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UK Pig Disease Quarterly Surveillance Report - May 2004

by 5m Editor
20 May 2004, at 12:00am

By Veterinary Laboratories Agency - This report monitors trends in the major endemic pig diseases and utilises the farmfile and VIDA (Veterinary Investigation Disease Analysis) databases. The report is compiled using disease data gathered by the network of 15 VLA regional laboratories which carry out disease investigation in the field.

Quarterly Surveillance Report Pigs: Vol. 8 No. 1
Jan - Mar 2004 - Published May 2004

Contents

OVERVIEW (here)

NOTIFIABLE DISEASES

ZOONOTIC DISEASES

ENDEMIC DISEASES

Highlights: Third Quarter 2003

  • National pig population may stabilise this year after several years of decline
  • ZAP initiated salmonella investigations starting to take place
  • Yet again, PMWS identified as the major issue affecting pig health.

Overview

The Meat and Livestock Commission Economics (www.mlceconomics.org.uk), Pig Market Outlook: 04/2 April 2004, provides an overview of the pig sector. Pig prices fell throughout January to around 100p/kg dw (GB Deadweight Average Pig Price: DAPP) before rising by 9p/kg to some 3p/kg better than one year previously. The UK breeding herd began to stabilise in 2003 after five years of contraction. The December 2003 figures were only one percent down on a year earlier. However, slaughter pigs were down 10 percent over the year, reflecting the deterioration in average sow productivity. In addition, declining inpig gilt replacement and maiden gilt numbers suggest that breeding sow numbers will continue to fall during the first half of 2004. Higher feed costs continue to adversely affect profit margins, and lack of investment remains a chronic problem.

Notifiable Disease:

No suspect incidents of swine fever investigated.

Zoonotic Diseases and Food Safety

POTENTIAL FOOD SAFETY INCIDENTS:
There were no reports of potential food safety incidents involving pigs.

SALMONELLOSIS AND SALMONELLA ISOLATIONS:
Salmonella isolates: Salmonella enterica serovar Typhimurium again predominated with unremarkable antimicrobial susceptibility patterns. Many pig isolates of Salmonella Typhimurium do not demonstrate the 05 antigen, unlike those of other species. Definitive types (DTs) of Typhimurium included 193, 104A, U288 and 93.

Salmonella incidents: Typhimurium DT93 occurred in two 10- week-old pigs on a completely outdoor unit. A quarter of rearing pigs on another unit died with Typhimurium infections. Postweaning multisystemic wasting syndrome (PMWS) was again a significant finding in many of the salmonella incidents.

Two initial farm visits and one follow-up visit were made under the ZAP scheme initiative. One visit resulted after 86% of the meatjuice ELISAs from the unit were positive. The unit is a contract finisher receiving pigs from five different sources. Results indicated that a Group B salmonella infection was persisting on the unit rather than being brought in with the pigs. Rodent control and improvement of cleansing and disinfection were identified as areas for urgent attention.

The second investigatory visit again involved a contract finisher. Pigs were received from 12 sources, all of which were outdoor herds. Cleansing and disinfection were only performed once a year although the system was run on an all-in/all-out basis. Other identified risk factors included poor buildings, a high incidence of PMWS during the finishing period, and also overworked and demoralised staff. It was suggested that sampling of pigs on arrival at the unit would identify sources of infected animals.

A follow-up visit to a unit with a previously high ZAP score found that overall mortality had dropped from 9% to 1.5%. However, these pigs were still excreting salmonellas in at least 30% of the pens. The next ZAP results are awaited with interest.

BRUCELLOSIS:
Brucellas were not isolated under the surveillance initiative to provide evidence that pig herds remain free of Brucella suis; an organism that has never been isolated from pigs or hares in the UK.

STREPTOCOCCAL INFECTIONS AND DISEASE:
First quarter diagnoses of streptococcal incidents are illustrated over five years (vertical bars represent 95% confidence limits):


% of submissions submitted with Streptococcal infections

The percentage of submissions with streptococcal infections increased significantly in 2000 following the upsurge of PMWS and porcine dermatitis and nephropathy syndrome (PDNS). The dip in 2001 is attributed to few carcase submissions during the FMD outbreak but the diagnosis rate is now stable at around 7% of submissions. The continuing predisposing presence of PMWS is illustrated in this report.

