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2000). Sequencing of a conserved region of the 3′UTR of the IBV to ten days after as a booster dose given in drinking water (Ign-
genome revealed that CoVs isolated from turkey and pheasants jatovic and Sapats, 2000).
are 90% genetically similar to IBV (Cavanagh et al., 2001, 2002).
Inactivated vaccines
Inactivated vaccines, unlike live vaccines, can deliver high and
Prevention and control uniform doses of antibody in pullets that persists for an extended
period, resulting in long-lasting immunity (Dhama et al., 2014).
Exclusion and eradication To harness the full potential of inactivated vaccines, the only
Given the highly infectious nature of the virus, basic management prerequisite is that layers and breeders between 13 and 18 weeks
practices such as ensuring personal hygiene, limited site access of age must be previously primed properly with live vaccines. In
and separate footwear and equipment for each site/house can addition, the interval between the live and inactivated vaccines
all minimize IBV and disease spread. However, it is important to should be between four to six weeks to obtain the highest titre of
note even with the strictest preventative measures in place, it is antibodies.
impossible to fully eradicate IB in countries which have an inten- The benefit of inactivated vaccines lies particularly in the
sive poultry industry. Flock management also plays a major role absence of vaccinal reactions and the ability in providing protec-
in preventing IBV from being passed on from the older flocks to tion for the internal organs by preventing virus spread. Practically,
the younger replacements. With an ‘all-in/all-out’ system, poultry they could also provide protection against egg reduction which
grower can clean and disinfect sites/houses between batches and might not always be afforded by the live vaccines (Box et al.,
limit the level of infection to a minimum. This system also pro- 1980). The only disadvantage of inactivated vaccines is the cost
vides at least two economic benefits, which include an increase in and the need to administer each fowl individually via subcutane-
egg production and simplification of vaccination schedule, since ous route.
each batch of chickens are of the same age and can be on the same
vaccination schedule (Dhama et al., 2014). Molecular vaccines
In recent years, biotechnology research aimed at developing
Breeding to increase resistance new IBV vaccines has produced a new class of vaccine, known as
It is possible to protect chickens against IBV by ‘controlled expo- molecular vaccines (Kapczynski et al., 2003; Cook et al., 2012).
sure’ – exposing chickens to attenuated IBV and letting it spread Including subunit- and DNA-vaccines, virus-like particles and
naturally though the rest of the flock (Cook et al., 2012). Albeit recombinant vaccine vectors, these molecular vaccines have each
a crude method, breeding to increase resistance to IBV is effec- been tested for its efficacy against IBV and had displayed remark-
tive as it provides maternal antibodies to progeny chicks (Cook et able potential for their use in the future (Cook et al., 2012). In
al., 2012). However, the outcome of infection may differ among one case, a recombinant vaccine developed by replacing the
different lines, and therefore it is not practised in the poultry ectodomain of the S1 gene of IBV Beaudette provided 80% of
industry. immune protection against M41 challenge in young chicks (Wei
et al., 2014).
Vaccination
IBV vaccines are produced by virus passage in embryonated
eggs, and they come in two types, namely the live-attenuated and Perspectives
inactivated vaccines. Each has an intended use for broilers (live Despite major breakthroughs in IBV research, many fundamental
attenuated) and layers and breeders (inactivated), respectively problems remain to be resolved by future studies. One critical
(Ladman et al., 2002; Jackwood et al., 2009). More recently, question would be to understand the viral determinants that
molecular vaccines are emerging as the third type of IBV vaccines. control virulence and immunogenicity of IBV. More systematic
comparison and swapping of sequences between IBV Beaudette
Live-attenuated vaccines strain and a virulent strain using the available reverse genetics
Live vaccines have been widely used against IBV from as early as tools would be a useful approach to address this issue. However,
the 1970s, with the live attenuated M41 most widely used world- this effort has been partially hampered by the lack of a robust cell
wide (Gelb et al., 1991; Cook et al., 1999). Live vaccines work by culture system for most IBV isolates. The second issue would
reducing the virulence through passage in chicken embryonated be then to establish a reliable cell culture system for IBV field
eggs. They are administered in masses either through coarse spray, isolates. While most laboratory-based molecular biology stud-
aerosol or drinking water, depending on the live vaccine used ies are conducted in cells or chicken embryos infected with the
(Gough and Alexander, 1979; Ratanasethakul and Cumming, Beaudette strain, this chicken embryo- and cultured cell-adapted
1983b; Martin et al., 2007), although the oculonasal route is IBV is highly attenuated in terms of both pathogenicity and
deemed to be the ideal route of vaccination (De Wit, 2010b). To immunogenicity and has lost infectivity to young chicks. It would
boost the immunity of chicks through live vaccines, vaccination be ideal if comparative studies would be readily carried out with
programs at the site/house usually comprises of two vaccinations, a virulent strain in parallel experiments in cells and in embryo-
the first dose with a low-virulence, or mild vaccine in day-old nated eggs. Such a cell culture system would be used to replace
chicks, followed by a more virulent vaccine approximately seven or complement the current practice of relying on embryonated