Field experience and studies demonstrate that infectious bronchitis (IB) variants can be controlled by using two vaccines of different serotypes, or what many specialists now call a Protectotype strategy.
Research has demonstrated
that some IB vaccine viruses
can induce effective crossprotection
against strains from
serotypes other than those of
the vaccines used, explains
Aris Malo, DVM, global
technical director for
Intervet/Schering-Plough
Animal Health.
A combination that is proving
to be effective in the field is
Nobilis IB Ma5 and Nobilis IB
4/91, an approach that Malo
calls “a Protectotype protocol.”
Nobilis IB Ma5 is based on the
Massachusetts serotype,
while Nobilis IB 4/91 is built
on the IB-variant 4/91 serotype
— one of the most common
IB virus variants in Europe,
the Middle East, Asia and Africa.
Extensive field monitoring
Evidence that the Protectotype
concept works when these
vaccines are utilized comes
from x-OvO, a diagnostic
services company headquartered
in the UK. Richard
Currie, DVM, president of
x-OvO, says his company’s
extensive field monitoring of
Nobilis IB Ma5 and Nobilis
IB 4/91 shows that “the
combination of these two
vaccines provides extremely
broad protection against a wide
variety of IB-variant viruses.”
Any vaccine coverage, he
explains, will favor the selection
of immunological escape
mutants that will naturally
“escape” the protective
response of that vaccine.
“By using a vaccine, you are
encouraging the variation that
will lead to the generation of
a new variant,” he explains.
“However, because the Ma5
and 4/91 combination gives
the broadest protection,
it is less likely than other
vaccine combinations to select
immunological escapes since
it is more likely to completely
neutralize any challenge.”
Monitoring of the vaccines
by x-OvO has also involved
confirming the exact genetic
sequence of the vaccine strain
circulating on farms and has
demonstrated that both
vaccines are stable. “We have
shown that the viral sequences
of these two vaccines remain
consistent, despite widespread
cycling through the chicken
population on farms,” he says.
Long track record
Malo says that Nobilis IB Ma5
has been available worldwide
for over 20 years and Nobilis
IB 4/91 for more than a
decade. Both vaccines, which
are manufactured by
Intervet/Schering-Plough
Animal Health, can be
administered by coarse spray,
eye drop or in drinking water,
although the eye-drop and
coarse-spray methods are
preferable because they better
stimulate local immunity.
In one study, administration
of the Ma5 vaccine alone at
1 day of age provided excellent
protection against the Arkansas
IB isolate from the US and IB
isolates from Brazil and Japan.
The IB 4/91 vaccine used alone
at 14 days of age protected
against the same three isolates
plus an IB isolate from Italy.
Cross-protection was best, however, when birds received
both vaccines, Malo says.
In a study published in the
October 2008 issue of Avian
Pathology, Italian investigators
concluded that the use of
Nobilis IB Ma5 and Nobilis IB
4/91 “may be instrumental in
reducing the economic impact
of QX IB virus infections” on
layer and broiler farms.
Strategic combinations
The Ma5 vaccine can also be
used with the live Newcastle
disease vaccines such as Nobilis
Clone 30. In layers, the Ma5
and IB 4/91 vaccines have
been shown to be effective
“primers” for an inactivated-IB
Massachusetts booster before
the onset of lay, he says.
Recent experience on two
poultry farms in the Middle East
demonstrated that after using
IB vaccine protocols for broilers
that featured three vaccines —
Nobilis IB Ma5, Nobilis IB Ma5 +
Clone 30 and Nobilis IB 4/91 —
bodyweight increased and
mortality from IB virus and days
until slaughter decreased,
Malo adds.
Currie sees one other advantage
to the use of Nobilis IB Ma5
and Nobilis IB 4/91: flexibility.
Having two individual vaccines with different serotypes
enables veterinarians to time
administration of each so that
vaccine-strain replication is
optimal when the challenge is
highest. In contrast, bivalent
products administered at a
single time point rely on an
extended duration of immunity,
which can be “very variable” in
a field situation, he says.
A practical example of this
would be concern among
veterinarians that hatchery
administration of a bivalent
vaccine may not give adequate
protection toward the end
of the commercial broiler’s
lifespan, particularly in birds
grown for 6 weeks or longer.
Administration of the Nobilis
combination program, with IB
4/91 administered at day 14 of
age, will often relieve concerns
about maintaining adequate
protection during this critical
economic period of the broiler’s
life, Currie says.
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