Diagnosis and therapeutic management of staphylococcal dermatitis in a sheep: A case report

Introduction

Skin disorders are frequently diagnosed in sheep and represent an important health concern in small-ruminant practice. These conditions can lead to economic losses by reducing growth performance, lowering wool quality, increasing treatment costs and affecting the overall welfare of the animals. A wide range of factors may contribute to the development of dermatological lesions, including ectoparasites, bacterial and fungal infections, nutritional imbalances, environmental influences and disorders of the immune system. Among the bacterial agents, Staphylococcus aureus is considered a significant opportunistic pathogen that commonly infects damaged skin, resulting in conditions such as pyoderma, folliculitis, furunculosis, pustular dermatitis, cutaneous abscesses and exudative dermatitis in domestic animals (Foster, 2012; Quinn et al., 2016) [2,6] . Staphylococcus aureus is an opportunistic pathogen equipped with several virulence determinants, such as coagulase, hemolysins, exfoliative toxins, adhesins, proteolytic enzymes and the ability to produce biofilms. These characteristics enhance its capacity to adhere to damaged tissues, evade host defenses, invade the skin and establish persistent infections (Lowy, 1998) [3] . Infection generally occurs when the integrity of the skin barrier is compromised by mechanical injury, prolonged moisture, ectoparasite infestation, environmental stressors or inadequate hygiene and management practices (Bath et al., 2011) [1] . In recent years, the emergence of antimicrobial-resistant Staphylococcus isolates from livestock has become an increasing concern, underscoring the importance of bacterial culture and antimicrobial susceptibility testing for selecting effective treatment protocols (Wesołowska et al., 2023) [9] . The present case report describes the clinical findings, laboratory confirmation through bacteriological isolation, antimicrobial susceptibility pattern and successful treatment of naturally occurring staphylococcal dermatitis in a sheep.

Case History and Clinical Examination

A 14-month-old female sheep weighing approximately 14.8 kg was presented to the Veterinary Clinical Complex with extensive cutaneous lesions that had progressively worsened over a period of 15 days. According to the owner, the lesions first appeared as small moist patches over the hindquarters and gradually spread to adjacent areas. The animal had not received recent vaccination or deworming. On physical examination, the sheep was mildly febrile (103.5°F) with a heart rate of 118 beats/min and a respiratory rate of 11 breaths/min. Mild enlargement of the prescapular lymph nodes were also noted. Dermatological examination revealed multiple exudative lesions involving the thigh and mammary regions. The affected skin showed patchy alopecia, erythema, superficial erosions, ulceration, serous discharge, crusting, localized thickening and areas of hyperpigmentation. The lesions were largely non-pruritic and varied from focal to multifocal in distribution. Based on the clinical presentation, bacterial dermatitis was considered the primary tentative diagnosis.

Materials and Methods

Deep skin scrapings were collected aseptically from the active margins of skin lesions and examined microscopically following 10% potassium hydroxide (KOH) digestion to exclude ectoparasitic and fungal involvement (Scott et al., 2013; Moriello, 2014) [, 5] . Sterile swabs collected from active lesions were transported under chilled conditions and cultured on 5% Sheep Blood Agar and Mannitol Salt Agar (MSA). The inoculated plates were incubated aerobically at 37°C for 24-48 h and examined for bacterial growth and colony characteristics. Bacterial isolates were identified based on colony morphology, Gram staining and standard biochemical tests, including catalase, coagulase, and mannitol fermentation tests. Identification was performed according to standard Veterinary microbiological procedures described by Quinn et al. (2016) [6] . Antimicrobial susceptibility testing (AST) was performed using the Kirby-Bauer disc diffusion method on Mueller-Hinton Agar following Clinical and Laboratory Standards Institute (CLSI) guidelines (CLSI, 2024). The susceptibility profile was used to guide antimicrobial therapy.

Results

Microscopic examination of deep skin scrapings was negative for mites, fungal hyphae, and dermatophyte spores, thereby ruling out parasitic mange and dermatophytosis.

