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UK Pig Disease Quarterly Surveillance Report - July-September 2008

by 5m Editor
8 December 2008, at 12:00am

The latest Surveillance records that there have been no outbreaks of Notifiable Disease or zoonoses associated with pigs, nor any food safety incidents. Porcine enterovirus A CPE type II was identified in tissue collected as part of an investigation into encephalomyelitis in young pigs. Multi-drug resistant <em>Brachyspira hyodysenteriae</em> has been isolated, and the incidence of swine dysentery in on the rise. The industry continues to show interest in disease eradication.

Quarterly Surveillance Report Pigs: Vol Q3 2008
July-September 2008
Published November 2008

Contents

HIGHLIGHTS

INTRODUCTION TO GB PILOT REPORT

OVERVIEW PIG DEMOGRAPHICS AND DIAGNOSTIC SUBMISSION RATES NOTIFIABLE DISEASES REPORTED FARM VISIT INVESTIGATIONS FOOD SAFETY INCIDENTS

ENDEMIC DISEASE SURVEILLANCE

UNUSUAL AND NEW DISEASES

SYNDROMIC DISEASE SURVEILLANCE

SCANNING SURVEILLANCE FOR NEW AND EMERGING DISEASE

Highlights

  • There have been no outbreaks of Notifiable Disease or zoonoses associated with pigs.
  • There were no food safety incidents involving pigs.
  • Porcine enterovirus A (PEV A) formerly known as PEV 8, CPE type II was identified from central nervous tissue collected as part of a five-day investigation into encephalomyelitis in young pigs. This virus has previously been associated with porcine infertility and nervous signs but without recent additions to the literature.
  • Multi-drug resistant Brachyspira hyodysenteriae isolated and increased incidence of swine dysentery reported particularly in East Anglia.
  • The industry continues to show much interest in disease eradication with particular attention to swine dysentery and PRRS.
  • There have been financial improvements with relation to meat prices but there is still some way to go before pig farming can be determined as profitable.

Introduction

This is the second pig surveillance report that combines information from all areas of Great Britain into a single, integrated overview of pig health across the whole region. It has been made possible through a partnership between Defra, SEERAD, the Veterinary Laboratories Agency (VLA) and Scottish Agricultural Colleges Veterinary Services (SAC VS) Division.

A key objective for any pig disease scanning surveillance system is to increase the likelihood of early detection of important changes in pig health. Any major disease occurrence, such as the FMD outbreak of 2001, can have a major impact either by threatening public health and/or animal welfare, or through its economic impact on the agricultural industry and ancillary related industries like tourism across the whole of GB. The possibility of the incursion of exotic diseases, the emergence of a new disease, or changes in known diseases are all risks which scanning surveillance seeks to mitigate. Until now, the surveillance networks north and south of the Scottish border have reported their findings separately, which reduced the likelihood of early detection of important changes in health in this single epidemiological population. The newly unified GB-wide data resource, coupled with new collaborative analytical processes should make detection of all these scenarios both easier and quicker.

The network of 14 VLA Regional Laboratories (RLs) and two Surveillance Centres (at Veterinary Schools) in England and Wales and 8 SAC VS Disease Surveillance Centres in Scotland provides a diagnostic service to private veterinary practitioners across GB. Clinical scanning surveillance information derived from diagnostic samples and carcasses is collected and analysed to determine baseline disease levels in the pig population. The aim is to provide an assessment of the current disease status of the GB pig population and to warn of potential risks from changing disease trends or new diseases and of zoonotic diseases of human health significance.

Since 1975, diagnostic data from both the VLA and SAC has been merged in the veterinary investigation diagnosis analysis (VIDA) database. This database has been an invaluable source of epidemiological trends for over 30 years, but was limited in the range of data recorded and the analyses available. In 1998, the VLA started to produce a more detailed dataset within FarmFile - a powerful database, linked to the VIDA database, containing a greater amount of descriptive epidemiological data on all submissions and incorporating analysis tools used for disease surveillance purposes. These tools provide automated statistical analysis and built-in “alerters” which highlight statistically significant, and therefore potentially clinically significant, changes in diseases diagnosis and trends enabling more extensive analysis of data for England and Wales from 1999 onwards.

