Question

Case study #1

Respiratory system

Scenario

Mr. F, age 46 years has a history of persistent unproductive cough for several months that has not responded to cough medication, fatigue, and anorexia. Following a chest radiograph (showed a cavity and infiltrate), tuberculin testing (positive), and sputum culture (acid-fast bacteria), a diagnosis was made of active TB infection in the lower right lung. Mr. F was prescribed three antitubercular drugs, and his family was scheduled for testing and prophylactic medication.

1. a) Why was his TB not detected when it was in the primary stages?

b) Why was it necessary to do more than just a tuberculin test? Why was a sputum test done?

2. What factors could have caused Mr. F to go from primary TB to a secondary or active infection?

3.If Mr. F's disease continued to progress undiagnosed what other signs and symptoms would he eventually start having? Explain.

4.Why is it such a problem for people to be treated for TB?

5.Why were his family members tested? Why were they put on prophylactic medication?

Answer 1

1a. TB is lung infection caused by Mycobacterium tuberculosis. It is spread via the droplets released by sneezing, coughing from an infected person. These particles when inhaled reach the lung and the alveoli. The bacteria are engulfed by the macrophages and can live and divide within them. They will then lyse the macrophages and infect other macrophages. The bacteria then infect the lymph nodes to form Ghon complex.

In the initials stages of infection, the lymphocytes can contain the infection. Hence, there is no spread of infection and the bacteria. This will result in generation of no symptoms in the patient.

b. Tuberculin test is used to test for TB status. In this test, small amount of tuberculin protein extracted from M. tuberculosis is injected in the upper arm and development of delayed hypersensitivity response is looked at after 48-72 hrs. However, even people who have prior exposure to M. bacterium will test positive. Further, if the person is vaccinated with BCG vaccine, a positive test may result. A Tuberculin test does not confirm active infection. A negative test also does not indicate that the person is not suffering from TB.

A sputum test involves culturing of the organism as well as acid fast staining. This test will detect the actual presence of the organism in the lungs from where sputum is collected. Hence, sputum test are confirmatory test for checking whether there is active TB or not.

2. If the T cell response to the organism is decreased, then the bacterium is able to evade the immune response and will develop active infection. Thus, if Mr F has a weak immune system, then there are more chances to develop active TB. Certain immunodeficiency diseases such as HIV will also be a risk factor for developing active infection. Alcohol, smoking and drug abuse will also weaken the lung, allowing the bacilli to infect the lung macrophages easily. This increases pathogen load, thereby easing progression from primary to secondary TB.

3. If the TB is undiagnosed, the bacteria can overcome the immune system and will infect other organs. Symptoms of prolonged undiagnosed TB are coughing blood, persistent cough, breathlessness, weight loss, persistent loss of appetite. The Mycobacteria can then infect the kidneys, bones, lymph nodes and even the brain membranes causing meningitis. Meningitides is caused when the bacilli infects the meninges in brain and spinal cord. The person coughs blood because there is rupture of artery or tubercle in the lung. Peritonitis and Tuberculous lymphadenitis are seen if there is infection of lymph nodes. Cutaneous TB causes enlarged ulcers on skin.

4. Mycobacterium tuberculosis has a tough cell wall made up of mycolic acid that is impermeable to a number of antibiotics. Only a few select antibiotics can work. Mycobacteria also divide asymmetrically. Hence, bacilli formed after cell division is of different sizes, with different susceptibilities to antibiotics and rates of growth. This increases the chances that some of these bacteria may survive the antibiotic treatments. Older cells are susceptible to isoniazid while younger cells respond to rifampicin. The number of bacteria in active infection is also large. Hence, it takes longer duration treatment to kill these bacteria.

5. Mr F was diagnosed with T after a history of several months of TB symptoms. Hence, he may have contracted the disease prior to symptoms being seen. Hence, he may have been shedding the bacterium via droplets during coughing. Family members have been in close contact with these droplets and have increased chances of developing TB infections. As primary infection if asymptomatic, these infected family members need to be identified and treated. Prophylactic medication is initiated to prevent the transmission of TB to the uninfected family members during the log duration of TB treatment of Mr F. This will prevent transmission of TB to uninfected family members.