When a sore throat strikes, the cause is most often a virus that the body can clear on its own. If the infection is caused by the bacterium Group A Streptococcus (GAS), commonly known as strep throat, leaving it untreated opens the door to severe, systemic health risks. This bacterial infection is typically addressed with a short course of antibiotics, which clears the acute illness and prevents serious complications. The most dangerous long-term effects of untreated strep are caused by the body’s immune response mistakenly attacking its own tissues. Prompt medical intervention is necessary because the stakes involve the health of the heart and kidneys.
Local Progression and Acute Complications
The most immediate danger of ignoring strep throat is the unchecked multiplication of Streptococcus pyogenes bacteria in the throat. Prolonged, severe symptoms like high fever, intense throat pain, and difficulty swallowing can persist for weeks without treatment. The infection can spread directly from the tonsils into neighboring tissues, leading to localized, pus-filled pockets.
One common local complication is a peritonsillar abscess, often called quinsy, which forms near the tonsil. This abscess causes severe, one-sided throat pain and can make it difficult or impossible to open the mouth fully (trismus). The infection can also spread to the middle ear, causing acute otitis media, or move into the sinus cavities, leading to bacterial sinusitis.
Scarlet Fever: When Strep Releases Toxins
A distinct systemic complication of untreated strep is scarlet fever, or scarlatina, which occurs when the GAS bacterium produces specific toxins. This condition is caused by strains of Streptococcus pyogenes that release streptococcal pyrogenic exotoxins (SPEs). These toxins circulate through the bloodstream, triggering a widespread reaction in the skin.
The most recognizable symptom is a characteristic rash that feels rough, like sandpaper, often starting on the neck and chest before spreading across the body. The face may appear flushed, with a pale area around the mouth, and the tongue can take on a bumpy, red appearance referred to as “strawberry tongue.” Scarlet fever is a toxin-mediated illness. While highly treatable with antibiotics, leaving the underlying infection untreated still leaves the patient vulnerable to the most severe systemic after-effects.
Long-Term Cardiac Damage: Rheumatic Fever
The most devastating consequence of untreated strep throat is Acute Rheumatic Fever (ARF), a severe inflammatory disease that develops in genetically susceptible individuals approximately two to four weeks after the initial infection. ARF is an autoimmune response where the body’s immune system mistakenly attacks its own tissues. This phenomenon is termed molecular mimicry, where proteins on the surface of the GAS bacteria, specifically the M protein, closely resemble proteins found in human tissues.
The resulting antibodies cross-react with the body’s own cells, particularly those in the heart valves, joints, brain, and skin. Heart inflammation, or carditis, is the most serious manifestation, affecting up to 60% of ARF cases, and is the only component that can lead to permanent damage. Repeated episodes of ARF can lead to Rheumatic Heart Disease (RHD), causing irreversible scarring and malfunction of the heart valves, which often necessitates lifelong medication or valve replacement surgery.
Diagnosis of ARF is guided by the Jones Criteria. Major criteria include:
- Carditis
- Painful arthritis (inflammation of the joints)
- Sydenham chorea (involuntary, jerky movements)
- Erythema marginatum (a ring-shaped rash)
- Subcutaneous nodules
The arthritis associated with ARF is often migratory, moving from one large joint to another. Sydenham chorea is a delayed neurological manifestation that can appear months after the initial infection has resolved.
The Risk to Kidneys: Post-Streptococcal Glomerulonephritis
Another serious autoimmune complication following an untreated strep infection is Post-Streptococcal Glomerulonephritis (PSGN), which targets the renal system. PSGN typically develops one to three weeks after a streptococcal throat infection, or several weeks after a skin infection caused by a nephritogenic strain of GAS. The mechanism involves the deposition of immune complexes within the kidney’s filtering units, the glomeruli.
These immune complexes, formed by the binding of streptococcal antigens and antibodies, become trapped in the small capillaries of the glomeruli, activating the complement system and triggering inflammation. Specific streptococcal antigens, such as Nephritis-associated Plasmin Receptor (NAPlr) and Streptococcal Pyrogenic Exotoxin B (SPEB), contribute to this process. This inflammation damages the filtering barrier, leading to acute nephritic syndrome.
The damage to the glomeruli results in symptoms such as hematuria, or bloody urine, which may appear dark or tea-colored, and edema, noticeable as puffiness, especially around the eyes and in the extremities. Patients may also experience high blood pressure and reduced urine output as kidney function is compromised. While most cases of PSGN resolve completely, a small percentage of individuals can progress to chronic kidney disease or require dialysis for kidney failure.