EPIDEMIOLOGICAL SURVEY OF THE LEVEL AND SIGNIFICANCE OF ANTIBODIES TO POLIOMYELITIS VIRUS IN KADUNA STATE, NIGERIA

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Date
2000-10
Authors
AMINU, MARYAM
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Abstract
While data is available on the incidence of poliomyelitis and the vaccination coverage against the disease in Nigeria, there is a dearth of information on the herd immunity and the immune status of vaccinees. This study was therefore, undertaken in 1999/2000 to determine the immune status to poliomyelitis in primary school children aged 1-11 years in Kaduna State, Nigeria, an area where high vaccination coverage has been reported. Two schools each were selected in eleven randomly selected local government areas (LGAs) of the state. Questionnaires were sent through the teachers to the parents of randomly selected children from these schools in order to obtain information concerning these children's vaccination status to poliomyelitis. Blood samples were collected from 1200 respondents, but a total of 1087 sera from which clear and adequate quantity of sera could be obtained were analyzed according to LGA, age, sex and vaccination status. Serum levels of poliovirus neutralizing antibodies were investigated in the sera using poliovirus types 1, 2 and 3 in HEp-2 cells. The results of the analysis of questionnaires indicated that, of the 161 (14.8%) children with no history of vaccination, 77 (47.8%) had demonstrable antibodies to poliovirus. And of the 926 (85.2%) children with a history of vaccination, 128 (13.8%) had no demonstrable antibodies to poliovirus. These results show that there was poor correlation between the history of vaccination and the presence and absence of antibody in the children, implying that vaccination history might not be an accurate index of immunity. Children with antibody titre <1:10 were considered seronegative (susceptible). Antibody titration results indicated that 42.2% of the children had ix antibodies to the three serotypes of poliovirus, 19.5% had no anti-poliovirus antibodies at all, and 65.5, 71.4 and 66.7% had antibodies to poliovirus types 1, 2 and 3 respectively. A total of 80.5% of the children had demonstrable antibodies to one or more serotypes of poliovirus. The proportion of potentially susceptible children to one or two poliovirus serotypes was 57.8%, while 34.5, 28.6 and 33.3% of the children were potentially susceptible to poliovirus types 1, 2 and 3 respectively. Statistical analysis of the results by Chi-square tests at P<0.05 showed that the prevalence varied significantly in the LGAs, with the highest in Kagarko LGA and the lowest in Zaria LGA. Antibody prevalence was higher in the older age group (7-11 years) with lower geometric mean titre (GMT) values than the younger age group (1-6 years) that had higher GMT values. No significant difference was observed in the antibody distribution by sex. Seropositive rates were higher in children who received five doses of oral polio vaccine (OPV) and the observed difference in the prevalence rates by number of vaccine doses received was highly significant. The results of this study also confirmed the known higher immunogenicity of poliovirus type 2 with respect to the other two types. The level of protection against the three poliovirus serotypes in Kaduna State is unacceptably low (42.2%), indicating low herd immunity to poliomyelitis. This finding is difficult to explain in view of the high (140%) level of vaccination coverage reported by Kaduna State Ministry of Health. It is concluded that the potential risk of an outbreak of poliomyelitis in the susceptible population in Kaduna State is real. This necessitates the need for improved vaccination efforts and the monitoring of vaccination efficacy by serological survey of the vaccinated population.
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A THESIS SUBMITTED TO THE POSTGRADUATE SCHOOL, AHMADU BELLO UNIVERSITY, ZARIA, IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE MICROBIOLOGY DEPARTMENT OF MICROBIOLOGY, FACULTY OF SCIENCE, AHMADU BELLO UNIVERSITY, ZARIA -NIGERIA OCTOBER, 2 0 00 i
Keywords
EPIDEMIOLOGICAL,, SURVEY,, LEVEL,, SIGNIFICANCE,, ANTIBODIES,, POLIOMYELITIS,, VIRUS, KADUNA STATE,
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