Leptospirosis (Rat Fever) in Dogs in Kerala: Signs, Risk to Your Family and Prevention

Leptospirosis is caused by Leptospira bacteria. Infected animals carry the bacteria in their kidneys and pass them out in urine, and the US Centers for Disease Control and Prevention (CDC) notes that infected animals can shed bacteria for several months or years. The bacteria can survive in contaminated water or soil for weeks to months.

• •Rats are the main carriers. They can shed the bacteria without falling ill themselves.
• •Dogs, livestock and many wild animals can also carry and spread the infection.
• •There are many different strains, called serovars, and immunity to one does not guarantee protection against another.

For a dog, infection means a range of outcomes: some show no signs at all, others develop sudden kidney failure, liver failure or bleeding problems. Kidney damage can be permanent even when the dog survives.

Kerala's own Directorate of Health Services has described how leptospirosis, once a problem mainly in the waterlogged areas of Alappuzha and Kottayam in the 1990s, spread to become a public health problem in every district. Its article notes that heavy monsoons, intermittent rain and waterlogging create ideal conditions, because flooding forces rats out of their burrows and their urine contaminates stagnant water. It also notes that a disease once reported mainly in the monsoon is now reported throughout the year.

Dogs share that environment. In a seroprevalence study published in Veterinary World in 2013, researchers tested blood from 205 dogs in Kerala and found antibodies to Leptospira in 71.12% of them. Antibodies show exposure, not necessarily illness, but the figure shows how widely Kerala dogs meet these bacteria. The most common serovar was Autumnalis, and the authors argued that vaccines should include the serovars actually circulating, because immunity is serovar-specific.

Kerala has two monsoons, the southwest monsoon from June to September and the northeast monsoon from October to December, so the high-risk season covers much of the year. Trivandrum's low-lying roads, paddy fields, canals and drains all collect water after heavy rain.

According to the CDC and the Merck Veterinary Manual, dogs usually become infected through:

• •Contact with infected urine, or with water or soil contaminated by it, especially slow-moving or still water such as puddles, floodwater, ponds, canals and drains.
• •Drinking from, wading in or swimming in contaminated water.
• •Bite wounds and broken skin.
• •Catching or eating infected animals, such as rats.
• •Less commonly, from an infected mother to her puppies.

The CDC says almost every dog is at some risk, with higher risk for dogs that roam near water, wildlife or farm animals, and those that visit dog parks, boarding or training facilities. City dogs are not safe by default: rats live in drains and waste heaps in every town, and floods carry contamination into streets and compounds.

Signs can appear quickly and vary a lot. The CDC and Merck list:

• •Fever, low energy and reduced appetite.
• •Muscle or joint pain, stiffness, or reluctance to move.
• •Vomiting and dehydration.
• •Back pain, from inflamed kidneys.
• •Changes in urination: drinking and urinating much more, or much less, or not at all.
• •Yellow gums, eyes or skin (jaundice), a sign of liver involvement.
• •Discharge from the eyes or nose, eye inflammation, or coughing and breathing difficulty.
• •Bleeding problems, such as small red spots on the gums or blood in vomit, urine or stool.

Many of these overlap with tick fever and other illnesses, which is why testing matters. Some infected dogs show no signs at all and still shed bacteria.

Go to a vet now if your dog shows any of these signs, especially after walking through floodwater, mud or puddles, swimming in a canal or pond, or catching a rat. Call ahead so the clinic knows leptospirosis is possible and can take precautions.

Leptospirosis is confirmed with laboratory tests. The Merck Veterinary Manual explains that specialised tests can detect the bacteria in blood or urine, while others measure the dog's immune response. Blood and urine tests, X-rays and ultrasound show which organs are affected.

Treatment is a vet's job and often means hospital care, with fluids and medicines to fight the infection and support the kidneys and liver. Early treatment gives the best chance of recovery. Follow your vet's plan fully and return for every recheck, because the kidneys may need monitoring after the dog seems better.

Do not try to treat a suspected case at home, and do not wait to see if it settles. A delay of even a day or two can mean more kidney damage.

Leptospirosis is a zoonosis: it spreads between animals and people. In people, the CDC lists fever, muscle aches, headache, vomiting, red eyes, jaundice and other symptoms, usually starting 2 to 30 days after exposure, with a severe second phase in some people that can involve kidney or liver failure or meningitis. Kerala's health department has long counted leptospirosis among the communicable diseases causing the most deaths in the state.

