VLA: H1N1 Virus and Endemic Strains Cause Influenza

UK - Outbreaks of swine influenza caused by both pandemic (H1N1) 2009 virus and contemporary endemic strains have been noted in pigs, according to the Veterinary Laboratories Agency (VLA) in its report for August 2010.
calendar icon 19 October 2010
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Alimentary tract diseases

Intestinal Adenomatosis and Brachyspira pilosicoli infection

Two live seven week old mixed breed pigs were presented at Shrewsbury for post-mortem examination with a history of wasting affecting one to two animals per batch of 50. The pigs were in poor body condition and post-mortem examination revealed marked thickening of the mucosa of the ileum and proximal large intestine. Acid-fast curved intracellular rods were seen with MZN staining of ileal mucosa consistent with Lawsonia infection. Histopathological findings included moderate to severe, sub-acute to chronic, proliferative ileitis with acute multi-focal purulent enteritis and acute to sub-acute colitis with silver-positive palisading bacteria. Brachyspira pilosicoli was identified by PCR and anaerobic culture and a diagnosis of intestinal adenomatosis and B. pilosicoli infection was made.

Swine dysentery

Luddington diagnosed Swine dysentery in yarded 10-week-old weaner pigs, part of a 50 sow outdoor herd. Ill thrift in weaners had been a growing problem in recent months with a rising mortality. Six of 28 pigs at risk in one group had died post weaning. Evidence of concurrent Group B Salmonella and Lawsonia intracellularis infections was also found at necropsy. Both of the latter can be associated with similar necrotic lesions. To meet point of sale needs, additional purchases of weaners directly into the yards had taken place previously and, in the absence of swine dysentery in the sow population, it was suspected that infection may have been introduced directly into the yards following purchase.

Thirsk also diagnosed Swine dysentery as the cause of diarrhoea in post weaned pigs from a weaning to finishing unit.


Bury diagnosed five outbreaks of salmonellosis in pigs aged between five and nine-weeks-old. Diarrhoea was the most common sign reported, together with wasting and/or mortality. Mortality was reported to be 0 to 3 per cent at the time of submission with scour affecting 5 to 10 per cent of pigs. All five outbreaks involved Salmonella Typhimurium (phage type U288 or 193).

Thirsk isolated Beta haemolytic E. coli O8:K87, K88, Salmonella Derby and Salmonella Copenhagen from five-week-old piglets with diarrhoea and wasting. The E. coli isolate was a recognised porcine pathogen associated with enteric disease and oedema disease. It is likely that the E. coli was playing a significant primary role with the Salmonella being secondary.

Respiratory Diseases

Swine Influenza

Bury investigated three outbreaks of swine influenza. In the first pandemic H1N1 2009 influenza virus was confirmed as the cause of acute respiratory disease in finisher pigs in which approximately 20 per cent were coughing and lethargic. No deaths had occurred at the time of submission and diagnosis was achieved through collection of deep nasal swabs from affected pigs very early in the course of disease. The second also involved pandemic H1N1 2009 virus and was confirmed in weaners in which 20 per cent had been coughing for approximately two weeks, the cough failed to respond to in-water antimicrobial treatment, although the meningitis seen at the same time in approximately 5 per cent of pigs did respond to the treatment. The third outbreak was due to a contemporary endemic strain and was diagnosed when two fresh plucks were submitted from coughing 14-week-old pigs from a multisource indoor unit.

Langford also diagnosed an outbreak caused by pandemic (H1N1) 2009 and enzootic pneumonia affecting a recently established 6,000 pig finishing unit (with pigs sourced from two units only) which suffered acute onset respiratory symptoms affecting 10 per cent of the pigs with a 12 per cent case fatality rate. Subsequently, two pigs were submitted for post mortem. The gross appearance of both lungs was suggestive of enzootic pneumonia. Histopathology subsequently revealed bronchial epithelial necrosis consistent with influenza infection together with chronic bronchointerstitial pneumonia typical of Enzootic Pneumonia.

Actinobacillus Pleuropneumoniae

Thirsk diagnosed an outbreak of pneumonia caused by Actinobacillus pleuropneumoniae (APP), in some cases in combination with Pasteurella multocida, affecting seventeen-week-old finisher pigs on a 550 sow, three-weekly batch farrowing indoor unit. Potential viral involvement in the form of swine flu, PRRS and PCV2 was ruled out by further testing and a diagnosis of uncomplicated APP was made.


Parasitic disease was diagnosed in a three-month-old Saddleback pig submitted to Starcross that had been losing body condition and had become recumbent. At necropsy there were small pale foci in the colon and numerous nematodes (Metastrongylus sp) were present in the lungs. On histological examination the colonic lesions were eosinophilic granulomata, probably associated with Oesophagostomum sp.

Other diseases


Winchester necropsied two five-month-old gilts and a boar which were kept together, and had been seen to eat windfall apples recently. One gilt became recumbent and pyrexic, initially improved but then deteriorated and died overnight; the second gilt was also very dull. Erysipelas was confirmed post-mortem with E.rhusiopathiae isolated in septicaemic distribution. Long acting penicillin was given to the survivors and a vaccination programme put in place.

Another case was diagnosed in five-month-old gilt which was submitted with a history of anorexia and vomiting.

Further Reading

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