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June 21, 1994 Commission Decision 94/382 on the approval of alternative
heat treatment systems for processmg animal waste
June 30, 1994 Results of further BSE experiment announced Extension
of SBO ban Implemented vohmtanly by mdustry
July 27, 1994 Commisston Dectston 94/474 introduced new certificatton
reqmrements for bone-m beef exported to other
Member States of EC
November 2, 1994 Bovme Offal (Prohibitton) (Amendment) Regulations 1994
came mto force, extending ban on use of SBO m human
food The Spongiform Encephalopathy (Mtscellaneous
Amendments) Order 1994 came mto force, extending the
ban on use of SBOs m animal feed, banning the use of
mammahan protem m rummant feedingstuffs, and makmg
nottfiable laboratory suspicion of spongiform encepha-
lopathies m species other than cattle, sheep, and goats
December 1994 GB progress report placed m the Library of the
House of Commons
December 14, 1994 Commisston Decision 94/474 amended by Decision
941794 Beef from cattle born after January 1, 1992
excluded from certtfication requtrement
February 1995 SEAC report “Transnussible Spongtfonn Encephalopathies
a summary of present knowledge and research” pubhshed
182 Tyrrell and Taylor

being introduced and semen and embryos from UK stock were traded mterna-
tlonally. Endemic bovme diseases, such as tuberculosis and brucellosls, were
controlled, and imported infecttons, such as foot and mouth disease, were
promptly eradicated. Infections, such as salmonellosls and hstenosis, had sen-
sitized the public to the dangers of contammated poultry and dairy products.
The rendering Industry, which exlsted to dispose of animal waste from the
slaughtering and knackering industries, refined its production methods to
improve the value of its products (fat, and meat and bonemeal) and the use of
organic solvents to recover additional fat was discontinued m most plants. At
the same time, concern about salmonellosls led to the mtroductlon of leglsla-
tlon requiring the end products to be salmonella-free. Changed condltlons
Implied changed risks, and “new” mfectlons, for example, swine vesicular dls-
ease, had turned up from time to time It was an accepted philosophy that the
best way of detectmg and understanding both “old” and “new” epidemics was
to maintain a network of highly competent chmcal and laboratory veterinary
experts, m good relationship with the veterinary profession m practice, who
could identify and study promptly anything unusual that turned up.
Thus it was that among the 11 million cattle m Great Britain cases of unusual
neurological disease were identified m 1986 and the brains of two cattle exam-
ined at the Central Veterinary Laboratory (CVL) Weybrldge in November of
that year were recognized as showing the characteristic changes of a spon-
glform encephalopathy. Although common m sheep, such a condition had
never been seen m cattle before and it was quite unclear what the cause was,
and whether the findings were simply an isolated curiosity or signified the start
of a major epidemic. As a first step it was important to collect mformatlon
about the new condition to enable epldemiologlcal studies to be carried out and
to facilitate further pathological studies, and to attempt experimental transmls-
slon to cattle and to mice. Voluntary reporting of suspect cases to Veterinary
Investigation Centres was encouraged, and further cases were reported m all
parts of Great Bntam. In April 1987 an epidemlologlcal study to identify the
risk factors was initiated and when completed early m 1988 the study (of some
200 affected cattle) showed that although some possible risk factors, such as
contact with sheep or admmlstratlon of vaccines or medlcmal treatments, were
not important, a history of ruminant-derived protein having been fed was. It
was concluded that the new disease, by now called Bovine Sponglform
Encephalopathy (BSE) by the scientific commumty, and “Mad Cow Disease”
by the media, was a common source epidemic caused by the inclusion in cattle
feed of ruminant-derived protein (m the form of meat and bonemeal) contam-
mg a scraple-like infectious agent
In April 1988 the Government decided it was necessary to have an external
review of the state of knowledge and the Mmlster of Agriculture and Secretary
Handling the BSE Epidemic In the UK 183
of State for Health Jomtly appointed a small working party of scientific experts
under the chairmanship of Sir Richard Southwood to consider the situation and
report on it. As background to their discussions the committee could draw on
the findings of years of research on scrapie, which had been studied at Compton
and Edinburgh and in the United States so that the peculiar properties of the
causative agent, the slow way it spread wlthm the organs of infected animals,
the importance of genetics, and the route of transmission m determining sus-
ceptlblllty were all known and published. However, scraple was not considered
to be a subject of great importance in 1988, and research was running down.
The decision to introduce statutory control measures for BSE in Great Brit-
am was taken m May 1988, before the Southwood committee had even met,
and the first controls were Imposed on June 21 of that year when the disease
was made notifiable. The objectives were:
1. To discover the true incidence of the disease (it was recognized that under the
voluntary reporting system m use until then many suspect cases would escape
notlce);
2. To facilitate the collection of clinical and epldemlologlcal mformatton from all
cases, rather than only a proportion, and so test on a wider database the eplde-
miological hypothesis on which the control pohcy was based, and
3 To prevent cattle that were not already infected becommg Infected, and so to
eventually eradicate BSE.
The statutory obligation to nottfy suspectcasesof BSE underpins other con-
trol measures. Following notlficatlon, the suspect animal IS examined by a vet-
erinary officer of the Mmlstry of Agriculture, Flshenes, and Food If BSE IS
suspected on the basis of the clinical signs observed, a restriction notice IS
served to prevent the suspect animal being removed from the premises, and to
require isolation if about to calve. The notice applies only to the mdivldual
suspect animal: BSE IS not beheved to be a contagious disease, so there is no
justification for restricting the movement of other animals in the herd. From
June 21 until August 7, 1988 it was permissible to move a restricted animal,
under license, to a slaughterhouse. After slaughter, for human consumption or
otherwise, the head was removed and taken-again under license-to a labo-
ratory so that the bram could be removed, fixed, and subjected to a hlsto-
pathological examination to confirm the clinical diagnosis. Since August 7,
1988, as a result of an interim recommendation from Sir Richard Southwood,
the carcassesof all suspect cattle have been destroyed after the animal has been
compulsorily slaughtered, m order to protect public health against any risk that
BSE may pose. Compensation is paid to owners.
The key measure taken to prevent further infection of cattle is a prohlbitlon
on feeding ruminant protein (the definition of which excludes milk and milk
products, and dlcalcmm bone phosphate) to ruminant animals. This was first
184 Tyrrell and Taylor
implemented on July 18, 1988, 1 mo after the disease had been made notifi-
able: The delay was intended to allow feed that had been manufactured already
and that contained ruminant protein to be used up. If rtgorously observed the
ruminant feed ban prevents scrapie-like agents being transmitted m feed from
one ruminant species to another and, probably more important, prevents recy-
cling of infection wtthm the same species. If there is no other significant route
of transmission this measure alone will eradicate BSE
A theoretical alternative approach, which was considered and reJected,
would have been to destroy any mfectivtty m meat and bone meal by heat
treatment This was not possible because the combmations of time and tem-
perature needed to destroy the BSE and scrapte agents had not been deter-
mined, and without such mformatton tt was impossible to know which, tf any,
commercial rendering processes could continue to be used. In 1994 the pre-
liminary results of a collaborative study on the effect of different rendering
protocols on BSE mfectivity showed that at least two systems used m Great
Britain were ineffective, but the limited sensitivity of the study means that it IS
still impossible to identify “safe” systems and the rummant protein feed ban
remains the only practical method of preventing infection through feed. The
banning of processes that are known to be ineffective is, however, a useful
additional measure to strengthen the effecttveness of the feed ban.
The posstbihty that BSE would be transmitted via the placenta of the partu-
rient female, as is scrapie in sheep, was also recognized To counter this, legis-
lation required that a suspect must be isolated m approved accommodation
while calving, and for 72 h afterward, and that the placenta, discharges, and
bedding must be burned or buried and the isolatton premises cleaned and dtsm-
fected after use The purpose of this measure is not to prevent mfection of the
calf, which would be Impractical, but to reduce the opportunity for horizontal
spread of mfection to other cattle m the herd.