If your dog is diagnosed or suspected, the CDC advises:

• •Avoid contact with your dog's urine and blood until your vet says treatment has worked.
• •Wear gloves to clean up urine, and cover any cuts on your hands with a waterproof bandage.
• •Disinfect surfaces your dog has urinated on. The CDC suggests an antibacterial cleaner or a solution of 1 part household bleach to 10 parts water.
• •Wash your hands after handling your dog, its bedding or anything that may have urine on it.
• •Make sure your dog finishes all its prescribed treatment. The CDC notes infected animals can shed bacteria in urine for up to 3 months.
• •Keep children and anyone with a weakened immune system away from the dog's toileting areas.
• •Tell your doctor that your dog has leptospirosis if anyone in the home develops fever or body aches.

The same habits, especially avoiding floodwater and covering cuts, protect the people walking the dog as much as the dog.

The World Small Animal Veterinary Association (WSAVA), whose guidelines most vets follow, changed its position in 2024. Its guidelines now say that where canine leptospirosis occurs, the implicated serogroups are known and suitable vaccines are available, vaccination of all dogs is highly recommended and the vaccine should be considered core. Leptospirosis is clearly present in Kerala, although Kerala researchers have pointed out that some locally common strains are not included in every vaccine, which is one more reason to ask your vet which vaccine they recommend.

Points to raise with your vet:

• •Which leptospirosis vaccine they use and which strains it covers. Vaccines protect against several common strains but not all of them.
• •The first course: WSAVA describes two doses 2 to 4 weeks apart to start, then regular boosters as your vet advises, usually yearly.
• •Timing: many owners like the booster done before the June monsoon.
• •What happens if a booster was missed. WSAVA advises restarting with two doses when protection has lapsed for a long time.

The CDC and Merck both note that vaccination does not give complete protection. A vaccinated dog can still be infected by a strain the vaccine does not cover, so keep up the prevention habits below as well. Our puppy vaccination schedule post shows where leptospirosis doses fit in the first months.

• •Do not let your dog wade, swim or play in floodwater, flooded paddy fields, canals, ponds, drains or roadside puddles, especially after heavy rain.
• •Carry clean drinking water and a bowl, so your dog is not tempted to drink from puddles.
• •Keep your dog on a leash near water, drains and waste heaps.
• •Rinse and dry paws, legs and belly after walking through mud or wet ground.
• •Check paws for cuts, and keep any wound covered and clean until it heals.
• •Do not let your dog chase, catch or eat rats.
• •Skip walks through flooded areas during and just after floods, and use indoor games instead.

The CDC advises keeping food, water and rubbish in closed containers and dealing with rodents promptly. At home, that means:

• •Store dog food in sealed containers, never open sacks.
• •Pick up food bowls after meals and take water and food bowls inside at night.
• •Keep waste bins closed and clear rubbish, coconut husks and clutter where rats nest.
• •Drain standing water from the yard, kennel area and any containers after rain.
• •Keep the dog's sleeping area raised and dry, and clean it regularly.
• •If you use rat poison or traps, place them where your dog cannot possibly reach them. Rat poison is itself a common emergency in dogs.

Screenshot this before each monsoon.

• •Ask your vet about leptospirosis vaccination, and book the booster before the rains.
• •No floodwater, puddles, canals, drains or flooded fields for your dog.
• •Clean water carried on every walk.
• •Rinse and dry muddy legs; cover cuts.
• •No rat hunting.
• •Dog food sealed, bowls in at night, bins closed, standing water drained.
• •Go to a vet now for: fever, vomiting, weakness, stiffness, yellow gums or eyes, much more or much less urine, or bleeding.
• •If your dog is ill: gloves for urine, hand washing, disinfect, and tell your doctor if anyone at home gets a fever.

If your dog is going into boarding or daycare, ask the facility what vaccinations and parasite prevention it requires. Neolokam, a cage-free dog farm east of Trivandrum city towards Kattakada, asks for a trial visit and temperament assessment; up-to-date rabies and core vaccinations with the record; current tick and parasite prevention as advised by your vet; and dogs must be comfortable around other dogs. Talk to your own vet about whether your dog's leptospirosis protection is current before any stay.