Pig Quarterly Update

Author: Animal & Plant Health Agency
Reviewed:
Published: October 2018

Pig Diseases – Selected Highlights from the GB Emerging Threats Quarterly Report. Vol 22: Q2, April to June 2018

The following material is taken from the GB Emerging Threats Quarterly Report. Vol 22: Q2, April to June 2018. The full report can be found on the Animal & Plant Health Agency (APHA) web pages:

https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/738912/pub-survrep-p0418.pdf

For information about pig disease diagnosis and to access diagnostic support, please see:

http://ahvla.defra.gov.uk/vet-gateway/surveillance/diagnostic/index.htm

Diagnostic submission trends

Surveillance details for all diagnostic submissions to the GB scanning surveillance network in the second quarter of 2018 from an enhanced dashboard are summarised in Figure 1.

Figure 1: Pig disease surveillance enhanced dashboard submission output: total diagnostic records April to June 2018 – 304

These diagnostic submissions are voluntary and subject to several sources of bias. However it is interesting to note that respiratory disease was prominent in this second quarter of 2018. The main clinical sign most commonly reported was “respiratory” in Q2-2018 (Figure 2) while in the same quarter of 2017, the three most common main clinical signs reported were “diarrhoea & GIT”, “found dead” and “wasting”. This difference was also reflected in the classification of submissions by syndrome; in Q2-2017 the enteric syndrome was most common while in Q2-2018, systemic and miscellaneous then respiratory syndromes are the two most common.

Carcase submission numbers were similar to the same period in previous four years. Submissions of carcases are more likely to achieve a diagnosis as postmortem examination with fuller diagnostic investigation is possible; for example for the first six months of 2018 for enteric syndrome, a diagnosis was made in 89% of carcase submissions and 33% of non-carcase submissions while for respiratory syndrome a diagnosis was reached in 98% and 38% of carcase and non-carcase submissions respectively. The areas offering free carcase collection to post-mortem examination sites within the APHA network were expanded in 2017 (APHA, 2017) and the availability of this service is regularly publicised.

NEW AND RE-EMERGING DISEASE THREATS

First Report of African Swine Fever in China and Further Spread in Europe

The risk of introduction of African Swine Fever to China was highlighted in the literature last year (Vergne and others, 2017) and the first African Swine Fever (ASF) outbreak in China was confirmed on August 3rd 2018 in domestic pigs in the north eastern Liaoning province. Whilst this development and spread of ASF to China is of great concern, there is a closer ongoing threat of ASF nearer to the UK, as ASF persists in wild boar in Eastern and Central Europe with regular outbreaks in domestic pigs. There has been a significant and rapid increase in backyard pig outbreaks in Romania since June 2018 which is described in the recent POA update from IDM: https://www.gov.uk/government/publications/african-swine-fever-in-pigs-in-poland-lithuania-and-latvia.

This spread in Romania and the continuing outbreaks elsewhere in affected countries in the region have not been associated with significant westward movement of ASF in the last two months and the domestic pigs outbreaks were within zones where the intra-community trade of live pigs or fresh or frozen pig meat is not allowed. However the continuing outbreaks emphasise the importance of vigilance in both preventing introduction of ASF to the UK and the messages about not feeding kitchen waste to pigs remain highly relevant: https://www.gov.uk/government/news/pig-keepers-warned-not-to-feed-kitchen-scraps-to-pigs-due-to-african-swine-fever-risk.

An ASF poster is also available for pig keepers:

http://apha.defra.gov.uk/documents/surveillance/diseases/african-swine-fever-poster.pdf

 

 Figure 2: ASF in Eastern and Central Europe since January 2018

In order to raise awareness of the disease amongst pig keepers and veterinarians and assist early recognition of the disease, images of the clinical signs and pathology of ASF were compiled in conjunction with the Pirbright Institute and disseminated widely: http://apha.defra.gov.uk/documents/surveillance/diseases/african-swine-fever-images.pdf.

