Isolation and characterization of influenza C viruses in the Philippines and Japan

Area of Science:

• Virology
• Epidemiology

Background:

• Influenza C virus (ICV) is a significant cause of human respiratory infections.
• Limited data exists on ICV circulation and genetic diversity in Southeast Asia.

Purpose of the Study:

• To report the first isolation and characterization of ICV in the Philippines.
• To investigate the genetic relationship of ICV strains from the Philippines and Japan.

Main Methods:

• Viral isolation from clinical specimens using Madin-Darby canine kidney (MDCK) cells.
• Antigenic analysis using monoclonal antibodies against the hemagglutinin-esterase (HE) glycoprotein.
• Phylogenetic analysis of the HE and internal genes.

Main Results:

• Fifteen ICV strains were isolated from children with severe pneumonia and influenza-like illness (ILI) in the Philippines (2009-2013).
• Seven ICV strains were isolated from children with acute respiratory illness (ARI) in Japan (2008-2013).
• All 19 strains were antigenically similar to the reference strain C/Sao Paulo/378/82 (SP82).
• Phylogenetic analysis of the HE gene placed Philippine and Japanese strains into distinct clusters within an SP82-related lineage, diverging around 1993.
• Phylogenetic analysis of internal genes indicated reassortment events in both Philippine and Japanese strains, with distinct internal gene compositions.

Conclusions:

• This study reports the first isolation of ICV in the Philippines, expanding knowledge of its geographic distribution.
• Philippine and Japanese ICV strains share a common ancestor and belong to the SP82-related lineage.
• Evidence suggests distinct reassortment events contributed to the emergence of these ICV strains, highlighting viral genetic diversity.