tuberculosis or tb

8/7/2019 Tuberculosis or TB

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Pulmonary Tuberculosis

Tuberculosis or TB (short for tubercles bacillus) is a common and often deadly infectious disease

caused by various strains of mycobacteria, usually Mycobacterium tuberculosis in humans.Tuberculosis

usually attacks the lungs but can also affect other parts of the body. It is spread through the air when

people who have the disease cough, sneeze, or spit.Most infections in humans result in an

asymptomatic, latent infection, and about one in ten latent infections eventually progresses to active

disease, which, if left untreated, kills more than 50% of its victims.

The classic symptoms are a chronic cough with blood-tinged sputum, fever, night sweats, and

weight loss. Infection of other organs causes a wide range of symptoms. Diagnosis relies on radiology

(commonly chest X-rays), a tuberculin skin test, blood tests, as well as microscopic examination and

microbiological culture of bodily fluids. Treatment is difficult and requires long courses of multiple

antibiotics. Contacts are also screened and treated if necessary. Antibiotic resistance is a growing

problem in (extensively) multi-drug-resistant tuberculosis. Prevention relies on screening programs and

vaccination, usually with Bacillus Calmette-Gurin vaccine.

The following people are at higher risk for active TB:

* Elderly

* Infants

* People with weakened immune systems, for example due to AIDS, chemotherapy, or antirejection

medicines given after an organ transplant

Your risk of contracting TB increases if you:

* Are in frequent contact with people who have the disease

* Have poor nutrition

* Live in crowded or unsanitary living conditions

The following factors may increase the rate of TB infection in a population:

* Increase in HIV infections

* Increase in number of homeless people (poor environment and nutrition)

* The appearance of drug-resistant strains of TB

History

Tuberculosis has been present in humans since antiquity. The earliest unambiguous detection of

Mycobacterium tuberculosis is in the remains of bison dated 18,000 years before the present. Whether

tuberculosis originated in cattle and then transferred to humans, or diverged from a common ancestor


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infecting a different species, is currently unclear. However, it is clear that M. tuberculosis is not directly

descended from M. bovis, which seems to have evolved relatively recently.

Skeletal remains from a Neolithic Settlement in the Eastern Mediterranean show prehistoric humans

(7000 BC) had TB, and tubercular decay has been found in the spines of mummies from 30002400 BC.

Phthisis is a Greek term for tuberculosis; around 460 BC, Hippocrates identified phthisis as the mostwidespread disease of the times involving coughing up blood and fever, which was almost always fatal.

In South America, the earliest evidence of tuberculosis is associated with the Paracas-Caverna culture

(circa 750 BC to circa 100 AD).

Health Statistics > Incidence of tuberculosis > per 100,000 people

Date Amount Rank

2005 291.23 #30

2004 293.99 #29

2003 296.77 #28

2002 299.58 #27

2001 302.41 #26

2000 305.28 #25

1999 308.16 #22

1998 311.08 #20

Classification System for TB Class

Type Description

0 No TB exposure

Not infected No history of exposure

reaction to tuberculin skin test

1 TB exposure

No evidence of infection History of exposure

Negative reaction to tuberculin skin test

2 TB infection


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No disease

Positive reaction to tuberculin skin test

Negative bacteriologic studies (if done)

Fibrocaseous cavitary lesion (usually in upper lobe of lungs)

3 TB, clinically active M. tuberculosis cultured (if done)

Clinical, bacteriologic, or radiographic evidence of current disease

4 TB

Not clinically active History of episode(s) of TB

Or Abnormal but stable radiographic findings

Positive reaction to the tuberculin skin test

Negative bacteriologic studies (if done)

And No clinical or radiographic evidence of current disease

5 TB suspect Diagnosis pending

TB disease should be ruled in or out within 3 months

Signs and Symptoms

The primary stage of the disease usually doesn't have symptoms. When symptoms do occur, they may

include:

* Cough (sometimes producing phlegm)

* Coughing up blood

* Excessive sweating, especially at night

* Fatigue

* Fever

* Unintentional weight loss


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Other symptoms that may occur with this disease:

* Breathing difficulty

* Chest pain

* Wheezing

Diagnostic Test

* Biopsy of the affected tissue (rare)

* Bronchoscopy

* Chest CT scan

* Chest x-ray

* Interferon-gamma blood test such as the QFT-Gold test to test for TB infection

* Sputum examination and cultures

* Thoracentesis

* Tuberculin skin test

Tuberculosis is diagnosed definitively by identifying the causative organism (Mycobacterium

tuberculosis) in a clinical sample (for example, sputum or pus). When this is not possible, a probable -

although sometimes inconclusive - diagnosis may be made using imaging (X-rays or scans) and/or a

tuberculin skin test (Mantoux test).

The main problem with tuberculosis diagnosis is the difficulty in culturing this slow-growing

organism in the laboratory (it may take 4 to 12 weeks for blood or sputum culture). A complete medical

evaluation for TB must include a medical history, a physical examination, a chest X-ray, microbiological

smears, and cultures. It may also include a tuberculin skin test, a serological test. The interpretation of

the tuberculin skin test depends upon the person's risk factors for infection and progression to TB

disease, such as exposure to other cases of TB or immunosuppression.

