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Emerging Threats Quarterly Report – Pig Diseases – October to December 2011

by 5m Editor
20 March 2012, at 12:00am

Continued reassortment of pH1N1 with other strains continues to be reported worldwide, and this virus appears to reassort quite readily. The situation is being monitored in the UK.

Highlights

  • Leptospirosis outbreaks in herds with rodent infestations
  • Molecular analysis of Klebsiella pneumoniae isolates
  • Nutritional osteodystrophy cases in pigs on non-commercial diets
  • Actinobacillus suis isolated from APP-like pneumonic lesions
  • Swine dysentery outbreaks in Yorkshire and Scotland

New and Emerging Diseases

Leptospirosis Outbreaks

Three leptospirosis outbreaks in pigs were diagnosed between May and November 2011. Before May 2011, only two positive PCR results had been obtained in pig kidneys since the test was implemented as a diagnostic method in 2004. The test has recently been improved and it is difficult to determine whether the recent cases represent a true increase or have been recognised due to the test improvement. In all three outbreaks (two of reproductive failure, one of systemic disease) there have been clear links of disease to contact with rodents or small mammals which are recognised reservoirs of leptospire infection.

The first outbreak was the wildlife-associated L. Pomona infection detailed in previous quarterly threats reports and below. The two November outbreaks were not associated with each other and it was only possible to investigate one in detail. Kidney from aborted piglets on the unit tested positive for pathogenic leptospira by PCR and on-farm investigation identified a severe rat infestation as the likely source of infection. This was supported by high antibody titres in sows with reproductive failure to several Leptospira serovars including rodent-associated ones (Icterohaemorrhagiae, Copenhageni) as well as Canicola and Bratislava. The unit was a recently established gilt herd where varying forms of reproductive loss were occurring, including increased regular and irregular returns to service, abortions and weak neonatal piglets. The naivety of the gilt herd to leptospire infection was likely to have influenced the morbidity rate. The clinical situation was complicated by concurrent cases of erysipelas and, although gilts were supposed to be vaccinated for erysipelas prior to arrival on the unit, no further cases were seen once the farm began vaccinating gilts for erysipelas after arrival. Active rodent control was implemented and is ongoing and vermin-proof carcase disposal bins were put in place. Leptospire vaccination was not undertaken but in-feed antimicrobial treatment was used and the clinical situation has improved. In the third outbreak which was not investigated further, a jaundiced grower pig was submitted with liver and kidney pathology and tested PCR positive, this unit also noted a significant rat infestation at the time clinical disease emerged. No sera could be obtained to investigate the infecting serovar further; however, based on the clinical signs and pathology, L. Icterohaemorrhagiae was considered a likely candidate.

Interestingly, VMD reports that applications for licences to import leptospire vaccines have increased significantly since 2007. Although the number of applications only rose from 22 to 26 between 2010 and 2011, this corresponded to almost a doubling of the number of pigs vaccinated.

In all cases, appropriate advice was given regarding measures to take to reduce the zoonotic risk posed by leptospires. Leptospirosis diagnoses will be kept under review and a new VIDA code has been established for outbreaks which do not involve reproductive disease.

Ongoing Emerging Disease Investigations

Leptospiral infection in breeding unit with high sow antibody titres to L. Pomona

This investigation was initiated in May 2011 and detailed in Q2 and Q3 Emerging Threats reports. It was begun following the detection of pathogenic leptospire infection by PCR in the kidney of a neonatal pig on a unit with reproductive disease. Affected sows had high antibody titres to L. Pomona, a serovar exotic to the UK. Breeding pigs on the unit are now vaccinated with imported vaccine and were treated with antimicrobials. Leptospires were successfully cultured from the kidneys of insectivores and small rodents collected from the farm by FERA under licence. L. Pomona and L. Canicola were identified from a shrew and vole respectively by the Leptospirosis National reference laboratory in Amsterdam (Royal Tropical Institute) (KIT), funded jointly by ED1200 and FZ2100, the nonstatutory zoonoses project. This investigation has been concluded. As breeding pigs are vaccinated it is not possible to determine by serology whether there is continuing exposure to infection. The Pig Expert Group has indicated to the lead investigator that if the unit stops vaccinating in the future, serology can be funded to determine if there is continued exposure of unvaccinated pigs to L. Pomona. The isolation of L. Pomona from a small mammal collected from the farm supports the likelihood that the sows were infected with a wildlife-adapted L. Pomona strain rather than a pig-adapted L. Pomona. Control measures have been successfully implemented on the single affected unit and include antimicrobial treatment and vaccination. An information sheet on the investigation was sent to BPEX, BPA, HCC Wales and the Pig Veterinary Society and is available here.

