When your immune system mistakes your own heart for a bacterial invader
Rheumatic fever is not a contagious disease, but a profound biological error. It occurs when the body’s defenses, triggered by a streptococcal infection, fail to distinguish between invading bacteria and your own healthy tissues, leading to a life-threatening autoimmune attack.
The mechanism behind rheumatic fever is a phenomenon known as molecular mimicry. When the body fights *Streptococcus pyogenes*—the bacterium responsible for strep throat and scarlet fever—it produces antibodies to attack the bacterial cell wall. However, because certain proteins in the bacteria share structural similarities with human proteins, these antibodies mistakenly target the body's own tissues. Specifically, antibodies against the bacterial M protein may cross-react with cardiac proteins like myosin and smooth muscle cells, triggering a type II hypersensitivity reaction.
This inflammatory cascade can affect the joints, skin, and brain, but the most devastating impact is often on the heart. In about 50% of cases, the disease involves the heart, potentially leading to rheumatic heart disease (RHD). This condition is characterized by the scarring and thickening of heart valves, such as the mitral or aortic valves, which can result in stenosis or regurgitation. Over time, repeated attacks can cause permanent damage, leading to severe complications like heart failure, atrial fibrillation, or the need for valve replacement surgery.
While the disease is most common in children aged 5 to 15, it remains a significant global health burden, particularly in the developing world and among indigenous populations. In 2015, the disease was responsible for approximately 319,400 deaths, a decrease from 374,000 in 1990. Risk factors such as malnutrition, poverty, and crowded living conditions exacerbate the spread of the initial streptococcal infections. Fortunately, prompt treatment of strep throat with antibiotics like penicillin can significantly reduce the risk of developing the fever.
Genetic predisposition also plays a role. Variations in the HLA class II genes on chromosome 6, such as the DR7 allele, are associated with increased susceptibility to the autoimmune response. Researchers are also investigating the role of the TNF-α cytokine and MBL2 gene variants in how the body manages this inflammatory destruction.
Source: Rheumatic fever
