Strep throat is caused by a bacterial infection, specifically by a group of bacteria known as Group A Streptococcus (GAS), or Streptococcus pyogenes. These bacteria are gram-positive cocci that thrive in the throat and tonsils, leading to inflammation and the characteristic symptoms of strep throat. The infection typically begins when these bacteria enter the body through the mouth or nose, usually after close contact with an infected person who spreads the bacteria via saliva or nasal secretions.
Group A Streptococcus bacteria have several tools, called virulence factors, that help them invade tissues and cause illness. These include enzymes like streptolysins, which destroy cells, DNAases that break down DNA, and hyaluronidase that helps the bacteria spread through connective tissue. Some strains also produce exotoxins that can trigger an intense immune response, releasing substances called cytokines that cause inflammation and sometimes severe complications.
The infection usually affects children between 3 and 14 years old, although it can occur in adults as well. When the bacteria infect the throat, they cause symptoms such as a sudden sore throat, fever, swollen and tender lymph nodes under the jaw, and a red, inflamed throat often with white or yellow pus spots on the tonsils. Unlike viral throat infections, strep throat typically does not cause coughing, runny nose, or hoarseness. The bacteria spread most easily in winter and spring, especially in crowded settings like schools.
Transmission happens primarily through direct contact with respiratory droplets from an infected person’s cough or sneeze. However, recent research shows that indirect contact with contaminated surfaces or objects can also spread the bacteria. This means touching something with the bacteria on it and then touching the mouth or nose can lead to infection. The bacteria can survive on surfaces for some time, making hygiene and handwashing important in prevention.
Once the bacteria colonize the throat, they multiply and cause inflammation, leading to the painful symptoms. If untreated, strep throat can sometimes lead to complications. One serious complication is rheumatic fever, an autoimmune condition where the body’s immune system, while fighting the bacteria, mistakenly attacks the heart, joints, skin, and brain. This happens because some proteins on the bacteria resemble proteins in human tissues, confusing the immune system. Rheumatic fever can cause inflammation of the heart (carditis), which may damage heart valves permanently, leading to long-term heart problems.
Other complications include peritonsillar abscess, where pus collects near the tonsils, causing severe pain and difficulty swallowing, and in rare cases, streptococcal toxic shock syndrome, a life-threatening condition caused by toxin-producing strains of the bacteria.
People can also carry Group A Streptococcus bacteria in their throat without showing symptoms, known as being an asymptomatic carrier. These carriers can still spread the bacteria to others, especially in close-contact environments.
In summary, strep throat is caused by infection with Group A Streptococcus bacteria, which spread through respiratory droplets and direct or indirect contact. The bacteria’s ability to produce enzymes and toxins helps them invade the throat tissues and cause inflammation. While many recover without problems, untreated infections can lead to serious complications like rheumatic fever, highlighting the importance of early diagnosis and treatment.
