Profile of a pathogen

Tuberculosis

Tuberculosis (TB), a highly infectious disease caused by a rod-shaped Mycobacterium tuberculosis (MT), has been lurking on the fringes of humanity’s story for millennia. It has been hypothesised that the genus Mycobacterium originated more than 150 million years ago and that an early progenitor of MT may have been abroad among early hominids in East Africa. What we do know is that TB has had time to reach every corner of the globe. According to a World Health Organisation report, in 2022 the disease was reported in territories containing more than 99% of the world’s population. It’s everywhere.

As far back as 1720, the physician Benjamin Marten conjectured about person-to-person transmission of the disease. In March 1882, Robert Koch announced that he had isolated the tubercle bacillus. This discovery was followed by the development of the Pirquet and Mantoux tuberculin skin tests, Albert Calmette and Camille Guérin’s BCG vaccine, and antituberculous drugs like streptomycin. Yet in 2018 an estimated 1.5 million people died from the disease and in 2021 an estimated 10.6 million people contracted it globally.

There are two basic types of tuberculosis: pulmonary and extrapulmonary. Pulmonary tuberculosis takes hold in the lungs. Symptoms can include a bad cough lasting three weeks or longer, tightening of the chest, night sweats, weight loss, fatigue, pain in the chest and the coughing up blood or phlegm from deep inside the lungs. But the disease can also spread to other organs, resulting in extrapulmonary tuberculosis (EPTB) which is on the rise. Organs affected can include the central nervous system, eyes, lymph nodes, musculoskeletal system, genitourinary tract and gastrointestinal tract. With EPTB the symptoms depend on the organ infected, making it difficult to spot. Sufferers may present with abdominal pain, diarrhoea, infertility, monoarticular joint pain, headache, meningismus, or lymphadenopathy. Tuberculosis is particularly dangerous for people living with HIV, which must be taken into account during an outbreak.

The bacilli are spread by infected airborne droplets, making TB extremely contagious. Once a person is exposed it can take three to nine weeks for the symptoms to appear. However, it can remain as a latent tuberculosis infection (LTBI) for years before the disease breaks out. The good thing is that people with LTBI are generally not infectious. However, once the disease is established patients can remain infectious for two to three weeks after treatment starts.. For this reason, tuberculosis is a ‘notifiable’ condition, which means that local health authorities must be informed in writing within five days of a confirmed diagnosis or suspected case.

The bacteria can be detected by two tests: a TB skin test (TST) such as the Mantoux skin test, and TB blood tests such as interferon-gamma release assays (IGRAs). However, these only detect the presence of the bacteria, and cannot tell whether the person has LTBI or has progressed to TB disease. Other tests, such as a chest x-ray and a sample of sputum, are needed to confirm this.

There are several potential treatment regimens, all of which can last for between four and nine months – not a quick fix. Also, TB has developed resistance to some antibiotics, meaning that any treatment path must be modified if the patient has been in contact with an individual with drugresistant TB.

Tuberculosis has been with us for so long it can almost be seen as part of being human. But we are making progress. For most of its history, tuberculosis has been associated with a high mortality rate, and untreated this is a very dangerous disease, but modern treatments are highly effective if delivered in time. The hope is that one day a disease that has stalked us for as long as we have walked the earth will eventually be consigned to the history books.

Mycobacterium A genus of over 190 species of bacteria. This genus includes bacteria that cause serious illnesses such tuberculosis and leprosy. Hominid The group consisting of all modern and extinct Great Apes. The includes modern humans, chimpanzees, gorillas and orang-utans plus all their immediate ancestors. Tubercle bacillus The small, rod-shaped bacterium that causes tuberculosis. Monoarticular joint pain Pain isolated to a single joint. Meningismus A group of symptoms similar to meningitis (stiff neck, reaction to light and headache), without inflammation of the membranes lining the brain.