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Canine leptospirosis: A re-emerging disease in the United States (Proceedings)
Canine leptospirosis is a zoonotic disease that small animal veterinarians are likely to encounter in routine clinical practice.
Canine leptospirosis is a zoonotic disease that small animal veterinarians are likely to encounter in routine clinical practice. The clinical presentation of a dog with leptospirosis can vary, and practitioners should include leptospirosis in their differential diagnosis list when appropriate—for example, for dogs with acute renal or hepatic disease. All veterinary staff should be informed that it is on the differential list, and client education about transmission should begin immediately. All staff should know what precautions to take when caring for infected dogs to reduce risk for zoonotic transmission throughout the course of hospitalization. Negative serologic test results are not uncommon during the acute phase of leptospirosis; therefore, treatment decisions must often be made in the absence of a serologic diagnosis of leptospirosis. Strategies for prevention of canine leptospirosis should include lifestyle management in addition to administration of commercially available bacterins.
- Leptospirosis is a zoonotic disease with worldwide prevalence.
- The Leptospira serovars most commonly reported to be associated with canine leptospirosis currently include Grippotyphosa, Pomona, Bratislava, and possibly Autumnalis.
- While there are some demographic characteristics associated more commonly with leptospirosis, all dogs may be considered to be at risk for leptospirosis if they come into contact with infected animals or their urine.
- Leptospirosis should be considered as a differential diagnosis for many clinical presentations, particularly acute renal failure and/or hepatic disease.
- Leptospirosis is a zoonotic disorder that can be transmitted directly from dogs to humans or indirectly though contact with infected urine.
Transmission and epidemiology
Pathogenic Leptospira species include over 200 serovars. The list of serovars most commonly associated with disease in dogs has changed recently. When canine leptospirosis was first described in the United States, the serovars Canicola and Icterohemorrhagiae were reported to be the cause of most cases of leptospirosis. However, serovars identified in most recent cases of canine leptospirosis, based on serologic test results, now include Grippotyphosa, Pomona, Bratislava, Icterohaemorrhagiae, and possibly Autumnalis. Leptospira organisms are maintained in reservoir hosts, and the reservoirs commonly associated with the serovars currently implicated in causing disease in dogs include rodents, cattle, swine, raccoons, opossums, and several other species. Dogs are considered the reservoir host for the serovar Canicola.
Leptospires are shed in the urine of infected animals, and infection is most commonly acquired when mucous membranes or abraded or water-softened skin come in contact with urine or urine-contaminated water or other objects. Infection may also occur by ingestion, and direct transmission from pets to humans can occur. Persons with certain occupations (veterinarians; farmers; and abattoir, kennel, and zoo employees) and recreational activities (campers, swimmers, triathletes) are reported to have increased risk for leptospirosis. Dogs may be sentinels for human exposure to Leptospira organisms.
The organisms can survive outside the host for several weeks. Survival is enhanced if the environment is warm and moist with a neutral to mildly alkaline pH. Outbreaks of leptospirosis have occurred following periods of heavy rainfall and flooding, and a seasonal distribution of cases is reported, with most cases occurring in the late summer and early autumn.
It has been reported that the dogs that are most likely to be diagnosed with leptospirosis are middle-aged, intact male dogs of working or sporting breeds living in rural areas. However, pet dogs living in suburban and urban areas are also at risk. The recent "urbanization" of some rural areas may provide more opportunities for pet dogs to come into contact with wildlife or livestock and livestock waste. Recent studies have indicated that dogs living in areas recently "urbanized," dogs that drink or swim in "outdoor" water, and dogs that are exposed to wild animals including raccoons, opossums, coyotes, skunks, and rodents, among others, are at the greatest risk for leptospirosis.
Disease in dogs
Several clinical presentations have been reported for canine leptospirosis. The severity and type of presentation are thought to vary with the virulence of the infecting organisms, the dose of infecting organism, the route of exposure, and host factors. It should also be noted that infected dogs may not exhibit any signs of clinical illness. When clinical signs are present, they may be peracute, as described for "classic" canine infection with serovar Icterohaemorrhagiae, including sudden onset of fever and severe multisystemic signs. Acute renal failure is thought to be the most common presenting clinical condition associated with Leptospira infection in dogs, al though a combination of acute renal failure and hepatic involvement is common. Chronic hepatitis and chronic renal failure have also been reportedly associated with leptospirosis in dogs.
