AHVLA Surveillance Monthly Report - September 2011

by 5m Editor
10 November 2011, at 7:37am

UK - Acute peritonitis secondary to a ruptured gastric ulcer was observed in a group of Saddleback pigs after they were purchased.

Alimentary Disease

Unusual Brachyspira species infection

Brachyspira murdochii was isolated in three pooled faecal samples from eight, 11 and 14-weekold 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, Vol. 47, pages 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.

Suspected whey bloat in sows

Eight sows were reported to have died suddenly over a two week period on an indoor 550 sow farrow to finish unit. Two sows submitted from the same farrowing house, one three weeks farrowed and the other five weeks farrowed, had similar findings. There was extensive purpleblack discolouration to the entire jejunum and the intestinal mesentery was oedematous. Blood vessels around the jejunum were engorged. There was no evidence of Lawsonia or other pathogens. Histopathology revealed widespread capillary distension in the jejunum mucosa, submucosa, mesenteric lymph nodes and spleen with widespread haemorrhages at the base of the jejunal mucosa and no inflammatory or degenerative changes. Further investigation revealed that a powdered feed supplement, containing a small amount of lactose derived from whey, was top-dressed onto the sows’ food. Although only 150 grams per sow was given per day, it was speculated that this amount may have led to whey bloat and the deaths in these sows. However, 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 to AHVLA Thirsk had received the supplement. Since withdrawal of the supplement, no further sow deaths have so far occurred. The method of feeding (top dressing of a powder) may have meant that a relatively large amount of lactose was consumed at once, predisposing to rapid gas formation. Caution should be exercised when feeding lactose to sows especially if there is scope for some sows to receive more than intended.

Salmonellosis outbreaks in growers

Two seven-week-old grower pigs were received from a large unit with the history of four sudden deaths on the day of submission. Post-mortem examination revealed enteritis with diphtheritic/necrotic debris in the contents of the lower small intestine. There were also pale grey fluid contents in the large intestine accompanied by similar diphtheritic/necrotic debris. Salmonella Typhimurium was isolated in heavy growth from intestines of both pigs, confirming acute salmonellosis.

Three eight-week-old pigs were received from a rearing unit with a history of non-responsive scour, affecting approximately 10 per cent of pigs overall. Post-mortem examination revealed severe lesions in the large intestine of necrotic colitis or typhlocolitis from which a monophasic Typhimurium-like strain of Salmonella was isolated.

Gastric ulceration causing losses after purchase

A group of 30 Saddleback pigs were purchased from a market and approximately one week later two died and six were showing signs of poor condition despite feeding well. Post mortem examination revealed acute peritonitis secondary to a ruptured gastric ulcer. PRRSv testing was performed, as active PRRS infection can predispose to gastric ulceration, and the virus was not detected. It was suspected that the diet change following the recent purchase may have predisposed to ulceration. The cause of the condition loss in the other pigs was not clear and further submissions were encouraged.

Respiratory Diseases

Underlying swine influenza with mortality due to mulberry heart disease and salmonellosis

Three successive batches of weaners entering a single source indoor nursery-finisher developed widespread coughing in the second week on the unit with poor response to antimicrobial treatment. 280 of 700 pigs were coughing; mortality was minimal. Three dead pigs were submitted, one of which had been culled due to its poor body condition. Findings were mixed with one pig in good body condition having marked pulmonary oedema and patchy discolouration of the heart suggestive of mulberry heart disease which was confirmed by histopathology. In the two other pigs which were severely wasted, gross lesions pointed to chronic salmonellosis which was confirmed by the isolation of Salmonella Typhimurium phage type 193. The pigs also had patchy cranioventral pulmonary consolidation and, given the history of respiratory disease on the unit, testing for swine influenza was undertaken and all three pigs tested positive for swine influenza virus (not pandemic H1N1 2009).

PRRS underlying respiratory disease on two rearing units

Actinobacillus pleuropneumoniae and Pasteurella multocida were both isolated from the lungs of a 16-week-old pig from a large indoor finishing unit on which 20 per cent of a group of 240 were affected with coughing over a period of a week, loss of weight and malaise with one death. A severe subacute necrotising bronchointerstitial pneumonia was present. Only a single pluck was submitted and wider testing for the involvement of viral infection was recommended; sera submitted subsequently tested positive for antibody to PRRS virus indicating field challenge during rear.

Three six-week-old pigs were submitted from a continuous indoor nursery finisher supplied from a single source every three weeks. Approximately 20 per cent of 2,200 pigs were showing respiratory disease, malaise and weight loss, and mortality had risen in the last two batches entering the unit. The unit had a history of PRRS which was controlled by vaccination, however, vaccination had recently ceased and it was suspected that the problem had re-emerged. This suspicion was confirmed when PRRS virus was detected in the spleen of two of the three pigs submitted. Findings were somewhat mixed with a fibrinous polyserositis in one pig and polyarthritis in another and none of the pigs had eaten recently prior to death. Streptococcus suis type 14 was isolated from the pig with polyarthritis, together with Actinobacillus suis isolated from this pig’s lungs also. Whilst Streptococcus suis type 14 can be a primary pathogen in post-weaned pigs, its presence with A. suis in this outbreak is likely to reflect immunosuppression due to the PRRS virus.

