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to isolate the bacillus from a considerable proportion of the case investigated, together with the fact that the disease could not b experimentally passed on to either man or animals by inoculatio with Pfeiffer's bacillus, caused a revolt from the orthodox beliei It is considered by many that the primary aetiological factor sti remains undiscovered and that the B. influenzae, like the Strepto coccus and the Pneumococcus (the three pathogenic microorganism most usually found associated with the disease), is but a secondary invader of the tissues, and even though of such malignancy as tc be frequently the occasion of the fatal termination, still not th original causa causans. Owing to their negative findings, a large number of bacteriologists have concluded that this must be placec in the ever-growing ranks of the filtrable invisible viruses, organism so minute that even with the aid of the ultra-microscope they are not or barely to be seen ; of so diminutive a size that they are capable of passing through the pores of even the finer porcelain filters. An accepted instance of such a deposition of an organism from the position of causative agent to that of a mere secondary invader may be found in the case of B. suipestifer in the disease hog cholera. The true virus here has been demonstrated to be a filter-passer.

From many parts of the world came reports of the proof of such theories of a filtrable virus in influenza, but in no case have they stooc the test of criticism. With regard to the tiny globoid bodies shown in the filtered fluids, no evidence of their true influenzal nature from an infective point of view was forthcoming. They have been con- sidered to be inanimate particles of disintegrating protein or even ordinary contaminating bacteria gaining access to the culture tubes through a faulty technique.

Those investigators who resent the attack on the orthodox beliei in the B. influenzae as an aetiological factor point out that not all workers failed to find that organism in their cases; that those employing more satisfactory media for the growth of the bacillus were able to isolate it in as many as 90%. They further point out that an illness recognizable as influenza has not so far been trans- ferable to ordinary experimental animals. That man is not infected by inoculations with living B. influenzae is, they hold, discounted by the observation that it has not been possible voluntarily to transmit the disease from one person to another, even by such drastic methods as the swabbing of the mucous membranes with the inflammatory secretions taken from the eyes, nose and throat of pronounced cases. This paradoxical indication of a low infectivity of influenza is qualified by the fact that the experiments have been carried cut during and subsequent to the pandemic, when persons chosen for the experiment as normal, because of their not having succumbed to an attack of the disease, may be regarded on those very grounds as possessing a considerable degree of natural immunity, and therefore as not being acceptable as normal at all. More recently, experi- mental infection of both monkeys and man with influenza bacilli and the production of acute respiratory disease have been demon- strated, but the identity of the illness evoked with that of epidemic influenza is far from established. The whole question of the aetiology of influenza is still sub judice.

A New Paratyphoid. Early in the war, in a number of the armies engaged in the Near East, an illness was noticed which, although it corresponded clinically in many ways with enteric, did not yield a virus agreeing with any of the three well-known organisms of that group of diseases B. typhosus, B. paratyphosus A or B though culturally it was identical with the last-named. The bacillus that was isolated by Hirschfeld from cases occurring in the Serbian army was called by him B. paratyphosus C, and included in the anti- enteric vaccine used in the Serbian forces. Neukirch, recording recognition of it earlier on the Turkish front, gave it the name of B. Erzindjan. As the organism agrees culturally with and is serologically_ related to B. paratyphosus B, it has been suggested by others that it should, for simplicity's sake, be regarded as one of the many paratyphoid B types. Some workers have insisted on the identity of this so-called paratyphoid C with the bacillus found in pigs suffering from swine fever and called variously B. suipestifer, B. of hog cholera, and B. Voldagsen, but, though the relationship is very close, identity does not seem to have been proved. This newly recognized type of paratyphoid B, apparently in the main of Eastern habitat, has no doubt often in the past masqueraded as an atypical or inagglutinable paratyphoid bacillus.

Typhus Fever. Another disease that sprang into special promi- nence during the war, and the aetiology of which has received con- siderable elucidation, is typhus. Nicolle and his collaborators first gave experimental proof of the transmission of typhus to monkeys by the body louse. In the case of man such laboratory demonstra- tion has, however, because of the severity of the disease, been mainly accidental and therefore incomplete. But while there are other theories of supplementary means of infection, such as that it is air- borne or transmitted by droplet infection, evidence that the louse is the only carrier or communicator of typhus has accumulated to a great _extent. The sole measure for the successful combating of an epidemic^ has been a de-lousing campaign. The effect of good ventilation in preventing infection spreading from patients in a ward, at first regarded as a proof of its air-borne nature, can now be explained by the fact that lowered temperatures are inimical to the activities of lice. In cool, well-ventilated rooms these vermin will refrain from leaving the bodies of their hosts, and should they be

