Carditis in Lyme disease susceptible and resistant strains of laboratory mice infected with Borrelia burgdorferi.

The clinical and pathologic evolution of cardiac Lyme disease was evaluated in four-week-old susceptible C3H/He (C3H) and resistant C57Bl/6 (B6) mice on days 3, 6, 10, 15, 30, 60, and 90 after intradermal inoculation with Borrelia burgdorferi strain N40. Culture, DNA polymerase chain reaction, in situ nucleic acid hybridization, immunoperoxidase histochemical analysis, and silver stain were used to detect spirochetes. Spirochetes were first detected by culture on day 6 in two of four C3H mice. The hearts of all mice of both genotypes were culture positive by day 10 and infection persisted through day 90. The spirochetes had a predilection for connective tissue in the heart base, especially around the aorta, epicardium of the upper ventricles and atria, myocardial interstitium, and endocardium. Carditis was first detectable on day 10, reaching a maximum severity on day 15, then resolved, except for persistence of periaortic lymphoplasmacytic infiltrates through day 90 in C3H mice and through day 60 in B6 mice. The C3H mice developed more severe disease than the B6 mice, and this was associated with the earlier appearance, greater numbers, and later clearance of spirochetes in C3H mice. Electrocardiographs of infected and control mice revealed bradycardia and tachycardia in many C3H mice, but in very few B6 mice. Serum creatinine phosphokinase levels did not become elevated at any interval.