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Overview of Salmonella in Livestock and People

7 September 2012, at 12:00am

Summary of the 2011 edition of 'Salmonella in Livestock Production in GB', an annual publication from the Veterinary Laboratories Agency, providing data on salmonella reports from livestock species in Great Britain (England, Wales and Scotland).

This chapter provides information on Salmonella isolated from livestock from samples taken on all premises, including farms, hatcheries, veterinary surgeries, zoos, slaughterhouses and human food premises.

An overview of the number of incidents and isolations of Salmonella reported in farm animal species is given in a table; 'poultry' refers to reports from chickens, turkeys, ducks, geese and game birds.

For comparison purposes, data have been reproduced on the number of laboratory reports of human isolations of Salmonella reported in England and Wales to the Health Protection Agency (HPA), Colindale and in Scotland to Health Protection Scotland (HPS). There are a number of factors that influence the reporting of these data by clinical microbiology laboratories. These are discussed in the Zoonoses Report UK 2011 (Defra 2012, in press).

A table ranks the most common Salmonella serovars isolated from livestock in Great Britain in 2011 alongside the most common serovars isolated from human cases of salmonellosis in Great Britain. Similar tabulation is given for phage types of S. Typhimurium and S. Enteritidis in livestock and humans.

Apart from Salmonella Typhimurium and Salmonella Enteritidis, the other serovars associated with human cases are reported relatively rarely from British livestock. Usually S. Newport is the only other serovar that occurs amongst the 'Top 10' serovars in both humans and animals. However, in 2011, S. Montevideo, commonly found in animal feed, chickens, cattle, sheep and to a lesser extent, turkeys was at the fifth position among human isolates.

Although the monophasic S. Typhimurium variants S. 4,5,12:i:- and S. 4,12:i:- have become prominent in pigs and cattle, they may be reported as S. Typhimurium or Salmonella unnamed in human surveillance data so totals can not currently be compared. The total number of isolation reports to the HPA from human cases of salmonellosis decreased by 11.3 per cent in 2011, compared with 2010.

In previous years, tables have been produced comparing the relative frequency of Salmonella serovars in each animal species over the previous five years. These data should be considered alongside absolute numbers of reports, as the relative proportions may remain similar despite a change in number of reports, in which case VLA concludes that the change in number of reports is likely to be constant across serovars. Similarly, if there is a change in serovar relativity, it is only by examining changes in absolute numbers that one can ascertain the size of any increase or decrease. For example, in 2011 the total number of Salmonella incident reports from livestock decreased by 15.7 per cent compared with 2010. However, this was not consistent across serovars; for example, in 2011 reports of S. Dublin decreased by 22.2 per cent, reports of S. Ohio decreased by 45.5 per cent, and reports of S. Derby and S. Montevideo increased by 3.7 per cent and 20.4 per cent, respectively, compared with 2010.

Perhaps the most important factor which may bias the number of Salmonella reports is the submission rate. This report presents numerator data but the denominator, in most cases, is unknown and may change over time. Most Salmonella incident reports from cattle, sheep and pigs result from the investigation of clinically diseased animals and economic factors may exert a strong influence on diagnostic practices, such as whether a veterinary surgeon is consulted and whether samples are submitted for laboratory examination.

The number of diagnostic submissions to the Animal Health and Veterinary Laboratories Agency (AHVLA) and the Scottish Agricultural College (SAC) decreased by 10.3 per cent in 2011 compared to 2010; this decrease was seen in all species except pigs and poultry where diagnostic submissions increased by 1.4 per cent and 18.2 per cent, respectively. Additionally, as most of the data from species other than poultry relate to clinical investigations, the prevalence of subclinical infection in these species of livestock is not usually known.

Changes in the denominator population for Salmonella reports from poultry, particularly chickens, turkeys and ducks, are difficult to assess and most sample submissions are associated with statutory or voluntary surveillance activities. Although trends in Salmonella reports can be compared with diagnostic submission rates to AHVLA/SAC, it should be remembered that not all submissions will have been examined for Salmonella. Private laboratories also report the isolation of Salmonella and the total number of submissions to these laboratories is unknown.

