The other day, my son began complaining of a sore throat and headache. Not long after, he developed chills and a fever. The quick onset of his sickness combined with the lack of other cold or flu symptoms made me suspect that he may have strep throat. Instead of waiting it out, we took a trip to our local urgent care. A quick throat swab and rapid strep test later and a strep diagnosis was confirmed. Within an hour, he took his first dose of amoxicillin. While I’m a huge advocate of avoiding antibiotics if at all possible, as a microbiologist I learned to never mess around with the bacteria that cause strep throat. Here’s why.
While the vast majority of sore throats are caused by viruses, strep throat is caused by bacteria, specifically Streptococcus pyogenes (S. pyogenes). Bacteria are fundamentally different than most life on the planet, even at the cellular level. While humans, plants, animals, protozoa, fungi, and algae all have eukaryotic cells, bacteria have prokaryotic cells. Eukaryotic cells contain a nucleus, mitochondria, and other organelles. In contrast, prokaryotic cells lack a nucleus or any membrane-bound organelles. While it’s true that prokaryotic cells are simpler than eukaryotic cells, they are by no means simple, as we will soon see.
For any germ to cause disease, it must do several things. First, it must get into or onto a host. Then, it must grow and reproduce while at the same time evading the host’s defenses. Many bacteria come equipped with mechanisms to “fly under the radar” of our natural defenses, and the bacteria that cause strep are no exception.
S. pyogenes possess a cell wall, a type of membrane that surrounds the bacteria, providing structural support and protection from the environment. The cell wall of S. pyogenes contains a protein, M protein, which protects the bacteria from being engulfed and killed by phagocytes, cells which are the first responders of the human immune system. Because the strep bacteria are not killed by phagocytes, the bacteria are able to hide in plain sight and grow to high number.
Eventually, other cells from the immune system respond to the infection. Within a week, specialized cells of the immune system are activated and begin to manufacture antibodies specific to S. pyogenes. These antibodies, along with other components of the immune system, are able to kill the bacteria and clear the infection.
The Problem with Strep: Molecular Mimicry
So what’s the problem? The problem is the S. pyogenes cell wall. It turns out that biologically, proteins on the cell wall of S. pyogenes look a lot like proteins found on the surface of human cells including those in cardiac (heart) tissue, the central nervous system, joints, and in the brain. In fact, that’s one way S. pyogenes avoids being engulfed by phagocytes: to the phagocytes the bacteria look like part of the human body (an example of molecular mimicry). Since phagocytes are programmed not to attack anything that looks like “self”, they leave the bacteria alone.
But the cells that produce antibodies are another matter. When they produce antibodies to target S. pyogenes, some of the antibodies are designed to target the bacterial cell wall proteins. Some of these antibodies can cross-react with the similar proteins found in human tissue. These cross-reactive antibodies (auto-antibodies) can cause damage to human tissue resulting in complications including rheumatic fever and PANDAS.
Rheumatic Fever/Rheumatic Heart Disease
Rheumatic fever can occur 1-5 weeks following a strep infection. Because it is the result of the body’s immune response, it is not contagious. Symptoms may include fatigue, arthritis, fever, and jerky, uncontrollable movements (called chorea). Heart damage, specifically damage to heart valves, can occur if auto-antibodies attack the heart tissue.
As a consequence of ineffective antibiotic therapy (or no treatment at all), rheumatic fever occurs in 3-5% of the population following strep infection. Because antibiotics are effective at halting strep infection, rheumatic fever is more common in developing countries where access to antibiotics is limited. If rheumatic fever isn’t treated promptly, permanent heart damage (called rheumatic heart disease) can occur. According to the CDC, approximately 30 million people are living with rheumatic heart disease and 305,000 people die each year from rheumatic heart disease or its complications.
In recent years, doctors and scientists have recognized another complication of untreated strep infection: PANDAS. PANDAS is an acronym for Pediatric Autoimmune Neuropsychiatric Disorders Associated with Streptococcal Infections. PANDAS often manifests as a sudden onset of obsessive compulsive disorder (OCD) and/or tics in children following a strep infection. As with rheumatic fever, PANDAS is thought to be an autoimmune response. In individuals with PANDAS, antibodies directed at the strep bacteria cross-react with proteins found in the brain, causing damage.
What Can You Do?
The best course of action is to treat strep throat as soon as possible. Symptoms of strep throat include:
- A sore throat that starts very quickly (often with pain when swallowing)
- Red and swollen tonsils (sometimes with white patches)
- Swollen lymph nodes (glands) in the front and sides of the neck
- Other symptoms can include headache, stomach pain, nausea/vomiting.
- Sometimes a rash known as scarlet fever is present
Amoxicillin is the antibiotic of choice for treating strep throat as it is able to kill the bacteria quickly and halt the spread of infection. The trick is to eliminate the infection before the immune system has time to mount an immune response that may potentially contain auto-antibodies. Building immunity to infectious diseases is typically a good thing, but with strep it’s just too risky.
As always, only take antibiotics when necessary and only those antibiotics prescribed by your doctor to treat your infection. Since most cases of sore throat are caused by viruses, antibiotics aren’t needed to treat most sore throats. Furthermore, taking the wrong antibiotics or taking antibiotics for viral infections can lead to the development of antibiotic-resistant strains of bacteria. However, if strep is going around in your neck of the woods (most cases occur in late winter/early spring) and symptoms are consistent with strep throat, a quick visit to the doctor may be a good idea.
Please understand that I write this post not to scare but to educate. While I have no personal experience with rheumatic fever, I personally know of at least two families with children who have been diagnosed with PANDAS. I am all for “toughing out” most illnesses and letting natural immunity take its course, but strep is one illness I won’t mess around with.