Emerging Threats Quarterly Report Small Ruminant Diseases

Transcription

1 Emerging Threats Quarterly Report Small Ruminant Diseases Safeguarding public and animal health Quarterly Report 2010: Volume 14 No. 4 Date: February 2011 The VIDA diagnoses are recorded on the VLA FarmFile database and comply with agreed diagnostic criteria against which regular validations and audits are undertaken. The investigational expertise and comprehensive diagnostic laboratory facilities of both VLA and SAC are widely acknowledged, and unusual disease problems tend to be referred to either. However recognised conditions where there is either no diagnostic test, or a clinical diagnosis offers sufficient specificity to negate the need for laboratory investigation, are unlikely to be represented. The report may therefore be biased in favour of unusual incidents or those diseases that require laboratory investigation for confirmation. Contents page Introduction 2 New and emerging diseases 3 Ongoing emerging disease investigations 4 Unusual diagnoses 4 Changes in disease patterns and risk factors 5 Highlights Ulcerative leg lesions affecting sheep Chronic fasciolosis continues to cause problems in Scotland, although less disease reported in England and Wales Severe weather conditions in December impacts on submissions Disease in sheep associated with feeding bakery waste VLA RLs have UKAS Accreditation and comply with ISO standard. SAC Veterinary Services have UKAS accreditation at all their Disease Surveillance Centres which comply with ISO standard.

2 INTRODUCTION This report aims to identify emerging small ruminant disease related threats. It contains analysis of disease data for the last quarter of year 2010 and annualised data for the whole year compared to previous years. The report will qualify the description of any important disease events by stating whether this is based on quarterly or annualised data analysis. The production of the report is underpinned by a large amount of surveillance data and information compiled as part of the Defra Food and Farming Group animal disease surveillance programme. Some of these data can be viewed on the VLA website. Figure 1: GB sheep diagnostic submissions October - December 2006 to Sheep Diagnostic Submissions and Carcasses, Q4 of VLA Submissions SAC Submissions VLA Carcasses SAC Carcasses Figure 2: GB goat diagnostic submissions October - December 2006 to 2010 Goat Diagnostic Submissions and Carcasses, Q4 of VLA Submissions SAC Submissions VLA Carcasses SAC Carcasses 2

3 There was a 23% (1,262 vs 1,638) decrease in total sheep diagnostic submissions in GB and a reduction of 43.5% (443 vs 784) in sheep diagnostic carcase submissions compared with the equivalent quarter in 2009 (figure 1). Diagnostic goat submissions fell by 21% (126 vs 160) and diagnostic carcase submissions fell by 40% (27 vs 45) during the quarter (figure 2). The fall in submissions is likely to be due to the severe weather conditions experienced in late November and throughout December, which hampered transport particularly in Scotland. In England and Wales the change in prices, including charging for carcase disposal, is also likely to have affected submissions. The poor weather conditions in December also influenced the markets. This led to high prices as processors struggled to ensure a supply for the Christmas market, due to some producers being unable to reach markets. NEW AND EMERGING DISEASES Analysis of Diagnosis Not Reached (DNR)* SHEEP: There was no significant increase in overall %DNR for GB for the fourth quarter (15%) compared to equivalent previous quarters (14%). Neither was there any significant increase in overall %DNR for GB for the year 2010 (21%) compared to equivalent previous years (20%). GOATS: There was no significant increase in overall %DNR for GB for the period October to December or for the year 2010, but figures are low and limit statistical interpretation. Analysis of DNR by syndrome and presenting sign SHEEP: Table 1: Syndromes showing a significant increase in %DNR in sheep compared to equivalent previous period (October December and Jan December) GB Syndrome Oct Dec prior years (2008 and 2009) Oct Dec 2010 Jan Dec prior Jan Dec 2010 years (2008 and 2009) Enteric 6% (67/1062) 10% (36/348) 11% (580/5335) 12% (330/2662) October December 2010: There was a statistically significant increase in %DNR for syndrome enteric for October to December 2010 (table 1). As with the increase observed in July 2010 (see Vol 14 No 3), this is attributable to the decrease in submissions for this syndrome following the price increase in England and Wales: 245 submissions to VLA RLs between October and December 2010, compared to 355 and 378 submissions for the same quarter in 2008 and 2009 respectively. No increase in %DNR was seen in submissions to SAC disease surveillance centres. Further analysis identified that the increase in %DNR occurred in December when the severe weather conditions may have further reduced the numbers of submissions. No other factors for the increase in %DNR have been identified and there have been no reports of an increase in this syndrome from neighbouring countries. The DNR trend will be monitored, although a new and emerging disease is not suspected. Annual 2010: There was statistically significant increase in %DNR for syndrome enteric in 2010 compared to previous years (Table 1). As discussed, this is likely due to decreased submissions. No new and emerging disease is suspected. GOATS: There were no significant increases in %DNR in goats by presenting sign or syndrome for the period October to December, although there was a significant increase for the respiratory syndrome for the whole of

