Why they did it
The clinicopathologic features of leptospirosis are evolving, with atypical findings such as proteinuria and coagulopathy becoming more common, which may lead to misdiagnoses and increased public health risks. The authors of this study sought to identify the percentage of atypical features found in dogs with leptospirosis as well as evaluate the clinical utility of convalescent titers.
What they did
Researchers retrospectively evaluated data on 51 dogs with a diagnosis of leptospirosis based on a positive microscopic agglutination test (MAT) result, which was defined as a titer ≥ 1:1600 in vaccinated dogs, a titer ≥ 1:800 in nonvaccinated dogs, or a ≥ fourfold increase in convalescent titers. All dogs had a complete medical record, baseline laboratory data performed, and clinical signs consistent with leptospirosis.
What they found
Convalescent titers were required to make a diagnosis in 45% (23/51) of dogs, and 10 of the 23 dogs radiographed demonstrated radiographic evidence of pulmonary disease (interstitial or alveolar patterns, or both) at the time of initial evaluation. Seven of the 51 dogs only had evidence of hepatic involvement, while 26 of 51 only had renal involvement. Other atypical findings included proteinuria (34/51), thrombocytopenia (26/51), coagulopathy (7 out of 24 tested), hypoalbuminemia (14/51), and glucosuria (9/51).
There was a significant association between antibodies to serogroup icterohemorrhagiae and dogs with hepatic involvement as well as serogroup grippotyphosa and dogs with renal involvement. It is important to note, however, that MAT titers may not accurately predict the infectious serogroup.
Since leptospirosis is a zoonotic disease, misdiagnosis could have large consequences. The fact that 45% of dogs required a convalescent titer to make a diagnosis underscores the importance of obtaining this titer two to four weeks later to avoid misdiagnosis. The authors note that atypical clinical signs are possible and “leptospirosis should be considered as a differential diagnosis in cases of primary hepatic disease and pulmonary disease.” Leptospirosis should also still be considered in patients up-to-date on annual leptospirosis vaccination given that vaccination failed to protect nine dogs in this study.
Tangeman LE, Littman MP. Clinicopathologic and atypical features of naturally occurring leptospirosis in dogs. J Am Vet Med Assoc 2013;243(9):1316-1322.
Link to abstract: http://avmajournals.avma.org/doi/abs/10.2460/javma.243.9.1316