What exactly is leptospirosis and why does it target the kidneys?

Leptospirosis is caused by corkscrew-shaped bacteria called Leptospira, and more than 250 serovars exist worldwide, though only a handful account for most canine infections in North America, including Icterohaemorrhagiae, Canicola, Grippotyphosa, and Pomona (Merck Veterinary Manual, 2023). After entering through mucous membranes or broken skin, the bacteria multiply in the bloodstream within days and then colonize the renal tubules and liver, where they trigger acute inflammation. The kidneys are particularly vulnerable because Leptospira has a specific affinity for renal tissue, and infected dogs continue shedding live bacteria in their urine for weeks to months even after antibiotic treatment begins (Cornell Riney Canine Health Center, 2022).

This is also a zoonotic disease, meaning infected dogs can pass the bacteria to the people and other pets in their household through contact with urine or contaminated water, which is part of why the CDC tracks canine leptospirosis as a public health concern rather than purely a veterinary one (CDC, 2023).

What are the first signs a dog owner usually notices?

Early leptospirosis often looks like a vague, flu-like illness: lethargy, fever, muscle soreness, and reduced appetite that can easily be mistaken for an upset stomach. As the infection progresses over 2 to 7 days, more specific signs emerge, including vomiting, increased thirst, and either a marked drop in urine output or unusually frequent urination as the kidneys start to fail (AVMA, 2023). Some dogs develop jaundice, a yellowing of the gums, skin, or whites of the eyes, which signals liver involvement and is considered a hallmark presentation in more severe cases.

Because these signs overlap with many other illnesses, owners frequently wait a day or two before seeking care, which the ACVIM notes is one of the biggest risk factors for a poor outcome, since kidney injury from leptospirosis can become irreversible within days if untreated (ACVIM, 2023).

How does a dog actually get infected with leptospirosis?

Dogs contract Leptospira primarily by drinking, swimming in, or wading through water contaminated with infected urine, including puddles, ponds, slow-moving streams, and flooded yards after heavy rain. Wildlife reservoirs such as raccoons, skunks, opossums, and rats shed the bacteria continuously without necessarily showing illness themselves, which is why suburban and even urban dogs are increasingly diagnosed, not just rural or farm dogs (Cornell Riney Canine Health Center, 2022). Warm, humid climates and standing water after rainfall dramatically increase environmental survival of the bacteria, and Merck notes that outbreaks often cluster in late summer and early fall in temperate regions (Merck Veterinary Manual, 2023).

Risk climbs further for dogs that roam off-leash near creeks, hunt or work on farms, or live in households near livestock, since cattle and pigs can also carry and shed certain Leptospira serovars into shared water sources.

What tests do vets run to confirm the diagnosis?

Because early signs are nonspecific, veterinarians typically start with bloodwork and a urinalysis to check kidney and liver values, looking for elevated BUN, creatinine, and liver enzymes along with protein or blood in the urine. Confirmatory testing usually involves a PCR test to detect Leptospira DNA directly, often paired with a microscopic agglutination test (MAT), which measures antibody titers against multiple serovars and may require a repeat sample 2 to 4 weeks later to confirm rising titers (Cornell Riney Canine Health Center, 2022).

Because treatment often can't wait for lab confirmation, many veterinarians start antibiotics based on clinical suspicion and history, such as recent exposure to standing water or wildlife, while test results are pending, since delaying therapy increases the risk of permanent organ damage (AVMA, 2023).

How is leptospirosis treated once it's diagnosed?

Treatment centers on antibiotics, most commonly doxycycline, which clears the bacteria from the bloodstream and helps stop the dog from shedding it in urine; a typical course runs about 2 weeks (Merck Veterinary Manual, 2023). Dogs with significant kidney involvement often need hospitalization for IV fluid therapy to support kidney function and correct dehydration and electrolyte imbalances, sometimes for several days, and severe cases with acute kidney injury may require more intensive interventions such as dialysis at a specialty referral hospital.

Supportive care, including anti-nausea medication and nutritional support, is common during hospitalization, and veterinary staff typically take precautions such as gloves and dedicated cleaning protocols when handling urine from a suspected leptospirosis patient, given the zoonotic risk (CDC, 2023).

What does home care and recovery look like after treatment?

Once a dog is stable enough to go home, owners usually finish the full course of oral antibiotics and monitor appetite, energy, water intake, and urination closely for signs of relapse or worsening kidney function. Because dogs can continue shedding Leptospira in urine for weeks after clinical recovery, veterinarians commonly recommend keeping the dog away from other pets' water bowls, cleaning up urinated areas promptly with a disinfectant, and washing hands after handling the dog during this period (Cornell Riney Canine Health Center, 2022).

Follow-up bloodwork, typically at 2 to 4 week intervals, helps confirm that kidney and liver values are trending back toward normal, since some dogs are left with reduced kidney reserve even after the infection clears.

What's the long-term outlook, and can dogs get it again?

Dogs treated early, before significant kidney or liver damage sets in, generally have a good prognosis and often return to normal life within a few weeks. Dogs diagnosed later in the disease course, especially those requiring dialysis for acute kidney injury, face a more guarded outlook, and some studies cited by veterinary internal medicine specialists report mortality rates ranging from roughly 10% to over 20% in severe hospitalized cases (ACVIM, 2023). Surviving dogs can sometimes have lasting reduced kidney function that requires a therapeutic renal diet or ongoing monitoring.

Because immunity from natural infection or vaccination is serovar-specific and doesn't cover all strains, previously infected or vaccinated dogs can still contract leptospirosis from a different serovar, which is why annual revaccination with a 4-serovar vaccine is recommended in areas with ongoing exposure risk (AAHA, 2022).

How can pet parents actually prevent leptospirosis?

The core prevention tool is vaccination: the American Animal Hospital Association's canine vaccination guidelines now classify leptospirosis vaccination as a non-core but broadly recommended vaccine for most dogs, given how widespread wildlife reservoirs have become even in suburban settings (AAHA, 2022). The vaccine covers the four major serovars and is typically given as an initial two-dose series followed by annual boosters. Beyond vaccination, limiting access to stagnant water, controlling rodents around the home, and avoiding areas with heavy wildlife traffic after rainfall meaningfully cut exposure risk.

For households with young children, elderly family members, or immunocompromised individuals, extra hygiene precautions around a dog with suspected or confirmed leptospirosis are worth discussing with both a veterinarian and a physician, since the CDC classifies leptospirosis as a nationally notifiable zoonotic disease in humans (CDC, 2023).