ENTEROVIRAL DISEASES Poliomyelitis is a common acute viral infection. It occurs naturally only in man. Various parts of the central nervous system, especially lower motor neurons, cranial nerves, the medulla, autonomic nervous system, cerebral cortex, and posterior columns of the spinal cord are involved in the most severe form. Nervous system invasion does not occur in most instances. Infection may produce no apparent illness, non-specific syndromes, or disease of the nervous system in which evidence of neurologic dysfunction, notably motor paralysis, may or may not be present.. History. Poliomyelitis has unquestionably been known since ancient times. It was not until 1789, however, that an English physician, Underwood first recorded a description of this disease in the medical literature.
A German orthopedist, Heine, discussed the deformities resulting from this infection and their therapy in a monograph published in 1840. The latter part of the nineteenth century witnessed a number of epidemics; the contagious character of poliomyelitis was established during this period, especially by the work of Medin, a Swedish physician. who described the epidemic form of the disease in 1890. Two. important discoveries were made in 1908: Wickmarr established the basic epidemiologic principles, and Landsteiner isolated the responsible, virus in monkeys. The twentieth century has seen an increasing number of epidemics of poliomyelitis in various areas of the world.
The most significant advance in recent years in the field of poliomyelitis was the development of a method into growing the virus in tissue culture by Enders, Weller, and Balb-bins in 1949. This made it possible, for the first time, to vaccines of predictable antigenic potency and minimal ENTEROVIRAL DISEASES preparation of formalin-inactivated virus suspensions Salk, and later of “live virus” vaccines by Sabin, by Cox, aini, Koprowski in the latter half of the 1950s, has made the reduced incidence or even eradication of poliomyelitis a goal. Etiology. The causative agent of pa is a virus that ranges from 8 to 30 MIL in and is pathogenic for man, monkeys.. and panzees. Three antigenically distinct types have • been defined: Type I, Type II, and Type though some degree of cross-neu demonstrable in highly immunized animals, infection in man with one type does not protect against invasion by another.
ENTEROVIRAL DISEASES Poliomyelitis virus has been cultivated in human and monkey kidney cells, HeLa cells, and human amnion; characteristic cytopathic changes •neutralizable by type-specific antiserum are produced. Poliomyelitis virus remains viable in water or sewage, under proper conditions, for as long as four months. It is not killed by ether, Merthiolate, tincture of Zephiran, ethyl alcohol, or low concentrations of phenol, but it is inactivated by heat, bichloride of mercury. oxidizing agents, 2 percent tincture of iodine, ultraviolet light, and 10 minutes’ exposure to a chlorine concentration of 0.05 part per million. Epidemiology. Poliomyelitis is worldwide in distribution, but epidemics have been limited to a relatively small number of areas.
That it has been much more prevalent than it would appear to be on the basis of the number of clinically obvious cases is proved by the widespread distribution of neutralizing antibody to the virus in population groups in which the disease is recognized only rarely. Even in outbreaks in which infection with involvement of the nervous system is present, as many as 95 percent of the cases may be clinically inapparent. The highest frequency of poliomyelitis is from July through September in the temperate zone, although it may appear as early as April or as late as December. In tropical or subtropical regions, the “season” may be prolonged. Certain environmental factors may play a role in conditioning the risk of exposure to poliomyelitis virus and the development of infection. Most persons who live in areas of poor sanitation develop neutralizing antibodies in early childhood;• the peak of population immunity is not reached until 15 years of age or older, however, in those who reside in localities where sanitation is good.
ENTEROVIRAL DISEASES In regions with a relatively high level of sanitation, urban dwellers are apt to become immune earlier than those who live in rural areas, probably as a result of the relative crowding. Evidence of contact with poliomyelitis virus appears at a younger age in low-income groups than in those whose financial status is good; this may merely reflect differences in crowding and sanitation. In some but not all parts of the world, certain racial groups appear to be more susceptible to the disease than others. Until about 30 years ago, poliomyelitis was most common in preschool children. Since then, however, it has been occurring more frequently in older age groups; in some recent epidemics, 25 to 30 per .cent of the patients have been older than 15 years. This increased incidence in adults is not due merely to the aging of the population or increased reporting of the paralytic and nonparalytic cases but is probably related to a decreasing rate of exposure to the virus, associated with a general improvement in socioeconomic status. Young children are still affected more often than adults.