Establishment and maintenance of a longitudinal study of bovine spongiformencephalopathy (the ULiSES scheme)

This paper addresses the issues of tracing and compliance encountered in se tting up and maintaining a UK-wide 5-year observational study of beef cattl e. The 5-year prospective study was initiated in 1997 to investigate the oc currence of bovine spongiform encephalopathy (BSE) in a single herd of pedi gree Aberdeen Angus cattle, in which BSE had been detected at low prevalenc e. The study was given the acronym ULiSES (University of Liverpool Spongifo rm Encephalopathy Scheme). All cattle present on the farm at the start of t he scheme were registered as members of the study population (n = 320), as were all calves subsequently born on the farm (n = 350). Animals that were sold (n = 291) were traced and monitored at destination farms. Farmers were requested to give advance notification of slaughter of any ULiSES animal a nd an attempt was made to collect post-mortem samples of nervous tissue, pe ripheral lymphoid tissue and striated muscle from all animals in the scheme at the time of slaughter, death or euthanasia. Sections of medulla were ex amined (by standard histopathological techniques) for the presence of spong iform change. Remaining samples were stored at -70 degreesC for future inve stigation by alternative tests. At the halfway point of the scheme in Octob er 1999, 75.2% (506/673) of the study population was still alive; 42% (284) of the population was still alive on the study farm and 33% (222) was dist ributed on other farms throughout the UK. Complete set,, or specimen,, had been recovered from 77% (129/167) of dead animals. All brainstem sections w ere negative by histopathological examination. No suspect cases of BSE were reported in ULiSES animals. Failure to recover specimens occurred principally in animals which had left the study farm. The main cause of specimen loss was a failure of complianc e in a small number of individuals who had them without purchased large num bers of ULiSES animals, and subsequently slaughtered them without contactin g the University. Despite this. farmer compliance was generally high. The U LiSES scheme shows the feasibility of a country-wide longitudinal observati onal study spanning a period of several years and indicates the large impac t of small numbers of non-compliant individuals. (C) 2001 Elsevier Science B.V. All rights reserved.