Introduction

• Inflammation of the hair follicle caused by Staphylococcal bacteria.
• Cause: Staphylococcus aureus Staphylococcus aureus Staphylococcus spp, S. intermedius, S. hyicus.
• Signs: papules, pustules, crusts, scales, nodules and annular areas of alopecia more commonly over the saddle and tack areas.
• Diagnosis: history, examination, cytology, bacterial culture, histopathology.
• Treatment: topical antibacterial agents, systemic antibiotics.
• Prognosis: good.

Pathogenesis

Etiology

• Staphylococcus aureus Staphylococcus aureus is the most common, followed by S. intermedius, and rarely S. hyicus.
• Less commonly coagulase-negative Staphylococci.
• Staphylococcus spp Staphylococcus spp are part of the normal skin flora but may also be opportunistic pathogens.

Predisposing factors

General

• Hot and humid environment.
• Frequent riding/heavy workload.
• High insect/tick population.
• Poorly maintained/muddy paddocks or stalls.
• Ill-fitting tack Saddlery: principles.
• Poorly groomed horses.
• Wounds.
• Immunosuppressive disease (PPID) Pituitary pars intermedia dysfunction (PPID).
• Allergies.

Pathophysiology

• Bacterial infection of the hair follicle secondary to cutaneous trauma.
• Advanced lesions may → rupture of the hair follicle (furunculosis) with corresponding dermal inflammation.
• Damage to skin, eg insect bite, trauma → staphylococcal bacteria invades and infects the hair follicle → small papule forms and overlying hairs may become erect → a pustule may arise from the papule, rupture and form a crust or → papule enlarges and may develop a central ulcer with purulent discharge → hair follicle may eventually rupture resulting in free hair shafts in the dermis (furunculosis) and an inflammatory foreign body reaction.
• Bacterial toxins may act as superantigens and trigger an immunologic response.

Epidemiology

• Can be spread via fomites, eg shared tack.

Diagnosis

Treatment

Prevention

Outcomes