The current edition of the Veterinary Record - May 12, Volume 148, Number 19, pages 600-604 - has two short communications that relate to the current

FMD epidemic in the UK.

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 premises 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".