The number of reports of S. Typhimurium in cattle, sheep, pigs and poultry decreased by 31.6 per cent in 2011 (160 reports) compared with 2007 (234 reports). This decrease was most marked in cattle (down 37.3 per cent compared with 2007) and pigs (down 32.5 per cent compared with 2007). At the same time, reports of the monophasic strains of S. Typhimurium S. 4,5,12:i:- and S. 4,12:i:- both increased. Salmonella 4,5,12:i:- increased from 20 reports in 2007 to 73 reports in 2011, and Salmonella 4,12:i:- increased from four reports in 2007 to 30 reports in 2011. These increases were most notable in pigs.

Highlights

Cattle

  • The number of incidents in cattle decreased by 19.7 per cent compared with 2010. However, the number of incident reports were still higher than those reported in 2007 and 2008.
  • Salmonella Dublin was, once again, the most commonly reported serovar (463 reports; 65.0 per cent of total cattle incidents).
  • The second most common serovar was S. Mbandaka (92 reports; 12.9 per cent of total cattle incidents).
  • There were 52 reports of S. Typhimurium (7.3 per cent of total cattle incidents) and of these 17 (32.7 per cent) were DT104 and 10 (19.2 per cent) were DT193.
  • Six incidents of S. Enteritidis were reported; four (67 per cent) were associated with clinical disease, one resulted from a farm visit to follow up a report of clinical disease and one was from voluntary surveillance.
  • Reports of the monophasic variant of S. Typhimurium, Salmonella 4,5,12:i:- fell slightly compared to 2010, however the relative percentage of this serovar increased (27 reports; 3.8 per cent of total cattle incidents in 2011 compared with 32 reports; 3.6 per cent of total cattle incidents in 2010). The related variant Salmonella 4,12:i:- remained at a similar level and relative percentage to 2010.

Small ruminants

  • Salmonella enterica subspecies diarizonae serovar 61:k:1,5,7 (and variants) remained the most common serovar in sheep (51 reports, 58 per cent of total sheep incidents).
  • Salmonella Montevideo was the second most commonly reported serovar (20 reports, 22.7 per cent of total sheep incidents).
  • Reports of S. Dublin, the third most commonly reported serovar (13.6 per cent of total sheep incidents in 2011), fell from 21 in 2010 to 12 in 2011.
  • There were no reports of Salmonella in goats.

Pigs

  • Salmonella Typhimurium was the most common serovar reported in pigs (77 reports; 42.3 per cent of total pig incidents). The most common phage types reported were U288 (29 reports; 37.7 per cent of total S. Typhimurium incidents in pigs) and DT193 (17 reports; 22.1 per cent of total S. Typhimurium incidents in pigs).
  • The increasing trend in the emerging monophasic variant of S. Typhimurium, S. 4,5,12:i:- continued (40 reports; 22.0% of total pig incidents compared with 30 reports; 17.3 per cent of total pig incidents in 2010). The most common phage type was DT193 (31 reports).
  • Reports of the monophasic variant of S. Typhimurium, Salmonella 4,12:i:- also increased (20 reports, 11.0 per cent of total pig incidents, compared with 13 reports, 7.5 per cent of total pig incidents in 2010).

Deer, Horses and Rabbits

  • There was a single report from deer (S. Newport); the first reported case of this serovar in deer since recording began.
  • The number of reports from horses increased by 16.2 per cent compared with 2010, although total numbers of reports were low (n=43).
  • The most common serovar reported from horses was S. Typhimurium (18 reports, 41.9 per cent of total horse incidents).
  • There have been no reports from rabbits since 2003.

