The EU salmonella baseline survey in pigs has now been released but where do we go from here?

The EU salmonella baseline survey in pigs has now been released but where do we go from here?

We have surveyed over 19,000 pigs and their lymph nodes and an average of 10.3% of all pigs going to slaughter carry Salmonella.

Salmonella enterica Typhimurium and S. Derby are the two most common isolates, so no surprises there. S. Typhimurium was found in 4.7% and 2.1% were S. Derby, ‘which are two common serovars found in Salmonella infections in humans’. Is that so?

S. Typhimurium is significant accounting for up to 20% of human cases but occurs in most animals and poultry. S. Derby, which is primarily found in pigs, usually accounts for less than 1% (the figure is often so low it is not recorded) and in a UK survey in 2000, only 0.2% of human cases were associated, which can hardly be called common. On a proportionate basis, Salmonella from pigs may only account for 1.0% of human cases.

Carcass contamination
The second part of the study looked at contamination of the carcass with Salmonella and the EU average was 8.3% (see Figure 1) and 3.9% for S. Typhimurium and 2.6% for S. Derby.

Interestingly, some countries had higher carcass contamination than lymph nodes, suggesting that the carcass contamination is occurring in the slaughter house. In most countries there is a fall, which fits in with good slaughterhouse management and hygiene.

IPVS Congress
At the recent International Pig Veterinary Society (IPVS) congress there was a very interesting paper by De Busser and others (2008) from Belgium showing the impact of the slaughter house on carcass contamination with Salmonella (see Figure 2).

Samples from five slaughterhouses at various stages of production were taken: – in the lairage, after the scalding tank and polishing, after splitting of the carcass and finally in the chilling room. Contamination of the lairage seemed to have the most impact on subsequent carcass contamination and the difference between the best and the worst slaughterhouses.

The best one had slatted lairage floors. Carcass contamination usually goes up after splitting and the opening of the carcass. There was a surprisingly low prevalence of carcass contamination in the chilling room, which was well below their national average but it was still markedly higher in the worst slaughterhouse than the cleanest but lower than the infected lymph nodes of the pigs coming in.

What next?
So where do we go from here? The study was set up so that Salmonella reduction targets could be set for pigs regarding serovars with public health significance, “supported by a cost/benefit analysis”. This is difficult when “there is convincing evidence that some cases of salmonellosis are attributable to infection derived from Salmonella infected pigs or products of pig origin but the population attributable fraction for the EU has not been estimated”. That is, they don’t know how important pigs are in the transmission of Salmonella to man, so how can they calculate a benefit?

Shouldn’t this be one of the first things that they do find out, with all the thousands of isolates they have, before they spend any more millions of euros on these studies?

Investigating slaughterhouse best practices might also be the most cost-efficient way of reducing the incidence of carcass contamination, which the Danes have shown several years ago.