Abstract
The newly emerging, highly pathogenic avian influenza (HPAI) H5N8 virus of clade 2.3.4.4 was recently detected in wild birds and domestic poultry in Egypt in the 2016/2017 winter season. Vaccination based on commercial H5 vaccines is used as an essential control strategy in Egyptian poultry. Here, we studied the efficacy of the eight most common commercial H5 poultry vaccines in the Egyptian market and compared them with an experimental vaccine based on the Egyptian LPAI H5N8 virus that was prepared by using reverse genetics. The experimental vaccine and Re-5 commercial vaccine were able to completely protect chickens and significantly reduce virus shedding. Our results indicate that most of the commercial poultry H5 vaccines used in the present study were ineffective because the seed viruses in these vaccines are genetically distinct from the H5N8 viruses currently circulating in Egypt. Although some of the commercial vaccines protected chickens from mortality, they failed to prevent chickens from shedding the virus. Accordingly, we recommend updating and reinforcing the H5N8 prevention and control strategies in Egypt. The vaccination strategy should be reconsidered based on currently circulating viruses.
Highlights
Since 2006, clade 2.2.1 of highly pathogenic avian influenza (HPAI) H5N1 viruses has been widely circulating in Egypt, causing massive economic losses in the Egyptian poultry industry[1]
The maternal antibodies at one week of age cross-reacted with H5N1, H5N8, and H9N2 viruses, with log[2] mean titers of 4.5, 1.7, and 3, respectively
According to the manual for vaccine evaluation by the World Organization for Animal Health (OIE), an effective poultry vaccine should protect at least 80% of vaccinated chickens from death and should reduce viral shedding after a challenge infection
Summary
Since 2006, clade 2.2.1 of highly pathogenic avian influenza (HPAI) H5N1 viruses has been widely circulating in Egypt, causing massive economic losses in the Egyptian poultry industry[1]. The control plan included establishing biosafety and biosecurity measures in poultry farms, increasing public awareness through the media, culling infected poultry, restricting poultry movement between governorates, and implementing emergency vaccination[2,3]. Despite these efforts, the H5N1 virus became enzootic, and the virus evolved into 3 antigenically distinct subclades (2.2.1.1, 2.2.1.1a, and 2.2.1.2)[4]. We assessed the efficacy of eight commercial vaccines based on different lineages of AI/H5 viruses against the newly emerging HPAI H5N8 virus in Egypt
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