Renee Herbers
Dr. Palenske
BIOL 341
13 October 2017
Tuberculosis
According to the Mayo Clinic, an estimated 2 billion people are infected with latent tuberculosis. At one point this past summer, I was included in that 2 billion. I am fortunate to say that my diagnosis was incorrect; however, there are billions of people who face this highly infectious disease everyday. Thankfully, more and more research is being done everyday to try to eradicate the tuberculosis currently present in the world and prevent future outbreaks.
Tuberculosis is caused by the bacteria Mycobacterium Tuberculosis (Knechel 35). The bacteria are inhaled, where a majority of the bacteria is trapped in the mucus-lined portions of the upper respiratory tract (Knechel 35). Because of the presence of cilia in the upper respiratory tract, the body is able to eliminate the bacteria with the upward motion of the cilia. However, some bacteria make it past the mucus membranes and into the lungs, with the final destination of the alveoli. Here the bacteria are “surrounded and engulfed in by alveolar macrophages” (Knechel 35). The successfulness of the macrophages in phagocytizing the bacteria determines how the course of the disease continues. After the macrophages ingest the bacteria, they will continue to grow (Knechel 35). The body releases cytokines, attracting T-lymphocytes; this response initiates an immune response that can continue for 2 to 12 weeks (Knechel 36). This is a typical response for individuals who may already have a compromised immune system. The other pathway for elimination of the bacteria is to form granulomas around the bacteria (Knechel 36). Activated T lymphocytes and macrophages accumulate in the granuloma, which creates an environment that does not support further replication or spread of the bacteria (Knechel 36). These granulomas develop lesions, which can either calcify thus controlling the bacteria, or they can liquefy, allowing the infection to spread within the lungs and create the potential for spreading the disease to other individuals (Knechel 36). Tuberculosis is most commonly found within the lungs, but it can also be found in the kidneys, spine, or brain (Mayo Clinic Staff). Tuberculosis is typically not found in developed countries; despite this notion, the number of tuberculosis cases has risen in the United States since 2015. The number of cases of tuberculosis in the United States was 9,557 in 2015 (CDC).
Tuberculosis can be diagnosed in a variety of methods. Common methods include the following: sputum smear, sputum culture, polymerase chain reaction, tuberculin skin test, QuantiFERON-TB Gold test, and chest x-ray (Knechel 37). Of these tests, the skin test is most commonly used because of its low cost and convenience, especially in high-burden low-income countries (Chang et al. 1). Although this test appears to be convenient, it also has several disadvantages including low specificity in individuals who have been vaccinated with the Bacille Calmette-Guerin vaccine and low sensitivity in immunocompromised individuals (Chang et al. 1). The skin test also requires individuals to see a healthcare professional twice within a 48 to 72 hour span; once to have the test implanted, once to have the skin test read. The QuantiFERON test is a more recently developed method for detecting the presence of the tuberculosis bacteria. The premise behind the test is that interferon gamma release assays detect anti-tuberculosis cytokine interferon-gamma (Change et al. 2). The skin test is efficient at identifying cases of active tuberculosis but can sometimes result in false positives. The QuantiFERON-TB Gold test is more efficient at identifying cases of latent tuberculosis.
Symptoms of tuberculosis vary depending on what type of tuberculosis an individual has. For the purposes of this discussion, the symptoms of pulmonary tuberculosis will be discussed. In an individual with latent tuberculosis, they typically display no symptoms. Despite the fact that latent tuberculosis typically presents with no symptoms, because the bacteria are still being harbored within the body, it has the potential to become active tuberculosis (Mayo Clinic Staff). Active tuberculosis is the infectious form of tuberculosis. Signs and symptoms of active tuberculosis include the following: “coughing that last three or more weeks, coughing up blood, chest pain or pain breathing, unintentional weight loss, fatigue, fever, night sweats, chills, and loss of appetite” (Mayo Clinic Staff).
Tuberculosis is spread through the air. The tuberculosis bacteria are released into the air when an individual with tuberculosis coughs, speaks, or sings (CDC). When another individual breathes in the bacteria, either the bacteria are filtered out or it settles in the lungs. Once in the lungs, the bacteria can grow and become infectious. It is important to note that pulmonary tuberculosis is typically the infectious form of the disease. Tuberculosis of the spine and kidneys are usually not infectious (CDC). Even though tuberculosis is spread through the air, it is not as infectious as it might seem. To become infected with tuberculosis, typically individuals are in a compact space with an individual infected with tuberculosis for long amounts of time over an extended period of time. Therefore, family members and roommates are susceptible to becoming infected if an infected individual lives with them.
A complication factor to the spread of tuberculosis is individuals with compromised immune systems. According to the Centers for Disease Control and Prevention, the following conditions make individuals more susceptible to becoming infected with tuberculosis: “HIV infection, substance abuse, silicosis, diabetes mellitus, severe kidney disease, low body weight, organ transplants, head and neck cancer, corticosteroid treatments, treatments for rheumatoid arthritis, and treatments for Crohn’s disease.” Out of all of these conditions, the most concerning is HIV. Countries that experience large numbers of HIV infections typically also experience high numbers of tuberculosis cases. In individuals with latent tuberculosis and HIV, the risk of developing active tuberculosis is much higher (CDC). According to the CDC, tuberculosis “is one of the leading causes of death among people living with HIV.
