)

  • Serjoe – contains serovar Hardjo, Saxoebing and Serjoe (usual hosts include cattle, sheep and rodents)

*The host is infected with the bacteria but might not have any symptoms or signs.

 

How do dogs catch lepto?

Leptospira bacteria are either free-living in the environment or inside a mammal. Dogs catch lepto the same way as any other mammal (including people).

In the environment, the bacteria can survive for months in (warm) moist soil. So it's more common in areas with high rainfall, flooding or where the ground is irrigated. The bacteria get into the soil via the urine of an infected mammal. From the soil, the bacteria wash into bodies of water, including dams, rivers and puddles. The bacteria die if they dry out.

The bacteria get into mammals either:

  • directly – through contact with infected host tissues or secretions

  • indirectly – through contact with contaminated water, soil or food.

The most common means of transmission is by urine-contaminated water.

Coming into contact with lepto bacteria doesn't mean you'll automatically get sick. The bacteria have to get into the bloodstream. They get there through damaged skin and some mucous membranes (ie the lining surface of the mouth, nose, eyelids, lungs and gut).

Once the bacteria enter the bloodstream, they spread rapidly through the body. Whether they survive in the body and what damage they do depends on the serovar of the bacteria and the immunity of the mammal.

 

What are the signs of lepto in dogs?

The signs of leptospirosis in dogs vary. Some infected dogs do not show any signs of illness. Some have a mild 'flu-like' signs and then recover. Others develop severe illness and death.

There is no symptom that waves a big red lepto flag. All signs of lepto occur with other (much more common) diseases.

Initially, when the bacteria get into the bloodstream, you might see (acute) signs such as:

  • fever, shivering

  • lethargy, depression

  • muscle tenderness, joint pain (with reluctance to move)

  • loss of appetite

Think of how you feel when you're coming down with the flu. Most dogs survive this acute phase and many recover completely.

If the bacteria get past the immune cells in the blood, they can go to the organs. Which organs are most affected depends on the serovar of the organism, the immunity of the dog, and the age of the dog. Younger dogs tend to be more severely affected than older ones.

The most commonly affected organs are the kidneys and the liver. In the kidneys, the bacteria reproduce (and end up in urine) as well as causing kidney damage. They can do enough damage to cause kidney failure. Up to 20% of patients also experience liver failure.

Signs of kidney and liver damage may show up 1–2 weeks after the acute phase and include:

  • vomiting, diarrhoea

  • increased thirst

  • changes in the frequency or amount of urination

  • dehydration

  • jaundice (yellowing of the skin and mucous membranes)

  • bleeding disorders (blood-tinged vomit, urine, stool or saliva; nosebleeds; pinpoint bruises on gums or on light-coloured skin)

Dogs may occasionally develop severe lung disease and have difficulty breathing.

 

How is leptospirosis diagnosed?

If we suspect lepto, we'll recommend further testing. Because the signs shown are non-specific for any one disease and lepto is rare, we start with routine blood and urine testing.

If we can't rule out lepto with routine testing, we may run more specific tests.

It is very hard to detect the bacteria themselves. It is more practical to look for antibodies the body has made against them. Finding antibodies tells us that the dog has either been infected with lepto or has been vaccinated.

Antibody levels are expressed as titres. A titre is a ratio that tells you how much a sample needs to be diluted before it's too dilute to detect antibodies. For example, a titer of 1:32 means that serum diluted out 32 times still has detectable antibody.

MAT testing

The traditional antibody test for Leptospira interrogans sensu lato is the MAT test. This stands for microscopic agglutination testing.

A value of 1:800 or higher is supportive of a positive diagnosis. But confirmation is not made until a second titer is run 2–4 weeks later and it shows a four-fold increase. Running paired titres isn't always practical – we might not want to wait 2–4 weeks to start treatment. A very high initial titre (in a dog who hasn't been vaccinated in the last 3 months) might be enough to make a provisional diagnosis.

ELISA testing

ELISA testing can distinguish between two types of antibodies: IgM and IgG. This is helpful in working our whether a titer is high from vaccination or from natural disease.

Finding a high IgM titre indicates a new and active immune stimulation. Unless the dog was recently vaccinated, this means active infection.

Other tests

We can detect small amounts of leptospire DNA with PCR testing. This is an excellent test if vaccination has been recent because it's not looking at antibodies. But PCR testing detects dead organisms, making it hard to interpret in a recovering patient.

Lepto bacteria can be detected in urine by doing what is called darkfield microscopy. By making the background dark, the paler leptospire organisms may show up better. Although this sounds simple, there are problems with it, including:

  • the urine sample must be fresh to see the bacteria and getting it to a lab in the right timeframe can be difficult

  • bacteria are only shed intermittently into the urine

 

How is lepto treated?

Leptospirosis is generally treated with antibiotics and supportive care.

Chances or recovery are good if treatment is started early. There is still a risk of permanent residual kidney or liver damage in treated dogs.

 

What about vaccination?

Vaccinations against lepto do exist.

Of the 250 or so disease-causing serovars, about 10 of them can cause disease in pets. Vaccines have been developed against four of these:

  • canicola

  • grippotyphosa

  • pomona

  • icterohaemorrhagiae

Some cover the four serovars listed above, while others cover only two.

Remember back when we were looking at serovars and serogroups? Well, here's where that becomes relevant. Vaccination against one serovar can trigger a cross-immunity to ones in the same serogroup. But, there will be no immunity to other serogroups. For example, a dog vaccinated against L. canicola would have no protection against the outbreak of L. copenhageni in Sydney earlier this year.

If we do have a vaccination for the serovar present in an area, we can say that:

  • vaccine-derived immunity gives 6–12 months protection (ie revaccination is necessary)

  • vaccination will reduce the severity of disease but it does not prevent infection or infected dogs becoming carriers

  • there is a risk of vaccination reaction (there is a lot of conflicting information about this)

 

In summary

We are not currently recommending lepto vaccination for all the dogs we see at Elwood Vet. This is because:

  • risk of infection is low

  • we don't know what the serovar is that is responsible for the Melbourne 'outbreak'

  • we base vaccination on a case-by-case need rather than media reports (that are high on fear and low on detail)

Now, this may change. And if it does, we'll let you know.

Oh, and while cats are mammals and can be infected. Lepto in cats is extremely rare and there is no vaccination available.