Emerging Threats Quarterly Report – Pig Diseases - April-June 201306 November 2013
Among the highlights of the latest quarterly surveillance report for the second quarter of 2013 from AHVLA are that Klebsiella septicaemia has been diagnosed for the third consecutive summer and swine influenza remains prevalent in England and Wales. The report also covers the outbreak of porcine epidemic diarrhoea in the US.
These reports aim to identify emerging animal disease related threats. Their production is underpinned by a large amount of surveillance data and information compiled as part of the Defra Food and Farming Group animal disease surveillance programme. Some of these data can be viewed on the AHVLA website.
- Emergence of virulent porcine epidemic diarrhoea in the USA
- Klebsiella septicaemia diagnosed for third consecutive summer
- Swine influenza remains prevalent in England and Wales
Ongoing Emerging Disease Investigations
Klebsiella species septicaemia outbreak on an indoor unit
The first 2013 outbreak of Klebsiella pneumoniae subsp pneumoniae septicaemia was diagnosed in May, continuing the seasonal occurrence of this disease in summer months for a third consecutive year within the East Anglian region. Disease occurred slightly earlier in the year but was typical of outbreaks in 2011 and 2012 with sudden deaths of well-grown preweaned pigs from two-weeks- old.
This outbreak was the first to be diagnosed on an indoor unit.
Clinical signs of malaise and skin discolouration were observed in some piglets for a short time before they died, reflecting the greater ease of close inspection of litters on indoor units.
In-contact pigs in affected litters were treated with antimicrobial and further deaths did not occur in treated litters. Approximately 40 piglets died from a farrowed batch of 800. So far, all the outbreak isolates of Kpp are a particular sequence type with a small plasmid and rmpA virulence gene. This combination of characteristics has not yet been identified in any non-outbreak Kpp isolates including those obtained by swabbing pigs received by AHVLA for diagnostic post-mortem examination from farms with no history of disease.
Figure 1 illustrates Kpp septicaemia diagnoses to date, disease was diagnosed in two consecutive years on one unit. On units where disease was diagnosed in previous years, postmortem examination on a batch of suspect cases has been offered free of charge in 2013, specifically to investigate whether Kpp is continuing to cause losses. No such submissions have yet been received. The disease was highlighted at a recent presentation to European pig veterinarians (Bidewell and others, 2013) to maintain awareness of this emerging seasonal disease which appears to be associated with a particular Kpp strain and is, to date, of low herd prevalence.
Unusual Diagnoses or Presentations
There were a number of unusual diagnoses this quarter; details of these have been included in monthly AHVLA and SACCVS 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.
Meningoencephalitis of likely viral aetiology in growers
A severe non-suppurative meningoencephalitis considered likely to be of viral aetiology was detected by histopathology in one of three six-week-old pigs submitted from a rearing unit to investigate sudden deaths and meningitis-like signs.
The affected pig was non-pyrexic, in lateral recumbency and paddling. No significant bacteria were isolated and histopathological lesions in the brain were suspicious of teschovirus infection. There was marked cerebral and, particularly, cerebellar involvement, which contrasts to the distribution observed in past cases of porcine sapelovirus-associated encephalitis. Immunohistochemistry did not detect intralesional PTV antigen to confirm porcine teschovirus involvement, nor that of PCV2, porcine sapelovirus or louping ill virus. The lesions were distinct from those seen in Aujesky’s disease.
The affected batch of pigs responded to antimicrobial treatment with losses limited to 30 of 4,000 over one week, making it likely that the presumptive viral meningoencephalitis was a minor component of the clinical problem.
Porcine teschovirus causes Teschen/Talfan disease, of which Teschen disease is notifiable and is distinguished from Talfan disease by the scale and severity of clinical disease. As a precaution, in spite of the low disease incidence, this case was discussed with the Veterinary Exotic and Notifiable Disease Unit, AHVLA, who kept a watching brief while investigations were in progress to make sure that no indication of Teschen disease developed on the unit.
The cause of the lesions in the pig were typical of those associated with neuronotropic viral infection and post-mortem examinations have been offered on pigs if similar clinical signs occur in future batches for further investigation, including virology.
Changes in Disease Patterns and Risk Factors
Swine influenza remaining prevalent in England and Wales
Swine influenza remained prevalent, with a higher per cent of diagnosable submissions being diagnosed in this quarter of 2013 compared to the same quarter in 2011 and 2012 as illustrated in Figure 2. All the diagnoses this quarter were in England and Wales.
