Common hematologic changes include neutrophilic leukocytosis and thrombocytopenia. BUN and creatinine may be elevated. Renal failure may occur alone, as with serovar grippotyphosa infections, or concurrently with hepatic disease. Elevations in total bilirubin, serum alkaline phosphotase, ALT and AST may be present. Hyperamylasemia and elevated lipase may occur due to increased release from hepatic and intestinal tissue and decreased renal excretion. Urinalysis frequently reveals cellular casts, proteinuria, bilirubinuria and glucosuria resulting from tubular damage.

Microscopic agglutination testing (MAT) is the standard serologic test for leptospirosis. Cross reactivity between serovars is common, and the serovar with the highest titer is assumed to be the strain causing clinical disease. The screening serum dilution is typically 1:100. Negative serology in the first 7–10 days after infection is common, and repeated serology in 2–3 weeks may be necessary to confirm the diagnosis. An accurate vaccination history is helpful in interpreting titers. Although vaccinal titers can be very high immediately after vaccination, titers tend to fall quickly. Vaccinal titers can be as high as 1:400 in animals evaluated more than twelve weeks after vaccination. Vaccines contain more than one serovar, and titers for all serovars from a vaccine are expected to be comparable in magnitude.

Successful therapy is dependent on aggressive supportive care and appropriate antibiotics. Penicillin and its derivatives are the drugs of choice for leptospiremia. Procaine penicillin G can be given at a dose of 40,000 u/kg IM or SQ BID. Adjusting the dose for animals in renal failure can be accomplished by dividing the dose by the serum creatinine concentration. Animals that do not need parenteral antibiotics can be treated with oral amoxicillin. After 14 days or resolution of the azotemia, the patient can be changed to doxycycline (5 mg/kg q 12 hr) to eliminate the carrier state. Recommendations between 2 and 6 weeks have been given for this phase of therapy; and it is likely that at least one month of doxycycline is appropriate.

Supportive care with IV fluids is indicated in many dogs to treat dehydration and promote diuresis. Oliguria and anuria are treated with osmotic diuretics, furosemide, and dopamine after correcting dehydration. Peritoneal dialysis has been necessary in some cases to support the patient until renal function is restored.

Presently, although vaccination is available for four strains of leptospirosis, there is no cross-protection between vaccinal serovars. There are two bivalent vaccines; serovars grippoty-phosa and pomona are paired in one, and serovars canicola and icterohemorrhagiae in the second. There is also a quadrivalent vaccine containing all four available serovars. More information is needed regarding prevalence and and incidence of various serovars. At the present time, practitioners need to rely on knowledge of the incidence of the various serovars in their geographic area and the risk factors of each patient. The vaccines presently available are bacterins, which are relatively allergenic for the patient. As always, the risk: benefit ratio must be evaluated for each patient prior to vaccination.

Leptospirosis is a zoonosis. Urine from infected animals is infectious, and veterinary personnel should avoid contact with it by using gloves to handle infected animals, and masks and goggles when cleaning contaminated areas to avoid infection with aerosolized bacteria. Recovering animals should not urinate in areas where people frequent. Iodophor disinfectants are effective against bacterial contamination in the environment. One part bleach in 10 parts water can also be used.

Leptospirosis has not been a federally reportable disease since 1995, and the Centers for Disease Control (CDC) has no current published statistics on human incidence. When leptospirosis was federally reportable, 10-25% of human cases had an identified canine source. Please note that some states, including California and Louisiana, list leptospirosis as a reportable disease. The CDC is not aware of an increased incidence in people correlating to the present increase in canine cases, however, they acknowledge that their data may be incomplete (underdiagnosed and underreported). Human infection associated with treatment of infected dogs appears to be rare.

References: Greene CE et al, Infectious Diseases of the Dog & Cat, 2nd ed, 1990, pp. 273-281; Manual of Clinical Microbiology, 7th ed, ASM Press, 1999, pp. 739-745; Ross LA, Rentko V, Leptospirosis, CVT XIII, WB Saunders, 2000, ppg. 308-310.