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Food poisoning: the bacteria lurking in your chicken

amb206 — Wed, 17 Jun 2015 12:52:44 +0000

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Poultry is an important source of protein; almost half the meat we eat in the UK is chicken. And the popularity of chicken is rising: it’s convenient, tasty and cheap. On average we eat around 190g per person per week. Poultry, however, harbours a hidden problem. Around two-thirds of raw chicken sold by British retailers is infected with bacteria called Campylobacter.

Campylobacter is ubiquitous in the environment. All chicken flocks, large or small, factory-farmed or free range, are susceptible to infection. ̽��ֱ��bacteria have the ability to survive the production chain from farm to fork.

Adequate cooking, however, kills the bacteria and makes chicken safe to eat. Consumers are advised not to wash chicken before cooking and to follow basic hygiene rules when handling raw chicken.

If Campylobacter is ingested by humans, it can lead to diarrhoea. Four out of five cases of food poisoning in the UK can be traced to poultry; sickness from Campylobacter costs the economy an estimated £900 million each year. Recovery can take a week or more, and infection with the bacteria is also associated with serious complications – including reactive arthritis and Guillain-Barré Syndrome.

These facts are the driving force behind research being undertaken by microbiologists Dr Andrew Grant, Professor Duncan Maskell and their groups at the Department of Veterinary Medicine. “Campylobacter is the leading source of bacterial gastroenteritis, affecting half a million people and killing an estimated 100 people each year in the UK,” says Grant. “This is why it’s a major target for research efforts.”

Poultry is big business. Production units supplying the major supermarkets can house 50,000 birds or more. Even when stringent biosecurity measures are taken, incursions occur when barriers are broken. “It takes just a couple of bacteria, or perhaps even one, entering a unit for a flock of thousands of birds to be infected in less than a week,” says Grant. “ ̽��ֱ��chicken gut is the ideal vessel for Campylobacter to flourish. Transmission is guaranteed by a continual process of consumption and excretion known as coprophagy.”

There are no vaccines – either for poultry or humans – to protect against Campylobacter. ̽��ֱ��ubiquity and resilience of Campylobacter jejuni (the strain that colonises poultry and causes most gastroenteritis in humans) have prompted a government-led push to reduce the level of infection by developing ways in which to contain, and ultimately eliminate, its presence in the nation’s most popular meat.

“We need to look at the problem both on an industry-wide scale and on a microbial scale. ̽��ֱ��first approach involves working hand-in-hand with producers and processors and the second working in the lab to understand the structure and behaviour of Campylobacter,” says Grant.

“Working with the industry, we’re building a picture of the highly dynamic process of transmission from one bird to another and also at the ways in which Campylobacter is spread during slaughtering and processing. In the lab we’re looking at how we can manipulate Campylobacter so that it can’t spread – essentially we’re trying to identify and target its Achilles heel.”

One avenue being explored is the identification of the Campylobacter genes required for chicken colonisation, which could make good targets for therapeutic intervention. Another approach is to disarm Campylobacter by altering its characteristic shape from spiral to rod-shaped. Once rod shaped it loses its ability to colonise chickens and cause disease in humans.

Scientists working on Campylobacter face formidable challenges. Highly successful in the environments where it thrives best, the bug is difficult to culture in the lab where scientists need to work with live bacteria.

In the food production and retailing sectors, a reluctance to take ownership of the problem has led to lack of investment in measures to address an issue that each sector sees as the other’s problem. ̽��ֱ��profit margins made by farmers are tiny – as low as one or two pence per bird produced. ̽��ֱ��onus therefore is seen to lie with processors and retailers to invest in intervention and control strategies.

There is a mounting sense of urgency in the drive to eliminate Campylobacter from the nation’s food chain. Incidents of Campylobacter food poisoning are continuing to rise. Around 75,000 cases per year are ‘culture confirmed’ and, due to under-reporting, the true total is estimated to be equivalent to at least 460,000, and possibly 750,000, cases.

“Campylobacter found in raw chicken sold to consumers is generally on the surface of the birds, which means that adequate cooking quickly destroys the bacteria. But we now think that it might be entering chickens’ muscle tissue and internal organs,” says Grant.

