Tuberculosis

Tuberculosis (TB) is a bacterial infection that is caused by the bacteria Mycobacterium tuberculosis.

Disease

MTB is transmitted via droplet nuclei when a person coughs or sneezes and is then inhaled by another individual. The MTB travels to the alveoli where it comes into contact with Macrophages that engulfs the MTB Pathogen. MTB evades the immune system by binding to mannose receptors and is phagocytosed where it secretes a protein that modifies the Phagosome to prevent Phagosome - Lysosome fusion thus preventing Antigen presentation. The MTB then multiplies within the Macrophage until it bursts. However, some MTB Antigen s are still presented which activate T-cells which then activate Cytokines including IFN. IFN causes activation of macrophages which can now destroy the MTB. This is a cell-mediated response and helps to control the infection but MTB can still multiply in inactivated macrophages and eventually spreads to the Bronchi where it can spread to the rest of the body - extrapulmonary tuberculosis .

TB is considered to be either 'Latent' or 'Active'. A patient with a latent TB infection will not experience any of the usual symptoms that are characteristic of tuberculosis and is unable to spread the infection to others. According to the World Health Organisation, "the overall lifetime risk of developing active TB is about 10%" for a patient with a latent infection who is otherwise in a good state of general health. This risk of the infection becoming active increases in those with compromised immune systems, such as HIV patients and the elderly. If TB becomes active then the infected patient will be symptomatic and contagious and must be treated.

At Risk:

• HIV
• Diabetes
• Immunocompromised
• Smokers
• Elderly
• Healthcare workers who deal with hih risk clients
• High risk racial or ethnic minority populations wit high prevalance of TB

Symptoms

Symptoms include:

• Cough
• Night sweats
• Appetite loss
• Fever
• Fatigue
• Swollen neck

Prevention

• Good personal hygiene
• Cover mouth and nose when coughing/sneezing
• Vaccination: BCG
• Screening and early diagnosis

Treatment:

Two main antibiotics:

• Isoniazid - synthesis of essential mycolic acids by inhibiting NADH-dependent enoyl-ACP reductase (can cause nerve damage (peripheral neuropathy) so patients are given supplements of vitamin B6
• Rifampicin – affects transcription - β-subunit of RNA polymerase, where it binds and inhibits the elongation of messenger RNA. (side effect: reduced effectiveness of combined contraceptive pill)
• Individuals affected by Tuberculosis are typically prescribed daily doses of isoniazid and the antibiotic rifampin for two months, followed by biweekly doses for a total of 9 months. This treatment is now less effective due to resistance of M. Tuberculosis to isoniazid and other drugs, especially in HIV patients who are more likely to have a TB infection. They develop "multi-drug-resistant tuberculosis strains" which can only be killed  by a second-line tuberculosis drugs that are more toxic and expensive than isoniazid and rifampin.