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Osteochondrosis, APP Feature in AHVLA June Report

17 August 2012, at 1:52pm

The AHVLA Surveillance Monthly Report for June 2012 states that osteochondrosis is manifesting at weaning in young sows and erysipelas is causing sudden deaths in gilt litters. There have also been several outbreaks of Actinobacillus pleuropneumoniae (APP) infection.

Reproductive Disease

PRRS confirmed as the cause of multiple stillborn and aborted litters

A batch of stillborn foetuses was received by Shrewsbury for investigation of a severe reproductive problem in which the last 20 farrowings in a herd of 300 sows had resulted in stillborn/aborted litters in which every piglet was dead. The sows were reported to be well and were vaccinated for porcine parvovirus and erysipelas. Post-mortem examination revealed some piglets to have inflated lungs and there was some straw-coloured fluid in the thoracic cavity; the livers were moderately haemorrhagic. Porcine respiratory and reproductive syndrome virus (PRRSv) was detected in foetal spleens by PCR and PRRS was diagnosed.

Musculoskeletal Disease

Osteochondrosis manifesting at weaning in young sows

An indoor breeding unit reported an ongoing problem of recumbency or hind limb lameness in at least one sow in each batch of parity one sows after weaning. The sows were in freedom farrowing crates and, at weaning, walked to a strawed service area to mix in groups of 20. Sows showed poor response to antimicrobial and anti-inflammatory treatment and two were euthanased and submitted to Bury St Edmunds investigate the problem. In one there was bilateral arthritis of the stifles and deep erosion of articular cartilage on the femoral condyles consistent with osteochondrosis dissecans. In the second there was bilateral septic arthritis of the hips and endocarditis involving the pulmonary semilunar valve, both of these lesions involving Trueperella pyogenes infection. It was considered that the gilt with osteochondrosis dissecans lesions was most likely to be representative of the problem described on farm; however, further submissions were encouraged to determine whether this was the case. Increased activity after weaning and mixing was suspected to account for sows showing clinical signs at that time.

Alimentary Disease

Postweaning rotaviral diarrhoea

Faecal samples were submitted from four-week-old weaners of which 13 were affected with diarrhoea and seven had died. The only enteropathogen identified was rotavirus which was considered likely to be significant with respect to the diarrhoea; however, significant mortality is unusual with rotaviral enteritis without complicating infections or issues such as dehydration and it was recommended that, if deaths were continuing, freshly dead pigs be submitted to investigate further.

Diarrhoea or wasting due to salmonellosis on two units

A rearing unit reported two deaths in 5-week-old weaned pigs from a group of 90 with a further eight affected with diarrhoea. Both pig carcases showed evidence of severe fibrinonecrotic typhlocolitis and in one there was also evidence of severe fibrinonecrotic gastritis. Tests for swine dysentery proved negative. Gross lesions were more suggestive of salmonellosis which was confirmed by the recovery of S. Typhimurium Copenhagen (multi-drug resistant) from the intestines of both pigs.

Two twelve-week-old pigs were submitted to Thirsk from a finishing unit to investigate wasting. Disease was affecting 20 to 30 from each batch of 500 pigs, with some affected pigs eventually recovering. Pigs were vaccinated against enzootic pneumonia and PCV-2 associated disease. Post-mortem examination revealed colitis and thickening of the distal third of the small intestine and mesenteric lymph node enlargement. Salmonella Typhimurium Copenhagen (phage type U288). Histological examination revealed severe acute to subacute enteritis and colitis consistent with Salmonella or other bacterial infection. PRRS virus was also detected in one of the pigs by PCR. The Salmonella isolated was considered to be the main clinical problem.

Respiratory Disease

PRRS virus underlying other respiratory infections in finishers

Approximately 100 of 1000 12-week-old pigs on a continuous indoor nursery-finisher unit were affected with respiratory disease (coughing, dyspnoea, cyanotic ears) with some nasal discharges in older pigs. The problem began approximately 10 days prior to submission and 20 pigs died. Three dead pigs were submitted and all had lesions of the respiratory tract, together with a fibrinous polyserositis in one pig. Streptococcus suis type 2 was isolated from two of the pigs and was likely to have been clinically significant while Trueperella pyogenes isolated from the third pig was considered to represent a secondary infection. Porcine respiratory and reproductive syndrome virus (PRRSv) was identified by PCR in the spleen and also in the lung of one pig by immunohistochemistry, confirming involvement of PRRS virus in the pathology.

