Latent Tuberculosis: Causes, Diagnosis, Treatment
What is Latent Tuberculosis?
Latent Tuberculosis is a latent form of Tuberculosis in which after the actual infection has been treated the bacteria causing the Tuberculosis infection which is called Mycobacterium Tuberculosis still remain but are in dormant state and do not cause any symptoms of active TB. It is estimated that about a third of the population in the world have Latent Tuberculosis meaning that they currently may not have active TB but are at risk of developing this condition in the near future.
It is estimated that about 10% of people with known tuberculosis have a chance of reactivation of this disease within the first five years of the infection. This risk is significantly increased in people who have predisposing factors like a weak immune system or are being treated for some other medical condition. This is when these individuals are most vulnerable to get Latent Tuberculosis.
What Causes Latent Tuberculosis?
Latent Tuberculosis develops when the immune system of an individual is not good enough to keep the growth of the bacteria causing TB in check. The presence of these bacteria causes the white cells to form a kind of a wall or lesion around these bacteria and the bacteria tends to survive within this lesion for decades. When the individuals becomes sick with an illness or tends to have a weakened immune system due to any reason this is when the bacterium breaks free from these walled lesions of white blood cells resulting in an active Tuberculosis.
Prevalence Rate of Latent Tuberculosis
Studies have shown that, in the world population 1 out of every 3 individual has latent tuberculosis. That is, these individuals have been exposed to tuberculosis bacteria and they have acquired the infection; however, the bacteria though alive is in inactive state. They do not have symptoms of tuberculosis and cannot transmit the disease to other individuals. However, they are always at a risk of developing symptomatic and contagious form of tuberculosis. It has been seen that 3% to 5% of latent tuberculosis acquire active form in the first year of infection, and about 5 to 15% develop after that.
Pathogenesis of Latent Tuberculosis
Latent tuberculosis becomes active tuberculosis when there is weakness in the immune system which under normal circumstances keeps the bacteria in check. In patients who are positive for tuberculosis, Mycobacterium tuberculosis bacteria cause development of an immune response where a large number of white blood cells are formed around the area where the bacteria are growing. A walled lesion is formed known as tubercle or granuloma. The bacteria can survive inside the walled tubercle for decades. Any condition leading to weakening of the immune system can cause spillage of bacteria from the lesion which develops into active tuberculosis.
Risk Factors for Latent Tuberculosis
Individuals with HIV/AIDS and other immuno compromised diseases are at higher risk of acquiring active tuberculosis. The risk factors include young age, old age, cancer patients, IV drug users etc.
How is Latent Tuberculosis Diagnosed?
The best way to diagnose Latent Tuberculosis is by a Tuberculin Skin Test and Interferon-Gamma Release Assays. Individuals with Latent Tuberculosis will have a negative bacteriological tests and hence a diagnosis of Latent Tuberculosis is based on the results of the above two mentioned tests which is the TST and IGRA which will be positive in cases of Latent Tuberculosis. These tests are although inconclusive and are not able to predict whether an individual with Latent Tuberculosis will go on to develop active Tuberculosis.
The suspected individual can take a specialized test called as TB skin test or PPD test. The test is easily available and it is carried out by a health care worker, who injects a small amount of TB extract under the skin of the forearm. In positive cases, a swelling in noted within 2 to 3 days after the test has been conducted as an immune reaction to the TB extracts. In some cases, where the time span between exposure and test is too small, the test may show negative result. Therefore, a second test may be considered usually after 8 to 10 weeks post exposure as a confirmatory test. The test is usually done when someone joins a new workplace or school to eliminate the risk of developing tuberculosis.
Even though the suspect may not show symptoms of the disease, it is advised to get a TB skin test done especially in the following cases:
- Recent history of exposure to hospitals, prisons, orphanage, homeless shelters, active tuberculosis patients or recent history of travel to countries where TB is known to be endemic such as Africa, Latin America, Asia, Eastern Europe, Russia.
- Presence of underlying condition such as HIV/AIDS with weak immune system, which increases the risk of developing TB.
- History of taking immunosuppressive drugs; e.g. drugs for rheumatoid arthritis.
- History of working in medical facilities
Presence of symptoms of active tuberculosis such as fever, chronic cough, weight loss, blood stained mucus, fatigue, night sweats etc.
How is Latent Tuberculosis Treated?
Fortunately, there is adequate treatment available to treat Latent Tuberculosis successfully and prevent an individual from progressing on to developing active TB. The current treatments available reduce the risk of an individual with Latent Tuberculosis going on to develop active TB by over 70%, although there are certain side effects like hepatotoxicity that exist with administration of medications to treat Latent Tuberculosis. The following are the front line treatments for Latent Tuberculosis:
- Utilization of isoniazid on a daily basis for up to at least 10 months.
- Using combination of rifapentine and isoniazid on a weekly basis for up to four months.
- Using combination of isoniazid and rifampicin on a daily basis for about four months.
- Using just rifampicin on a daily basis for about four months are the most preferred modes of treating Latent Tuberculosis.
It is advised to take vitamin B6 supplements with INH to avoid the development of side effects such as tingling sensation in nerves. In certain cases, prophylactic treatment may be suggested especially in children and in HIV positive patients, who have recent history of exposure to tuberculosis pathogens. If latent tuberculosis is treated, it reduces the possibility of developing active tuberculosis drastically.
Latent tuberculosis is a respiratory condition which is best described as an inactive version of tuberculosis. It has a tendency to pop up during fall in immune system and when someone is sick, not eating well or getting adequate rest. It is a contagious disease, and when activated, it needs to be treated at the earliest.