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• Leptospires usually enter through mucous membranes or broken skin. Replicate in blood, renal tubules and liver.
• Disease depends on dose and serovar of leptospire and on age of dog and degree of immunity: pre-existing high antibody titre leads to elimination of organism, moderate antibody to mild or asymptomatic infection.
• Full blown peracute clinical disease is generally seen only in unvaccinated dogs.
• Peracute disease due to massive leptospiraemia: pyrexia, shivering, muscle tenderness, vomiting, dehydration, shock and death.
• Sub-acute infections - fever, anorexia, vomiting and dehydration. May be reluctant to move owing to abdominal pain. Mucous membranes congested, petechial haemorrhage. Infection of kidney then leads to progressive renal failure - oliguria and anuria.
• Dogs which eliminate infection may return to normal in 2-3 weeks. But widespread damage may lead to chronic renal failure. Hepatic infection may lead to jaundice and chronic hepatitis.
• Most infections, however, are chronic rather than acute or subacute, with rather vaguer clinical signs such as pyrexia, or progressive chronic renal or hepatic failure.
• Infected dogs may excrete leptospires in urine for months or even years.

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