The harmonisation project was initiated in 2006 to allow the extension of FarmFile analysis to cover Scotland as well. This involved the development of a single, standardised data collection system; consistent diagnostic criteria and harmonised recording, which enables the collation of the disease surveillance data from all three countries. This has been achieved by collaboration between staff and disease consultants at the VLA and SAC VS, funded by Defra and SEERAD.

Detailed surveillance data from laboratory submissions for all three countries can now be collated, providing a far greater amount of data for analysis and interpretation by disease consultants at a GB level, resulting in improved disease understanding and efficient use of relevant expertise. This should enable action to be taken and resources to be appropriately targeted at an earlier stage than was previously possible, as the dataset is now much more extensive and drawn from the whole pig population of GB. Further analyses will be developed and refined to improve disease surveillance and the health and welfare of the pig population of GB.

Overview

Pig Meat Consumption

There has been a 5% reduction in pig meat consumption across the EU compared to last year with the exception of Germany, which has increased consumption by 3.4%. The United Kingdom is the fourth lowest consumer of pig meat in the EU with an average consumption of 26 kg/person/ annum.

Trade

Trade The United Kingdom has resumed exporting to China and this is primarily made up of offal material that is not used in the UK. This trade is worth about £17,000,000 per annum.

One supermarket will be sourcing its bottom range of pig meat entirely from outside of the United Kingdom whilst another will only stock British pork in its welfare range.

EU

European law on identification and registration of pigs has been consolidated in current Directive 2008/7/EC. This has not led to any changes of importance to UK producers or veterinarians.

Fertiliser/seed

Fertiliser and seed prices may each rise by 48% before next years crops are planted and consequently there may be a fall in profits next year. Higher fertiliser prices will occur in the UK because of the weak pound.

Production

There is room for improvement from UK producers. At the moment the top 10% of EU pig farmers produce 26.38 pigs/sow/year compared with the average UK producer with 23 pigs/sow/year. If UK producers reached the production levels of the EU top 10% for pigs produced/sow/year and were also in the top 10% for numbers born alive, this could result in the rearing of 28.79 pigs/sow/year. This would assist the financial situation for pig farmers as the average UK cost of production is 140-145p/kg. At present the price received by producers is 135.91p/kg.

Global cereal supplies

There is more wheat available than before. Wheat production worldwide has increased 11.4% to reach a record of 680.20 million metric tons. Major increases have been seen in Europe, Russia and Ukraine. The US corn crop for 07-08 was the fourth biggest ever at 2.98 billion bushels and as a consequence the corn prices have dropped from $7.54/bushel to $3.81/bushel.

Intact males

Boars raised for meat production are not castrated as a general rule. To avoid taint producers are currently sending pigs to slaughter earlier than the optimum point on the growth curve. The Pfizer anti-testosterone vaccine has been made available in Switzerland. It improves feed conversion and produces a leaner carcase. In addition, because it reduces testosterone there is less aggression and boars are easier to manage and less likely to injure one another. The meat quality tests show it is as good as castrates or gilts. There is zero meat withdrawal and no safety issues. The vaccine prevents testosterone and androsterone (boar taint compounds). Both of these break down to the third component of boar taint skatole.

Endemic Disease Surveillance

A note about the disease trends charts.
This section of the report gives information on the data collected and analysed for diseases that were especially prevalent during the quarter due to seasonal influences or are especially topical or noteworthy for the period covered. For this report, data for England and Wales and Scotland have been combined onto a single histogram. Our charts show the number of diagnoses (numerator) as a proportion of the number of submissions in which that diagnosis was possible (denominator). These proportions are represented as blocks and the GB, combined, proportion as a line. The blocks are accompanied by bars indicating 95% confidence limits – generally, the greater the number of samples examined, the smaller is this range and the greater the confidence that reported figure is true. Note that the y-axis scale of the charts varies and therefore care must be taken when comparing individual charts.

