CARRIAGE OF THE VIRUS OF POLIOMYELITIS, WITH SUBSEQUENT DEVELOPMENT OF THE INFECTION

Naked Viruses That Aren't Always Naked: Quasi-Enveloped Agents of Acute Hepatitis

Historically, viruses were considered to be either enveloped or nonenveloped. However, recent work on hepatitis A virus and hepatitis E virus challenges this long-held tenet. Whereas these human pathogens are shed in feces as naked nonenveloped virions, recent studies indicate that both circulate in the blood completely masked in membranes during acute infection. These membrane-wrapped virions are as infectious as their naked counterparts, although they do not express a virally encoded protein on their surface, thus distinguishing them from conventional enveloped viruses. The absence of a viral fusion protein implies that these quasi-enveloped virions have unique mechanisms for entry into cells. Like true enveloped viruses, however, these phylogenetically distinct viruses usurp components of the host ESCRT system to hijack host cell membranes and noncytolytically exit infected cells. The membrane protects these viruses from neutralizing antibodies, facilitating dissemination within the host, whereas nonenveloped virions shed in feces are stable in the environment, allowing for epidemic transmission.

PERSISTENCE OF THE VIRUS OF POLIOMYELITIS IN THE NASOPHARYNX

The virus of poliomyelitis occurs in the nasopharynx of man and monkeys. In man it has been detected by the inoculation test in washings from acute cases, rarely in similar washings from healthy contacts, in the nasopharyngeal tissues obtained from fatal cases in the 1st week of infection, but rarely, if ever, from nasopharyngeal tissues removed surgically at later periods in the course of the disease. In monkeys, also, the virus has been detected in the secretions from acute experimental infections, in the nasopharyngeal tissues derived from early cases, and rarely from cases several weeks or months after recovery from the acute symptoms. The inoculation of tonsils and adenoids obtained from cases of undoubted poliomyelitis either yielded definite results in the form of typical paralysis and histological lesions in the central nervous organs of the monkeys injected, or no symptoms or lesions which could be confounded with poliomyelitis. The indefinite symptoms and atypical lesions described in a certain class of inoculated animals by Kling, Pettersson, and Wernstedt were not encountered in our experiments. The deduction from the experiments reported is to the effect that the virus is regularly present in the nasopharynx in cases of poliomyelitis in the first days of illness, and especially in fatal cases; that it diminishes relatively quickly as the disease progresses, except in rare instances; and that it is unusual for a carrier state to be developed. Hence the period of greatest infectivity of patients would appear to be early in the disease, which is probably the time at which communication of the virus from person to person takes place. Available evidence proves that healthy carriers of the virus occur. We do not, however, possess data which indicate the frequency with which carriage arises. The fact that even after a severe and wide epidemic, such as occurred in the United States in 1916, the disease may virtually disappear within 2 or 3 years, points to the probability that enduring carriers of the active virus, whether healthy or chronic, are of exceptional occurrence.

THE DETECTION OF POLIOMYELITIS VIRUS IN SO CALLED ABORTIVE TYPES OF THE DISEASE

Experiments are reported which describe the isolation of poliomyelitis virus from the throats of two patients during an attack of so called abortive poliomyelitis (Wickman type), or what we have termed characteristic minor illnesses in association with poliomyelitis. This finding represents added evidence in favor of the belief, previously held by many observers, that certain types of minor illness, which accompany an epidemic of poliomyelitis, probably represent mild cases of the disease.

FATE OF NASALLY INSTILLED POLIOMYELITIS VIRUS IN NORMAL AND CONVALESCENT MONKEYS WITH SPECIAL REFERENCE TO THE PROBLEM OF HOST TO HOST TRANSMISSION

