Leptospirosis in Dogs
Dogs are the maintenance host for Leptospira interrogans serovar Canicola, and before widespread vaccination programs, serovars Canicola and Icterohaemorrhagiae were the most common serovars in dogs in the USA. The prevalence of canine serovars has shifted significantly in the last 20 years; currently the most prevalent serovars are believed to be Grippotyphosa, Pomona, and Bratislava; however, this belief is largely based on serologic results that are now known to be inaccurate in predicting the infecting serovar in dogs with leptospirosis. The serovars that cause disease in dogs are likely to vary with geographic region and the presence of reservoir hosts. Unfortunately, current understanding of the serovars that cause natural disease in dogs is limited by the fact that isolation of leptospires is rarely performed; thus, studies to date have relied on serologic data. As noted above, it is now accepted that the results of the MAT do not reliably predict the infecting serovar in dogs (or people) with leptospirosis; thus, the true infecting serovar is unknown in most cases. However, it is likely that the serovars that cause disease in dogs are those circulating in local wildlife. Experimental infections and isolation of organisms from a small number of sick dogs have shown that serovars Icterohaemorrhagiae, Canicola, Autumnalis, Pomona, Bratislava, Sejroe, and Ballum are capable of causing disease in dogs. Knowledge of the infecting serovar in dogs is essential for epidemiologic studies and vaccine development; it is less important for clinicians managing individual cases. It is currently not known whether specific serovars are associated with specific clinical signs in dogs, and there is no published evidence to guide therapy based on serovar identification. It is, however, extremely important for veterinarians to maintain a high index of suspicion for leptospirosis, because this is a zoonotic disease and has a wide range of clinical presentations in dogs. Any age, breed, or sex of dog is susceptible to leptospirosis, and the diagnosis should not be excluded on the basis of signalment or lifestyle. Canine leptospirosis is not restricted to large-breed dogs, male dogs, or dogs with a predominantly outdoor lifestyle.
Acute kidney injury has been the most common presentation for canine leptospirosis in recent years. Affected dogs may present with lethargy, anorexia, vomiting, abdominal pain, and history of polyuria, oliguria, or anuria. Dogs that survive acute renal failure may return to baseline or progress to chronic kidney disease. Leptospirosis should also be considered in any dog with previously diagnosed chronic kidney disease that develops “acute-on-chronic” kidney injury. Renal tubular damage in leptospirosis may manifest as cylindruria, proteinuria, or glycosuria. In people, acute kidney injury due to leptospirosis is often nonoliguric and can be associated with hyponatremia and hypokalemia. These electrolyte changes have also been noted in canine leptospirosis, along with the expected changes of azotemia, hyperphosphatemia, and acidosis of renal failure. Hyperkalemia is also possible. Polyuria and polydipsia (PU/PD) in the absence of azotemia is a less common manifestation of the renal effects of leptospirosis. PU/PD may be due to a decrease in glomerular filtration rate that is sufficient to cause loss of renal concentrating ability without azotemia. However, PU/PD can also be due to nephrogenic diabetes insipidus.
Acute liver disease may accompany acute renal failure in dogs with leptospirosis, or it may occur alone. Affected dogs may be icteric, and serum biochemistry analysis reveals increased bilirubin and alkaline phosphatase. ALT is typically less markedly increased than alkaline phosphatase. In people and dogs, the jaundice of acute leptospirosis appears to be associated with minimal histopathologic changes in the liver, suggesting that it is due to the “cholestasis of sepsis” rather than to hepatocellular damage.
Muscle pain, stiffness, weakness, trembling, or reluctance to move can be seen in dogs with leptospirosis. These may be the result of vasculitis, myositis, or nephritis. Myalgia is commonly reported in human leptospirosis and is associated with the septicemic phase of the disease.
Less common manifestations of canine leptospirosis include bleeding disorders characterized by petechial hemorrhages, epistaxis, melena, and hematemesis. These findings are most likely due to vasculitis. Affected dogs may also be thrombocytopenic; however, platelet counts are rarely low enough to be responsible for spontaneous bleeding. The causes and mechanisms of bleeding disorders in leptospirosis are poorly understood, but they have been suggested to be associated with endothelial cell damage. Pulmonary hemorrhage is now one of the most common clinical signs in outbreaks of human leptospirosis. This is a less common finding in canine leptospirosis; however, cough or dyspnea, or radiographic abnormalities have been noted in a number of affected dogs. Uveitis is an uncommon manifestation of leptospirosis in dogs. It appears to be infrequently associated with experimental canine leptospirosis, but rare case reports exist. Additional clinical signs reported in dogs with leptospirosis include vomiting, diarrhea, weight loss, fever, hypothermia, oculonasal discharge, lymphadenopathy, effusions, and edema.
