Tuberculosis

Tuberculosis (TB) is the leading cause of death in the world from a single infectious disease. Little is known of the pathogens that cause it and how to treat it effectively. There was a decline in tuberculosis in the United States in the last century but the disease is now increasing. This increase has multiple causes including changes in social structure in cities, HIV epidemic, and a failure by some public entities to improve their public health programs. In the United States since 1985 there has been an increase in cases of tuberculosis. This is due largely to the increase of Human Immunodeficiency virus (HIV) infections which occurred during the same period of time. More recently there has also been an increase in the number of cases of multi drug resistant (MDR) strains of tuberculosis due to patient non compliance with medication. M Resources Fitzgerald DW, Sterling TR, Haas DW. Mycobacterium tuberculosis. In: Mandell GL, Bennett JE, Dolan R, eds. Mandell, Douglas, and Bennett’s Principles and Practice of Infectious Diseases. 7th ed. Orlando, FL: Saunders Elsevier; 2009:chap Iseman MD. Tuberculosis. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; http://www.cdc.gov/TB/ ycobacterium tuberculosis is the cause of TB in humans. Humans are the only known reservoir for the bacterium. Mycobacterium bovis is the etiologic agent of TB in cows and rarely in humans, but both cows and humans can serve as reservoirs. Humans can also be infected by consuming unpasteurized milk. This method of transmission can cause the development of extra pulmonary TB, as seen in history by bone infections that caused hunched backs. Tuberculosis has two forms; latent infection and disease. In the infection form of TB the immune system is able to keep the bacteria under control. The body is able to do this by producing macrophages that surround the tubercle bacilli and form a hard shell, thereby isolating the mycobacterium tuberculosis and keeping it under control. In a person with the latent infection form of mycobacterium tuberculosis, there will be a positive TB skin test with no other symptoms present. The chest X-ray will be normal and a sputum test for acid fast bacilli will be negative. A person with this form cannot spread it to others. A person with tuberculosis will have a cough that lasts longer than 2 weeks, pain in the chest, cough up blood or sputum. They will also experience fatigue, weight loss, chills, fever and night sweats. They are also contagious and will have a positive skin test and an abnormal chest x-ray and sputum smear will be positive for acid fast bacilli. Treatment of tuberculosis is generally treated with four different antimicrobial drugs. This is because the administration of only a single drug contributes to the development of bacterial resistant organisms. When two or more drugs are used for treatment simultaneously each helps prevent the emergence of the tubercle bacilli resistant to the others. At the beginning of drug therapy when it is unknown which drugs the patient’s bacilli is susceptible to then choosing the wrong drug can lead to further development of drug resistant tuberculosis. Therefore it is treated with four different antimicrobial agents. The drug therapy usually lasts from 6-9 months. The most commonly used drugs are rifampin, isoniazid, pyrazinamide, and ethambutol or streptomycin. When a patient adheres to this drug regimen it is highly effective. Based on the prevalence and characteristics of the drug resistant organisms present 95% of patients will receive an adequate regimen of at least two drugs to which the bacilli is susceptible, if this four drug regimen is used at the beginning of therapy. A patient that is treated with a four drug regimen but who is non compliant with the treatment is more likely to be cured and not relapse when compared with a patient treated for the same length of time with a three drug regimen. There is also a vaccine available for tuberculosis. It is called Bacillus of Calmette and Guerin (BCG), after the two Frenchmen that developed it. It consists of a live attenuated strain derived from mycobacterium bovis. The vaccine is not 100% effective and there are studies that suggest the rate of effectiveness in children is 60-80%. The vaccine is not administered in the United States for several reasons. The vaccine does not prevent infection only the disease. The vaccine cannot prevent disease reactivation in previously exposed individuals. The vaccine may also complicate the way the TB skin test is read in this country. Tuberculosis is a serious disease and should be studied more to find a better, more effective cure. With the technology we have come up with, it should not take very long until something is developed to better study the disease, find it’s causes, and find a better treatment.