Oocyst-counting method ensures proper administration of Paracox-5
A practical method of counting oocysts after the first shedding
in birds vaccinated with Paracox-5 has proved to be an
excellent method for assessing the effectiveness of vaccine
administration.
Gobbi: ‘It is effective and
useful’
The method was developed for birds receiving Paracox-5 via
spray cabinet in the hatchery. It is the brainchild of Schering-
Plough Animal Health’s technical service manager in Italy, Dr.
Luciano Gobbi, and his associates in the company as well as
poultry field veterinarians.
“We devised the method after discovering that other, similar
methods requiring collection of individual droppings were time
consuming and difficult to implement on a routine basis,”
Gobbi explains. “They also resulted in failures monitoring the
oocyst count in birds vaccinated with Paracox-5.”
The newer method, in use since 2005, indirectly evaluates
the accuracy of vaccine hatchery spray by monitoring the first
oocyst shedding. “We now have enough experience with this
method to conclude that it is effective and useful,” he says.
Fecal samples are usually collected by Schering-Plough
Animal Health employees, who work with poultry farm managers
or their deputies. Diagnostic labs handle fecal sample
processing and oocyst counting because they have the necessary
facilities and expertise, Gobbi says.
The oocyst-counting method provides data and figures that
enable judgments to be made about how effectively the spray
cabinet has worked and whether uniform vaccine coverage has
occurred. It helps determine whether chicken preening and
vaccine swallow are adequate, he says.
The procedure starts with day-old chickens, when they are
released from transport cages and placed on the floor. One
chicken per cage is caught randomly.
The selected chickens are
confined in one or two wirefloored
poultry cages with legs
that raise the cages from 40 to 50
centimeters (16 to 20 inches)
above the floor. This ensures that
birds have no contact with the
litter.
Starting at 96 to 97 hours after
Paracox-5 vaccination by spray
administration and until 148 to
156 hours post-vaccination, stainless
steel trays are placed under
the poultry cages so that all feces
can be collected and pooled every
20 to 24 hours.
This is the time when birds shed only Eimeria oocysts from
the vaccine. The collection of oocysts and subsequent counting
at a lab can demonstrate that a large amount of chickens
ingested the vaccine and, above all, that vaccinal oocysts have
“multiplied” within the intestine epithelial cells, stimulating
immunity, Gobbi says.
Studies have shown, Gobbi adds, that the litter oocyst pattern
in birds that receive Paracox-5 for broilers differs from
birds that receive Paracox-8, which is designed for layers and
breeders. One of several possible reasons could be that
Paracox-5 has three fewer Eimeria species compared to
Paracox-8, which may reduce the number of oocysts produced
after vaccination. In addition, Gobbi prefers fecal sample collections
be taken after several hours of fecal deposition as
opposed to collecting individual droppings at one specific
time, as previous methods required.
UK flu outbreak in turkeys posed
no threat to Paracox vaccine safety
The outbreak of H5N1 avian influenza in February at a farm
belonging to Britain’s largest poultry producer poses no
threat whatsoever to the safety of Paracox vaccines, says
Philip Grose, plant director for Schering-Plough Animal
Health’s manufacturing facilities in the United Kingdom.
Every step of production for Paracox vaccines is carefully
controlled under strict biosecurity procedures to ensure the
purity of both Paracox-8 for breeders and layers and
Paracox-5 for broilers, he says.
For instance, Paracox vaccines are made with specificpathogen-
free (SPF) birds hatched from SPF eggs, which are
tested to be doubly certain they are free of any pathogens,
including avian influenza. Feed used during production is
irradiated and water used for production is purified, he says.
The vaccines are chemically sterilized and, during this procedure,
are handled either in a biological safety cabinet or
laminar flow hood. The sterilization process has been tested
to verify its effectiveness. “Specifically, our sterilization
process fully inactivates H5N1 avian influenza (Thailand origin),
which has been demonstrated by the Australian Animal
Health Laboratory,” Grose says. “In addition to all this, our quality control procedures
include testing of finished products to confirm the vaccines
are sterile and free of extraneous agents,” he adds.
Biosecurity procedures for manufacture of Paracox vaccines
include strict control of production facilities, he continues.
Positive pressure cascades are used to prevent entry of
extraneous agents into the facilities. Air is filtered and production
areas and equipment are routinely sanitized. The
production facilities have pressurized airlocks for the transfer
of materials; raw materials and equipment are passed
through the airlocks and are sanitized using approved disinfectants.
During the secondary manufacturing stage, clean rooms
are used and employees handling antigens before packaging
wear full, sterile gowns. All materials in the clean rooms are
autoclaved, Grose says.
Employees and contractors are screened before entering
the plant to make sure they pose no risk. If they have been
anywhere that non-SPF birds are held or visit facilities where
infectious avian agents are handled, they are forbidden from
entering Paracox vaccine manufacturing facilities for three
days.
“Both Paracox-8 and Paracox-5 customers can rest assured
that our vaccines are completely safe for use,” he says.
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