CONDITION
Leptospirosis
Why this matters now
Leptospirosis is a bacterial infection that affects dogs and can spread to humans—a zoonotic disease. The bacteria are carried by wildlife, particularly rats, and persist in water and moist environments. Dogs contract infection through contaminated water, soil, or contact with infected animals. Urban and rural dogs alike can be exposed, though risk varies with lifestyle and geography.
Following exposure, the bacteria spread through the bloodstream to various organs, particularly the kidneys and liver. Signs can range from subclinical infection to severe, life-threatening illness. Acute cases may present with kidney failure, liver damage, and bleeding disorders. Less severe infections may cause vague illness that resolves but can lead to chronic kidney changes. The incubation period is typically five to fourteen days.
Signals & patterns
Early signals
Sudden fever and lethargy
Initial infection often causes high fever and marked decrease in energy.
Loss of appetite
Affected dogs typically refuse food.
Muscle pain and stiffness
Dogs may be reluctant to move and appear painful, particularly in the back and legs.
Vomiting and diarrhoea
Gastrointestinal signs are common early in the disease course.
Later signals
Increased thirst and urination, or reduced urination
Kidney involvement affects urine production—either increased or dangerously decreased.
Jaundice
Yellowing of the skin, gums, and whites of the eyes indicates liver involvement.
Bleeding
Some dogs develop bruising, bloody vomit or stool, or nosebleeds due to clotting abnormalities.
Difficulty breathing
Lung involvement can cause respiratory distress in severe cases.
Click to read about the biological mechanisms
How this is usually investigated
Diagnosis combines clinical findings with laboratory testing. Because leptospirosis can mimic other conditions and poses zoonotic risk, thorough investigation is valuable.
Blood tests (biochemistry)
Complete blood count
Urinalysis
Leptospira serology (MAT)
PCR testing
Options & trade-offs
Treatment involves antibiotic therapy to eliminate the bacteria and supportive care for organ damage. Early treatment improves outcomes.
Antibiotic therapy
Specific antibiotics that target leptospira, typically given in two phases.
Trade-offs: Initial intravenous antibiotics address the acute phase. A second antibiotic course eliminates kidney carriage to stop shedding.
Intravenous fluid therapy
Aggressive fluid support to maintain kidney perfusion and correct dehydration.
Trade-offs: Essential for supporting kidney function. Requires hospitalisation and careful monitoring of fluid balance.
Management of kidney failure
Supportive care for acute kidney injury, potentially including dialysis.
Trade-offs: Severe cases may require intensive intervention. Some dogs recover kidney function; others may have permanent damage.
Treatment of bleeding disorders
Plasma transfusions or other interventions for clotting abnormalities.
Trade-offs: May be lifesaving in severely affected dogs. Addresses a serious complication of infection.
Zoonotic precautions
Handling precautions to protect humans caring for infected dogs.
Trade-offs: Gloves, hand hygiene, and care with urine reduce human exposure risk. Particularly important for immunocompromised individuals.
Common misconceptions
"Leptospirosis only affects dogs that swim in ponds"
Dogs can be exposed in urban environments through rat urine contaminating gardens, puddles, or parks. Risk is not limited to rural or water-associated activities.
"Vaccination prevents all leptospirosis infection"
Vaccines protect against specific serovars included in the product. Other serovars may still cause disease. Vaccination significantly reduces risk but is not absolute.
"Leptospirosis is not found in the UK"
Leptospirosis occurs throughout the UK. Certain regions and seasons carry higher risk, but exposure can occur anywhere wildlife is present.
Understanding local risk factors helps inform vaccination decisions. Noting whether dogs swim in natural water, encounter rodents, or have access to areas with standing water provides context. Observing for early signs like sudden fever, reluctance to move, or appetite loss allows prompt attention. Awareness that humans can acquire leptospirosis informs sensible hygiene practices when caring for unwell dogs.
Last reviewed: 24 April 2026 · Dr Alastair Greenway MRCVS