oa South African Medical Journal - Poliomyelitis in South Africa - studies in an urban native township during a non-epidemic year
It has been noted that Europeans are more liable to Paralytic poliomyelitis than the Bantu and that the Majority of paralytic cases in the Bantu occur in the 0-5 Year age group. It has been suggested that the relatively Low incidence of paralytic poliomyelitis in the Bantu and its main incidence on the lowest age group is to some extent due to an immunity of the older age groups acquired as a result of previous infection. This hypothesis is supported by serological surveys which have shown that in all age groups a greater proportion of Bantu than Europeans have neutralizing antibodies against the Lansing strain of poliomyelitis virus. To determine whether this serological immunity is developed in response to an infection, a group of Bantu Infants born and living in a Native location have been examined for the virus of poliomyelitis at regular monthly intervals. The first test was carried out within two weeks of birth. Of 29 infants selected 16 have remained under observation for the first full year of this study. Of these 16 infants, four (25%) were proved to be infected with the virus of poliomyelitis during this time. One contracted the infection in the fourth month, one in the eighth month and two in their twelfth month. The virus isolated from the infant in its fourth month proved not to be of the Lansing type. One of the other three was proved to be of the Lansing type. The remaining two were presumably also of the Lansing type. The infant infected with the non-Lansing virus did not subsequently develop antibodies against the Lansing strain. Two of the infants infected with the Lansing type of virus developed Lansing antibodies following their infection. It appears, therefore, that the Lansing antibodies demonstrable in the sera of older Bantu children develop as a result of a previous, usually silent infection. With this type of virus, it is significant that four of 16 Infants (25%) were proved to be infected with the virus of poliomyelitis during a non-epidemic year, in which no cases of clinically recognizable poliomyelitis occurred amongst the 18,200 inhabitants of this Native location. None of the four infants who were proved to be infected had signs or symptoms suggestive of poliomyelitis at the time of their infection with the virus.
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