Session #3004

Abstract

Pododermatitis is the most frequently encountered foot disease of captive raptors and it is a significant welfare concern. It is also the most common husbandry-related disease. Pododermatitis is rarely seen in free-living birds and consequently, management of cases frequently requires identification and correction of husbandry and environmental deficiencies that have causal roles in the condition. Pododermatitis can be simply defined as inflammation of the skin of the foot. In avian medicine it is considered a degenerative, inflammatory condition of the plantar surface of the foot, most commonly involving the plantar metatarsal pad or plantar digital pads. It is best considered a disease syndrome where disruption of the plantar epithelium allows microbial invasion and secondary infection. If not identified quickly and managed effectively, pododermatitis can progress and affect deeper tissues including tenosynovitis, osteomyelitis, and septic arthropathy. This masterclass describes causes, investigation, and treatment of pododermatitis in birds of prey.

Introduction

Falconiformes and Strigiformes represent a group of birds commonly referred to as birds of prey or raptors. The order of the Falconiformes comprises five families: Cathartidae, Pandionidae, Accipitridae, Sagittariidae, and Falconidae.

Pododermatitis is a condition commonly encountered in captive birds of prey, particularly the larger species.^1-3 Different etiologic factors have been proposed as responsible for the development of pododermatitis in birds of prey including increased body weight, inadequate perches, lack of exercise, sudden cessation of exercise, bruising of the plantar surface of the feet, unequal weight-bearing on one foot, overgrown talons, and inadequate diets.^1-4 Members of the Falconiformes, but in particular the gyrfalcon (Falco rusticolus) and saker falcon (Falco cherrug), are more likely to develop pododermatitis. Owls are the next most presented, with larger species (such as snowy owls [Bubo scandiacus]) particularly susceptible. Hawks and eagles have a significantly lower prevalence and typically only develop significant pododermatitis due to concurrent injury or significant husbandry limitations.

Clinical Examination

Initial diagnosis is made based on clinical examination and clinical history. Body condition score, general condition, and weight are important to note when assessing underlying causes of pododermatitis. It is worth also examining other birds from the collection to determine if the case is localized or a more general problem in the collection.

Differential diagnoses for pododermatitis include the following:

• Trauma (soft tissue, fracture, dislocations)
• Gout
• Septic arthropathy (hematologic spread)

With the majority of these conditions, there will not be disruption to the plantar skin, facilitating a diagnosis. These will need to be ruled out based on signalment, bloodwork, imaging, and cytology.

Diagnostic Tests

To determine whether infection has spread to underlying tissues and to differentiate the higher grades of pododermatitis (grades 3–5), imaging often will be required. Radiography or computed tomography (CT) imaging are best used to evaluate skeletal involvement (e.g., osteomyelitis). Imaging also is required to assess associated disease that could be contributing to uneven weight distribution and be an underlying cause of the pododermatitis (e.g., degenerative joint disease, previous misaligned fracture healing, metabolic bone disease, intra-abdominal disease causing sciatic nerve compression). Ultrasound, on the other hand, can be used to assess soft tissue structures (such as tendon sheaths and tendons), particularly in larger birds, although the scales may hinder proper visualization of the structures. Computed tomography or magnetic resonance imaging (MRI) also may be used to detect more subtle bone and soft tissue pathologies.

The author regularly collects clinical pathology samples from the lesions for cytology and/or culture. Cytologic samples should be stained with Gram stain as this can help with the selection of first-line antimicrobial therapy while awaiting culture results. Culture and sensitivity performed on a deep portion of the lesion or a piece of infected tissue will generally lead to the best results. Frequently, Staphylococcus aureus is isolated from lesions, although other bacteria (such as E. coli, Corynebacterium spp., Pseudomonas spp., and yeasts) are regularly cultured from the lesions.

A complete blood cell count (CBC) and biochemistry panel can be performed to identify concurrent diseases or predisposing factors (such as elevated uric acid with gout). In advanced stage of disease, there is frequently an elevated white blood cell count (WBC) with heterophilia. Fibrinogen also is elevated to boost clotting (hyperfibrinogenemia). Changes in the protein electrophoresis fractions may be seen with severe cases.

Grading Pododermatitis

Pododermatitis grades by identification characteristics, treatment options, and prognosis are presented in Table 1.

Table 1. Pododermatitis grades, treatment options, and prognosis

Representative photographs of pododermatitis grades 1–5 are presented in Figures 1–6.

Figure 1. Grade 1 pododermatitis

Figure 2. Grade 2 pododermatitis

Figure 3. Grade 3 pododermatitis

Figure 4. Grade 4 pododermatitis

Figure 5. Grade 5 pododermatitis

Figure 6. Radiographic changes in grade 5 pododermatitis

Treatment

Low grade (grade 1 or 2) pododermatitis is frequently managed with husbandry changes and topical therapies, with or without the addition of pressure-relieving dressings. Overall aims of this treatment are to:

• Provide analgesia
• Control swelling and inflammation
• Prevent formation of (further) necrotic tissue
• Prevent progression of pododermatitis to higher grade disease
• Prevent colonization of pathogens
• Promote granulation and healing (thus avoiding cytotoxic therapies)

Higher grade pododermatitis (i.e., grades 3–5) frequently requires more extensive therapy to be successful. Surgical intervention is often required and aims to:

• Debride necrotic and avascular tissues, and remove caseous material and pyogenic membranes
• Minimize disruption to the normal foot structure
• Allow primary closure, where possible; many cases will require healing by granulation and secondary intention
• Expedite healing and allow the limb to return to full function as soon as possible
• Prevent spread of infection into bone, tendons, tendon sheaths or joints

References

1.  Cooper J. Veterinary Aspects of Captive Birds of Prey. London, UK: Standfast Press; 1978.

2.  Degernes L, Talbot B, Mueller L. Raptor foot care. J Assoc Avian Vet. 1990;4(2):93.

3.  Cooper J. Foot conditions. In: Cooper JE, ed. Birds of Prey: Health and Disease. 1st ed. Oxford, UK: Blackwell Science; 2002:121–131.

4.  Zsivanovits P, Monks D. Bumblefoot (pododermatitis). In: Samour J, ed. Avian Medicine. 3rd ed. St Louis, MO: Elsevier; 2016:260–264.

5.  Samour J, Wernick M, Zsivanovits P. Therapeutic management of pododermatitis in falcon medicine: historical and modern perspective. Arch Vet Anim Sci. 2021;3(1):1–11.