Page 30 - Avian Virology: Current Research and Future Trends

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Additional information and recommendations about biosecurity, in all states where LPAIV cases were detected. The last isolation
surveillance, and reporting AI activity can be found at the Animal of H5N2 HPAIV in Mexico was in May 1995 and by December
and Plant Health Inspection Service, United States Department 1995 the Mexican government declared the country to be free of
of Agriculture (http://www.aphis.usda.gov). the virus (Villarreal, 2009). It is important to note that although
If infection is detected in a flock, the OIE Terrestrial Animal vaccination is a useful tool, it is not sufficient to eradicate the
Health Code recommends culling infected and contact animals disease if not properly implemented. Vaccination should be
(or within a short radius around infected premises), appropriate used for a short duration and always be coupled to stringent,
disposal of carcasses and all animal products, as well as quarantine reliable, and transparent monitoring programmes and appropri-
and movement restrictions (OIE, 2015). Some measurements ate management. Unsuccessful vaccination programs can be a
can reduce the virus environmental contamination in live mar- result of poor-quality vaccines or vaccine antigen mismatch, as
kets, such as the separation of aquatic and poultry species, the well as improper administration (Swayne et al., 2014). Vaccina-
prohibition of selling live aquatic birds, and the incorporation of tion is used routinely in some countries where avian influenza
monthly rest days, where markets are completely emptied and dis- viruses have become endemic to prevent spread and protect
infected before new birds are brought in. Prevention programmes at-risk populations, most commonly against H5, H7, and H9
in some countries include some form of incentive or financial viruses (Domenech et al., 2009; Spackman and Pantin-Jackwood,
compensation to farmers and producers affected by mandatory 2014). Almost all vaccine doses used in the field have been used
culling of their animals, which is important to stimulate transpar- in Mexico (H5N2 and H7N3) and China, Egypt, Vietnam and
ent reporting and early detection; however not all countries have Indonesia (H5N1) in response to epizootics; however, the dis-
an indemnification program in place for AI. ease remains endemic in these countries (Swayne et al., 2011).
The same measures taken to prevent the spread of AI in poultry The vast majority of poultry influenza vaccines used in the
can reduce the risk for human exposure to the virus. The World field are inactivated whole virus products combined with potent
Health Organization, through its Global Influenza Surveillance oil-based adjuvants delivered by the i.m. route in multiple doses
Program, together with other national and international agencies, (Swayne et al., 2011). Several inactivated avian influenza vac-
assists in reducing the risks of AI for public health. Poultry work- cines are licensed in the USA and other countries, in addition to
ers, as well as people involved in the culling of infected poultry live recombinant vectors (fowlpox, Avian paramyxovirus type 1
flocks should wear protective clothing and also receive antiviral -NDV, Duck enteritis virus, Turkey Herpesvirus) (Swayne et al.,
drugs as a prophylactic measure. In addition, vaccination of 2000, 2001; Halvorson, 2002). Recombinant vector vaccines
people at high risk of exposure to infected poultry (e.g. poultry against avian influenza are not as commonly used in poultry as
workers, live market workers, veterinarians, etc.) using seasonal inactivated vaccines. However, this type of vaccine could be
vaccines can reduce the likelihood of co-infection with human administered by automated methods as a spray or in drinking
and avian influenza strains, and thus reduce the risk of reassort- water for mass-immunization, providing a rapid, efficient, and
ment. economical immunization method. NDV-vectored H5 and H7
vaccines induced high levels of HI antibodies and protected
chickens from challenge with a H7N9 or HPAI H5N1 viruses,
Vaccination respectively (Liu et al., 2015a). However, pre-existing immunity
Vaccination can be considered the third line of defence against to the NDV vector could limits the protective efficacy of these
avian influenza; however, vaccination of poultry is still seen with vectored vaccines in the field (Spackman and Pantin-Jackwood,
reluctance because they usually protect against clinical signs but 2014). An alternative chimeric NDV-vectored with F and HN
not against infection and, therefore, could mask outbreaks and ectodomains replaced by those of avian paramyxovirus serotype-2
favour the spread of HPAIV. Obstacles to effective implementa- was shown to be safe, not cross-react with NDV, and to partially
tion of vaccine programs include the interference of maternal protect 1-day-old immunized chickens against H5N1 HPAIV
antibodies on vaccine immune response, costs to implement challenge (Kim et al., 2017). Additionally, a recombinant turkey
program, the prohibitive withdrawal period post-vaccination, the herpesvirus vector vaccine expressing the HA gene of H5N1
difficulty to differentiate vaccinated from infected animals and the HPAIV consistently demonstrated a high degree of homologous
masking of clinical signs that can result in trade restrictions (De protection as well as cross-protection against heterologous clades
Vriese et al., 2010; Spackman and Pantin-Jackwood, 2014). of the H5N1 HPAIV (Gardin et al., 2016). Recently, a single-
Vaccination has been successfully used in countries where cycle, propagation-defective alphavirus-like (Venezuelan equine
the regular stamping-out protocols are not enough to control encephalitis virus) replicon particle vaccine expressing the H5
spread, may cause an irreversible impact on the poultry industry HA was shown to provide partial protection against a HPAIV
or pose a threat to food supply (Naeem and Siddique, 2006; H5N2 strain in turkeys vaccinated with an alphavirus replicon
Villarreal, 2007). Such approach was used in Mexico during the (Santos et al., 2017).
H5N2 HPAIV outbreak in 1994–1995. Between January and Alternative approaches for avian influenza vaccines have
December 1995, approximately 380 million vaccine doses were included the use of subunit HA protein, DNA immunization and
administered, in both affected and at-risk bird populations, cover- live vaccines (Brown et al., 1992; Fynan et al., 1993; Kodihalli et
ing approximately 55% of the country and 70% of the commercial al., 1994, 1997; Bright et al., 2003). These different approaches
poultry population. Vaccination was performed in layer farms have shown promising results protecting against disease and