Emerging Threats Quarterly Report – Pig Diseases – July to September 2011

Highlights

• Posterior paralysis in sows attributed to Talfan virus
• Likely wildlife source of leptospire infection to breeding pig unit
• Klebsiella species septicaemia outbreaks in preweaned pigs
• Home-mix diet associated with nutritional osteodystrophy
• Whey bloat in sows associated with likely excess lactose intake

New and Emerging Diseases

Posterior paresis in sow attributed to Talfan disease

Details of an organic herd in Scotland with cases of hindlimb paralysis in sows and histopathological findings of myelitis suspected to be viral in aetiology were described in the Emerging Threats Q3 2010 report 2010.

The same herd had one affected sow in the summer of 2011. Early signs were of a wide-based hindlimb stance and slightly abnormal gait. This progressed over two to three weeks to quite severe hindlimb paresis but with individual care from the farmer, the sow made a full recovery over a further tow to three weeks. No other animals were reported to be affected, no extra reproductive disease has occurred and no young pigs showed signs.

Paired serology performed at AHVLA Weybridge revealed strong seroconversion to Teschen-Talfan virus. The sow was four years old and had not recently entered the herd, which is an extensive outdoor unit. As a result of the serological results, a veterinary investigation was undertaken by Animal Health veterinary officers. In the absence of any further disease, no further action was taken.

It is likely that this was a very limited clinical presentation of Talfan disease. Talfan disease, also known as benign enzootic paresis, is caused by a virus closely related to porcine teschovirus, formerly porcine enterovirus 1. Talfan virus has a global distribution in pigs, most infections are subclinical and outbreaks of clinical disease are mild. If any further cases occur in the herd and require post-mortem examination, virological investigations will be progressed to identify the infecting virus.

Negated swine fever report case

A retrospective investigation was requested by Defra on an indoor rearing unit that tested negative for swine fever following suspicious clinical signs and mortality reported by the attending veterinarian. The aim was to determine whether the incident raised the possibility of a new and emerging disease.

The farmer cooperated fully with the investigation and it was noted that, until the problem occurred, health and productivity of the pigs on the unit were good. Taking into consideration all the reported facts, in particular the rapid resolution of the clinical signs, restriction of significant mortality and signs to a single day and single shed, and absence of disease developing in pigs leaving the unit, a transient environmental cause was considered most likely, with heat stress probably a major part of the problem. Several additional factors were speculated to have played a role and, in collaboration with the veterinary surgeon, advice was given to the farmer to prevent a similar incident occurring in the future. A new and emerging disease was not suspected.

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 the Q2 Emerging Threats report. 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. An improvement in reproductive performance in this herd was reported after the antimicrobial therapy and this has continued.

Leptospira serology on housed unvaccinated finisher pigs in October did not detect antibodies to L. Pomona, thus there is no evidence of ongoing active infection in rearing pigs with the serovar that stimulated high Pomona titres in the sows.

Leptospires were successfully cultured from the kidneys of 12 of 50 insectivores and small rodents collected from the farm by FERA under licence. These leptospire isolates are being identified by the Leptospirosis National reference laboratory in Amsterdam (Royal Tropical Institute) (KIT), funded jointly by ED1200 and FZ2100, the nonstatutory zoonoses project.

The isolation of leptospires from a high proportion of wildlife collected from the farm supports the likelihood that the sows were infected with a wildlife-adapted L. Pomona strain or a different serovar closely related to L. Pomona, rather than a pig-adapted L. Pomona and multiple isolates are being definitively identified.

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 and the Pig Veterinary Society.

Inco-ordination in growing pigs with unusual peripheral neuropathy

This investigation was initiated in May 2011 and detailed in the Q2 Emerging Threats report. Pigs aged six to 11 weeks old from three units have been diagnosed with this unusual radiculitis, ganglionitis and peripheral neuropathy with myelin deficits.

Clinical and histopathological findings are very similar in affected pigs. Morbidity is low (maximum two per cent) and pigs are affected from four weeks old, mortality is due to culling if the pigs become too uncoordinated to feed and drink.

No cases have been reported since the end of August, when two 11 week-old pigs were submitted from a unit on which 10 to 15 pigs were affected on a unit of 4,200. Affected pigs have been on multi-source outdoor rearing units. No virus was identified using the pan viral microarray on cervical and lumbar spinal cord from four pigs; two pigs from each of the first two units affected.

Further investigation is focused on more specialised pathological investigation, including electron microscopy. The myelin deficits raised the possibility of a primary myelin defect, as seen in experimental riboflavin deficiency. However, this is hard to reconcile with the degree of inflammation seen and the small numbers of pigs affected.

An immune-mediated aetiology remains possible, as in humans with similar pathology. A sampling protocol has been circulated around Regional Laboratories should further suspect cases be submitted.

