The computer modelling team from Imperial College, headed by
Professor Roy Anderson, has led government policy throughout the foot
and mouth disease (FMD) epidemic. It was their analysis that proposed
the greatly increased slaughter of the contiguous cull, and warned that
anything less would allow the epidemic to spiral right out of control,
with the eventual loss of half the total UK livestock population. On
11th May, a paper detailing this work was published in Science
Five months later, on 4th October, a second paper was published in
Nature magazine, updating their work and claiming to justify
their earlier predictions. Media reports have widely publicised these
claims -- for example, Channel 4 news reported "If what was then the
Ministry of Agriculture had acted immediately on their advice to
slaughter infected farms in 24 hours and neighbouring or contiguous
farms in 48 hours, a million of the 4 million slaughtered animals would
have been saved, and 400 of the 2,000 outbreaks would have been
averted." But no independent scientific review of their work has taken
place, and no one in the media is questioning whether their claims have
As a small-scale specialist sheep keeper, I have studied every aspect
of the foot and mouth epidemic, and successfully resisted the contiguous
culling of my own flock in April. I do not believe that there is any
scientific basis for the extended culling policies, and find the
Imperial College papers entirely unconvincing and scientifically flawed.
Moreover, an independent analysis can reasonably draw the opposite
conclusions to those that have been given such public prominence.
The Imperial College team are biomathematicians who apply standard
mathematical techniques to complex biological phenomena, in this case
epidemiology - the spread of disease. Modern computing power enables the
rapid calculation and display of many possible outcomes, described as
"modelling". This is a useful technique but as with all
computing, it relies entirely upon the quality of the input data - put
rubbish in, get rubbish out. So to appreciate the true value of the
Imperial team's work, a close look at their input data is required.
Back in May, the first paper declared "Contact tracing for all
FMD-affected farms has produced unique data on the spatial scale of
disease transmission (provided by MAFF), clearly demonstrating that
farms closest to index cases of FMD are at greatest risk of infection."
This, of course, promoted the concept of contiguous culling to remove
those farms at highest risk before they, in turn, became infectious to
others. But in October, the second paper contradicts this by stating
"The newly estimated spatial kernel differed significantly from that
previously derived from the infectious contacts identified by MAFF, with
considerably more long-distance transmission events being predicted.
This implies significant biases in the MAFF contact-tracing process,
with closer contacts being more easily identified." Worse, it goes on,
"The median distance of the newly estimated kernel is about 4 km,
suggesting that most transmission probably occurred through the movement
of animals, personnel or vehicles, rather than through animal contact or
It is hardly necessary to look any further, since this admission,
that the original data were completely wrong, has entirely destroyed the
rationale for contiguous culling. Contiguous premises are now found to
be no more at risk than any others within the locality of an infected
premises; indeed the average transmission distance of 4 km argues
powerfully against slaughter of contiguous premises since this cannot
influence disease spread over such long distances, except by the very
negative effect of swallowing up valuable resources of time and manpower
for no benefit.
By looking further into these reports, more such contradictions are
easily found. The May paper states "We did not differentiate between
host species but instead used a time-varying infection-to-report
distribution averaged over species." However, by October the Imperial
team are saying "Farm susceptibility and infectiousness both varied
significantly, with smaller farms being substantially less infectious
and less susceptible than larger ones. Stratifying farms by the most
prevalent species revealed a trend for cattle farms to be more
susceptible, and pig farms to be least susceptible."
This, of course, is precisely what veterinary scientists had been
saying all along, but it was completely ignored in the earlier modelling
work. In fact, Professor Alex Donaldson of Pirbright laboratory has
shown that there is wide variation between the livestock species in
their capacity to catch and to transmit the disease; while the current
strain of FMD virus is extremely unlikely to spread by windborne means
from a source farm to its contiguous neighbours in most practical
situations, whatever the livestock species involved. So here again, the
conclusion is clear - that the original input data to the computer
modelling programme were completely wrong.
A key parameter, central to the Imperial team's calculations, is that
of farm infectivity, which they denote as (r). This is a ratio
"representing the infectiousness of a farm after the disease has been
reported, relative to that just before reporting". As with any viral
disease, livestock exposed to FMD go through an incubation period
lasting a few days before they themselves become infectious to other
animals. Symptoms do not develop for a further day or two, so that by
the time clinical signs are seen in the first animal on a farm, it is
likely that several others are also incubating the disease. By the time
these several individuals develop symptoms, more animals are entering
the incubation and infectious phases; and so on, in a progressively
accelerating pattern. During the heightened awareness of a large-scale
epidemic, early recognition of FMD can be expected because farmers are
looking closely for the clinical signs on a daily basis. So the farm
infectivity ratio, r, will be much greater than one as the disease
spreads at an increasing rate through the herd or flock following
recognition of the first signs.
