Updated: May 22
At one level, the numbers look good, but if you look again, maybe not. Once upon a time, TB started out as something else, probably some environmental predecessor that lived in watery or other environments, perhaps starting out in another animal, but eventually, it got to humans. There was a ‘patient zero’ for TB, just as there is for all new and emergent pathogens, and for TB, it is guessed that this happened around 5,000 to 10,000 years ago. There is evidence that it has been with us since the Neolithic, so it has been with us for most of what we consider to be human cultural history. But that’s not that long ago in evolutionary time, and it didn’t keep itself to people; it infected cows, goats, seals, and probably other things too. In all likelihood, it was us who gave it to the cows, where it evolved into the bovine version, and them to the badgers – since there are no cow or badger hosts crossing the oceans to get it to them. From patient zero … it spread to infect.
Now numbers are falling overall, and the control of the TB epidemic is one of the 17 United Nations Sustainable Development Goals that were ratified in 2015. An interim progress report was given in 2020 (A/75/236 - E - A/75/236 -Desktop (undocs.org)). The only region to achieve an interim target of a 20% reduction by 2020 was Europe, where the majority of countries are amongst the 54 with low incidence. Elsewhere reduction is happening but far more slowly than intended, except for the WHO African region, while the incidence in the WHO Region of the Americas was actually increasing slightly. These numbers aside, the drug resistant strain numbers aren’t decreasing at all – they are increasing.
This includes a specific increase in strains called Beijing because of where it was first characterized. A combination of higher virulence (ability to spread, which is related to having symptoms and coughing) and a greater association with drug resistance (meaning infectious patients stay infectious for longer) is combining to see remarkable increases in the proportion of cases it is associated with. For example, in Mumbai, a global centre of infection for drug-resistant TB, the proportion of cases caused by this one strain (or group of related strains) has increased from 4% to 40% in just 10 years. It has emerged to cause around 50% of infections in East Asia and at least 13% worldwide. The point is that looked at separately, rather than with all the other strains together, there is effectively a new pandemic with rapid spread and expansion of this version of TB. The expansion of this pathogenic strain demonstrates that current methods of control are inadequate to contain it, let alone eradicate it. It also illustrates the importance of being able to identify new emergent challenge strains long before they get to spread globally, as this one has.
Dr Nigel Saunders, Chief Scientific Officer