Health expert warns there 'will probably be human cases' of bird flu WHO scientist made claim despite H5N8 strain never infecting a human Elizabeth Mumford said possibility low but 'flu viruses are unpredictable' She stressed that even then, virus would not pass between humans It comes as 6,000 ducks culled at breeding farm in Nafferton, Yorkshire Owner has 33 sites and sells ready meals to Tesco, Lidl, Aldi and M&S EXCLUSIVE: Defra testing up to 15,000 eggs at second site 50 miles away Top vet: 'Everybody in the UK that owns birds should be on lockdown' A leading health expert has claimed there will 'probably be human cases' of bird flu after an outbreak in Yorkshire - despite the strain never infecting a human before. Elizabeth Mumford from the World Health Organisation warned the virus was 'unpredictable' as the government confirmed it is from the same H5N8 strain found in Germany and the Netherlands. All 6,000 white Pekin ducks are being culled today on a breeding farm in Nafferton, East Yorkshire, and up to 15,000 eggs are being tested at a second site 50 miles away. Cull: Ducks are dumped into containers - some of them falling to the ground instead - after being gassed As thousands of carcasses were emptied into a container, a WHO scientist claimed there will 'probably be human cases' of bird flu after an outbreak in Yorkshire - despite the strain never infecting a human before Dr Mumford, a scientist with the WHO's Global Influenza Programme, told reporters today in Geneva, Switzerland: 'I think we will probably see some human cases. 'I don't see why we wouldn't. If it's really circulating widely, there's no reason we shouldn't see human cases.' 294 shares Speaking of the outbreaks in Germany, the Netherlands and Britain she said there could be 'a few sporadic cases', adding: 'We believe any time that humans are in close contact with poultry, there's a possibility of transmission to humans'. Asked if more bird populations were likely to be infected, she added: 'Absolutely, I would say.'Â It is the first time an expert has claimed the H5N8 strain could pass to humans. It comes after other top scientists, including Britain's chief vet and Public Health England, stressed repeatedly that the risk of transfer to humans is negligible. Dr Elizabeth Mumford (left) said although the risk of human infection was low, 'flu viruses are unpredictable' Hosing down: The culled ducks are washed with disinfectant before their carcasses are disposed of today Final moments: Ducks are packed into crates and taken to be culled today at a bird flu-hit Yorkshire farm Dr Mumford said genetic tests show the H5N8 strain 'very much remains an avian virus,' and even if a human was infected it would not be passed from person to person. However, she said:Â 'The first thing I always say is that flu viruses are unpredictable. That's the caveat of influenza.' Linda Klavinskis, a specialist in immunobiology at King's College London, added: 'The risk for humans is always a possibility because of the massive shedding of these viruses by infected chicken flocks, however in my opinion the chances are very low'. MailOnline can reveal a second site will be tested for the virus, as it is incubating between 14,000 and 15,000 eggs which left the stricken farm two weeks ago. The admission was made by Cherry Valley, the owner of both sites and Britain's largest duck supplier which sells ready meals to Tesco, M&S, Lidl and Aldi.Â The shipment left Nafferton on November 5, which means the eggs are already in incubators waiting to be hatched at Cherry Valley's Usselby hatchery near Market Rasen, Lincolnshire. Because incubation takes 28 days it is still two weeks before the eggs are due to hatch. Normally the ducks would live for seven weeks before being slaughtered. The Department for Environment, Food and Rural Affairs (Defra) is now set to test the eggs and work out whether they need to be destroyed. A Defra spokesman said: 'As part of our robust action in response to the confirmed case of avian flu, we are considering a range of measures including destroying a shipment of eggs sent to a separate farm for hatching earlier in November. This is in line with our tried and tested procedures for dealing with avian flu outbreaks. Strain: The cull took place in Nafferton, East Yorkshire, as the government confirmed the virus was from the same H5N8 strain found in the Netherlands and Germany. Some 15,000 eggs are being tested 50 miles away Preparations: A worker unloads gas cylinders this morning at a farm hit by a bird flu outbreak in Nafferton, East Yorkshire, where it is believed gas may be used as the most humane method to cull 6,000 ducks A Cherry Valley spokesman told MailOnline: 'Defra will establish where eggs are that could have left the farm and will test them and if necessary destroy them. As the World Health Organisation, the Minister, the Food Standards Agency, Public Health England and others have made clear, there is absolutely no risk to humans and people should continue to eat all forms of poultry. Any eggs that are destroyed are done so to protect the integrity of the supply chain and ensure that the disease does not affect more birds. Cherry Valley has 33 British sites for breeding, hatching, growing or slaughtering 7million ducks a year, mostly in Lincolnshire and Yorkshire.