Currently, latent infection is diagnosed in a non-immunized person by a tuberculin skin test,

which yields a delayed hypersensitivity type response to an extract made from M. tuberculosis.Those

immunized for TB or with past-cleared infection will respond with delayed hypersensitivity parallel to

those currently in a state of infection, so the test must be used with caution, particularly with regard to

persons from countries where TB immunization is common.[51] Tuberculin tests have the disadvantage


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of producing false negatives, especially when the patient is co-morbid with sarcoidosis, Hodgkins

lymphoma, malnutrition, or most notably active tuberculosis disease. The newer interferon release

assays (IGRAs) overcome many of these problems. IGRAs are in vitro blood tests that are more specific

than the skin test. IGRAs detect the release of interferon gamma in response to mycobacterial proteins

such as ESAT-6.These are not affected by immunization or environmental mycobacteria, so generate

fewer false positive results.There is also evidence that the T-SPOT.TB IGRA is more sensitive than the

skin test.

New TB tests are being developed that offer the hope of cheap, fast and more accurate TB

testing. These include polymerase chain reaction assays for the detection of bacterial DNA. The

development of a rapid and inexpensive diagnostic test would be particularly valuable in the developing

world.

Treatment

Treatment for TB uses antibiotics to kill the bacteria. Effective TB treatment is difficult, due to

the unusual structure and chemical composition of the mycobacterial cell wall, which makes many

antibiotics ineffective and hinders the entry of drugs.[77][78][79][80] The two antibiotics most

commonly used are rifampicin and isoniazid. However, instead of the short course of antibiotics typically

used to cure other bacterial infections, TB requires much longer periods of treatment (around 6 to 24

months) to entirely eliminate mycobacteria from the body.[10] Latent TB treatment usually uses a single

antibiotic, while active TB disease is best treated with combinations of several antibiotics, to reduce the

risk of the bacteria developing antibiotic resistance. People with latent infections are treated to prevent

them from progressing to active TB disease later in life.

Drug-resistant tuberculosis is transmitted in the same way as regular TB. Primary resistance

occurs in persons infected with a resistant strain of TB. A patient with fully susceptible TB develops

secondary resistance (acquired resistance) during TB therapy because of inadequate treatment, not

taking the prescribed regimen appropriately, or using low-quality medication. Drug-resistant TB is a

public health issue in many developing countries, as treatment is longer and requires more expensive

drugs. Multi-drug-resistant tuberculosis (MDR-TB) is defined as resistance to the two most effective

first-line TB drugs: rifampicin and isoniazid. Extensively drug-resistant TB (XDR-TB) is also resistant to

three or more of the six classes of second-line drugs.

The DOTS (Directly Observed Treatment Short-course) strategy of tuberculosis treatment

recommended by WHO was based on clinical trials done in the 1970s by Tuberculosis Research Centre,

Chennai, India. The country in which a person with TB lives can determine what treatment they receive.This is because multidrug-resistant tuberculosis is resistant to most first-line medications, the use of

second-line antituberculosis medications is necessary to cure the patient. However, the price of these

medications is high; thus poor people in the developing world have no or limited access to these

treatments.


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Drugs

Most patients with TB can recover if given appropriate medication for a sufficient length of time.

Three principles govern modern drug treatment of TB:

* Lowering the number of bacilli as quickly as possible. This measure minimizes the risk of transmitting

the disease. When sputum cultures become negative, this has been achieved. Conversely, if the sputum

remains positive after five to six months, treatment has failed.

* Preventing the development of drug resistance. For this reason, at least two different drugs and

sometimes three are always given at first. If drug resistance is suspected, at least two different drugs

should be tried.

* Long-term treatment to prevent relapse.

Five drugs are most commonly used today to treat tuberculosis: isoniazid (INH, Laniazid,

Nydrazid); rifampin (Rifadin, Rimactane); pyrazinamide (Tebrazid); streptomycin; and ethambutol

(Myambutol). The first three drugs may be given in the same capsule to minimize the number of pills in

the dosage. As of 1998, many patients are given INH and rifampin together for six months, with

pyrazinamide added for the first two months. Hospitalization is rarely necessary because many patients

are no longer infectious after about two weeks of combination treatment. Follow-up involves

monitoring of side effects and monthly sputum tests. Of the five medications, INH is the most frequently

used drug for both treatment and prevention.

Prevention

TB prevention and control takes two parallel approaches. In the first, people with TB and their

contacts are identified and then treated. Identification of infections often involves testing high-risk

groups for TB. In the second approach, children are vaccinated to protect them from TB. No vaccine is

available that provides reliable protection for adults. However, in tropical areas where the levels of

other species of mycobacteria are high, exposure to nontuberculous mycobacteria gives some

protection against TB.

The World Health Organization (WHO) declared TB a global health emergency in 1993, and the

Stop TB Partnership developed a Global Plan to Stop Tuberculosis that aims to save 14 million lives

between 2006 and 2015. Since humans are the only host of Mycobacterium tuberculosis, eradication

would be possible. This goal would be helped greatly by an effective vaccine.


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