Complete Heart Block in a Dog Seropositive for Borrelia burgdorferi: Similarity to Human Lyme Carditis

Lyme disease has been recognized in humans since 1975 when it was associated with an outbreak of oligoarthritis in children in Lyme, Connecticut. Erythema chronicum migrans (ECM) is a clinical marker for the human disease, which usually appears within 3 to 32 days after an infected tick bite. Lyme disease is caused by spirochete, Borrelia burgdorferi, which is vectored by the hard ticks Ixodes dammini or Ixodes pacificus in the United States. In humans, Lyme disease has been found to cause a variety of clinical syndromes including cardiopathy, neuropathy, dermatopathy, and arthropathy. Human Lyme carditis is characterized by varying degrees of atrioventricular (AV) heart block that usually resolve regardless of therapy. Lyme disease has been reported in the dog as an arthropathy. This article reports a case of complete heart block and myocarditis in a dog with a positive titer for B burgdorferi, in which clinical and pathologic findings were similar to those seen in human Lyme myocarditis.