Canine leptospirosis: A re-emerging disease in the United States (Proceedings)
Canine leptospirosis is a zoonotic disease that small animal veterinarians are likely to encounter in routine clinical practice. The clinical presentation of a dog with leptospirosis can vary, and practitioners should include leptospirosis in their differential diagnosis list when appropriate—for example, for dogs with acute renal or hepatic disease. All veterinary staff should be informed that it is on the differential list, and client education about transmission should begin immediately. All staff should know what precautions to take when caring for infected dogs to reduce risk for zoonotic transmission throughout the course of hospitalization. Negative serologic test results are not uncommon during the acute phase of leptospirosis; therefore, treatment decisions must often be made in the absence of a serologic diagnosis of leptospirosis. Strategies for prevention of canine leptospirosis should include lifestyle management in addition to administration of commercially available bacterins.
Pathogenic Leptospira species include over 200 serovars. The list of serovars most commonly associated with disease in dogs has changed recently. When canine leptospirosis was first described in the United States, the serovars Canicola and Icterohemorrhagiae were reported to be the cause of most cases of leptospirosis. However, serovars identified in most recent cases of canine leptospirosis, based on serologic test results, now include Grippotyphosa, Pomona, Bratislava, Icterohaemorrhagiae, and possibly Autumnalis. Leptospira organisms are maintained in reservoir hosts, and the reservoirs commonly associated with the serovars currently implicated in causing disease in dogs include rodents, cattle, swine, raccoons, opossums, and several other species. Dogs are considered the reservoir host for the serovar Canicola.
Leptospires are shed in the urine of infected animals, and infection is most commonly acquired when mucous membranes or abraded or water-softened skin come in contact with urine or urine-contaminated water or other objects. Infection may also occur by ingestion, and direct transmission from pets to humans can occur. Persons with certain occupations (veterinarians; farmers; and abattoir, kennel, and zoo employees) and recreational activities (campers, swimmers, triathletes) are reported to have increased risk for leptospirosis. Dogs may be sentinels for human exposure to Leptospira organisms.
The organisms can survive outside the host for several weeks. Survival is enhanced if the environment is warm and moist with a neutral to mildly alkaline pH. Outbreaks of leptospirosis have occurred following periods of heavy rainfall and flooding, and a seasonal distribution of cases is reported, with most cases occurring in the late summer and early autumn.
It has been reported that the dogs that are most likely to be diagnosed with leptospirosis are middle-aged, intact male dogs of working or sporting breeds living in rural areas. However, pet dogs living in suburban and urban areas are also at risk. The recent "urbanization" of some rural areas may provide more opportunities for pet dogs to come into contact with wildlife or livestock and livestock waste. Recent studies have indicated that dogs living in areas recently "urbanized," dogs that drink or swim in "outdoor" water, and dogs that are exposed to wild animals including raccoons, opossums, coyotes, skunks, and rodents, among others, are at the greatest risk for leptospirosis.