Chickens

  • Incidents of Salmonella reported in chickens decreased by 13.5 per cent compared with 2010; this was mainly due to a fall in the number of reports from statutory surveillance.
  • The most commonly reported serovars from chickens were S. Montevideo (86 reports; 21.0 per cent of total chicken incidents), S. Kedougou (79 reports; 19.3 per cent of total chicken incidents), S. Senftenberg (48 reports; 11.7 per cent of total chicken incidents), S. Livingstone (42 reports; 10.2 per cent of total chicken incidents) and S. Mbandaka (39 reports; 9.5 per cent of total chicken incidents). Most of these incidents were in broiler flocks sampled for statutory purposes.
  • There were eight reports of S. Enteritidis (2.0 per cent of total chicken incidents) in 2011 compared with 18 reports (3.8 per cent of total chicken incidents) in 2010.
  • Information and data are given in another chapter 6 of the report on the National Control Programmes (NCPs) for Salmonella in breeding flocks of chickens, in chicken egg-laying flocks and in chicken broiler flocks. The estimated prevalence of regulated serovars in all NCPs was within EU targets.

Turkeys

  • The most common serovar reported from turkeys in 2011 was S. Derby (121 reports; 42.9 per cent of total turkey incidents).
  • Information and data are given in Chapter 7 (Reports of Salmonella in Turkeys) on the National Control Programme (NCP) for Salmonella in turkey flocks. S. Enteritidis was not isolated, there were two fattening flocks detected with S. Typhimurium, four fattening flocks detected with Salmonella 4,12:i:- and one flock detected with Salmonella 4,5,12:i:-.
  • S. Panama which had not been reported in turkeys since 1989, was reported during 2011.

Ducks and geese

  • There were only 27 reports from ducks, a decrease of 65.4 per cent compared with 2010 (78 reports).
  • The most commonly reported serovars in ducks were S. Typhimurium (13 reports, 48.1 per cent of total duck incidents) and S. Indiana (three reports; 11.1 per cent of total duck incidents).
  • There were no reports for geese in 2011.

Other statutory birds (as specified in the Zoonoses Order)

  • The number of reports from game birds (partridges and pheasants) remained the same as in 2010 (12 reports), although the number of incidents from each species changed with reports from partridges increasing (five reports in 2011 compared to one report in 2010) and reports from pheasants decreasing (seven reports in 2011 compared with 10 in 2010). There were no reports from guinea fowl in 2011 whereas there was a single incident in 2010.
  • The most commonly reported serovar in game birds was S. Kedougou (three reports; 25.0 per cent of total game bird incidents).
  • S. Muenchen was reported from pheasants, this serovar has never previously been reported from game birds.
  • There have been no reports from quail since 2005.
  • There were 14 reports from pigeons in 2011, 13 (92.9 per cent) of which were S. Typhimurium.
  • S. Bareilly was reported from pigeons for the first time.

Wildlife

  • There were seven incidents of S. Enteritidis from wildlife during 2011, six were PT11 reported from hedgehogs and one was PT1 from a bustard.
  • There were three reports of S. Typhimurium from wild birds (DT41, DT104 and DT193).

Feedingstuffs

  • The percentage of tests carried out under the Animal By-Products Regulations (ABPR) 2011 and Defra Codes of Practice during 2011 that were positive for Salmonella was 0.9 per cent. This is the same as in 2010.
  • The isolation rate of Salmonella from domestic processed animal protein increased to 1.65 per cent in 2011 compared with 0.49 per cent in 2010.

Antimicrobial Susceptibility Testing

  • Of the 453 Salmonella Dublin cultures tested during 2011, 96.0 per cent were susceptible to all 16 antimicrobial drugs tested against.
  • The number of cultures of Salmonella Typhimurium examined in 2011 was 427, of which 34.4 per cent were susceptible to all the antimicrobials tested against. This is a slight increase compared with 2010 (33.5 per cent susceptible to all antimicrobials tested against).
  • 1,982 isolates of serovars other than S. Dublin or S. Typhimurium were tested in 2011 and 56.4 per cent were susceptible to all the antimicrobials tested against.

Further Reading

- You can view the full report by clicking here.


September 2012