With a method of intranasal instillation of poliomyelitis virus that brings about infection of all M. rhesus monkeys subjected to it, a study was undertaken of the fate of nasally instilled virus in normal and convalescent, immune animals. Control experiments revealed that nasal mucosa of normal monkeys contained no observable antiviral factors and that when five or ten minimal cerebral infective doses were added to the mucosa, virus could be detected by the employed procedure. In the olfactory bulbs even a single infective dose could be recovered, since suspensions of both bulbs could be transferred to the brain of a monkey without any loss of material. After nasal instillation of virus in normal monkeys, it disappeared quickly (4 hours or less) and could be recovered neither from the excised nasal mucosa nor from the olfactory bulbs during the first 48 hours. At 72 hours, just before or coincident with the first rise of temperature, virus was found in very small amounts in the nasal mucosa and for the first time also in the olfactory bulbs. At 96 hours, at least 3 days before the appearance of nervous signs, and later, while virus continued to be present in considerable amounts in the olfactory bulbs (and presumably elsewhere in the central nervous system), none was detected in the nasal mucosa. In convalescent, immune animals receiving the same strain of virus intranasally which caused the original infection, none could be recovered from the nasal mucosa or central nervous system at 4 hours, 1, 2, 3, 4, 5, and 7 days. The bearing of these observations on the problem of host to host transmission of poliomyelitis virus is discussed.

ISOLATION OF POLIOMYELITIS VIRUS FROM THE NASOPHARYNX

A single example of mild illness diagnosed as suspected abortive poliomyelitis is described in which the virus of poliomyelitis was recovered from the nasopharynx by three different methods. Failure to recover virus from a total of twenty-six cases diagnosed as suspected or abortive poliomyelitis and fourteen contacts is also reported. The original material from the nasopharynx of the positive case proved unusually infective for the monkey, apparently even more so than are the majority of suspensions of spinal cords from fatal human cases of poliomyelitis. An explanation of this fact is not clear. The method of isolating human virus from the throat, by means of preserving the sediment of washings from this site in glycerine, has been shown to be efficient in one case for a period of 101 days.

DETECTION OF THE VIRUS OF POLIOMYELITIS IN THE NOSE AND THROAT AND GASTRO-INTESTINAL TRACT OF HUMAN BEINGS AND MONKEYS

Five strains of virus were recovered from nasal washings and feces. Four strains were of human origin, the fifth strain came from a monkey sacrificed at the height of the disease. Of the four human strains the first was isolated from the feces of a 14 year old child 7 days after the onset of illness. The second strain was from the nasal washings of a 6½ year old child, 5 days after the onset of illness. The third and fourth strains were recovered from the same patient, a 2½ year old child, 9 days after the onset of illness. One of these strains was obtained from nasopharyngeal washings and the other from the feces. The single monkey strain was isolated from the upper intestinal segment and appears to be the only instance of its isolation from this source in the literature. We believe that the detection of the virus in the nasal washings of two additional patients during convalescence lends further support to the belief that the virus of poliomyelitis is spread by human contact. Furthermore, the recovery of the virus from the gastro-intestinal tract with as great or greater frequency as from the upper respiratory tract, need not, it appears to us, alter our concept of the mode of entrance of the virus into the body, namely, by way of the upper respiratory tract. If the presence of the virus is conceded, then a consideration of the physiologic passage of nasal and oral secretions into the gastro-intestinal tract by reflex swallowing would serve to explain adequately the presence of the virus in those organs. It might even be further predicated that since the gastro-intestinal tract functions as a temporary reservoir for secretions from the upper respiratory tract, the gut should, after a time, contain the virus in higher concentration than any single sample of secretion obtained from the upper respiratory tract by nasal washing. It appears to us that failures to detect the virus in the gastro-intestinal tract are perhaps more indicative of inadequate procedures for its detection than of its absence. The recovery of the virus from the feces 7 and 9 days after the onset of illness takes on added significance. It indicates first, that the virus withstands the gastric acidity which under normal physiological conditions tends to keep gastric contents relatively free of bacteria. It further suggests that improper disposal of feces from patients with poliomyelitis may have serious public health consequences, particularly in smaller communities where inadequate sewage disposal may result in contamination of surrounding beaches or even local water systems.

