I was always a sickly child – when I was eleven years old, doctors injected my forearm with tuberculin in order to check whether my immune system raised a response to the bits and bobs of dead tuberculosis (TB) bacteria in it. If it did, it meant my immune system had already been prodded into battling TB, that is, it had previously encountered or was currently encountering an infection with TB bacteria. The injection site swelled like a furious bee sting, the doctors decided TB was the root cause of all my troubles, and I was intensely medicated for the next six months. My symptoms improved, and I have since evolved (visibly even!) towards the hale and hearty end of the healthiness spectrum.
In retrospect, now that I am medically trained and pursuing a PhD in TB immunology, I can appreciate all that my care team must have had to consider before starting an eleven-year-old child on a rigorous anti-TB treatment based on an educated guess. My symptoms were not typical of classical lung TB, the most common and infectious form of TB, they were mostly gastrointestinal, but then TB has also been known to stitch the gut into uncomfortable knots. My mother had recently been diagnosed with a cold abscess, due to TB of the bone, and though this could not possibly be infectious (based on centuries of observation) it still raised flags as it meant I had a history of contact with a TB patient. I showed an immune response to the tuberculin skin test (TST), but then I had received the BCG vaccine, which is a close relative of TB bacteria. This meant I could elicit a cross-reactive immune response and result in a positive TST even in the absence of TB infection due to the similarity of the two bacteria. (more…)