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UK Pig Disease Quarterly Surveillance Report - April-June 2008

by 5m Editor
14 October 2008, at 12:00am

The latest report from the Veterinary Laboratories Agency (VLA)highlights an upturn in the incidence of PMWS, pneumonia and pleurisy, but there is evidence of benefits following the use of PCV2 vaccines. There have been no outbreaks of Notifiable Diseases or zoonoses associated with pigs.

Quarterly Surveillance Report Pigs: Vol.12 No.2
April-June 2008
Published August 2008

Contents

HIGHLIGHTS

INTRODUCTION TO GB PILOT REPORT

OVERVIEW PIG DEMOGRAPHICS AND DIAGNOSTIC SUBMISSION RATES NOTIFIABLE DISEASES REPORTED FARM VISIT INVESTIGATIONS FOOD SAFETY INCIDENTS

ENDEMIC DISEASE SURVEILLANCE

UNUSUAL AND NEW DISEASES

SYNDROMIC DISEASE SURVEILLANCE

SCANNING SURVEILLANCE FOR NEW AND EMERGING DISEASE

Highlights

  • There have been no outbreaks of Notifiable Disease or zoonoses associated with pigs.
  • There were no food safety incidents involving pigs.
  • Unfortunately, the decline in the incidence of PMWS, pneumonia and pleurisy noted in the last QR report was not maintained and incidence rose to previous levels.
  • There are reports of major benefits following the use of PCV2 vaccines either in sows or piglets.
  • The culling of sows continues although there was some improvement in retail price of pig meat, with some way still to go.

Introduction

This is the first pig surveillance report that combines information from all areas of Great Britain into a single, integrated overview of pig health across the whole region. It has been made possible through a partnership between Defra, SEERAD, the Veterinary Laboratories Agency (VLA) and Scottish Agricultural Colleges Veterinary Services (SAC VS) Division.

Endemic Disease Surveillance

Salmonella and Salmonellosis

In the second quarter of 2008, 5.9% of porcine submissions tested were diagnosed with salmonellosis. This compares with 10.9% in the first quarter of 2008. The downward trend in total submissions continues. This is likely reflecting the contraction of the UK herd.

Brucellosis

No positive cases were identified in the UK.

Streptococcal Infections

The predominant type identified this quarter was SS2, as previously seen. Higher levels of untypable strains were found in 2008 than were previously seen in this quarter but this is not thought to be significant as this is the normal pattern with type 2 predominating. Total number of S.suis diagnoses is higher than we have seen for some time. The reason is unclear.

Porcine Reproductive and Respiratory Syndrome (PRRS)

The quarterly percentage of relevant diagnostic submissions with a diagnosis of PRRS showed an increase, which was not statistically significant, on the same quarter of the last two years. This data includes diagnoses of pneumonia associated with PRRS, systemic PRRS and foetopathy associated with PRRS.

The contribution of these individual diagnoses to the overall PRRS data for 2008 in the first and second quarters of 2008 is shown in Figure 1. The difference in systemic PRRS diagnoses between Q1 and Q2 2008 is of statistical significance but no explanation for this was offered.


Figure 1. Diagnoses of PRRS in Q1 and Q2 of 2008

Respiratory Diseases

The quarterly percentage of relevant diagnostic submissions with a diagnosis of pneumonia and/or pleurisy showed a non-significant increase on the same quarter of last year. This increase is in part due to the inclusion, for the first time, of diagnoses of pneumonia due to PRRSV and PCV2 in the data.

Compared with the same quarter for 2007 there were falls in the quarterly percentage of relevant diagnostic submissions with a diagnosis of pasteurellosis and pneumonia due to Actinobacillus pleuropneumoniae but increases, none of which were statistically significant, in diagnoses of swine influenza, PRRS and enzootic pneumonia (Mycoplasma hyopneumoniae). This quarter diagnoses for enzootic pneumonia are the highest for any quarter since recording began in 1999. The cause of the increase in M. hyopneumoniae diagnoses in Q2 2008 is unknown however the use of vaccines against PRRS and PCV2 may have focused producers’ attention on Mycoplasma hyopneumoniae as another cause of pneumonia and may have resulted in increased testing of suspected cases.

