The body's response to TB

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What is TB?

caused by mycobacterium tuberculosis

Respiratory or pulmonary TB is the most common form. affecting the lungs and is highly contageous

improved housing, living conditions, with the development of antibiotics, saw a decline in numer of TB cases in the UK.

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Symptoms of the disease

infecrion may occur when the bacteria are inhaled and lodged in the lungs

they start to multiply

two phases of the disease:

primary infection

actve phase

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Primary infection of TB- The immune system respond

can last for several months and may have no symptoms

M. tuberculosis causes an inflmmatory response from the hosts immune system

in a healthy indivisual the macroophages engulf the bacteria

a mass of tissue calles the granuloma forms produced in response to infection

these TB masses are anaerobic and have dead bacteria and macrophages in the middle, they are called tubercules.

after 3-8 weeeks the infection is controlled and the infected region of the lung heels. most primary infection occurs during childhood and most are healed without noticed

Bacteria invade the immune system- M.bacteria can survive inside macrophages, the bacteria taken up by phagocytosis, once inside they resist the killing mechanisms. The bacteria have thick waxy cell walls, making them difficult to break down. they can lie dormant for years, if the immune system is weakened again then the infection becomes active again.

TB bacteria can also target cells of the immune system, surpressing T cells. Thus reducting antibody production and attack by killer T cells.

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Active TB

occurs when the patients immune systen cannot contain the disease when it first arrives in the lungs

could be beacuse the number of bacteria is too great, or an old infection may break our if the immune system no longer is working properly

about 80% of active TB cases are reactivations of previously controlled infections

the activity of the immune system may be reduced for several reasons

old age or very young (0-5) less able to respond quickly to pathogens

malnutrition and poor living conditions

recent infections AIDS, HIV is the virus that causes AIDS, it targets white blood cells and reduces ability to fight any infection.

TB is aggressive disease that kills many people with AIDS

the bacteria multiply rapidly and destroy the lung tissue, creating holes or cavities. the lung damage will eventually kill the sufferer if they are not treated with approprate antibiotics

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Symptoms of active TB

  • coughing- may cough up blood
  • shortness of breath
  • loss of appetitie and weight loss
  • fever and fatigue
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Role of fever

fever and night sweats

part of the inflammatory response, fever-causing substances are released from neutrophils and macrophages.

the chemicals affect the hypothalamus and alter the set point for the core body temperature to a higher temp

effectors act to warm up the body to a new set point

the patient has a high fever and temp- 40.5C

the raised temperatire enhances immune functioning and phagocytosis.

bacteria and virus may reproduce more slowly at a higher temo

TB is heat sentiive and will stop reproducing at remps above 42C but this is threatneing to humans as enzymes are increasingly denatured.

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Glandular TB

TB affects bones, lymph nodes and CNS.

main sympom is enlarged lymph glands, in neck or armpit

Xrays- show lymph glands in the chest

Aisan people more likely to get glandular TB

caucasions get ore pulmonary TB

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How is TB diagnosed?

History is taken

Skin and blood tests-

small amount of tuberculin is injected under the skin in the forearm

a positive resdult shows an inflammed area of the skin around the site

antibodies cause this inflammation indicating TB antigens already present

can also give negative result, if TB is latent.

also give false positive- anti TB vaccination

Blood tests tested for T cells specific to antigens only occuring on Mycobacterium

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TB diagnosed?

Identification of bacteria-

a sample of sputum coughed up by the patient is taken and cultured to see what bacteria are present.

different bacteria can be identified from the culture using staining techniques

only some bacteria take up particular stains depending on the make up of their cell walls

chest Xrays- to see the damage and disease in the lungs

TB is contageous, all friends and fmaily have to be tested.

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