In dogs, leptospirosis most commonly results in acute renal failure (ARF) with or without concurrent (or subsequent) hepatic
disease. Although leptospirosis can cause ARF along with acute liver disease (or liver failure), ARF without liver disease
has become the most common clinical presentation of the predominant serovars of leptospirosis affecting dogs in the US. Failure
to recognize leptospirosis as the cause of ARF may result in exposure of veterinarians, technicians and other hospital personnel
to this zoonotic disease.
Major causes of acute renal failure in dogs include ischemic, infectious (leptospirosis, Lyme disease) and toxic causes.
Leptospirosis has re-emerged as a clinical disease in North America and has become a common cause of acute renal failure in
most areas of the US. Ischemic causes include hypotensive events such as anesthesia/surgery, hypovolemic shock, and severe
dehydration. Common toxins causing ARF include ethylene glycol, arsenic, zinc, and lead. Two recently reported toxic causes
or ARF are raisin ingestion in dogs and lily ingestion in cats. Pet food contamination with melamine and cyanuric acid resulted
large numbers of cases of ARF in dogs and cats in 2007. Antibiotics that may cause ARF include aminoglycosides, amphotericin
B, cephaloridine, and oxytetracycline. Miscellaneous drugs that may cause ARF include thiacetarsamide, cis-platinum, methoxyflurane, and rarely radiographic contrast agents. Pigment nephropathy from hemoglobinuria or myoglobinuria
is uncommon in dogs and cats. In areas where leptospirosis is endemic, any dog with ARF should be assumed to have leptospirosis
unless another cause is known.
Overview of leptospirosis
Leptospirosis is one of the most common causes of ARF at Purdue VTH and the most commonly implicated serovars include grippotyphosa, bratislava, pomona, and autumnalis. Unlike traditional leptospirosis infection with canicola and icterohaemorrhagiae, hepatic involvement with these serovars may be absent, minimal or delayed compared to the onset of ARF. Leptospirosis is
important to recognize because it is potentially reversible and because of the potential for zoonosis to owners and veterinary
personnel. Clinical presentations may include acute renal failure, acute hepatic disease, fever, uveitis and acute pulmonary
hemorrhage. Common laboratory findings in dogs with leptospirosis include azotemia (with isosthenuria), elevated liver enzymes,
hyperbilirubinemia, neutrophilic leukocytosis, thrombocytopenia and renal glucosuria with normoglycemia.
The re-emergence of leptospirosis has been linked to exposure to wildlife species that act as reservoirs for the organism.
The reservoir or maintenance hosts develop low antibody titers to leptospirosis and can carry the organism for longer periods
of time than incidental hosts like dogs and humans. Not all maintenance hosts are well understood for all the serovars.
Leptospira spp are motile spirochetes that are able to penetrate mucus membranes or through breaks in the skin. During the spirochetemia,
the organism spreads throughout the blood including brain, lung, blood vessels, liver and kidney. Next there is localization
of the organism to the liver and kidneys (renal tubules) predominantly. In incidental hosts (humans and dogs), high antibody
titers develop and there is a brief period of urine shedding of the organism. Infections can be subclinical, clinical or
even fatal. In maintenance hosts (raccoons), there are low antibody titers and may be low term urine shedding of leptospires
in the urine.
All dogs are susceptible to leptospirosis. Young adult large breed dogs have higher risk of leptospirosis in epidemiological
studies because they are more likely to be exposed to infected ground water than other dogs; however, this does not represent
an increased susceptibility. Likewise, male dogs are at greater risk than female dogs. One study showed that dogs that lived
in areas that were formerly considered farm or woodland that had become developed into urban areas had greater risk for leptospirosis.