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.

Source: Cocciforum issue 14