Salmonella and Salmonellosis

Thirteen cases of clinical disease in pigs due to salmonellosis were diagnosed in the third quarter of 2008. This comprises 5.18% of all porcine diagnostic submissions and represents a statistically insignificant drop in diagnostic rate from this quarter last year (see figure 3). It also represents a drop from the previous quarter (Q2 2008) wherein salmonellosis accounted for 8.9% of all pig diagnostic submissions (data not shown).


Figure 3. VIDA Incidents of salmonellosis in pigs during Q3 of 2008 as a percentage of diagnosable submissions.

The predominant serotype this quarter was again Salmonella Typhimurium (STM), which was isolated from eleven of thirteen (85%) cases investigated under the endemic diseases project. Salmonella Derby was the only other serotype occurring in the quarter under this project, accounting for 15% of isolates.

Of the Salmonella Typhimurium (STM) isolates, the predominant phage type was ST PT U288, accounting for 62.5% of STM isolates. Next was ST PT 193, which accounted for 25% of isolates. ST PT 208 and an untypeable ST occurred once each.

Seasonal trends in diagnoses of salmonellosis in pigs as a percentage of diagnosable submissions are shown in figure 4. The most recent quarter from which data are available is Q1 2008. This graph highlights an increase in the percentage of submissions diagnosed with salmonellosis (as a proportion of diagnosable submissions) in mid 2007. This trend is not statistically significant and has not been maintained in the first 3 quarters of 2008 (only Q1 2008 shown on figure 4).


Figure 4. Seasonal trends in VIDA Incidents of porcine salmonellosis for England and Wales as a percentage of diagnosable submissions, Q1 1999-Q1

Of the thirteen recorded cases of salmonellosis in pigs in this quarter, four diagnoses were made from submission of a carcase, one from a lung submission and the remainder (eight) from faeces or rectal swabs. Concurrent disease was identified in all cases but one.

Salmonellosis can affect pigs of any age, but is most commonly recorded in grower/ finisher age pigs. This month however was notable for two investigations into clinical salmonellosis contributing significantly to ill thrift, scour and wasting in younger pigs, reared outdoors, one involving five-week-old pigs; the other involving eight-week-old pigs. Details of some of the Salmonella investigations undertaken this quarter are outlined below:

  • In the five-week old pigs diagnosed with salmonellosis typical gross postmortem changes of fibrinonecrotic enterotyphlocolitis were accompanied by polyserositis caused by Streptococcus suis serotype 2. Gastric infarctions were seen histologically alongside the septicaemic salmonellosis.

  • Two live 8-week-old rearing pigs were submitted as typifying a problem of ill thrift, scouring and wasting among a group of 1200 weaners. As well as enterotyphlocolitis due to Salmonella Typhimurium PT208, infective arthritis and PRRS viraemia were present. It is generally thought that passive and acquired immunity to Salmonella in pigs is serotype and phage type-specific. This means that mixing of pigs from different sources may result in suboptimal immunity in some pigs, as pigs encounter new serotypes when mixed that they have had no previous exposure to. Problems are especially likely to arise in the face of concurrent disease challenge by other pathogens, e.g. Streptococcus suis and PRRSv.

  • Fixed and fresh lung samples were submitted as part of an investigation into respiratory problems in growing pigs. The lung cultured positive for Pasteurella multocida and Salmonella Typhimurium PT193, and a PCR for the presence of PRRSv RNA performed on the fresh lung was positive. Immunosuppression and direct respiratory disease due to PRRSv were thought to have predisposed to septicaemic salmonellosis.

  • Two dead pigs were examined to investigate ill thrift, coughing and scour among a group of 100 pigs. Multiple pathological processes were identified including chronic low-grade pneumonia, PDNS, PRRS viraemia, and chronic active enterocolitis. Salmonella Typhimurium PTU288 was isolated in a septicaemic distribution implying that septicaemic salmonellosis will have been the cause of death, probably prompted by debility as a result of multiple insults.