Incoordination in growing pigs with unusual peripheral neuropathy

This investigation was initiated in May 2011 and detailed in Q2 and Q3 Emerging Threats reports. Pigs aged 6-11 weeks old from three units have been diagnosed with this unusual radiculitis, ganglionitis and peripheral neuropathy with myelin deficits. Further investigation is focused on characterizing the pathology in more detail, including electron microscopy. An immune-mediated aetiology remains possible, as in humans with similar pathology. The possibility of applying methods to detect anti-myelin antibody is being explored. Details of the condition, including videos of affected pigs, were shown at two meetings: the European Pathology Surveillance meeting in Edinburgh in September and the European Scanning Surveillance meeting in Switzerland in October. None of the participants at either meeting reported anything similar in their countries. Veterinary practices, BPEX and Pig Veterinary Society have been made aware through AHVLA reports and a presentation was given at the Pig Veterinary Society Spring meeting in May. An oral presentation has been accepted for the European Symposium of Porcine Health Management in Bruges in April 2012.

Klebsiella pneumoniae subsp. pneumoniae septicaemia

This investigation was initiated in August 2011 and six outbreaks of septicaemia due to Klebsiella pneumoniae subsp. pneumoniae infection were diagnosed as the cause of sudden death of preweaned pigs on outdoor breeding units between July and September, all in East Anglia. Details were included in the Q3 Emerging Threats report. Characterisation of the outbreak isolates was undertaken by AHVLA Weybridge. Molecular analysis was performed on six Klebsiella pneumoniae subsp. pneumoniae outbreak isolates. Five historical isolates of the same Klebsiella species were included in the analysis to allow comparison. Multilocus sequence typing, which evaluates the relatedness within a bacterial species, revealed that the six septicaemic Klebsiella isolates belonged to the same sequence type (ST25). The historical isolates had different sequence types. Analysis of virulence gene content showed that the six septicaemic ST25 Klebsiella strains possessed identical virulence gene profiles which differed from historic isolates. These preliminary findings suggest that a distinct strain of this Klebsiella species may be associated with the disease outbreaks. Further investigation is in progress to compare outbreak isolates to a wider range of historic isolates. A presentation on the condition was given at the European Scanning Surveillance meeting in Switzerland in October and at the Pig Veterinary Society Autumn meeting in November. A new VIDA code and diagnostic criteria have been established for this condition. Details have been included in AHVLA reports to veterinary practices, BPEX, BPA, HCC Wales and the Pig Veterinary Society and information is available here. A poster presentation has been accepted for the European Symposium of Porcine Health Management in Bruges in April 2012.

Unusual Diagnoses or Presentations

There were a number of unusual diagnoses this quarter; details of these have been included in monthly AHVLA reports and AHVLA highlights to BPEX, BPA and Pig Veterinary Society. These will be kept under review to assess whether they justify initiation of emerging disease investigations.

Congenital tremor and panencephalitis

Panencephalitis was observed histologically in postweaned pigs with persistent congenital tremor (CT) together with lesions consistent with type A2 CT. Pigs were alert and feeding and those on farm were reported to recover. In view of the panencephalitis, ruminant pestivirus involvement was ruled out using the panpestivirus PCR and it was hypothesised that the panencephalitis reflected part of the ‘repair’ process. Pigs with type A2 CT are usually submitted much earlier as neonates so it is not known whether the pathology seen is unusual in postweaned pigs with persistent type A2 CT. Material from these cases was retained for future use in an AHVLA RDIIF virus discovery project, as type A2 CT is believed to be caused by an, as yet, unidentified virus.

Actinobacillus suis pneumonia

Actinobacillus suis was isolated from lesions resembling those usually caused by Actinobacillus pleuropneumoniae (APP) in an outbreak of pneumonia causing deaths in finishing pigs. As lesions can be confused with typical APP, culture is essential to achieve a diagnosis. This is documented in the literature especially associated with minimal disease herds (Jubb, Kennedy and Palmer’s Pathology of Domestic Animals 5th Edition Vol. 2 p588) and http://www.aasv.org/shap/issues/v3n5/v3n5p209.pdf) but is a rare finding in the UK and will be kept under review.

Coal tar poisoning

Two confirmed cases of coal tar poisoning were diagnosed in 2011. One was highlighted in the Q1 Emerging Threats report due to road planings being used for pig pen flooring under straw. The other was due to ingestion of remnants of clay pigeons and caused four sudden deaths from a group of replacement gilts in an outdoor paddock. Post-mortem examination of one gilt revealed hepatopathy and jaundice raising the possibility of coal tar poisoning and farm staff found the clay pigeon remnants. The gilts had been placed on fresh ground and it came to light that clay pigeon shooting had taken place in the past, but was thought to be too long ago to be of concern. The pigs were for breeding and not destined for the food chain; however, a voluntary 28-day period of restriction was agreed and the gilts were moved from the paddock. A review of common poisonings in pigs is planned with a view to producing information for producers. A poster presentation on the road planings incident has been accepted for the European Symposium of Porcine Health Management in Bruges in April 2012.

Skin lesions due to summer midge bites

SAC reported skin lesions suspected to be due to biting midges (Culicoides obsoletus and Culicoides impunctatus) causing significant losses in the abattoir due to condemnations. Of all insects caught in traps these species comprised 25 per cent and 6 per cent respectively. Both these species are known to feed on pigs. No other species capable of biting pig skin were detected. No Stomoxys species flies were found which have been suspected of causing skin lesions in other parts of UK. The lesions are illustrated here.