Actinobacillus pleuropneumoniae associated with increasing respiratory disease and mortality

Increased mortality, respiratory disease (mainly coughing) and unevenness in growth was described in finisher pigs starting approximately two weeks after entry on to a continuous single-source indoor unit. The problem had been on-going for several months but had been controlled well by tylosin in feed; more recently coughing and mortality began to rise and one pig found dead was submitted. This pig had a severe subacute chronic pneumonia with fibrous pericarditis and pleurisy and at least one area of lung had lesions suggestive of Actinobacillus pleuropneumoniae (APP) infection and APP was isolated confirming the diagnosis. No viral involvement was identified; however, as the disease was chronic, it was recommended that more acute cases be submitted.

Three 12-week-old outdoor pigs presented with signs of acute pneumonia. Two died and one was euthanased and one pluck was submitted for post-mortem examination. There was severe dark consolidation of the majority of the right lung. Histopathology revealed severe subacute fibrinopurulent and necrotising pneumonia consistent with APP infection and this was confirmed with a rich growth of A. pleuropneumoniae serotype 3,6,8 from lung. There was no evidence of underlying viral disease.

APP and Glässer’s disease were detected in pre-weaned piglets submitted to Sutton Bonington to investigate an ongoing problem with ill-thrift and respiratory disease on an indoor unit. The piglets showed increased respiratory noise, weakness and abdominal breathing. Post-mortem examination revealed cranioventral pulmonary consolidation and polyserositis and both APP and Haemophilus parasuis (the cause of Glässer’s) were isolated from the lungs.

Systemic and Miscellaneous Diseases

Likely Glässer’s disease outbreak in growers after environmental stresses

Over a period of seven days, 21 seven to eight-week-old pigs died from a batch of 1,400 on a single source all-in, all-out indoor nursery-finisher unit. The problem began with pigs being found recumbent and paddling then dying, this progressed to pigs being seen with subcutaneous oedema and dying over a two day period. There was some response to penicillin treatment. The remainder of pigs in pens where pigs had died looked healthy. Three dead pigs were submitted, all in quite poor body condition and one with marked subcutaneous oedema of the ventral abdomen and scrotum associated with extension of the fibrinous peritonitis through the inguinal canal. All three pigs had severe fibrinous polyserositis suggestive of Glässer’s disease, although this organism was not isolated, nor was any other pathogen, probably due to the recent antimicrobial treatment. It was suspected that fluctuating environmental temperature predisposed to clinical disease resulting in this outbreak which resolved.

Erysipelas causing sudden deaths in gilt litters

Erysipelas was diagnosed as the cause of malaise and rapid death in two to three-week-old pigs on an outdoor weaner-producer unit. Five litters were affected, all of which were gilt litters and in which from two piglets to the whole litter died. Six farrowing gilts were also inappetent and lethargic and one of these died but was not submitted for post mortem examination. Five dead piglets in good body condition were submitted to Bury St Edmunds with red to purple skin discolouration particularly affecting ears, snout and ventral abdomen and two of the carcases showed slight jaundice. Spleens were slightly enlarged and lymph nodes were generally reddened. There was cortical petechiation of the kidneys in three pigs. Erysipelothrix rhusiopathiae was isolated from internal sites in all five pigs with no evidence of active swine influenza or PRRS virus infections. As disease was limited to gilts which previously occupied a single paddock, it was suspected that although they should have been vaccinated for erysipelas, one group of gilts missed vaccination and, as a precaution, the next batches of pregnant gilts were immunised again prior to farrowing to prevent further problems. Figure 1 shows the carcase of one of the dead piglets. Erysipelas was definitively diagnosed in these piglets; however, laboratory investigation was necessary to confirm this diagnosis which is particularly important where clinical signs and some gross lesions may resemble notifiable disease (swine fevers). The restriction of disease to a few gilt litters derived from pregnant gilts from the same paddock was an important feature which pointed away from notifiable disease in this case but it is important that the possibility of porcine notifiable disease is considered in similar cases and, if suspicion remains, that this is reported to the AHVLA.

PDNS diagnosed in finishers

Two 11-week-old fattening pigs were submitted to Shrewsbury with signs of wasting and skin lesions suggestive of porcine dermatitis and nephropathy syndrome (PDNS). There were variable patches of reddened skin on the flanks and hind legs, generalised lymphadenopathy and enlargement of the kidneys with diffuse generalised pinpoint haemorrhages. Histopathological findings included severe necrotising glomerulonephritis and a granulomatous lymphadenitis with amphoteric intracytoplasmic inclusion bodies (typical of porcine circovirus-2 infection). These findings confirmed the suspected diagnosis of PDNS.

Further Reading

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