what is the cause of tuberculosis?

tuberculosis has been known in science for a very long time. the bacterium causing tuberculosis, mycobacterium tuberculosis, existed 15000-20000 years ago and was found in the ancient Egypt, China and India. In the middle ages tuberculosis was called king’s evil and was believed to be cured by the touch of the king of France or England. Tuberculosis was found with the evidence in the lymph nodes. Tuberculosis became a very serious problem in western Europe in the 18th century and it caused many deaths. From the 19th century onwards people thought the only option was to isolate people with tuberculosis.  In 1921 the BCG, a vaccine against tuberculosis, was finally introduced. Doctors started doing surgeries of TB patients and after that there antibiotics developments started. In 1944 the first antibiotic drugs were used for TB patients. The development of para amino salicylic acid followed later on. Because of that more effective antibiotics came in in the1950’s. Also the usage of rifampicin treatments started, rifampicin is a antibiotic that is used to treat different infectious diseases.

 

Tuberculosis can either be pulmonary or extrapulmonary. when it is pulmonary the bacterium will be in the lungs of the patients and when it is extrapulmonary the bacterium is outside of the lungs.

Tuberculosis is caused by a bacterium called Mycobacterium tuberculosis. The spread of tuberculosis is similar to the spread of the flu but with a smaller probability. The condition will be spread when a tuberculosis infected patient sneezes or coughs and another person inhale the expelled droplet. A person with the flu can infect people surrounding him very easily however with tuberculosis a person should spend a long period of time with an infected person to become infected too. A good example is spreading the bacterium while living together.  A person will not get infected by meeting someone with the infection once. Also, not everyone with tuberculosis is infectious. Tuberculosis can also occur outside of the lungs, in that case the patient will not be infectious. Children won’t spread  the disease either.

 

The tuberculosis bacteria can sometimes be latent or active. When the bacteria is latent it enters the body but doesn’t show any symptoms. And when it is active the symptoms will only show after a couple of weeks or months. While the immune system can normally kill the tuberculosis bacteria it isn’t able to kill it when it is either latent or active. the immune system of a  person with  the latent form of TB will wall off the organism in the granuloma, which is a localized inflammation found in the tissue.  These people form of the bacteria can eventually develop tuberculosis too, this happens when their immune system is weakened. The chance for these people to develop tuberculosis is 10%.

                                                                                              

Tuberculosis mainly affects people in developing countries and young adults. One specific type of tuberculosis is Multidrug resistant tuberculosis, which caused when antibiotics are used but they can't kill all the targeted bacterium. Because of the antibiotics usage the left over bacteria will become resistant to the antibiotics drugs. MDR tuberculosis can only be treated with a specific drug which is often not available of very limited.  

 

One the bacterium enters the body, a macrophage cell will absorb the infectious particles when they reach the alveoli which are small air cells in the lungs. After that the particles will move to the lymphatic system, which is part of the circulatory system, and to the bloodstream. this will cause the bacteria to spread to other organs and  tissues. In the organs with a high oxygen pressure the bacteria will multiply these organs include the lungs, bone marrow, kidney and the covering of the brain and spinal cord.

 children get infected with tuberculosis in the same way as adults, by inhaling the bacterium. the bacterium will reach the lungs, multiply and spread to the lymph nodes. most children have a strong immune system  that will cause the multiplication to stop however this is not always the case. If the immune system is too weak to do this the child will develop the disease. If the children have a compromised immune system there is a bigger chance for  the tuberculosis to progress. the biggest progression chance is for children below the 4 years old. having malnutrition or a HIV infection will also make the risk of getting tuberculosis bigger. the development of the disease usually happens after two years of being infected

 

HspX knock-out experiment.:

the worldwide tuberculosis control is hindered because of the  prolonged needs for chemotherapy. there has been a huge desire for a drug that shortens the duration of chemotherapy and prevents the relapse of tuberculosis. HspX is a protein which was shown to be connected to with the growth of the mycobacterium tuberculosis with a previous experiment. in the new experiment HspX was evaluated as a target for controlling the growth of the mycobacterium tuberculosis combined with antibiotics usage in mouse models.  the mice were infected with a HspX deletion mutant dHspX and after three weeks they were treated with rifampicin isoniazid and pyrazinamide for a period of 14 weeks. after that they were treated with hydrocortisone for 8 weeks. the effectiveness of the chemotherapy  was measured by looking at the bacteria and relapse in the different organs. the conclusion was that HspX could be very promising and if combined with other antibiotics it could possibly shorten the amount of treatments and lessen the disease relapse.  So if this will be further elaborated it could bring a big change to the future of tuberculosis control.

written by: Loebna Sabbah