Â An expert told MailOnline it was possible the virus was carried onto the Lincolnshire site on the outside of eggshells - though he insisted there was still no risk to humans. Dr Colin Butter, head of avian viral immunology at The Pirbright Institute for animal health, said: 'It's certainly possible that eggs from an infected flock could carry influenza on their surface. The other issue here is the time period. In chickens you would know very fast because they die. With highly pathogenic bird flu, which this is, the can die within a couple of days, so you know very fast that you have a problem in the flock. However, with some water fowl such as ducks, the symptoms of influenza can be much less severe, so farmers have to be on a very sharp lookout. Hosed down: All farm equipment is being cleaned at the stricken farm, where 6,000 ducks are being culled Necessary: An expert told MailOnline toxic gas would be the most humane way to kill the affected ducks Gap: The hatchery where 15,000 eggs were delivered this month is almost 50 miles from the restriction zone One of the things that will be very important to know will be when influenza got into this flock. But he added: 'There's all evidence to suggest this farm picked it up extremely quickly... [And] I'm quite sure the scientists from Defra have this question in hand. There is still no risk to humans, so the "no cause for alarm" message really is the key one. British Poultry Council chief executive Andrew Large confirmed the 15,000-egg shipment was to be tested. The H5N8 strain, the one found in the Netherlands, Germany and Britain, has never been known to pass to humans.Â 'Any decision on whether eggs or ducks or ducklings will be destroyed will be taken as a result of tests', he told MailOnline. 'I'm not aware of there being any other sites than this particular hatchery but we're checking with the firm. The issue to be crystal clear with this is none of these eggs were ever destined for human consumption. They were to be reared and slaughtered for their meat. 'There's no risk to the food chain and outside the restriction zone people are continuing to rear, slaughter and ship poultry meat as normal.'Â Emergency measures have been declared after the 'highly pathogenic' outbreak was declared on Sunday night, two days after a vet first raised concerns. There were restrictions on the movement of birds and eggs in a six-mile zone around the farm as Defra carried out the cull today. 'As part of our robust action in response to the confirmed case of avian flu, the culling of 6,000 ducks on the affected farm in east Yorkshire is underway,' a Defra spokesman said. The cull to prevent the spread of potential infection is being carried out in a safe and humane manner by fully trained APHA staff. Our response to this outbreak follows tried and tested procedures for dealing with avian flu outbreaks and we expect the cull to be completed later today. Additionally, our animal health laboratory at Weybridge has confirmed that the outbreak of avian influenza in East Yorkshire is the H5N8 strain. The advice from the Chief Medical Officer and Public Health England remains that the risk to public health is very low. The Food Standards Agency have said there is no food safety risk for consumers.'Â The European Commission said it is possible the virus is still being carried around Britain by migrating swans which are showing no signs of disease. But environment secretary Liz Truss insisted there was no risk to human health - as the H5N1 strain which has killed 400 people globally was ruled out at an early stage. Instead it is the H5N8 strain found in Germany and the Netherlands, which has never been known to cross over into humans. Widening investigation: Staff in protective clothing at the Nafferton farm this morning, as it was revealed a shipment of 15,000 eggs left less than two weeks ago. The eggs are still in incubators in Lincolnshire Crates: Workers at the duck farm donned protective gear and gas masks today as the cull got under way The animals are being killed as a precaution and will have to be disposed of under a vet's instructions Precautions: A full-scale animal health investigation has been under way at the farm since the weekend Cull: Final preparations are being made to slaughter 6,000 ducks on a bird flu-stricken farm in Yorkshire She told MPs: 'Whilst we're never complacent about such an important issue, we do have a very strong track record in controlling outbreaks of avian flu'. The farm is run by Britain's largest duck supplier Cherry Valley as a breeding site. The 6,000 white Pekin ducks lay eggs which are taken away immediately and hatched in incubators at other farms. This led to concern that the virus could have spread to other farms run by the firm, which supplies ready meals to M&S, Tesco, Lidl and Aldi. In chickens you would know very fast because they die within a couple of days. With ducks, the symptoms of influenza can be much less severe, so farmers have to be on a very sharp lookout Dr Colin Butter, The Pirbright Institute All four supermarkets have given assurances that the stricken farm is not one of their suppliers. The farm does not supply meat directly. Red signs declaring 'Caution: Avian Flu Livestock Restriction Zone' have been placed in the small East Yorkshire village and staff at the farm were seen bringing Tamiflu pills to work. Professor Andrew Easton, professor of virology at the University of Warwick, told MailOnline it was likely gas would be used to cull the animals. 