3. Monitoring the Epidemic
It was realized that it would be important to monitor the progress of the
epidemic, and that clinical diagnosis without any supportmg laboratory evt-
dence would be problematic, at least until farmers and veterinary surgeons
became more familiar with a disease that few had seen at that time. Videos
showing clinical cases therefore were prepared and widely distributed, and
diagnostic capacity was increased by trammg Investtgatton Centre staff m the
techmques developed at the Central Veterinary Laboratory (CVL). The results
of the laboratory mvestigations were sent to the State Veterinary Service head-
quarters, where veterinary staff assessed the mformatton and confirmed those
cases for which there was appropriate evidence. The field data from all these
cases were sent to the CVL eptdemiology department, which had to be greatly
Handling the BSE Epidemic m the UK 185
Table 2
BSE Statistics as of December 31,l 9948
Cases Number Number Percent
Year reported slaughtered confirmed confirmed
1988 2516 2376 2184 91 9
I989 8447 8061 7137 88 5
85 2
1990 17,323 16,641 14,181
1991 30,009 29,025 25,032 86 2
1992 44,846 43,154 36,680 85 0
1993 42,932 41,081 34,370 83 7
1994 30,247b 26.443b 20,884 82 7b
“Total cases= 140,910 on 3 1,747 farms
˜These figures are subject to change.