Penicillin resistance in Streptococcus suis isolate from aborted pig foetuses

Penicillin-resistant Streptococcus suis serotype 5 was identified in a diagnostic submission to APHA as the cause of abortion in a single sow. The penicillin minimum inhibitory concentration was 0.75μg/ml (CLSI breakpoint indicating resistance is > 0.5μg/ml) This is an unusual disease presentation due to a less common serotype of S. suis and is likely to have been a sporadic disease event. The isolate was also resistant to tetracyclines, lincomycin, tylosin and potentiated sulphonamide. There is no ongoing disease issue on the farm and minimal antimicrobial use. Free diagnostic investigation at APHA was offered should further possible S. suis disease occur on the farm. Penicillin resistance in S. suis very likely equates to resistance to betalactams (includes amoxicillin and ampicillin) and is a rare resistance in APHA S. suis isolates, not being detected in S. suis isolates from APHA scanning surveillance submissions over the period 2015-2017. Prior to that, a collaborative study reported penicillin resistance in 5% of S. suis isolates collected by APHA from 2009-2014 (Hernandez-Garcia and others, 2017). S. suis is a potential zoonosis hence there is concern from both pig health and welfare, and human health, perspectives if this type of resistance is found more widely; however laboratory confirmed reports of S. suis cases in humans are rare in the UK (1-7 each year, Public Health England 2016). Public Health England (PHE) confirmed no human S. suis cases have been reported in England in 2018 to date. A factsheet from the Health and Safety Executive was provided to the farmer: http://www.hse.gov.uk/agriculture/zoonoses-data-sheets/streptococcus-suis.pdf. This indicates that it is important to practise good occupational hygiene, cover cuts and abrasions, use suitable disinfectant, and people who are immunosuppressed or splenectomised should avoid contact with pigs. The APHA antimicrobial resistance lead reported this finding to the Veterinary Medicines Directorate (VMD), APHA Zoonoses Team and PHE and VMD will raise it at the next Defra Antimicrobial Resistance Coordination (DARC) Group meeting.

UNUSUAL DIAGNOSES

Aortic haemorrhage likely due to copper deficient

An interesting finding was made outside the GB scanning surveillance network which was discussed with APHA when deaths and anaemia in growing pigs of different ages were being investigated. The pigs were in a small 10-sow herd rearing pigs indoors on a barley and wheat mix, together with waste milk but without vitamin, mineral or trace-element supplementation and without use of vaccines. A number of pigs died and post-mortem examination revealed large blood clots in the pericardial sac. Such cases have been seen before in growing pigs on milk diets, associated with copper deficiency. Low liver copper and selenium concentrations were confirmed in this case and it is likely that the pigs were also iron deficient. The low selenium was also significant in relation to cases of hepatosis dietetica which were also confirmed.

Potential food safety and toxicity issues

An investigation into possible exposure of pigs to difenacoum-based rodenticide is described in the APHA Chemical Food Safety quarterly report for Q2-2018: . The second generation rodenticides have very long half-lives such that residues can remain in tissues, particularly liver, for many months. In brief, eight fattening pigs escaped from their pen and may have accessed bait in a box containing a difenacoum-based rodenticide. The pigs were placed under voluntary restriction and monitored. Blood samples were analysed for clotting factors and clotting metabolites. The pigs remained healthy and results provided no evidence that the pigs were likely to have been exposed to rodenticide and restrictions were lifted with the agreement of the Food Standards Agency. As an additional precautionary measure, offal from the pigs was discarded when they went to slaughter six weeks later.

Several incidents in ruminants of hemlock water dropwort (Oenanthe crocata or dead man’s fingers) poisoning were diagnosed within the GB scanning surveillance network this summer. None were in pigs but this is of potential relevance to smallholder pigs which may be allowed outdoors in less controlled situations than commercial pigs, with access to a range of wild plants in woodland or rough grazing, and may encounter toxic plants such as this. Hemlock water dropwort contains a neurotoxin, oenanthotoxin, which causes seizures and death. The plant is found in damp, marshy ground and typically in ditches. The roots are more pathogenic than the stems and leaves but all can cause toxicity and dry weather with sparse grazing may have predisposed to animals eating unusual vegetation. Livestock must be prevented from having access to these plants and images are on the link below.

http://wildflowerfinder.org.uk/Flowers/W/WaterDropwort(Hemlock)/WaterDropwort(Hemlock).htm