4 Respiratory disease: A statistically significant increase was observed in the %DNR for goat respiratory syndrome over the year (table 2). There has been an increase in submissions for this syndrome in 2010 compared to 2008 and 2009 (24 in 2010 compared to 14 in 2009 and 15 in 2008). The increase was mainly seen in VLA carcase submissions, with no particular region, age or seasonal pattern. Review of the individual submissions did not suggest a new or emerging disease. The number of submissions for goats is low and care must be taken not to over interpret increases in %DNR in light of this. Table 2: Syndromes showing a significant increase in %DNR in goats compared to equivalent previous period (Jan December) GB Syndrome Jan Dec prior years (2008 Jan Dec 2010 and 2009) Respiratory 1 / 29 (3%) 7 / 24 (29%) * - When a VIDA diagnostic code is assigned to a specific submission, the decision has to be made if it meets the stated diagnostic criteria. If the criteria are not met, it is marked as Diagnosis Not Reached or DNR. If it is a DNR, the next step is then to decide if this was due to limited testing or if reasonable testing had been done. If it is deemed that reasonable testing had been done, there may be reasons why a diagnosis could not be reached and this should be recorded and can include inappropriate disease phase, treatment, inconclusive results, or other reasons. Typical examples of such submissions include; coccidiosis cases where speciation was not done and Johne s cases in live sheep where the test results may be inconclusive. However, in some cases there is no apparent reason to explain why a diagnosis could not be reached and these are the submissions, if present in significant numbers, which may indicate new and emerging disease. Other emerging issues: Ulcerative skin disease of unknown cause affecting sheep: Three Regional Laboratories investigated four outbreaks of ulcerative skin disease in ewes affecting haired areas only, predominantly the lower leg. Although the clinical presentation is similar to Strawberry footrot, no definitive aetiological diagnosis has been reached in the outbreaks, with none of the common skin pathogens (orf virus, Dermatophilus congolensis and Staphylococcus aureus) being demonstrated despite relatively extensive laboratory examinations. In one outbreak, involving a 600 ewe flock, crusty raised lesions on the skin of the lower legs in shearling ewes were first noticed in autumn Since then many sheep throughout the flock have shown similar lesions. The current flare up of the problem started in the late summer 2010 and affected 40% of the shearlings. Typically a granulomatous lesion plus purulent material is noted beneath superficial scabs, these lesions being very sensitive to the touch, bleeding easily and causing significant lameness. Healing is very slow and takes many months. One shearling ewe that did not have leg lesions showed a similar lesion on the upper lip. Although the lesions may be relatively limited in some animals, deep bacterial infections do occur and these have a significant adverse affect on the animals welfare. Systemic antibiotic treatment may be needed to treat these deeper bacterial infections, even though they may not be the initiating cause of disease. Very variable success has been encountered using different topical treatments. Similar cases have been seen in other flocks in previous years and can present a significant diagnostic challenge. Cases presented as new by the farmer have been found to have chronic pathological changes on histological examination of skin biopsies, which makes identification of the initial aetiological agent difficult. Since the exact diagnosis is unclear, it is difficult to know if this is a new disease. Extensive flock examination, careful case selection and collection of good quality skin biopsies will be essential for further investigations into this sporadic, but as shown by the case description above, potentially serious, welfare problem. 4

