Information on MRSA in Animals
VETERINARY SURVEILLANCE STRATEGY
Draft profile for methicillin-resistant Staphylococcus aureus (MRSA) in animals

 1. What is Staphylococcus aureus?
Staphylococcus aureus (S. aureus) is a bacterium. Strains of S. aureus live completely harmlessly on the skin and in the nose of about one third of normal healthy people. However, S. aureus can cause problems when it gets the opportunity to enter the body, with people who are unwell being particularly susceptible.

2. What illnesses are caused by S. aureus?
S. aureus causes abscesses, boils, and it can infect wounds - both accidental wounds such as grazes and deliberate wounds such as those made for a drip or during surgery. These are called local infections. It may then spread into the body and cause serious infections such as bacteraemia (blood poisoning). S. aureus can also cause food poisoning.

3. How is S. aureus infection treated?
Infections caused by many varieties of S. aureus are easily treated with antibiotics such as some types of penicillin and erythromycin.

4. What is MRSA?
MRSA stands for meticillin-resistant Staphylococcus aureus. It is a variety of S. aureus that is resistant to meticillin (a type of penicillin) and to some of the other antibiotics that are usually used to treat infections caused by S. aureus.

5. Is MRSA treatable?
MRSA is no more virulent than other varieties of S. aureus, but it is much more difficult to treat because the range of antibiotics which are effective against it is reduced.

6. Who is at risk of MRSA infection?
MRSA is one of the most prevalent micro-organisms involved with healthcare-associated infections. It is usually confined to hospitals and in particular to vulnerable or debilitated patients. These include patients in intensive care units, and on surgical or orthopaedic wards. Some nursing homes have experienced problems with this bacterium. MRSA does not pose a risk to hospital staff (unless they are suffering from a debilitating disease) or family members of an affected patient or their close social or work contacts.

7. How are human and animal S. aureus strains related?
Animal and human strains of S. aureus are usually different and are particularly adapted to colonising and/or infecting their preferred host species. For example, the staphylococci that commonly infect and colonise dogs are usually from a different species, known as Staphylococcus intermedius, which differs in certain characteristics from S. aureus. Although strains of S. aureus may have a preferred host species, they may opportunistically infect other species in some circumstances.

8. When was MRSA first detected in animals in the UK?
There have been recent reports of MRSA in animals in the UK in both the popular media and in the scientific press. These recent UK reports all date from 1999 or later. There is an earlier report of the isolation of MRSA from a cat resident on a rehabilitation ward for the elderly in the mid-1980’s. MRSA was isolated from the paws and back of the cat, but sampling of the carpet and ledges of the ward revealed them to be heavily contaminated with MRSA as well. Isolation from the cat was perhaps therefore unsurprising.

9. What species of animals are affected?
In the UK, since 1999, there are published reports that MRSA has been isolated from dogs, cats and from a rabbit and a horse.

10. Are there any reports of MRSA in animals from other countries?
In previous years MRSA has been recovered from a number of different animal species and from a number of different parts of the world. The animal species involved include dogs (USA, Korea and the Netherlands), pigs (Netherlands), horses (USA and Japan), dairy cows and chickens (Korea) and cats (Brazil). Some early reports of MRSA in animals in the scientific literature (pre-1980) did not use molecular techniques to confirm definitively the identity of the suspect MRSA organisms and these reports may not be comparable with current reports.

11. Is MRSA increasing in prevalence in companion animals in the UK?
Some of the reports in the scientific literature report an apparent increase in MRSA infections in companion animals in the UK. In general, these reports relate to series of clinical cases or clinical veterinary diagnostic material and good baseline data to assess how the position may be evolving is currently limited. A recent review of the literature on MRSA in dogs and cats concluded that a number of studies indicate that MRSA isolates from animals are uncommon.

