Canine Leptospirosis

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Etiology

Leptospirosis is a disease of humans and animals caused by infection with the motile spirochetal bacterium of the genus, Leptospira.1 Leptospirosis as a zoonotic disease worldwide cannot be overstated, because it causes human disease and deaths in much of the world, but mostly in areas of Asia and South America. The bacteria are highly motile, thin, flexible, and filamentous, made up of fine spirals with hook-shaped ends. Motility is gained by writhing and flexing movements while rotating along

Epidemiology

There are two types of mammalian hosts when it comes to Leptospira infections. Each serovar is adapted to one or more mammals as a primary, also called the definitive or reservoir, host. Adapted resevoir hosts are thought to harbor persistent infection, often without severe signs of disease and can shed organisms in their urine for months to years after infection. The bacteria are maintained in the renal tubules of reservoir hosts and excreted in the urine. The other type of mammalian host is

Pathogenesis

The sequence of events after infection seems amazingly variable and likely depends on

  1. Virulence, serovar, and perhaps even strain in addition to numbers of bacteria infecting the host. The author and colleagues have recently shown that suspected L interrogans serovar pomona infections induced significantly more severe kidney disease and had a worse outcome than infection suspected to be from other serovars in a study of naturally occurring leptospirosis in dogs in New York State.7

  2. Immune response. Previous exposure (naturally occurring or vaccinal) to the same serovar is likely

Diagnosis

Achieving as definitive a diagnosis as possible should be of special importance to veterinary practitioners because of the zoonotic potential of the disease and the possibility of the dog serving as a reservoir for other dogs and humans. Unfortunately, achieving a definitive diagnosis is often difficult with the tools in use today. The first difficulty faced is that the clinical signs associated with this disease are often vague and are typically nonspecific. The clinicopathologic data are

Signalment and history

Identifying dogs more likely to become infected with Leptospira organisms is important to narrow down the need for specific and sometimes expensive and repetitive testing. A profile of the kind of dog more likely to be infected is also beneficial when deciding which dogs should be vaccinated against the disease. There are likely large geographic differences in these considerations and so the region and season should be taken into account, although large amounts of epidemiologic data by region

Clinical signs

Clinical signs of dogs with leptospirosis can vary from subclinical or minimal clinical disease or mild fever to severe kidney, liver, and pulmonary disease. The literature is biased by the testing that was performed in each study, meaning that if only test azotemic dogs are tested, then all dogs diagnosed will be azotemic. It seems, however, that subtle to severe signs of kidney and liver damage as well as coagulation defects predominate. It is unknown what percentage of naïve naturally

Clinicopathologic data

Unfortunately there are few or no single clinicopathologic changes on a chemistry panel, complete blood count (CBC), or urine analysis that are pathognomonic for leptospirosis. Practitioners must take multiple, often subtle, abnormalities into account to try and build a case for the diagnosis of this disease in dogs. The most common abnormalities found in the chemistry panel of confirmed cases include azotemia, increased serum liver enzyme activity, electrolyte disturbances, and mild increases

Imaging

As in many types of infectious disease, imaging modalities of radiographs and ultrasound are helpful in ruling out additional causes of the clinical disease but are less helpful in confirming a diagnosis of leptospirosis. Characteristic changes have been described in the lungs on thoracic radiographs29, 30 and in the kidneys on abdominal ultrasound31 in dogs with leptospirosis. Both of these studies were retrospective uncontrolled case series and it is unclear how often or how specific these

Specific testing

The most commonly used test today in veterinary practice in North America is the MAT.26 This test is performed by mixing serial dilutions of the canine sera with cultured Leptospira organisms of different serovars representing different serogroups. The titer against a specific serogroup is defined as the highest dilution of the sera that caused 50% or more agglutination of the organisms representing that serogroup. There are many inherent problems with the performance of this test. One is the

Treatment

Treatment of leptospirosis involves supportive care, treating the renal or hepatic manifestations of the disease, and the use of antimicrobials. Antimicrobial therapy should be started as soon as the disease is suspected and samples have been drawn (if PCR is submitted). This is essential to eliminate bacteremia and the potential for live organisms in the urine that pose a zoonotic risk to humans. This should be started before confirmation of the diagnosis. A study in humans revealed that if

Prevention

Prevention ideally should start by limiting contact of pet dogs with wild animal reservoirs of the disease as well as sources of contaminated water. This is, of course, easier said than done, given the close contact of pets to wild animals, including rodents, even in urban areas. Thus vaccination is crucial to prevent the disease in at-risk dogs. All available vaccines are culture based and contained whole units or subunits of inactivated bacterins of serovars icterohaemorrhagiae and canicola.

Summary

Leptospirosis is a common zoonotic disease with a worldwide distribution. Dogs become infected by exposure to contaminated urine from shedding wild animals. The bacteria penetrate mucus membranes cause endothelial damage in organs, such as the liver and kidneys. The clinical signs and clinicopathologic data are nonspecific and a high index of suspicion is needed by practitioners. Testing today is highly based on serology (MAT) and perhaps PCR. Treatment of leptospirosis involves supportive care

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