Highlights

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 web site.

• Reduction in carcass submissions; rise in non-carcass submissions
• Re-emergence of Klebsiella pneumoniae septicaemia in pre-weaned pigs
• Bracken poisoning cases reported as potential food safety incidents
• Swine influenza in young weaners predisposing to salmonellosis
• Swine dysentery diagnosed in small herd in East Anglia

Ongoing Emerging Disease Investigations

Re-emergence of Klebsiella pneumoniae septicaemia in pre-weaned pigs

In 2011, outbreaks of septicaemia due to infection with Klebsiella pneumoniae subsp. pneumoniae (Kpp) were diagnosed on six pig farms in East Anglia. A further three farms had similar outbreaks diagnosed between July and August in 2012. All nine outbreaks have occurred in the same region on outdoor units and causing sudden deaths in pre-weaned pigs. Molecular analysis has been conducted and found:

• Isolates from outbreak cases are all of multi-locus sequence type (MLST) ST25, compared to a range of MLST types identified in historic isolates from a variety of infections in individual pigs.
• There have also been small numbers of Kpp isolates recovered from unaffected pigs on affected farms during investigations (vaginal, oral and nasal). In 2011, these were MLST ST25 and in 2012 these were different MLST types.
• In order to try and establish whether the MLST ST25 occurs on farms not apparently affected with the Kpp septicaemia problem, nasal and tonsil swabs from pigs submitted for diagnostic post-mortem examination are being cultured. The few Kpp isolates obtained to date are to be examined for MLST ST type.
• The outbreak and historic isolates were screened for their virulence gene content (Brisse et al., 2009). A common factor to the outbreak strains was the presence of the rmpA gene, which is a regulator of mucoid phenotype and has been associated with pathogenic strains of Klebsiella. Phenotypically there was little to no different in the mucoid phenotype of the isolates. Additionally, biofilm formation at 15°C and 37°C did not highlight any correlation with disease presentation.
• Plasmid profile analysis was conducted and showed the majority of isolates carried at least one plasmid. However only the outbreak isolates possessed a small plasmid of ~4.5kb.

These results support the hypothesis that the presence of either the small plasmid or some other unknown factor has enabled Kpp ST25 to emerge as a cause of septicaemia in pigs. The next step in the investigation is determine the whole genome sequence of outbreak Kpp including the plasmid DNA.

An information sheet for farmers and veterinarians has been disseminated. The disease appears to be seasonal in nature and self limiting on affected farms and the impact, to date, is relatively low. The re-emergence of Kpp septicaemia was highlighted in monthly reports and an information sheet.

One further case of novel peripheral neuropathy

A diagnosis of hypomyelinating radiculitis and peripheral neuritis causing severe incoordination in pigs was made on one farm in July 2012. This was the first case in 2012 and matched the three diagnosed in 2011 clinically and pathologically except that the farmer described the pigs as being affected at birth.

Previous cases have been affected around or post-weaning. This is a novel pathology of very low herd and within-herd incidence causing disease for a limited period and of unknown aetiology and pathogenesis. Due to resemblance to similar pathology in other species (humans and domestic fowl), it was suspected of being immune-mediated but this case in neonates (submitted at four weeks old) again raised the possibility of viral involvement. The attending veterinarian was requested to submit any further affected pigs as early as possible after being noticed, no further cases are being seen on the unit.

Virus microarray produced a weak enterovirus signal which was not confirmed by further PCR work. Further virological investigation using an alternative method of virus discovery is being progressed. Details of the case were included in AHVLA August monthly reports. Video and details of this condition have been disseminated at national and international pig veterinary meetings. Further information is in previous quarterly reports.

Investigation of anomalous swine influenza H3N2-positive serology results

Routine HAIT serology detected swine influenza strain H3N2 antibody in five pig herds with histories of respiratory disease between May and July 2012. This is of potential significance as the virus strains detected in UK pigs in recent years are pandemic H1N1 2009, avian-like H1N1 and H1N2, while the H3N2 virus strain has not been detected in pigs in UK since 1997.

These serology results do not in themselves prove exposure to H3N2 and investigations were initiated. The H3N2 positive sera were tested against a range of H3N2 strains including those known to previously circulate in UK pigs; contemporary H3N2 viruses from pigs in Europe; the latest H3N2 variant virus infecting pigs in North America together with contemporary H1N2 viruses from the UK.

In two cases, there were potential reactors at herd level to H3N2, which showed greatest reactivity with H3N2 viruses known to be circulating in UK pigs up to the mid 1990s. In others, cross-reactivity with H1N2 virus was considered a probable explanation for the H3N2 positive results.