CBC changes may include neutrophilia, lymphopenia, monocytosis, and mild anemia. These changes are nonspecific; however, mild to moderate thrombocytopenia is seen in >50% of cases and, if detected in combination with azotemia or evidence of cholestasis, should prompt diagnostic testing for leptospirosis. Coagulation abnormalities may include increased fibrin degradation products and prolonged prothrombin time (PT) or activated partial thromboplastin time (APTT). Urinalysis may reveal hyposthenuria, isosthenuria, or hypersthenuria, depending on the degree of renal involvement. Other changes may include proteinuria, glucosuria, cylindruria, hematuria, and pyuria. Leptospirosis could also potentially be associated with renal tubular acidosis.
Reticulonodular pulmonary opacities have been described in the thoracic radiographs of dogs with leptospirosis and attributed to pulmonary hemorrhage. These changes may be diffuse or predominantly involve the caudodorsal lung fields. Abdominal radiographs may be unremarkable or may show renomegaly or hepatomegaly. Changes noted on ultrasonography include renomegaly, pyelectasia, increased cortical echogenicity, perinephric effusion, and a hyperechoic medullary band. However, these changes are not specific for leptospirosis, and absence of these findings does not exclude the diagnosis.
Gross necropsy findings can include jaundice, effusions, and petechial or ecchymotic hemorrhages on any organ, pleural, or peritoneal surface. The kidneys and liver may be enlarged, and lungs may be wet, heavy, and discolored. The liver is often friable with an accentuated lobular pattern and may have a yellowish brown discoloration. The kidneys may have white foci on the subcapsular surface. Microscopic findings in the liver may include mild random hepatocytic necrosis, nonsuppurative hepatitis, and intrahepatic bile stasis, while swollen tubular epithelial cells, tubular necrosis, and a mixed inflammatory reaction may be seen in the kidneys.
Ideally, a combination of serology and organism detection should be used for diagnosis of canine leptospirosis. Serology is the most frequently used diagnostic test for dogs. Acute and convalescent titers may be necessary to confirm a diagnosis; hence, the use of the MAT is preferred over the ELISA. PCR-based tests are widely available, and collection of both blood and urine samples before administration of antibiotics should be considered for maximal sensitivity. The results of all diagnostic tests should be interpreted in light of the animal's vaccination history, clinical signs, and clinicopathologic findings.
Renal failure and liver disease are treated with fluid therapy and other supportive measures to maintain normal fluid, electrolyte, and acid-base balance. Supportive measures may include antiemetics, GI protectants, phosphate binders, and hepatic support medications. Renal replacement therapy with intermittent hemodialysis or continuous renal replacement therapy should be considered for dogs that are anuric or oliguric despite appropriate supportive therapy. Antibiotic therapy is indicated whenever leptospirosis is suspected and should be instituted before confirmatory test results are available. There are no experimental studies in dogs to guide selection of antibiotic protocols for this species. Current recommendations are to treat with doxycycline (5 mg/kg/day, IV or PO) for 2 wk. For dogs that cannot tolerate doxycycline, initial therapy with a penicillin is appropriate, but this should be followed by a 2-wk course of doxycycline to eliminate the renal carrier phase of infection. Dogs recently exposed to leptospirosis may be treated prophylactically with oral doxycycline for 14 days.
Commercial bacterins for dogs are available for serovars Canicola, Icterohaemorrhagiae, Grippotyphosa, and Pomona. Vaccinated dogs may potentially be susceptible to infection with other serovars, although this has not been tested in an experimental setting. In general, currently available vaccines provide good protection from clinical disease and also appear to reduce renal colonization and urine shedding. Concerns exist regarding hypersensitivity reactions after leptospiral vaccination in dogs, but these appear to be unjustified based on more recent studies and perhaps associated with the use of more highly purified vaccines. Canine challenge studies have demonstrated duration of immunity of at least 1 yr; thus, prior recommendations for vaccinating every 6 mo are no longer justified.
Because leptospirosis is a zoonotic disease, all veterinary personnel should take appropriate precautions when handling known or suspected infected animals. Such dogs do not need to be placed in isolation but should be nursed with barrier precautions, paying particular attention to avoiding exposure of skin or mucous membranes to urine or blood. Infected dogs should be allowed to urinate in designated areas that can subsequently be cleaned and disinfected. The organisms are killed by all commonly used disinfectants. Owners of dogs recently diagnosed with leptospirosis should be advised of the zoonotic nature of the disease and contact their physicians with any health concerns. Owners should wear gloves when cleaning up urine and should wash their hands after handling the dog, at least until the course of antibiotic therapy is completed.