5 Pneumonia associated with Staphylococcus aureus: A total of 16 Staphylococcus aureus pneumonia diagnoses were made between the beginning of 2008 and the end of 2010, compared to a total of 9 cases recorded between 1999 and the end of This increase was investigated, to determine if a primary infection, and potentially new bacterial strain, was emerging. These were a single recorded diagnosis in the flocks involved, with group submissions showing only individual animals with the infection. Examination of the individual cases revealed the majority were diagnosed in preweaned lambs, aged three months or less. Concurrent disease was diagnosed in the majority of cases and the evidence suggests an underlying immunosuppression due to varying causes was likely in the affected sheep. Suggested potential predisposing or causal factors were: inhalational pneumonia; navel infection; ear tagging; waning maternal antibodies; concurrent lung infections; parasitic gastroenteritis; tick pyaemia; dental disease and endocarditis. There was no evidence of a group problem associated with the diagnosed cases and at this stage there is no evidence to indicate the emergence of a new strain of S. aureus. ONGOING EMERGING DISEASE INVESTIGATIONS Nephropathy in Zwartbles Sheep: Following necropsy of a series of Zwartbles sheep with consistent unusual renal gross pathology, a possible link between this breed and renal disease was suspected. Analysis of VIDA data between 2002 and 2009 showed that the incidence of diagnosis of renal disease was higher in the Zwartbles breed (13 of 175 submissions - 7.2%) than in all other breeds combined (800 of submissions %). Further analysis of these data revealed that in 7 of the 13 cases of urinary disease involving the Zwartbles breed, the gross appearance and histopathology was similar. Fixed tissues from seven submissions were reviewed where available; very large numbers of oxalate crystals in the renal tubules of affected animals were seen histologically. As far as possible, historical information from suspect cases was traced and in most cases there was no history of access to oxalate-containing plants (e.g. sugar beet tops, rhubarb) or substances (e.g. tea, ethylene glycol). Given the association with the breed, a diagnosis of hereditary primary hyperoxaluria (PH) is suspected. The condition is recognised in humans and has been documented in cats, beefmaster cattle and Tibetan spaniels. Definitive confirmation of the condition can be achieved by urinalysis for a combination of specific metabolites. The findings are relevant to the Zwartbles breed society, which has been appraised of these findings. Q fever in goats: A VLA investigation continued into an abortion outbreak in a commercial dairy goat herd in May 2010 where Q fever was confirmed (funded by FFG project OZ0152). The investigation looked at seroconversion of the goats on the unit; collect samples for test validation of ELISA on individual and bulk milks and for evaluation of the PCR test on samples from individual animals and the environment. The third and final herd sampling has now been completed and the data will be analysed and a final report issued at the end of the financial year. Q fever survey of placental material: The Q fever PCR survey on routine abortion material collected from submissions to VLA RLs, where Q fever was not suspected, has to date tested 192 ovine placental samples, with no positive results. This suggests the zoonotic risk of Coxiella burnetii infection to people working with lambing ewes is low in England and Wales. Testing of placental samples from other species is in progress. UNUSUAL DIAGNOSES Deaths in ewes fed bakery waste: Concerns were raised about deaths in ewes fed on bakery waste, variously described as icing/fudge type mixture, or as mince pie mix. Several 5

