Issues concerning vaccine safety are likely to come to the fore as egg producers face increasingly stringent sampling for salmonella following the EU zoonoses directive.
While findings of salmonella in UK commercial layer flocks have been the lowest among EU countries with large poultry populations, some eight per cent still tested positive for Salmonella enteritidis and typhyimurium, the salmonella serotypes most commonly associated with food poisoning in humans.
"Put into perspective, this represents a potential 2.4 million birds or, in more practical consumer-related figures, 60 million cartons of a dozen eggs," pointed out veterinary surgeon, Eduardo Bernardi who is vaccine marketing director for Lohmann Animal Health.
"This percentage should be reduced by all possible means, including the identification of flaws in the system, such as poor vaccination technique, biosecurity, hygiene, disinfection and monitoring. Identification of any weak spots is essential to reduce the overall load of salmonella since a challenge can always be high enough to break through the immune system.
"The UK producer has the aid of the most advanced technology in terms of salmonella vaccines. Live vaccines administered through the drinking water provide a convenient, welfare-friendly way to build up immunity but because we are dealing with a zoonosis matter it is important that the live vaccine strains are not found in the environment — for example in faeces or dust — or in other species, such as rodents."
He explained that important safety features in a live vaccine needed to be considered by egg producers, including the fact that it could be easily differentiated from field strains through routine methods and that it should be excreted for a minimum amount of time after vaccination. In particular, it should not be excreted when birds were already in production. Where salmonella-free status is aimed at, no vaccine strain should be detectable in the environment. This was already an essential requirement in many countries for the licensing of live vaccines.
In addition, vaccine strains should not be shed in or on the eggs. "As a matter of principle, eggs should not contain live salmonella, whether vaccine strain or not, regardless of whether contamination comes via the ovary or through faecal matter on the shell," declared Mr Bernardi.
Although, the British approach, which includes compulsory vaccination against Salmonella enteritidis under the Lion Code, had been mirrored by the rest of the European Union, he suggested that UK producers could not afford to become complacent.
