Merlin’s prognosis was excellent. His seropositive result indicated exposure to a tick weeks or months before the wellness visit. Because signs of disease were not present, it was unlikely that disease related to that exposure would develop. Seropositivity is common in endemic areas, yet disease is anecdotally fairly rare, meaning most exposed dogs mount an immune response and therefore become seropositive but do not develop disease.
Lyme nephritis is of concern because of the severity of disease; however, it is rarely reported, and the pathogenesis of disease and factors that predispose to disease are unknown.2 B burgdorferi is rarely found in the kidneys of dogs with Lyme nephritis, and disease manifests as an immune complex glomerulonephritis.3,4 As such, immune-mediated disease—rather than active infection—is the apparent etiology, raising questions about whether an infection to treat is still present by the time Lyme nephritis is identified or whether disease occurs during a postinfectious state. Although there is no universal approach to seropositive but clinically normal animals, treatment of seropositivity in the absence of proteinuria is likely not warranted. The owners submitted urine samples from Merlin twice over the next year, and proteinuria was not identified. Merlin was clinically normal at his next annual wellness visit. His owners had been diligent with tick prophylaxis and had not observed any ticks on him since the previous visit. At his latest wellness examination, antibodies against B burgdorferi were identified but were likely residual levels from his prior exposure. Twice-yearly rechecks were recommended to assess for proteinuria.