Page 8 - Avian Virology: Current Research and Future Trends

Avian Influenza Virus

Daniel R. Perez*, Silvia Carnaccini, Stivalis Cardenas-Garcia, Lucas M. Ferreri, 1
Jefferson Santos and Daniela S. Rajao*

Department of Population Health, Poultry Diagnostic and Research Center, College of Veterinary Medicine, University of
Georgia, Athens, GA, USA.
*Correspondence: dperez1@icloud.com and daniela.rajao@uga.edu
https://doi.org/10.21775/9781912530106.01

Abstract based on the antigenic differences on the virus’ two major surface
Influenza is one of the most devasting respiratory diseases of poul- glycoproteins, haemagglutinin (HA) and neuraminidase (NA).
try. Avian influenza (AI) is a viral disease caused by influenza A To date, 16 HA subtypes (H1–H16) and nine NA subtypes
viruses (IAVs) that affects the respiratory, digestive, and nervous (N1–N9), in multiple combinations, have been identified in birds
systems of several bird species, including domestic poultry and around the world (Alexander, 2000). The past couple of decades
wild aquatic birds. The World Organization for Animal Health have seen a sharp increase in the number of AI outbreaks, which
(OIE) has included highly pathogenic avian influenza (HPAI) as have led to devastating economic losses to the poultry industry
a List A notifiable disease. The past couple of decades have seen due to direct effects of the infection, as well as trade limitations
a sharp increase in the number of AI outbreaks, which have led and public opinion repercussions. AI also has public health
to devastating economic losses in the poultry industry as a direct implications, in particular zoonotic strains that have emerged
result of infection, as well as trade limitations and public opinion in Southeast Asia with the ability to cause lethal infections and,
repercussions. AI also has public health implications, in particular therefore, are of great pandemic concern.
zoonotic strains that have emerged in southeast Asia with the The World Organization for Animal Health (OIE) has
ability to cause lethal infections in humans and, therefore, are of included highly pathogenic avian influenza (HPAI) as a List A
great pandemic concern. Over the past two decades, particularly notifiable disease (OIE, 2015). From a disease management and
with the development of reverse genetics systems for influenza reporting perspective, the OIE defines ‘avian influenza’ as an
viruses, we have learned a great about the mechanisms involved infection of poultry and other birds, including wild birds, caused
in pathogenesis and transmission of avian-origin influenza viruses by any IAV with high pathogenicity (HPAI) or by any IAV of H5
in birds and humans. Avian influenza surveillance efforts around or H7 subtypes when detected in poultry. HPAIV are character-
the world have provided the discovery of novel hotspots of influ- ized by an intravenous pathogenicity index (IVPI) greater than
enza activity in wild birds as well as novel influenza A viruses in 1.2 (≈ 75% mortality) in chickens. Infections caused by other
fruit bats and have greatly improved our understanding of the subtypes (H1–H4, H6, and H8–H16) that do not meet the
ecology and the evolution of these viruses. Novel and upcoming IVPI criteria are simply referred to as influenza A (N. Zhang et
sequencing technologies are allowing pen-side diagnostics and al., 2014). In 2017, a new nomenclature was added to the OIE
rapid phylogenetic characterization of influenza viruses from list of diseases to refer to HPAIV infection of species other than
a variety of sources and animal species. Improvements in vac- poultry as ‘non-poultry’, including wild birds (OIE, 2017). In this
cine technologies and vaccination regimens are paving the way chapter, the term LPAIV refers to all IAVs of low pathogenicity
for more efficient control of AI in poultry. Yet many challenges regardless of subtype, while the terminology HPAIV is used for
remain. It is the objective of this chapter to provide an overview any IAV with high pathogenicity. Here, we introduce a historical
of what is known about AI and its implications for animal and perspective of avian influenza and its causative agent, the influ-
human health. enza A viruses. We dive into the virus itself, its molecular features
and effects on the host cell and discuss the disease in natural and
non-natural avian hosts. Finally, we provide an overview of the
Introduction current tools for diagnosis, prevention and control and highlight
Influenza is one of the most devasting respiratory diseases of the economic and animal and public health importance of these
poultry. Avian influenza (AI) is a viral disease caused by influenza viruses. We have made an effort to cover as much as possible and
A viruses (IAVs) that affects the respiratory, digestive, and nerv- to be as thorough as possible to cite the most relevant literature,
ous systems of several bird species, including domestic poultry although we realize that we cannot reference every single piece
and wild aquatic birds. IAVs are further divided into subtypes of work. We apologize to the authors whose work has not been