Rheumatic fever is still classified as a disease of unknown origin. However, authorities are pretty well agreed that the disease is infectious, and many students are convinced that it is closely associated with streptococcic infection. Whether the various inflammatory lesions are the actual sites of infection or whether they are the expression of some toxic reaction is still a matter for investigation. Recently the theory has been advanced that rheumatic fever is a virus disease, but so far the work of Schlesinger and his co-workers1 has not been widely confirmed.
The pathologic changes observed in rheumatic fever are usually divided into two groups: (1) exudative lesions, such as those seen in the joints and in rheumatic pleurisy, and (2) proliferative lesions, such as those which occur in the myocardium and in the walls of the blood vessels. However, a sharp line of demarcation cannot be drawn between the two.
CECIL RL. THE THERAPY OF RHEUMATIC FEVER. JAMA. 1940;114(15):1443-1447. doi:10.1001/jama.1940.62810150005009