Causes of Rheumatic Fever
Rheumatic fever is the result of group A beta-hemolytic streptococcal infection of the throat. Streptococcal infection of the throat usually leads to strep throat, although sometimes it can cause scarlet fever. Streptococcal infection of the skin and other parts of the body rarely causes rheumatic fever.
Approximately 0.3-3% of the people with streptococcal infections of the throat develop rheumatic fever afterwards. This percentage rises to 3-6% in people who are genetically predisposed to rheumatic fever.
Recent studies have also shown that not all serotypes of group A streptococci lead to rheumatic fever.
Rheumatic fever develops due to abnormal immune responsewhich happens due to molecular mimicry. This prevents the immune system from distinguishing between streptococcal pathogens and certain tissues of the human body. These tissues are primarily located in the heart, skin, joints, and central nervous system. The immune system attacks these organs causing inflammation.
If the child or person with strep throat or scarlet fever is immediately treated using a sufficient amount of antibiotics over a recommended period of time, the chances of developing rheumatic fever are very slim. This is the reason why so many children in the developing countries who do not receive adequate treatment, develop rheumatic fever after streptococcal infection.
There are a number of risk factors which contribute to the development of rheumatic fever:
- Familial history. People whose close relatives had rheumatic fever are more likely to develop rheumatic fever themselves after a streptococcal infection. People with genetic predisposition are about 2-3 times more susceptible to this disease in comparison to general population.
- Type of streptococcus bacteria. Some strains of group A streptococcal bacteria do not cause rheumatic fever at all. These strains include M types 4, 2, 12. On the other hand, serotypes 3, 5, 6, 14, 18, 19, and 24 are the ones responsible for rheumatic fever.
- Environmental factors. People who live in overcrowded places and have poor sanitation are more likely to have multiple exposures to streptococcal infection. Malnutrition is also a contributing factor as it lowers the body’s immune response to infection, making people more susceptible to it.
Next Chapter: Symptoms of Rheumatic fever