AHVLA Reports Oedema Disease, Pleurisy and PRRS in January 201408 April 2014
UK - The Animal Health and Veterinary Labratories Agency has reported Oedema disease in weaners, sudden deaths due to Actinobacillus pleuropneumoniae on a unit with pleurisy problems, porcine reproductive and respiratory syndrome diagnosed in vaccinated pigs and heart failure due to erysipelas in finishers, in its January 2014 report.
Rotaviral enteritis diagnosed causing high incidence neonatal diarrhoea
Rotavirus infection was diagnosed by Luddington as the cause of diarrhoea in neonatal piglets on a 200-sow unit. Virus was detected in faeces and histopathological findings consistent with rotaviral enteritis were detected in euthanased piglets. The clinical presentation of diarrhoea with 50 per cent morbidity without a concurrent increase in mortality had prompted laboratory investigation.
Oedema disease in weaners
Five-week-old pigs were submitted to Thirsk to investigate sudden deaths of growing pigs kept in two straw yards, each containing 400-500 pigs. Some pigs were also described as unwell, “staggering about” as if having meningitis and with “puffy eyes”. The pigs were vaccinated against Mycoplasma hyopneumoniae and PCV-2 at weaning and were from a source where previous batches of weaners had developed suspected Mulberry heart disease two to three weeks after weaning. In this batch, the mortality occurred earlier than had been seen previously. Postmortem examination revealed subcutaneous oedema of the ventral body, oedema of the mesentery and/or spiral colon and also of the eyelids. Despite the first suspicion that a bacterial septicaemia was involved, the final diagnosis reached was E. coli oedema disease with E. coli O139:K82 isolated in profuse growth from the small intestines of multiple pigs. E. coli serogroup O139 is enterotoxigenic and is associated with both oedema disease and postweaning E. coli diarrhoea. No other bacterial pathogens were isolated and no PRRS and swine influenza viruses were detected. Oedema disease is mainly seen in recently weaned pigs as in this outbreak, but occurs less commonly than postweaning E.coli diarrhoea.
Outbreaks of illthrift and diarrhoea in weaners due to salmonellosis
Combined salmonellosis and rotavirus infection was diagnosed as the cause of diarrhoea and illthrift in approximately 10 per cent of 1,400 four and a half week old weaners kept outdoors on a multisource rearing unit. The pigs submitted to Bury St Edmunds were markedly dehydrated with dark green diarrhoea and a monophasic Typhimurium-like Salmonella was isolated from the intestines by direct culture. There was also evidence of septicaemia due to salmonella infection with a pure growth of the same salmonella isolate from the meninges of one of the pigs. The pigs were young for salmonellosis and other issues such as exposure to significant contamination with salmonella periweaning and/or environmental or climatic factors are likely to have played a role in disease developing early post-weaning.
Salmonellosis due to a monophasic Salmonella Typhimurium-like isolate was also diagnosed as the cause of illthrift and occasional diarrhoea in approximately 20 per cent of a batch of seven-week-old weaners on an indoor nursery unit on which 25 had died. On this occasion, no other enteropathogen was identified but the pigs were in poor body condition and the involvement of earlier disease making them more susceptible to salmonellosis could not be ruled out.
Sow deaths on outdoor units due to gastric ulceration and torsion
A sow was submitted from an outdoor breeding unit on which a total of six were found dead over a period of five weeks. The majority were lactating and were found dead with no signs being seen prior to death. The submitted sow had a pale carcase and was anaemic due to fatal gastric haemorrhage from an ulcerated pars oesophagea, the sow also had a chronic fibrosing epicarditis.
Testing for swine influenza and PRRS viruses was undertaken to determine whether there was any intercurrent disease which may have caused the disruption of normal feeding and predisposed to gastric ulceration, neither were detected. It is possible that other climatic or managemental factors were involved.