Bacteriological culture of lesion swabs yielded pure growth of smooth, circular, convex, opaque, creamy-to-golden yellow colonies on 5% Sheep Blood Agar. On Mannitol Salt Agar, characteristic yellow colonies surrounded by zones of mannitol fermentation were observed. Gram staining revealed Gram-positive cocci arranged in grape-like clusters. The isolates were catalase-positive, coagulase-positive and mannitol fermenting, confirming their identity as Staphylococcus aureus (Quinn et al., 2016) [6] . Antimicrobial susceptibility testing demonstrated a favorable susceptibility profile with the isolate showing sensitivity to the antimicrobial selected for treatment. The AST results enabled evidence-based antimicrobial selection and contributed to the successful clinical management and recovery of the animal.

Treatment and Outcome

Based on the antimicrobial susceptibility profile, the animal was treated with Ceftriaxone administered intramuscularly at a dose rate of 15 mg/kg body weight once daily for five consecutive days. Supportive therapy included meloxicam (0.5 mg/kg body weight, IM) for three days to alleviate inflammation and discomfort, along with antihistaminic medication. The affected skin was gently cleansed with povidone-iodine solution at regular intervals to reduce surface bacterial contamination and facilitate wound healing.

In addition, the owner was advised to improve housing hygiene and maintain a clean, dry environment throughout the treatment period. A noticeable clinical response was observed within one week of therapy, characterized by reduction in erythema, exudation and lesion severity. Progressive drying of the lesions, regression of crust formation and re-epithelialization of the affected areas were evident during subsequent examinations. By the second week, marked improvement in skin integrity accompanied by initiation of hair regrowth was observed. Complete resolution of the dermatitis, with restoration of normal skin architecture and hair coat, was achieved within three weeks. No recurrence of lesions was recorded during the follow-up period, indicating a favourable therapeutic outcome.

Discussion

Dermatitis caused by Staphylococcus aureus represents an important but often under reported dermatological condition in sheep. The organism is considered an opportunistic pathogen capable of exploiting breaches in the cutaneous barrier and establishing infection through a variety of virulence mechanisms (Lowy, 1998; Foster, 2012) [3,2] . The production of coagulase, homolysis, proteases, exfoliative toxins, and biofilm-associated factors facilitates tissue invasion, epidermal destruction and persistent inflammation. The clinical findings observed in the present case including alopecia, moist dermatitis, crust formation, hyperpigmentation and epidermal erosions are consistent with previous descriptions of ovine staphylococcal dermatitis (Bath et al., 2011; Foster, 2012) [1,2] . Similar lesion characteristics have been reported in sheep affected by pyogenic dermatitis and staphylococcal skin infections in which S. aureus was recovered as the predominant bacterial pathogen (Roccaro et al., 2018) [7] . The absence of mites and fungal elements in skin scrapings strengthened the diagnostic significance of the bacteriological findings. Differential diagnoses considered included dermatophytosis, parasitic mange, dermatophilosis, photosensitization, zinc-responsive dermatosis and ectoparasitic dermatitis. Laboratory confirmation was therefore essential for establishing an accurate diagnosis. Isolation of coagulase-positive S. aureus in pure culture from active lesions strongly supports its etiological role in the present case. Similar observations have been reported by Bath et al. (2011) [1] , who demonstrated the importance of S. aureus as a significant pathogen associated with ovine dermatitis. Antimicrobial resistance among livestock-associated staphylococci is increasingly recognized as a global veterinary and public health concern (Wesołowska et al., 2023) [9] . Consequently, empirical antimicrobial therapy may result in treatment failure and contribute to the emergence of resistant strains. Culture-guided antimicrobial therapy based on susceptibility testing is therefore recommended to ensure therapeutic success while promoting antimicrobial stewardship. The favourable clinical response observed in the present case highlights the importance of integrating microbiological diagnosis, antimicrobial susceptibility testing and supportive dermatological management for successful treatment outcomes.

Conclusion

The present report documents a laboratory-confirmed case of staphylococcal dermatitis in a sheep successfully managed through culture-guided antimicrobial therapy. Isolation and identification of Staphylococcus aureus, coupled with antimicrobial susceptibility testing, enabled definitive diagnosis and effective therapeutic intervention. Routine bacteriological investigation and susceptibility profiling should be considered in cases of ovine dermatitis to improve treatment outcomes and support prudent antimicrobial use.

References

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