Investigations were also initiated to attempt to detect and isolate virus from the farms concerned and no swine influenza virus was isolated, nor have H3N2 titres persisted on the farms.

These investigations are ongoing, particularly as there is recent evidence of confirmed H1N2-infected pig units where convalescent sera gave higher HAIT titres to H3N2 virus than to H1N2.

Several initiatives are ongoing in the final quarter of 2012 as part of this investigation: funding of HAIT serology on swine influenza ELISA positive sera, genetic analysis of recent H1N2 viruses isolated, and testing of sera submitted against a recently isolated H1N2 strain. AHVLA (Ian Brown 'What's new in 'flu'?') gave a comprehensive update on swine influenza including the above issues at the November 2012 Pig Veterinary Society meeting.

Sporadic cases of Haemorrhagic Disease resembling swine fever

In July and September, two further cases of haemorrhagic disease occurred in individual pigs, both of which prompted consultation swine fever report cases with AHVLA, in one case by the attending veterinarian and in the other by a VIO when a pig was submitted for post-mortem examination.

In both cases, swine fever was ruled out on clinical grounds as only one pig was affected, there was no pyrexia and in-contact pigs were unaffected. These superficially resembled the two cases in Kune-Kune pigs described in the previous quarter's Emerging Threats report and prompted a review of the four cases, particularly in view of the similarity of the gross lesions to those seen in swine fever. The cases have been in Kune-Kune, Saddleback and commercial hybrid pigs aged three to seven months and presenting with histories of lethargy, weakness, haemorrhages (skin, urinary, oral).

Low concentrations of anticoagulant rodenticide were detected in two of three cases tested raising the possibility of chronic anticoagulant toxicity and advice regarding safe use of rodenticides was provided by a Natural England wildlife biologist.

Pathogenesis in the Saddleback pig differed from others as there was severe megakaryocyte hypoplasia resulting in thrombocytopaenia and haemorrhages, and together with other findings, this was considered most likely to have occurred due to an immune-mediated reaction.

This case series was presented at the November 2012 Pig Veterinary Society by AHVLA (Cornelia Bidewell: 'Sporadic cases of multiple haemorrhages in pigs') to raise awareness of this clinical presentation and the differential diagnoses to consider.

Figures 1 a-c: (a) multi-focal skin haemorrhages, (b) enlarged mottled lymph nodes and (c) haemorrhages on the oral mucosa

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.

Severe Pasteurella multocida septicaemia in finishers

A continuous finishing unit reported a two per cent rise in mortality over 14 days in pigs of finishing age. Clinical signs were of acute deaths, occasional signs of meningitis and reduced growth rate.

Four pigs were submitted with polyserositis or pulmonary consolidation. These lesions were found to be due to systemic infection with Pasteurella multocida and no concurrent viral disease was diagnosed.

In the seven days following the diagnosis, a further 25 deaths occurred despite in-water antimicrobial medication and a further batch of pigs were examined. Again Pasteurella multocida was isolated in septicaemic distribution. This second batch of pigs was in poor bodily condition with chronic lesions that treatment began when these pigs were already compromised.

Three weeks later, a follow-on group of 11-week-old pigs from the same unit presented with respiratory disease in approximately 30 per cent of pigs with occasional nervous signs. One fresh pluck was submitted with severe cranioventral pulmonary consolidation from which Actinobacillus pleuropneumoniae was isolated and concurrent PRRS was diagnosed. Pasteurella multocida septicaemia is an unusual diagnosis in finishers, the later submission from younger pigs indicates that intercurrent viral disease was playing a role on the unit, although it was not active in the first submission of older pigs. This case emphasises the importance of follow-up submissions where clinical disease continues and of submitting pigs early in the course of disease.

Muscular hypertrophy of the ileum

Hypertrophy of the smooth muscle of the ileum, not associated with Lawsonia intracellularis infection, was diagnosed on two occasions in single pigs from different farms between July and September.

This unusual finding has been diagnosed four times in the last two years by AHVLA. In one case, four recent deaths had occurred in adult pigs following short-term malaise and it was recommended that further pigs be submitted to determine whether the case diagnosed was representative of the wider clinical problem or a sporadic finding as was assumed on the other units. The hypertrophy can be secondary to stenosis of the ileocaecal valve, but the valve was grossly unremarkable in all four cases.

