An animal model of chronic rheumatic valvulitis induced by formalin-killed streptococci
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Rheumatic heart disease is the most severe complication of rheumatic fever. Till date, very few successful animal models of rheumatic valvular disease have been reported. This study aimed at developing a suitable animal model of chronic rheumatic valvulitis for further investigation and prevention of rheumatic heart disease. Lewis rats were immunized with one administration of formalin-killed and sonicated group A streptococci together with Complete Freund’s Adjuvant every 7 days for three cycles followed by group A streptococci alone till killing. Control rats were administered adjuvants and saline. Rats in group 1 were killed 12 weeks after the initial injection. Rats in group 2 and control group were killed 24 weeks after the initial injection. Results 62.5% (5/8) of rats in group 1 developed myocarditis and 50% (4/8) developed valvulitis. Histological examination of cardiac sections showed only cellular infiltrates. In contrast, 75% (6/8) of rats in group 2 developed rheumatic-like myocarditis and 62.5% (5/8) developed chronic valvulitis. Histological manifestations of the hearts in group 2 animals involved not only acute damage such as cellular infiltrates, Aschoff-like cells, verrucous vegetation, but also chronic lesions such as fibrosis, vascular neogenesis. None of the rats (0/8) in control group presented myocarditis or valvulitis. Lewis rat repeatedly immunized with formalin-killed GAS may be a suitable animal model of chronic rheumatic valvulitis. It may be useful for future investigation of the pathogenesis and possible preventive strategies of human rheumatic heart disease.
KeywordsGroup A streptococcus Lewis rat Rheumatic valvulitis Rheumatic heart disease
We thank Professor Tingchung Wang (University of Rochester Medical Center) for critically reviewing the manuscript.
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