The Western World has been fretting about SARS and Avian Influenza for some time now, but all the while there’s been another bug that we thought we had previously conquered sitting in the wings evolving drug resistance, and it could be far deadlier.
Mycobacterium tuberculosis (or M. tuberculosis, Tubercle Bacillus or just TB) was a killer throughout history (think “consumption”) up until just after the second world war with the advent of antibiotics such as streptomycin when people thought they had TB beaten. The disease was beaten down around the world and the worlds attention wandered.
But TB (like any bacteria or virus) mutates, and sometimes those mutations confer resistance to our drugs and are then selected for when the antibiotics kill off the non-mutated strains. This is evolution at work. But whilst we have a number of antibiotics available nobody paid it that much attention because we could use two variants so that one of them would kill them off. Then we had to use more, because there were new TB strains that were called MDR (multiple drug resistant). But evolution doesn’t sleep and the blind watchmaker tinkered on and so XDR-TB – Extensively Drug Resistant TB – arose, resistant to many of our remaining antibiotics that worked against TB.
In September 2006 in South Africa a worrying new strain of XDR-TB was identified by the WHO, much more lethal than previous strains. In January 2007 the journal PLoS Medicine published an open access article (CC licensed) called
XDR-TB in South Africa: No Time for Denial or Complacency – PLoS Med. 2007 January; 4(1): e50.
This article talks about the new strain in South Africa and contains some rather worrying facts.
Of these 221 cases, 53 were identified as XDR-TB, i.e., MDR-TB plus resistance to at least three of the six classes of second-line agents. This reportedly represents almost one-sixth of all known XDR-TB cases reported worldwide. Of the 53, 44 were tested for HIV and all were HIV infected.
All but one of those 53 individuals died shortly afterwards.
The median survival from the time of sputum specimen collection was 16 days for 52 of the 53 infected individuals, including six health workers and those reportedly taking antiretrovirals. Such a fatality rate for XDR-TB, especially within such a relatively short period of time, is unprecedented anywhere in the world.
There is also a concern that we are looking at the tip of the iceberg with these figures, a fact which is not helped by the way that testing for XDR-TB was being done in South Africa, and the fact that the government there currently suspends welfare payments for patients hospitalised with MDR-TB or XDR-TB.
The WHO is taking this very seriously.
In recognition of the global threat posed by these factors, on September 9, 2006, WHO urged a response to the outbreak akin to recent global efforts to control severe acute respiratory syndrome (SARS) and bird flu.
Unfortunately as you’ve probably not heard about this (unless you read New Scientist or similar) you can guess that it’s not been that well publicised. The journal article goes on to say:
The emergence of XDR-TB is also an uncomfortable reminder of the failure of health systems to control problems at a tractable scale. If, in the recent past, TB were to have been adequately managed when it was completely drug sensitive, we would not be in such a dire situation as is currently the case. This failure rests upon us all.
Of course, evolution will not stop now either, and we must prepare for this.
We should begin to contemplate the response when we move to the predictable next phase: completely drug-resistant tuberculosis.
New Scientist recently reported that the first case of CDR-TB – completely drug resistant TB has been documented.