Reducing the burden of foodborne infection from poultry
Around 50 billion chickens are reared each year for meat and eggs, around 1 billion in the UK alone. One of the great challenges in poultry production is reducing the levels of bacterial pathogens such as Campylobacter and Salmonella in chickens that can be transmitted from meat and eggs to people causing gastroentertitis which can be life threatening.
In Europe it is estimated 1 in every 100 people are infected with Campylobacter each year and that most of these cases are from infected poultry meat. Recent surveys have shown 70% of supermarket chicken in the UK has Campylobacter. So reducing the levels in chicken flocks should lead to a reduction in human cases.
Our work in Liverpool has focused on understanding how Campylobacter behaves within the chicken, how it moves between birds in flocks and importantly what type of immune response the chicken produces. Each of these is important in developing interventions we can use on farms and especially in developing vaccines which have been a success story in helping control Salmonella. We have recently made three important findings. The first of these is that most people had considered that Campylobacter had little effect on the chickens themselves. We were able to show that infection leads to poor gut health which in turn leads to poorer welfare of the animal. Animal behaviour scientists have also built upon our work and shown infection leads to negative behavioural changes in flocks too. Secondly we have shown that Campylobacter is very varied in how it behaves. Previously it was thought that the bacteria lived in one part of the chicken gut called the caeca, but we know that some variants can survive through the full length of the gastrointestinal system. Some variants can also spread more easily from the gut to the liver and even muscle tissue. Understanding this is important in processing poultry carcasses to reduce the risk of contamination. Finally we now understand the immune response that chickens make to Campylobacter may be exploited by some forms of vaccination and we are working with a vaccine company to develop these vaccines.
Our work uses experimental infections in the type of chicken used commercially. Unlike many experimental systems we are not trying to model a human disease, but are re-creating what happens on farms in a controlled and contained environment. We are fortunate in having a dedicated poultry unit and expert technical staff in Liverpool. Work with zoonotic pathogens requires high biological containment with the ability to keep chickens under high welfare conditions. We also use cultured chicken cells, the waxworm (Galleria melonella) insect infection model and mathematical modelling approaches which has allowed us to use fewer animals in better designed experiments but ultimately most of our work requires the complexity of the whole animal.
Improving the metabolic welfare of domestic horses and ponies
Modernisation and changes in economic focus have served to shift the demographics of the UK equine population away from traditional working roles and towards leisure and recreation. Improvements in equine husbandry, in combination with increased emotional investments in the human-horse bond, have promoted longevity in our animals.
Unfortunately, not all changes have been positive. The incidence of obesity in the equine population has dramatically increased. Currently around 70% of leisure horses are overweight or obese. Obesity and insulin resistance (IR) are major risk factors for laminitis, a systemic condition that presents as extreme foot pain and often warrants euthanasia. These conditions are recognised as the major welfare challenges facing domestic horses and ponies.
However, not all animals sharing a common pasture become obese and/or insulin resistant and some ponies develop laminitis in the absence of either factor. Horse and pony owners are acutely aware of the challenges of both maintaining body weight in elderly animals and minimizing the risk of laminitis in obese ponies. These concerns have been matched by an ‘owner-led’ demand for improved nutritional management of senior (older than 20 years) and obese (body condition score more than 7/9) animals.
The situation is complex and ‘simple solutions’ such as ‘feeding the horse more or less’ are far from simple to effect under domestic conditions, without causing further negative impacts on health.
Our research groups are working to understand why some animals are more susceptible to obesity and laminitis, in order to find practical solutions to minimise risk and to provide veterinary surgeons with evidence-based advice, with which to direct animal owners and managers. Local horse and pony owners, motivated to help find solutions to these issues, have been highly supportive of our work.
When we began, we understood very little about equine fat biology and its association with health in horses. We have developed robust, stable-isotope methods for evaluating ‘fatness’ and metabolic rate in horses and ponies and have improved our understanding of how fat deposited at specific anatomical sites can vary in function. With this knowledge we have been able to develop clinically-safe, nutritional protocols to promote controlled weight loss and decrease IR in obese animals.
These studies identified that not all animals respond in the same manner to the same weight loss diet. Some animals are relatively weight loss resistant and may require severe ‘dieting’ under veterinary supervision in order to lose weight. Linked studies have allowed us to explore variation in the glycaemic response of ponies to different feedstuffs.
Furthermore, horses depend on the bacteria which populate their guts to convert forage-foods to substrates they can use as energy sources. This ‘microbiome’ is altered in obese and old horses in a way that can leave them susceptible to metabolic disease when challenged with ‘energy-rich’ but commonly used foods, including grass and cereals. We have learned that the bacteria in spontaneously passed faeces are representative of the gastrointestinal microbiome.
Maintaining ponies of a common breed (Welsh Mountain ponies) and gender (mares), under normal but carefully standardised husbandry and nutritional conditions, allows us to minimise sources of variation between animals. These controlled conditions allow us to better understand the impact of age, body fat content and weight loss on the microbiome. This is important as the microbiome can be readily altered by changes in nutrition and it is possible that this work could lead to nutritional interventions which could help to reduce disease risk.
Underpinning evidence for meningitis clinical trials
Cryptococcal meningitis is a rapidly lethal fungal infection that involves the brain and the lining of brain. This disease causes approximately 600,000 deaths per year, with most cases in low to middle income countries in Africa and South East Asia. There are only several agents that can be used to treat this infection.
The standard-of-care is to use intravenous antifungal agents for 2-weeks. The best antifungal drug is amphotericin B, which is highly potent, but also toxic and causes a multitude of side effects, some of which are serious.
The administration of amphotericin B for a prolonged period is infeasible in the health care settings where cryptococcal meningitis is most frequent. There are simply inadequate resources to enable this to be done safely. Thus, alternative approaches are required.
The Antimicrobial Pharmacodynamics and Therapeutics laboratory has been studying innovative ways that amphotericin B can be used in health care settings. We asked the question whether very short courses of therapy result in the same antifungal effect as standard daily therapy. We used well-characterised laboratory animal models of cryptococcal meningitis in mice and rabbits to test this idea.
We have studied two formulations of amphotericin B: amphotericin B deoxycholate and liposomal amphotericin B. For both agents, the results were strikingly similar. One-to-three dosages produced the same antifungal effect as daily therapy over a 2-week period. We published this work in leading peer-reviewed medical journals.
The findings from this experimental work are now being tested in patients from Africa with cryptococcal meningitis. The results from a clinical trial were recently presented at the CROI meeting in Seattle in 2017. Preliminary results from patients with cryptococcal meningitis receiving a single shot of amphotericin B appeared to be the same as patients receiving the standard daily therapy.
The results from this preliminary trial have been used to design the largest clinical trial on cryptococcal meningitis that has ever been performed with over 800 patients being enrolled. This trial has been funded by the EU and will open for enrollment in the latter part of 2017.
This case study is an exemplar of the use of laboratory animal models to provide the vital underpinning evidence for clinical trials. Without this evidence, the clinical trials are too risky to conduct and cannot proceed. Findings from both mice and rabbits predicted the response to patients and is a testament to the value of laboratory animal models for defining new treatments for lethal untreatable human infectious diseases.