6 unexplained deaths occurred in groups of sheep being fed this material on one farm in Lancashire. Although hay was available as forage, there was snow on the ground, limiting grass intake and perhaps leading to intake of greater quantities of bakery waste than might otherwise have been the case. It is likely that the high fat and sugar content in the material would have disrupted the function of rumen microflora. There were no further deaths after the feeding rate of the material was reduced. The VLA Small Ruminants Expert Group and the Sheep Veterinary Society Discussion Group were consulted to see whether feeding of bakery waste to sheep was a common management practice, or possibly increasing because of concerns about the price of concentrate feeding. It seems that the practice is not widespread, and thus not a risk to the industry. Further cases are not expected. Pituitary abscessation in sheep: Two incidents of pituitary abscessation on separate units were reported in the quarter. These involved an adult ewe showing nervous signs and an adult tup which was lethargic. Arcanobacterium pyogenes was isolated from the abscesses and infection was thought to have derived from a tooth abscess and skin abscess respectively. Pituitary abscesses are uncommon in sheep and have been reported more frequently in cattle. These are likely to reflect sporadic incidents, but the situation will be monitored. Iatrogenic skin abscesses: The potential to cause significant harm to a large number of animals by poor injection hygiene was highlighted in one incident. Following vaccination of a group of 300 lambs in one flock, almost all developed abscesses in the neck region, which in some, spread to beneath the ribs and abdomen. Many of the lambs with the extensive abscessation died (30). The attending veterinarian surgically lanced the swellings in approximately 100 lambs. Cultures of what remained in the two vaccine bottles were sterile, suggesting the needles were the source of bacterial contamination. Wet weather was a potential contributory factor. Farmer knowledge of good injection technique and continued improvements in drug delivery systems are key areas for avoiding this type of incident. CHANGES IN DISEASE PATTERNS AND RISK FACTORS Cl. Perfringens type D infection (pulpy kidney disease): There was a significant annual increase in Cl. Perfringens type D infection in EW, but not in Scotland (figure 3). The increase is likely to reflect normal variation. Outbreaks with significant losses can occur in flocks that have not been fully vaccinated, usually at times of change in management or nutrition. Control is by vaccination and should be part of a farm health plan. Figure 3: Annual incidents of Cl. Perfringens type D infection, as a percentage of diagnosable submissions (Vertical bars represent 95% confidence limits) 6

7 Cryptosporidiosis: There was a significant increase in annual incidents (as a percentage of diagnosable submissions) of cryptosporidiosis infection in England and Wales, but not in Scotland (Figure 4). A similar annual increase was seen for cattle (data not shown). Cryptosporidium is one of the infectious causes of neonatal diarrhoea in many different farm animals and also an important zoonosis. The exact reasons for the increase remain unclear, but could be linked to the effect of the adverse weather. The analysis of submissions for the second quarter indicates increases in lowland sheep and in western England. This increase will be monitored, although yearly variation is seen (figure 4) Figure 4: Annual VIDA incidents of cryptosporidiosis, as a percentage of diagnosable submissions (Vertical bars represent 95% confidence limits) Acute and chronic fasciolosis (liver fluke): There was a significant fall in the number of incidents (as a percentage of diagnosable submissions) of acute fasciolosis in the final quarter of 2010 compared to 2009 (figure 5). The lower than average rainfall experienced in 2010, which was only 84% of the thirty-year average between 1971 and 2000, will have contributed to this fall. Figure 5: VIDA incidents of acute fasciolosis, as a percentage of diagnosable submissions October December (Vertical bars represent 95% confidence limits) There was also a significant fall in the number of incidents (as a percentage of diagnosable submissions) of chronic fasciolosis in England and Wales in the final quarter of 2010 compared with the equivalent period in This contrasted with a rise in Scotland (figure 6). This is an unusual finding as the rainfall in Scotland was 69% of the average from The reason for this rise is therefore not immediately apparent, but may reflect the build up in pasture metacercariae infection that occurred over the previous three years, where the spring and summer weather was much wetter. 7

