Although leptospirosis was reported sporadically in the 1980s, it is now recognized as an important cause of acute renal disease in dogs as well as one of the most significant waterborne zoonotic diseases in the world.
• Leptospira species are gram-negative bacteria.
• Leptospira species are maintained in the kidneys of mammalian reservoir hosts. Leptospires are passed via urine from reservoir hosts and can contaminate ground water, which serves as the source of infection for other animals.
• More than 200 serovars have been identified. Serovars Icterohaemorrhagiae and Canicola were prevalent in dogs in the 1950s to 1970s, but Grippotyphosa and Pomona have been dominant during the past 20 years.
• Originally, leptospirosis affected mostly sporting, working, or herding dogs with extensive exposure to the outdoors. Today, smaller breeds (including toy breeds) are diagnosed more frequently.
• All ages and breeds are susceptible.
• Leptospirosis has been reported in all 50 states, with greater numbers noted in the Midwest, Northeast, and along the West Coast.
• Climate may be responsible for major differences in prevalence internationally but probably causes only small variations in the U.S.
• Prevalence estimates are greatly influenced by clinical suspicion of the disease and diagnostic testing choices.
• Unvaccinated dogs that come into contact with contaminated water sources are considered the most at-risk. Leptospirosis is also seen in rural and suburban areas with large areas of mammalian wildlife host habitats.
• New infections are commonly seen in the autumn months because of increased wildlife movement and territorial marking. After heavy rains, areas of standing water increase, which can lead to greater exposure to all waterborne bacteria.
• The helical shape of bacteria facilitates penetration of mucous membranes or broken epithelia (Figure 1 below).
• Leptospires have an affinity for renal proximal tubules, the biliary tract, and vascular endothelium. They may also spread to the spleen, central nervous system, eyes, and genital tract.
• Cellular damage from disease is most likely caused by leptospiral ipopolysaccharides and other components of the outer membrane.