  • An enquiry was received from a proactive specialist pig veterinary surgeon whose client is planning a total herd depopulation/ repopulation for eradication of PRRSv and Mycoplasma hyopneumoniae. The farm has historically suffered from sporadic bouts of disease in finishers, manifesting as scour, sudden deaths and reduced growth performance, always associated with Salmonella Typhimurium PTU288. ZAP scores (now ZNCP scores) have been variable. This veterinary surgeon was wondering how best to use this opportunity to improve salmonella control measures, both from the point of view of pig health and productivity, and because of the political focus on salmonella in the UK pig industry as a source of zoonotic infection for humans. The pig-free down time associated with the depopulation would seen to present an excellent opportunity to break the cycle of infection where pigs acquire Salmonella from contaminated buildings and from infected older pigs in front of them. The problem then arises of producing a Salmonella-free weaner to move into Salmonella-free accommodation.

  • It is at present impossible to source salmonella free breeding stock. VLA is collaborating in this case to effect adoption of likely effective interventions such as batch production of growing pigs, All-in All-out policies, scrupulous cleaning and disinfection of buildings between batches, and a firm focus on rodent control during the pig-free periods. Given that immunity is phage-type specific, concerns were raised about introducing new phage types with incoming high health gilts. Also the risk of creating a naïve population, which may be highly susceptible to introduction of new infection, was considered.

Brucellosis

19 cultures for Brucella suis were undertaken in Q3 and were all negative. A total of 46 cultures have been made in the first three quarters of 2008.

Fulfilling their role as OIE Reference Laboratory for brucellosis, staff at VLA Weybridge were involved in trials assessing proposed International Standard sera that will be used for Brucella suis and Brucella melitensis species specific tests. The six other OIE Reference Laboratories (Argentina, France, Germany, Italy, Canada and Israel plus three recognised European laboratories in Belgium, Portugal & Spain) all assessed the Standards in the full range of tests used for diagnosis, i.e. (complement fixation test (CFT), ELISAs and Rose Bengal test (RBT)). Results were discussed at OIE headquarters in Paris recently and minimum standards of sensitivity for each test were agreed. If accepted by the International Committee, changes will be made to the on-line version of the OIE Manual of Diagnostic Tests & Vaccines in May 2009. Sera will be made available to all National Reference Laboratories and the use of such should assist in the harmonisation of diagnostic tests used for diagnosis and International Trade.

False positive serological reactions (FPSR) are a major problem in serodiagnosis of brucellosis, attributed to the presence of antibodies which cross-react with the LPS antigen used in the assays. For example, following an outbreak of brucellosis in pigs in Germany Defra received a notification that the farm in question imported pigs from a farm in England. An on-farm investigation for porcine brucellosis on that farm was immediately undertaken. Detailed examinations of production records gave no indication of porcine brucellosis and revealed that the farm had no unusually high infertility records. The animals had been regularly visited by vets that were pig specialists. Additionally, animals from the same farm had been sent to other farms in the UK with breeding pigs without problems. There was no evidence of transmission from this farm but with the continuing cross reaction problem it makes it increasingly difficult to clear a ‘suspect’ herd.

PMWS


Figure 5. Percentage of submissions diagnosed with PMWS in Q3 compared with previous years same quarter

There was little difference in the rate of post weaning multisystemic wasting syndrome (PMWS) diagnoses from the same quarter last year, although the number of cases diagnosed fell from 12 last quarter to six this quarter so far. The numbers still remain too small to reflect any impact from vaccination.

