Vet Tail Views

An Afternoon of Infectious Disease: Part I - Leptospirosis 

By Dr. Nicola Parry

On August 19^th, the IVMA hosted its 2^nd annual CE event at the Indiana State Fair, An Afternoon of Infectious Disease, presented by Lynn Guptill, DVM, PhD, Associate Professor of Small Animal Medicine at Purdue University College of Veterinary Medicine.

During the first half of the session, Dr Guptill focused on leptospirosis, a zoonotic disease that small animal veterinarians are likely to encounter in routine clinical practice.

Although infection of dogs with leptospires may result in several clinical presentations, and illness of varying severity, Dr Guptill reminded the audience to suspect leptospirosis in particular in patients with signs of acute renal failure. Hepatic involvement is also common, and some dogs may even present with a combination of renal and hepatic failure.  

The zoonotic potential and occupational health hazard of leptospirosis cannot be over-emphasized, and Dr Guptill highlighted a case in which a veterinarian developed the disease after handling a rat which, unbeknown to him, was infected with Leptospira spp. During clinical examination, the rat urinated on the vet’s ungloved hands and, despite washing his hands, he still became infected and was hospitalized with leptospirosis for 12 days. He was able to return to work 1-month post-discharge, but only part-time due to the debilitating effects of the disease.

She therefore reminded the audience to take necessary precautions when managing a dog that either has, or is suspected to have, leptospirosis.

Minimizing the Risk of Zoonotic Transmission in the Clinic

·       Implement barrier nursing techniques for the patient.

·       Make sure all staff members know which dog is infected or potentially infected, and about the zoonotic risk of the disease.

·       Place warning labels on the dog’s cage—and on the dog if necessary, especially if movement to other areas of the hospital is required. Any diagnostic specimens, trash, or laundry from the infected dog should also be appropriately labeled.

·       Staff must wear appropriate personal protective equipment when handling infected patients, including gloves, a barrier gown (composed of water-repellent material), shoe covers, and a face shield (to avoid splashing of urine on mucous membranes). Remember that the organism can be transmitted across intact skin, so all areas of exposed skin must be covered.

·       Where possible, avoid the use of materials that require laundering—disposable materials are a better option. For example, incontinence pads can be used for the dog’s bedding—or even an inflatable mattress that can be easily cleaned and disinfected.

DIAGNOSTIC TESTS

Some of the more commonly used diagnostic tests for leptospirosis include:

Serologic Tests to Detect Antibodies to Leptospira spp.

Microscopic agglutination test (MAT): The MAT represents the gold standard test in the diagnosis of leptospirosis in dogs, and is the one used most commonly. According to conventional wisdom, the serovar with the highest MAT titer is considered to be the infecting serovar. However, Dr Guptill emphasized that, in an infected dog, the serovar with the highest MAT titer not only changes during the course of infection, but there is also considerable inter-laboratory variation in MAT results. Consequently, the MAT does not accurately predict the infecting serovar—although definitive knowledge of the infecting serovar is somewhat academic, because it has no bearing on treatment decision-making.

Enzyme-linked immunosorbent assay (ELISA): The ELISA test provides a qualitative positive or negative antibody result. In addition to the standard ELISAs performed on samples submitted to a diagnostic laboratory, the new Canine SNAP Lepto Test is a pet-side antibody test, using ELISA technology, that is now available from IDEXX.

One limitation of serologic tests, however, is that they will produce a negative result in the early phase of the disease, because antibodies typically do not appear until about 7 days after clinical signs arise. One way to circumvent this problem is to use an antigen-detecting molecular technique.

Molecular Testing

Polymerase Chain Reaction (PCR): PCR testing offers a highly sensitive molecular option to detect leptospiral DNA, and can be used on samples of blood and urine. And, unlike the serologic tests, PCR may also provide a diagnosis during the acute phase of infection. However, because antimicrobial therapy will quickly remove leptospires from the blood, pre-treatment samples should be used to ensure a high test sensitivity. So be sure to collect and refrigerate samples of blood and urine upon initial suspicion of leptospirosis in your patient—before initiating treatment—even if you do not intend to immediately submit them for testing. Samples will remain stable for about 7 days when refrigerated.

Some Final Take-Home Points from Dr Guptill:

·       About 25% of dogs without leptospirosis will test positive for Leptospira spp. using serologic tests. Consequently, you can’t ever be 100% sure that your sick patient has leptospirosis, regardless of a positive serologic test result. Naturally, however, seropositivity in a sick “leptospirosis suspect” patient will make a diagnosis of leptospirosis highly likely, but Dr Guptill reminded the audience to always remain open-minded to even the remote possibility of another cause—just in case.

·       Although cats can become infected with Leptospira spp., they typically do not develop clinical signs of disease and are considered to be resistant. However, a few clinical cases of feline leptospirosis have been reported, manifesting mainly as kidney and liver damage.

·       Adverse reactions to leptospirosis vaccines appear to be more likely in younger dogs (especially those <2 years) and smaller dogs (especially those weighing <10 kg).

·       The primary treatment of choice in dogs (regardless of serovar)—based on studies in hamsters and on data in the human medical literature—is doxycycline. Penicillin pre-treatment no longer seems necessary, and treatment with doxycycline alone appears to be effective. The recommended dose is 10 mg/kg/day, either as a single daily dose, or divided over 2 doses. A minimum treatment duration of 2-3 weeks is advised, although a 4-week treatment duration is better.

Studies have shown that “leptospirosis season” appears to arise during late fall and early winter in Indiana, with most positive cases arising in November and December. And because the number of positive cases increases during a rainy year, we should prepare ourselves for a “good lepto season this year”, Dr Guptill concluded.