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Emerging Threats Quarterly Report – Pig Diseases – April to June 2011

by 5m Editor
22 September 2011, at 12:00am

Among the highlights of this report – previously known as the Quarterly Surveillance Report from VLA – are the first case of confirmed PCV2-associated foetopathy in British pigs.

Highlights

  • Leptospiral infection in breeding pigs on a breeder-finisher unit
  • First case of confirmed PCV2-associated foetopathy in GB pigs
  • Ongoing investigation of unusual peripheral neuropathy in growing pigs
  • Investigations continue to determine the cause of pre-weaning mortality on one pig unit
  • Streptococcus suis serotype 7 diagnosed as the primary cause of septicaemia and meningitis
  • Klebsiella species septicaemias in pre-weaned pigs on two outdoor units
  • Polyserositis and endocarditis due to Aerococcus species infection in growers
  • Reassortant swine influenza virus described in AHVLA publication

PCV2-Associated Foetopathy

In the course of routine surveillance for PCV2-associated foetopathy, the heart of a stillborn piglet with mild myocarditis was found to have significant specific staining for PCV2 by immunohistochemistry.

The PCV2 was considered likely to have been clinically significant although the myocarditis was mild, because of fibrosis following chronic damage to the heart with the extra demand on the heart around birth resulting in the pig being stillborn.

This is the first confirmed GB case of PCV2-associated foetopathy, but has been reported elsewhere in the field in Europe and North America (West and others, 1999, J Vet Diagn Invest 11:530–2) and following experimental infection of pregnant pigs (Park and others, 2005, J Comp Pathol 2005;132:139–44). Disease manifested on the unit as SMEDI, mainly in second-litter sows, with mummified pigs and stillbirths, not abortions, and there was evidence of sequential foetal infection, consistent with the pathogenesis of PCV2-associated foetopathy as the virus spreads from foetus to foetus in utero.

PCV2-associated reproductive disease is only likely to occur following primary infection of the sow at service or during pregnancy. On the affected GB farm, gilts leave the main unit as weaners and are reared on a distant separate unit, returning to farrow.

Manifestation of PCV2-associated foetopathy on this farm is suspected to be linked to poor acclimatisation of gilts when they first had contact with older sows after weaning their first litter.

Since this diagnosis was confirmed, gilts have been re-vaccinated prior to first service.

The possibility that PCV2-associated foetopathy could occur under certain management conditions prompted increased surveillance for the condition and this is the first confirmed diagnosis.

As time passes since the emergence of PCVAD, and following widespread control of PCV2, it is possible that the epidemiology of PCVAD will change. The patterns and various manifestations of PCVAD will be monitored with the aim of detecting any such change.

Findings will be presented to the Pig Veterinary Society and published to ensure pig specialists are aware of this occurrence.

Leptospire Infection in Neonatal Pig

An investigation is in progress into leptospiral infection on a breeder-finisher unit with long term reproductive disease.

There has been an increasing problem since the end of 2010 with pigs found not in pig, mummified piglets, stillbirths and weakly piglets from older sows.



Kidney from a jaundiced neonatal pig tested positive in the pathogenic leptospire PCR and most sows tested had MAT antibody titres to L. Pomona. No pathogens were identified in aborted foetuses submitted at the same time.

Sequencing of the PCR product has not provided a full definitive identification of the leptospire and, as a wildlife source of infection is possible, as reported in previous outbreaks of leptospirosis in sows (Barlow, 2004, Pig Journal 54, 123–131), attempts to isolate leptospires are now in progress on wild rodents and insectivores on the unit with the assistance of Fera.

Pigs have been treated recently so attempted isolation of leptospires is not being undertaken on them. The unit buys in replacement breeding pigs and a recent cohort of gilts were seronegative at entry, suggesting that infection may be being acquired on the unit. All pigs leaving the farm go to slaughter.

The unit farrows indoors with dry sows run outside during the day and housed at night in large yards, thus there is opportunity for contact with wildlife.

Investigations are in progress in this herd and it is important to note that Leptospira Pomona infection has not been confirmed in this herd at this stage. This outbreak may be due to a wildlife-adapted L. Pomona strain or a different serovar closely related to L. Pomona, rather than a pig-adapted L. Pomona. Control measures have been implemented on the affected unit and include antimicrobial treatment and vaccination. L. Pomona has never been isolated from UK pigs. It is not reportable or notifiable to Government veterinary authorities.

L. Pomona infection is widespread globally and has caused significant reproductive disease in pigs in the Americas, parts of Asia, and Central and Eastern Europe. Pig-adapted strains have not been reported in Western Europe. Antibodies to L. Pomona are occasionally detected in dogs and horses tested prior to export from the UK. L. Pomona is also zoonotic causing similar disease to L. Hardjo, which is endemic in cattle in GB. Appropriate advice on the zoonotic risk has been given.

