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