Veterinary Investigation Diagnosis Analysis (VIDA)

Introduction

Source of data

The Veterinary Investigation Diagnosis Analysis database, VIDA, contains a record of every diagnostic submission from livestock to wildlife in Great Britain made to the Veterinary Investigation Centres of the Animal and Plant Health Agency (APHA) and to Scotland's Rural College (SRUC) Veterinary Services (SRUC VS) and has been operating since 1975.

More information about the APHA's Veterinary Investigation Centres and laboratories and out partner postmortem examination (PME) providers that make up the diagnostic network in England and Wales can be found here: http://apha.defra.gov.uk/vet-gateway/surveillance/diagnostic/national-network.htm

Information about veterinary surveillance and diagnostic services offered by SRUC VS in Scotland is available here: https://www.sruc.ac.uk/info/120144/farm_animal_diagnostics

APHA produce an annual VIDA report that comprises both summary data by month for VIDA diagnoses recorded during the previous year and annual totals for the previous eight years:

In addition, further analysis and comments are provided for three diseases, selected by the representative Species Expert Group:

Past annual VIDA Reports are available on GOV.UK.

As well as the production of this report, VIDA is used for a wide range of ad-hoc investigations, and for the GB disease surveillance dashboards for cattle, chickens, sheep and pigs that were launched during 2017 and 2018: https://public.tableau.com/profile/siu.apha#!/

Livestock and wildlife disease-related threats identified are reported in the Quarterly GB Emerging Threats Reports for each species. More details on each threat, or potential threat, are included in these Quarterly reports which are produced by the APHA Species Expert Groups and include any actions taken to address identified threats. The reports can be found online: http://apha.defra.gov.uk/vet-gateway/surveillance/reports.htm

Bias in VIDA

Submissions recorded on VIDA represent only the clinical material submitted for veterinary investigation to APHA Veterinary Investigation Centres, the non-APHA partner PME providers and SRUC VS’s Disease Surveillance Centres; hence this represents a source of bias.

This clinical material includes samples of different types (e.g. blood samples, faeces, tissues) and carcases for post-mortem examination. This bias is influenced by many factors, for example:

  • the clinical presentation of a suspected disease
  • the level of awareness of a disease and its perceived importance
  • the value of the animal/s affected and
  • the general economic climate.

Particular diagnoses may also be affected by a range of factors, such as improved scientific test methods, and knowledge of these may also affect rates of submission. These factors will also usually vary differentially with time. This bias should be considered when interpreting both individual figures, and apparent trends, from VIDA data.

VIDA diagnosis totals are intended to represent only cases of clinical disease. For APHA submissions there is no diagnosis code assigned in VIDA if the submission is not diagnostic. However, SRUC VS assign some submissions a diagnosis code meaning “DIAGNOSIS NOT APPLICABLE” (code 991) and “SCREENING – No clinical problem” (code 980).

When examining annual diagnosis figures for a particular disease, it is therefore advisable to relate them not just to the total diagnoses in that year and class, but also to exclude submissions where the diagnosis is 'not applicable' and those for “screening – no clinical problem” before comparing one year with another.