8 Farmers may have heeded fluke forecasts of a moderate risk of infection for the last quarter and treated their sheep. Also, the drier weather conditions in 2010 will have inhibited the parasite s life cycle with less infective metacercariae on the pasture by this quarter. Added to the very cold weather in December, which is likely to have affected the survival of infective metacercariae, the impact could be less fasciolosis in However, treatment should be maintained as a very wet year in 2011 will allow the parasite to recover. Figure 6: VIDA incidents of chronic fasciolosis, as a percentage of diagnosable submissions, October December (Vertical bars represent 95% confidence limits) Nematodirosis: There were significantly more incidents of parasitic gastroenteritis due to Nematodirus battus in 2010 in England and Wales than in 2009 (201 vs 100). Closer examination of the data has shown that this was due to an increased number of diagnoses in April when compared to the previous six years (figure 7). Seventy-three percent of these incidents were in Wales, the south west and the west midlands of England. There was also a smaller rise in incidents in Scotland. The infective stage of this parasite hatches from eggs when climatic conditions are correct (e.g. temperatures between o C) and disease typically coincides with susceptible lambs grazing infected pastures in spring. The early appearance of the diagnoses in 2010 is likely to be due to the climatic conditions leading to a more prolonged period of hatching. If repeated in subsequent years it will make treatment for this parasite more difficult with repeated anthelmintic treatment necessary. VLA is collaborating with researchers at Bristol and Liverpool universities to validate a model that could be used to predict a regional risk of this disease. Figure 7: VIDA incidents of nematodirosis in England and Wales by month Number of incidents of PGE nematodirosis diagnosed by VLA in England and Wales jan feb mar april may june july aug sept oct nov dec 8

9 Coccidiosis: There were significantly more incidents recorded in 2010 in England and Wales, as a percentage of diagnosable submissions, than in the previous year. This was not the case in Scotland, where incidents dropped. The reason for this is not clear. Management factors such as high price of straw for bedding, poorer hygiene and adverse weather condition could be involved, but these are also likely to have adversely affected Scotland. The situation will be monitored. Maedi visna: An increase was reported in the previous report, for the third quarter. The annual figures show an increase from three incidents for 2009 to nine in 2010 for GB. This trend will be monitored as this is a disease that can have an impact on the health and welfare of the national flock. This was discussed in the previous report (Vol 14 No 3). Pneumonia due to Bibersteinia trehalosi: The numbers of incidents of pneumonia associated with Mannheimia species recorded annually decreased in 2008 and 2009 when compared to 2007 and the years preceding 2007, but in 2010 the number of incidents was again equivalent to Overall the number of incidents of sheep respiratory disease and pneumonia had also reduced during 2008 and The number of incidents diagnosed annually with Bibersteinia trehalosi pneumonia between when compared to years prior to 2008 however has increased. The B.trehalosi pneumonia diagnoses despite the increase still remain at only 14% of the numbers of sheep diagnosed with Mannheimia species pneumonia. The likelihood of pneumonic disease due to B.trehalosi appeared to increase with age; adult sheep appeared more likely to have true pneumonic lesions. In post and preweaned lambs the significance of the B.trehalosi lung infection was often less clear and potentially confused by mixed concurrent diseases. The cause for an increase in B.trehalosi pneumonia cases is uncertain so numbers will continue to be monitored. Cerebro-cortical necrosis (CCN): There was a significant increase in incidents of cerebrocortical necrosis (CCN) this quarter with 13 recorded incidents compared to six in Although diagnoses by SAC remained relatively static, there was a notable increase in incidents diagnosed by the VLA (9 in 2010 vs 3 in 2009). Potential causes of CCN include thiamine deficiency (usually a result of recent dietary changes), sulphur toxicity, salt poisoning (water deprivation) and lead toxicity. Where appropriate the possibility of lead poisoning has been excluded. This increase in cases could therefore be a reflection of a change in diet due to increased supplementation with concentrates and water deprivation from frozen water troughs, both a result of the severe weather conditions seen during the end of this quarter. Interestingly, cases were reported mainly from eastern and northern England; the areas hardest hit by the wintery weather in England. The situation continues to be monitored. Pregnancy toxaemia: Given the severe winter conditions and early snow in November increased problems with pregnancy toxaemia and possibly poor lamb crops in late lambing ewes in the coming lambing season might be expected. However, this is not necessarily the case, as there was no observed increase in pregnancy toxaemia in the 2010 season according to VIDA data, despite similar harsh conditions through the winter of ; suggesting farmers were offering adequate supplementary feed to compensate for the increased nutritional needs of pregnant ewes during the cold weather. SAC has again offered subsidised testing of ewes to assess adequacy of nutrition. 9