Dogs are the primary host of Leptospira serovars, and many other mammal species can also be infected. Clinical signs range from mild, subclinical infection to multi-organ failure and death. Diagnosis includes serologic testing and identification of leptospires in tissues, blood or urine. Doxycycline is the primary drug used for treatment in dogs, along with appropriate supportive care. Polyvalent vaccines are available for prevention. Specific serovars in a geographic area vary, so vaccines with the appropriate types should be used.
■Signs and Symptoms of Leptospirosis in Dogs:
Acute kidney injury has been the most common presentation for canine leptospirosis in recent years. Dogs affected by leptospirosis may show these clinical signs:
•lethargy
•anorexia
•vomiting
•abdominal pain
•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
•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
•proteinuria
•glucosuria
•cylindruria
•hematuria
•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
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
Diagnosis of Leptospirosis in Dogs:
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.
By –
1.Katharine F. Lunn, BVMS, MS, PhD, MRCVS, DACVIM, Department of Clinical Sciences, College of Veterinary Medicine, North Carolina State University;
2.Katharine F. Lunn, BVMS, MS, PhD, MRCVS, DACVIM, Department of Clinical Sciences, College of Veterinary Medicine, North Carolina State University
