Final answer:
Mitral stenosis typically develops 20-40 years after an episode of rheumatic fever, a response to a childhood infection by Streptococcus pyogenes, leading to rigid, calcified heart valves and subsequent heart malfunction.
Step-by-step explanation:
Mitral stenosis typically presents 20-40 years after an episode of rheumatic fever, or scarlet fever, which is an autoimmune response following an infection by the bacterium Streptococcus pyogenes. This infection is commonly seen in childhood. When the inflammation occurs, it can lead to valvular disorders such as mitral stenosis, resulting in the heart valves becoming rigid and possibly calcified.
Valves like the mitral and aortic are susceptible to such issues, causing the heart to work harder and subsequently weakening it over time. Valvular malfunction disrupts blood flow and leads to insufficiency, specifically named for the valve affected.