Molecular characterization of the surface glycoproteins of influenza B viruses isolated in Kenya from 2011-2012

Abstract

Influenza B viruses can cause severe respiratory disease and occasionally epidemic outbreaks. Vaccination is the mainstayof prevention and reduces disease impact. Vaccine efficacy is determined mainly by the degree of haemagglutinin (HA) antigen matching between the vaccine and circulating strains. Neuraminidase inhibitor (NI) antivirals are important for prophylaxis and treatment of severe cases of influenza disease. However, mutations in the two major surface proteins, hemagglutinin (HA) and neuraminidase (NA) can cause the virus to escape host defenses leading to failure of the host immune system to recognize the viruses as well as failure to antiviral therapy. Due to these mutations, antibodies produced against these viruses may become ineffective against anew emergent viral strain or the changes may lead to antiviral therapy failure. This is further complicated by the existence of the two distinct lineages.- B/Victoria/2/87-like viruses and B/Yamagata/16/88-like viruses- that continue to co-circulate globally in the human population. These viruses exist as independent lineages and antibodies against one lineage are generally not cross-protective. The World Health Organization (WHO)Strategic Advisory Group of Experts which issues vaccine component recommendations to be included in the annual influenza vaccine formulations recently revised the seasonal vaccine composition from atrivalent to an alternative containing quadrivalent components. Thus, information about lineage of circulating influenza B viruses is important for determination of the appropriateness of either a trivalent or a quadrivalent vaccine composition. The objective of this study wasto investigatethe molecular characteristicsof influenza B viruses that circulated in Kenya from 2011-2012 and the appropriateness of antiviral therapies including the WHO vaccine recommendationsusing bioinformatic analyses on nucleotide sequences of NA and HA glycoproteins of selected virus isolates. Nasopharyngeal swab specimens obtained from patients meeting WHO case definition for influenza-like-illness (ILI) were screened by real-time PCR for influenza B viruses. Positive samples were inoculated onto monolayers of Madin-Darby Canine Kidney (MDCK) cells and the lineages of the isolates determined by hemagglutination inhibition assay (HAI). To confirm the lineages and susceptibility to neuraminidase inhibitor drugs, HA and NA gene segments of selected isolates were amplified by conventional PCR, sequenced and analyzed using bioinformatic tools. The isolates were also tested for phenotypic antiviral susceptibility. The findings of this study showed that influenza B viruses that circulated in the study period were B/Brisbane/60/2008-like belonging to the B/Victoria/2/87 lineage. Thus the WHOrecommended vaccine for both the Southern and Northern hemispheres was appropriately matched in the influenza B component and was protective in Kenya. In addition, the influenza B viruses in circulation were all susceptible to Oseltamivir and Zanamivir drugs thus indicating the appropriateness of these drugs used in the treatment of Influenza B in Kenya. No positive selection was observed amongst the codons of HA and NA genes in the Kenyan influenza B viruses. Reassortment was observed in the Kenyan influenza B viruses within the NA gene segment. This study has underscored the importance of sustained monitoring of drug susceptibility as well as the antigenic characteristics of the influenza viruses as a measure of epidemic preparedness. It has also shown that the WHO recommendations for vaccine and antiviral usage cover Kenya well and theMinistry of health should continue to implement these recommendations. Full genome sequencing of the Kenyan influenza B viruses that circulated during the study period is recommended to unravel the extent and probable consequences of the reassortments amongst these viruses.