Poliomyelitis: its highly invasive nature and narrow stream of infection in a community of high socioeconomic level

Current status of poliovirus infections

Two scientists who played leading roles in the conquest of poliomyelitis died recently. In 1954, Jonas Salk provided the first licensed polio vaccine, the formalin (and heat)-inactivated virus. Albert Sabin gave us the attenuated live virus vaccine, which was licensed in 1962. This paper takes the reader through the history of the disease, including its pathogenesis, epidemiology, vaccines, and future directions. The emphasis is on vaccines, for it seems that with proper vaccination the number of new cases is falling dramatically. It is hoped that by the year 2000, we will accomplish the goal of the World Health Organization of "a world without polio." Then, because there is no animal reservoir, we can seriously discuss when and how to eliminate the need for vaccination and ultimately destroy our stocks of poliovirus.

Abortive poliomyelitis or minor illness as a clue to genetic susceptibility

The model of genetic susceptibility to poliomyelitis has been used to examine minor illness caused by poliovirus infection. It is suggested that persons who are genetically susceptible but who have not converted to phenotypic susceptibility are those who develop minor illness. The overall rates of the sum of paralytic and minor illness are close to the predicted 26%. For families with a case of illness, the prediction that 58%--71% of the children become ill has been examined. The rates of illness in children of different ages in the same families should be similar. Data from a number of epidemics is shown to be consistent with the predictions of the model.

Sociological factors in the spread of variola minor in a semi-rural school district

The mechanism of spread of an epidemic of variola minor (alastrim) occurring in 1956, in Vila Guarani, a semi-rural school district of the City of São Paulo, Brazil, is examined. Cases were grouped according to time and space relationships corresponding to either a household or a school class, as once variola minor was introduced into a household or a school class spread was independent of occurrences in neighbouring social units. The constant occurrence of a single introduction in school classes and households implied that the chance for transmission of the disease outside the homes or the school was very small. The secondary attack rate was higher in households than in school classes. Twenty households with cases had more pre-school children and school children and a lower vaccination level than twenty-two neighbouring households without cases but also including one or more persons who were known to have had personal contacts with patients.

Examination of the chain of contagion clearly shows that spread in the school was directly and indirectly responsible for the majority of cases in the epidemic, for the peak of the epidemic curve and for the extent of topographical spread of the epidemic. This predominant role of the school was accentuated by incomplete preventive measures (vaccination campaign and isolation of patients) applied late in the epidemic and it is attributed to the following facts, (a) There was a single school in the district, and school children were thus concentrated, (b) The school was the only place of the district where persons living in different neighbourhoods had regular, repeated contacts, (c) The great majority of school children had had no previous variola and many had no vaccination scar, (d) The social activities of school children gave them the highest potential as transmitters of variola minor.

The incidence of infection with poliovirus and other viruses in cases of aseptic meningitis (nonparalytic poliomyelitis) in Sheffield in 1954

1. Sixteen cases of paralytic poliomyelitis and twenty-four cases of aseptic meningitis (‘non-paralytic poliomyelitis’) occurring in the Sheffield area were studied clinically and by virological methods.

2. Poliovirus was isolated from thirteen of the sixteen cases of paralytic poliomyelitis and from three of the twenty-four cases of aseptic meningitis. In another two of the cases of paralytic poliomyelitis and another six of the cases of aseptic meningitis serological evidence of poliovirus infection was obtained.

3. Serological evidence of Coxsackie virus infection was found in four of the cases of aseptic meningitis; but in one there was also clear-cut evidence of poliovirus Type 3 infection, and in another it seemed that the infection was contracted in hospital. Evidence of Coxsackie virus infection was also obtained in five cases of paralytic poliomyelitis.

4. Serological evidence of Adenovirus infection was found in one case of aseptic meningitis.

5. No acceptable evidence was found of infection with Columbia SK or related viruses, or with the virus of lymphocytic choriomeningitis.

6. From one patient with aseptic meningitis an unidentified virus was isolated.

We wish to thank Dr J. Kennedy for permission to study patients and Prof. C. P. Beattie and Prof. C. H. Stuart-Harris for help in preparing the manuscript.