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It is almost certain that the Institute of Animal Health complex at Pirbright was the source of the foot-and-mouth disease outbreak, but the route by which the virus was released may never be conclusively determined, scientists said yesterday.
Several possible scenarios are being considered by the Health and Safety Executive (HSE) and other experts, but there is no “smoking gun” that identifies any as the most probable cause of the infection.
The chances of the virus escaping by each route is very low, and once it did get out, the chances that it would reach and infect susceptible livestock would be low.
Tony Wilsmore, the director of the Veterinary Epidemiology and Economics Research Unit at the University of Reading, said: “For both to happen you are multiplying two probabilities that are less than one, and when you do that, you get a lot less. If you multiply 0.1 by 0.1, you get 0.01.”
When the full genetic code of the virus is sequenced, it may pinpoint whether the source was the institute or the commercial Merial vaccine laboratory, but even that is uncertain.
The foot-and-mouth virus is composed of about 8,300 “letters” of RNA, a cousin of DNA. It is possible but not certain that the strain used in vaccine production has acquired a mutation in one of these, that would set it apart from the institute’s reference strains.
Mark Woolhouse, Professor of Infectious Disease Epidemiology at the University of Edinburgh, who worked on the 2001 foot-and-mouth epidemic, said: “It is important that we do establish what happened here, or it will be very difficult to rebuild confidence in these laboratories. But it is not immediately obvious what has happened. The truth is that we may never know.”
Airborne release
Until the HSE report was issued, this was the scenario that many experts had considered most likely. The virus can spread on the wind and a leak could have been carried for several miles given the right conditions. Laboratories with category four biosecurity status, such as the Pirbright complex, however, have safety mechanisms that should prevent pathogens from escaping in the air. The HSE found no evidence that any of these had failed.
Facilities must be isolated by an air lock, and air passing out is cleaned by two high-efficiency particulate arrestance filters. Category four labs are also maintained at negative pressure, so that if there is a leak of any sort, air will move into the lab from outside and not vice-versa.
The HSE confirmed that the pressure and filtration systems at the lab were adequate, and also noted that local wind conditions allowed only very small windows at which there could have been any risk. It ruled that there was only a “negligible combined likelihood” of airborne release.
Liquid waste
Experiments at the institute and vaccine manufacture by Merial would have used solvents and other liquid reagents. These would have been contaminated with virus and would have needed treating before disposal.
Merial, in particular, would have had to dispose of large amounts of fluid waste from the production of 10,000 litres of vaccine between July 14 and July 25. The institute conducted only small experiments over that period, each using less than 10 millilitres of virus, so presented less of a risk.
Decontamination can be done with heat or chemicals. The institute’s animal isolation unit relies on thermal decontamination of effluent, and a chemical system covers the rest of the site. If either failed, fluids contaminated with foot-and-mouth could have been flushed out of the laboratory through an effluent pipe.
This ought not to have posed much risk under normal circumstances. The effluent would have flowed into the sewage system, and would have come into contact with neither animals susceptible to foot-and-mouth nor with people, vehicles or wild animals that might have spread it to farms.
There are two concerns here. One is that the HSE reported “doubts about the integrity of the drainage system, including pipework that leads to the final effluent treatment plant” at the Merial site. A leak could have allowed contaminated fluids to accumulate on the ground, from which the virus could have been picked up on workers’ shoes or a passing vehicle.
A similar problem may have arisen because of flooding. The HSE considered that there was a negligible chance that the virus reached farms directly through floodwater: the distance is too great and the Normandy farm is uphill from the Pirbright plant.
It is possible, though, that standing water containing the virus contaminated shoes or tyres, which then carried it to the farms. Professor Woolhouse said: “It would have to have been a double failure: both the decontamination and drainage systems would have to have been compromised. Even so, out of all the scenarios, this has to be one of the most plausible. The others seem even more remote.”
Human transmission
The HSE report considered this to be a “real possibility”, despite extensive safety measures. Scientists, however, thought the risk low. Workers must enter the laboratory through an air lock and change into sterile gowns that fit tightly at the wrists and cover the shoes. They must also wrap over the chest, hair is covered and masks are worn.
All this protective clothing must be removed when leaving the laboratory. It is sterilised in a machine called an autoclave, which uses pressurised steam heated well above 100C to kill any germs. After changing out of their gowns, workers must then shower before leaving the secure area.
