Influenza viruses are RNA viruses belonging to the Orthomyxoviridae family. Influenza A and B are the most important human pathogens causing annual epidemics associated with significant morbidity and mortality. The Influenza A and Influenza B genomes consists of 8 negative strand RNA segments separately encoding three polymerase subunits, a haemagglutinin (HA), neuraminidase (NA), nucleoprotein, two matrix proteins and two non-structural proteins.
Reassortment of HA and NA genes of Influenza A within the animal reservoir permit major antigenic changes leading to worldwide pandemics. Influenza B viruses lack animal reservoirs, however antigenic variation is still significant.
Highly pathogenic avian influenza (HPAI) H5N1 caused by certain subtypes of Influenza A virus in animal populations, particularly chickens, poses a continuing global human public health risk.
To date there is no convincing evidence that sustained transmission of HPAI has occurred between humans. However the virus is mutating constantly and it is possible that a transmissible strain will evolve. Mortality rates in recognised human infections have been high which raises the spectre of pandemic disease. WHO and CDC have therefore recommended enhanced surveillance for suspected H5N1 human cases especially among travellers with unexplained severe respiratory illness who have come from H5N1 affected countries. Early diagnosis and strict isolation of patients are essential to any containment strategy.
The Influenza Panel consists of 7 (8 when H7 is included) real time RT PCRs which run concurrently under an identical protocol. These assays are:-
|
Influenza A matrix gene |
Identifies all influenzas A |
|
Influenza B NS1 gene |
Identifies all influenzas B |
|
Influenza A type specific H1 |
Identifies H1 haemagglutinin of influenza A |
|
Influenza A type specific H3 |
Identifies H3 haemagglutinin of influenza A |
|
Influenza A (avian) type specific H5a |
Identifies H5 haemagglutinin of influenza A |
|
Influenza A (avian) type specific H5b |
Identifies H5 haemagglutinin of influenza A |
References
1. Zhang W and Evans DH. Detection and identification of human influenza viruses by the polymerase chain reaction.J. Virological Methods.33;165-189.1991
·2. National Laboratory Guidelines for Pandemic Influenza. NZ Ministry of Health http://www.moh.govt.nz
3. CDC Realtime RTPCR (rRT-PCR) Protocol for detection and characterization of Influenza (version 2007
4. KY Yuen, PKS Chan et al. Clinical features and rapid viral diagnosis of human disease associated with avian influenza A H5N1 virus. The Lancet 1998,351:467-471