The Wellcome Trust Sanger Institute has received funding to sequence the genome of Streptococcus suis. The work is nearly complete and the sequence is to be published in a peer-reviewed journal. The genome is approximately 1.7 Mb in size with a G+C content of around 40%.

Streptococcus suis isolates: Twenty-five Streptococcus suis isolates were serotyped this quarter:


Over half of these were Streptococcus suis serotype 2 compared with proportionally fewer in previous quarters:

Quarter 1st 1st 2003 2nd 2003 3rd 2003 4th 2003 1st 2004
Serotype 2 as % of isolates 25.6 46.1 23.1 28.0 52.0

Streptococcus suis incidents There were 11 incidents of Streptococcus suis infection; four (36.4%) were serotype 2. There were three incidents of serotype 3 infection and single diagnoses of serotype 1, 4, 8 and untypeable. It was noted that seven of these incidents (64%) had underlying PMWS/PDNS.

Two of the serotype 2 incidents involved typical meningitis cases, but unusually one of these involved pigs from ten to 23 weeks-of-age. The other two outbreaks both involved respiratory disease with underlying PMWS. The three S.suis serotype 3 incidents all involved respiratory disease as commonly reported previously. One outbreak had concurrent PMWS and another PDNS. The disease outbreaks, where 4, 8, and untypeable serotypes were isolated, had PMWS. In one of these, Glasser’s disease was confirmed and S.suis serotype 8 was a secondary isolate. The other two incidents were of respiratory disease with S.suis isolated and other respiratory pathogens identified. The final incident was suspected Glasser’s disease but surprisingly S.suis serotype 1 was isolated rather than Haemophilus parasuis. Similar previous incidents are reported but associated with S.suis serotype 14.

Other streptococcal infections Streptococcus dysgalactiae equisimilis was involved with disease in two groups of neonatal piglets. Both cases were predisposed by trauma. In one, rough flooring was judged to have caused skin lesions over the limb joints leading to polyarthritis. S.equisimilis was isolated from the affected joints. The other was due to a poor teeth clipping technique leading to tooth root infection. Welfare advice was given.

ENDEMIC DISEASES – SUBMISSIONS:

PIG-RELATED QUARTERLY SUBMISSIONS 2003-2004


PIG-RELATED QUARTERLY SUBMISSIONS 2002-2003

Note: ‘diagnostic’ refers to initial submission in an incident

Total submissions were lower mainly due to previous completion of non-diagnostic project work. Carcase diagnostic submissions and specimens (primarily submitted for a differential diagnosis) were at their highest since foot-andmouth disease in 2001. The ‘diagnoses not reached’ category, where reasonable testing was possible on diagnostic submissions, was unremarkable when compared with data for the previous three years.

POSTWEANING MULTISYSTEMIC WASTING SYNDROME (PMWS)/
PORCINE DERMATITIS AND NEPHROPATHY SYNDROME (PDNS):

Diagnoses of PMWS - as a percentage of diagnostic submissions tested - remain high at 23%, but are down on the same quarter of 2003 (26%), and 2002 (33%). This is, in part, attributed to a decreasing need to confirm clinical diagnoses. The widespread presence of porcine circovirus type 2 (PCV-2) associated diseases continues to exacerbate and precipitate many disease conditions making control and treatment difficult. The high mortalities associated with some outbreaks and increased culling are demoralising for farm staff.

Despite the widespread occurrence of PCV-2 there are still herds experiencing their first recognised cases. One such herd, which had been closely monitored and previously shown no clinical or pathological signs of PMWS/PDNS, had an increased mortality rate and PMWS was suspected. The findings of wasting, enlarged inguinal lymph nodes, stomach ulcers, pulmonary interlobular oedema and pallor were confirmed as associated with PCV-2 infection.

On an indoor unit mortality increased in 7 to 10-week-old pigs with signs reported of scour, illthrift and respiratory disease. Histopathology confirmed the presence of PCV-2 associated disease for the first time. The disease had affected 100 of 1100 pigs and resulted in the death of 50.

Disease was associated with pasteurellosis including pleurisy and bronchopneumonia. Mortality reduced rapidly to between 2% and 3% following antimicrobial therapy. On a small unit of just 12 sows, wasting and deaths were reported in several litters preweaning. PMWS was first observed at 6-weeks-old despite weaning at 9 to 10 weeks of age. Various lesions were seen in the 6-week-old pigs including enteropathy, lymphadenopathy, and polyserositis.

