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| CANINE LEPTOSPIROSIS: A PERSPECTIVE ON RECENT TRENDS reflects geographic influences on the sampled popu- lation. It is important to emphasize that serogroup Icterohemorrhagiae appears to be the most common cause of leptospirosis in dogs and humans in certain cities, such as Baltimore, Detroit, New York City, and St. Louis, where the Norway rat remains the predomi- nant vector. In most other parts of the United States, serogroup Grippotyphosa and, to a lesser extent, sero- group Pomona predominate.7,8,9 RISK FACTORS Understanding risk factors that affect the incidence of leptospirosis in any region helps increase a veterinar- ian's index of suspicion with regard to canine patients that present with clinical signs and laboratory analysis consistent with leptospirosis. A number of recent studies have used geospatial anal- ysis of various hydrographic and land cover features to better define these risk factors. When interpreting the findings of these studies, awareness of the pitfalls associated with them is crucial; however, a few com- mon themes have emerged: UÊRural environments: Although exposure to wildlife/livestock and walking in rural environ- ments have been supported as risk factors in 2 studies, other studies have noted that dogs living in urban areas are at greater risk.7,10-13 UÊUrban environments: Urban wildlife that may contribute to this higher risk is commonly pre- sumed to be rats and raccoons. In addition, recent reports have raised the concern that bats may be a significant source of transmission due to their abundance and proximity to domestic animals.14 UÊWater proximity & exposure: Most studies agree that proximity and exposure to water bod- ies and frequently flooded areas are risk factors for leptospirosis in dogs. Flooding, in particular, liberates leptospires from urine-contaminated soil, resulting in exposure to dogs and humans. UÊWeather: Most every study has reported an increased incidence of canine leptospirosis in the fall months, although cases are reported for every month of the year. UÊPredispositions: There have been conflicting findings on the age, gender, and breeds of dogs that are at increased risk, suggesting that all dogs are susceptible to leptospirosis. German shep- herd dogs may be at increased risk; however, it is unclear whether this is a true breed-specific sus- ceptibility. CLINICAL SYNDROMES Acute Kidney Injury The most common syndrome associated with canine leptospirosis is acute kidney injury (Figures 2 through 4), which can manifest clinically as: UÊ iÌh>À}Þ UÊ noÀiÝi> UÊ*olÞÕÀi>Ê>n`Ê«olÞ`i«Ãi> UÊ6omiÌin}°Ê In these dogs, azotemia can vary in severity and is usually dependent on the time between onset of clini- cal signs and presentation to the veterinarian for diag- nosis and care.15 Leptospirosis was identified as the most common cause of acute kidney injury in a recent study, account- ing for 31% (56/182) of all cases and 54% (98/182) when known causes (ethylene glycol, nonsteroidal anti-inflammatory drugs, and hemodynamic causes) were excluded.16 Liver Disease The suspicion of leptospirosis is increased in dogs with acute kidney injury that have concurrent evi- dence of acute hepatocellular injury or cholestatic liver disease, which may manifest as increased serum alkaline phosphatase, with or without hyperbilirubi- nemia. When hepatitis occurs without acute kidney injury, elevations in serum alanine transaminase and serum alkaline phosphatase occur with variable severity, along with hyperbilirubinemia. Figure 2. Interstitial nephritis consisting predominantly of lymphocytic and plasmacytic inflammation, with low number of macrophages and neutrophils 28 Figure 3. Warthin-Starry silver stain demonstrating leptospiral organisms within the renal tubule Figure 4. Petechial and ecchymotic hemorrhages on the cortical surface of the kidneys Today's Veterinary Practice July/August 2012