» Leptospirosis






Leptospirosis, also known as « rat fever » or, in its severe form, Weil’s disease, is an infection caused by the bacterium Leptospira interrogans, which has more than 200 different variations. This bacterium is found in many animal species (rats, mice, voles, hedgehogs, dogs, cows, pigs and horses) and also in humans. The main hosts are rodents, which then pass on the disease, primarily to dogs and humans but sometimes also to livestock and horses, and exceptionally to cats.

This disease is zoonotic, which means it can be transmitted from animals to humans (another example is rabies). It is estimated that leptospirosis affects at least 1 million people and causes 60,000 deaths each year worldwide, including Belgium.


The bacteria, or leptospires, are transmitted through:

  • Direct contact: contaminated urine, bites, ingestion of contaminated meat, transplacental route ;
  • Indirect contact: plants, soil, water, food contaminated with urine or blood from an infected rodent.

Leptospires are particularly well suited to an aquatic environment (ponds, marshes, streams, etc.), so are more likely to be found in places like these, especially in autumn and spring.

The bacteria gain entry to the body through the mucous membranes of the eyes, mouth and nose, through wounds, abrasions and cuts in the skin or through thin-skinned areas such as the ears. After an incubation period of 3-20 days, they disperse through the bloodstream. They then colonise and proliferate in different organs: kidneys, liver, meninges, eyes, placenta and foetus.


  • Dogs

In its acute form, the disease causes fever (39.5°C – 41°C), tremors, muscle weakness, vomiting, dehydration, and an increased respiratory and heart rate. Infected animals may show blood in their stools, vomiting, nose bleeds and small bruises on the skin. The disease progresses quickly to death due to cardiovascular shock.

In its more common sub-acute form, the disease causes fever, appetite loss, muscular pain and bruising. Other symptoms include conjunctivitis, rhinitis, coughing and breathing difficulties. Infected animals drink a lot and urinate either frequently or infrequently, or not at all if their kidneys are severely affected. They lose weight and develop ascites (build-up of fluid in the abdomen) and icterus (yellowing of the mucous membranes). They may also show vomiting, diarrhoea, dehydration, anaemia and blood in their urine.

  • Cats

Cats are particularly resistant to this infection, which is good news because they hunt the mice that cause it!

  • Horses

Symptoms include jaundice, conjunctivitis, keratitis (inflammation of the cornea) and depression. Mares spontaneously abort. Horses have difficulty moving and experience nervous and digestive disorders, as well as skin problems.

  • Cattle

Cows suffer from fever and loss of appetite, and stop chewing the cud. Milk yield drops and the milk may be blood-tinged. Abortion rates rise. Animals may develop a limp or become anaemic.


Only your vet can confirm this disease. He or she will ask if your dog has been walking or swimming in high-risk areas, such as ponds, marshes or streams, or has been in contact with live or dead rodents. Depending on the symptoms, your vet will then do a blood test and possibly a urine test to make sure of the diagnosis.


Luckily it can!

A minimum two-week course of antibiotics will kill the bacteria. If necessary, your vet will prescribe anti-diarrhoea medication and Regul TM, supplements to support the kidneys (e.g. Reno Pro TM) and liver (e.g. Hepa Supp TM), as well as a treatment to reduce fever.


This is the easiest and safest way to protect your pet. All it needs is a first vaccination as a pup, followed up by annual boosters.

Transmission from dogs to humans is very rare, but special hygiene precautions are recommended when handling sick pets (gloves, protective clothing, etc.). Humans can contract leptospirosis through contact with infected domestic or wild animals or with contaminated water.

Some occupations are at higher risk, such as vets, farm workers, sewer workers, roadmen and freshwater fishermen, as are people participating in certain water sports. As in animals, the disease in humans is characterised by fever, jaundice and nephritis (kidney infection).


Dr Eric Witvrouw
DMV | Animal Behaviourist
Veterinary Center ÉducaVet’s

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