Skin Disease

Outbreaks of greasy pig disease

Greasy pig disease was diagnosed at Bury St Edmunds as the cause of crusting skin lesions developing in the first one to two weeks of life in three of nine litters in a batch of farrowing sows. Lesions began as red papules on the ventrum and then spread all over the body. Approximately 36 piglets were affected from 150 with three deaths. Three piglets were submitted with brown flaking/crusting exudate all over their bodies, particularly affecting the nose and ears. In one piglet, lesions were focal to coalescing, red and excoriated, particularly on the ventral body and extending along the flanks. Histopathology confirmed skin lesions consistent with those expected in exudative epidermitis due to Staphylococcus hyicus. The piglets tested negative for PRRSV and no specific underlying cause for the outbreak was identified from examination of the piglets. Risk factors can include any causes for increased abrasion of the skin and a build-up of staphylococcal bacterial challenge in the environment.

Greasy pig disease was also confirmed by Luddington by isolation of Staphylococccus hyicus, the bacterial cause, from swabs of characteristic skin lesions seen in piglets and weaners on an indoor pig herd. Approximately 50 of a group of 200 pigs at risk were affected with earliest lesions observed in the farrowing house. Three deaths were reported but in severe outbreaks both morbidity and mortality can be significantly higher.

Nervous Disease

Incoordination in growing pigs

A third case of peripheral neuropathy (radiculitis and neuritis) was confirmed in pigs with incoordination and abnormal gait but remaining bright and alert and able to eat and drink. Approximately fifteen 11-week-old pigs were showing signs on a large all-in, all-out unit and a few pigs had been seen affected soon after their arrival at four-weeks-old. The two worst affected pigs were euthanased and submitted for post-mortem examination to confirm the diagnosis. We are interested to examine pigs from other units with signs which resemble those seen in these pigs, please contact your local AHVLA Regional Laboratory to discuss submission of possible cases.

Systemic Disease and Miscellaneous

Klebsiella species septicaemia in preweaned pigs

Two further cases of Klebsiella pneumoniae subsp pneumoniae septicaemia were confirmed at Bury St Edmunds. Both presented as sudden deaths of pre-weaned pigs in good body condition on outdoor breeding units. Pigs were found dead from two-weeks-old, although most were dying nearer to weaning at four-weeks-old. Investigations are in progress on affected units.

Iron deficiency anaemia

Nearly all of two groups of litters had died at approximately two-weeks of age. These were from a small, housed grower fattening unit. Necropsy at Langford revealed pale pigs with watery blood, excess fluid within body cavities, pulmonary oedema and a pale liver. Iron deficiency anaemia was suspected and further enquiries revealed that although routine iron injections are given, the two affected litters had not received these.

PCV2 associated disease

Investigation of malaise with ocular discharge, ataxia and diarrhoea was undertaken in weaners kept in an orchard, part of a 70 pig Gloucester Old Spot herd. Post-mortem examination of one of five pigs dying in a litter of six pigs found the pig to be in very poor condition with enlarged lymph nodes. Circumstantial evidence had associated the ataxia with apple consumption and alcohol intoxication, however, histopathology and immunohistochemistry confirmed porcine circovirus-2 associated disease with a granulomatous lymphadenitis in the submitted pig.

Necrotic lesions due to Fusobacterium species infection in anaemic pigs

One dead and two live piglets aged four weeks were submitted to Preston to investigate listlessness, anorexia and death 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. Serum iron was not low but the pigs were treated just four days before submission. Inclusion bodies consistent with Mycoplasma (Eperythrozoon) suis, a recognised cause of haemolytic anaemia, were seen in red blood cells of both 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.

Musculoskeletal disease

Lameness due to polyarthritis in finishing pigs

The carcases of two freshly euthanased finishing pigs were submitted to investigate lameness on a large unit utilising by-products for feeding. Finishing pigs developed arthritis when moved into finishing accommodation with a good response when treated with lincomycin. The involvement of Mycoplamsa hyosynoviae was suspected based on the response to therapy and the clinical signs. In one pig all joints were affected, in the second, only the left stifle and hock. Joints contained increased volumes of haemorrhagic to turbid fluid and variable amounts of fibrin clots and tags. Synovial membranes in the joints were thickened and reddened with pinpoint haemorrhages. No bacteria were cultured and no Mycoplasma species was detected by DGGE. Histology revealed a lymphoplasmacytic synovitis which supports a diagnosis of mycoplasmal arthritis, although chronic erysipelas remains a possible differential.

Further Reading

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

5m Editor