Bancroftian filariasis and the reticulo-endothelial system

Abstract

In Bancroftian filariasis the rise and the fall of the microfilarial tide are caused by different mechanisms. There is now anatomical evidence, furnished by O'Connor, that the rise is caused by timed parturition of female worms, and here the significance of spent worms has been imperfectly grasped either as a normal daily event or as a result of their sterilization by drugs. The fall of the tide is caused by the mobile cells of the reticulo-endothelial system, for which statement the line of argument runs thus. When helminths enter the tissues of a host animal, it is these very cells which collect and attack them actively. For Bancroftian filariasis their presence was reported years ago, but their fundamental importance has been missed. They destroy microfilariae in lymph nodes before they get into the blood, and by their accumulation and their development to the end cell of the series, the fibroblast, they cause lymphatic obstruction; the lymph conditions then become those of a culture medium which may be four million times better suited to the haemolytic streptococcus than is normal lymph, and when infection with this bacterium has set in they become still more favourable for growth of fibroblasts and increase of elephantiasis. When microfilariae have got, or been put, into the blood, many events are those which would take place were the reticulo-endothelial cells active in their destruction, the others those which would be seen were the system blocked by them; these are taken up in detail, and it is shown, first that protein shock is not caused when injected microfilariae disappear from the circulation at once and for good, even by the million, and second that the remarkable post-mortem flow of lymph, which is caused by cyanide poisoning, would have taken any microfilariae in the post thoracie lymphatics to just those positions in the great arteries in which Manson found them in his now classical case; that he found them there after death is no evidence that they were there during the man's life. Of anatomical evidence that destruction of microfilariae causes the fall of the microfilarial tide there is little—not surprising since almost no one has looked for it. But in one of two cases sectioned by O'Connor there had been that massive destruction of microfilariae in spleen and liver which would be expected did the reticulo-endothelial system get rid of them daily. This finding calls for investigation of these organs, and of the bone marrow, after death has taken place at different hours in persons in whom periodicity is known to have been maintained to the end, in order to see what relationship there is between the microfilarial tide and the extent of destruction of microfilariae. Limited biopsy may help there. There is the possibility of great benefit to those with this infection were there found a drug which would safely sterilize, even if it could not kill, all female worms. A detailed and unbiased examination of the whole subject to the cause of periodicity is urgently needed.