CHANGES IN DISEASE PATTERNS AND RISK FACTORS

Genotyping of porcine circovirus 2 associated with disease outbreaks  

Genotyping of porcine circovirus 2 (PCV2) involved in porcine circovirus 2-associated disease (PCVD) outbreaks was prompted by a cluster of three diagnoses in May and June 2018 at Starcross and Thirsk Veterinary Investigation Centres. These three cases were described in the July surveillance report (APHA, 2018b). One was in a small unvaccinated herd and two incidents were diagnosed in post-weaned commercial pigs supposed to be vaccinated for PCV2. In the small herd, the PCVD manifested in rapid deaths of six-week-old pigs showing jaundice due to PCVD-associated hepatitis. In the commercial pigs, the PCVD presented with primarily respiratory signs in one herd and wasting associated with colitis or pneumonia in the other, in both herds together with disease due to bacterial pathogens. When PCVD is diagnosed in vaccinated pigs, a review of compliance with vaccine storage and administration requirements and an assessment of the scale of disease are important in determining whether vaccine failure may have occurred. Where suspected, lack of vaccine efficacy should be reported to the Veterinary Medicines Directorate. Previously, issues identified include batches of pigs not having received their PCV2 vaccination and changes in timing of PCV2 vaccination (APHA, 2014). The cluster of PCVD outbreaks in Q2-2018 resulted in a small increase in the diagnostic rate for PCVD, as illustrated in Figure 3, however data is incomplete for 2018 and this may not be significant; there is no known association between the two incidents in commercial pigs.

The sequencing of open reading frame 2 (ORF2) of PCV2 involved in 11 cases of PCVD confirmed at APHA since 2016 showed that nine were genotype PCV2D and two were genotype PCV2B. All three 2018 PCVD cases were PCV2D. Previously, although PCV2D has been detected, it was in the minority of cases with PCV2B being predominant (Grierson and others, 2017). This shift to PCV2D is reported in pigs globally, currently there is no clear evidence that vaccine efficacy is affected. Monitoring of the diagnostic trend of PCVD and PCV2 genotype will continue.

Figure 3: GB incidents of PCVD as a % of diagnosable submissions (annual data incomplete for 2018)

Reassortant H1avN1 swine influenza strain present since 2012

A reassortant avian-like H1N1 (H1avN1) swine influenza A virus (SIV) strain was identified retrospectively in APHA pig scanning surveillance submissions in which swine influenza A was previously diagnosed. This H1avN1 SIV variant has been detected in three submissions to date: once each in 2012, 2014 and 2016, suggesting that it is being maintained at some level in the GB pig population.

The Defra-funded swine influenza surveillance is provided at no charge to submitting veterinarians and tests diagnostic samples from pigs with acute respiratory disease for swine influenza virus. More details are given on this link: http://apha.defra.gov.uk/documents/surveillance/diseases/swine-influenza.pdf

Actinobacillus pleuropneumoniae isolate detected bearing Apx1 toxin gene

As part of investigation into an increase in Q1-2018 in the VIDA diagnostic rate of disease due to Actinobacillus pleuropneumoniae (APP) (APHA, 2018c), APP isolates archived since January 2016 were analysed for their Apx toxin gene content. Apx1 toxin gene was detected in one of 36 isolates, from the lung of a pig with typical APP lesions submitted to APHA in August 2017. Isolates with Apx1 toxin gene of APP are found in serotypes 1, 5, 9, 10, 11 and 14. Virulence is multifactorial in APP and is influenced by exotoxin production and other factors. In general, serovars producing Apx1 are considered to be more virulent and to cause higher mortality in pigs, especially when in combination with Apx2. Serotype 9 (which produces Apx1 and Apx2) was reported historically in UK pigs (McDowell and Ball, 1994), but testing between 1995 and 2015 in England and Wales did not detect serotypes producing Apx1, and serotype 8 was predominant (O'Neill and others, 2010; Li and others, 2016) while in Scotland, one serotype 9 isolate was identified in 2012 on a single occasion (APHA, 2012). In Europe, serovar 9 is prevalent in the Netherlands, Spain, France and Germany. The other archived APP isolates tested had either Apx2, or Apx2 with Apx3, toxin genes, as is usual for GB APP isolates. The rise in the diagnostic rate for disease due to APP in January to March 2018 is likely to have reflected seasonal factors and no unusual patterns of antimicrobial resistance were noted in the isolates. The Apx1 toxin gene-bearing isolate was from a 17-week-old pig in a small (40-sow) herd and disease was not reported to be unusually severe. It is possible that serotype(s) of APP with Apx1 toxin gene have remained in discrete, small parts of the UK pig population at a very low level since they were last detected prior to 1995. Serotyping is in progress and periodic toxin typing of future APP isolates will be undertaken.