Two dead replacement breeding gilts were submitted from an outdoor breeding herd, the gilts were in a batch moved into a paddock a week prior to submission. One was found dead on the morning of submission, the other was found recumbent and died within two hours. One had an intestinal torsion which was likely to have been predisposed to by a large quantity of gravel accumulated in the large intestine. The second pig had a perforated colon with evidence of necrosis and fibrinous peritonitis.
There was no evidence of an infectious basis to the disease and small ‘outbreaks’ of intestinal torsion have been seen in past years with similar histories of recent introduction of young breeding animals to an outdoor situation with excessive ingestion of sand and stones.
Swine influenza as part of more complex disease including salmonellosis
Swine influenza due to pandemic H1N1 2009 virus was diagnosed as a component of more complex disease in five-week-old weaners with respiratory disease and 3 per cent mortality since weaning. Three dead pigs examined at Bury St Edmunds had cranioventral pulmonary consolidation consistent with swine influenza and the virus was detected in all three. The pigs were also dehydrated with no evidence of recent feed intake and all also had diarrhoea and necrotic colitis consistent with salmonellosis. This was confirmed by the isolation of Salmonella Typhimurium phage type U288 and, in one pig, rotavirus was also detected. In addition, Streptococcus suis type 7 and S.suis type 2 were isolated from the lungs of individual pigs, likely secondary to the swine influenza infection. This is one of several similar recent cases where swine influenza infection postweaning has occurred prior to, or concurrent with, salmonellosis. Although swine influenza alone does not generally cause mortality in pigs, it may affect the ability of young weaners to establish normal feeding and drinking when infection occurs immediately postweaning which could predispose them to salmonellosis and other enteropathogens. In addition, where antimicrobials are used to treat the respiratory disease seen, these tend to favour colonisation of salmonella organisms which are resistant to the commonly used antimicrobials for respiratory disease.
Nasal swabs used to diagnose swine influenza in coughing weaners
Acute respiratory disease with coughing in a batch of seven-week-old pigs on a nursery unit was investigated by submission of nasal swabs to Bury St Edmunds from pigs early in the course of disease.
These were tested under AHVLA’s Defra-funded swine influenza project free of charge and swine influenza was detected by PCR in five of the six swabs submitted, confirming active swine influenza virus infection. The swine influenza strain was subsequently confirmed to be H1N2 which is one of the two predominant strains currently circulating in GB pigs, the other being pandemic H1N1 2009.
Sudden deaths due to Actinobacillus pleuropneumoniae on a unit with pleurisy problems
Actinobacillus pleuropneumoniae (APP) infection was diagnosed as the cause of sudden death of two out of 250 12 to 14-week-old housed finishers found dead one morning. There were no other clinical signs in the group but a concurrent problem of severe pleurisy (approximately 50 per cent of a recent batch of pigs) was reported from the abattoir and was also being investigated. PRRSv PCR on cohorts of rearing pigs had recently revealed active PRRS infection postweaning in unvaccinated pigs. Both dead pigs examined at Bury St Edmunds were in good body condition with APP-like lesions in the lungs and, in one pig, there was a significant tracheitis with fibrin occluding the lumen of the left bronchus. APP was isolated from the lungs of both pigs confirming the diagnosis and immunohistochemistry also found evidence of PRRSv involvement in the pneumonia in one pig, supporting the likelihood that PRRS was clinically significant earlier in rear in these pigs. This was the first diagnosis of APP infection in the herd and involved serotype 2 which has been identified previously in GB pigs but is not one of the most common serotypes. The APP was likely to be significant with respect to the pleurisy identified at the abattoir.
Porcine reproductive and respiratory syndrome diagnosed in vaccinated pigs
Porcine reproductive and respiratory syndrome (PRRS) was diagnosed in 12-week-old finisher pigs submitted from an indoor multi-source finishing unit. An increase in mortality was reported over the four-week period after entry with approximately 20 per cent of pigs affected with respiratory disease including blue ears, and some with dyspnoea without coughing, although few pigs were reported to be showing significant malaise. Three pigs were euthanased and submitted. They were in fair to poor body condition with varying degrees of pneumonia with a lobular pattern of purple consolidation affecting caudal as well as cranial and middle lung lobes, raising suspicion of viral involvement. Genotype 1 PRRS virus was detected by PCR in the lungs, although testing of spleen and pooled serum had initially given negative results, possibly reflecting a low viral load.
