KEGS Biology Blog

Monday 17th December Section 2
December 16, 2012, 5:23 pm
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Here are the notes I currently have on TB as we have not covered malaria yet.

TB is an often lethal bacterial disease caused by Mycobacterium Tuberculosis this is what is known as the “causative agent” being a bacteria, they have thick cell walls.

The disease is spread through coughs and sneezes which releases droplets of water from the mouth (approximately 40,000 per sneeze) the bacteria is very infectious and as little as 10 bacteria can lead to the development of TB

Although most infections are asymptomatic and lay dormant in the alveoli in the lungs. 1 in 10 of these going on to develop the active disease and 50% of those that develop the active disease die as a result of the disease.
When the disease does become active several symptoms become present
-Chronic cough with blood
-Fever (as a result of producing anti bodies to fight the bacteria)
-Night sweats
-Weight loss (TB used to be called consumption for this reason)

Diagnosing TB is not easy
1 – Medical history is taken and contact tracing takes place ( to rule out other causes and may make it easier to diagnose; if it TB does get diagnosed then all the people you have been in recent contact with are contacted to prevent further spread of the disease)
2 – An X-Ray is taken to visualise the granuloma*
3 – A Culture of Sputum is produced (This is not very effective because the bacteria may be dormant and takes a very long time as it is a very slowly replicating bacteria; a mycobaterium tuberculosis will replicate every 2 days)
4 – Tuberculin skin test shows if anti bodies to fight the TB bacteria have been produced or not

*- The immune system has a way of attempting to rid the lungs of the bacteria this is by forming what is known as a granuloma around the bacteria.
– A granuloma is a formation of macrophages (A type of White Blood Cell) and is the immune systems way of detecting a foreign body and preventing it from doing any harm)
– The granuloma releases chemicals which causes necrosis
– Necrosis means to destroy tissue or cells as lung tissue is destroyed by the bacteria and the immune response
– It is then replaced by the scar tissue and necrotic tissue. The necrotic tissue is a creamy white substance
– This irritates the Lungs and Bronchioles, this leads to the coughing up for blood and bacteria as a common symptom.

Treatment for TB
– Antibiotics – unfortunately the antibiotics are very flawed
1) Low quality
2) Most don’t finish the Therapy (death or otherwise)
3) The TB bacteria can form an acquired resistance if treatment times are missed
4) The bacterium is very effective at preventing the entry of the antibiotic as of its thick cell wall
5) The drugs are very expensive

The Acquired resistance is known as specifically MDR – TB (multi drug resistant tuberculosis)

There are several ways to get patients to regularly take their medication
1) DOTS – Directly Observed treatment (short course)
-This is where the patient is directly observed taking their medication either in a home for the duration or with daily visits to the Hospital

Is there a vaccine?
– Up until 2005 there was a vaccine taken by all children in year 10
– It was phased out because
– it was not very effective (patients needed re vaccinating every 5 years)
– Painful; the vaccine was intramuscular and also left a noticeable scar.

The vaccine was developed around 1920 and was called the BCG vaccine.

What conditions increase the chance of being infected with TB?
– Crowded areas (tubes in London for example)
– Poor health
– Poor diet
– Smoking
– Other diseases

– An infected individual can infect 10-15 people a year
– The bacteria replicate in the Alveoli

Comment by matthewbesley

Interesting article on how X-Ray diagnosis for TB may not be very effective and a new blood test may be the way forward

Comment by candicetam

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