ARCHIVE: Zoonoses: Meticillin-Resistant Staphylococcus aureus (MRSA) in Animals

The guiding principle of Defra’s policy, with respect to antimicrobial resistance, is to seek to reduce the impact of antimicrobial resistance in organisms in animals on public health and animal health in a proportionate way, in conjunction with partners and in accordance with the Animal Health and Welfare Strategy.

Meticillin-Resistant Staphylococcus aureus (MRSA) is an emerging issue in veterinary medicine. In response, Defra have produced this summary of our position and a Question and Answer paper which will help give a better overview of the issues surrounding MRSA in relation to livestock and companion animals. Defra believes that it can most usefully assist in this area by providing input into certain specific cases and also by co-ordinating the responses of the many interested parties and, in so doing, ensure that the roles and responsibilities of stakeholders are adequately represented.

29 July 2009 - News release: 2nd International Conference on Meticillin-Resistant Staphylococcus aureus (MRSA) in animals taking place 22-25 September 2009, London.

Background

MRSA was first reported to have been isolated from animals in 1972 and over the subsequent years there have been a limited number of other reports. In the last few years more reports have occurred, some involving animals in the UK. Defra has set up a subgroup of the Defra Antimicrobial Resistance Coordination (DARC) group to advise on how best the Department can contribute to the knowledge on and understanding of the role of MRSA in animals, in the light of the increasing number of reports in animals and the increasing concern about MRSA in the public health sector. It is of note that a number of these reports in the scientific literature suggest that humans may have been the source of the MRSA strains found in colonised or infected animals.

The overall significance of the detection of MRSA in animals in relation to public health is not known. Defra is assisting initiatives from industry and the veterinary profession such as developing a code of practice for veterinary hospitals, assistance in harmonising testing methodology, and funding research to better understand the epidemiology of MRSA in companion animals and livestock and any role it may play in human infections.

Recently, there has been concern expressed over the increase in reported infections caused by S. aureus strains producing the Panton-Valentine Leukocidin (PVL) toxin. Infections caused by these strains are more likely to have deleterious consequences for affected patients. PVL can be expressed by meticillin-sensitive or meticillin-resistant strains of S. aureus. Internationally, PVL containing MRSA strains have been isolated from animals in the USA but, to date, none have been detected in livestock or companion animals in the UK.

MRSA and companion animals

MRSA has been isolated from companion animals in particular cats and dogs, but also from horses and in rabbits. MRSA isolates that are indistinguishable from each other have been recovered from companion animals and humans in contact with them, suggesting that they represent the same strain. It is not known, however, if MRSA is increasing in prevalence in companion animals in the UK or to what degree animals can form a reservoir of the organism that could pose a risk to man or other animals. The Animal Health and Welfare Strategy for Great Britain identifies that Defra has a role to play in diseases and infections of companion animals and in particular must have regard for the risk that they pose as transmitters of disease to humans.

The strategy also highlights the need for working in partnership. In this regard, and recognising that the industry has primary responsibility for taking this forward, considerable progress in several areas has been made since the establishment of DARC’s MRSA subgroup. This progress, in addition to measures that Defra is taking forward, is described below.

MRSA and companion animals – research

Defra has commissioned a research project at The Royal Veterinary College (RVC), London that is currently investigating aspects of the epidemiology of MRSA in companion animals, focussing upon risk factors for MRSA related disease. This project began in September 2005. The data collection phase of the project will be successfully completed in March 2007, with 100 cases and 100 controls having been recruited. Results from the project are expected to appear in the peer-reviewed literature in due course. In addition, an industry-funded project investigating the prevalence of MRSA in companion animals is due to be undertaken by the RVC shortly. Further work at the RVC is focussing on the general area of infection control in veterinary hospitals.

Defra has received and commissioned external peer-review of a number of research proposals received in response to a request for research investigating the epidemiology of antimicrobial resistance and companion animals, issued in June 2006. Of these, one proposal with an MRSA-related component has been short listed and is expected to commence in spring 2007.

Preliminary findings from the RVC project currently underway were discussed at the First International Conference on MRSA in Animals, hosted by the University of Liverpool School of Veterinary Medicine in June 2006. The conference, supported by Defra, was attended by delegates from a number of different countries and provided a unique opportunity for the presentation and discussion of the issues related to research in this area. Following the success of the meeting, further conferences are being considered in the future.

MRSA and companion animals – advice and guidance

The British Small Animal Veterinary Association (BSAVA), as part of the British Veterinary Association (BVA), have prepared advice for practising veterinary surgeons on MRSA in animals, in consultation with Defra, and the Veterinary Laboratories and Health Protection Agencies. Also, a collaborative paper is being produced, providing guidelines for veterinary practices on procedures for decolonisation of animals, should this be required. Further discussions in this area and on developing advice for animal keepers are ongoing.

