Relative resistance of pigs to infection by natural aerosols of FMD virus -
A.I. Donaldson, S. Alexandersen; concludes that:
"the probability of pigs being infected as a result of exposure to a plume
of FMD virus under field conditions is very low"....."the results of
computer simulations showed that the airborne spread of the UK/2001 strain
of the FMD virus between pig herds over a distance of greater than 0.1 km
would require more than 100 pigs to be affected on the source farm".
Relative risks of the uncontrollable (airborne) spread of FMD by different
species - A.I. Donaldson, S. Alexanderson, J.H. Sorensen, T. Mikklesen;
specifically addresses the two main 'planks' of the slaughter policy
adopted by Govt./MAFF in the UK 2001 epidemic, slaughter and disposal of
animals on infected prremises within 24 hours or reporting, and culling
within 48 hours of susceptible animals in all premises contiguous to the
infected premises.
The authors state that experimental and field evidence broadly supports
slaughter and disposal of animals on infected premises within 24 hours of
reporting.
However they are highly critical of the 48 hour contiguous cull policy.
They criticise the advice given by the biomathematicians from Imperial
College, (Anderson, Ferguson and Donnelly) , on which this policy was
based. And they are very critical of the theoretical assumptions and
"over-simplications"
in the modelling work, and conclude that the flawed model would  'in
certain circumstances generate inaccurate forecasts'.
They say that "when the disease is diagnosed and movement control is fully
implemented around an infected premises, the animals on contiguous premises
should not be at risk from uncontrollable spread, that is, from airborne
spread unless (a) there are pigs or very large numbers of cattle or sheep
on the affected premises with early clinical signs AND (b) the
concentration of the virus in the plume was at the same or higher
concentration than the threshold concentration required to infect them."
The authors go on to discuss rational approaches to the assessment and
management of the risks posed to animals on farms neighbouring infected
premises.
They conclude:
"The implementation of the 48-hour contiguous herd culling policy has
resulted in the slaughter of hundreds of thousands of animals and created
severe disposal problems. The potential benefits of culling all animals on
all contiguous premises within 48 hours should be weighed against the
likelihood that many of the contiguous premises did not contain infected
animals, the impact of having to dispose of the resultant carcases and the
diversion of very limited veterinary resources and support staff from
surveillance activities".

 


Personal comments:
As a non-vet friend said " I guess that's a scientific way of saying 'the
48 hour contiguous cull policy sucks'".