Sunday, April 29, 2012

Tuberculosis

A stained sample of sputum (mucus that has been coughed up from the lungs) from someone with tuberculosis (TB). The red slivers are Mycobacterium tuberculosis, the bacterium that causes this disease. The presence of bacteria in this sputum is why coughing can spread the disease.
A poster advising good hygiene
It seems there are a lot of misconceptions about TB, especially when it comes to how deadly it is.

To begin, the bacterium that causes the disease is spread through the air. Specifically, this is only through people who have had the bacterium heavily infesting their lungs. When an individual with this level of infection sneezes and coughs, or even speaks, the tiny bacteria are expelled into the air. Then, when someone breaths in the bacteria, they may become infected. Luckily, unlike many other diseases, you can only contract TB through this method. Touching the spit or sputum of an infected individual will not make you sick. Nor will sharing objects with that person such as food and drinks, a toilet seat, or linens. You can't even contract it by kissing them.

In addition to the very specific mode of transmission, not everyone who is exposed to the bacteria will become ill. Many will not become infected, and many of those are are infected will be asymptomatic. This asymptomatic form is known as latent tuberculosis. Those with this form are indeed infected, but their body is effectively fighting off the disease. The vast majority of infected individuals will have this form, and they cannot pass the disease on to other people. A few of those who have latent TB will eventually become symptomatic and develop full-blown TB.

M. tuberculosis bacteria in culture form
So, what are the symptoms of tuberculosis? They include a persistent, bad cough that lasts for three weeks or more. Chest pain can also occur, as well as bringing up sputum which may contain blood. The lack of appetite, weight loss, and fatigue are the sources of one of the common names for this disease: "consumption." This term was used because it appeared as if the person were being consumed from the inside out.

There are also a number of risk factors of tuberculosis, all of which can greatly increase your likelihood of developing active TB. After exposure to the bacterium, the biggest risk factor is a weakened immune system. Reasons for a weakened immune system include being infected with HIV, having certain cancers, being too thin, abusing drugs, having received an organ transplant, diabetes, scoliosis, severe kidney disease, and receiving treatments that suppress your immune system so as to treat certain diseases.
A person receiving a Mantoux skin test

How can you be tested for TB? You can receive either a skin test or a blood test. The skin test is done by insertion of the chemical tuberculin under the skin. Time is given for the body to react to the chemical, and then the injection spot is observed and measured to determine whether it is positive or negative. A negative result indicates it is highly unlikely the individual has been infected, and a positive test indicates a possible infection of either latent or active TB. One downside to the skin test is that people who have previously received a tuberculosis vaccine may test positive, even if they are not infected with the bacteria. I have met someone who was born in Namibia who received a false-positive skin test after being vaccinated in his youth. The other test that is available is the blood test, which takes a blood sample and then tests its reaction to the TB bacteria itself. This test is preferred for those who have previously received a vaccination, as false positives don't occur. If you think you've been exposed to tuberculosis, you should get tested.

Prevalence of TB worldwide, with red being highest incidence and gray being least incidence.
How do you prevent tuberculosis infection? Vaccination is one preventative measure, and is commonly given to babies in countries where infection rates are high. In countries like the United States, the vaccination is rarely used due to the overall rather low incidence. Only people who meet very specific requirements will receive the vaccine, such as people who regularly work with infected patients or with the bacterium itself. In countries where infection is uncommon, prevention mostly involves prompt identification of infected individuals, followed by measures to prevent further infection while the infected individual is being treated.

TB can be seen in a lung X-ray
Treatment is suggested for anyone who tests positive for TB, whether they have the latent or active form of the disease. In the United States, this is partly in an attempt to eliminate the disease from the population. Overall, measures have been rather successful, considering the low infection rate in this country. Latent TB is far easier to treat than active, as you might expect. If someone has active TB, they have to be sure to follow dosing instructions on their medication to the letter. If this isn't done, its possible that they may develop drug-resistant tuberculosis. The drug-resistant form of the disease is the most difficult to treat. The more drugs the disease is resistant to, the more difficult to treat and the higher the possibility the treatments will not be effective. For the most, tuberculosis can be a highly treatable disease when handled correctly.

Despite the fact that treatment can be quite effective against the bacterium, approximately one-third of the world's population is infected with the tuberculosis bacterium, mostly as latent cases. About one and a half millions deaths were attributed to tuberculosis in 2010.  TB is also a leading killer of those who have become infected with HIV.

Source is the Center for Disease Control and Prevention. Images are from Wikimedia Commons and are copyright free: one, two, three, four, five, six.

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