The peak in diagnoses seen in the first quarter of 2012 has not been exceeded in any quarter since. Annual diagnoses of swine influenza are illustrated in Figure 3, the significant increase since 2009 is likely to reflect a combination of the incursion of pandemic H1N1 2009 into a pig population which was naïve, introduction of the diagnostic PCR for routine diagnosis in early 2009, improved awareness and use of the Defra-funded swine influenza surveillance available and possibly other factors.
Virus was detected in nine submissions between April and June 2013. The virus strain involved was only identified in three of these; two were H1N2 and one was pandemic H1N1 2009, which are the two predominant strains detected in GB pigs in the last 12 months.
Virus was not isolated in six m gene PCR-positive submissions, which may just reflect the greater sensitivity of the PCR detection method. However, further investigations have been initiated to try to identify the infecting strain as the proportion of submissions in which the strain involved was not identified is higher than desirable.
These investigations include tissue culture in addition to conventional virus isolation in eggs and, where possible, swine influenza serology on convalescent pigs in affected cohorts.
Identification of the infecting strain does not change the overall diagnosis of active swine influenza infection but assists veterinary practitioners in determining whether it is appropriate to use swine influenza vaccination as part of disease control and, sometimes, in identifying possible sources of infection.
Identifying swine influenza strains circulating in pigs is a vital component of the national Defra-funded swine influenza surveillance project which aims to monitor what strains are present, any changes within them, and detect novel strains. It is also important for directly informing appropriate strain selection for use in subtype-specific serological assays and to match to vaccine strains.
Porcine circovirus-2 associated disease as a cause of paralysis
Marked spinal cord pathology associated with PCV-2 infection was reported by Zlotowski and others (2013) in three to four-month-old pigs in two finishing herds in southern Brazil.
Clinical signs observed were staggering gait and paraparesis progressing to paralysis and permanent lateral recumbency. The neurological signs related to areas of necrosis and oedema in spinal cord, and the results of histopathological and immunohistochemical analyses strongly implicated PCV2 infection in the pathogenesis of the lesions. A non-haemorrhagic panencephalitis in pigs with porcine circovirus2- associated disease (PCVD) and PCV2-associated cerebellar vasculopathy have both been detected in GB pigs in past years.
This publication raises the need to consider PCVD as another cause of paralysis in pigs and examination of spinal cord as well as brain would be worthwhile in cases of PCVD-associated neurological disease.
A novel cause of porcine colitis, Brachyspira hampsonii, identified in North America
Enteric disease in growing pigs in the USA and Canada, clinically indistinguishable from swine dysentery was diagnosed as spirochaetal colitis due to infection with a novel Brachyspira species, namely B. hampsonii.
Recent findings were presented at a Pig Veterinary Society meeting (Harding, 2013). Since its first detection in Canada, B. hampsonii has been identified in a high proportion (43 per cent) of samples from pigs with loose bloody or mucoid diarrhoea in growing pigs and disease has been reproduced by experimental infection. This species is distinct from B. hyodysenteriae and B. pilosicoli, and would be distinguished from them by standard Brachyspira species identification methods used at AHVLA and SACCVS.
Cornelia Bidewell, Susanna Williamson, Jon Rogers, Therese Carson, Cath Clark, Richard Ellis and Manal AbuOun (2013). Klebsiella pneumoniae subsp. Pneumoniae sequence type 25: re-emergnece as a cause of septicaemia in piglets in 2012. In Proceedings of Joint Meeting of the European Symposium of Porcine Health Management and 50th Anniversary Meeting of the Pig Veterinary Society of Great Britain O5 p57
Harding, J. (2013). ‘Brachyspira hampsonii’ – Discovery of a novel porcine spirochaete causing mucohaemorrhagic colitis in Canada. Pig Journal 68: 95-96
Susanna Williamson, Ben Strugnell, Jill Thomson, Grace Webster, Steven McOrist, Helen Clarke and Derek Armstrong (2013). Emergence of severe porcine epidemic diarrhoea in pigs in the USA. Veterinary Record 173: 146-148
P. Zlotowski, S. P. Pavarini, M. B. Bandinelli, I. M. Langohr, D. Driemeier (2013). Paralysis in pigs with spinal cord injury due to porcine circovirus type 2 (PCV-2) infection. Veterinary Record 172:637
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