The Resurgence of Tuberculosis

When many people think of tuberculosis (TB) they imagine an archaic or even eradicated disease. Unfortunately, this is far from reality. In the World Health Organization's 2016 Global Tuberculosis Report, it was estimated that in 2015, 10.4 million new TB cases emerged worldwide. Of note, people living with HIV accounted for 1.2 million (11%) of all new TB cases. The resurgence of TB is a cause of serious concern for global health monitoring organizations and it may be attributed to several factors including a comorbidity with immunosuppressive diseases and antibiotic resistance (World Health Organization, 2016).

TB is an infection primarily of the lungs caused by a mycobacteria, predominantly Mycobacterium tuberculosis. TB is a communicable disease that is usually acquired by inhalation of the bacteria as it spreads through the air from the cough, sneeze, or spit of an individual with an active infection. When the bacteria invades the lungs, the immune response causes the pathogens to be isolated in a tubercle. As the disease progresses, caseous necrosis results in the tissue within the tubercle (Huether and McCance 86). Symptoms of an active infection include coughing, bloody sputum, extreme weight loss, and fatigue. The mycobacterium is an opportunistic pathogen and it preys on the immunocompromised. In people with healthy immune systems, the pathogen is defeated 90% of the time without the host every knowing he/she was infected (Tortora, Funke, and Case 687). Up to 95% of those infected do not have any symptoms of the disease. This is called a latent TB infection. Without treatment, the remaining 5-10% of people infected by the bacteria will develop active and contagious TB (CDC.gov).

Tuberculosis is comorbid with many diseases that depress the immune system such as malnutrition, diabetes, malaria, and HIV. The immunodeficiency that manifests in people living with HIV leaves them susceptible to the initial TB infection. Additionally, those with HIV who are infected with the mycobacterium, are much more likely to rapidly develop active and contagious TB over those who are not HIV positive. The higher prevalence of active TB in HIV positive patients significantly attributes to the resurgence of TB, especially in sub-Saharan Africa and Asia (CDC.gov). Antimicrobials are used to treat TB, usually a combination of antimicrobials for a minimum of 6 months and up to 130 doses of the antibiotic cocktail. Some patients fail to finish the full course of treatment which results in mycobacterium resistance to the antibiotics. There are now multi-drug-resistant (MDR) strains which are resistant to isoniazid and rifampin, two first-line antimicrobials. Additionally, there are emerging strains that are resistant to all first and second-line treatments called extensively drug-resistant (XDR) strains. These XDR strains are almost untreatable with current drug-therapies and have also contributed to the resurgence of TB (Tortora, Funke and Case 684-687).

TB is usually spread through aerosols and therefore susceptible populations in very close quarters contribute to the prevalence of the disease. Overcrowded correctional facilities, homeless shelters, and refugee camps are breeding grounds for TB. Additionally, extensive international travel or immigration also contribute to the rise of the disease as individuals can contract TB in another country and carry it to less infected populations (CDC.gov). The mycobacteria that cause TB are different from other bacteria primarily in their cell wall composition. The cell wall of mycobacteria contain a high lipid content and mycolic acids. Two first-line treatments against the mycobacteria that cause TB are isoniazid and ethambutol which both act on mycolic acid. Isoniazid can effectively penetrate the tubercles or macrophages that hold the bacteria inside the host. Isoniazid then inhibits the synthesis of mycolic acids, disrupting the bacterial cell wall and causing cell death. Ethambutol prevents mycolic acid from being incorporated into the cell wall, causing cell death. It is less effective at penetrating tubercles but is used as a secondary drug to prevent drug resistance. Both isoniazid and ethambutol are used worldwide (Tortora, Funke and Case 559). Fluoroquinolones in combination with other antimicrobials can be used especially against drug resistant strains. Fluoroquinolones work by inhibiting bacterial DNA gyrase during DNA replication. Fluoroquinolones are used primarily in less developed countries where TB is prevalent and drug-resistant strains are spreading (Tortora, Funke and Case 562).

References

Bates, Matthew, Ben Marais, and Alimuddin Zumla. “Tuberculosis Cormorbidity with Communicable and    

          Noncommunicable Diseases.” Cold Spring Harb Perspect Med (2015): 5:a017889. Retrieved from      

          Perspectivesinmedicine.cshlp.org. 
Huether, Sue, and Kathryn McCance. Understanding Pathophysiology. St. Louis: Mosby, Inc, 2012. Print.

Tortora, Gerard, Berdell Funke, and Christine Case. Microbiology: An Introduction. United States of America: 

          Pearson, 2016. Print.

“Tuberculosis (TB) Fact Sheets.” CDC.gov. Centers for Disease Control and Prevention, n.d. Web. Retrieved from   
          www.cdc.gov.
World Health Organization (2016). Global Tuberculosis Report 2016. Retrieved from http://apps.who.int/ 
          iris/bitstream/10665/250441/1/9789241565394-eng.pdf