Diagnoses of PDNS were far less common than PMWS with first quarter rates remaining fairly stable at between 3% and 4% of diagnostic submissions for the years 2002 to 2004. A single diagnosis may be misleading as illustrated on one unit where increasing mortality resulted in 20 of 250 16-weekold pigs dying acutely within one week. A single pig was initially submitted for necropsy, and Glasser’s disease (Haemophilus parasuis) was diagnosed. Subsequently a further three pigs were submitted and all were confirmed as having PDNS.

ENTERIC DISEASE:
There was only one confirmed swine dysentery incident in which one percent mortality was reported in 16-week finishers. This follows the annual trend of declining diagnoses over the previous five years:


% of submissions diagnosed with Swine Dysentry

Lawsonia intracellularis infection was more frequently reported than swine dysentery. One outbreak of haemorrhagic enteropathy caused 14 deaths in finishers over a short period. Affected pigs showed severe pallor due to anaemia. A second serious incident involved 90% of Gloucester Old Spot growers that showed dysentery, weight loss and sudden death. Gross and histopathological findings confirmed classical lesions of porcine intestinal adenomatosis.

Gastric ulceration is a common subclinical condition in finishing pigs but clinical disease is usually sporadic. The exact pathogenesis is still unknown. An outbreak presenting as illthrift with vomiting in an AI boar stud was interesting because one typical casualty showed histological evidence of helicobacter infection associated with chronic gastric ulceration and oesophageal stenosis with marked muscular hypertrophy. Other noninfectious factors were thought to be contributory, particularly reduced fibre intake following a move from straw-based pens to fully slatted accommodation.

Coccidiosis due to Isospora suis is well recognised as a cause of diarrhoea in sucking pigs. In contrast, clinical disease due to Eimeria species is rarely reported and most strains are considered relatively non-pathogenic. A 7-month-old boar did however die from Eimeria-associated necrotic enteritis a few days after purchase. The timing and the parasite’s pre-patent period suggested that coccidia must have arrived with the animal as a latent or incubating infection rather than picked up from the new farm environment. Other recent purchases in the same group remained unaffected.

RESPIRATORY DISEASE:
Percentage of submissions diagnosed with respiratory disease (excluding PRRS and PCV-2 associated disease) were similar this quarter to the same quarter in 2000, 2002 and 2003:


% of submissions diagnosed with Pneumonias and Pleurisy

Pasteurella multocida was the most commonly diagnosed (19) cause of respiratory disease and this is partly attributable to it being more readily identifiable than other respiratory pathogens. P.multocida was isolated with avian-like H1N1 influenza virus from lungs submitted to investigate respiratory disease within one week of weaning.

Some 70% of weaners were affected but with minimal mortality. A problem of growth check, wasting and coughing affecting around 25% of growers was investigated in pigs 5 to 15 weeks old. P.multocida and Actinobacillus pleuropneumoniae (App) were isolated and there was histological evidence of PMWS.

Incidents of pneumonia due to App as a percentage of diagnostic submissions were up this quarter (3.4%) on the same quarter last year (2.4%). An outbreak of respiratory disease in which 20% of 3 to 6-month-old pigs were affected with 3% mortality was again multifactorial. On this occasion swine influenza virus was isolated with App but without histopathological evidence of PCV-2 or PRRS. In another outbreak, mortality increased from 0.5% to 3% in pigs that were the first to follow a programme of partial depopulation and treatment for App. Serotype 8 App was isolated from typically affected lungs. On another unit A.pleuropneumoniae infection killed 7/800 pigs aged 14 weeks, and a further 60 pigs were ill. The unit had used an autogenous APP vaccine but apparently without success.

Quarterly diagnoses of enzootic pneumonia remain at a low level, in part attributable to introduction of vaccination in recent years:


% of submissions diagnosed with enzootic pneumonia

This quarter there was a reduction in diagnoses of PRRS, which may in part result from the lack of a quick, cheap and effective diagnostic test. The use of vaccines for PRRS (one is a live attenuated vaccine and the other two are inactivated) may result in greater difficulty interpreting serological results. These vaccines all became available in the UK in September 2000. An outbreak of respiratory disease in 4 to 5-month-old finishers, with an increase in mortality from 2% to 10%, was investigated by serology. Seroconversion to PRRSV was demonstrated.

