Causes of TB

  • TB is caused by two bacteria; Mycobacteria tuberculosis and Mycobacteria bovis.
  • Tuberculosis is ultimately caused by the Mycobacterium tuberculosis, a bacterium that is spread from person to person through airborne particles. Inhaling infected particles does not necessarily mean that a person becomes infected.
  • One of three things may happen when Mycobacterium tuberculosis enters the human body:
  • the bacterium is destroyed because the body has a strong immune system 9attacked by the macrophages in the lungs);
  • the bacterium enters the body and remains as latent TB infection. The patient has no symptoms and cannot transmit it to other people;
  • the patient becomes ill with TB;


Signs and symptoms of TB

Most people who become infected with Mycobacterium tuberculosis do not present symptoms of the disease.

However, when symptoms are present, they include:

  • unexplained weight loss
  • shortness of breath
  • fever
  • fatigue
  • night sweats
  • chills
  • loss of appetite


Symptoms specific to the lungs include:

  • coughing that lasts for 3 or more weeks
  • coughing up blood
  • chest pain
  • painful breathing
  • pain when coughing.

Transmission of TB

  • TB is a communicable disease that is spread primarily by tiny airborne particles (droplet nuclei);
  • the disease spreads when infected people with the active form of the illness cough or sneeze;
  • the bacteria spread through droplets in the saliva or sputum
  • it spreads most rapidly among people living in overcrowded conditions;
  • when a person with active TB coughs, sneezes, talks, or spits, tiny droplets containing the bacteria are released into the air and can be inhaled by people who are close by.
  • the bacteria can spread from the initial location in the lungs to other parts of the body through the bloodstream.
  • only a small number of bacteria are needed to cause an infection.
  • persons with latent TB infection cannot transmit TB because bacteria are not present in their saliva or sputum.
  • bovis causes TB in cattle and is spread to humans in meat and milk; – most people with TB are infected with M. tuberculosis.
  • people with active TB can transmit the bacteria through the air by coughing and sneezing.


People at risk

Although anyone can be exposed to or get TB, some people are at higher risk for both exposure and infection (though exposure does not necessarily result in infection). These higher risk groups include, among others:

  • the close contacts of someone who is infectious
  • immigrants from areas where TB is common, such as Asia, Africa, and Latin America – the poor
  • the medically underserved
  • racial and ethnic minorities
  • persons living in congregate settings, such as correctional facilities;
  • alcoholics and persons who inject drugs
  • the homeless
  • persons with HIV infection


Persons who are exposed to infectious TB on the job. Of those infected with TB, the following run an especially high risk of developing active TB disease:

  • persons with HIV
  • persons whose infection is relatively recent (within the previous 2 years)
  • injection drug users
  • those with a history of inadequately treated TB.
  • Persons infected with both HIV and TB has the highest known risk factor for developing active TB disease.
  • Whereas TB-infected persons who are not HIV-positive run a 10 percent lifetime risk of developing active disease, those with both TB and HIV run a percent to 10 percent chance per year of developing active disease


Global distribution of TB

  • Worldwide


Explain the possible reasons for the global distribution of TB

  • it is a pandemic disease (globally distributed)
  • it is an endemic disease (always present)
  • most prevalent in developing countries
  • some of the TB strains becoming more resistant
  • AIDS pandemic
  • poor housing – overcrowding
  • breakdown of TB control programme
  • partial treatment of TB
  • poor sanitation
  • poor medical facilities
  • TB spread in meat and milk
  • high rate of transmission – droplet infection


Problems associated in the prevention and control of TB

  • some strains of TB bacteria resistant to drugs;
  • the AIDS pandemic;
  • poor housing and rising homelessness in inner cities in the developed world;
  • the breakdown of TB control programmes particularly in the USA;
  • partial treatment for TB increases the chance of drug resistance in Mycobacterium;
  • attacks many of the poorest and socially disadvantaged because it is spread by airborne droplets;
  • so people who are overcrowded are particularly at risk;
  • those with low immunity particularly because of malnutrition or being HVI+ are also vulnerable;
  • transmission is easily achieved but the bacteria may remain in the lung, or in the lymphoid tissue for years until they become active;


Link between TB and HIV/AIDS

  • TB is often the first opportunistic infection to strike HIV+ people;
  • HIV infection may reactivate dormant infections of Mycobacterium tuberculosis;
  • TB is now the leading cause of death of HIV+ people;
  • The HIV pandemic has been followed very closely by a TB pandemic;
  • There are high rates of incidence of all across the developed world and in the countries of the former Soviet Union;
  • Very high rates are also found in areas of destitution in developed countries;
  • Social factors such as homelessness, neglect of primary health care and urban decay, contribute to the spread of TB and these need to be addressed if the pandemic I to be curbed