Clinical signs commonly include vomiting, lethargy, anorexia, polyuria, and polydipsia. Other signs reported include myalgia, joint pain or stiffness, petechiation, and icterus. Physical examination findings may also include fever and abdominal or renal pain (sometimes renomegaly), and ophthalmologic abnormalities (uveitis, retinal hemorrhage). Clinicopathologic findings include azotemia, increased hepatic enzyme activities, hyperbilirubinemia, thrombocytopenia, hypoalbuminemia, leukocytosis, and nonregenerative anemia. Dogs may have isosthenuric urine, and glucosuria and bilirubinuria may be noted. Serologic testing using the microscopic agglutination test is currently the standard for diagnosing canine leptospirosis. Negative serologic test results in the acute phase of infection are common; therefore, dogs should be tested again in 2 to 3 weeks if a diagnosis of leptospirosis is suspected but not supported by the initial serologic test. Serum should be tested for antibodies to multiple serovars. Although there is cross-reactivity, it is possible to miss a diagnosis of leptospirosis if some serovars are not included when serologic testing is done. The serovars currently recommended for inclusion are Grippotyphosa, Bratislava, Icterohaemorrhagiae, Canicola, Pomona, and Hardjo. Other diagnostic tests to consider are histopathology with immunofluorescent labeling and/or silver staining, blood culture for leptospires, culture of urine for leptospires, and polymerase chain reaction testing of urine or tissues. Culture generally is not routinely offered by diagnostic laboratories.
Treatment with ampicillin or penicillin G for 2 weeks during the initial leptospiremia is commonly recommended. Following treatment with ampicillin, doxycycline treatment is recommended for approximately another 2 weeks to minimize shedding and, ideally, to eliminate or minimize the carrier state. Treatment with doxycycline in the initial leptospiremic phase has also been suggested, as there is evidence that doxycycline may also clear leptospiremia. Aggressive supportive care including intravenous fluids and nutritional support are nearly always necessary for severe clinical cases. Specific supportive measures are dictated by the condition of the individual patient. If oliguric renal failure occurs, then placement of an indwelling urethral catheter is often necessary to allow accurate monitoring of urine production. Some experts have recommended placement of indwelling catheters in all dogs hospitalized for treatment of leptospirosis with the intent to minimize exposure of health care workers to contaminated urine. However, the risk for ascending urinary tract infection in dogs with indwelling urethral catheters must also be considered.
The following steps should be taken to manage dogs hospitalized for leptospirosis to minimize risk for transmission to hospital staff and to other dogs:
- Keep dogs separated.
- Wear gloves and protective outerwear (e.g., lab coat, barrier gown) when examining and treating infected dogs.
- Follow accepted standard hygiene, including proper hand washing after handling infected animals.
- Clean and disinfect the environment—all organic matter must be removed from the environment before disinfection, and disinfectants should be allowed adequate contact time with the cleaned surfaces. A comprehensive compendium of veterinary standard precautions is available on the web site of the National Association of State Public Health Veterinarians (www.nasphv.org/Documents/VeterinaryPrecautions.pdf). This is an excellent document that should be readily available in all practices.
Bacterins for the serovars Icterohaemorrhagiae, Canicola, Pomona, and Grippotyphosa are currently marketed for prevention of leptospirosis in dogs. The bacterins are available as individual products and in combination with other common canine vaccines. The manufacturers recommend that the products be initially administered in two doses, given 2 to 3 or 3 to 4 weeks apart, followed by yearly booster injections. The currently available bacterins are not labeled for protection against serovars other than the ones listed above. In addition to the administration of bacterins, prevention strategies should include "lifestyle" management measures. Contact with reservoir hosts and potentially contaminated sites should be avoided or minimized.
It is important to educate staff and clients regarding the zoonotic potential of leptospirosis. Blood and urine samples collected from dogs with confirmed or suspected leptospirosis should be labeled to indicate that they may contain Leptospira organisms. Place caution signs on cages where infected dogs are housed. Protective equipment, such as gloves and a lab coat or other protective outerwear, should be readily available for staff members handling dogs that have or are strongly suspected of having leptospirosis. Goggles or face shields should be provided for all staff who clean or may be exposed to droplets. Urine and materials used for handling infected animals should be disposed of properly. As noted, cages and runs used to house infected animals should be thoroughly cleaned to remove organic matter and then disinfected, allowing the disinfectant adequate contact time with the cleaned surface. Infected dogs should not be allowed to urinate in common-use exercise areas while hospitalized. If human exposure occurs, wash thoroughly and contact a physician for further recommendations.
Owners should follow similar precautions (wear gloves when handling urine; keep the dog being treated away from common areas, such as parks; and if possible, limit the dog's urination to a low-traffic area of their yard) when their pet is being treated for leptospirosis. Written materials should be provided for owners when their pet is diagnosed with leptospirosis. The Centers for Disease Control and Prevention Web site has useful information for pet owners (www.cdc.gov/ncidod/dbmd/diseaseinfo/leptospirosis_g_pet.htm). This document, "Leptospirosis and Your Pet," can be printed and distributed to owners.
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