Ongoing Emerging Disease Investigations

Inco-ordination in growing pigs with unusual peripheral neuropathy

This is now the subject of a new and emerging disease investigation. Two outdoor nursery units were affected in May with progressive ataxia and unusual gait as decribed in the last quarterly threat report.

Disease was of low morbidity in pigs between six and 11 weeks old. Three submissions were received, all with similar histopathological findings of radiculitis and peripheral neuropathy not previously reported in pigs. Videos and a description of the condition were presented at the May PVS meeting and submission of cases was encouraged. Virological investigations by virus microarray, electron microscopy (EM) and sapelovirus PCRs have not, so far, identified viral involvement.

Evidence of PCVAD has not been detected by routine histology and targeted PCV2 immunohistochemistry. The pathology is being characterised in more detail, including EM studies to assist the investigation and to help establish a possible aetiology.

Pig veterinarians have been made aware and clinical signs are unusual, thus 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. Publication and presentations at pathology and porcine disease meetings are planned to further disseminate the information.

Preweaning mortality with suspected heart failure

The investigation into undiagnosed preweaning mortality suspected to be due to heart failure, is ongoing. The problem has only been identified on a single pig unit.

The typical case history is sudden death of an otherwise healthy piglet in the first three weeks of life. At necropsy, cases are recognised by a blotchy appearance of the skin, the stomach contains clotted milk, there are haemorrhages on the surface of the heart, and no other cause of death is diagnosed. Further investigation has not shown any significant differences in heart morphometrics between cases and controls.

A student has collected five weeks of on-farm data on litters that was analysed by the veterinary practice. These investigations during May recorded 23.1 per cent of litters to be affected with a total of 18 likely cases with an age range of two to 26 days (average 10.2 days). Preliminary analysis of the weight data indicates that case piglets are not necessarily heavier than the average for the litter, whereas previously it was thought that only the heaviest piglets were affected.

Taken together with the cardiac morphometric data, it no longer appears that the mortality is associated per se with rapid growth, strong hybrid vigour and good sow milk supply. Case piglets are found dead in the sow huts, usually when first inspected in the morning, but invariably after a period of feeding from the sow. Case piglets are most often the offspring of multiparous sows, and rarely of primiparous gilts.

In view of the possible association between increased mortality and warmer weather, testing for the malignant hyperthermia ‘halothane’ gene was undertaken on six case piglets with negative results. No alternative diagnosis has been achieved and functional heart disease is still considered a possibility.

This piglet mortality problem remains unresolved and has continued in the affected herd throughout the last quarter with no reports of other units being affected. Discussions are being held with the unit veterinarian to decide how to progress investigations.

Unusual Diagnoses

Streptococcus suis 7 primary disease

An outbreak of septicaemia/meningitis, indistinguishable from that seen with Streptococcus suis 2, was identified due to S. suis 7 with no evidence of underlying viral infection or other intercurrent disease. S. suis 7 is the predominant serotype in several European countries. When isolated in GB pigs, it is more usually secondary to other pathogens. Such outbreaks have occasionally occurred before in GB pigs and the S. suis survey will be monitored for evidence of any significant change in frequency of disease due to S. suis serotype 7.

Klebsiella pneumoniae subsp. pneumoniae septicaemia

Unusually, two outbreaks of septicaemia due to this Klebsiella species were diagnosed within a week of each other. In both cases, it caused sudden deaths in good condition pre-weaned pigs on outdoor units independent of each other. On one farm, only pigs in gilt litters were affected, with approximately 10 per cent of litters affected and one to three piglets dying per affected litter. 16S rRNA sequencing confirmed the identity of the organism.

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.

Various risk factors for the septicaemias are being considered. Increased environmental levels of the organism could occur in moist or contaminated bedding and contaminated wallows (hot weather increasing wallowing time); ammonia favours growth of the organism and it would thrive in urine-contaminated bedding and wallows. Pig-related risk factors include the possibility that gilts have inadequate immunity to a resident strain, increased mastitis due to this organism, or high levels of vaginal carriage in the gilts. No concurrent disease was detected.

Further investigation is in progress into links between the units and, if logistics allow sampling, by culture of mastitic milk and vaginal swabs from one unit. The organism is readily isolated and identified by standard AHVLA culture methods.

A description of the condition was included in the Bury St Edmunds Regional Laboratory monthly report and will be in the July highlights report for BPEX and PVS websites and may encourage submissions.

Aerococcus viridans polyserositis and endocarditis

Aerococcus species infection was found associated with polyserositis (similar to Glassers) and endocarditis lesions in several successive batches of eight- to 12-week-old growers submitted from a single unit in Scotland. The organism was present in pure and profuse growths on multiple occasions in several pigs and was not a sporadic finding. There was no obvious predisposing factor. No further affected units have been identified.

Martin and others (2007, Journal of Clinical Microbiology, 45:3053-3057) characterised A. viridans isolates isolated in purity from a range of lesioned sites in pigs and concluded that A. viridans should be included in the list of possible bacteria causing disease in pigs. Findings on this unit support that conclusion and no further action is planned.

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.

September 2011