Consumers and pet owners are also represented on the DARC MRSA subgroup by the Bella Moss Foundation, which aims to provide support and advice to pet owners and to raise awareness of MRSA within the veterinary profession. The foundation has recently organised a series of seminars about MRSA in animals for professionals in the area and plans to develop a web-based infection control learning tool that can be taken by professionals seeking career development in this area.

MRSA and companion animals – data collection and standardisation of sampling and testing

Members of the DARC MRSA subgroup have agreed to consider providing input into the proposed animals MRSA database at the new University of Liverpool Zoonoses Research Institute. It is envisaged that this will represent a useful source of epidemiological data about animal MRSA isolates in the UK, but a firm proposal was required.

The development of this MRSA database has underlined the requirement to establish some degree of standardisation of test methodology for veterinary MRSA diagnostics. To this end, the BVA working group on MRSA is developing a flowchart describing a standardised approach to the isolation and identification of MRSA isolates from veterinary patients. It is intended that this flowchart be ready for distribution in spring 2007.

MRSA in livestock

MRSA has been isolated from dairy cows, pigs and chickens outside the UK and an ongoing assessment of the international picture is being maintained. There is no current evidence that food-producing animals form a reservoir of infection in the UK and the organism has not been detected in farmed livestock in the UK. Defra has initiated a study undertaken by the VLA to test Staphylococcus aureus isolates obtained from bovine clinical submissions for MRSA. This project commenced in Autumn 2006 and, to date, 425 samples have been tested, with no MRSA identified.

The issue of MRSA in other livestock species was discussed at the January meeting of the DARC MRSA subgroup. Members felt that, at present, broadening the scope of work in this area should only be considered if recommended by colleagues specialising in public health and that, in the absence of such recommendations, speculative investigation of other species was not an appropriate use of the limited resources available.

MRSA in European Livestock

A number of European countries have identified a strain of MRSA (termed ST398) in the last few years, which appears to have emerged only recently. The majority of these isolations have been made in pigs, although similar isolates have been identified in other animal species too. MRSA strain ST398 has also been isolated from people in Holland. The data published so far suggests that it is more prevalent in individuals associated with pig farming, compared to the general human population in Holland. Researchers in both Holland and Denmark have already published articles on their respective findings,  and Defra is aware of research carried out in other EU countries that is being prepared for publication and also relates to MRSA strain ST398. How (and when) this strain initially arose remains unclear, as does the epidemiology of animal and human colonisation. The particular strain of MRSA (ST398) that has been isolated in some other parts of Europe has not been reported in animals in the UK at present. Three cases of ST398 were reported in human infants in Scotland in late 2007 / early 2008, the first report of this strain of MRSA in people or animals in the UK. These individuals had no direct or indirect contact with livestock.

The European Food Safety Authority is looking at the issue of MRSA in food-producing animals and considering what surveillance and other actions would be most appropriate for EU Member States to undertake to address the issue. The UK have been actively participating in the development of these proposals, and a Europe-wide survey for the presence of MRSA on farms keeping breeding pigs will be implemented throughout 2008. This MRSA survey will be undertaken during an already planned surveillance programme to ascertain Salmonella prevalence, so that it can be undertaken promptly. It is anticipated that the findings will direct further MRSA surveillance effort in the future.

The targeting of Defra research resources will remain under active review by the MRSA sub-group of DARC (the Defra Antimicrobial Resistance Coordination group). The sub-group will continue to base its advice on Defra-funded research and other relevant information, including findings in Europe and elsewhere.

Assistance in human cases of MRSA where animal involvement is suspected

Where brought to our attention, Defra and the VLA will assist public health colleagues in investigations into human MRSA cases where animal involvement is suspected. It is likely that this assistance would extend to similar cases involving meticillin-sensitive S. aureus (MSSA) if the causative organism was known or suspected to carry the PVL toxin.

Policy responsibility

Policy responsibility for MRSA in animals falls to Defra’s Surveillance, Zoonoses, Epidemiology and Risk group, which lies within Defra’s Food and Farming group, with provision of advice from the VLA expert on Antimicrobial Resistance. The Division liaises closely with the Veterinary Medicines Directorate and the Department of Health, and policy in this area is guided by the DARC MRSA subgroup; involving DARC group members and external specialists in MRSA. To date, there have been eight meetings of this MRSA subgroup, the most recent taking place in July 2008.

Organisations represented on the DARC MRSA subgroup include: