Mycobacterium tuberculosis

Mycobacterium tuberculosis

INTRODUCTION


CLASSIFICATION


Kingdom: Bacteria
Phylum: Actinobacteria
Order: Actinomycetales
Suborder: Corynebacterineae
Family: Mycobacteriaceae
Genus: Mycobacterium
Species: M. tuberculosis






HISTORY
M. tuberculosis, then known as the tubercle bacillus, was first described on 24 March 1882 by Robert Koch, wh o subsequently received the Nobel Prize in physiology of medicine for this discovery in 1905; the bacterium is also known as Koch's bacillus.
PHYSIOLOGY
M. tuberculosis is an obligate aerobe while mycobacteria do not seem to fit the Gram-positive category from an empirical standpoint (i.e., they do not retain the crystal violet stain), they are classified as acid-fast Gram-positive bacteria due to their lack of an outer cell membrane.
M. tuberculosis divides every 15-20 hours, which is extremely slow compared to other bacteria, which tend to have division times measured in minutes . It is a small bacillus that can withstand weak disinfectants and can survive in a dry state for weeks. Its unusual cell wall, rich in lipids (e.g., mycolic acid), is likely responsible for this resistance and is a key virulence factor.

METHODOLOGY
All cases of TB are passed from person to person via droplets. When someone with TB infection coughs, sneezes, or talks, tiny droplets of saliva or mucus are expelled into the air, which could be inhaled by another person.
• Once infectious particles reach the alveoli, small sacs in your lungs, another cell called the macrophage engulfs the TB bacteria.
o Then the bacteria are transmitted to your lymph system and bloodstream and spread to other organs.
o The bacteria further multiply in organs that have high oxygen pressures, such as the upper lobes of your lungs, your kidneys, bone marrow, and meninges-the membranelike coverings of your brain and spinal cord
.
• People who have inhaled the TB bacteria, but in whom the disease is controlled are referred to as infected. They have no symptoms, frequently have a positive skin test, yet cannot transmit the disease to others.
• Risk factors for TB include the following:
o HIV infection
o Low socioeconomic status
o Alcoholism
o Homelessness
o Crowded living conditions
o Diseases that weaken the immune system
REFERENCES www.wikipedia.com


SYMPTOMS
. Mostly fever,appetite loss, energy loss,high night sweats
.

• Tuberculous pleuritis may occur in 10% of people who have the lung disease from tuberculosis.
o The pleural disease occurs from the rupture of a diseased area into the pleural space, the space between your lung and the lining of the abdominal cavity.
o These people have a nonproductive cough, chest pain, and fever. The disease may go away and then come back at a later date.

• In a minority of people with weakened immune systems, TB bacteria may spread through their blood to various parts of their body.
o This is called miliary tuberculosis and produces fever, weakness, loss of appetite, and weight loss.
o Cough and difficulty breathing are less common.

• Generally, return of dormant tuberculosis infection occurs in the upper lungs.
o Common cough with a progressive increase in production of mucus
o Coughing up blood
o Other symptoms include the following:
 Fever
 Loss of appetite
 Weight loss
 Night sweats

• About 15% of people may develop tuberculosis in an organ other than their lungs. About 25% of these people usually had known TB with inadequate treatment. The most common sites include the following:
o Lymph nodes
o Genitourinary tract
o Bone and joint sites
o Meninges
o The lining covering the outside of the gastrointestinal tract
DIAGNOSIS
Diagnosis of tuberculosis is made by a positive tuberculin skin test, an immune reaction to a small quantity of tuberculosis antigens. It can be confirmed by X rays of the chest and microscopic examination of sputum. Detection of significant numbers of acid-fast bacilli (using the Ziehl-Neelsen stain) in sputum or tissue samples is considered a positive diagnosis, although disease may confirmed by laboratory culture of the bacterium (difficult, dangerous and slow - takes at least 4 weeks).
Ziehl-Neelsen acid-fast staining procedure:
1. Heat fix cells on glass microscope slide.
2. Flood the slide with carbol fuchsin stain.
3. Heat the slide gently until it steams (5 min).
4. Pour off the carbol fuchsin.
5. Wash slide thoroughly with water.
6. Decolourize with acid-alcohol (5 min).
7. Wash slide thoroughly with water.
8. Flood slide with methylene blue counterstain for 1 min.
9. Wash with water.
10. Blot excess water and dry in hand over bunsen flame.
EXAMS AND TESTS
The doctor will complete the following tests to diagnose tuberculosis. You may not be hospitalized for either the initial tests or the beginning of treatment.

• : The most common diagnostic test that leads to the suspicion of infection is a chest x-ray.
o In primary TB an x-ray will show an abnormality in your mid and lower lung fields, and lymph nodes may be enlarged.
o Reactivated TB bacteria infiltrate the upper lobes of your lungs.
o Miliary tuberculosis exhibits diffuse nodules.

• Mantoux skin test: This test helps identify people infected with M tuberculosis but who have no symptoms. A doctor must read the test.
o The doctor will inject 5 units of purified protein derivative (PPD) into your skin. If a raised bump of more than 5 mm (0.2 in) appears at the site 48 hours later, the test may be positive.
o This test can often indicate disease when there is none (false positive). Also, it can show no disease when you may in fact have TB (false negative).

• Sputum testing: Sputum testing for acid-fast bacilli is the only test that confirms a TB diagnosis. If sputum (the mucus you cough up) is available, or can be induced, a lab test may give a positive result in up to 30% of people with active disease.
o Sputum or other bodily secretions such as from your stomach or lung fluid can be cultured for growth of mycobacteria to confirm the diagnosis.
o It may take 1-3 weeks to detect growth, but 8-12 weeks to be certain.

REFERENCES www.wikipedia.com

TREATMENT
Today, doctors treat most people with TB outside the hospital. Gone are the days of going to the mountains for long periods of bed rest. Doctors seldom use surgery.
• Doctors will prescribe several special medications that you must take for 6-9 months.
o Standard therapy for active TB consists of a 6-month regimen:
 2 months with Rifater (isoniazid, rifampin, and pyrazinamide)
 4 months of isoniazid and rifampin (Rifamate, Rimactane)
 Ethambutol (Myambutol) or streptomycin added until your drug sensitivity is known
o Treatment takes that long because the disease organisms grow very slowly and, unfortunately, also die very slowly.
o Doctors use multiple drugs to reduce the likelihood of resistant organisms emerging.
o Often the drugs will be changed or chosen based on the laboratory results.
 If doctors doubt that you are taking your medicine, they may have you come to the office for doses. Prescribing doses twice a week helps assure compliance.
 The most common cause of treatment failure is people's failure to comply with the medical regimen. This may lead to the emergence of drug-resistant organisms. You must take your medications as directed, even if you are feeling better.

• Another important aspect of tuberculosis treatment is public health.
o Doctors likely will contact or trace your relatives and friends.
o Your relatives and friends may need to undergo appropriate skin tests and chest x-rays
PREVENTIONS
• Treatment to prevent TB in a single person aims to kill walled-up germs that are doing nodamage right now, but could break out years from now and become active.
o If you should be treated to prevent sickness, your doctor usually prescribes a daily dose of isoniazid (also called INH), an inexpensive TB medicine.
o You will take INH for up to a year, with periodic checkups to make sure you are taking it as prescribed and that it is not causing undesirable side effects.

• Treatment also can stop the spread of TB in large populations.
o Tuberculosis vaccine, known as bacille Calmette-Guerin (BCG) may prevent the spread of tuberculosis and tuberculous meningitis in children,

o but the vaccine does not necessarily protect against pulmonary tuberculosis. .




EPIDEMIOLOGY


. According to the World Health Organization (WHO), nearly 2 billion people—one third of the world's population—have been exposed to the tuberculosis pathogen. Annually, 8 million people become ill with tuberculosis, and 2 million people die from the disease worldwide. In 2004, around 14.6 million people had active TB disease with 9 million new cases. The annual incidence rate varies from 356 per 100,000 in Africa to 41 per 100,000 in the Americas.Tuberculosis is the world's greatest infectious killer of women of reproductive age and the leading cause of death among people with HIV/AIDS.
The rise in HIV infections and the neglect of TB control programs have enabled a resurgence of tuberculosis. The emergence of drug-resistant strains has also contributed to this new epidemic with, from 2000 to 2004, 20% of TB cases being resistant to standard treatments and 2% resistant to second-line drugs. The rate at which new TB cases occur varies widely, even in neighboring countries, apparently because of differences in health care systems.
In 2005, the country with the highest estimated incidence of TB was Swaziland, with 1262 cases per 100,000 people. India has the largest number of infections, with over 1.8 million cases. In developed countries, tuberculosis is less common and is mainly an urban disease. In the United Kingdom, TB incidences range from 40 per 100,000 in London
to less than 5 per 100,000 in the rural South West of England; the national average is 13 per 100,000. The highest rates in Western Europe are in Portugal (31.1 per 100,000 in 2005) and Spain (20 per 100,000). These rates compare with 113 per 100,000 in China and 64 per 100,000 in Brazil. In the United States, the overall tuberculosis case rate was 4.9 per 100,000 persons in 2004.
The incidence of TB varies with age. In Africa, TB primarily affects adolescents and young adults. However, in countries where TB has gone from high to low incidence, such as the United States, TB is mainly a disease of older people, or of the immunocompromised .
There are a number of known factors that make people more susceptible to TB infection: worldwide the most important of these is HIV. Co-infection with HIV is a particular problem in Sub-Saharan Africa, due to the high incidence of HIV in these countries.Smoking more than 20 cigarettes a day also increases the risk of TB by two to four times. Diabetes mellitus is also an important risk factor that is growing in importance in developing countries. Other disease states that increase the risk of developing tuberculosis are Hodgkin lymphoma, end-stage renal disease, chronic lung disease, malnutrition, and alcoholism.
Diet may also modulate risk. For example, among immigrants in London from the Indian subcontinent, lacto vegetarian Hindu Asians were found to have an 8.5 fold increased risk of tuberculosis, compared to Muslims who ate meat and fish daily. Although a causal link is not proved by this data, this increased risk could be caused by micronutrient deficiencies: possibly iron, vitamin B12 or vitamin D. Further studies have provided more evidence of a link between vitamin D deficiency and an increased risk of contracting tuberculosis. Globally, the severe malnutrition common in parts of the developing world causes a large increase in the risk of developing active tuberculosis, due to its damaging effects on the immune system. Along with overcrowding, poor nutrition may contribute to the strong link observed between tuberculosis and poverty.




REFERENCES www.wikipedia.com





RESULTS AND CONCLUSIONS

When people suffering from active pulmonary TB cough, sneeze, speak, or spit, they expel infectious aerosol droplets 0.5 to 5 µm in diameter. A single sneeze can release up to 40,000 droplets. Each one of these droplets may transmit the disease, since the infectious dose of tuberculosis is very low and the inhalation of just a single bacterium can cause a new infection.
People with prolonged, frequent, or intense contact are at particularly high risk of becoming infected, with an estimated 22% infection rate. A person with active but untreated tuberculosis can infect 10–15 other people per year. Others at risk include people in areas where TB is common, people who inject drugs using unsanitary needles, residents and employees of high-risk congregate settings, medically under-served and low-income populations, high-risk racial or ethnic minority populations, children exposed to adults in high-risk categories, patients immunocompromised by conditions such as HIV/AIDS, people who take immunosuppressant drugs, and health care workers serving these high-risk clients.
Transmission can only occur from people with active — not latent — TB . The probability of transmission from one person to another depends upon the number of infectious droplets expelled by a carrier, the effectiveness of ventilation, the duration of exposure, and the virulence of the M. tuberculosis strain The chain of transmission can, therefore, be broken by isolating patients with active disease and starting effective anti-tuberculous therapy. After two weeks of such treatment, people with active TB generally cease to be contagious. If someone does become infected, then it will take at least 21 days, or three to four weeks, before the newly infected person can transmit the disease to others.TB can also be transmitted by eating meat infected with TB. Mycobacterium bovis causes TB in cattle


REFERENCES
www.wikipedia.com