What is leptospirosis?

Leptospirosis (“lepto”) is a disease caused by infection with Leptospira bacteria. These bacteria are found worldwide in soil and water. There are many strains that can cause disease.

Where does it occur?

Leptospirosis is more common in warm climates with high rainfall but can occur anywhere. Exposure to slow-moving or stagnant water is a major risk factor. It can also be contracted from wet, shaded grass or along rivers and lakes.

In the United States, southwestern states tend to have lower risk. Cases occur most often in late summer and fall, although timing varies by region.

How is it spread?

Dogs and cats can become infected through:

• Contact with infected urine
• Contact with contaminated soil, water, food, or bedding
• Open wounds or mucous membranes
• Bites from infected animals
• Eating infected tissues or carcasses
• Transmission from mother to offspring (rare)

What animals are at risk?

Dogs are most commonly affected. Leptospirosis in cats is rare and usually mild.

In some areas, nearly all dogs are at risk regardless of environment (urban, suburban, or rural).

Common risk factors include:

• Drinking from rivers, lakes, or streams
• Roaming rural properties
• Exposure to wildlife or farm animals
• Contact with rodents or other dogs (parks, kennels, urban areas)

What are the symptoms?

Symptoms vary widely. Some dogs show no signs, while others develop severe illness.

Possible symptoms include:

• Fever, shivering, muscle pain
• Increased thirst or urination changes
• Vomiting, diarrhea, loss of appetite
• Lethargy or dehydration
• Jaundice (yellowing of skin/eyes)
• Kidney or liver failure
• Breathing difficulty
• Bleeding disorders

How is it diagnosed and treated?

Diagnosis may include blood tests, urine tests, imaging, or PCR testing.

Treatment typically involves:

• Antibiotics
• Fluid therapy
• Supportive care

Severe cases may require hospitalization, oxygen support, or dialysis.

Are people at risk?

Yes. Leptospirosis is a zoonotic disease, meaning it can spread from animals to people.

In humans, it may cause flu-like symptoms or more serious illness affecting the liver or kidneys. Most U.S. cases are linked to water exposure rather than pets.

How is it prevented?

Vaccination is effective and typically protects dogs for at least 12 months. Annual vaccination is recommended for at-risk dogs.

To reduce exposure:

• Avoid stagnant or slow-moving water
• Limit contact with wildlife and rodents
• Prevent access to contaminated environments

If your dog is infected

Take these precautions:

• Give medications exactly as prescribed
• Avoid contact with urine
• Wear gloves when cleaning
• Disinfect contaminated areas promptly
• Wash hands after handling your pet