Yet this very obvious conclusion eludes the Imperial college team.
Back in May, they state, "Because data do not exist with which to
estimate the infectiousness of a farm as a function of time since
infection, prudence dictates that in addition to more rapid culling of
infected farms, it is necessary to consider other interventions."
They continue, "If r is greater than one, ring culling still
accelerates the decline of the epidemic but at the cost of a larger cull
than rapid index case slaughter alone". Clearly, a contiguous cull
cannot be justified if the net result is a higher slaughter total
overall. So, they simply assumed that r wasn't greater than one. In the
notes of small print at the end of the paper, they state, "We assumed
constant infectiousness from 3 days after infection until slaughter, for
an average of eight infectious days."
Using this most extraordinary assumption, they calculate figures that
appear to support a contiguous culling policy. But for values of r
greater than one, which in reality it clearly is, they admit "Our
analysis shows that ... slaughtering on all farms within 24 hours of
case reporting can significantly slow the epidemic ... and results in
rapid control if we assume that infectivity increases throughout the
time from infection to slaughter."
Yet five months later, the October paper re-states "Infectiousness is
assumed to be constant from the day after a farm is infected until the
day the animals are culled". There is no attempt made to model for
alternative, realistically higher values of the ratio, r - the
original erroneous assumption is simply repeated. Again, the inescapable
conclusion is that the wrong input data have been used.
Those of us who actually experienced the holocaust of mass slaughter
have seen for ourselves the inconsistencies between official control
policy and reality. Farms with cattle were seen to be infected far more
often than sheep holdings, yet sheep were blamed throughout for the
spread of disease (a claim now being disproved by widespread blood
testing). Most contiguous farms that were slaughtered tested negative
for disease; and of those that refused the cull, none that I know
of went on to develop disease.
My own experience was not untypical. Two neighbouring dairy farms
reported FMD within a few hours of each other; both recognised clinical
signs in one cow. These two herds were slaughtered within 24 hours
before any other animals developed signs. Large numbers of sheep and
cattle were then slaughtered on contiguous farms - except for my own
small flock, which had been protected with commonsense biosecurity
arrangements. After a long struggle against slaughter, the flock was
eventually cleared as disease-free by blood testing, demonstrating that
the animals slaughtered all around us on other contiguous farms were
How had the disease reached our parish? The nearest infected premises
lay 6 km away downwind, and no other farms in between were affected, so
windborne spread was illogical. The farms concerned had taken
biosecurity precautions, but being dairy farms could not avoid regular
visits from milk tanker and feed lorries. Time and again, dairy farms
became infected at some distance from previous outbreaks, yet the
obvious link with these vehicles was consistently denied by the
authorities, until the later outbreaks in Yorkshire and Northumberland
eventually led to the introduction of "blue box" high-security measures;
these included the direct supervision of milk tanker and feed lorry
movements and disinfection procedures, with the result that these
regional outbreaks quickly subsided.
Even the Imperial College team, so remote from the reality of the
situation on the ground, observed in their October report "Our analyses
have demonstrated that ... changes in culling policies explain less than
50% of observed past variation in transmission rates, indicating that
effective movement restrictions and rigorously maintained biosecurity
are equally vital."
But the final condemnation of the computer modellers' claims is
simply this - that their proposed policies have never actually been
implemented. Their targets of slaughter within 24 hours on infected
premises, and within 48 hours on contiguous premises, have never come
close to being met on a national basis.
As the October report admits, "In no week of this epidemic have more
than half of contiguous premises been culled within the specified target
of 48 hours from report of a new case." In other words, the gruesome
experiment has been so incomplete that no conclusions may reasonably be
drawn from it.
In summary, I submit that the computer modelling analyses of the
Imperial College team, under Professor Roy Anderson, are fundamentally
flawed through the use of wrong input data and wrong assumptions. The
original field data from MAFF were wrong; assumptions about airborne
spread were wrong; crucial differences between livestock species were
ignored; the significance of long-distance spread via movements of
animals, personnel and vehicles was underestimated; and assumptions of
the change in farm infectivity over time were wrong.
There can be only one, inevitable, result of using such inaccurate
input data -- the output data obtained are wrong, no matter how clever
and convoluted the statistical analysis applied.
This is appallingly bad science, the unquestioning acceptance of
which has led to the unjustified slaughter of millions of healthy
animals, and has actually hindered disease control by diverting
resources away from the more important task of rapid slaughter on
infected farms. Upon close examination, therefore, Roy Anderson turns
out to be a Professor, not of zoology, but of mythology.