Even if one of these steps was not conducted properly, it is still unlikely that a worker could have carried the virus to the infected farms. “The normal procedure is that anyone who has been into these facilities shouldn’t go onto a livestock farm for five days,” Professor Woolhouse said. One possibility is that a contaminated worker walked somewhere near a farm. An allotment adjacent to the first infected farm, which is said to be used by some laboratory staff, was under investigation yesterday.
Professor Woolhouse said: “We need to think about whether the spirit as well as the letter is being observed.”
If the foot-and-mouth virus did contaminate a person’s clothing or body there are two ways in which it could have reached the infected animals.
“The most likely route is that someone walked on something that the animals ate,” Professor Woolhouse said. “That is the rationale for closing footpaths.”
Keith Plumb, a biosafety expert from the Institute of Chemical Engineers, said that the second possibility was that virus spread by contaminated boots could have been picked up by a fox or rodent and carried to the farm.
Sabotage
Deliberate release is being considered as an option by the HSE, partly because all the other possibilities are so remote. In every other case, several events that are all unlikely would have had to have happened at once: a decontamination failure, followed by a drainage failure, then movement of a contaminated person on to a farm.
Professor Wilsmore said: “If you’ve got somebody who wants to spread it, that’s a different story.
“Until we got this report, I thought that airborne spread was the likeliest cause. But when you start to think that mechanical spread – by so-called fomites such as straw, manure, a car wheel or boots – is unlikely, then you start to think. . . I’m sure they will be looking very hard at anybody who has a motive to spread the disease.”
The main case against sabotage is that there is no positive evidence that it has taken place.
Solid waste
Though solid waste is not explicitly discussed in the HSE report, it remains a possibility. Used pieces of equipment such as vials and disposable gloves must be treated before they leave the lab, again by thermal or chemical methods, and there is a chance that this was not done properly.
Dr Plumb said: “Most of this is decontaminated by autoclave, but autoclaves have failed in the past. It certainly can’t be ruled out, particularly as anyone handling this waste would have assumed it had been decontaminated and wasn’t a risk.”
source: 9aug2007
Farmers are consulting lawyers in the hope of bringing a multimillion-pound compensation claim for damages caused by foot-and-mouth disease.
National Farmers’ Union (NFU) officials said that they were considering action after the publication of a report that pinpointed a laboratory complex as the most probable source of infection. Peter Kendall, NFU president, said that members had lost money because of the outbreak and had incurred many costs through no fault of their own.
Health and safety inspectors have said that the virus probably escaped from either Merial, a private research company, or the Institute of Animal Health, a government-funded organisation. Further tests are under way in an attempt to determine which of the two was responsible for a viral leak.
A spokesman for the NFU said: “We are taking legal advice on behalf of our members. We are looking at the possibility of legal redress.”
Legal experts said that the outcome of a court case was by no means assured but that farmers would be likely to have a strong argument for damages to be awarded.
Peter Cusick, a partner with the solicitors Thring Townsend and a specialist in agricultural litigation, said a previous leak of the virus from the Pirbright site in 1959 had established that such installations can owe “a duty of care” to neighbours when they bring alien substances on to the land.
He said there was also a precedent to show that laboratories that leaked viruses, if it could be proved who was responsible, faced strict liability. Rather than negligence having to be proved, all a neighbouring farmer would need to do, he suggested, was show who had leaked the virus.
However, the question of whether a farmer with uninfected holdings could claim compensation for loss of income was likely to be the subject of a test case. Similarly, it remains unclear whether farmers with culled livestock would be likely to win a court case for damages if the disease were to spread farther afield from farm to farm, rather than being directly infected by a research laboratory.
source: 9aug2007
Restrictions on livestock movements were relaxed yesterday despite animals on a third farm showing symptoms of foot-and-mouth disease.
The animals, believed to be a mix of cattle and sheep, were ordered to be killed after “suspected clinical signs” of the disease were spotted at the farm within the two-mile radius protection zone around farmland in the village of Normandy, Surrey, where the original infection was discovered.
Nevertheless, Debby Reynolds, the chief veterinary officer, decided that the spread of the disease was sufficiently limited for movement orders to be relaxed outside the six-mile surveillance zones around the infected areas, allowing farmers to take livestock for slaughter as long as certain conditions are adhered to.
