Leptospirosis in dogs is caused by Leptospira, a genus of bacteria with around 17 different species. They are found in rivers, streams and swamps, living on the surface layers of water. Hence Leptospirosis is mainly a waterborne disease.
Dogs get infected with the bacteria through wounds coming in contact with water or urine that contain them, or by eating contaminated flesh. The leptospires that enter through the wounds find their way into the blood through the lymphatic system. From the blood they spread to other tissues. If the dog has a strong immune system, it will fight the infection and eliminate the bacteria from the blood and the tissues. But certain organs like the kidneys may continue to harbor the bacteria as they are not easily accessed by the immune mechanism. As long as they remain in the kidneys, the dog remains a carrier, excreting the bacteria through urine. It may take up to a year to completely eliminate the microbes from the body.
Leptospirosis may be asymptomatic in some cases, but the common symptoms include fever, muscular pain, general weakness and pain in the joints. The dog may lack appetite and develop jaundice. Runny eyes and nasal discharge are the other symptoms. As the disease progresses and the kidneys get affected, pain develops in the lumbar region due to inflamed kidneys. Severe thirst and consumption of water followed by frequent urination is a typical symptom. There may be vomiting too, and the dog may become dehydrated. 80 to 90 percent of dogs with the severe form of the disease may develop kidney failure. Antibiotic therapy is initiated to treat the infection, along with fluid supplementation to maintain the electrolyte balance if there is kidney failure.
Vaccination against leptospirosis is limited to 4 subtypes, which means there is a risk of the dog getting infected with any of the other types. If it is known that the dog has come in contact with any dog with the disease, a preventive course of oral antibiotic therapy for 7-10 days may help.