RESPIRATORY VERSUS GASTRO-INTESTINAL INFECTION IN POLIOMYELITIS

The debated problem of gastro-intestinal versusrespiratory mode of infection in poliomyelitis has been restudied by several investigators recently, with conflicting findings. Kling and Levaditi in Europe carried out experiments from 1929 to 1933, which led them to the conclusion that the digestive tract affords a ready entrance of the virus of the disease into the body. They believe that the substitution of Macacus cynomolgus for Macacus rhesus as the animal of choice for the tests supports this point of view. Toomey in the United States has arrived at a similar conclusion, not by employing a particular species of monkey for experiment, but by the use of drastic measures of inoculation, which insure that the virus makes contact with the unmyelinated nerve fibers embedded in the intestinal wall. Toomey's methods are so severe and artificial that his results cannot be regarded as simulating a natural mode of infection. We have repeated the tests of Kling and Levaditi, but in a far more comprehensive manner than was followed by them, and, like Clark and his associates who early repeated them, we have failed to confirm them. Indeed, we do not find Macacus cynomolgusand rhesus to differ in any essential way in their response to the presence of the virus of poliomyelitis in the body. Cynomolgido not respond to virus introduced into the stomach when contamination of the buccal and nasal cavities is avoided; they respond, as do rhesi, to virus directly injected into the intestine when virus passes into the intestinal wall and makes the necessary nerve fiber contact. Both Macacus cynomolgus and Macacus rhesus which have resisted feedings of virus are subject to nasal instillations of the same strains of virus and in the same degree. On the basis of the experiments reported in this paper we can reaffirm the conclusion previously arrived at by ourselves, and confirmed independently by investigators in Europe and America, namely that the only established portal of entry of the virus of poliomyelitis into the central nervous system of man is the nasal membrane, and especially the olfactory nervous areas in that membrane.

SURVIVAL OF THE VIRUS OF POLIOMYELITIS IN THE ORAL AND NASAL SECRETION OF CONVALESCENTS

The positive detection of the virus of poliomyelitis in the nasal secretions of 2 children, 16 and 13 days after the onset of the disease, is described. 7 animals which had been inoculated with other concentrates became ill with symptoms and temperature elevations suggestive of poliomyelitis, from 1 to 3 weeks following inoculation, but without definite paralysis. In 2 of these animals which were sacrificed, the histologic findings were compatible with the diagnosis of poliomyelitis but were not typical. Of the serums of the 5 remaining animals 4 failed to neutralize stock virus, whereas the serum of the fifth neutralized the virus on two different occasions. This serum was obtained from a monkey that had been inoculated with concentrated nasal secretions of a child 43 days after the onset of illness. It is suggested that the present quarantine period of 3 weeks is compatible with the available data. It is further suggested that the methods of procedure described may be useful in similar investigations.

Studies on entry and egress of poliomyelitis infection. III. Excretion of the virus during the presymptomatic period in parenterally inoculated monkeys

Excretion of poliomyelitis virus has been demonstrated in monkeys after four different parenteral routes of inoculation. Virus has been found in both the pharyngeal secretions and the stools after infraorbital nerve dip and after inoculation of the Gasserian ganglion; in the pharyngeal secretions after intrathalamic inoculation; and in the stools after inoculation of the celiac ganglion. Excretion began as early as the 2nd and as late as the 7th day after inoculation, in all instances before the onset of symptoms. The immediate source of the excreted virus appeared to be infected peripheral ganglia with neural connections to the mucous membranes of the upper and lower portions of the alimentary tract, notably the pharynx. Primary infection of the body surfaces was excluded in the experiments and therefore could not account for the excretion of virus. The mode of elimination was probably by centrifugal spread through axons of peripheral nerve fibers and not by way of the blood stream or lymphatics. Evidence was obtained that when excretion of virus has once occurred, reinvasion from the implicated surface to other, previously uninfected peripheral ganglia ensues, thus providing new sources for excretion and other potential pathways for invasion of the CNS. It is suggested that such reinvasion may occur serially until the immunological defenses come into play. Our experiments lend support to the view that during the initial stage of poliomyelitis, and perhaps throughout its course in some cases, e.g. the asymptomatic and the mild cases without central nervous symptoms, infection is confined to the peripheral nervous system. Involvement of the CNS when it occurs is a secondary phase of the infective process and is not a necessary prelude to elimination of the virus. Excretion is explainable on the basis of the established neurocytotropism and axonal conduction of the virus without resort to the hypothesis of extraneural infection.