Tuberculosis mortality in Europe has been declining for a long time. These data suggest that it peaked in London 250 years ago, with annual rates approximating 1%.
While the data must be interpreted with caution as diagnostic accuracy was surely limited, particularly before the identification of M. tuberculosis as the causative agent of tuberculosis, it is certain that the epidemic in Europe has been declining for a very long time.
The reasons for this decline are not entirely clear. Certainly, medical progress cannot possibly have played an important role as effective chemotherapy became available only at the end of the above observation period. Improvement of nutrition, followed by improvement of social conditions have been proposed. They cannot, however, fully explain this observation.
The shape of the course of the mortality epidemic resembles that of any epidemic, the sole difference being the time frame it is spanning. One possible hypothesis is selective pressure on the population. Tuberculosis is most frequent in the early reproductive age as has been shown earlier. In other words, it removes many people before they had a full chance to reproduce. If such a selection has taken place, it will unlikely have been by selecting people more likely to survive if they develop tuberculosis, because case fatality of untreated pulmonary tuberculosis has been so large even up to the end of the above observation period. Selection must thus have taken the form of a lower risk of developing tuberculosis among those infected.
This hypothesis is entirely speculative and models are needed to evaluate whether the force of mortality of close to 1% and the young age at which it occurred suffice to strengthen this hypothesis. |