  • In one case PMWS was diagnosed in 12-14 week old finishing pigs from an indoor 250- sow breeder finisher unit where, in the last month, two to three pigs per batch of 100 were coughing, scouring and wasting with poor response to antibiotic treatment. Vaccination of sows for PCV2 was ongoing for one year with a good response. The farmer selected three typical early cases which had reduced growth for one week. All were in fair body condition, one was pyrexic and coughing. Bronchopneumonia and scour were present in two of the pigs; Pasteurella multocida and Streptococcus suis 2 were isolated from the lungs of both pigs and PRRS virus was detected in the pig with the most severe lung lesions. Histopathology revealed lymphoid changes typical of PCV2 together with intracytoplasmic viral inclusions confirming a diagnosis of PCV2 associated disease, with lung lesions also indicating PCV2 associated respiratory disease. In another pig, which was scouring without lung lesions, Brachyspira pilosicoli was isolated and histopathology suggested past PCV2 activity. In this pig there was also a moderately severe interstitial nephritis. Thus complex multifactorial disease was diagnosed in which PCV2 associated disease was a component. The reasons for a rise in incidence of disease in the finishers were speculated to be PRRS virus infection playing a role in the respiratory disease (the herd had been considered to be stable for PRRSV) and the fact that recent larger litter sizes (up to 15 live born) may have meant that some piglets received inadequate colostral protection on which efficacy of sow vaccination for PCV2 depends.

  • A recent questionnaire based pilot study looked at cases of porcine circovirus associated disease between 1st May and 30th September 2008 and the history of PCV2 vaccine use. Of 15 cases of PCV2 associated disease identified during this period further information was available for 11. Of these three were in herds using sow vaccination and another was in a herd were the sow vaccination status for PCV2 was unknown. There were no cases found where piglet vaccination for PCV2 was undertaken. One of the cases had only PDNS, which is still of uncertain aetiology and which vaccines make no specific claims to protect against. Combined diagnoses with PMWS included PCV2 related pneumonia, two cases of Streptococcus suis and PRRS infection were seen. In the case with concurrent PCV2 associated pneumonia there was also Streptococcus suis infection and arthritis recorded.

    In one case a visit was carried out to investigate disease manifesting as PMWS on a closed 80-sow indoor farrow-finish unit which had previously been completely free of clinical signs of porcine circovirus associated disease (PCVAD). Two affected grower/ finisher pigs had been submitted to the VLA for post mortem examination although histological examination of tissues did not confirm typical PCV2-associated changes. Further wasted pigs were necropsied and at least one demonstrated typical histological lymph node changes. Also demonstrated on-farm was moderate to severe pneumonia due to Mycoplasma hyopneumoniae, a disease from which the unit was previously considered free. The practice of introducing pigs at 40kg into the finishing house without disinfection of pens was considered to have increased PCV2 challenge to incoming pigs. Madec’s 20-point plan was suggested as an adjunct to minimise the impact of PCV2 on this unit, and vaccination protocols against enzootic pneumonia and PCV2 were contemplated.

PDNS

Figure 6 shows that cases of PDNS increased in GB (but not with statistical significance) compared with this quarter last year. Figures remain static when compared with the previous quarter (see histogram below).


Figure 6. Percentage of submissions in Q3 diagnosed with PDNS compared with the same quarter in previous years

PRRS

The percentage of diagnosable submission confirmed with PRRS infection remained at the higher level we have become used to over the last two years (although this higher level does not represent a statistically significant increase from previous years) (see Figure 7). Of eight cases of PRRS infection diagnosed in this quarter in England and Wales, three were PRRS related pneumonia and five were systemic PRRS infection. In no cases were these infections diagnosed without concurrent disease being diagnosed, although no one additional diagnosis was prominent amongst these cases. Two cases of PRRS virus related reproductive diseases were also diagnosed this quarter. In one of these there was a sudden onset of early farrowing with a high rate of stillbirths and non-viable piglets. The herd was regularly vaccinated against parvovirus and erysipelas. The reproductive disease component of PRRS is not represented in the analysis below.


Figure 7. Percentage of submissions diagnosed with PRRS in Q3 compared with the same quarter in previous years

Respiratory Disease

The quarterly percentage of relevant diagnostic submissions with a diagnosis of pneumonia and/or pleurisy (excluding PRRS virus and PCV2 associated diseases) was slightly increased from the same quarter last year. Scotland recorded a greater percentage of cases from their diagnosable submissions compared with England and Wales (see Figure 8).


Figure 8. Percentage of submissions with a history pneumonia and pleurisy in Q3 compared with the same quarter in previous years

Further Reading

- You can view the full report by clicking here.
- Find out more information on PRRS by clicking here.
- Find out more information on PMWS by clicking here.


December 2008