  • once someone appears with the symptoms of TB, the sputum (mucus and pus) from their lungs is collected for analysis;
  • the identification of tuberculosis can be made very quickly by microscopy;
  • isolation of sufferers while they are in their most infectious stage;
  • this is particularly the case if they have an infection of a drug resistant strain;
  • the treatment involves use of several drugs to ensure that all bacteria are killed, not just a few; otherwise drug resistant strains are left behind to continue the infection;
  • the WHO promotes a scheme to ensure that patients complete their course of drugs;
  • DOTS (Direct Observation Treatment Short Course) involves health workers or responsible family members, making sure that patients take their medicine regularly for 6 – 8 months;
  • contact tracing and the subsequent testing of contacts for the bacterium is an essential part of controlling TB;
  • though contacts are screened for TB, the diagnosis can take up to two week;
  • In children TB is prevented by vaccination;
  • the BCG vaccine is derived from bovis and protect up to 70% of teenagers and its effectiveness decreases with age unless there is an exposure to TB;
  • the vaccine is effective in some parts of the world and less effective in others e.g. India;
  • an effective method of control is the dual approach of milk pasteurisation and TB testing of cattle;
  • any cattle found to test positive are destroyed;
  • these measures have reduced the incidence of TB caused by M. bovis considerably it is hardly a hazard to health in countries where these controls operate.




  • the treatment is long (6 months to 1 year), but many people do not complete their course of the drug as they think that when they feel better they are cured;
  • however it takes months to kill mycobacteria because they are slow growing;
  • they are intracellular parasites surviving inside cells of the immune system, where they are metabolically inactive therefore they are difficult to treat with drugs;
  • strains of drug-resistant tuberculosis were identified when treatment with antibiotics, such as streptomycin, began in the 1950s;
  • antibiotics act as selective agents killing drug-sensitive strains and leaving resistant ones behind;
  • drug resistance happens as a result of mutation;
  • if three or four drugs are used in treatment, then the chance of resistance occurring is greatly reduced,
  • if TB is not treated or the person stops treatment before the bacteria are completely eliminated, bacteria spread throughout the body increasing the likelihood that mutation will arise;
  • prematurely stopping treatment means the tuberculosis develops resistance to all the drugs being used;
  • patients under poorly managed treatment programmes return home to infect others – multiple drug resistant forms of TB (MDR-TB) now exist


Explain how an understanding of the disease tuberculosis (TB) can be used in its control and prevention

  • TB cause by Mycobacterium tuberculosis/bacillus;
  • bacteria can be treated/controlled by antibiotics;
  • sputum infected therefore dispose of sputum hygienically;
  • associated with poverty/poor housing/poor living conditions;
  • therefore social remedies important;
  • overcrowding facilitates spreading;
  • because droplet infection;
  • also spread by physical contact/can be contagious;
  • re-house if infected people cannot have own bedroom;
  • education needed – poor education associated with poor hygiene e.t.c.;
  • notifiable so can trace contacts;
  • infectious phase brief/spread easily/spread by droplets so can isolate patients;
  • bacteria can remain dormant for several years;
  • so people who recover should not work in the food industry /become teachers;
  • can be transmitted in milk, therefore pasteurize milk;
  • test cattle (TT herds) and slaughter affected cattle;
  • BCG vaccination given to children (aged 10 – 13 years);
  • poor diet reduces resistance therefore good nutrition needed;
  • all teachers X-rayed before starting job;
  • screening possible in areas of high risk because X-rays show up lung damage
  • high risk groups can have early vaccination (e.g. Asian immigrants I inner city poor housing);
  • to MDR/cocktails of antibiotics used;
  • importance of finishing course of antibiotics;
  • AVP;


Reasons for classifying TB as a social disease and lung cancer as a self-inflicted disease


  • social disease is due to social conditions/behaviour
  • social factors aid to the spread of TB;
  • poor housing;
  • poverty/social class;
  • poor diet, i.e. people with low immunity from malnutrition are also vulnerable;
  • overcrowding living conditions;
  • TB droplet infection/airborne infection;
  • people sleeping/living together are at increased  risk;
  • prolonged exposure;
  • poor unlikely to seek/complete treatment;
  • TB is classified in other disease categories e.g. infectious;


Lung cancer

  • Self-inflicted disease is due to one‘s behaviour;
  • most lung cancers are caused by smoking;
  • tar in tobacco smoke is a carcinogen;
  • which alters DNA In epithelial cells;
  • mutation
  • development of malignant tumours;
  • epidemiologists discovered a correlation between smoking and lung cancer, i.e. smokers are 18 times more likely to develop lung cancer than non-smokers;
  • risk of development of lung cancer decreases as soon as smoking decreases;
  • personal choice to smoke;
  • once started difficult to give up;
  • addiction to nicotine;
  • physical dependence;
  • psychological dependence;
  • lung cancer is classified in other categories e.g. degenerative, non-infectious;


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