Leptospirosis (Zoonotic): Infection and Prevention

ImmunityDiseasesMeongsiljang Veterinary Advisory Board

Leptospirosis is a zoonotic bacterial infection spread through contaminated water and urine from rodents. Vaccination and avoiding puddles are key to prevention, and if you notice fever or jaundice, seek veterinary care immediately.

What is Leptospirosis?

Leptospirosis is a zoonotic disease caused by Leptospira bacteria, which can damage the liver and kidneys. Early treatment is crucial. Infection occurs when pets lick water puddles, streams, or soil contaminated with rodent urine, or when the bacteria enter through wounds. If symptoms such as fever, vomiting, jaundice, or changes in urine output appear, seek veterinary care within 24 hours. Since this disease can also affect humans, if your pet is infected, you should also practice strict hygiene to protect yourself.

How is it transmitted?

Leptospira bacteria spread through water or soil contaminated with the urine of infected animals, primarily rodents like rats and other wildlife. Dogs can become infected by drinking contaminated water or when the bacteria enter through small skin wounds or mucous membranes while wading through puddles. Cats often contract the infection by hunting and eating infected rodents. The risk of infection increases during warm, humid rainy seasons and summers, when standing water and soil are more easily contaminated with urine. Dogs that frequently walk in urban parks or along rivers, as well as cats that go outdoors and hunt rats, are at particularly high risk.

Suspect Leptospirosis if you notice these symptoms

In its early stages, leptospirosis can resemble a common cold, making it easy to overlook. If your pet exhibits any of the following symptoms, please seek veterinary testing immediately: - Fever or hypothermia: Body temperature may spike or drop, accompanied by shivering and lethargy. - Vomiting and loss of appetite: Your pet may refuse water and fast for more than a day. - Jaundice: The gums, whites of the eyes, and inner ears may turn yellow. - Urinary abnormalities: Urine output may decrease drastically (anuria) or, conversely, increase in frequency and volume. - Muscle pain: Gait may become stiff, and muscles may be tender to the touch. - Bleeding tendencies: In severe cases, blood may appear in vomit or diarrhea, or respiratory issues such as coughing and panting may develop.

A lethargic dog lying down without energy

Emergency signs requiring immediate veterinary care

If you notice any of the following symptoms, your pet needs emergency veterinary care within 24 hours. Leptospirosis can rapidly progress to acute kidney or liver failure, significantly increasing the risk of death. 1. Inability to urinate for more than 12 hours, or conversely, passing large amounts of very pale, watery urine 2. Yellowing of the gums or the whites of the eyes (jaundice) 3. Vomiting or diarrhea containing blood 4. Rapid breathing and coughing up blood 5. Seizures or decreased level of consciousness

How is it diagnosed?

At the clinic, we first check for abnormalities in liver enzymes (ALT), kidney markers (BUN and creatinine), and electrolytes (potassium and phosphorus) through blood and urine tests. To confirm leptospirosis, we use both the MAT test (serum antibody titer) and PCR testing (DNA detection). During the first week of infection, antibodies may not yet have developed, so the MAT test can come back negative. Therefore, we collect blood samples twice, 7 to 14 days apart, to confirm diagnosis by checking if antibody levels rise fourfold or more between the acute and convalescent phases. PCR is useful for early diagnosis because it directly detects the bacteria’s DNA in blood or urine during the early stage (within 7 to 10 days of onset), before antibodies develop. However, if antibiotics are administered first, PCR results may be falsely negative, making the order of testing important. We also use ultrasound to examine the kidneys and liver to assess the extent of organ damage.

How is it treated?

Leptospirosis is primarily treated with antibiotics. Typically, veterinarians start with intravenous ampicillin or amoxicillin, followed by approximately three weeks of doxycycline, adjusting the medication and duration based on the pet’s weight and liver and kidney function. Alongside antibiotics, fluid therapy is essential to correct dehydration and electrolyte imbalances, using balanced electrolyte solutions to maintain kidney blood flow and regularly monitoring hydration status. Severe cases with significant kidney impairment require hospitalization for close monitoring of urine output and intensive supportive care. To prevent transmission to owners and family members, it is essential to wear gloves when handling feces and urine throughout the treatment period.

A puppy receiving intravenous fluids at the hospital

Home care management

Even after discharge, the risk of infection remains, so maintaining strict hygiene is crucial. - Waste disposal: Wear disposable gloves and wash your hands thoroughly with soap and warm water after handling urine or feces. - Cleaning and disinfection: Disinfect floors and litter areas with 70% alcohol or diluted bleach. - Walk restrictions: Avoid puddles, streams, and grassy areas until treatment is complete. - Drinking water management: Provide only clean, purified water and do not use outdoor water bowls. - Human safety: Pregnant women, children, and immunocompromised individuals should minimize direct contact during the recovery period. If there was liver or kidney damage, regular blood tests are necessary for 3 to 6 months post-recovery to monitor progress.

Vaccination and environmental management are the best prevention

Prevention is far more important than treatment for leptospirosis. - Dog vaccinations: Included in the combination vaccine (DHPPL) or administered as a separate leptospirosis vaccine. Annual booster shots are required. - Cats: Since there is no dedicated vaccine, minimizing outdoor exposure is key. - Environmental management: Remove attractants for rodents around your home, such as food waste and open food containers. - Walking habits: Prevent access to standing water and areas near drains, and avoid puddles after rain. Before traveling, camping, or visiting rural areas, please consult your veterinarian to review vaccination schedules.

Reviewed by a veterinarian

Dr. Tony — Punnawat Phongkittirak

Veterinarian

A veterinarian who majored in veterinary medicine at Khon Kaen University, Thailand, and completed the IVSA program at North Carolina State University in the United States. Drawing on clinical experience at animal hospitals, he works in the pet healthcare field and is dedicated to building a digital care environment that connects pet parents with veterinarians.

Frequently Asked Questions

Can dogs transmit leptospirosis to humans?

Yes, it is a classic zoonotic disease. Humans can become infected through direct contact with the urine or blood of an infected animal. Please be sure to wash your hands thoroughly, wear gloves, and disinfect properly.

Can my pet still get sick even after being vaccinated?

Yes, it’s possible. Vaccines only protect against a few common serotypes, so they don’t offer complete protection against all strains. Additionally, even vaccinated dogs can become infected and shed the bacteria in their urine. However, vaccination often results in much milder clinical symptoms, so it’s best to combine it with proper environmental management.

Can it still be transmitted to other pets even after recovery?

Once antibiotic treatment is completed, bacterial shedding typically decreases significantly. However, bacteria may persist in the urine for several weeks to months after recovery, maintaining infectious potential. We recommend confirming the absence of bacterial shedding through a follow-up test before reintroducing the pet to a multi-cat or multi-dog household, and exercising caution with urine handling until then.

Should dogs that live exclusively indoors still receive vaccinations?

If your dog never goes for walks or outside, the risk is low, but if they go to the park even once, vaccination is safer. If your dog lives in an environment where rodents are present (such as a house or rural area), we recommend vaccination even for indoor dogs.

Can cats get leptospirosis?

They can get infected, but they tend to be more resistant than dogs, so most cases are mild or asymptomatic. For outdoor cats, testing should be included if high fever and loss of appetite persist.

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References

[1] Sykes JE, Canine and Feline Infectious Diseases, Chapter 50 Leptospirosis, 2013

[2] Greene CE, Infectious Diseases of the Dog and Cat, 4th Edition, 2012

[3] ACVIM Consensus Statement on Leptospirosis in Dogs (2010)