Histopathology and immunohistochemistry on the lungs confirmed the involvement of PRRS virus in the pneumonias, showing the virus to be clinically significant despite PRRSv vaccination earlier in rear. No swine influenza or PCV2 involvement was detected. The ORF5 genes of the viruses detected in each of the three pigs were sequenced and were very similar (99 to 99.5 per cent) to each other. They were not closely related to live vaccine strains licensed in GB.
Porcine circovirus 2-associated disease in unvaccinated pigs
The carcases of four 14-week-old pigs were submitted to Thirsk to investigate increased mortality on a 4,300 pig straw-based unit. Piglets entered the unit at weaning and were just about to move to their finishing site, they had not received any vaccines at weaning. The most striking finding was widespread pulmonary oedema which was especially marked around the hilus of the lungs. There was also some cranioventral consolidation affecting around 30 per cent of the lung fields. In two of the four pigs there were marked fibrinous pericardial effusions. In all, the tracheobronchial and mediastinal lymph nodes were enlarged with purple discolouration. Several pathogens were isolated from the lungs, Pasteurella multocida, Streptococcus suis Type 3 and Streptococcus suis Type 4, and underlying viral disease was suspected. Histopathology revealed moderate subacute bronchointerstitial pneumonias and granulomatous lymphadenitis with intracytoplasmic inclusions visible in both lung and lymph nodes pointing to porcine circovirus 2-associated disease which was confirmed by immunohistochemistry for PCV-2 which was strongly positive and a diagnosis of PCV-AD was made. Advice to resume vaccination of the pigs at weaning was given.
Systemic & Miscellaneous Disease
Sudden deaths due to Mulberry heart disease
Mulberry heart disease was diagnosed at Thirsk by histopathology of heart from a six-week-old weaned pig. Twenty two pigs from of a group of 1,000 had died suddenly and on-farm postmortem examination revealed peritoneal haemorrhage from a ruptured liver and pericardial and pleural effusions. The gross appearance of the heart surface was reported to be suggestive of Mulberry heart disease and this was confirmed.
Heart failure due to erysipelas in finishers
Erysipelas was diagnosed as the cause of red ear discolouration and dyspnoea in a euthanased 20-week-old finisher from a batch of finishers on an indoor breeder-finisher unit on which there had been occasional sudden deaths and occasional pigs show dyspnoea. Post-mortem examination revealed severe vegetative endocarditis lesions affecting the aortic and left atrioventricular valves and the pig had developing heart failure. The continuous management system and lack of cleaning and disinfection in the finisher accommodation may have allowed a build up of Erysipelothrix species organisms in the environment. Breeding pigs on the unit were vaccinated for erysipelas, the rearing herd was not.
Sudden death of six fattening pigs from a group of 25 that had been showing signs of diarrhoea prompted submission to Newcastle of heart, small intestine, lung and liver from one of the pigs that had been examined on-farm. Large vegetative lesions were found on the left atrioventricular valve raising a suspicion of erysipelas, a diagnosis that was subsequently confirmed by recovery of Erysipelothrix rhusiopathiae from the valve lesions.
Skin tumour in a young Tamworth pig
An ulcerated skin mass, 3cm in diameter, on the back of a three-week-old Tamworth pig was submitted for histopathology. A cutaneous tumour of melanocytic origin was diagnosed. These are sometimes seen as congenital variants in several breeds of pig. No morphological classification of these neoplasms is available for pigs, there is marked variation in clinical behaviour and some may undergo spontaneous regression while others metastasize. Histological or other characteristics that will distinguish these differing biological behaviours have not been reported.
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