Pathogenicity of an H5N1 avian influenza virus isolated in Vietnam in 2012 and reliability of conjunctival samples for diagnosis of infection

Abstract

The continued spread of highly pathogenic avian influenza virus (HPAIV) subtype H5N1 among poultry in Vietnam poses a potential threat to animals and public health. To evaluate the pathogenicity of a 2012 H5N1 HPAIV isolate and to assess the utility of conjunctival swabs for viral detection and isolation in surveillance, an experimental infection with HPAIV subtype H5N1 was carried out in domestic ducks. Ducks were infected with 107.2 TCID50 of A/duck/Vietnam/QB1207/2012 (H5N1), which was isolated from a moribund domestic duck. In the infected ducks, clinical signs of disease, including neurological disorder, were observed. Ducks started to die at 3 days-post-infection (dpi), and the study mortality reached 67%. Viruses were recovered from oropharyngeal and conjunctival swabs until 7 dpi and from cloacal swabs until 4 dpi. In the ducks that died or were sacrificed on 3, 5, or 6 dpi, viruses were recovered from lung, brain, heart, pancreas and intestine, among which the highest virus titers were in the lung, brain or heart. Results of virus titration were confirmed by real-time RT-PCR. Genetic and phylogenetic analysis of the HA gene revealed that the isolate belongs to clade 2.3.2.1 similarly to the H5N1 viruses isolated in Vietnam in 2012. The present study demonstrated that this recent HPAI H5N1 virus of clade 2.3.2.1 could replicate efficiently in the systemic organs, including the brain, and cause severe disease with neurological symptoms in domestic ducks. Therefore, this HPAI H5N1 virus seems to retain the neurotrophic feature and has further developed properties of shedding virus from the oropharynx and conjunctiva in addition to the cloaca, potentially posing a higher risk of virus spread through cross-contact and/or environmental transmission. Continued surveillance and diagnostic programs using conjuntcival swabs in the field would further verify the apparent reliability of conjunctival samples for the detection of AIV.

Evolutionary dynamics of highly pathogenic avian influenza A/H5N1 HA clades and vaccine implementation in Vietnam

“…The emergence of newly introduced clade 2.3.2 and further evolution of clade 2.3.2.1 into 2.3.2.1a/b was noted in the North; and the continual evolution of clade 1.1 of the Cambodian lineage into 1.1.1 and 1.1.2 occured in the South [42,43,47,64]. Re-1 and Re-5 vaccines were in use.…”

“… In 2010: This year was the time for the new clades emerged, and alternatively, for the appearance of periodically existed viruses [ 42 ]. The emergence of newly introduced clade 2.3.2 and further evolution of clade 2.3.2.1 into 2.3.2.1a/b was noted in the North; and the continual evolution of clade 1.1 of the Cambodian lineage into 1.1.1 and 1.1.2 occured in the South [ 42 , 43 , 47 , 64 ]. Re-1 and Re-5 vaccines were in use.…”

Impact of vaccination on infection with Vietnam H5N1 high pathogenicity avian influenza virus in hens and the eggs they lay

“…These Vietnamese variants possess distinct antigenic properties and virulence [7,9] which enable them to escape immunity with some of the currently used vaccines [8,41,42]. A recent study reported suboptimal protection against clade 2.3.2.1 H5N1 HPAIV from Vietnam in ducks vaccinated with commercial poultry vaccines, with a substantial proportion of ducks having prolonged virus shedding and, in some cases, even mortality [42].…”

Corneal Opacity in Domestic Ducks Experimentally Infected With H5N1 Highly Pathogenic Avian Influenza Virus

“…6 These findings suggest that H5N1 HPAI virus can be present on the ocular surface of domestic ducks and wild swans infected with the virus. 5,6 One of the unique features of Asian-lineage H5N1 HPAI virus is that it can cause severe clinical signs to waterfowl, which have been considered natural reservoirs of avian influenza virus in nature. 39 Aside from rare exceptions, 7 clinical disease severity by low pathogenic or HPAI virus infection has been considered very mild in ducks until the emergence of H5N1 HPAI virus virulent to waterfowl.…”