Abstract:
Influenza virus is a negative-sense segmented RNA virus belonging to the family of
Orthomyxoviridae. The circulating human influenza viruses i.e., influenza A virus (subtype H1, H3) and
influenza B virus can be identified by multiplex RT-PCR which is specific to the hemagglutinin (HA)
genes. The amplified products of influenza A virus subtype H1, H3 and influenza B virus were 944 bp,
591 bp and 767 bp, respectively. The objectives of this study were: 1) To evaluate the multiplex RTPCR
method for detection influenza A virus (H1, H3) and influenza B virus from clinical specimens; 2)
To study influenza virus types and subtypes in patients with acute upper respiratory tract infection by
isolation and multiplex RT-PCR; 3) To determine sensitivity and specificity of multiplex RT-PCR in
comparison to isolation; 4) To study the susceptibility of influenza virus reference strains to amantadine
by hemagglutination inhibition assay.
Sensitivity of multiplex RT-PCR for detection of influenza A/New Caledonia/20/99 (H1N1)-like
virus, A/Moscow/10/99 (H3N2)-like virus and B/Hong Kong/330/2001-like virus were 10
HAU/reaction for each strain. Multiplex RT-PCR was used to detect influenza virus in 221 throat swab
samples collected from Out-patients with acute upper respiratory tract infection during May 2002 to
March 2003 at Health Center 17, Bangkok and Clinic of Department of Pediatric, Siriraj Hospital. Of
221 throat swab samples, 50 (22.62%) were found positive for influenza viruses by multiplex RT-PCR.
The detected influenza viruses were 45 (20.36%) influenza A viruses (H3) and 5 (2.26%) influenza B
viruses. The isolation rate of influenza virus was 21.26% (47/221). The isolates were 30 (13.57%)
A/Moscow/10/99 (H3N2)-like virus and 17 (7.69%) B/Hong Kong/330/2001-like virus. In comparison
to isolation, sensitivity and specificity of multiplex RT-PCR for detection of influenza virus were
55.32% and 86.21%, respectively. The sensitivity and specificity of multiplex RT-PCR for detection of
influenza A (H3N2) virus were 70% and 86.21%, respectively and for detection of influenza virus B
was 29.41% and 100%, respectively. We conclude that multiplex RT-PCR can be used for detection,
identification of type and subtype of human influenza viruses in respiratory samples. Multiplex RTPCR
is a convenient, rapid and useful method for detecting the genome of replicative incompetent
influenza viruses.
Susceptibility of influenza virus to amantadine was performed by hemagglutination inhibition
assay. The 50% cytotoxicity concentration (CC50) of amantadine was 174.65 μg/ml. Concentrations of
50 and 12.5 μg/ml were 100% inhibitory concentration (IC100) of amantadine to influenza A/New
Caledonia/20/99 (H1N1)-like virus and A/Moscow/10/99 (H3N2)-like virus, respectively. Amantadine
could not inhibit infectivity of influenza B virus. This preliminary study demonstrated that
hemagglutination inhibition assay, a simple method, could be used for testing anti-influenza drug
susceptibility.