Details of the condition with videos of affected pigs were shown at two presentations: at the European Pathology Surveillance meeting in Edinburgh in September and at 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. As clinical signs are unusual and distinctive, the fact that no further cases have been submitted and no other units have been reported to be affected suggests the clinical condition is not widespread and impact is, at this stage, low.

Klebsiella pneumoniae subsp. pneumoniae septicaemia

This investigation was initiated in August 2011 and six outbreaks of septicaemia due to Klebsiella pneumoniae subsp. pneumoniae infection have now been diagnosed as the cause of sudden death of preweaned pigs on outdoor breeding units between July and September, all in East Anglia. Mortality is relatively low (one to four per cent mortality), disease is no longer being seen on four of the six units and in ongoing on two.

Klebsiella pneumoniae subsp. pneumoniae is a recognised cause of mastitis in sows and occasionally causes opportunistic infections in individual pigs. However, it is unusual to find it causing outbreaks as on these units. The organism is widely distributed in the environment and is part of the normal flora of the pig intestinal tract, usually in low numbers compared with E. coli.

A case definition has been established: ‘Pigs found dead with lesions consistent with septicaemia and pure/predominant growths of Klebsiella pneumoniae subsp. pneumoniae isolated from internal sites in multiple pigs’ and a questionnaire completed for five units. Investigation is focused on identifying features on the affected units that might explain either greater persistence of the organism in the environment, or greater susceptibility of the piglets.

Characterisation of the outbreak isolates, and comparison with historical isolates of this organism is being initiated at AHVLA Weybridge, using multilocus sequence typing (MLST). This septicaemia was the predominant diagnosis in preweaned submissions to the Bury St Edmunds Regional Laboratory in Q3. The organism is readily isolated and identified by standard AHVLA culture methods and there is no evidence that Klebsiella septicaemia is being missed in suitable material submitted to other AHVLA or SAC laboratories.

A presentation on the condition was given at the European Scanning Surveillance meeting in Switzerland in October and another is planned for the Pig Veterinary Society Autumn meeting in November. Details have been included in AHVLA reports to veterinary practices, BPEX and Pig Veterinary Society.

Unusual Diagnoses

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 type A2 with unusual cerebellar lesions

Forty of a batch of 100 neonatal piglets were affected in an outbreak of type A2 congenital tremor with 10 affected piglets dying. A deficiency of stainable myelin was demonstrated in the spinal cord, consistent with congenital hypomyelination, of which porcine congenital tremor A2 is the commonest cause.

Brain histopathology also revealed cerebellar cortical degeneration characterised by Purkinje cell necrosis. This type of cerebellar lesion is unusual in porcine congenital tremor and further piglets were submitted for examination and had similar lesions.

The nature of the lesions suggested regional hypoperfusion was the most likely cause, although excitotoxicity (secondary to lack of myelin) or other cause could not be ruled out. The cerebellar lesions were not like those seen in Classical Swine Fever (CSF)-associated cerebellar dysgenesis. Type A2 is a recognised form of congenital tremor considered to be due to an unknown virus and is regularly diagnosed at a low rate in GB herds, although outbreaks can be dramatic with 80 per cent of litters born being affected, often gilt or young sow litters in particular.

Material collected from this case will be analysed in the RDIIF virus discovery project RD0044 to investigate further.

Likely hemlock toxicity causing congenital limb defects in piglets

A gilt from a smallholding farrowed 13 piglets, six of which had multiple severe congenital limb contracture / arthrogryposis and were euthanised. The seven others were less severely affected. This gilt was kept in an uncultivated field during pregnancy.

A field walk confirmed the presence of hemlock (Conium maculatum). This grows in damp places and open woodlands throughout Britain. The stems are smooth with characteristic purplered blotches and the fleshy white tap root resembles a parsnip.

As far as AAHVLA is aware, the last recorded case of hemlock poisoning in pigs occurred in the Langford area over 25 years ago (Barlow, 2006, Pig Journal, 57:254-258). The control of hemlock is by cutting or digging up and disposing of the plants safely; alternatively, a glyphosate herbicide can be used.

Mycoplasma suis infection with necrosis of the alimentary tract due to Fusobacterium species

Listlessness, anorexia and death occurred in seven of 12 pigs in a single litter. All were pale and jaundiced and had varying degrees of oedema and enlarged hearts suggestive of an anaemia. Inclusion bodies consistent with Mycoplasma (formerly Eperythrozoon) suis, a recognised cause of haemolytic anaemia, were seen in red blood cells of two piglets. There were also black necrotic lesions in the oral cavity, tonsils and caecum from which Fusobacterium necrophorum, an anaerobic bacterium, was isolated, and one animal showed signs of arthritis in a hock joint associated with infection with Actinobacillus equuli equuli.

These bacterial infections may have been secondary to the pigs’ debilitated condition and no underlying viral component to the problem was identified.

