Tuberculosis: epidemiology, transmission, and clinical management

Biology

Microbiology GT-SC1

Tuberculosis

Tuberculosis (TB) is a communicable disease that is caused by bacteria known as Mycobacterium tuberculosis. It was first discovered in 1882 by a German physician named Robert Koch who received the Nobel Prize for this discovery. TB usually has an effect on the lungs but also can attack almost any organ in the body. There is also a group of organisms known as atypical tuberculosis. These entail additional kinds of bacteria that are in the Mycobacterium family. Frequently, these organisms do not cause illness and are referred to as colonizers. This means that they simply live alongside other bacteria in the body without causing damage. Sometimes these bacteria can cause an infection that is just like typical tuberculosis. When the time occurs that these atypical mycobacteria cause infection, they are very hard to cure. Drug therapy for these organisms must be given for one and a half to two years and requires multiple medications to be used (Schiffman, 2010).

Tuberculosis is a major health problem that continues to exist worldwide. In 2008, the World Health Organization (WHO) anticipated that one-third of the global population was infected with TB bacteria. Statistics show that:

there have been 8.8 million new cases of TB developed.

there were nearly 1.6 million people who died of this disease in 2005.

every person with active TB that goes untreated will go on to infect an average of 10-15 people every year.

a new infection happens every second (Tuberculosis, 2010).

A person can become infected with tuberculosis bacteria when they breathe in minute particles of infected sputum that are in the air. The bacterium ends up in the air when someone who has a tuberculosis lung infection sneezes, coughs, shouts, or spits. People who are close by are then at a risk to possibly breathe the bacteria into their lungs. A person can't' get TB by just touching the clothes or shaking hands with someone who has it. Tuberculosis is mainly spread from person to person by breathing infected air while in close contact. There is also a form of atypical tuberculosis that is spread by drinking unpasteurized milk. A related bacterium, called Mycobacterium bovis, causes this form of TB. Before now, this type of bacteria was a major cause of TB in children, but is rarely seen now since most milk is pasteurized (Schiffman, 2010).

There are two organisms that cause tuberculosis - Mycobacterium tuberculosis and Mycobacterium bovis. These organisms are rod-shaped, slow-growing bacterium. Their cell walls have high acid content. This makes them hydrophobic, meaning that they are resistant to oral fluids. Their cell walls absorb a certain dye used in the preparation of slides for examination under the microscope and maintain this red color despite attempts at de-colorization, thus they have been given the name acid-fast bacilli (Tuberculosis, 2010).

The symptoms of TB in the lungs that are often seen include:

a bad cough that lasts 3 weeks or longer weight loss coughing up blood or mucus weakness or fatigue fever and chills night sweats

If not treated properly, TB can be deadly. It can usually be healed by taking several medicines for a long period of time. It is also possible for people with latent TB to take medicine so that they do not develop active TB (Tuberculosis, 2010).

Mycobacterium tuberculosis is a slow-growing facultative intracellular parasite. During infection the parasite is exposed to many different environmental conditions. It is able to increase inside the macrophage phagosome, in which the environment is normally hostile for most bacteria. It can also replicate extracellularly in the open lung cavities that are found during the late stages of the disease. M. tuberculosis can extend to other tissues or organs such as the lymph nodes, joints, skin, bones, the central nervous system, the urinary tract and the abdomen. The host immune reaction to M. tuberculosis originally involves the employment of activated macrophages to the site of infection in the lung, where they can form a tuberculous granuloma that serves to restrict the infection. Bacteria that are trapped in the granuloma face aggressive surroundings that become anoxic and rich in toxic fatty acids. M. tuberculosis under these circumstances has been assumed to take for granted a dormant status in which it can remain viable for years without causing observable disease. A succeeding breakdown of the immune system of the host may permit its emergence from this dormant status, resulting in reactivation of the latent disease (Manganelli, Dubnau, Tyagi, Russell and Smith, 1999).

In order to diagnosis TB a doctor will complete a battery of tests in order figure out what is going on. A person is often not put into the hospital for either the initial tests or the beginning of treatment.

a Chest X-ray is the most common diagnostic test used to diagnose tuberculosis. An X-ray will show any abnormality in the mid and lower lung fields, and any lymph nodes that may be enlarged. Reactivated TB bacteria usually penetrate the upper lobes of the lungs.

A Mantoux skin test which is also known as a tuberculin skin test (TST). This test helps discover people who are infected with M. tuberculosis but who have no symptoms. A doctor must read the test (Tuberculosis, 2010).

Doctors will set down several special medications that must be taken for six to nine months. Standard therapy for active TB consists of a six-month regimen:

two months with Rifater (isoniazid, rifampin, and pyrazinamide)

four months of isoniazid and rifampin (Rifamate, Rimactane)

ethambutol (Myambutol) or streptomycin is often added until their drug sensitivity is known