Dicrocoelium dendriticum fluke lesions at slaughter

Liver lesions were found at slaughter in 25% of outdoor-reared finishers from one herd. The very small flukes were located within the central cavities of focal fibrotic liver lesions which looked like large white spot lesions. This was an incidental but interesting finding and is illustrated here.

Changes in Disease Patterns and Risk Factors

Swine influenza strains

In the last quarter of 2011, there were 29 submissions tested under the swine influenza surveillance project SV3041, eight were positive for influenza m gene by PCR. Two influenza virus strains were detected; H1N2 predominantly and pandemic H1N1 2009 (pH1N1). Avian-like H1N1 has not been detected since April 2011. Pandemic H1N1 2009 virus has been detected on 40 pig units since it emerged in UK in November 2009. Evidence suggests that pH1N1 is replacing avian-like H1N1 in the UK. Several pig units are reporting the use of killed influenza vaccine containing H1N1, H3N2 and H1N2 strains, but the efficacy of the vaccine against pH1N1 is not stated. As the vaccine contains several strains, interpretation of the haemagglutination inhibition test (HAIT) after vaccination is likely to be difficult. Viruses isolated under the surveillance project continue to be checked to detect novel reassortant strains. No further reassortant viruses have been identified in UK pigs since that reported previously (Howard et al, 2011. Reassortant pandemic (H1N1) 2009 virus in pigs, United Kingdom. Emerging Infectious Diseases 17 (6) 1049-1052).

Swine dysentery diagnoses

A recent upsurge in swine dysentery on farms in the Thirsk region has been documented by BPEX (http://www.pighealth.org.uk/health/news.eb) and confirms that swine dysentery remains a problem in some areas. The infected units are a combination of newly infected farms and farms with endemic infection which remain a persistent threat to others. Eight Brachyspira hyodysenteriae isolates are available from six units. Tiamulin MICs were established for the recent isolates funded by the ‘Monitoring of Antimicrobial Resistance in Bacteria from Animals and their Environment Project’ within AHVLA and all have been sensitive to tiamulin. Molecular analysis is planned at AHVLA Weybridge to attempt to determine whether infections on the different units are linked to assist epidemiological investigations.

Swine dysentery is also causing concern in Scotland. SAC diagnosed swine dysentery in 38.6 per cent of submissions tested (32 of 83) in the last quarter of 2011 compared to 7.1 per cent of submissions tested in the same quarter in 2010, and 12.3 per cent in the previous quarter in 2011. Increasing numbers of outbreaks are being diagnosed on all-in all-out grower units on which pigs are often healthy at four-weeks old but are affected by dysentery around ten-weeks old. Investigations are required to determine whether the pigs arrived with infection or were infected at the grower unit.

Osteodystrophy in growing pigs

Further to the SAC case of rickets-type osteodystrophy and osteoporosis in fattening pigs described in the Q3 Emerging Threats report, two further cases of nutritional osteodystrophy have been recorded in AHVLA. In all three cases, pigs were fed home-mixed rations or food waste and dietary mineral and/or vitamin imbalances were suspected. In the SAC case, the diet was found to be low in phosphorus and it had been assumed, incorrectly in this case, that high phytase in the diet would compensate for low dietary concentrations of phosphorus. Information is being prepared to be circulated to BPEX, BPA and Pig Veterinary Society to alert producers to the importance of ensuring adequate and balance mineral intake, particularly where noncommercial diets are fed.

Horizon-Scanning

Novel swine-origin influenza strains

Continued reassortment of pH1N1 with other strains continues to be reported worldwide, and this virus appears to reassort quite readily. In the US, some reassortant strains of swine origin (H1N2 and pH1N1) have been found in people, some with association with pigs. These have not been detected in people in Europe. There has also been an avian-like H1N1 infection of a person in Germany. These events probably occur regularly and are usually of no consequence as there is no human-to-human transmission. Their recent detection probably reflects improved human influenza surveillance rather than a new pattern of events. Human-derived pH1N1 remains infectious to pigs and vice versa. The situation is being monitored in the UK.

Peri-weaning failure to thrive syndrome (PFTS)

Information on this postweaning wasting syndrome reported from North America was circulated to BPEX, BPA, HCC Wales and the Pig Veterinary Society and is available here. No cases have been identified in UK to date.

African Swine Fever

The continued outbreaks in Russia maintain the threat of introduction of infection to Eastern Europe. Maintaining awareness of the threat of the disease, and knowledge of the clinical signs and pathology is important and recent Pig Veterinary Society meetings have included two presentations on the disease. FAO have a useful publication with details on the Russian situation. Further information is available on the Defra website.

PRRSv genotype 2

Introduction of PRRSv genotype 2 (North American) remains a threat, particularly if live pigs are imported from Europe without appropriate pre and post import testing to ensure they are not infected with PRRSv. As PRRSv is not a statutory pathogen, testing is voluntary. The National Pig Association is finalising a consultation to establish recommended protocols for testing pigs for selected non-statutory pathogens to address this threat. Methods of increasing awareness of potential risks amongst those who import live pigs are also being explored.

Further Reading

- You can view the full report by clicking here.

- Find out more information on the diseases mentioned in this report by clicking here.

March 2012