Two less common causes of respiratory disease were diagnosed this quarter. Actinobacillus suis was isolated in septicaemic distribution from 4-week-old pigs that had a sudden rise in mortality associated with purpura, respiratory distress, and polyserositis. A sow 11- weeks in-pig was necropsied after a few days of inappetance, lethargy and dyspnoea. There was a severe polyserositis from which Haemophilus parainfluenzae was isolated. This organism is a commensal of the human upper respiratory tract but has been reported to cause a Glasser’s-like disease in pigs.

Swine Influenza: Continuing surveillance of influenza virus isolates has not identified significant changes in circulating strains:

Isolates obtained January to March 2004:

Received Positive (%)
Submissions 33 3* (9.1)
Samples 96 4 (4.2)
* avian-like H1N1 x2; HIN2 x1

REPRODUCTIVE DISEASE: Fetopathy diagnoses, regardless of whether the cause was identified, show a steady upward trend from 2000 despite a concurrent decline in the national sow population:


% of submissions diagnosed with fetopathies

Provisional numbers of the first quarter submissions for abortion and nonabortion reproductive disease, and the non-diagnostic rates for both categories, are given in the following tables:

Quarter No of Submissions
Abortion Non-abortion
1st 14 37

Quarter Diagnosis not reached
Abortion Non-abortion
1st 8 (57%) 11 (30%)

The ‘diagnosis-not-reached’ figure for abortion submissions is higher this year than it was in the same quarter of 2002 and 2003, but is based on fewer submissions. The diagnostic rate for non-abortion reproductive disease is apparently better than for the previous two years. No single aetiology appeared to dominate diagnoses in either category.

Project OD0214 - Isolation and characterisation of leptospires in pigs: PCR and culture of kidneys is currently in progress at VLA Weybridge and has already resulted in successful isolation of Leptospira Bratislava.

MUSCULOSKELETAL DISEASE:
An outbreak of lameness affecting pigs aged from approximately 6 to 12 weeks was investigated. The farm had a total of 9,000 piglets and growers, and within this age group it was estimated that about 5% of pigs were affected. Clinical signs included ‘shifting lameness’ particularly of the hind limbs, stiff gaits, arched backs, a preference for ‘dog sitting’, and recumbency. This had resulted in reduced feed intake and subsequent reduction in growth rate. Two batches of pigs were necropsied prior to a farm visit.

Reduced bone density was identified in all the carcases and involved the long bones, but notably also the flat bones of the skull, ribs and vertebrae. The ribs were easily bent, and cortical bone of the long bones was thin. A single pig fractured the distal tibia. Affected pigs were also hypocalcaemic. However, the clinical picture was confused by the presence of colitis due to Salmonella Typhimurium in these worst affected pigs. During the farm visit colitis was not identified as a problem on the farm and appeared to have occurred, as a terminal event, in severely compromised recumbent pigs. Results of gross and clinical pathology, and feed analyses indicated an imbalance/inadequacy of dietary calcium and phosphorus as a likely cause of the problem. A change in ration, with increased mineral content, was instigated within days of the visit and preliminary reports indicated that there were almost immediate improvements.

Individual attention was given to the worst affected pigs to enable them to reach feed and water without competition – a priority from the welfare viewpoint. Although there were two other units where pathological fractures were reported in similar age pigs, there is currently little information available.

MYCOPLASMAS:
Seventeen isolates, all from lungs, were identified as Mycoplasma hyorhinis. The precise role of M.hyorhinis in disease is worthy of further investigation.

Historically it has always been considered a commensal, but internationally is increasingly associated with more disease, including otitis media, eustachitis, bacterial meningitis, and even abortion.

WELFARE
A ruptured oesophagus was identified during an investigation of disease in neonatal pigs. This was a sporadic incident thought to result from a dosing gun injury. Nevertheless, the private veterinary surgeon was asked to investigate and advise the farmer further. Remnants from poorly clipped teeth resulted in osteomyelitis from Streptococcus dysgalactiae equisimilis infections – advice was given to improve teeth clipping procedures.

Two 5-week-old pigs were submitted for investigation into poor growth and deaths affecting 12 from a group of 60. Both pigs had navel infections with fibrous calluses and skin abscessation of the distal limbs. Arcanobacterium pyogenes was isolated form the navels. Although the herd had previous PMWS cases there was no evidence of PCV-2 associated disease in these two pigs to account for increased susceptibility to infection.

Source: Veterinary Laboratories Agency - May 2004