Fluctuating Virulence in Common Organisms

NZMJ, 1924

We would draw attention to an important article by Dr. Lynch in this number, in which he gives a convincing account of the great virulence acquired by the staphylococcus aureus following the epidemics of influenza which occurred in Dunedin in 1918 and 1923. The knowledge that various disease-producing bacteria show a seasonal or periodic variation in their activities is, of course, commonplace, and forms one of the axioms of epidemiology. Such diseases as plague, sleeping sickness, measles, etc., are well-known to exist in a comparatively mild endemic state, and then for reasons that are by no means clear to take on the character of a raging epidemic. Doubtless this may be explained to some extent, by conditions affecting the carrier or its host, by lowered resistance in the population from famine, or the hardships and anxieties of war; but there is ground for the belief that the causal organism itself acquires from within, as it were, an awakening from its hibernation and an increased vigour apart from that which is imparted by the better soil for growth and multiplication, supplied by a diminished resistance in its victims. The phenomena of the decline and termination of epidemics can, moreover, be with difficulty explained in toto by considering that all suitable pabulum has been exhausted by a general increase of resistance, as the survivors, through anxiety and weariness following the tending of the sick might be considered more liable to attack. Nor can it be fully accounted for by change in environment and seasonal conditions. There must be, in addition, an inherent tendency in the germ itself to revert to its pristine innocuous state. The rise and fall of these hosts of death, like the rise and fall of nations, however difficult to fully understand, are at least facts of common knowledge, but it is rather a startling reflection that the secondary organisms that accompany or follow their ravages are able to share in their conquests, and going on from strength to strength reach a pitch of virulence little short of the primal germ, and indeed carry on with their increased powers long after the latter has relapsed into a state of impotence. The conquering army, weary of the slaughter, has retired on its base, but the camp followers, unsatiated, carry on the campaign.

The facts suggested, and indeed proved, for such a relatively harmless germ as staphylococcus will cause the profession to consider whether other bacteria have not equally benefited by recent influenza epidemics. We have a strong feeling that the bacillus coli and its congeners also, have taken a more prominent place than formerly in every-day pathological conditions. The ordinary inhabitant of the intestine is, of course, a creature of little pathogenicity compared with its fellow as found in appendix abscess. Whether that increased virulence is entirely due to its growth in unusual tissues, or whether all the colon bacilli of that particular patient have a more virulent character, which predisposes him to the attack, is open to question. At any rate it is not uncommon to see cases where the bacillus passes through the pelvis of the kidney in large numbers, causing few or no symptoms, while others suffer an intense and intractable pyelonephritis. May it be that all of the bacillus coli of the latter are more potent than those of the former?

We think that the subject may force itself on the notice of the profession in other directions. It may serve to explain some of our puerperal problems. It shows that the possible changes in the nature of bacteria whose operations and effects are supposed to be well-known may enable them to show manifestations that will leave us in bewilderment. It brings home to us that the devastating effects of such an epidemic as influenza are not limited to the time of the duration of that epidemic; and that much of the sickness that follows may be due not alone to permanent damage to organs and general lowering of vitality caused by the primary disease; but probably also to the more permanent lodgment in the body of other organisms whose enhanced virulence, gained at the time of the epidemic, enables them to propagate and initiate disabling conditions long after the principal germ has ceases to operate.