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driven to do so by the high temperature of a very feverish case or the lowered one of a corpse, they will be handicapped in their search tor a new host. Against the complicity of other insects, such as the ttea and the bed-bug, there are the observations that typhus is con- tracted only after close contact, which for flea-borne diseases is not necessarily the case; while, did the bed-bug play a part in infection typhus would be a house disease and not one transmitted for the mam part through the agency of lice-ridden clothes. . In 1910 Ricketts and Wilder described very small bodies seen in the gut of lice taken from typhus patients. In 1916 Rocha Lima repeated the observation. He regarded them as protozoal in nature and classified them as chlamydozpa. The chlamydozoa are organisms more minute than bacteria, consisting at one stage of but a speck of chromatin with no cytoplasm or membrane of any kind. At some period of their life-cycle they are filtrable. The viruses of rabies poliomyelitis, scarlet fever and vaccinia have among others been regarded as belonging to the chlamydozoa. The form seen in typhus lice was called by Rocha Lima Rickettsia prowazeki, to commemorate two workers who had succumbed to typhus infection during their investigations; Ricketts being also, in 1909, the first to describe bodies of this nature in the tick which transmits the disease known as Kocky Mountain fever. The aetiological relationship of these -bodies to typhus is being generally recognized. The criticism that mlar bodies have been found where no typhus existed has been countered by. the discovery that a different species, the Rickettsia qmntana, is associated with the disease trench fever, and the as- sumption that, as there are a variety of Rickettsia, some may well be apathogemc for man Belief in the causative nature of such bacilli as that of Plotz and the Proteus X 19 of Weil and Felix now finds little support. Indeed, when lice are fed with the latter or- ganism, they die within the period it takes a louse to become infec- tive after it has had access to a typhus patient. The defenders of a hltrable virus as the infecting agent are met by the fact that some orms o\.KlckeUs^a have been described of so small a size that their passage through a filter fine enough to retain bacteria would be possible Trench fever. In 1916 Topfer recorded the occurrence of Rick- ettsia bodies in the blood of and in lice taken from individuals suffer- ing irom what has in different countries been called trench or Volhyman fever. The justification for the association of this Rickettsia qmntana or Volhynia with the febrile disease rests on much the same kind of evidence as that furnished in the case of typhus; but here experimental work on man has been possible, and Arkwnght, Bacot and Duncan have definitely proved the in- fectivity of the -Ric^etoa-containing lice and their excreta for human beings.

Yellow Fever and Infectious Jaundice. A great deal of enlighten- ing work was carried out on yellow fever during 1919-01 by the Japanese research worker Noguchi, of the Rockefeller Institute Previous to his investigations most of our knowledge of the aetiolog- ical factors in this most dreaded of tropical diseases rested on the courageous work with its attendant loss of human life performed by the American Yellow Fever Commission in 1900. It was then established that yellow fever was an insect-borne disease, the vector being the mosquito Stegomyia calopus. Many other data, concerning the incubation period of the disease and the life-cycle of the virus which was shown to be filtrable, were also established. But the causal agent was neither isolated nor seen. It remained for Noguchi to detect in yellow-fever cases a spirpchaete, an organism of similar "ature to the specific agent of syphilis, a protozoon, and to prove, short of reproduction of the disease in man, its aetiological relation- ship to yellow fever. This organism he named Leptospira icteroides. He found it to be very closely related to, though not identical with the leptospira discovered independently by Inada and Ido in Japan and by Uhlenhut and Fromme in Germany in cases of infective jaun- dice or Weil s disease. This latter organism has for hosts both rats and mice, and has been named L. icterohaemorrhagiae; an anti-serum is made with the leptospira of infectious jaundice and possesses considerable curative value. Noguchi's reports on anti-yellow fever inoculation are only just beginning to appear but already show avourable results.

Wassermann Test. Among laboratory diagnostic methods of a

serological_ character, the _Wassermann test for the detection of

syphilitic infection still maintains its position of prominence. The

reaction, which is a complicated one, declares itself as positive or

negative by the power the patient's serum has or has not of going

nto combination with guinea-pig complement and an extract of

animal tissues. This was at first regarded as an immunity reaction,

nvplvmg the usual antigen, anti-body and complement, with the

bpirochaeta pallida (the virus of syphilis) acting as antigen. But

t is now known that that organism does not play a part at all in

he test, which is considered to be an interaction between lipoid

bodies (in the tissue extract), anti-lipoid bodies (present in syphilitic

era owing to the abnormal production of lipoids during the course

>f the disease) and complement (guinea-pig serum). Many modifica-

lons of the original Wassermann reaction are in use, mainly charac-

enzed by increased complexity of technique, but the new diagnostic

method of Sachs and Georgi is comparatively simple, consisting

merely of interaction between the patient's serum and a lipoid solu-

ion ; it is apparently of satisfactory reliability.