The treatments for tuberculosis vary based on if the infection is latent or active and if the form of tuberculosis is drug-resistant or not. For a typical case of latent tuberculosis, the treatment is isoniazid once a day everyday for 9 months. In conjunction with the isoniazid, a vitamin B supplement is also usually prescribed to protect nerve integrity. Isoniazid is toxic to the liver, so individuals on this treatment need to have their liver enzymes checked once a month during the duration of the treatment. The treatment for active tuberculosis typically consists of two different phases: the intensive phase, which lasts for 2 months, and a continuation phase, which lasts anywhere from 4 to 7 months (CDC). In the intensive phase, the commonly prescribed drugs are isoniazid, rifampin, ethambutol, and pyrazinamide (CDC). After the intensive phase, isoniazid and rifampin are the two drugs prescribed. During both phases, the drugs are taken once a day, everyday. The treatment duration can vary based on patient tolerance and the concomitant presence of an HIV infection. Again, these drugs are toxic to the liver, so liver enzymes need to be checked regularly to ensure that the liver is functioning properly. For drug-resistant tuberculosis, treatment involves using whatever drugs will be effective in treating the infection. Fluoroquinolone can be used, but this drug has severe side effects (CDC). Treating drug-resistant tuberculosis is tricky and can be life-threatening to the patient, but active tuberculosis is a condition that absolutely most be treated.
Prognosis for individuals with tuberculosis again depends on if the infection is latent or active and whether a comorbid condition exists. Individuals with latent tuberculosis have a good prognosis. In many individuals with latent tuberculosis, they can harbor the bacteria in their lungs but never develop active tuberculosis (CDC). Treating latent tuberculosis lessens the chance that active tuberculosis will develop. However, if the immune system of an individual with latent tuberculosis becomes comprised, it is much easier for active tuberculosis to develop. With proper treatment, individuals with active tuberculosis experience a good prognosis as well. Complicating factors to a good prognosis would be drug-resistant tuberculosis and having HIV. Unfortunately, for those with HIV and tuberculosis, the prognosis is not as formidable. Despite going through treatment, tuberculosis bacteria remain in the body. Thus, individuals are susceptible to relapsing if the conditions are suitable. Therefore, individuals should have a chest x-ray done every couple of years to ensure that the infection remains dormant. Individuals who have experience tuberculosis should not have the skin test done because it will always be positive after being exposed to tuberculosis.
While tuberculosis is not an easy condition to treat, research that is currently being done will provide more options for prevention and treatment than are currently available. Right now, there is a vaccine called the Bacille Calmette-Guerin vaccine that is given to children in countries where tuberculosis is common. The World Health Organization notes there are 15 new vaccinations that are in the clinical trial stage. This is promising news because preventing tuberculosis would solve the issue of trying to treat tuberculosis. In addition, there are currently 10 FDA approved drugs for treating tuberculosis (CDC), and there are 2 new drugs and 8 repurposed drugs that have either been introduced in the last decade or are being developed (WHO). Research is also focusing on treating individuals with tuberculosis and HIV, but no significant evidence has been found yet.
While tuberculosis is not incredibly common in the United States, in other countries, this disease is a rather normal occurrence. I was surprised to find that tuberculosis is one of the leading causes of death in individuals with HIV. Fortunately, the current research that is being done appears to be promising in the current treatment options as well as making an effort to prevent tuberculosis. Even though I was only taking isoniazid for one month, the side effects were dreadful; I cannot even imagine the side effects for active tuberculosis treatment. Therefore, I would love to see effective vaccines developed so we do have to worry about this disease going forward.
Literature Cited
Chang, Ping-Chin, et al. “Use of the Quantiferon-TB Gold In-Tube Test in the Diagnosis and Monitoring of Treatment Efficacy in Active Pulmonary Tuberculosis.” International Journal of Environmental Research and Public Health, vol. 14, no. 3, 27 Feb. 2017. EBSCOhost, doi:10.3390/ijerph14030236.
Knechel, Nancy A. “Tuberculosis: Pathophysiology, Clinical Features, and Diagnosis.” Critical Care Nurse, vol. 29, no. 2, Apr. 2009, pp. 34-43. EBSCOhost, doi:10.4037/ccn2009968.
Mayo Clinic Staff. “Tuberculosis.” Mayo Clinic. 8 Aug. 2017. http://www.mayoclinic.org/diseases-conditions/tuberculosis/symptoms-causes/syc-20351250.
“Tuberculosis.” Centers for Disease Control and Prevention. 24 Oct. 2016. https://www.cdc.gov/tb/default.htm.
“Tuberculosis.” World Health Organization. http://www.who.int/tb/en/.