Swine influenza
Four samples were positive from 64 samples from 35 submissions. All four isolates of swine influenza virus were H1N1 poultry-like viruses. The number of samples tested is similar to previous years.

Mycoplasmas
96 samples from 48 cases were submitted to the Weybridge Mycoplasma section. M. hyopneumoniae was identified on 12 occasions, once mixed with M. hyorhinis. All M. hyopneumoniae isolates were from lung samples. Additionally, M. hyorhinis was detected on 14 occasions from lungs. On two occasions, M.hyorhinis was identified as a mixed infection with M. hyosynoviae, once from a joint sample and once from a lung sample.

M. hyosynoviae was identified in four joint samples. M. arginini was identified twice from lung samples. M. flocculare is rarely detected but was identified twice (both from lung samples) once mixed with M. Hyopneumoniae.

Reproductive Diseases

There were 18 submissions for the diagnosis of abortion, most of which were in April, and 13 for other reproductive diseases, most of which were in April and May. Most of these submissions resulted in no diagnosis.

In one herd, PRRS virus was detected by PCR from sow blood samples, even though the herd had been vaccinated with live PRRS vaccine. Clinical signs included malaise, abortions and foetal mummifications.

In another herd, Actinobacillus ureae was an unusual isolate from an aborted foetus. The aetiological significance of this isolate is unclear.

Enteric Diseases

Swine Dysentery (Brachyspira hyodysenteriae)
In the second quarter of 2008, swine dysentery, caused by Brachyspira hyodysenteriae was the most commonly diagnosed enteric disease of pigs from diagnosable submissions.

Swine dysentery accounted for 41% of all enteric disease diagnosed in pigs in this quarter, and if disease due to the closely related B. pilosicoli (porcine intestinal spirochaetosis is included, these two pathogens account for 75% of all diagnoses of enteric disease recorded in pigs during this quarter (excluding salmonellosis). These figures may slightly over-estimate the significance of brachyspira as it is possible that more multifactorial diseases involving this agent are still to be identified. It is probable however that the impact of brachyspira is significant.

Recent trends (between Q2 2006 and Q4 2007) have been towards an increased incidence of swine dysentery (as a proportion of diagnosable submissions), as demonstrated in Figure 8 (purple line). The drop in diagnosable submissions in Q1 2008 may or may not be a continued but should not be overinterpreted as it is statistically insignificant. It is interesting to note the recent (Q3 2007-Q1 2008) increase in submissions tested (blue bars) which may reflect increased suspicion of disease among clients submitting samples.

Porcine Intestinal Spirochaetosis (PIS; B. pilosicoli)
This quarter saw an increase in percentage of diagnosable submissions diagnosed with nonhyodysenteriae colitis. Numbers are small so any increases do not approach statistical significance (see Figure 9).

Colitis due to B. pilosicoli is documented to be only mildly pathogenic in most cases so it is essential that co-incident pathogens (ETEC, EPEC, Salmonella, ileitis, B. hyodysenteriae, PCVD) are looked for. This is borne out by the fact that in all carcases testing positive for PIS this quarter, other pathogens or management factors, including PCVD, M. hyopneumoniae, PRRSv or a recent change of diet, were also identified. Diagnosis must be made using a combination of gross findings, FAT, PCR and phenotypic biochemical characteristics of bacterial isolates from enrichment cultures.

Increasingly, the FAT test cannot be considered specific for B. hyodysenteriae, indeed 66% of B. pilosicoli isolates this quarter subjected to FAT testing, were positive.