Among the conditions imposed on farmers and abbatoirs was that strict biosecurity measures must be observed and that a vet must examine every animal taken in for slaughter.
Dr Reynolds also gave permission for dead animals, referred to as fallen stock, to be removed under licence from farms. The issue of dead livestock being left to rot where they fell had been causing concern.
Dr Reynolds said: “The decision has been taken to permit the movement of live animals directly to slaughter and the collection of dead animals from farms. The decision has been made following a veterinary assessment of the risks.”
She emphasised, however, that yesterday was still only the fifth full day of the outbreak and that the operation to tackle the disease was still in full swing. It remains a possibility that the disease will spread beyond the protection zone.
The third farm suspected of foot-and-mouth infection is next to the second farm, where 102 cattle were culled. The original infection was found on land in Normandy that formed part of a farm based in Elstead, about four miles away, where a second animal was later found to be infected.
Peter Ainsworth, the Shadow Environment Secretary and a Surrey MP, said: “The news that further culling is to take place in Surrey will come as a bitter blow to the farmer concerned and he has my deepest sympathy.
“The fact that the need for this arises from a dangerous contact, however, suggests that the disease is not spreading widely, but we can only wait and hope at this stage.”
He added: “I welcome today’s limited relaxation of the movement ban outside the affected area. However, I am disappointed that the Government, unlike the Administration in Scotland, is still refusing to permit on-farm burial of sheep and other smaller animals.
“On-farm burial would be quicker, and more efficient than waiting for dead animals to be collected, and would limit unnecessary movement.”
Kevin Pearce, of the National Farmers’ Union, welcomed the movements ruling: “For a big chunk of the country, this is clearly a step forward.”
He added: “Clearly we want to do more but we need to do it when it is right to do it. We are supportive of this move and we are encouraging everyone to comply with the conditions.”
Roger Williams, for the Liberal Democrats, said: “If the risk assessment suggests it is safe to move animals to slaughter, then that is excellent news. Slaughterhouses have now been shut for three days and the supply of meat only lasts for seven, so shops have come worryingly close to running out of food.”
An investigation by the Health and Safety Executive has found that the most likey source of the infection is a research complex in Pirbright, three miles from the original outbreak. Results of HSE tests which may determine whether the virus escaped via an an effluent disposal system are expected to today. Investigators are continuing their efforts to find how it escaped from either the Institute of Animal Health, a government-funded research facility, or Merial, a research company producing vaccines.
The European Union agreed that Britain should remain a “high-risk zone” and that a meat and livestock import and export ban would stay in place until at least August 25. The ban covers cattle, sheep, goats and pigs and products made from them, although those produced before July 15 are acceptable, as are heat-treated products and those made in Britain from imported animals.
"Movements outside the surveillance and protection zones present a low risk provided the conditions and licence are strictly followed" Debby Reynolds
"This is both a measured and very necessary first step on the road towards getting the industry back to normal" Peter Kendall, NFU President
"At present we have a good supply of meat in our stores. We hope to support our British farmers and suppliers as best we can" Sainsbury’s spokesman
Open for business
— Butchers and independent traders have seen short-term disruptions in their meat supplies but the crisis is unlikely to affect consumers this weekend
— The largest supermarket chains say their shelves are stocked full of lamb, beef and pork
— We spend around £2.8 billion a year on British-reared red meat and prices this weekend will remain unchanged. There has been no sign of panic buying
— Since foot-and-mouth disease was first discovered, supermarkets have been seeking alternative suppliers. Beef from Brazil, lamb from New Zealand and Ireland and pork from the Netherlands has replaced domestic supplies
— However, traders at Smithfield market in Central London were beginning to feel the pinch. One wholesaler, Simon Glyn, said yesterday had been the worst day so far, with trade down two-thirds
— Had restrictions not been lifted, experts predict that home-produced lamb and pork would have lasted until the end of the week, with stocks of beef, which has a longer maturation process, lasting for around two weeks
— Fear of creating a shortage was one of the reasons why the Government delayed introducing a ban on livestock movement during the 2001 outbreak. The delay led to a spread of the infection, and the slaughter of millions of animals in the British countryside. This time, the Government immediately imposed a total ban
source: 9aug2007
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