Infection of dogs with leptospires results in illness of varying severity, depending on the infecting strain, geographical location, and host immune response. Some dogs display mild or no signs of disease, whereas others develop severe illness or death, often as a result of renal injury. In general, veterinarians should suspect leptospirosis in dogs with signs of renal or hepatic failure, uveitis, pulmonary hemorrhage, acute febrile illness, or abortion.
Fever occurs early in the course of illness, and may be accompanied by shivering, generalized muscle tenderness, and reluctance to move. Dogs presenting with acute renal failure may show polyuria, polydipsia, dehydration, vomiting, diarrhea, inappetence, lethargy, or abdominal pain or some combination of these signs.13,16–20
Oliguria or anuria also may occur. Dogs may present with signs of hepatic failure, including icterus.19,20
Other reported manifestations of infection include conjunctivitis,18,21
and tachypnea or dyspnea because of acute respiratory distress syndrome or leptospiral pulmonary hemorrhage syndrome (LPHS), which has been reported most frequently in dogs from some parts of Europe.19,20,23,b
LPHS is increasingly recognized in human patients, appears to have an immune-mediated basis, and is associated with high mortality.4,24,25
Pathologic lesions in dogs resemble those described in humans.20
Changes suggestive of pancreatitis have been detected in some dogs by abdominal ultrasonography. Hematuria can occur after natural and experimental infection.19,20
Bleeding tendencies also may be manifested as hematemesis, hematochezia, hemoptysis, melena, epistaxis, and petechial hemorrhages.19,20,21,26
The pathophysiologic mechanisms of bleeding in dogs and humans with leptospirosis are incompletely understood.27
Hepatic failure, disseminated intravascular coagulation (DIC), and direct vascular damage by spirochetes may play variable roles. Vasculitis also may be manifested as peripheral edema and mild pleural or peritoneal effusion. Meningitis is recognized in people with leptospirosis, but has not been documented in dogs. Cardiac damage occurs in human patients28
and ECG alterations suggesting myocardial damage can occur in dogs.26
Abortion has occurred in dogs after transplacental spread of serovar Buenos Aires,29
and 1 report suggested abortion associated with serovar Bratislava infection.30
Polyuria and polydipsia can develop in dogs with leptospirosis in the absence of azotemia. In some cases, this may result from a decreased glomerular filtration rate sufficient to cause impaired renal concentrating ability. However, these patients also may be hyposthenuric.19,31
Experimentally, leptospiral infection causes decreased vasopressin responsiveness of the inner medullary collecting ducts,32
suggesting polyuria may result from acquired nephrogenic diabetes insipidus.
Chronic active hepatitis was reported in 1 kennel in association with development of antibodies to serovar Grippotyphosa33
and in another to serovar Australis.34
Attempts to detect leptospiral DNA in liver samples from dogs with chronic hepatitis were unrewarding.35
Leptospirosis should be considered as a differential diagnosis in dogs with hepatitis or hepatic fibrosis. Similarly, dogs surviving acute renal tubulointerstitial injury may have residual chronic kidney injury that progresses over months to years, culminating in signs of decompensated chronic kidney disease.
Attempts have been made to correlate the infecting serovar with clinical presentation.13,14
Evidence for a correlation has been weak because of the poor ability of antibody tests to predict the infecting serovar, and lateral transfer of virulence attributes may occur between serovars.4,15
Thus at this time, no clear correlation has been made between the suspected infecting serovar based on antibody testing and clinical manifestations of disease in naturally occurring canine leptospirosis. No associations between clinical manifestations and infecting serovars have been detected in human patients,1
and multiple serovars have been isolated from humans in some outbreaks.36
Future attempts to correlate clinical presentation and infecting leptospiral strain should be based on a combination of isolation, serotyping, and genetic studies.