Infected ticks generally must attach for a minimum of 24 hours for transmission to occur. The spirochete replicates at the site of tick attachment, after which time it spreads to other sites. Although briefly found in blood, the organism primarily replicates and spreads through connective tissue. After invasion, the organism can persist in dogs for over a year, through evasion of host immune responses.
The initial signs in dogs occur 2 to 5 months after a tick bite and consist of variable fever, inappetence, thrombocytopenia, mild peripheral lymphadenopathy, and lameness due to neutrophilic polyarthritis. Clinical signs result from severe protein loss and renal failure and include inappetence, lethargy, weight loss, vomiting, and polyuria and polydipsia. Urine protein to creatinine ratios are often > 5 and may be > 15. Peripheral edema, pleural effusion or ascites may develop.
One widely used serodiagnostic test for canine Lyme disease is a C6 ELISA (SNAP 4Dx Plus), which detects antibodies against a portion of the Lyme proteins. The advantages of the C6 ELISA assay are that 1) it detects antibodies 3 to 5 weeks after the time of infection, so by the time dogs develop clinical signs they are virtually always positive, and 2) it is negative in dogs that have been vaccinated for Lyme disease, because the antigen is not expressed by organisms used in Lyme vaccines. The C6 ELISA is available as an in-house assay, in combination with Ehrlichia canis/Ehrlichia ewingii, Anaplasma spp. and Dirofilaria immitis (4Dx Plus SNAP) and as a quantitative ELISA which is sent to outside labs.