expanded to deal with the problem. About 93% of clinical diagnoses were con-
firmed m the early stages, but this declined with time: In 1993, 83.7% of sus-
pect cases were confirmed (see Table 2). Regular reports were issued on the
number of casesbeing confirmed, and the epidemic curve was plotted and fre-
quently updated (Fig. 1). The likely future course of the epidemic was estl-
mated from mathematical models
The ability to forecast the size and shape of the epidemic was of more than
academic interest. It was necessary to find the funds to pay compensation to
farmers whose cattle were killed, to provide sufficient diagnostic capacity, and
to encourage the private sector to provide mcmerators operating at a hearth
temperature of 800°C or higher in which carcassescould be destroyed without
having to be dismembered first. In the early stages of the epidemic these were
not available and at first some 30% of bodies had to be burled m sites that were
chosen carefully to avoid contammatlon of aquifers; others had to be burned m
the open. Since May 199 1 virtually all carcasseshave been incinerated in pur-
pose-built plants.
Some pessimists argued that suspect caseswould not be reported by farmers
because of adverse effects on trade and sales, but there was never any evidence
to support this view. New caseswere only infrequently detected at markets or
prior to slaughter, and when m February 1990 the level of compensation was
increased from 50-l 00% of the animal™s value there was no effect on the num-
ber of notifications received, It seems that notifications were honest and com-
plete. The numbers of reports did vary from one week to another m response to
other events on the farm, and always dropped precipitately over the Christmas
holidays, but any shortfall m one week was balanced by an increase in the
following weeks. Suspect cases were more likely to be observed and reported
Handling the BSE Epidemic in the UK 187
m the autumn, winter, and spring than during the summer months, although
this may reflect closer observation of housed cattle rather than a true seasonal
variation m mctdence.
4. The Public Health
There was ample evidence that scrapte did not pose a risk to humans; m
particular, that it was not associated epidemiologically with Creutzfeldt-Jakob
disease and other spongiform encephalopathies of humans. Individuals had
eaten sheep™s brain for centuries without apparent harm.
The initial BSE control measures m Great Britain were intended only to
protect animal health, it being assumed that tf scrapie posed no risk to human
health, neither would BSE. The carcassesand organs of suspect cases, other
than the brains (which were needed to confirm the clinical diagnosis) therefore
could be used for human consumption. The Southwood working party, how-
ever, concluded that even though scrapre may have caused BSE it could not be
assumed that BSE could not affect humans, even by the oral route, and m an
interim recommendation received the day after statutory controls were first
introduced advised that although there was no known hazard to human health it
would be a sensible precaution to remove suspect cattle from the food chain
while the working party considered the evidence. A slaughter poltcy was
introduced on August 8, 1988, the first public health control measure to be
implemented.
The change introduced a number of practical problems for which solutions
had to be found. The accuracy of diagnosis based on clinical signs alone was of
particular concern, since the disease was still unfamiliar to most veterinary
surgeons and there was no dtagnostic test available that could be used to assist
differential diagnosis in the live animal. Slaughter would be compulsory, and
any inaccuracy of the clinical diagnosis would be apparent to all when the
results of histopathological examination of the brain was received. New legis-
lation therefore distinguished between suspicion of disease,justifymg move-
ment restrictions, and conviction that an animal was affected with BSE,
Justifymg slaughter. Compensation is paid for cattle that are compulsorily
slaughtered, and an efficient disposal operation has been developed to deal
with their carcasses.After slaughter by injecting barbiturate intravenously, the
carcass is moved under license to one of a number of plants in different parts of
the country where, after the head has been removed and sent to a Veterinary
Investigation Centre for histopathologtcal exammatton of the brain, the rest of
the carcass is destroyed.
The effect of this change was to prevent any part of a clinically suspect
animal being used m human food, or fed to animals. It was clear, however, that
the measure did not prevent the consumption of tissues from cattle that were
188 Tyrrell and Taylor

infected and mcubatmg the disease but had not yet developed clmical symp-
toms. The Southwood Working Party report, published in February 1989, iden-
tified the systems m which mfectivtty was most likely to be present, and
although it did not recommend statutory action, it did suggest that baby food
manufacturers should avoid the use of ruminant offal and thymus Govern-
ment, however, concluded that preventing the use of these tissues in all human
food would provide a valuable additional safeguard
Work on natural scrapie m sheep had indicated that mfectivtty could be
present in the lymphoreticular and central nervous systemsof apparently nor-
mal animals and it was prudent to take account of this by assuming that the
same could be true of BSE, establishing the facts for the latter disease would
require an experiment of several years duration and sertous harm might be
done if action were to be delayed. A ban on the use of specified bovme offals
(SBO) therefore was introduced, first for human use, and later also for animals
The age at which cattle would be subject to SBO controls had to be timed
precisely, and the decision was based on the times at which scrapie mfectivity
was first detectable m different tissues m sheep and goats, as well as careful
checks on the distribution of the lymphoid tissue wtthm the alimentary tract
of cattle. The objective is to prevent the BSE agent from getting mto any food
chain, human or animal, and the bovine offals ban, if properly implemented,
should ensure that humans do not eat any bovine tissue contammg sign&ant
mfectivity. Subsequent research has suggested that the BSE agent may be less
widely distributed m infected cattle than is the scrapte agent m infected sheep,
and that the SBO ban is more extensive than necessary This is no bad thing m
a public health protection measure, and much more study is necessary before
the extent of the SBO controls can be reassessedwith confidence. It is also
pertinent to wonder whether a slaughter and destruction pohcy for suspectcattle
1sneeded UI additzon to SBO controls: In theory, the latter alone would suffice
to protect public health (and animal health is protected in other ways), but a
cautious view rightly has been taken and both sets of controls continue to
be applied.
Despite the effectiveness of present control measures, however, it is clear
that humans could have ingested infectivity before the disease was recognized
and the ban was introduced. The risk 1slikely to have been very small, but one
cannot not say it did not exist. Public concern about BSE, fanned by media

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