Leptospirosis is the name for disease caused by bacteria of the genus, Leptospira. The many strains of this bacteria survive in various hosts, including many wildlife species (raccoons, rodents, skunks,etc) and domestic food animals, such as cattle.
The affected animals shed the bacteria in their urine which can contaminate water sources (rivers, ponds, puddles). The Leptospira organisms usually infect animals by penetrating through the mucous membranes of the eye, mouth or nose or through breaks in the skin. Many of the strains cause damage to the liver and kidneys and can result in a permanent decrease in function or death.
Clinical signs can be fairly non-specific. It generally starts with a fever, diarrhea, vomiting and abdominal pain and can progress to jaundice and bleeding issues. The signs will depend on whether the strain of bacteria causes damage to the kidneys or liver. Early treatment with antibiotics can be curative.
An important note - this disease is zoonotic. That means that humans can also be infected by the bacteria. It most often happens when we are swimming in infected lakes or ponds, but we can get it through direct contact with an infected animal or its urine.
An effective vaccine is available and should be administered yearly to your dog to help prevent the spread of this disease.