Figure 2. Hose-pipe like appearance of ileum with muscular hypertrophy

In other species, the condition can be associated with parasitic infections and, interestingly, all four cases were on organic units on at least one of which intestinal nematodes had been causing problems in growing pigs.

SAC has also recognised this condition in past months as an incidental finding in slaughter pigs from conventional commercial herds being examined for intestinal adenomatosis and without intestinal nematodes.

These cases were included in monthly reports and will be kept under review , no further action is required.

Food refusal causing ill-thrift tentatively attributed to mould and/or mycotoxins in feed and straw

Ten per cent of a group of weaners began to show ill-thrift and failure to establish normal feeding from one week post-weaning on an indoor rearing unit. Salmonellosis was diagnosed by AHVLA in two submitted pigs with typical colitis lesions in both pigs.

Pigs ate better when the feed was changed and the enteric disease was considered to be a sequel to the debility caused by the earlier poor feed intake.

Investigations into the possible reasons for feed refusal by the attending pig practitioner revealed trichothecene (T-2) mycotoxin in both the feed and visibly mouldy straw, although concentrations did not exceed maximum guidance concentrations for animal feed. In the absence of an alternative explanation, the feed refusal was attributed to the presence of mould and/or T-2.

The consequences of salmonella infection have been shown to be more severe in mice experimentally exposed to oral T-2 (Tai and Pestka, 1988). Different food and bedding was provided to the next batch of pigs weaned which performed much better, allaying concerns that this might be a case of periweaning failure to thrive syndrome.

As there can be unequal distribution and 'hot-spots' of mycotoxin in feed and bedding, evaluating the significance of concentrations of mycotoxin detected in a single farmer-selected sample can be problematic. Following a wet summer, there is concern that mould and/or mycotoxin contamination of feed or bedding may cause pig health issues. BPEX has produced advice to producers on feed and straw management to reduce the risk of mycotoxins affecting pig health.

Changes in Disease Patterns and Risk Factors

Bracken poisoning cases reported as potential food safety incidents

Two diagnoses of bracken poisoning in pigs were made by AHVLA in September 2012. Bracken poisoning is the main cause of plant poisonings in pigs represents 12 of 13 cases of plant poisoning since 2007.

In pigs, bracken poisoning causes rapid death due to a cardiomyopathy and heart failure and post-mortem findings reflect this with pulmonary oedema, pleural effusion (see figure 3) and, sometimes pallor of the myocardium. Histopathology is necessary to confirm the diagnosis, together with a history of exposure to bracken. Harwood and others (Veterinary Record, 2007 160:914-915) give a full description of two typical cases.

Most cases occur in small outdoor groups of pigs with less controlled paddocking than in commercial pig herds and with access to heath-land, woodland or fell where bracken is present.

Bracken toxicity in pigs usually results from exposure over a prolonged period and is due to the thiaminase toxic component. The rhizomes and young leaves contain most thiaminase, thus natural rooting by pigs and access to growing bracken both predispose to ingestion and toxicity.

Figure 3. Pulmonary oedema and pleural effusion

Bracken poisoning is reportable to Food Standards Agency as a potential food safety incident and pigs must be withdrawn from potential exposure to bracken for at least 15 days prior to slaughter for human consumption of meat and offal. The Food Standards Agency were informed of these cases and an alert about bracken poisoning was sent out in laboratory newsletters, to industry and to Pig Veterinary Society.

Swine influenza in young weaners predisposing to salmonellosis

Swine influenza was diagnosed in weaners on two pig units in the week after weaning and was followed by wasting and deaths due to salmonellosis. Mortality reached 10 per cent between weaning and 35kg on one of the units. Successive batches of pigs were affected in both cases.

These cases emphasise the importance of selecting pigs early in the course of disease for diagnosis as no swine influenza virus was detected in earlier submissions of older pigs. It was speculated that the early swine influenza infection, whilst in itself not causing severe clinical signs, affected early establishment of feeding and drinking and made pigs more susceptible to adverse effects when exposed to salmonella infection.

Antimicrobial treatment for streptococcal or respiratory disease could also predispose to salmonellosis if the infecting salmonella was resistant to the treatment.

The strain on one unit was identified as H1N2 and to address the problems, improved hygiene at both the breeding unit lairage for weaners and at the rearing units, together with acidification of the water on arrival were undertaken to limit the salmonella infection, while the breeding pigs were being vaccinated for swine influenza to provide passive immunity and reduce virus transmission. Virus isolation is in progress on samples from the second unit.

These cases were highlighted in monthly reports and an advisory visit was made to one of the farms.

