Tuberculosis: The White Plague

The world’s number one infectious disease killer — once responsible for the death of one out of every seven American citizens. One of the world’s oldest leading cause of disease — around for over 3 million years. A scare at the University of San Francisco campus: Mycobacterium tuberculosis, more commonly known to today’s society as tuberculosis. Tuberculosis had a wide variety of names across countries of Planet Earth: “tabes” in ancient Rome, “schachepheth” in ancient Hebrew, and “phthisis” in ancient Greece.

All are names that I struggle to pronounce! Thankfully, Dr. Robert Koch coined its modern-day name and announced its formal discovery on March 24, 1882, which marked the first step in history towards eliminating this disease. Sadly, almost two centuries later, no cure has been made. Historically, this infection-causing disease is thought to have originated in the soil and traveled to cattles through domestication. The use of livestock directly allowed for the passage of a mycobacterial pathogen from animals like cattles to humans.

In the jump from cattle to humans, Mycobacterium tuberculosis adapted and evolved to its new host: us.

The bacterium M. tuberculosis has a waxy coating, made of mycolic acid, similar to the prokaryotic acid cell wall that we discussed in class. It’s thick, waxy layer is difficult to penetrate and features slow growth. Because of its protective layer, gram-staining is not achievable as the dye cannot seep into the cell wall; instead, acid-fast techniques are used. The bacteria is classified as gram-positive through the acid-fast stain, although it does not retain the crystal violet color.

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Nonetheless, it receives this label because of its tough outer cell membrane, rich in lipids. The bacteria is highly aerobic, meaning it requires oxygen to survive. Its growth is painfully slow — division rates are once every 15-20 hours in comparison to some of their bacterial counterparts which can undergo division within minutes or seconds, even. Mycobacterium tuberculosis is grown on a selective media plate known as Löwenstein-Jensen, and takes 6-8 weeks to grow, once again emphasizing the bacteria’s slow division rates.

Diagnosis of tuberculosis with modern medicine is quite simple. A simple skin test is performed where the patient is injected with a small amount of a substance called PPD tuberculin into the epidermis layer — the surface level of skin. The patient is then asked to return within 48 to 72 hours and a healthcare professional will proceed to check the insertion site for swelling or a hard, raised bump which is indicative of a TB infection. Smaller or larger bumps and radius of redness can be used to determine whether the test results are significant enough to generate concern. If it’s concluded from the skin test that a patient is positive for tuberculosis, a physician will likely order a chest X-ray to reveal an anomalies in the lungs, like white spots, which are indicative of active TB. Furthermore, the doctor may take samples of a patient’s sputum — the mucus, phlegm-like material that comes up from coughing. For convenience, however, blood tests are becoming increasingly common, as the titers can determine whether you test positive or negative for TB. Rather than the two-series PPD test that is typically required, a blood test takes only one visit to the doctor’s. This more sophisticated test can confirm or rule out latent or active tuberculosis.

Latent TB is like the name suggests — the bacteria are inactive and cause none of the symptoms listed above, and it is therefore not contagious. The risk, however, is that it can turn into active TB, which is characterized by the typical symptoms and is highly contagious and could easily be spread to the population. However, we can take a multitude of precautionary and preventive measures. For example, staying home from work, school or college until treatment is completed and your safety and the safety of others is not considered ‘high risk.’ Additionally, always covering your mouth when coughing or sneezing and disposing of any used tissues in the correct way, is a safe habit to grow accustomed to. Also, opening windows whenever possible — like in a closed car — is a great way to get fresh air circulating throughout the drive.

The symptoms of present-day active tuberculosis are debilitating and may sometimes require hospitalization, but can often be treated with antibiotics. Is it advisable to visit a doctor if you have a bad, persistent cough that lasts 3 weeks or longer, pain in the chest, coughing up blood or sputum (phlegm from the lungs), weakness or fatigue, weight loss, no appetite, chills, fever, and sweating at night. The historically listed symptoms are similar to ones seen today, although they were typically more severe and went untreated. Coughing up blood and tightness of the chest, for example, were two of the most common symptoms that Hippocrates wrote of in the fifth century B.C. Tuberculosis, if untreated, can also affect other parts of the body, like the kidneys, spine, or brain; it’s important to receive the treatment for TB upon first signs of symptoms so that it does not progress to an unmanageable state. The body may respond to Mycobacterium tuberculosis in up to three different ways. For starters, if the body’s immune system is strong enough, then our body’s lymphocytes — white blood cells which provide immune support — contain the bacteria so that the infection does not spread. The second refers to a weakened immune system where lymphocytes are unable to attack the bacteria and therefore, the infection spreads in the host and symptoms of TB are seen. The last scenario occurs if the body’s immune system is originally strong, but weakened at some point due to external factors; the bacteria that were originally dormant have an opportunity to attack and infect the host’s depleted immune system.

The most common forms of present-day treatment for TB are antibiotics over the course of a six month period. Pyrazinamide and Ethambutol are prescribed for the first two months of treatment, and Isoniazid and Rifampicin are taken for the remainder. Like many other strains of bacteria however, drug-resistant tuberculosis has emerged because these same antibiotics have been used for more than 6o years to fight off the disease. Thus, some TB microbes have attained immunity and ability to survive even when in the presence of antibiotics. In cases like these, injectable medications including amikacin and capreomycin are commonly used to fight off the drug resistant bacteria. With the proper treatment, survival rates in the 21st century for those affected by tuberculosis are high. Certain factors, however, can put an individual at higher risk and at an inability to fight off the infectious pathogen. Substance and tobacco use, for example, weaken the immune system and by doing so, an opportunistic pathogen has a greater chance of entering, attacking, and infects its host. If a patient is living with an illness such as HIV or AIDS, diabetes, kidney disease, cancer, or malnutrition, chances of contracting TB increase. Finally, being affected by tuberculosis is a more prominent problem faced by people who live in or travel to areas that have high rates of tuberculosis and drug-resistant tuberculosis, such as Africa, Eastern Europe, Asia, Russia, Latin America, and the Caribbean Islands.

Tuesday, March 24: World TB Day. Except, without a cure, there is not much to celebrate. The hope is that the future of tuberculosis continues to become less and less prominent in society, especially in those countries that lack the medical care to treat it proactively. Until then, tuberculosis is a medical battle — a war that we must fight to find a cure for together!