The Pulse Of Veterinary Medicine
Vet-To-Vet Conversation With IDEXX
Two cases of dogs contracting leptospirosis have been confirmed in the White Mountains, Arizona. Noting an increase in the disease, veterinarians are urging pet owners to vaccinate their dogs and are raising awareness that the disease can also sicken humans.
Leptospirosis, a zoonotic disease of worldwide significance, is caused by spirochetes of the genus Leptospira. Leptospirosis has been thought to most commonly affect young-adult, large-breed, outdoor dogs; however, small dogs in urban areas can also contract the disease. Important wildlife reservoirs in urban areas may include raccoons, skunks, opossums, and rats. Infected animals shed spirochetes in their urine that subsequently contaminate the environment. Susceptible animals and humans are most often infected through contact with contaminated water. Bacteria enter through damaged skin or mucous membranes.
Acute kidney injury (AKI) is the most commonly recognized disease in dogs, accounting for more than 90% of reported cases of leptospirosis. Hepatic disease occurs concurrently in 10%–20% of dogs with AKI but can also occur independently. Anorexia, lethargy, vomiting, polyuria, and polydipsia are common signs. Icterus, fever, abdominal pain, muscle pain and stiffness, uveitis, dyspnea, and coagulopathies occur as well but with less frequency. Infected dogs have also presented with only polyuria and polydipsia and normal chemistry findings with or without glucosuria.
Diagnosis of leptospirosis is best accomplished with a two-tier approach combining serology and PCR as we often don’t know when the dog was exposed. Serology in the form of the microscopic agglutination test (MAT) provides a quantitative antibody titer to Leptospira organisms. The serovar with the highest titer is often assumed to be the infecting serovar, but because of high cross-reactivity across the serovars, this may not be an accurate assessment. However, turnaround time is long, and clinical disease is similar and treatment the same regardless of serovar. In 2015, IDEXX introduced the SNAP® Lepto Test, a rapid and inexpensive ELISA, also available from IDEXX Reference Laboratories as the Canine Leptospira spp. Antibody by ELISA. This test provides a qualitative positive or negative antibody result, allowing a rapid assessment of exposure to Leptospira spp. Early in the course of disease, prior to production of antibodies, these tests may be negative despite the presence of clinical signs consistent with leptospirosis.
In these dogs, the Leptospira spp. RealPCR™ Test is recommended. Whole blood and urine specimens are collected, preferably prior to antibiotic administration, and tested simultaneously by PCR to allow for diagnosis of sick animals in the early stages of infection and for the detection of urinary shedding in sick animals. PCR testing on whole blood will be positive early in infection, usually prior to seroconversion and production of antibodies. Urine will become positive 7–14 days after infection, at which time DNA evidence of leptospires may or may not be detected in the blood, and serology tests will likely begin to turn positive. Vaccination may also produce positive serology (MAT and ELISA) in some dogs. A positive antibody result in a vaccinated dog should be confirmed with PCR testing (and/or convalescent quantitative MAT titer if PCR negative.) A diagnostic algorithm is available with guidance on interpretation of test results.
Supportive care, intravenous fluids, and specific antibiotic therapy are key to successful treatment of leptospirosis. Veterinary staff and pet owners should take precautions to avoid exposure to the infected dog’s urine. Antibiotics should be initiated as soon as possible when leptospirosis is suspected, after diagnostic specimens have been collected, even prior to confirmation of the diagnosis. Doxycycline (administered orally) or penicillin and its derivatives (i.e., ampicillin [intravenously] or amoxicillin [orally]) are the antibiotics of choice for initial treatment. These drugs terminate leptospiremia within 24 hours, which in turn prevents urinary shedding and transmission of the organism and significantly decreases the risk of zoonotic transfer. To clear renal infections and eliminate the carrier state and chronic shedding, doxycycline should be administered for 3 weeks once oral medication is possible or, if doxycycline is not tolerated, a fluoroquinolone can be administered in conjunction with a penicillin derivative. Cessation of urinary shedding should be confirmed by a follow-up RealPCR test in 2 weeks.