Salmonella is a common cause of human food poisoning across the EU, and legislators are working to minimise its prevalence in the pig and poultry sectors. Last year saw the introduction of a National Control Programme to reduce the incidence of it in UK breeding flocks, which is being rolled out to layers this year and will extend to broilers from 2009.

The programme sets out measures to reduce the prevalence of salmonella enteritidis and typhimurium – the strains which pose the highest human health risk – to 1% or less by 31 December 2011.

However, Britain is one of those leading the way, with its already comprehensive biosecurity and testing measures. Official tests found no S enteriditis and just one occurrence of S typhimurium out of 383 holdings sampled in 2005/06 – a prevalence of just 0.3%.

“We’ve already got a good system that’s working – this is a case of the EU taking good practice from us and rolling it out across the rest of the EU,” says Jeremy Blackburn, executive officer at the British Poultry Council.

In other parts of the EU, salmonella rates are significantly higher, with Portugal and Poland showing S enteritidis and typhimurium rates of 39% and 32%, respectively. The EU average for these serovars was 11%, but the total salmonella incidence, including serovars less hazardous to human health, was more widespread, averaging 24%. UK flocks showed an overall salmonella incidence of 8%, with other results ranging from 0% in Sweden, to 68% in Hungary.

“These findings are encouraging and show how effective control measures taken by industry in the UK have been,” says Judith Hilton, head of microbiological safety at the Food Standards Agency. “However, salmonella has not been entirely eliminated from broiler flocks and we need to continue to work hard to minimise salmonella and campylobacter levels in UK poultry.”

DEFRA published its draft National Control Plan (NCP) for salmonella in broilers in December 2007, and expects to have the required legislation in place by January 2009. This will require all commercial broiler flocks to take part in the NCP, testing each flock for salmonella in the three weeks prior to slaughter.

In addition, Animal Health will randomly test 10% of holdings with more than 5000 birds each year. All tests will be carried out using two boot swabs per house, covering 50% of each house. In the case of free range flocks, tests will only be carried out in the housed area.

“It will be interesting to see what results we get from free range and organic flocks,” says Mr Blackburn. “It is a continuous area of controversy, with some organisations maintaining that housed birds are more likely to suffer from salmonella.”

However, outdoor flocks may have higher levels of salmonella picked up from cattle, game and wild birds, he adds.

Producers will be allowed to apply for a derogation not to sample all flocks on the holding if they use an all in/all out system the management, feed and water is common to all flocks and they took samples for salmonella in all flocks on the holding during one year and at least six crops and all of which tested negative for S enteritidis and typhimurium. At least one of these tests must have been taken by Animal Health.

Poultry producers must keep records of the date when each flock is sampled for salmonella, the identity and age of the flock, the date of slaughter, the laboratory which undertook the analysis, and the result of the tests.

If a flock tests positive for salmonella, arrangements may be made with the abattoir to reduce the possibility of cross contamination of other batches, by arranging for slaughter to take place at the end of the day, for example.

Should a flock test positive for S enteritidis or typhimurium, producers must inform Animal Health. Disease control advice will be given and a notice may be served requiring the producer to clean and disinfect the infected building, which may then be re-tested to verify the serovar has been eliminated.

Although the regulations may sound onerous, about 95% of broiler producers are already testing for salmonella under the Assured Chicken Production scheme. With breeders also controlled, chicks placed on broiler units have an extremely good start, says Mr Blackburn.

A specialist broiler working group is now being set up between the industry and DEFRA, which Mr Blackburn hopes will address controls on imported poultry, which in many cases is more likely to carry salmonella than British birds. “Are we just running a risk by buying that meat in?”

Tips on reducing salmonella in broilers

Salmonella in broilers can be reduced relatively easily through stringent cleaning and bio-security measures, says vet Stephen Lister of Crowshall Veterinary Services, Attleborough, Norfolk.

“Salmonella control is now about preventing horizontal spread through improving bio-security and vermin control. Decent terminal cleaning and disinfection is very important, as is the hygiene and biosecurity of catching gangs, which are a potential source of problems.”

Broiler producers have made great strides in biosecurity, indicated by the low salmonella rates in this country, says Mr Lister. But attention still needs to be paid to measures like footbaths outside houses, effective cleaning and use of disinfectants, to keep infection rates down.

Most salmonella types in the UK are present in the environment, particularly in litter and faeces. Many will pass through the birds with no adverse effects on health or productivity whatsoever. However, infection with more virulent serotypes, including S enteriditis or typhimurium, while rare, can cause septicaemia and mortality in flocks.

Points to consider when planning flock biosecurity include farm location and layout, to prevent cross-contamination from neighbouring farms and wind-blown litter. Free-range flocks should be protected from contact with wild animals and birds as much as possible.

“Wild birds will carry Salmonella,” says Mr Lister. “Whereas it may be impossible to always prevent them entering a site or contaminating the range, they may be discouraged by avoiding standing water on the range, not feeding birds on range and cleaning up all feed spillages.”

Feed is now rarely a potent source of Salmonella, but if any scratch feed or added wheat is used it needs to be of the highest quality, having been stored in vermin proof areas before use.

Rats and mice are susceptible to salmonella and can even multiply the bug and make it more potent against poultry. “It is estimated that for every rodent seen or caught there are at least another 100 that go undetected,” says Mr Lister. It is, therefore, essential to check empty houses at night, keep areas around the units clean and tidy, and use traps and baits to both monitor and reduce rodent activity.

Vehicles and people are another potential source of infection, as is equipment used in catching and transporting birds. Equipment and vehicles must be thoroughly cleaned and disinfected on arrival and departure, and people should always use footbaths, hand washes and disposable clothing.

Although breeders have reduced infection rates dramatically over the years, it is still important to buy chicks from high quality breeders, and ensure they are not contaminated upon arrival, says Mr Lister. “It is following transport that birds are most stressed and vulnerable.”

One option may be to treat day-old chicks with a gut flora product, like Aviguard, to boost their natural immunity. “Aviguard has been used very successfully in laying hens over the years to exclude salmonella,” says Sarah Rennie, technical manager at Schering-Plough Animal Health.

The product contains a mix of normal avian gut flora, which works against potential infection by competitive exclusion. “The best way to describe it is like a Yakult for chickens.” Although not widely used in the broiler sector, Aviguard can also help against other bugs including necrotic enteritis bacteria and pathogenic E coli.

Vaccines are commonly used in laying hens, but are unlikely to become widespread in the broiler industry, claims Mr Lister. “Personally, I don’t see a future in salmonella vaccines in broilers – the effort is really concentrated on exclusion and you can probably get better control through bio-security measures.”

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