Host responses to Borrelia burgdorferi in dogs and horses.

By using paired sera the IgM and IgG host responses were analyzed in dogs with ELISA and Western blot techniques. Antibodies in clinical seropositive dogs bound to 4-25 IgM and up to 40 or more IgG antigenic determinants. Early IgM response to the 41-kDa flagellin persisted for at least 9 months and involved as many as seven other peptides. IgG response expanded later in the disease and involved more immunogens than are currently recognized in late human disease. A percentage of asymptomatic dogs that later developed clinical symptoms were seropositive. Immunoblot studies suggested that B. burgdorferi is persistent in both asymptomatic and weakly reactive animals and if untreated could lead to disease expression. Clinical seropositive, asymptomatic seronegative, and experimentally infected horses were similarly studied. In experimentally inoculated animals IgG antibodies were initially bound to flagellin and later to the 34- and 31-kDa polypeptides, even though ELISA values were considered only slightly reactive.