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Serological evidence for influenza virus activity in Nigeria (1985-1987)
O D Olaleye1, S A Omilabu, A O Olabode
1Department of Virology, College of Medicine, University of Ibadan, Nigeria.
Insights
Influenza A virus circulated widely in Nigerian children between 1985-1987, with 90% showing prior exposure. Influenza B virus showed lower activity. Continuous circulation poses epidemic risks, especially in populations with low immunity.
Area of Science:
- Virology
- Epidemiology
- Pediatrics
Background:
- Influenza virus activity in pediatric populations in Nigeria was not well-documented.
- Understanding local influenza epidemiology is crucial for public health interventions.
Purpose of the Study:
- To determine the activity and serotypes of influenza viruses circulating among children in Nigeria between 1985 and 1987.
- To assess the serological evidence of influenza virus infection in children presenting with respiratory illnesses.
Main Methods:
- Paired sera from 42 children with respiratory diseases were collected at the University College Hospital, Ibadan.
- Haemagglutination-inhibition (HI) tests were performed to determine antibody levels against various influenza virus serotypes.
Main Results:
- Ninety percent of children showed serological evidence of prior contact with influenza A virus subtypes.
- Only 24% tested positive for influenza B virus antibodies.
- Seroconversion to influenza A strains (H3N2 and H1N1) was observed in 22 children, with H3N2 A/Mississippi 1/85 being the most frequent.
- Influenza cases occurred year-round, with peaks during the rainy and harmattan seasons.
Conclusions:
- Continuous circulation of influenza viruses, particularly influenza A, was evident in the study area.
- The findings highlight the potential danger of influenza epidemics in Nigeria, especially in populations with low immunity.
Abstract:
A study to determine the activity of influenza virus among the children population was undertaken between 1985 and 1987 in Nigeria. Paired sera were obtained from children presenting with respiratory diseases at the children emergency and outpatient clinics of the University College Hospital, Ibadan. Forty-two paired sera were examined by haemagglutination-inhibition test to determine HI antibody level of the patients to different serotypes of influenza virus. Ninety percent of the children showed serological evidence of previous contact with influenza A virus subtypes while only 24% were positive when tested against influenza B virus. Twenty-two of the 42 children tested seroconverted to influenza A virus strains while only 2 seroconverted to influenza B virus strain used. Out of the 22 children that seroconverted to influenza A virus, 14 were due to H3N2 A/Mississippi 1/85, 4 to H3N2 A/Leningrad 360/86 and 2 each seroconverted to H1N1 A/Chile 1/83 and H1N1 A/Taiwan 1/180. Two other individuals showed serological conversion to either H3N2 A/Mississippi 1/85 and H1N1 A/Chile 1/83 or H3N2 A/Mississippi 1/85 and H1N1 A/Taiwan 1/86. While cases were seen throughout the year during the period under review, more cases occurred during early (April-May) to peak raining season (September) and during harmattan period (November) in Ibadan area where the study was conducted. It is evident from this study that continuous and synchronous circulation of influenza viruses occur in this environment. There is therefore danger of influenza epidemic under depressed immunity and if the virus is introduced into population with low level of immunity in other parts of the country.