Staphylococcus spp. continued
Staphylococcus aureus • Staphylococcus aureus is a cutaneous and mucocutaneous commensal in humans with approximately 30% of the human population thought to be asymptomatic carriers. 17 Three patterns of colonisation are recognised in humans: persistent colonisation, intermittent colonisation, and non-carriers. • Methicillin-resistant S. aureus (MRSA) is a significant and growing public health concern. Up to 3% of the general population may carry MRSA, predominantly in the nasal passages. Higher rates of carriage are reported in veterinarians, with a 5-fold higher prevalence in veterinarians working with dogs and cats than those with minimal animal contact. 18 • In humans, a range of presentations of MRSA infection may be seen. Localised infection is more common in people with underlying medical conditions – e.g. peripheral vascular disease or diabetes, and/or a history of hospitalisation. The strains causing this form of infection are usually hospital and long-term care facility associated strains (HA-MRSA). Sequence types ST22 and ST293 are the most prevalent in Australia. Invasive infection usually occurs when an MRSA colonised patient has an invasive procedure and sometimes follows cannulation and secondary line infection. Hence the focus of care is to reduce secondary complications of colonisation, using pre-operative decolonisation and prophylaxis and infection control management to prevent transmission in hospital. More recently, strains of MRSA causing recurrent localised and invasive infections in the community, have become more prevalent. These strains carry an associated virulence factor (PVL) which may enhance pyogenic potential. In Australia, ST93 is the most common. These strains may occur in patients without underlying diseases, including children, and are referred to as community-associated (CA-MRSA) strains. Decolonisation (e.g. using topical decolonisation with nasal mupirocin and chlorhexidine washes) is often used to prevent recurrent infection and intra-familial spread. • Isolation of S. aureus in healthy dogs is considerably less common than S. pseudintermedius . One study from rural
Victoria reported a prevalence of 14.5%, 4 with most of these animals having dual carriage with S. pseudintermedius. This study reported S. aureus isolation more commonly in female dogs. Another study in Australia reported a prevalence of 4.3% in dogs and 3.8% in cats in remote NSW. 5 Carriage of S. aureus in dogs may represent transient colonisation from cohabitating humans. In 50% of households where S. aureus was isolated from both dog and human, the strains were indistinguishable. 15 Interspecies transmission is evident, and although the direction of transfer is not certain, given the strains involved, this is likely to represent human-to- animal transmission. As with S. pseudintermedius, carriage of S. aureus is generally not associated with clinical signs, however opportunistic infections may occur. • MRSA carried by dogs are generally human adapted lineages. Several studies have failed to detect MRSA carriage in healthy urban pet dogs, while two studies in dogs from remote communities in NSW and WA have shown a carriage rate of 2.6%, with the sequence types isolated in dogs reflecting the prominent types present in the local human population. 9-11,19 The increased prevalence of MRSA carriage in these dogs likely reflects the comparatively high rate of carriage of MRSA among their owners. A study in healthy pet cats in Brisbane failed to detect MRSA. 9 • In other studies, being owned by human healthcare workers or being part of a hospital visitation program are risk factors for MRSA carriage in dogs, identifying that the carriage rate in pets reflects the prevalence in humans in their environment. • Most animals that carry MRSA have no clinical signs, however opportunistic infections may occur. MRSA infection is reported with increasing frequency in companion animals, and is associated with a range of different infections including skin and soft tissue infection, pneumonia, urinary tract infections, and surgical wound infections. Sequence types isolated often correspond to locally prevalent human strains. Nosocomial outbreaks are also reported. 20
ACAZAP RECOMMENDATIONS
dogs and cats may be a source of infection for humans. To reduce the risk of transmission, owners should minimise contact with areas most likely to harbour the organism, cover open wounds and practice good hand hygiene. • There are no validated methods for decolonisation of pets, and therefore this approach is not recommended. In most cases MRSA in dogs and cats will be a result of human-to-animal transmission and colonisation or carriage is likely to be transient. • Screening of dogs and cats for MRSA is generally not recommended, unless part of an overall strategy to manage recurrent MRSA in people. The clinical implications of carriage in pets may be low.
• Resistant skin infections in companion animals are more likely to be MRSP than MRSA, and while MRSP can be transmitted to humans (particularly if there are any predisposing risk factors such as breaks in the skin etc.) it is unlikely. To reduce risk of transmission, owners should minimise contact with areas most likely to harbour S. pseudintermedius (e.g. nose, mouth, or perineum), cover open wounds and practice good hand hygiene. • Dogs and cats are not primary reservoirs of S. aureus and colonisation is usually transient. The nose and perineum are high risk sites in pets. Colonisation will usually clear within a few weeks providing re-infection from a common source does not occur. Despite the generally transient nature of colonisation,
CONTENTS
Companion Animal Zoonoses Guidelines 11
Made with FlippingBook - professional solution for displaying marketing and sales documents online