Canine leptospirosis (Proceedings)


Canine leptospirosis (Proceedings)

Apr 01, 2010

Leptospirosis may be one of the most under-diagnosed diseases in veterinary medicine. We expect to see the classic triad of clinical disease: acute renal failure, hepatic failure, and intravascular hemolysis (usually low-grade). Although many dogs exhibit these forms of the disease, many exhibit clinical signs that are not routinely attributed to leptospirosis. Here are two atypical cases.

Case 1
A 9-year-old, spayed female German shepherd was presented for profound polyuria and polydipsia of several weeks duration. A complete blood count and serum chemistry profile were normal. The urinalysis showed hyposthenuria (urine specific gravity of 1.004), however the urine sediment was inactive and the culture was negative. Testing for hyperadrenocorticism was negative. A water deprivation test was performed and the dog failed to concentrate. Therapy with DDAVP also failed to resolve the clinical signs. A serologic test for leptospirosis was performed and the results showed a titer of 1:6400 for serovar Grippotyphosa and negative for all other serovars. Therapy with doxycycline for 4 weeks resolved the polyuria and polydipsia. Serology performed 3 months later showed conversion to negative on all serovars. The most important issue regarding this case was the constant exposure of the owner to leptospirosis-infected urine from the dog urinating in the house. We have seen a number of cases of non-azotemic PU/PD in dogs caused by leptospirosis.

Case 2
A 5-year-old, male Jack Russell terrier presented with a 2-day history of lethargy and depression associated with fever. On presentation, Buddy had a fever of 103.8, however the fever resolved within a few hours and Buddy was discharged without any medications. Buddy presented the following day with a temperature of 105 F. A CBC, chemistry profile, and urinalysis were completely normal. A PCR of the urine for leptospirosis organisms was strongly positive (the test was performed as part of a research project evaluating the utility of PCR in diagnosing leptospirosis: it was anticipated that this dog was ill for other reasons and would not have leptospirosis). A serology was subsequently performed and the dog had a titer of 1:12,800 against serovar Grippotyphosa. The dog was treated with doxycycline and responded rapidly to therapy. The other dog in the house, who was asymptomatic, also had a strong positive urine PCR for leptospirosis organisms and was also treated. The important aspect of this case is that the fever would have responded to amoxicillin, thereby eliminating further diagnostics, but the dog would have remained a public health risk by shedding leptospires in the urine. Treatment with doxycycline is necessary to eliminate the shedding phase.

Leptospirosis is a spirochetal bacterial zoonosis that is found world wide, most often in wetter climates. In man, leptospirosis infections can be subclinical, self-limiting febrile disease with or without meningitis, or a severe and potentially fatal illness known as Weil's syndrome that presents as hemorrhage, renal failure, and jaundice. As new communities encroach on areas inhabited by wildlife, the incidence of leptospirosis will continue to climb. In rural areas, pigs and cattle are the primary reservoirs of disease important for dogs, in suburban areas, rodents, deer, raccoons, possum, and other common wildlife are important reservoirs, and in the cities rats are the reservoir. The major concern with wildlife is the introduction of serovars that have been previously unrecognized, and for which there is no vaccination and they are not screened for on the available serologic tests. Infection with a different serovar that is not tested for and which does not cross-react can lead to a false negative diagnosis based on serology, however PCR typically should detect these infections.

     There are 3 classical presentations: hemorrhagic syndrome, icteric syndrome, and uremic syndrome. Dogs may have one, two, or all of these syndromes and any serovar can produce any clinical picture.

     Common clinical signs include arthralgia or myalgia (this may be the initial presenting complaint), vomiting and diarrhea, icterus, depression or lethargy, hematochezia or melena, intussusceptions, polyuria/polydipsia (may not be azotemic), dyspnea (from pulmonary hemorrhage or pneumonitis), oculonasal discharge, cough, and uveitis.

     Common laboratory findings include:
          1.      mild anemia: this often confuses the diagnosis, making the clinician think that chronic renal failure is present
          2.      thrombocytopenia
          3.      leukocytosis (most do not have a left shift)
          4.      azotemia (elevated BUN, creatinine, phosphorous)
          5.      elevated serum alkaline phosphatase (this is often dramatic with minimal increase in serum alanine transaminase)
          6.      hyperbilirubinemia

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