The accuracy of monitoring trends in disease incidence was improved by the provision of sample-based denominator data which allows for fluctuations in submission rates and to assess the reliability of the data.

For the third year running, summary disease reports were sent to veterinary practices to assist them with their herd and flock health planning.

Cattle

A total of 22 outbreaks of bovine botulism were recorded in 2003 (a full report appears under Food and Environmental Safety).

A strain of Salmonella Paratyphi B, variant Java (S.Java) multi-resistant to antimicrobials from two adjacent cattle premises was isolated at VLA Langford.

Despite the weather conditions being less favourable for the survival of the intermediate host, Lymnea truncatula, the incidence of chronic liver fluke infection in cattle did not decline markedly. This may have been as a result of a high level of infection carried over from last year or practitioners have become more familiar with the clinical signs of bovine fasciolosis and submitted more diagnostic material.

Blood samples from newborn calves with experimental persistent infection of Bovine Viral Diarrhoea (BVD) were subjected to several diagnostic tests and the only test able to detect the virus was an RT-PCR.

VLA is a partner in an EU Thematic Network on BVD control in Europe. Our role is to evaluate the current BVD genome information and to develop methods for the standardisation and validation of diagnostic tools and strategies to implement them in screening schemes.

Sheep

Tick-borne diseases were reported at several Regional Laboratories, with many areas anecdotally reporting the emergence of large numbers of ticks in the spring. Significant losses in some flocks were encountered in Cumbria, Wales and Devon. Losses were also recorded in Lancashire, where there had been a co-ordinated eradication campaign.

Several incidents of ryegrass staggers were recorded at diverse geographical locations including one case where ten animals from a flock of 400 ewes and lambs showed signs of tremor and convulsion when gathered for worming.

Nematodirus battus was a major problem during the year with over 100 cases reported from all around England and Wales.

The incidence of acute fasciolosis was less this year than in the last four years. This was due to the prolonged dry weather in the summer which had a detrimental effect on the transmission of infection and also the viability of the snail intermediate host. The incidence of Black disease, caused by Clostridia novyi and usually associated with migrating immature fluke, was also reduced. In contrast, chronic fasciolosis as a percentage of diagnosable submissions were slightly higher in 2003 than in 2002. This is consistent with the findings for cattle described above.

Outbreaks of Maedi-Visna presenting as primary neurological disease (Visna) were confirmed in two flocks. Visna has previously only been confirmed in three flocks in Britain but all had co-existent Maedi (respiratory disease).

Pigs

The surveillance of swine influenza virus isolates has not identified any significant change in circulating strains, however, there was an increase in the number of diagnoses of swine influenza compared to last year.

Post-weaning Multisystemic Wasting Syndrome (PMWS), associated with considerable economic loss, is still the most important endemic disease of pigs. The partial implementation of the Madec 20-point plan resulted in little clinical improvement, whereas the adoption of the full group of measures has helped on many units. The onset of disease at around 14 to 18 weeks of age was widely reported as were concurrent infections with other pathogens - such as Pasteurella multocida, Salmonella spp Haemophilus parasuis and Streptococcus suis.

Examination of Porcine Circovirus (PCV-2) strains and complete genome sequencing of viruses isolated from diseased and non-diseased farms, has strengthened the evidence that PCV-2 is necessary, but not sufficient for the development of the full range of clinical signs of PMWS.

Collaborations are important to the programme and include:

The Roslin Institute, Cambridge University, The Wellcome Trust Sanger Institute and Sygen International plc

• to examine the influence of pig genetics on Porcine Reproductive and Respiratory Syndrome (PRRS) and results have shown that the virus grows slower and titres are lower in different breeds of pigs, suggesting that certain breeds may be more resistant to infection.

The Royal Cornwall, The Royal Free and King’s College Hospitals and The HPA

• a project on hepatitis E viruses has revealed that the viruses acquired by humans in the UK are very closely related to those detected in UK pigs.

Avian

VLA Winchester described an outbreak of disease in a free-range layer flock where the birds livers showed white speckling throughout which was confirmed histologically as an acute multifocal hepatitis and vasculitis. The lesions were typical of ‘vibrionic hepatitis’, a disease of uncertain aetiology, which appears to be re-emerging in free-range poultry.

The incidence of Blackhead in turkeys increased this year compared to the number of cases reported for the last five years.
Both housed (with earth floors) and free range turkeys were reported to be affected, and in some cases contact with chickens was suggested as a possible source of Heterakis worms which may have carried the Histomonas parasite. Blackhead was also diagnosed in free-range layer chickens and in broiler breeders.

Cases of unexplained air sacculitis with neurological signs in rearing/fattening turkeys were reported from several areas of the country and appeared to arise in birds aged between 8 and 20 weeks. The clinical signs ranged from lethargy and dullness, sneezing, coughing, diarrhoea, loss of balance, ataxia, torticollis, and opisthotonos through to sudden death. Restriction Orders were served on two affected farms because of the similarity with Avian Influenza and Newcastle disease. The initial findings of extensive pathological and microbiological investigations suggested this may be an unusual manifestation of mycoplasmosis.

Exotic Species

A post mortem examination of a four year old alpaca suffering from progressive weight loss, showed that much of the lungs had been replaced with creamy coloured friable tissue and M.bovis was confirmed on culture. Both M.bovis and M.microti were diagnosed in Llamas. Fasciolosis was also diagnosed in alpacas and llamas during the year.

Malignant Catarrhal Fever was confirmed by histological examination in a water buffalo heifer and clinical signs included pyrexia, corneal opacity and nasal discharge. Although there were sheep on the farm, there was no apparent direct contact.

Wildlife

Since its inception on 2001 the WNV surveillance project has examined 990 birds from 87 different species using virus culture and PCR techniques. To date, no West Nile Virus infection has been detected.

Examinations at VLA Penrith, sponsored by the Cumbria Wildlife Trust, confirmed the first case of red squirrel parapox disease in north Cumbria. The virus, which is carried by the more common grey squirrel, poses a real threat to the red squirrel population in the area as they are more susceptible.

The cause of death of 30 swans in a flock of over 2000 Iceland Whooper swans on a wetland wildlife reserve in East Anglia was diagnosed as clostridial enteritis. Interestingly, an even larger number of Berwick swans on the same reserve appeared unaffected. There have been similar reports of deaths in swans elsewhere in the country.

Animal Welfare

VLA’s regional network continues to gather and assess welfare surveillance information alongside its endemic disease surveillance activities, across all farmed species. During the year, surveillance reports highlighted the variation in what individual livestock farmers considered to be an acceptable level of disease.

Several veterinary forensic examinations of carcases and laboratory specimens were carried out in support of welfare prosecutions taken out by either Defra or the RSPCA. VLA scientists supported these prosecutions by giving evidence in court hearings.

VLA provided the pathological and epidemiological analysis for a Defra funded trial involving over 1200 lambs to determine the optimal type and position of ear tags. The survey provided clear indications as to the best tag types and optimum methods of application.