Event Title First Global Alliance for Research on Avian Diseases (GARAD) Conference
Session Title Unknown
Event Date & Time On Mon, 29 Jun 2015 at 11:45:00 - 12:05:00
Venue Edmond J. Safra Lecture Theatre
Abstract Title HPAI H5N6 viruses in Vietnam
Authors Thanh Long To
Affiliations Natl. Ctr. for Vet. Diagnosis, Hanoi, Vietnam
Abstract Content

Avian influenza virus surveillance was carried out all the year round on clinical infected poultry and on those in live bird markets in Vietnam to monitor the circulation of highly pathogenic avian influenza (HPAI) H5 viruses. In 2014, the avian influenza outbreaks were caused by H5N1 and H5N6 subtype viruses. Specimens from clinically infected poultry and oropharyngeal swabs from those in live bird market were taken. Sequencing on RT-PCR positive samples was conducted to monitor the viral mutation. Virulent challenge experiments in vaccinated poultry were performed for choosing efficient vaccines against different clade viruses. In 2014, 36 provinces of Vietnam were found to be clinically infected with HPAI H5 viruses with different NA subtype including N1 and N6. Genetically, the HPAI H5 viruses fell in 3 clades, i.e. 2.3.2.1c; 1.1; 2.3.4 and 2 subtypes H5N1 (clade 1.1, 2.3.2.1c and 2.3.4) and H5N6 (clade 2.3.4). Of them, the H5N1 viruses, clade 2.3.2.1c were still widespread in all regions of Vietnam while the H5N1 viruses, clade 1.1 were present only in Southern part of Vietnam before March 2014. The H5N6 viruses of clade 2.3.4 were newly introduced into the North and the Central region since April 2014 and sporadically caused outbreaks in poultry. The H5N1 with the same clade 2.3.4 were detected earlier but only in surveillance samples. From the surveillance in live bird markets, there were about 15% - 30% of samples being positive with Influenza type A virus. Vaccine efficacy tests indicated that Re-5 and Navetvifluvac vaccines could provide good protection for chickens from all the virus clades 1.1; 2.3.2.1c and 2.3.4 whereas the Re-6 vaccine can only protect chickens from 2.3.2.1c virus challenge.

In conclusion, we submit that the recent H5N1/clade 2.3.2.1c viruses were the main cause of AI outbreaks in Vietnam. However, the number of cases positive with H5N6/clade 2.3.4 viruses that were increasing since april 2014 suggested that they might replace the H5N1/clade 2.3.2.1c viruses in the future. No existing vaccine could give protection to pountry against all detected, different clade viruses. It is recommended that a vaccine that could give protection to poultry against viruses of clade 2.3.2.1c and clade 2.3.4 should be used. The results also showed that the virus surveillence in live bird markets should be extended for LPAI viruses to know the potential reassortment between HPAI and LPAI viruses.