Neonatal Enteric Disease (Rotavirus, Clostridium perfringens type A enteritis, coccidiosis)
The trend in recent years has been for an overall decline in the incidence of enteric colibacillosis (affecting both sucking and post-weaned pigs), however a seasonal effect is recognised (most cases in winter).

Neonatal enteritis in which E. coli was involved was seen on four occasions this quarter, with isolates typically being K88 positive. E. coli O9 K103, a serotype associated with enteric disease, was found in 3-week-old suckling pigs.

Evidence of rotavirus in the form of PAGE-positive faeces were seen on two occasions.

Histological evidence of (historical) rotavirus-associated villus atrophy was seen frequently. An investigation was performed into scour in 10-15 day-old pigs whose mortality was reported to be 8-10%. Coccidial oocyst counts of 1600 O.P.G. were recorded and identified as Isospora suis. No histological evidence of Isospora-associated intestinal damage was found, but lesions can be localised. However, severe villus atrophy was seen in areas of the intestine, as well as histological evidence of type A Cl. perfringens enteritis and rotavirus. These findings suggest that the acute gut damage may have occurred some time prior to piglet submission, which is often the case.

The importance of preventing villus atrophy in suckling and post weaned pigs cannot be overstated, in terms of improving average daily weight gain, feed conversion efficiency in later life and preventing super-infection with co-pathogens in the acute phase of disease. In all cases the importance of farrowing house hygiene to combat the often multifactorial problems should be emphasised.

Helminthiasis
A single submission from a 21-week-old gilt revealed a moderate ascarid burden of 3900 eggs. Few samples for parasitic examination are received because there is no evidence of porcine anthelmintic resistance and treatment is routine and widespread.

The BPHS abattoir monitoring scheme continues to reveal higher than expected levels of white spot liver in slaughter pigs, especially from outdoor units.

Porcine Proliferative Enteritis (PPE; Lawsonia intracellularis)
No diagnoses of PPE were made this quarter.

Nervous Diseases

No nervous diseases of note besides an outbreak of encephalomyelitis (reported below).

PCV2-Associated Disease

In the first quarter of 2008, there was a significant drop in the percentage of relevant diagnostic submissions with a diagnosis of post-weaning multisystemic wasting syndrome (PMWS) (recorded at 3.8%). This was the first time a fall with statistical significance had been recorded when compared with the previous year since the first records in 2000.

For this quarter (Q2, 2008) the fall has not been repeated and diagnoses of PMWS remaining stable (recorded at 7.3%) compared with the same quarter in 2007 (see Figure 2).


Figure 2. Percentage of submissions diagnosed with PMWS. Q2 2008 compared with the same quarter in other years.

There was a non-significant decrease in cases of porcine dermatitis and nephropathy syndrome (PDNS) this quarter compared with the same quarter for the last 4 years (see Figure 3).


Figure 3. Percentage of submissions diagnosed with PDNS. Q2 2008 compared with the same quarter in other years.

In addition to the already authorised inactivated PCV2 vaccine for use in sows, an inactivated PCV2 vaccine for use in piglets from the age of two weeks is now available in the UK for use under licence. The sow vaccine provides passive immunisation of piglets via colostrum with a duration of immunity of up to 5 weeks. The piglet vaccine provides active immunisation of piglets for at least 17 weeks.

During this quarter the British Pig Executive (B-Pex Ltd) launched a PCV2 vaccine voucher scheme which is available to all English pig producers.

This initiative is part of a research project to measure the effects of PCV2 vaccination on pig health.

Unusual and New Diseases

Five-Day Investigation

This involved a case of infectious encephalomyelitis in weaned pigs, which is the subject of a separate report on ThePigSite and you can link to it by clicking here.

Combined Diagnosis Analysis

Porcine Circovirus-Associated Disease and Analysis of Combined Diagnoses

Since 2007, trends in combined diagnoses in pigs have been examined. This analysis is designed to focus on selected endemic viral diseases, such as PRRS and PCV2, which are known to predispose significantly to infection with other pathogens.

