July 16 ~ A letter expressing the very real concern of farmers about serological testing

procedures, and the reply it received on July 16, a month later. See the exchange between Lawrence Wright and Mr Bennett DVM

Received July 12 2001 - Results of serological testing to lift Protection Zones

"I have come by some information about the results of the serological testing to lift Protection Zones.

At the point of reporting 5640 flocks had been tested.

Of these 29 had one or more 'non-negative' results with the primary screening ELISA test.

Of these 29, 17 had a single animal with a positive ELISA result and 16 of these 17 were found to be negative when re-sampled and re-tested.

The remaining 13 flocks had positive results which were confirmed on further serological testing, suggesting that FMD infection had been present in the past.

These 13 flocks were culled - and testing at slaughter for the presence of virus confirmed current FMD infection in one flock in Devon. Serosurveillance of surrounding flocks showed no evidence of past infection.

The 'breakdown' of seropostive flocks was as follows:


Devon 6
Kent 1
Northumberland 2
North Yorkshire 1


Gwynedd 1
Powys 2

Total 13

From these data the current estimate of prevalence of seropositive flocks in Protection Zones is 0.23%, with a likely minimum and maximum prevalence of 0.11% to 0.36% (95% confidence interval).

Each filed disease centre has a quota for surveillance serology.

Serosurveillance is working from Protection Zones on the margins of Infected Areas towards the centres - so as to allow an orderly shrinkage of the Infected Areas.

Lab capacity for surveillance testing was at the time of reporting about 80,000 samples a week and should be 100,000 samples per week by the end of July (this is in addition to diagnostic serology)." ENDS

PREVIOUS FILE "Serological Testing"


They can't start sero surveillance in a Protection Zone until 21 days min. after the last culled farm in the PZ has undergone initial cleansing and disinfection and then they work Protection Zone by Protection Zone in from the margins of the Infected Area as sero testing quota and other resources permit. If and when all tested premises test negative then D notices will typically be lifted quickly and the Infected Area boundary rolled back

Sadly the virus makes no concessions for people being 'only human'.

If effective biosecurity is not maintained and there movements on and off the farm then the virus can and will continue to spread.

I am increasingly of the opinion that it may be unrealistic - at least it's beginning to appear that way - to expect people to establish and maintain effective biosecurity for long periods over a large area - especially when in some cases people/farms who not had the disease are now in worse circumstances than those who did.

If that's the case then the policy of containment by means of movement restrictions and biosecurity - followed by eradication via slaughter - cannot work effectively. In which case vaccination becomes the only effective solution - that, or just 'giving up' and letting the disease run rife.

An increasing number of cases are now being picked up on patrol visits rather then via farmer reports. This suggests inadequate inspection of stock, or, Heaven forbid, deliberate failure to report suspicions.

Inadequate inspection of stock/failure to report combined with ineffective/inadequate biosecurity is a recipe for disaster when using the current disease control policy. There have recently been rather a lot of cases outside existing Protection Zones - so-called 'sparks - that then sometimes go on to form new clusters. This has prompted Protection Zones to be expanded from 3KM to 10KM - and potentially further should the need arise.

There is a growing fear that FMD will spread into the dense pig populations of Humberside and East Yorkshire - towards which it is creeping/hopping ever nearer - where there are 730,000 pigs, 128,000 of which are held on premises that also have cattle or sheep. Whilst pigs are harder to infect than cattle or sheep initially they do emit many many time more virus than cattle or sheep and the way they are managed exacerbates the viral load generated so infection spreads very rapidly in dense pig populations and risks spiralling out of control very quickly.

July 12 2001