12. What is the source of animal MRSA isolates?
The available evidence suggests that humans are likely to be the source of MRSA strains infecting or colonizing animals. The increasing prevalence of MRSA in the human population appears to be spilling over into other environmental niches that MRSA is able to inhabit. The source of MRSA infections in animals has been speculated on in several reports in the scientific literature. In an outbreak of MRSA infection in horses at a veterinary teaching hospital in the USA, the human attendants were considered to be the likely source of the infection. In another incident a dog colonised with MRSA was thought to have contracted the organism from its owners.

13. What are the main reservoir species of MRSA?
The main species colonised by MRSA is man and man forms the principal reservoir of this organism. However, in some circumstances other animals can be colonised by MRSA and in some instances the organism has caused disease in animals. Animals colonised or infected with MRSA form a potential reservoir that could re-infect human contacts. The duration and degree of colonisation of animals has not been well-described. Companion animals carrying or infected with MRSA could be regarded as equivalent in risk to human carriers or patients infected with the organism. The advice from HPA regarding human carriers or infected patients is that MRSA does not pose a risk to hospital staff (unless they are suffering from a debilitating disease) or family members of an affected patient or their close social or work contacts.

14. Are food-producing animals a reservoir of MRSA?
There is no current evidence that food-producing animals form a reservoir of MRSA infection in the UK. MRSA infection has not been detected in farmed livestock in the UK. The Veterinary Laboratories Agency recently began testing S. aureus isolates from clinical material submitted from cattle for MRSA. None have been detected.

15. What are the infections caused by MRSA in animals?
Most MRSA infections in dogs and cats in the UK have been post-operative infections or wound infections. There have been lower numbers of skin, ear, urinary tract and bronchial infections.

16. What are the implications for animal health of these findings?
Clinical disease caused by MRSA infection in animals appears to remain rare, with only low numbers of cases reported worldwide. Treatment of serious MRSA infections in animals with antimicrobials faces similar difficulties to those encountered in human medicine, because of the extensive resistance to antimicrobials shown by this organism. The British Small Animal Veterinary Association have prepared a review article discussing MRSA in companion animals and this was recently published in the Journal of Small Animal Practice..

17. What are the implications for public health of these findings?
Companion animals if colonised or infected with MRSA will provide another potential source of the organism from which spread might occur. The advice of the HPA regarding colonised and infected people applies equally well to infected or colonised companion animals. This advice is that MRSA does not pose a risk to hospital staff (unless they are suffering from a debilitating disease) or family members of an affected patient or their close social or work contacts. The current view of Defra and the Department of Health is that animals are likely to be infected as the result of contact with colonised or infected humans.

18. What is PVL S. aureus?
PVL stands for Panton-Valentine Leukocidin. PVL is a toxin that can be produced by particular MRSA and meticillin-sensitive strains of S. aureus and is associated with increased ability to cause disease. More information about PVL and S. aureus is available on the Health Protection Agency website.

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.

19. What steps are being taken to monitor and investigate the situation?
Defra is liaising closely with other interested parties involved in monitoring and investigating the occurrence of MRSA in animals, including the University Veterinary Schools as well as the relevant agencies and departments with responsibility for public health. Consultation with these expert bodies will assist in further assessing the implications of the emergence of MRSA in animals and in devising possible measures to counter any deleterious effects.

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.

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.

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 and Emerging Issues Division with provision of advice from the VLA expert on Antimicrobial Resistance. The Division liases 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 five meetings of this MRSA subgroup, the most recent taking place in January 2007.

Organisations represented on the DARC MRSA subgroup include:
Animal Health and Welfare Directorate General, Defra
Veterinary Laboratories Agency
Health Protection Agency
Department of Health
Food Standards Agency
University of Liverpool
Royal Veterinary College
British Small Animal Veterinary Association
British Veterinary Association
Bella Moss Foundation

MRSA links:
British Small Animal Veterinary Association guidance on MRSA
Information on MRSA from the Health Protection Agency
Bella Moss Foundation
Defra’s background information on antimicrobial resistance
DARC Group home page, hosted by the Veterinary Medicines Directorate
Simple guide to MRSA from the Department of Health

http://www.defra.gov.uk/animalh/diseases/zoonoses/mrsa.htm
Page last modified: 1 March, 2007