Rheumatic Heart Disease [RHD] is by far the commonest Valvulopathy [disease of the heart valves], and the 3rd leading cause of heart failure in the tropics, Nigeria inclusive.
While it usually occurs at middle age, with the peak age of incidence being the 5th decade of life, the inciting event usually occurs in the second half of the first, and the whole of the second, decade of life [5 to 20 years of age].
The sequence of events that leads to chronic RHD starts from a strept sore throat infection, specifically the type caused by Streptococcus pyogenes [otherwise called Group A, Beta hemolytic, Streptococcus]. This, if left untreated, may be complicated by Rheumatic Fever: an immune mediated process in which the body's defense mechanism confuses some tissues in the body, including the heart valves, with molecules found in the organism, and ends up attacking them, leading to inflammation. Years later, the heart valves so attacked thickens and begins to malfunction, leading to RHD.
RHD, in some cases, is amenable to medical therapy. However, in most cases, it ultimately progresses to heart failure, and may need surgical intervention, a thing that is not yet common in these parts.
The best way to avoid this unfortunate cascade of events is simply not allowing it to start in the first place.
With prompt treatment of strept sore throat infection, using Penicillin V [or substitutes like Amoxicillin and Ampicillin; or macrolides like Erythromycin and Clarithromycin, for individuals with penicillin allergy], for at least 10 days; and optimal treatment of Acute Rheumatic Fever, if and when it occurs, the likelihood of developing RHD reduces drastically.
To prove how effective these measures can be: About a 100 years ago, ARF and RHD were a leading cause of death in the Western world. However, following the advent of antibiotics, case fatality rate for Rheumatic Fever has dropped to almost 0%; and the probability of developing RHD has dropped from 60-70%, to 9-30%.
Unfortunately, in Africa, for obvious reasons, the figures for both are still high.