Do TB bacteria form spores?
16 Jun 2009 Comments (1)A press release from the University of Uppsala in Sweden reports a study that opens the possibility that the organism responsible for tuberculosis (Mycobacterium tuberculosis) might be able to form spores. This goes against all current understanding of the Mycobacteria. It is known that M. tb. can remain latent in infected people for many years. Indeed this is one of the reasons why TB is so hard to control. But it is unclear how the organism manages to achieve its latency. Many other bacteria use spores but not, so it seemed, M. tb.
Leif Kirsebom and colleagues say they have now shown that, not M. tb. but a ‘close relative’, can form spores. Apparently their discovery was initially an accidental finding. The research has not yet been published but is expected to appear shortly in the Proceedings of the National Academy of Sciences. It is to be hoped that this new knowledge of the Mycobacteria might ultimately lead to new ways to control TB and other mycobacterial diseases in humans and animals. These include leprosy and Buruli ulcer.
21 Jan 2010 at 3:25 am
Transmission
When people suffering from active pulmonary TB cough, sneeze, speak, or spit, they expel infectious aerosol droplets 0.5 to 5 µm in diameter. A single sneeze can release up to 40,000 droplets. Each one of these droplets may transmit the disease, since the infectious dose of tuberculosis is very low and inhaling less than ten bacteria may cause an infection.
People with prolonged, frequent, or intense contact are at particularly high risk of becoming infected, with an estimated 22% infection rate. A person with active but untreated tuberculosis can infect 10–15 other people per year. Others at risk include people in areas where TB is common, people who inject drugs using unsanitary needles, residents and employees of high-risk congregate settings, medically under-served and low-income populations, high-risk racial or ethnic minority populations, children exposed to adults in high-risk categories, patients immunocompromised by conditions such as HIV/AIDS, people who take immunosuppressant drugs, and health care workers serving these high-risk clients.
Transmission can only occur from people with active — not latent — TB . The probability of transmission from one person to another depends upon the number of infectious droplets expelled by a carrier, the effectiveness of ventilation, the duration of exposure, and the virulence of the M. tuberculosis strain. The chain of transmission can, therefore, be broken by isolating patients with active disease and starting effective anti-tuberculous therapy. After two weeks of such treatment, people with non-resistant active TB generally cease to be contagious. If someone does become infected, then it will take at least 21 days, or three to four weeks, before the newly infected person can transmit the disease to others. TB can also be transmitted by eating meat infected with TB. Mycobacterium bovis causes TB in cattle.