“Infection by Campylobacter is considered to be the most prevalent cause of bacterial diarrhoeal disease worldwide. Compared to many other pathogens we know comparatively little about the bacteria and there are still many more questions than answers. There is a need for alternative strategies to reduce Campylobacter in chickens and Campylobacter-induced disease burden in humans.”

Next in the Cambridge Animal Alphabet: D is for a creature that prowls the Museum of Archaeology and Anthropology, confronts students in the Department of Anglo-Saxon, Norse and Celtic, and was a fertile symbol for medieval poets.

Inset images: Raw chicken in a pot (eltpics); Campylobacter jejuni (Andrew Grant).

The Cambridge Animal Alphabet series celebrates Cambridge's connections with animals through literature, art, science and society. Here, C is for Chicken – a popular source of protein that carries a hidden hazard in the form of Campylobacter.

In the lab we’re looking at how we can manipulate Campylobacter so that it can’t spread – we’re trying to identify and target its Achilles heel

Andrew Grant

U.S Department of Agriculture

Broiler chickens

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Field to fork: safeguarding livestock health

lw355 — Thu, 21 Jul 2011 09:45:03 +0000

About 17 billion chickens, almost 10 billion pigs, and nearly 2 billion each of cattle and sheep were produced as livestock worldwide in 2009. And, by 2050, demand for livestock is projected to double. With the added strain of increasing meat production on resources such as land, water, crops and energy, it’s vital to maximise the ‘output for input’, as Professor Duncan Maskell, Head of Cambridge’s Department of Veterinary Medicine and Marks and Spencer Professor of Farm Animal Health, Food Science and Food Safety, explained: “How you should apportion crops between food for animals and food and fuel for humans is a complex question, so it’s crucial to ensure that resource input counts in terms of output of meat, and one of the main moderators of this relationship is animal welfare, especially in terms of infectious disease.”

Viral epidemics can sweep through livestock, and endemic diseases such as respiratory infections can affect the rate at which animals grow. A further risk to food security is posed by bacterial infections of livestock that contaminate meat and cause food poisoning.

Research at the Department of Veterinary Medicine is tackling disease on all of these fronts in what Professor Maskell has described as “a perfect marriage between fundamental biological research and applied clinical outcomes.”

‘Flu-free’ chickens

A breakthrough was announced earlier this year that could prevent future bird flu outbreaks from spreading within poultry flocks. Dr Laurence Tiley, in collaboration with researchers in the Roslin Institute at the ̽��ֱ�� of Edinburgh, produced the world’s first genetically modified chickens that prevent the spread of avian influenza.

Since 2003, over 300 million poultry have been culled as a result of influenza outbreaks, and in some countries the virus is now endemic in wild bird populations. Preventing virus transmission in chickens would reduce both the economic impact of the disease and the risk for people who are exposed to the infected birds.

̽��ֱ��scientists introduced a new gene that manufactures a ‘decoy’ molecule into the chicken genome. In a clever move to confuse the flu virus into ignoring its own replication needs, the decoy mimics an important control element of the virus and diverts the viral replication machinery away from its own genetic material.

“Because the control element is absolutely conserved across strains, we expect that the decoy will work against all strains of avian influenza and be difficult for the virus to evolve around,” said Dr Tiley, whose research was funded by the Biotechnology and Biological Sciences Research Council (BBSRC). Although the birds become sick themselves, they don’t transmit the infection to other chickens, even those without the decoy molecule.

“At this stage, the chickens are not intended for consumption,” Dr Tiley added. “This genetic modification is a significant first step. Our objective now is to develop chickens that are completely resistant to avian flu.”

Threats from the wild

Viral epidemics are not just a concern in livestock, but also in relation to wildlife, as Professor James Wood explained: “Often, emerging infectious diseases originating from wildlife are a particular challenge because little might be known about the virus, how it’s transmitted to livestock and humans, or the potential for epidemics to spread.”

Nipah virus, for example, was first recognised in 1999 when an outbreak causing severe inflammation of the brain occurred in pigs and pig farmers in Malaysia. When the source of the virus was traced, it was found to be on fruit contaminated by infected fruit bats, the natural host of the virus.