Erysipelas outbreaks

AHVLA have received verbal reports from specialist pig practitioners of erysipelas occurring in replacement breeding pigs which should be fully vaccinated for erysipelas. Disease has mostly been diagnosed on clinical grounds (malaise, typical skin diamonds, response to penicillin treatment). Confirmation of two cases was achieved by isolation of Erysipelothrix rhusiopathiae, while others have been diagnosed on clinical grounds.

The farms follow vaccination protocols and the veterinarians involved have investigated and not found any obvious issues with vaccine storage or administration. Attending veterinarians are encouraged to report suspected vaccine failure to the Veterinary Medicines Directorate (VMD) and vaccine manufacturer. Current erysipelas vaccines available in the UK are based on serotype 2, in the past serotype 1 was also present in some vaccines, cross-protection is reported to occur between the two serotypes.

There has been no recent significant rise in erysipelas cases diagnosed by AHVLA. AHVLA's role at this stage is to encourage submission of suitable material and isolate the organism to confirm the diagnosis, or to establish an alternative diagnosis.

Erysipelothrix species isolates are stored in the AHVLA bacterial collection and available for serotyping should this be required.

Swine dysentery diagnosed in small herd in East Anglia

The first AHVLA diagnosis of swine dysentery (SD) in 2012 in East Anglia was made in September in a group of six rare-breed pigs purchased for fattening. Minimum Inhibitory Concentration testing showed that the Brachyspira hyodysenteriae isolated from the farm was sensitive to tiamulin and pigs responded to treatment.

SD in small herds such as this are of concern as there may be a delay in seeking veterinary advice and a lack of awareness of the serious risk this disease poses to commercial herds. It was suspected that infection had arrived with the group of pigs. There has been no overall increase in SD diagnoses by AHVLA with 12 in the first nine months of 2012, four of these between July and September compared to 15 in the same period of 2011, with six being between July and September.

This diagnosis was of particular concern as SD is considered to be uncommon in the region of East Anglia and is one of the four diseases targeted for regional control by the Pig Health Improvement Project. The attending vet was provided with advice on swine dysentery control and biosecurity, and informed of the SD Producer Charter.

Horizon-Scanning

Closure of major abattoir processing pigs in Scotland

The recent closure of an abattoir slaughtering approximately 9,000 pigs each week, which represented around 75 per cent of Scotland's finishing pigs, is of concern. This has resulted in more pigs being transported longer distances to northern England for slaughter or to be fattened nearer to the point of slaughter. These increased movements of live pigs are not only an additional financial cost to the industry, they also present associated organisational issues and potential risks to welfare if there are delays due to adverse weather conditions or traffic delays. The throughput in nearer smaller Scottish plants has also increased as much as their capacity allows.

This concern has been highlighted to DEFRA welfare team for awareness.

Hepatitis E and detection in pork and pork products

There has been recent publicity about hepatitis E infection in humans. This relates to an increase in 2010-11 in the proportion of cases of hepatitis E diagnosed where there is no history of travel by the affected person.

A recent publication (Berto and others, 2012) reported PCR detection of hepatitis E virus in 13 per cent of pig faeces and three per cent of pig livers at slaughter and 10 per cent of pork sausages at retail. Whether virus is infective at these different stages was not established.

The report of an extensive case-control study in humans is expected in 2013 and may identify risk factors and assist in determining whether there is evidence to support the putative link with consumption of pork and pork products. In the meantime, a multi-agency, joint-funded abattoir survey of pigs, expected to be conducted in early 2013, will seek to establish the prevalence of infection in slaughter pigs in the UK.

This is highlighted here as an issue which may cause adverse publicity for the pig industry at what is already a difficult time.

References

Berto A., Martelli F., Grierson S. and Banks M. 2012. Hepatitis E virus in pork food chain, United Kingdom, 2009-2010. Emerging Infectious Diseases 18(8):1358-1360.

Brisse S., Fevre C., Passet V., Issenhuth-Jeanjean S., Tournebize R., Diancourt L. and Grimont P. 2009. Virulent Clones of Klebsiella pneumoniae: Identification and Evolutionary Scenario Based on Genomic and Phenotypic Characterization.. PLoSOne 4(3):e4982. doi:10.1371/journal.pone.0004982

Harwood et al., 2007. Suspected bracken poisoning in pigs. Veterinary Record 160:914-915.

Tai J.H. and Pestka J.J. 1988. Impaired murine resistance to Salmonella Typhimurium following oral exposure to the trichothecene T-2 toxin. Food and Chemical Toxicology 26:691–698.

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February 2013