Читать книгу To Catch a Virus - John Booss - Страница 21

Thought to exist for centuries as a sporadic disease, polio was a rare crippler of infants and children. John Paul, a student of polio, used a figure of an ancient Egyptian stele showing a young priest with a withered leg as evidence of such early observations in his 1971 volume, A History of Poliomyelitis (47). As Paul described, “Under such endemic conditions paralytic poliomyelitis could have remained under cover for centuries in populations in which infant mortality was high.” Yet the individual experience of the paralytic form of the disease, from sporadic to epidemic times, has been consistent. Walter Scott was born in 1771 in an area characterized as “. . . a cramped dimly lit alleyway with poor sanitation and little fresh air” (15a). He described the onset of polio at 18 months: “One night, I have often been told, I showed great reluctance to be caught and put to bed, and after being chased about the room, was apprehended and consigned to my dormitory with some difficulty. It was the last time I was to show such personal agility. In the morning I was discovered to be affected with the fever which often accompanies the cutting of large teeth. It held me three days. On the fourth, when they went to bathe me as usual, they discovered that I had lost the power of my right leg” (47). The contagiousness of polio was not recognized in the centuries when polio was understood to be a sporadic disease, and Scott’s fever was attributed to the cutting of teeth.

The evolution of polio from an endemic, sporadic disease to an epidemic pattern occurred toward the end of the 19th century. In the United States, for example, Charles Solomon Caverly of the Vermont State Board of Health reported in November 1894 that “Early in the summer just passed, physicians in certain parts of Rutland County, Vermont, noticed that an acute nervous system disease, which was almost invariably attended with some paralysis, was epidemic” (7). Caverly investigated this “‘new disease” that was affecting the children and initially found 123 cases. He reported that “The territory covered is mainly the narrowest part of the Otter Creek Valley in Rutland County, bounded on the east by the Green Mountain range and on the west by the Taconic range. . . .” Of 110 cases in which paralysis occurred, 50 persons recovered fully and 10 died, “leaving fifty who are apparently permanently disabled.” It is of note that a microbe was suspected: “. . . the microbic or infectious nature of the disease is generally believed in by us. . . .” However, Caverly reported no evidence of contagiousness, since it “affected almost invariably but a single member of a household.” He published a fuller report of his investigations in 1896 (8). It is remarkable that in his first report just months after the epidemic, Caverly noted the apparent absence of communicability. Presciently, however, Caverly suspected the microbial nature of the disease, which was to be shown by Karl Landsteiner and Erwin Popper 14 years later (38). Thus, with reports by others, the stage was set for proving the contagious and filterable virus nature of this affliction.

Communicability was demonstrated by Ivar Wickman 11 years later in Sweden, showing the role of nonparalytic cases in sustaining the epidemic (67). John Paul emphasized Wickman’s contribution: “Considering the importance of the contributions of Ivar Wickman, I do not believe that his work is fully appreciated today” (47). Later, Wickman failed to be appointed the Chair of Pediatrics at Stockholm, a position formerly held by his mentor in polio studies, Karl Oscar Medin. Perhaps in despair, though the reason was never ascertained, Wickman took his own life at the age of 42. John Paul emphasizes Wickman’s contributions as identifying the contagious nature of the disease, describing the importance of nonparalytic forms, estimating the incubation period as 3 to 4 days, and classifying different forms of the disease (67). Polio transmission to monkeys was soon to be shown by others. While crucial in demonstrating the viral nature of the disease, studies with monkeys may have deflected attention from key pathogenic aspects of the human disease.

The first decade of the 20th century proved to be decisive in the demonstration of polio as caused by a contagious, filterable virus. Unfortunately, those proofs were dependent on the emergence of epidemics of polio in Europe and North America. Wickman’s extensive studies of the epidemic in Sweden in 1905 were published as journal reports and as a monograph which was translated into English in 1913 (67). While the infectious nature of the disease had been suspected, no bacterial cause had been successfully demonstrated. Small laboratory animals also had not yielded an agent. However, in a meeting in December 1908 in Vienna, Austria, Karl Landsteiner, acknowledging the assistance of collaborator Erwin Popper, reported transmission of polio to monkeys, demonstrating for the first time a virus as the etiological agent of polio (Fig. 4). Two monkeys inoculated by the intraperitoneal route with spinal cord from a fatal human case demonstrated the symptoms and microscopic lesions of polio (38). A fuller presentation of Landsteiner and Popper’s findings was published the following year (33). Clinical findings of paralysis were observed in one of the monkeys, and both showed the characteristic histopathological findings of polio in the spinal cord exactly like those observed in human cases. In contrast, rabbits, guinea pigs, and mice, also inoculated by the intraperitoneal route, were negative. Thus, the importance of the monkey for isolation of poliovirus was established.

Figure 4 Karl Landsteiner. Landsteiner was awarded the Nobel Prize in 1930 for the discovery of human blood groups. Another significant contribution was the demonstration that polio could be transmitted to monkeys by using spinal cord tissue from children who had died from the illness. (Courtesy of the Albert and Mary Lasker Foundation.)

doi:10.1128/9781555818586.ch2.f4

Simon Flexner and Paul A. Lewis at the Rockefeller Institute in New York, NY, quickly picked up the observations of Landsteiner and Popper and demonstrated serial passage of polio in monkeys using intracerebral inoculation (16) of spinal cord material. The importance of serial passage was to eliminate the possibility of a nonreplicating toxic factor, an experimental principle that had been established with the first demonstration of a viral disease in animals, foot-and-mouth disease by F. Loeffler and P. Frosch (37). Success in passage of polio to monkeys benefitted from serendipity. Landsteiner and Popper noted that the monkeys they had used had been left over from previous studies of syphilis (33). As pointed out by John Paul, Landsteiner and Popper used Old World monkeys, not the “relatively unsusceptible” New World monkeys (47). It remained to be shown that the experimental disease could be transmitted by filtered material. Landsteiner, teamed with Constantin Levaditi of the Metchnikoff Laboratory at the Pasteur Institute, reported on 28 November 1909 the successful transmission of polio to a monkey after intracerebral inoculation of an emulsion which had been passed through a Berkefeld V filter (32). Likewise, on 18 December 1909, Flexner and Lewis at the Rockefeller Institute reported transmission of polio to a monkey by intracerebral inoculation of spinal cord material passed through a Berkefeld filter (17). Thus, within 1 year, December 1908 to November and December 1909, clinical and pathological experimental replication of poliovirus in monkeys had been achieved, with serial passage and confirmed demonstration of the filterability of the infectious agent.