Rheumatic Heart Disease: Understanding the Causes

Rheumatic heart disease is a serious condition that arises as a complication of untreated or inadequately treated streptococcal infections, particularly those caused by group A beta-hemolytic streptococcus bacteria. This condition is the result of an abnormal immune response, where the body's defense system mistakenly attacks its own tissues following a strep infection.

The Role of Group A Streptococcus

At the core of rheumatic heart disease is an initial infection with group A beta-hemolytic streptococcus, the same bacteria responsible for strep throat and other infections. In some cases, if the infection is not properly treated with antibiotics, the immune system may begin to react abnormally to certain proteins on the surface of the bacteria.

Cross-Reactivity and Immune Confusion

One particular protein found on the streptococcus bacteria shares structural similarities with proteins present in the heart muscle and heart valves. Under normal immune function, the body is able to distinguish between foreign invaders and its own tissues. However, in some individuals, especially children and adolescents, the immune system misidentifies the heart tissue as a threat due to this molecular mimicry.

When the immune system is functioning correctly, it should eliminate the invading bacteria without harming the body's own cells. But in the case of rheumatic fever, the immune response becomes dysregulated. Instead of targeting only the bacteria, it launches an attack on both the streptococcus antigens and the similar-looking heart tissues.

Autoimmune Reaction and Tissue Damage

This autoimmune reaction leads to the production of specific antibodies that bind not only to the streptococcus bacteria but also to the heart valves and myocardial tissue. This results in inflammation and damage to the heart, particularly affecting the mitral and aortic valves. Over time, repeated episodes of rheumatic fever can cause permanent scarring and deformity of the heart valves, leading to chronic rheumatic heart disease.

Why It Happens in Some People and Not Others

Not everyone who contracts a strep infection develops rheumatic fever or heart disease. Genetic factors, immune system variations, and environmental influences such as living conditions and access to healthcare all play a role in determining who is at risk. Individuals with weakened immune responses or those exposed to repeated streptococcal infections are more likely to experience this harmful immune reaction.

In summary, rheumatic heart disease is primarily triggered by an autoimmune response following a group A streptococcus infection. The molecular similarity between bacterial proteins and heart tissue leads the immune system to attack the body's own organs, causing long-term damage. Early diagnosis and proper treatment of strep infections are crucial in preventing this potentially life-threatening condition.