Page 32 - Avian Virology: Current Research and Future Trends

Avian Influenza Virus | 25

in 16 countries in Asia, Africa, and Europe (and a traveller from Perspective
Canada), of which 454 were lethal (CDC, 2015; WHO, 2018). Influenza A viruses are the paradigm of emergent disease. The
LAIV H9 and LPAIV and HPAIV H7 subtype viruses are also past couple of decades have seen a unprecedented increased in the
among those of pandemic concern. Twenty-eight sporadic cases number of AI outbreaks, which have led to devastating economic
of human infection with H9N2 LPAIVs have been reported since losses to the poultry industry due to direct effects of the infection,
1999 with most cases restricted to Asia (Freidl et al., 2014; WHO, as well as trade limitations and public opinion repercussions. The
2017). All human cases reported to date, have been mild and have emergence zoonotic LPAI and HPAI viruses of pandemic concern
resolved without clinical complications or sequelae, except for has brought a new dimension to the importance of poultry-
one H9N2 positive case in an immunocompromised patient with adapted influenza viruses and has resulted in a renewed interest
a history of post-bone marrow transplant chronic graft-versus- into the molecular mechanisms that modulate influenza virus
host disease and bronchiolitis obliterans that went into respiratory interspecies transmission. Great advances have been made to
failure (Saito et al., 2001; Butt, 2005; Cheng et al., 2011). The better understand the evolution and transcontinental movement
relatively few human infections appear to have contacted the of LPAI and HPAI viruses as well as the mechanisms associated
virus from direct contact with infected birds and, so far, there has with increase virulence and zoonotic potential of these viruses.
been no evidence of human-to-human transmission (Uyeki et al., It is surprising to realize that only small changes in the virus
2002). Bird-to-human transmission of either LPAIV or HPAIV surface proteins or polymerase complex can have major effects of
of the H7 subtype have been occasionally reported, most of them the virus’ ability to switch its tissue tropism from the intestinal
have been associated with mild conjunctivitis (Fouchier et al., tract in wild birds to the respiratory tract in poultry and from
2004; Tweed et al., 2004; Eames et al., 2010; CDC, 2012; Belser et there viruses can jump into mammals. Technological advances
al., 2013; Lopez-Martinez et al., 2013; Abdelwhab et al., 2014). At in sequencing methods allow for rapid full genome virus charac-
least 92 HPAIV H7N7 human cases have been confirmed during terization and will likely become commonplace and routine and
HPAIV outbreaks in poultry in the Netherlands and Italy. Disease will allow for more expeditious responses in the face of new out-
symptom included conjunctivitis or mild respiratory symptoms breaks. Sequencing-based diagnostics will likely replace current
and only one person died of pneumonia and acute respiratory PCR-based diagnostic methods because the former does not rely
distress syndrome (Koopmans et al., 2004; Puzelli et al., 2014). on novel vaccines, adjuvants and vaccine regimens breakthroughs
In 2013, a novel LPAIV H7N9 emerged in poultry with the are steadily coming along with the potential to better prevent and
capacity to infect humans. Since then, human H7N9 IAVs infec- control the disease in poultry. Yet many challenges remain, future
tion have occurred during annual winter-spring epizootics in five research should be aimed at improving methods of analysis of
epizootic waves in Mainland China. In the first wave, the human sequence and phylogenetic data to predict antigenicity, virulence,
outbreak was mainly restricted to the Yangtze River Delta in eastern and zoonotic potential of avian-origin influenza viruses. Equally
China, including urban areas of Shanghai, Jiangsu, and Zhejiang important, it is to emphasize that future vaccine technologies for
Provinces. The number of cases was consistently low after peak- poultry use are likely going to require the stimulation of multi-
ing in 2013–2014, but the fifth wave revealed higher incidence dimensional immune responses, humoral and cellular, against
numbers than seen in previous waves (Zhou et al., 2017). Until multiple virus epitopes. In this regard, the poultry sector has been
November 2017 human infections with H7N9 were reported in hesitant to adopt live attenuated influenza virus vaccines, mostly
22 provinces, four municipalities, and five Autonomous Regions due to fear of reassortment with field strains. The advent of reverse
of China, Hong Kong and Macao SAR, as well as Canada to a genetics and the ability to manipulate at will the influenza virus
total of 1623 laboratory-confirmed cases and 620 deaths (FAO, genome should put those fears to rest. Overall, influenza viruses
2017). These H7N9 viruses usually result in severe acute respira- will not go away but we are closer than ever in finding solutions
tory disease, that included high fever, non-productive as well as for the prevention and control of the disease.
productive cough, shortness of breath, dyspnoea, and hypoxia.
Severe cases of H7N9 virus infection have included septic shock, References
respiratory failure, acute respiratory distress syndrome, refractory Abbas, A.K., Lichtman, A.H., and Pillai, S. (2012a). B cell activation and
hypoxaemia, acute renal dysfunction, multiple organ dysfunction, antibody production. In Cellular and Mollecular Immunology, Gruliow,
R., ed. (Saunders, Philadelphia, PA), pp. 243–268.
rhabdomyolysis, and encephalopathy. In addition, secondary Abbas, A.K., Lichtman, A.H., and Pillai, S. (2012b). Cellular and Molecular
bacterial and fungal infections have been reported, sometimes Immunology, 7th edn (Saunders, Philadelphia, PA).
associated with multi-drug resistant bacteria (Gao et al., 2013; Abbas, A.K., Lichtman, A.H., and Pillai, S. (2012c). Effector mechanisms
Yu et al., 2013; Xiang et al., 2016; Luo et al., 2018). On the fifth of cell-mediated immunity. In Cellular and Mollecular Immunology,
Gruliow, R., ed. (Saunders, Philadelphia, PA), pp. 225–242.
wave, HPAIV strains of the H7N9 were detected in a total of 54 Abbas, A.K., Lichtman, A.H., and Pillai, S. (2012d). Major histocompatibility
poultry or environmental samples (42 chickens, two ducks and complex molecules and antigen presentation to T lymphocytes. In
10 environmental samples) and from 25 human cases also associ- Cellular and Molecular Immunology, Gruliow, R., ed. (Saunders,
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(ferrets) (Imai et al., 2017). Mostafa, A., Hussein, I.T.M., Arafa, A., Erfan, A.M., Kilany, W.H., Agour,
M.G., et al. (2016). Introduction and enzootic of A/H5N1 in Egypt: