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Key takeaways

Leptospirosis is a bacterial infection that affects many animals, including dogs and humans.

  • Transmission most commonly occurs through contact with Leptospira bacteria of mucous membranes or skin wounds
  • Symptoms vary widely and asymptomatic transmission is possible
  • Left untreated, leptospirosis damages internal organs; in severe cases the infection can be fatal
  • Immediate veterinary attention is required for dogs showing symptoms of leptospirosis such as increased urination, lethargy, yellow gums, vomiting, and diarrhea
  • Diagnosis is complex. Strategies include physical exam, blood work, urinalysis, X-rays, and ultrasound
  • Treatment includes antibiotics and supportive care
  • Vaccination is available for 4 of the 10 known variants that affect dogs
  • Prognosis with early treatment is good; if organ damage has already occurred, prognosis is guarded
  • Leptospirosis is transmissible to humans through contaminated pet urine. Protective hygiene protocols are required when treating/cohabitating with infected animals
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A closer look: Leptospirosis in Dogs

The severity of leptospirosis depends on how far it has progressed and what systems it has affected.

In some cases, especially in dogs who have been vaccinated, leptospirosis causes no symptoms. Asymptomatic dogs can still pass the infection on to other animals and to humans.

In most cases, leptospirosis is acute, with symptoms appearing rapidly. If left untreated, infections in the kidney, liver, or lungs occur. Depending on the specific strain of bacteria causing infection, the length of time it remains untreated, and the overall health of the dog, damage to these systems progresses and eventually becomes fatal.

In some cases, leptospirosis becomes chronic, and the dog has recurring symptoms that seem to come and go.

In some cases, especially with young dogs, the onset is extremely sudden and overwhelming.

Onset of symptoms typically occurs approximately 7 days after contact with infected material or animals, although in some cases this may be as long as 30 days.

Dogs who have been exposed to Leptospira bacteria, or who are suspected of having leptospirosis, require immediate veterinary attention in order to mitigate damage to the organs.

Treatment begins to take effect within 24 hours, however the bacteria continue to be shed through the urine for up to 2 months. During this time, transmission to other animals and humans is possible.

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Risk factors

Risk factors for leptospirosis in dogs include:

  • Drinking from rivers, lakes, or streams
  • Roaming rural properties
  • Exposure to other animals including rodents, farm animals, wild animals, and other dogs
  • Open wounds, scrapes, or waterlogged skin

Dogs vaccinated against leptospirosis are less likely to become ill from the disease, but vaccinated dogs may still be carriers of the bacteria. Owners of dogs diagnosed with leptospirosis can become infected if they are in contact with the dog’s urine.

Young dogs (under the age of one) are particularly susceptible to leptospirosis infection.

Possible causes

The cause of leptospirosis is the bacteria Leptospira. These spiral-shaped bacteria are shed through urine from infected animals. They can live in contaminated soil for weeks or months. They can also live in standing or slow-moving water, as well as on surfaces contaminated by infected urine.

Transmission occurs when contact is made between contaminated water or soil and either skin wounds or the mucous membranes of dogs. In rarer cases, leptospirosis is transmitted by eating the flesh of a contaminated animal, or from mother to puppies through the placenta.

Humans are also susceptible to infection. Humans in contact with infected urine or surfaces contaminated with infected urine must take precautions against infection.

Main symptoms

The symptoms of leptospirosis are variable and non-specific (they relate to many different conditions).

If left untreated, symptoms worsen as other organs and systems are affected.

Testing and diagnosis

Diagnostic tools include:

  • Physical examination
  • Urinalysis
  • Blood work, including testing for the bacteria or antibodies against the bacteria
  • X-rays
  • Ultrasound

Leptospirosis can be difficult to confirm, as the tests currently available have shortcomings that may prevent diagnosis.

PCR tests are used to detect leptospire DNA, but are unreliable in cases where the dog has recently been on antibiotics. Also, PCR tests do not indicate which strain is present.

Microscopic Agglutination Tests (MAT) measure antibodies in the bloodstream and indicate the strain, but are unreliable in cases where the dog has been vaccinated. Also, MAT requires retesting after 2 to 4 weeks, during which the dog must stay in isolation.

In-house test kits cannot distinguish between strains, and are also unreliable in cases where the dog has been vaccinated, but a negative test is useful to rule out leptospirosis.

Using a combination of tests as well as urinalysis and other diagnostic tools is often the best route to diagnosis.

Steps to Recovery

The primary treatment for leptospirosis is antibiotics. Additional treatments include IV fluids to control damage to the kidneys. In some cases, blood transfusions are required.

Areas of the home that have been in contact with urine require disinfection with an iodine-based product. Gloves are required during cleaning.

With early and aggressive treatment, prognosis is good. In cases where damage has occurred to the lungs, liver, or kidneys, prognosis is guarded. Left untreated, or in particularly virulent cases especially in young dogs, leptospirosis is fatal.


Vaccination is available for 4 of the 10 strains of leptospirosis.

Vaccination reduces symptoms and prevents significant damage to other systems.

Environmental and lifestyle management strategies are necessary to prevent transmission of the strains for which a vaccine does not exist.

Limiting contact with the bacteria by removing standing water, controlling rodent infestations, and avoiding contact with other infected animals helps to prevent infection.

Preventing human infection requires pet parents with infected dogs to wear protective clothing while handling the dog, as well as while they are cleaning surfaces that have had contact with the dog’s urine. Washing hands with soap and water after contact is required to maximize prevention efforts.

Is Leptospirosis in Dogs common?

Leptospirosis is uncommon in dogs.

Typical Treatment

  • Antibiotics
  • IV fluids


Wendy Brooks, DVM, DABVP - Writing for Veterinary Partner
Phyllis DeGioia, Veterinary Partner Editor - Writing for Veterinary Partner
No Author - Writing for Centers for Disease Control and Prevention
No Author - Writing for American Veterinary Medical Association
No Author - Writing for Merck Animal Health

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