Suspected whey bloat in sows

Eight sows were reported to have died suddenly over a two-week period on an indoor farrow-to-finish unit and two dead farrowing sows were submitted in which there was was extensive purple-black discolouration to the entire jejunum and the intestinal mesentery was oedematous.

No infectious cause was identified and further investigation revealed that a powdered feed supplement, containing a small amount of lactose derived from whey, was top-dressed onto the sows’ feed and that this may have led to whey bloat and death in these sows, although a firm link was not proven.

Adult pigs do not possess lactase enzymes and therefore when they ingest lactose, there is potential for significant gas formation in the small intestine. This could lead to ileus, pressure damage to the mucosa and predispose to torsions. The supplement was to be fed between weaning and service to boost fertility but, in practice, was being fed from three weeks of lactation to service and both sows submitted had received the supplement. Significantly, since withdrawal of the supplement, no further sow deaths have occurred.

It was recommended that caution should be exercised when feeding lactose to sows especially if there is scope for some sows to receive more than intended. The assistance of Paul Toplis, Primary Diets in this investigation is gratefully acknowledged. A case report is being presented at Pig Veterinary Society Autumn meeting.

Mild colitis due to Brachyspira murdochii

Brachyspira murdochii was isolated in pooled faecal samples from eight- to 14-week-old home-bred outdoor gilts showing looseness with no pigs appearing ill or dying.

This Brachyspira species is generally considered a commensal in pigs, although there are reports that it can cause a mild catarrhal colitis in weaned pigs. (Jensen et al., 2010. Veterinary Pathology, 47: 334-338. Brachyspira murdochii Colitis in Pigs).

It was recommended that individual faecal samples be collected from pigs seen to be loose to investigate further. This spirochaete is generally considered to have minimal impact on production.

Rickets-type osteodystrophy and osteoporosis in fattening pigs

An investigation by SAC was prompted when lameness and limb deformity were noted in growing pigs and the abattoir reported rib fractures and callus formation in a high proportion of pigs at slaughter.

At post-mortem examinationm there were many fractured ribs, enlarged costochondral junctions and bones were softer than normal. Very low bone ash values confirmed poor mineralisation, although calcium to phosphorus ratios were normal.

Histopathology confirmed pathology consistent with rickets and osteoporosis. A dietary mineral and/or vitamin imbalance was suspected in the home-mix ration and an SAC nutritionist found the diet to be low in phosphorus. Weaners were exhibiting typical pica and urine drinking.

Appropriate nutritional advice was given, supplementation was carried out and investigations continue. This investigation was reported in the SAC Disease Surveillance report Veterinary Record 2011;169:202.

Changes in Disease Patterns and Risk Factors

Swine influenza strains

Twelve pig submissions were positive for influenza m gene by PCR out of 27 submissions tested in Q3; five were pandemic H1N1 2009, the rest non-pandemic and are being identified. The strains identified so far in 2011 circulating in GB pigs are pandemic H1N1 2009 and H1N2.

Evidence suggests that pandemic H1N1 2009 is replacing avian-like H1N1 and it is possible that immunity to pandemic H1N1 2009 is protecting against subsequent infection with avian-like H1N1.

This may affect the ability to interprete serology; if there is prior exposure to avian-like H1N1 and then challenge with pandemic H1N1, titres to avian-like H1N1 could be boosted and compromise interpretation at the farm level.

In time, if avian-like H1N1 disappears, serological interpretation will become simpler. There is evidence of a second H1N2 reassortant virus from a diagnostic case, this is epidemiologically linked to the first case (Howard et al 2011, Emerging Infectious Diseases 17(6): 1049-1052) and indicates persistence of this reassortant in the pig population. All H1N2 isolates are now being checked for this reassortant.

The 50 per cent positive rate for swine influenza infection in tested submissions indicates that there is good targeting of surveillance. The Defra-funded swine influenza surveillance project is approved for a further three years funding which is considered very beneficial for pig disease surveillance.

PRRS diagnoses

There has been a gradual, although not significant, increase in the percentage of GB scanning surveillance submissions diagnosed with systemic PRRSV annually from 2009 (5.3 per cent to 6.2 per cent) and a significant increase in the percentage of GB scanning surveillance submissions diagnosed with PRRSV in Q3, 2011 (6.9 per cent) compared to the same quarter in 2010 (2.2 per cent). This will be kept under review.

It is considered that this may reflect increased awareness of, and investigations for, PRRS, due to regional health initiatives and also investigations following reports of increased pleurisy following British Pig Health Scheme (BPHS) feedback from the abattoir.

Horizon-Scanning

Novel swine-origin influenza A H3N2 cases in USA

Human cases of infection with H3N2 swine influenza strains have been detected in USA. All have been mild infections without a detectable antibody response and did not transmit to other humans. It is likely that these infections occurred undetected in the past and their recent detection reflects improvement in human influenza surveillance rather than new events. The situation is being monitored, however, these H3N2 viruses have not been detected in European pigs. For more information, click here.

Further Reading

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