Lifting the lid on what happened at Pirbright site

13 September 2007

As foot-and-mouth returns, two hard-hitting reports have lifted the lid on the series of astonishing biosecurity lapses that lay behind last month’s outbreak.

ALISTAIR DRIVER reports on how mistakes at scientific laboratories ended up costing the farming industry tens of millions of pounds.

HOW DID IT HAPPEN?

Defra Secretary Hilary Benn described the events that led to the foot-and-mouth virus escaping from the Pirbright site to nearby farms as a ‘unique and unhappy combination of circumstances'.

Principally, these were weaknesses in the drainage system, the heavy rains of late July and building work taking place on the site.

LIVE VIRUS ENTERS THE DRAINAGE SYSTEM

The IAH and Merial were both working on the virus strain that caused the outbreaks on two nearby Surrey farms – O1BFS – between July 7-26.

The HSE investigators could not pinpoint the exact origin of the virus due to similarities in the strains used by the two laboratories, but believe it entered the drainage system from the Merial facilities.

Merial was involved in large scale foot-and-mouth vaccine production, using much greater quantities of live virus than IAH.

The HSE says it was ‘likely' that waste containing the live virus was flushed into Merial's effluent sump and passed into the drainage system.

EXISTING WEAKNESSES IN THE DRAINS

Underground pipes carry treated waste from the IAH and Merial plants to an effluent treatment plant, operated and managed by IAH.

HSE inspectors found evidence of long-term damage and leakage in the drainage system including cracked pipes, displaced joints, debris build-up, tree roots breaching pipework and unsealed manhole covers.

HEAVY RAINS FORCE VIRUS OUT OF DRAINAGE SYSTEM

The O1BFS virus from the Merial facility was probably released from the drainage system between July 22 and 26, following extreme wet weather on July 20 when the site experienced 62mm of rain and localised flooding, the HSE concluded.

Excess surface water entered the final treatment plant, and was ‘likely' to have entered the drainage system via a ‘series of poorly fitting manhole covers' on July 20, increasing the volume of liquid present.

Groundwater may also have entered the system through cracks and misalignments in the pipework, according to the report.

One particular manhole cover, known as FM1, was deemed likely to have overflowed. The use of two pumps to move the high volumes of water and blockages caused by ‘significant ingress of tree roots' and extra debris increased this likelihood.

CONSTRUCTION WORKERS ON SITE

During the period in question, construction workers – ironically surveying the site for a new drainage system and digging new manhole covers – were operating on the site.

On July 25-26 an excavation was undertaken around the main discharge pipe from the Merial effluent pump. Soil was placed in a heap in a designated area and the HSE has pictures of ‘potentially contaminated soil with vehicle tracks over them'.

Some of the probably contaminated vehicles then drove from the site along Westwood Lane, which passes the first infected farm at Normandy.

Report findings

Two reports into the foot-and-mouth outbreak were published last Friday (September 7).
- The Health and Safety Executive report revealed the findings of its investigation, led by Dr Paul Logan, into whether potential breaches of biosecurity at the Pirbright site – occupied by the Institute of Animal Health and Merial Animal Health – could have caused the foot-and-mouth outbreak at nearby farms.
- The report by Professor Brian Spratt, of Imperial College London, looks at the wider issues of biosecurity at Pirbright.