Leptospirosis, also known as fall fever or mud fever, is the most widespread zoonosis in the world that affects both animals and humans. The incidence of infections in domestic dogs has risen markedly in recent years in the United States and Canada. Pathogenic species of the genus Leptospira can cause a wide range of symptoms, from a mild, flu-like illness to a severe disease characterized by multiorgan system complications leading to death. In North America, a variety of wild and domestic animals can act as reservoir hosts that can shed the organism in their urine for months or years after being infected. These include dogs, rats, swine, cattle, raccoons and southern flying squirrels3. Pets may come into contact with Leptospira by contact with wildlife urine or farm animal reservoirs through activities such as swimming, drinking or walking through contaminated water, soil or mud.2 In dogs, leptospirosis is a serious disease with a case fatality rate of 10-20%.

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Leptospirosis is more common where the dog has some contact with rats or rat droppings and urine.

The bacteria attack the dog's kidneys and liver. The disease is more common where the dog has some contact with rats or rat droppings and urine. The signs of leptospirosis were once confused with those of canine hepatitis and distemper, and they still are. One of the signs of the disease is a change in the color and smell of the dog's urine which becomes a deep yellow, even orange, color, and has a strong, offensive smell. The dog may vomit any recently eaten food and will suffer considerable pain in the abdominal area. He will also be severely dehydrated and therefore very thirsty. The mucous membranes of the gums and palate, the eyes, and the skin itself may turn yellowish. By this time, the dog's condition is very serious. Probably his kidneys have been permanently affected, and most of the internal damage has been done. At the onset of the illness, which is sudden, the temperature will rise alarmingly, perhaps as high as 105° F, and fall almost 5 degrees on succeeding days. In some cases, the stools appear bloody, and there is a bloody discharge from the gums. If the dog vomits, the vomitus too may contain blood. The dog is very depressed and has difficulty in eating and swallowing. His muscles, especially those of the back legs, become stiff and sore. Most likely he won't get up from a sitting position.

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Despite all these signs, the disease is very difficult to diagnose. Laboratory tests are usually necessary. Very early diagnosis may save the dog. Antibiotics seem to help kill the bacteria, and many dogs recover without any further damage. It is best to prevent this kind of suffering in your pet by giving him vaccination. The treatment of a dog with leptospirosis is never left entirely to the owner. The ill animal may have to be kept in the hospital for a week or longer to receive medical treatment, usually antibiotics as well as vitamins and fluids. If the dog mounts an immune system response and survives, the bacteria will be cleared from most organs. However, the infection persists in sites hidden from the immune system, the most common hidden site being the kidneys. Sudden kidney failure occurs in 80 to 90 percent of dogs that are severely affected.

The best way to prevent the ailment is through vaccination, usually given now together with distemper and hepatitis vaccines. In this way you protect your dog, yourself, and your family. In general, chemoprophylaxis with antibiotics for members of families with an infected dog is not recommended, but it could be considered following consultation with an infectious disease specialist. Pregnant women are at risk of abortion following exposure to Leptospira and are prime candidates for prophylactic antibiotic therapy.2


  1. Leptospira as an emerging pathogen: a review of its biology, pathogenesis and host immune responses
  2. Leptospirosis in the family dog: a public health perspective
  3. Leptospirosis in Squirrels Imported from United States to Japan



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