Parasitic pneumonia due Metastrongylus apri

GB diagnoses of parasitic pneumonia in pigs showed a rise for the 12 months to the end of June 2018 with seven diagnoses, spread across each quarter, compared to an average of three in prior years. One diagnosis was in farmed wild boar and the other six in commercial pigs aged nine to 18 weeks. There were additional diagnoses in five of the cases. In the two cases where parasitic pneumonia was the only diagnosis made, the main clinical sign reported was “respiratory”. It is important that the lower airways are opened and inspected during post-mortem examinations of pigs with respiratory disease or pathology so that this lungworm is detected as illustrated in Figure 4.

 

Figure 4: Metastrongylus apri worms in lower airways of a pig's lung

Abortions suspected to relate to hot weather

Abortions induced by hyperthermia in association with the hot weather was suspected to have resulted in 20 abortions in one group of 45 sows at 10 weeks gestation.

Streptococcus suis serotype trends

During Q2-2018, for the first time in over a decade, Streptococcus suis serotype 2 was not the predominant serotype isolated from pigs in APHA diagnostic submissions in the quarter as shown in Table 1. This change in profile may be a transient effect and/or reflect more diagnostic investigations in younger pigs in which disease due to S. suis serotype 1 is mainly seen, reflecting efforts to reduce antimicrobial use. In some cases, S. suis isolates were required for autogenous vaccine production. The S. suis serotype 1 incidents were in either preweaned or recently weaned pigs except in one case which was in a six-week-old pig with porcine circovirus 2-associated disease. The profile of S. suis serotypes isolated will be kept under review.

 

Table 1: Streptococcus suis isolates from APHA diagnostic submissions



Lawsonia intracellularis - survey of practitioners

Following an increase in the annual diagnostic rate of Lawsonia-associated disease in submissions to the GB surveillance network in 2016 and 2017 (APHA, 2017b), a survey (survey monkey UK) of practitioner members of the Pig Veterinary Society (PVS) was undertaken to find out if these data reflected the situation in the field, and if so, the practitioners’ opinions on possible reasons. The survey report was circulated to PVS members, with a summary:

“Twenty seven PVS practitioner members responded, 18 of whom spend 50-100% of their time working with pigs. Nearly 60% have perceived a degree of increase in Lawsonia-associated disease in the last two years (Figure 5) and most of these respondents had confirmed disease by laboratory testing in at least some of the cases seen.

 

Figure 5: Percentage responses of veterinarians to survey question “Have you perceived more Lawsonia-associated disease in the last two years”

The most common reason selected for the increase in Lawsonia-associated disease was changes in antimicrobial use, with the second most common reason being increased use of diagnostics to aid more specific disease control. Disease was reported to have been successfully controlled in most cases, however recurrence in subsequent batches was reported and, in a few, only a partial response was seen although the comments indicate some of these may have been more complex disease situations. Over 60% of respondents suspected they were seeing an increase in certain diseases in relation to changes in antimicrobial use, necessitating additional interventions to control them, with the comments mentioning Glässers, Streptococcus suis and respiratory diseases most often. Only 20% of respondents thought that they were seeing certain diseases at greater frequency in relation to changes in antimicrobial resistance.”

The increasing GB diagnostic rate for Lawsonia-associated disease seen during 2017 which prompted the survey has not continued for the first six months of 2018 (Figure 6) but this will be kept under review.

 

 

Figure 6: Seasonality of GB incidents of Lawsonia-associated disease 2006-2018

HORIZON SCANNING

Novel bat-derived enteric virus in pigs in China

A useful update summarising information available on Senecavirus A (SVA) and vesicular disease outbreaks ongoing in the USA associated with infection with SVA was provided in Pig Progress (Yoon, 2018). The disease due to SVA is mild and short lived and the impact on pig health and welfare is not considered to be significant. However, concern arises due to the close similarity to notifiable vesicular diseases, including foot and mouth disease, of the vesicular manifestation of SVA which has not been detected in UK pigs. The message to pig keepers and veterinarians in the UK is that cases of vesicular disease must be reported promptly as suspect notifiable disease to APHA in order to investigate the possible involvement of notifiable vesicular disease viruses, in particular foot and mouth disease virus. Anyone wishing to report suspicion of notifiable disease in England should call the Defra Rural Services helpline on 03000 200 301. In Wales the contact telephone number is 0300 303 8268 while in Scotland the local APHA Field Services office should be contacted. Only after ruling out the presence of notifiable disease, would testing for Senecavirus A be undertaken. A diagnostic PCR is available at the Pirbright Institute for use in this scenario for early detection of an SVA-associated vesicular disease outbreak.

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