Epidemiology and microbial characteristics of canine dermatological conditions in Australia

Background: Canine skin and ear dermatological conditions are common in veterinary medicine, complicated by pruritus and bacterial infections, requiring anti-pruritic and antimicrobial therapies. Environmental (ENV) and socio-economic (SE) factors can exacerbate pruritic behaviours, influencing incidence. Staphylococcus spp., particularly Staphylococcus pseudintermedius, are predominant pathogens in canine skin and ear infections and may be complicated by methicillin resistance, limiting treatment options. Additionally, dogs with dermatological conditions exhibit microbiota dysbiosis; however, the influence of methicillin-resistant Staphylococcus (MRS) and methicillin-sensitive Staphylococcus (MSS) nasal carriage on microbial diversity in affected dogs’ nares is limited. As MRS can complicate treatment outcomes and with the risk of transferring antimicrobial-resistant genes horizontally to other Staphylococcus spp., identifying genotypic diversity and monitoring emerging MRS and MSS sequence types is crucial to improving clinical resolution.

Aim and Objectives: This thesis investigated the epidemiology and microbial characteristics of canine skin and ear dermatological conditions. The objectives were to a) identify the spatial patterns and ENV and SE risk factors associated with the incidence of canine dermatological conditions Australia-wide (Chapter 3), b) identify the geographical associations between antimicrobial resistances from bacteria cultured from clinical canine skin and ear samples and use of antimicrobial and anti-pruritic therapy in Queensland (QLD) (Chapter 4), c) profile the nasal microbiota of shelter dogs in Brisbane, QLD with dermatological conditions carrying MRS and MSS (Chapter 5), and d) investigate the molecular epidemiology of Staphylococcus pseudintermedius, Staphylococcus coagulans and coagulase-negative staphylococci cultured from canine skin and ear infections in QLD (Chapter 6).

Methods: In Chapter 3, the VetCompass Australia database (2008 to 2017), containing consultations of canine dermatological conditions across Australia, was interrogated. The incidence per clinic postcode per year was identified and visualised overall. Quantification of the role of ENV, SE geographic remoteness factors on the incidence was conducted using Generalised Estimating Equations (GEEs) for QLD, New South Wales (NSW) and Victoria (VIC). For Chapter 4, a veterinary diagnostic laboratory dataset (bacterial antimicrobial resistance isolated from canine skin and ear infections) was overlapped with the VetCompass Australia dataset (antimicrobial and anti-pruritic therapy usage prescribed to dogs with dermatological conditions) from 2016 to 2017, using clinic postcode locations. Antimicrobial resistance and MDR in the bacterial pathogens, and the prescribed antimicrobial and anti-pruritic therapies were reported. Generalised linear mixed models (GLMMs) were used to identified postcode-level associations between antimicrobial and anti-pruritic therapy use with resistance to aminoglycosides, beta-lactams, fluoroquinolones and polymyxins. In Chapter 5, nasal samples from shelter dogs with and without dermatological conditions were sampled at baseline and follow-up during their shelter stay. All samples were cultured for Staphylococcus spp., and microbiota analyses were performed on 52 samples. Elastic net regression was used in a pilot framework to detect preliminary nasal microbial associations of dogs with dermatological conditions. In Chapter 6, Staphylococcus spp. from clinical canine skin and ear samples were collected from two QLD veterinary laboratories, which underwent whole-genome sequencing to identify sequence types (STs), resistance and virulence genes.

Results: In Chapter 3, mapping the incidence of canine dermatological conditions revealed sparse VetCompass Australia data across Australia, particularly in the central and western States/Territories, with clinics concentrated in major cities. GEE models for QLD, NSW and VIC identified ENV, SE and remoteness factors associated with the observed incidence. For Chapter 4, among all 2,873 isolates, 8.0% were MDR, with Pseudomonas aeruginosa (34.1%) and Staphylococcus spp. (27.7%) being frequently cultured. Of the 15,714 consultations, 38.8% involved antimicrobial prescriptions, 35.4% glucocorticoids and 8.7% oclacitinib. GLMMs identified no postcode-level associations between therapeutic use with resistance to the antimicrobial classes. In Chapter 5, MRS was consistently isolated during the dogs’ shelter stay. Dogs with dermatological conditions exhibited decreased microbial diversity, with varying microbial features identified at baseline and follow-up. For Chapter 6, isolates (n = 42) were predominantly MRSP (57.1%), then methicillin-sensitive S. pseudintermedius (19.1%), methicillin-resistant (14.3%) and -sensitive (2.4%) S. coagulans, and methicillin-resistant coagulase-negative staphylococci (7.1%). MRSP ST496 and ST749 in Australia were also commonly identified, along with three novel MRSP and six novel MSSP STs.

Conclusion: In summary, this thesis contributes to the understanding of canine dermatological conditions in Australia and highlights potential practical applications. The findings provide insights into the geographical distribution of dermatological conditions and skin and ear infections and associated risk factors, which may help guide treatment and control measures. Areas with a high incidence of dermatological conditions in dogs and increased antimicrobial resistance prevalence may benefit from enhanced surveillance, and support efforts to mitigate risks and improve canine healthcare with further research.

Read the full PhD thesis: 

Horsman, S. Epidemiology and microbial characteristics of canine dermatological conditions in Australia. 2026, PhD Thesis, School of Veterinary Science, The University of Queensland. https://doi.org/10.14264/13cbe00