A dog charging toward a summer puddle can look harmless. But veterinarians warn that standing or slow-moving water can expose dogs to leptospirosis, a bacterial infection that can damage the kidneys, liver, lungs, and other organs.
The risk matters because it is not limited to hiking dogs or rural properties. The American Veterinary Medical Association says all dogs are at risk, regardless of age, breed, lifestyle, or where they live.
Leptospirosis is caused by Leptospira bacteria. AVMA says the bacteria can be found in soil, water, and infected bedding, and Cornell’s Richard P. Riney Canine Health Center says dogs are commonly exposed through water contaminated with urine, especially stagnant or slow-moving water such as puddles, ponds, and lakes.
That helps explain why summer can increase concern. AVMA says leptospirosis is more common in warm climates and Cornell says the bacteria thrive in warm, wet conditions, especially in late summer into fall, though the disease can occur anywhere at any time.
Exposure does not require a wilderness trip. AVMA lists ponds, marshes, puddles, and slow-moving sections of rivers or streams as common hotspots. It also points to rural properties, wildlife exposure, and contact with other dogs in urban areas, dog parks, and boarding or training facilities.
Rodents are a key part of the picture. Cornell says many animals can spread leptospirosis through urine, primarily rodents and small mammals, and AVMA notes that infected dogs can also shed the bacteria in urine while appearing healthy.
Once exposure happens, the bacteria can enter through ingestion, broken skin, or the eyes, nose, or mouth, according to Cornell. Cornell also says the organism attaches to cells lining blood vessels and then spreads through the body and organs, especially the liver and kidneys.
The consequences can be severe. AVMA warns leptospirosis can lead to kidney failure, liver failure, lung disease, heart muscle damage, bleeding disorders, and fluid buildup in the body. Both AVMA and Cornell note that some dogs can be left with lasting kidney or liver damage even after treatment.
Some dogs appear to face higher risk of infection or severe disease, including unvaccinated dogs, geriatric dogs, puppies as young as 11 weeks, rural dogs, and small-breed urban dogs. But a 2023 ACVIM consensus statement and AVMA guidance both stress the broader point: any dog can get it.
That is one reason symptoms can be easy to miss at first. Cornell lists increased thirst and urination, yellowing of the eyes or gums, small bleeding under the skin, and rapid or difficult breathing among the signs. AVMA also lists loss of appetite, vomiting, lethargy, abdominal pain, diarrhea, weight loss, stiffness, and muscle pain.
Those signs are not unique to leptospirosis, which makes veterinary care important. AVMA says diagnosis may involve a physical exam, blood tests, urine tests, X-rays, and sometimes ultrasound or other testing. Cornell also notes that PCR testing and antibody testing may be used to help confirm the diagnosis.
Treatment depends on how sick the dog is. AVMA says care generally includes antibiotics and supportive treatment, while Cornell says hospitalization with IV fluids is often needed at first. In severe cases, AVMA says dogs may need oxygen therapy, intensive care, or even dialysis.
Veterinary experts emphasize speed. Jenny Marin, a clinical assistant professor at the Virginia-Maryland College of Veterinary Medicine, said, “Immediate examination by a veterinarian is crucial.” She also said, “Avoiding exposure of people to urine of possibly infected pets is also very important to prevent transmission to people.”
That human-health point matters because leptospirosis is zoonotic. AVMA and Cornell both say people can be infected, though AVMA notes the risk from an infected dog is still considered low. Even so, handwashing and avoiding contact with urine are standard precautions if a dog is suspected to be infected.
The clearest prevention step is vaccination. AVMA recommends that all dogs be vaccinated for leptospirosis, and Cornell says prevention should include annual vaccination. The usual schedule described by AVMA and Cornell is two initial doses spaced about four weeks apart starting at 12 weeks of age, followed by annual boosters. AVMA also notes that expert guidance now supports annual vaccination for all dogs rather than every three years.
Vaccination is not the only step. Cornell advises limiting access to standing water, avoiding contact with wildlife, and preventing rodent problems. AVMA similarly recommends keeping dogs away from marshy areas, stagnant water, farm animals, and wild rodents.
For summer play, cleaner water choices can reduce risk without keeping dogs indoors. Pools and backyard sprinklers are safer options than puddles, marshy edges, or slow-moving water where contamination may not be visible.
The practical takeaway is calm, not panic. Dogs do not need to avoid the outdoors, but puddles and stagnant water deserve more caution than they seem to. If your dog has possible exposure and then develops vague signs such as vomiting, lethargy, increased thirst, or yellowing of the gums or eyes, it is time to call your veterinarian promptly. What would you do if your dog were in this situation? Share your thoughts in the comments.
By Sarah Mitchell — 8 years as a local-news reporter covering animal welfare, shelters, neighborhood disputes, and public-safety pet stories.
