Reports of Salmonella in Pigs

According to the 2011 edition of 'Salmonella in Livestock Production in GB', an annual publication from the Veterinary Laboratories Agency, surveillance revealed 182 incidents of Salmonella in pig meat in 2011, which has hardly changed over recent years.
calendar icon 25 September 2012
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By: Banrie

Results from the June Agricultural Census indicated little change in the size of the Great Britain pig herd from 2010, down 1.3 per cent to 3.99 million head. Pig numbers in England and Wales (combined) were essentially unchanged at 3.6 million head while in Scotland numbers fell from 410,700 to 390,000, a reduction of five per cent on the previous year.

In 2011, over 9.81 million pork and bacon pigs were slaughtered in the UK, including 8.2 million in Great Britain, an increase of 4.4 per cent on the previous year. Further increases of one to two per cent are forecast by the industry in 2012 and 2013 (as of January 2012). While finished pig prices (p/kg) were up on the 2010 figures for most of the year, feed prices rose sharply in the second half of 2010 and remained elevated into the first half of 2011.

A total of 5,685 pig submissions were received by AHVLA in 2011, an increase on 5,202 in 2010 and 5,334 in 2009. A total of 1,596 diagnostic pig submissions (which generate the bulk of Salmonella incidents in pigs) were received in 2011, which is up slightly on 2010 (1,574).

The British Pig Executive's Zoonoses National Control Programme for pigs (ZNCP) aims to control and reduce the risk of Salmonella in pig meat to the consumer by targeting action at every stage of the meat production chain. Under this programme, assured herds receive four-monthly reports containing their rolling annual meat juice (MJ) ELISA results and producers are encouraged to aim for less than 10 per cent of results in the positive or weak-positive categories. Nationally, 43 per cent of 59,742 results issued to assured units in 2011 were in these bands, a level essentially unchanged since 2008.

Under project FZ2015, which provides consultancy and testing support to the programme, AHVLA undertook five investigatory visits during the year, including two units with very low MJ scores to identify which, if any, Salmonella spp. were present, and one unit in which incursions of monophasic S. Typhimurium led to loss of seronegative status.

The report tabulates the overall number of Salmonella incidents and isolations recorded from pigs over the past five years (2007–2011) and the proportions afforded by the most frequent serovars.

There were 182 incidents of Salmonella in 2011, which is comparable to recent years.

Salmonella Typhimurium remained the most commonly found serovar, associated with 77 incidents in the year. This is, however, a reduction on the 99 S. Typhimurium incidents reported in 2010 and maintains the general decline in incidence of this serovar seen over the past decade. No Salmonella Enteriditis was isolated from pig submissions during the year.

In terms of its animal and human health implications, Salmonella 4,[5],12:i:- is considered to be an important monophasic variant of S. Typhimurium and was responsible for a significant outbreak in humans in the USA in 2012. Its relative contribution to the overall Salmonella burden in pigs in Great Britain has risen steadily since 2005 and it accounted for 40 incidents in 2011 (22.0 per cent of the total), up from 11 in 2009 and 30 in 2010. Another monophasic variant of Salmonella Typhimurium, 4,12:i:-, was identified in a further 20 incidents.

The majority of incidents of these two strains involved the phage type DT193, which appears to have enhanced virulence in pigs. For example, in AHVLA's monthly scanning surveillance report for April 2011, AHVLA Bury St. Edmunds diagnosed monophasic Salmonella Typhimurium phage type DT193 as the cause of diarrhoea in 27 pigs on one farm and this resulted in seven deaths. A similar monophasic S. Typhimurium-like organism (in this case Salmonella 4,12:i:- phage type DT120) was responsible for sudden deaths involving six to nine-week-old rearing pigs on an indoor breeder-finisher unit.

Salmonella Derby was the fourth most common serovar in 2011 (13 incidents), and has consistently accounted for between four per cent and eight per cent of incidents annually, over the last five years. Several other serovars accounted for small numbers of incidents each, including S. Bovismorbificans (6 incidents), S. Kedougou (a feed-associated serovar, 4 incidents), S. London (4 incidents) and S. Reading (3 incidents). Salmonella Panama was identified in four incidents in 2011. This is a Group D serovar which was more common in previous decades but subsided during the last ten years. A serovar newly reported in pigs this year was S. Bareilly.

DT193 and U288 continue to be the most commonly identified definitive (DT) and undefined (U) types of S. Typhimurium in pigs though incidents involving the former were down on 2010 (17 incidents, compared with over 30 in each of years 2007 – 2010). DT193 has recently been associated with outbreaks in people and thought to be associated with hog roasts. Definitive Type 32 was again isolated in 2011, having been reported in pigs for the first time in 2010. This is a very rare type which has been occasionally reported from cases.

There was a single report of non-GB origin from pigs during 2011; this was S. Derby and was reported from pigs originating in Canada.

A number of serovars were reported during 2011 from reasons other than routine surveillance; for example through research projects. These were: S. Cerro, S. Havana, S. Infantis, S. Mbandaka, S. Nottingham, Salmonella O rough:i:-, S. Ordonez, S. Senftenberg, S. Typhimurium DT9, S. Typhimurium DT41b, S. Typhimurium DT195, S. Typhimurium U310, S. Typhimurium U320, S. Typhimurium U323, Salmonella 4,12:i:- DT12, Salmonella 4,12:i:- DT104b, Salmonella 6,8:-:1,2 and Salmonella 9,12:l,v:-.

Further Reading

You can view the full report by clicking here.

For the summary of the AHVLA report, click here.

For the chapter on Salmonella in feedstuffs, click here.

September 2012
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