'Given the number of animals any other approach would be slow, cumbersome and potentially unpleasant for the animals and the people involved,' he said. These are flock birds, so they all come together in large numbers. That means gas is not an unusual method to be used for culling. The imperative here is to cull the animals as quickly and as painlessly as possible. On workers bringing Tamiflu tablets, he added: 'I think it is being over-cautious but it's very understandable. It would be perfectly understandable for people who are coming into close contact with large numbers of birds who are infected to take precautions. They will have been wearing protective clothing but taking Tamiflu is not an unreasonable further step. Who wouldn't?' Fences and signs were erected as Keith Warner, president of the British Veterinary Poultry Association (BVPA), said: 'Everybody in the UK that owns birds in any number should be on biosecurity lockdown' Preparations: Equipment is moved as staff prepare to cull all 6,000 ducks at the East Yorkshire farm Turning on the gas: Defra officials make the final preparations for culling the 6,000 breeding ducks Worried: At least one worker brought Tamiflu tablets, although the virus is not known to infect humans Scientists told MailOnline the outbreak could cause a disaster for the poultry industry, especially turkey and goose farmers, as movements of birds increase in the run-up to Christmas.Â The European Commission also claimed the virus may have been brought to Britain by 'a species of wild swans' which would still be flying around with no symptoms. A private vet raised the alarm at the Yorkshire farm on Friday, and on Saturday government tests confirmed the outbreak. But it was only late on Sunday night, after the lethal H5N1 strain was ruled out, that an emergency was declared and the wider public was told. Restrictions in the Netherlands - where 150,000 birds are being culled and there is a total ban on moving eggs, poultry and manure across the country - are far stricter than those in Britain. But the European Commission insisted both were adequate, and the Netherlands had chosen stricter restrictions because it had a more densely-packed bird population.Â A spokesman said: 'The measures aim at quickly bringing the disease under control and at preventing the spread of the highly pathogenic avian influenza within the affected member states, to other member states and to third countries while minimising the disturbance to trade.Â Red signs were placed around the small East Yorkshire village as environment secretary Liz Truss told MPs: 'Whilst we're never complacent about such an important issue, we do have a very strong track record' Dumped: Thousands of chickens and eggs were emptied out by a mechanical digger and destroyed in the Netherlands yesterday after the same virus was detected at a farm in Hekendorp in the province of Utrecht The measures include the culling of the poultry on the affected holding, the establishment of protection and surveillance zones, the introduction of sanitary measures (cleaning and disinfection), the prohibition of movements to sell live poultry, eggs, poultry meat and other poultry products to other EU countries and non-EU countries and the culling of affected flocks only in the restricted zones. 'The Commission is also informing other EU member states and non-EU countries, as well as international organisations, about the disease situation and on the measures taken.'Â The East Yorkshire outbreak is the first serious case of bird flu since 2008, when the H7N7 strand was found in free-range laying hens near Banbury, Oxfordshire. Most types of bird flu are harmless to humans but two types - H5N1 and H7N9 - have caused serious concerns. But experts have warned that further outbreaks could emerge in the coming days. Chief veterinary officer Nigel Gibbens said the British farm at the centre of the alert, where farm workers dressed in blue protective overalls and face masks could be seen entering and leaving six low sheds containing ducks, had good bio-security in place.Â Operation: The farm is run by Lincolnshire firm Cherry Valley, whose products from the 7million ducks it breeds in Britain every year include frozen duck meals for supermarket shelves such as the one above For sale: One example of a Cherry Valley duck on sale at Tesco. However, all the supermarkets involved said they do not take any ducks from the specific farm in East Yorkshire which has been affected by the outbreak Epicentre: The 3km protection zone has been set up around this duck farm, which had 6,000 animals The risk of spread is 'probably quite low', he said, but he warned farmers and their vets all over the country to be alert to the possibility of disease. Keith Warner, president of the British Veterinary Poultry Association (BVPA), added: 'Everybody in the UK that owns birds in any number should be on biosecurity lockdown'. He said there should be no unnecessary visits to farms, transport or sharing of equipment, and that all free-range birds in the restriction zone should be kept inside. Concerns have been raised about the impact on the poultry industry in the run-up to Christmas. Chris Dickinson, NFU county adviser for Yorkshire, said: 'It is obviously a worry for poultry farmers but I just ask farmers to keep up high levels of biosecurity and Defra will inform us of their findings in the coming days. 'It is a busy time coming up for poultry farmers but poultry isn't just for Christmas, it's a big industry all the year round.'Â