After infection with the neurotropic CAM/RBH measles virus (MV) strain, newborn Lewis rats succumb to an acute necrotizing encephalopathy. Passive transfer of neutralizing monoclonal antibodies directed against MV hemagglutinin prevented this disease process. Instead, either an antibody-induced acute or subacute measles encephalitis developed after a prolonged incubation period with a restricted expression of MV structural proteins. The molecular biological analysis of MV gene expression in brain tissue of rats treated with MV-neutralizing antibodies revealed a transcriptional restriction of viral mRNAs, particularly for the envelope proteins, leading to a steep expression gradient. Based on in situ hybridization, it was concluded that the efficiency of transcription of viral genes at the single-cell level is reduced compared with that of controls. Passive immunization with monoclonal antibodies directed against other MV structural proteins proved to be ineffective. Similar results were obtained in MV-infected weanling Brown Norway rats. These rats developed a clinically silent encephalitis in the presence of high titers of neutralizing antibodies. In such animals, a pronounced attenuation of the viral gene transcription was observed. These findings indicated that neutralizing antibodies directed against a restricted set of specific antigenic sites on the viral hemagglutinin protein expressed on cell membranes exert a modulating effect on the viral gene expression at the level of transcription. This phenomenon contributes to the switch from the acute cytopathic effect to a persistent infection in the central nervous system.
In recent years, there has been a remarkable increase in measles cases among preschool and secondary school children in Turkey, as in many other countries. The seroconversion and coverage rates of measles vaccine should therefore be evaluated in order to obtain data that could be used to determine the vaccination policy for Turkey. Measles immunity status was studied by an enzyme-linked immunosorbent (ELISA) test determining the anti-measles IgG antibody levels. Measles specific IgG antibodies were found to be positive in 77.88% of the entire study group of 800 children aged 11 months to 12 years, while 21.25% had negative sera. Seven (0.87%) subjects had borderline results. The results of this study indicate the need to administer a second dose of measles vaccine, preferably at 18 months of age concomitant with other vaccines. This vaccination policy, together with an increase in the extent of immunization coverage, may help to achieve the World Health Organization's (WHO) target of the complete eradication of measles.
A serologic survey was made in 15 health unit areas, testing some 5000 individuals in the age groups 4 to 6, 11 to 13, 15 to 17 and 23 to 45 years. Two types of serious deficiency were found. Only 65% of children 4 to 6 years old had antibodies to all three types of poliovirus, the antibodies being due almost entirely to immunization with Salk vaccine. Even in children who had had six or more doses only 74% had antibodies to the three types. The high percentage of students 11 to 13 and 15 to 17 years old with poliovirus antibodies can be attributed largely to natural infection and to Sabin vaccine in the mass campaign of 1962, as well as to Salk vaccine. In children who had received Sabin vaccine as well as Salk vaccine a very high level of immunity was found. The immunity of the school-age population will decline to an insufficient level unless Sabin vaccine is used after immunization with Salk vaccine. Of children 4 to 6 years old 18% had no diphtheria antitoxin and 6% had no tetanus antitoxin. Even in those who had had six or more doses of the antigens 5% had no diphtheria antitoxin and 1 to 2% had no tetanus antitoxin. This apparently refractory state is probably due to the use of unadsorbed toxoids, and it is clear that adsorbed toxoids should be used. In the adults, diphtheria antitoxin was found in only 55% and tetanus antitoxin in only 38%.
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In Sweden, a two-dose programme of vaccination against measles, mumps and rubella (MMR) was introduced in 1982 and the target groups were children aged 18 months and 12 years. In 1993 the first age group of 12-year-olds that were vaccinated with MMR at 18 months will appear. The majority of the 12-year-old vaccines for many years, however, had already been vaccinated against measles and the MMR measles component was thus a booster dose. As the benefit of a booster dose against measles has been questioned, this was studied in a group of 163 12-year-old children, 122 of whom had been vaccinated against measles as young children. Of the 41 unvaccinated children, 23 had a history of clinical measles. The mean neutralizing titre level of the earlier vaccinated children, prior to the booster, was lower than that of the naturally immune children (reciprocal titre level 8 versus 20). After the booster the corresponding titre levels were 13 and 23. Among the seronegative children receiving their first dose, this figure amounted to 14. A moderate rise in titre was seen in those with low prevaccination titres. As the antibody protection afforded by vaccination was slightly lower than that of natural infection, even after a booster, follow-up studies must be recommended to evaluate the long-term protection of both a single and a two-dose programme.
In 1982, a 2-dose regimen was introduced in Sweden for the combined vaccination against measles, mumps and rubella (MMR) in children aged 18 months and 12 years. In 1993, blood samples from 378 12-year-old children, i.e. the first age-group receiving a MMR booster, were collected prior to and 2 months after the vaccination. 82% had a certificate of a previous measles (M) or MMR vaccination (group I). The remainder was classified as children with 'no documentation' (group II). In group I, 5 (1.5%) lacked demonstrable antibodies to measles prior to the booster; in group II this figure was 39%. The pre-booster antibody pattern was similar in M vaccinees and MMR vaccinees. After the vaccination, 1 of the 378 children was seronegative. In both groups, children with low pre-vaccination levels responded with a titre rise, in accordance with a similar study 6 years earlier.