Page 209 - Avian Virology: Current Research and Future Trends

202 | Kibenge et al.

al. (2003) reported an experimental in ovo vaccination method (Lu et al., 2011). Avian orthoreoviruses were genetically char-
for commercial poultry. acterized by sequencing their σC proteins, into four genotypes
Current commercial vaccine strains are antigenically and (Goldenberg et al., 2010), and the σC proteins of the currently
serologically distinct from circulating variant field viruses associ- used vaccine strains were found to differ from those of most field
ated with clinical disease (Goldenberg et al., 2010; Sellers, 2017). isolates (Vasserman et al., 2004; Goldenberg et al., 2010). Since
Most of the orthoreovirus vaccines have been developed from σC is the major protein against which neutralizing antibodies are
various passage levels of avian orthoreovirus S1133 (Huang et produced, this mismatch might lead to vaccination inefficiency
al., 1987), 2177, 2408 or 1733 (Davis et al., 2012). Giambrone or failure. Lublin et al. (2011) tested the efficacy of a tetra-valent
et al. (1992) showed that S1133 was effective in the prevention inactivated vaccine consisting of a mixture of prototypes of the
of 2408 and CO8 enteric orthoreovirus infections when given four defined genotypic groups of avian orthoreovirus and found
by coarse spray to one day old SPF broiler chickens. Since 2012, that the vaccine was able to prevent disease and confer broad
there has been a dramatic increase in the number of tenosynovitis protection against field isolates. Also, vaccinations with avian
disease outbreaks in commercial poultry (Sellers, 2017). Despite orthoreovirus prototypes from all genotypes efficiently protected
vaccination, a high percentage of flocks have been infected with against other members of their respective genotypes (Lublin et
orthoreovirus, and the limited effectiveness of available vaccines al., 2011).
is likely due to the existence of many viral variants in the com- Although orthoreoviruses are difficult to eliminate from the
mercial poultry population (Lublin et al., 2011). Giambrone and environment because of their resistance to chemical and physical
Solano (1988) found all of the most common vaccine strains disinfectants, decontamination of a poultry facility following total
(S1133, 81-5, 2408, 1733 and UMI 203) belong to a single removal of infected birds and prior to reintroduction of a new
serotype by virus-neutralization test and ELISA, explaining their flock prevents infection of the new population (Stott, 1999). Pro-
inability to protect against field virus isolates belonging to other tection of commercial poultry flocks from wild birds by providing
serotypes. Other possible reasons for vaccination failure include high level biosecurity, quarantine of birds to be introduced to the
improper vaccination of pullets, decreased maternal antibody flock, monitoring of the flock for signs of illness, serological test-
titre in older hens, and the necessity for adequate induction of ing and vaccination for specific diseases, and good sanitation and
cell-mediated immunity (CMI) induced by live vaccines (Giam- hygiene practices are all critical methods to prevent the spread
brone et al., 1992). Subcutaneous vaccination at 1 day of age is of avian diseases between wild birds and commercial poultry
efficacious for induction of sufficient CMI to prevent orthoreo- (Hollmén and Docherty, 2007). In addition, the quick removal
virus infections (van der Heide et al., 1983). However, when of carcasses during a wild bird die-off reduces contamination of
orthoreovirus vaccines are combined with turkey herpesvirus the environment and the possibility of disease transmission to
vaccine and given subcutaneously, interference may occur, which other avian species and/or commercial poultry (Hollmén and
results in the reduced efficacy of both products (Giambrone and Docherty, 2007).
Hathcock, 1991). In areas where Marek’s disease virus exposure
is high, increased Marek’s disease has occurred when orthoreo-
virus and Marek’s disease vaccines were combined and given at Perspectives
1 day of age. Stott (1999) noted, despite in vitro cross reaction The host range of avian reoviruses includes all domestic and
between strains of orthoreovirus, in vivo vaccination ensures exotic or semi-domesticated poultry (chickens, turkeys, ducks,
protection only against the homologous virus. Producers now geese, pigeon, quail) and a wide range of free-ranging (wild)
use autogenous inactivated vaccines, however, identification and birds. By their very nature, avian reoviruses have most frequently
selection of field isolates for such use can be difficult especially been found in avian species that were clinically normal. The
when multiple reoviruses including new genetic variants are co- most common and readily diagnosed disease presentation is
circulating among flocks (Sellers, 2017). viral arthritis/tenosynovitis in commercial broiler chickens and
As conventional attenuated and inactivated orthoreovirus turkeys, and enteric disease and neurological disease in wild
vaccines are not totally efficacious (van Loon et al., 2002), new birds. Avian reoviruses belong to the genus Orthoreovirus, one of
approaches for vaccine production have been attempted. Vasser- 15 recognized genera in the family Reoviridae, but distinct from
man et al. (2004) demonstrated subcutaneous injection of σC mammalian orthoreoviruses by possessing a FAST protein and
protein, expressed in Escherichia coli, generated immunity in therefore inducing syncytial CPE in cell culture. The evolutionary
chickens. Wan et al. (2010) showed that the σC DNA vaccine relationships among avian reoviruses have been widely studied
orally delivered by attenuated Salmonella typhimurium elicited by phylogenetic analysis. Although there are commercially avail-
antibody production in SPF chicks. Wu et al. (2005) character- able avian reovirus vaccines for use in commercial poultry, new
ized the immune response of SPF chickens to orally administered genetic virus variants continue to emerge making these vaccines
recombinant σC protein produced in yeast and recommend inadequate. Moreover, the increasing diagnosis of avian reovirus
the development of a transgenic edible plant vaccine for use in infections in wild birds has raised the possibility of transmission
poultry. Protein σC of orthoreovirus was expressed in alfalfa, between wild birds and domesticated poultry. The application
Arabidopsis and tobacco plants (Huang et al., 2006; Wu et al., of the recently reported reverse genetics system using avian
2009; Lu et al., 2011), but the low expression of antigens in reoviruses will significantly increase our understanding of avian
plants limited their practical application in vaccination protocols reovirus biology and disease.