Virological surveillance in Africa can contribute to early detection of new genetic and antigenic lineages of influenza viruses

Abstract

Introduction: In Africa, the burden of influenza is largely unknown since surveillance schemes exist in very few countries. The National Institute of Hygiene in Morocco implemented a sentinel network for influenza surveillance in 1996.

Methodology: Epidemiological and virological surveillances were established and influenza viruses circulating in Morocco were characterised. Four practice-specific indicators were collected during the 1996-1997 season and nasopharyngeal swabs were collected from patients with an influenza-like illness during a three-year period (between 1996 and1998). Laboratory diagnosis was done by viral isolation. The isolates were characterized by hemagglutination- and neuraminidase-inhibition assays and by sequencing the hemagglutinin gene and phylogenetic analysis.

Results: Among a total of 673 specimens, 107 (16%) were positive for influenza virus. Seasonal influenza strains were isolated from November to February. Antigenically, A(H1N1), A(H3N2) and B isolates were related to the vaccine strains. Genetically, one 1996/97 isolate A/Rabat/33/96 and the 1997/98 A(H3N2) isolates clustered with the new drift variant A/Sydney/5/97, a vaccine component of the 1998/99 season.

Conclusions: These results indicate a seasonal circulation of influenza in Morocco concentrated between November and February. Further, the results demonstrate the importance of including the maximum number of countries in influenza surveillance to contribute to the definition of the influenza vaccine composition.