This additional analysis is employed as a tool to establish a background pattern against which changes suggesting alterations in pathogenicity or the early detection of new syndromes could be detected.

Since the recognition of PMWS in the UK in 1999, there have been alterations in the presentation of PCV2-associated disease. The original designation of PMWS referring to disease characterised by wasting and pallor often with secondary respiratory and enteric symptoms typically affecting pigs from six to eight weeks of age has changed to a later onset PCV2-associated disease.

A variety of other disease patterns such as severe bronchointerstitial pneumonia, fulminating hepatitis and neurological disease do still occur. The cause of these variations remains unclear however attention to variations in coexisting diagnoses may help to provide some clues to future changes.

Although there was a temporary reduction in diagnoses of PMWS in the first quarter figures of this year, the figures for the second quarter suggest that the impact of vaccination on the incidence of PCV2-associated disease has so far not been significant enough to be detected by our surveillance techniques.

Data for Q1 and Q2 2008 indicates that 65% of PMWS cases had additional diagnoses and in cases of PCV2 associated pneumonia 79% of cases had additional diagnoses.

Figure 4 shows the results of analysis of cases where in addition to a diagnosis of PMWS or PCV2 associated pneumonia, additional factors were also identified as contributing to disease.


Figure 4. Combination diagnosis

The data is for England and Wales from January 2007 to June 2008. All cases with a 'combined' diagnosis are included, i.e. cases with PMWS or PCV2-associated pneumonia and an additional diagnosis. The data is broken down based on the 'additional' diagnosis.

The pie chart shows information combined for PMWS and PCV-2 associated pneumonia. From the pie chart it is possible to see that the main disease causing death in pigs in combination with either PMWS and or pneumonia due to PCV2 was Pasteurella multocida followed very closely by systemic PRRS and Streptococcus suis.

Scanning Surveillance for New and Emerging Diseases

The overall percentage of pig diagnostic submissions for the first 6 months of 2008 (to second quarter, Q2) where a diagnosis was not reached (DNR) was 16.49% (31/188). This was not significantly increased from pooled data to Q2 of prior years for which DNR was 17.45%.

The DNR rate for the second quarter of 2008 was not significantly increased from the previous quarter (Q1, 2008) DNR, or from the DNR for equivalent quarters (Q2) in prior years.

In the first six months of 2008, there was no significant increase in undiagnosed disease for any individual syndrome or presenting sign compared with the same period in prior years.

Reproductive Syndrome

Analysing individual syndromes further, there was a significant increase in DNR for reproductive syndrome for non-carcase submissions from breeding pigs, with 88% (15/17) being undiagnosed in Q2 2008 compared to 59% to Q2 of prior years.

There was no significant increase in DNR for presenting signs of either 'abortion' or 'reproductive' disease. There is no evidence from these undiagnosed submissions of a new and emerging disease with a common presentation.

There continues to be a high DNR for reproductive syndrome compared to others for reasons which have been outlined by Bidewell and others (Pig Journal, volume 56, 88-106). The poor diagnostic rate for submissions of foetuses/stillborn piglets in part reflects the fact that laboratory investigations are geared to diagnosing infectious disease.

In pigs, non-infectious disease and management problems are prominent amongst the causes of reproductive disease and can only be adequately assessed by on-farm investigations supplemented with laboratory submissions to rule out infectious disease.

In addition, even where reproductive disease has an infectious cause, diagnosis of some of these remains problematic. Diagnoses are unlikely to be made from submissions of maternal bloods or tissues, however these may be the only material available; aborted and stillborn piglets may be scavenged, especially on outdoor units, or sow infertility may be the main problem without foetopathy.

Further Reading

- You can view the full report by clicking here.

Further Reading

- Find out more information on PMWS by clicking here.

Further Reading

- Find out more information on PRRS by clicking here.


October 2008