What is it?
Tuberculosis (TB) is an infectious disease caused by a bacterium. Approximately two billion people, one third of the Earth's population, are infected with TB. Developing nations are most affected by TB, although there has been a resurgence in the first world due largely to the spread of HIV/AIDS. There are approximately 8.5 million new active cases and 2 million deaths annually from TB. Most of these deaths are preventable with antibiotic treatment.
Causes of TB
The causative agent of tuberculosis is bacteria from the Mycobacterium species, mostly Mycobacterium tuberculosis, although other mycobacteria such as M. bovis can also cause TB disease in humans. The bacteria is spread through the air when an infected person coughs or sneezes. M. tuberculosis usually infects the lungs (pulmonary TB) but it may also infect the lymphatic system, circulatory system, the skin, and other organs (systemic TB). A vast majority of people infected with mycobacterium do not develop symptoms and do not spread the disease to others, this is known as latent TB infection. In latent TB infection a small amount of TB bacteria remains in the body but is kept in check by the immune system, unable to cause disease. If, however, the immune system is comprimized, such as through serious illness, it is possible that the latent infection can become an active TB infection.
Active TB infection can arise immediately after being infected with TB bacteria or it may develop from an existing latent infection. It is during active TB infection that it is possible to spread the disease to others and when symptoms are presented. Symptoms include coughing, weakness, weight loss, fever, chills and night sweats.
Both active and latent TB infection are treated with antibiotics. There are currently several antibiotics in use to treat TB infection, divided into the categories of first line drugs and second line drugs. Second line drugs are used when the first line drugs are not effective in eradicating the bacterium.
In over 95% of cases, TB disease is treatable using the first line drugs alone over a period of six to nine months. However, due to poor health care practices, two new strains of TB are emerging that are resistant to antibiotics, multidrug resistant TB (MDR-TB) and extremely drug resistant TB (XDR-TB).
MDR-TB is defined as TB that is resistant to the two most commonly used anti-TB antibiotics, isoniazid and rifampicin. A recent survey by the WHO has found that MDR-TB represents approximately 5% of all new TB cases worldwide, and represents over 15% of new cases in some countries. This is an increase from an earlier WHO survery, highlighting the need for new drugs to fight TB infection.
XDR-TB is MDR-TB that is also resistant to three or more of the existing six classes of second line anti-TB drugs, making it virtually untreatable. It also has a high mortality rate compared to normal TB. The WHO reports that XDR-TB has been identified all over the world but it is most commonly found in the former Soviet Union and Asia. In the U.S., 4% of MDR-TB cases met the criteria for XDR-TB.
The Sacchettini lab is part of a consortium of labs that are researching TB and looking for new ways to combat this bacterium. Please visit the following website to learn more: www.webtb.org