Diagnosing and preventing canine leptospirosis
NEW OREANS, LA – Canine leptospirosis is becoming recognized as a potentially zoonotic infectious disease now more frequently diagnosed in dogs located in urban/suburban areas than rural areas. Educating veterinary hospital staff about the exposure risks for dogs, clinical signs, diagnostic approach, and preventative measures play an important role in disease recognition and prevention through client education, explained Chad M. Johannes, DVM, DACVIM (SAIM), speaking at the ACVIM Forum. Veterinary technicians play a vital role in client education and awareness regarding the latest information on this potentially deadly but preventable disease.
Exposure in dogs
Leptospira spp. are thin, flexible, spiral bacteria that thrive in stagnant or slow-moving warm water and may remain viable for several months in moist soil. There is an increased incidence in summer and late fall, likely related to increased exposure to water sources harbouring the organism. Of the most common serovars infecting dogs in the United States, Canicola is most adapted to the canine host with the dog serving as the primary reservoir for this serovar. Common reservoir hosts for the other serovars recognized in dogs include the rat, raccoon, skunk, opossum, mouse, squirrel, cow, and pig.
Transmission from the reservoir host to dogs can occur directly via infected urine and bite wounds, or indirectly through contaminated water sources, soil, food, and bedding. Mucous membranes or abraded skin are common points of entrance with incubation period ranging from two to 30 days (seven days most common).
Clinical presentation
Many infected dogs become ill suddenly, with multiple body systems affected, including renal, hepatic, vascular (vasculitis, coagulopathies), pulmonary, ocular, and muscular (myopathies). The result is a myriad of potential non-specific clinical signs ranging from fever, vomiting, diarrhea, hematochezia, hematemesis, dehydration, and tachypnea, to epistaxis, icterus, petechiae, and pain on muscular or renal palpation. Dr. Johannes noted that a less common, more protracted presentation may occur. Clinical signs in the more chronic disease process may include fever, inappetance, weight loss, polydipsia, polyuria, and progressive deterioration in renal or hepatic function.
When to consider testing?
Newly diagnosed cases of:
- Renal failure
- Hepatopathy
- Polydipsia/polyuria
Unexplained cases of:
- Fever
- Uveitis
- Meningitis
- Immune-mediated condition
Diagnosis
Considering leptospirosis as a potential diagnosis involves obtaining an accurate and detailed history, with clinical signs and physical examination changes noted at presentation. Changes noted on initial diagnostics (CBC, serum biochemistry profile, urinalysis, abdominal ultrasound) may increase the index of suspicion of leptospirosis, especially in cases of acute renal failure or hepatopathy.
The microscopic agglutination test (MAT) remains the standard serologic test. Single timepoint titres of 1:800 or more along with corresponding clinical signs are supportive of the diagnosis of leptospirosis. In acute cases, initial titres (first 7 to 10 days) may be negative. Dr. Johannes said that in the cases where the initial titre is negative but leptospirosis is suspected, it is important to manage the case as a possible leptospirosis case and follow-up with repeat titres 2 to 4 weeks later with a 4-fold change in values being supportive of the diagnosis.
Polymerase chain reaction (PCR) testing of blood and urine can be helpful early in the course of infection to identify infected dogs that have not yet had time to produce antibodies (seroconversion) and thus are negative on MAT. It is also useful to confirm active infection in dogs with a positive MAT that also have a history of vaccination against Leptospira spp. This test can also be quite helpful in detecting infection in dogs with chronic renal or hepatic disease. Dr. Johannes stressed that false positives are possible and a negative result does not exclude the diagnosis of leptospirosis; therefore, results should be interpreted in light of clinical signs.
2010 ACVIM Small Animal Consensus Statement on Leptospirosis
Diagnosis – MAT
- Considerable variation in MAT results between labs
- Lack of consensus on what titre should be used as cut-off for negative result
- MAT does not accurately predict the infecting serogroup
Prevention – vaccination
- Current vaccines appear to effectively prevent disease resulting from experimental challenge
- To a large degree, prevent shedding caused by serovars in the vaccine
- Protect for at least 12 months
JE Sykes, et al. J Vet Intern Med 2011;25:1-13
Zoonotic potential
Though the incidence is fairly low, human infection can occur by swimming in contaminated water, which often results in small regional outbreaks of the disease. It can also occur among people who work outdoors or with animals. Infected dogs often shed Leptospira organisms in the urine, serving as a possible source of infection to people. Thus, veterinary staff and caregivers in frequent, close contact with urine or urine-contaminated bedding from infected dogs may be at increased risk for exposure.
In general, the risk of exposure via urine from an infected dog is believed to be significantly reduced 24 hours following initiation of appropriate antimicrobial therapy, but caution in handling urine is recommended for 3 to 5 days. The urine PCR test can be considered to help further verify the lack of urine shedding in an infected dog undergoing treatment.
Dr. Johannes said that knowledge regarding the mode of transmission of Leptospira spp. is important in preventing infection among veterinary personnel in close contact with infected dogs. Any dog suspected of potentially being infected with Leptospira spp. based on history, clinical signs, and/or diagnostic findings should be treated as having leptospirosis until determined otherwise. Protective measures include wearing appropriate protective attire (gloves, body gown, goggles) when handling suspected dogs or their urine/bedding, washing hands after handling patients, and preventing splashing or aerosolization of urine when cleaning cages/kennels.
Prevention
Immunization via Leptospira bacterin administration has been effective in reducing the prevalence and severity of canine leptospirosis. Multiple newer bacterins containing the four most common serovars infecting dogs in the U.S. (Icterohaemorrhagiae, Canicola, Grippotyphosa, and Pomona) are now available: Vanguard®L4 (Pfizer), Recombitek® 4 Lepto (Merial), Novibac® Lepto 4 (Merck), and Leptovax® 4 (Boehringer Ingelheim). The bacterins appear to provide protection for 12 months.
Annual vaccination with 4-serovar vaccines is recommended for at-risk dogs, regardless of breed. In regions where infection occurs in urban, backyard dogs, all dogs may be at risk and 4-serovar bacterin may be considered part of a core vaccination protocol. In other locations, only dogs that contact wildlife, swim, hunt, or roam on farmland may be at risk.
- Use care when handling urine from symptomatic dogs
- Disinfect kennels appropriately
- Isolate and treat infected dogs
- Vaccinate!
- Eliminate rodent infestations (kennels/bedding, food storage sites, water sources)
- Keep kennels clean and dry
- Avoid areas with high risk transmission
- Minimize contact with areas of standing water near dog’s normal habitat
Environment
Regardless of a dog’s geographic location and vaccination status, steps can be taken to reduce the risk of exposure to Leptospira spp. Dr. Johannes explained that one key element is reducing rodent/wildlife infestations and access to kennels/bedding, food storage sites, and water sources. Areas with high risk of transmission (standing water in dog’s normal habitat, farm ponds, etc) should be avoided. Infected dogs in a veterinary clinic or dogs suspected of being infected with leptospirosis based on history and clinical signs should be isolated.
Summary
Recognition of the common sources of infection, presenting clinical signs, and diagnostic considerations are key to understanding the best mechanisms of disease prevention. As an important member of the veterinary health care team having frequent communication time with dog owners, veterinary technicians play a vital role in client education and awareness regarding the latest information on canine leptospirosis. CVT