“Bats epitomise the growing challenges associated with the spread of wildlife diseases,” added Professor Wood: “They are associated with a wide range of viruses, live in close proximity to animals and humans, and many important puzzles remain about the social, environmental and biological dynamics that shape pathogen transmission.”

̽��ֱ��first steps to remedy this lack of information were taken last year when a unique network was created comprising experts from institutions worldwide including collaborators in Bangladesh, Ghana and Kenya. ̽��ֱ��consortium was funded by a Catalyst grant from the Medical Research Council and three other research councils.

“ ̽��ֱ��network has a long-term aim of creating vitally needed interdisciplinary knowledge,” said Professor Wood, one of the leaders of the network, “as well as pioneering interventions geared to enabling bats, animals and people to co-exist with reduced disease risk.”

Super-vaccination at one sniff

Respiratory infections in pigs are a major animal welfare issue and cost the pig industry millions of pounds each year. An innovative project has begun the process of developing a ‘super-vaccine’ to guard against infection by the bacteria that are responsible for the most serious infections.

Funded with £5.6 million from the BBSRC, the consortium links experts from the ̽��ֱ�� of Cambridge, Imperial College London (the project co-ordinator), the London School of Hygiene and Tropical Medicine, and the Royal Veterinary College.

Dr Dan Tucker, who together with Professor Maskell leads the Cambridge component of the five-year project, explained why these infections matter so much to food security: “When a pig gets sick it diverts its energy away from growth to fighting off the infection. This requires treatment with antibiotics and decreases the efficiency with which vegetable protein is converted into kilograms of meat.”

̽��ֱ��goal is to create a single super-vaccine that can be administered by nasal spray and protect against Actinobacillus pleuropneumoniae, Haemophilus parasuis, Mycoplasma hyopneumonia/hyorhinis and Streptococcus suis. “Our gold standard would be to create a live vaccine based on a mutated version of one of these bacteria that no longer causes the disease, and then engineer it to display portions of the other three bacteria so that a strong immune response is made to all,” said Dr Tucker.

High-throughout sequencing in collaboration with the Wellcome Trust Sanger Institute is enabling the scientists to assemble the largest ever sequenced collection of these bacteria. ̽��ֱ��team has begun to identify which genes need to be ‘knocked out’ to provide a live vaccine – information that will also help in understanding why some strains cause more virulent disease than others.

Alongside vaccine development, a diagnostic kit will be developed to detect all four pathogens in less than six hours. ̽��ֱ��goal is to have a diagnostic test and potential vaccine ready for field trials at Huazhong Agricultural ̽��ֱ�� in China within three years.

Safety first

Diseases can also be spread by meat. Although the global incidence of food-borne illness is difficult to estimate, up to 30% of the population in industrialised countries may be affected each year according to the World Health Organization.

Salmonella and Campylobacter – two of the most common sources of food-borne disease – are the basis of multiple research programmes at the Department of Veterinary Medicine, such as the research led by Professor Maskell. His team has particularly focused on understanding the dynamics of the interactions of bacteria with their animal hosts.

“Thanks to the completion of genome sequences for many of the chief culprits and the advent of high-throughput sequencing,” said Professor Maskell, “the door has been opened on many of the secrets of how pathogens such as salmonellae cause disease.”

“We are committed to maintaining strong basic research, but do this in the context of finding improved intervention strategies,” he added. “Health standards and life expectancy have gone up globally, and a large part of this is better nutrition. At many levels this means more meat and high-protein food. One key aim of our research is to provide the fundamental knowledge and clinical tools to keep livestock healthy and our food safe.”

For more information, please contact Professor Duncan Maskell (djm47@cam.ac.uk) at the Department of Veterinary Medicine.

Veterinary research in Cambridge is spearheading a new generation of preventive methods to protect livestock from disease.

One key aim of our research is to provide the fundamental knowledge and clinical tools to keep livestock healthy and our food safe.

Professor Duncan Maskell

Norrie Russell, ̽��ֱ��Roslin Institute, ̽��ֱ�� of Edinburgh

Genetically modified chicken

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