JPC SYSTEMIC PATHOLOGY
Signalment (JPC 21474-7,-8): 1-year-old, breed not specified, dog
HISTORY: This dog from Texas had a severe, ulcerative dermatitis involving the legs.
HISTOPATHOLOGIC DESCRIPTION: Haired skin: Multifocally obscuring the dermis, separating and surrounding collagen fibers and adnexal structures, infiltrating the subcutis and extending to all borders are coalescing, disorganized nodules composed of a core of cellular debris, fibrin and drop-out (lytic necrosis) centered on faint, negative images of 6-10µm hyphae with nonparallel walls, and poorly discernible, irregularly angled, non-dichotamous branching. Hyphae are surrounded by numerous degenerate and fewer viable neutrophils, epithelioid macrophages, fewer multinucleated giant cells (foreign body and Langhans types), and low numbers of eosinophils, plasma cells and lymphocytes. Inflammatory nodules are admixed with abundant hemorrhage, fibrin, hemosiderin-laden macrophages that often exhibit erythrophagocytosis, and colonies of 1-2um basophilic cocci. Separating nodules of inflammation there are numerous reactive fibroblasts and loose fibrous connective tissue with perpendicularly arranged small caliber blood vessels (granulation tissue), progressing to more mature fibrosis. Focally the wall of a large blood vessel is discontinuous with loss of endothelial cells and replacement by eosinophilic cellular and karyorrhectic debris and few previously described inflammatory cells (necrotizing vasculitis), and is partially occluded by a large fibrin thrombus. Small vessels are often lined by reactive endothelial cells and are variably occluded by moderate amounts of fine to coarse fibrin with enmeshed erythrocytes and few inflammatory cells (fibrin thrombi).
Gridley’s stain: Hyphae are 6-10µm (occasionally up to 15µm) wide, rarely septate, with irregularly angled, non-dichotamous branching and thick, unevenly stained, non-parallel walls.
MORPHOLOGIC DIAGNOSIS: Haired skin and subcutis: Dermatitis and panniculitis, pyogranulomatous and eosinophilic, multifocal to coalescing, severe, with hyphae, hemorrhage, fibrin thrombi, necrotizing vasculitis, and fibrosis, breed not specified, canine.
ETIOLOGIC DIAGNOSIS: Cutaneous pythiosis
CAUSE: Pythium insidiosum
CONDITION: Oomycosis (formerly phycomycosis)
- Pythium is a fungal-like aquatic oomycete
- insidiosum is the only Pythiaceae recognized as pathogenic in mammals
- Differences from true fungi: Motile, bi-flagellate zoospores; cell walls contain cellulose and beta-glucan but lack chitin; nuclear division, mitochondria and Golgi structures; plasma membranes lack sterols (ergosterol)
- Cutaneous, enteric or multisystemic granulomatous disease primarily in horses (cutaneous), dogs (enteric) and humans; sporadic reports in multitude of other species
- Requires contact with stagnant water and tissue trauma by aquatic plants or vegetation
- Found globally in tropical to sub-tropical regions and is expanding; more common in Gulf states in the U.S. though reported in others
- Equine disease was formerly referred to as bursatii, Florida horse leeches, granular dermatitis, hyphomycosis, destruens equi, phycomycosis, phycomycotic granuloma and swamp cancer
- Not transmissible
- Infectious motile zoospores demonstrate chemotactic preference for damaged plant and animal tissue
- Encysts on tissue and attaches by membrane glycoprotein
- Develops germ tube toward affected tissue, penetration and invasion of dermis and blood vessels aided by secreted proteases
- Causes eosinophilic granulomatous inflammation which forms ulcerative nodules with draining tracts
TYPICAL CLINICAL FINDINGS:
- Enteric form more common in dogs; likely no predispositions, but seen in young, immunocompetent animals most commonly; exposure to wet environments
- Cutaneous signs:
- Lesions found anywhere but most common on distal extremities, ventral abdomen and chest, face and tail head
- Lesion is intensely pruritic and self-mutilation can be severe
- Local inflammation, lameness
- +/- lymphadenopathy and peripheral eosinophilia
- Gastrointestinal signs:
- Anorexia, weight loss, diarrhea, vomiting, dysphagia, palpable abdominal mass, mesenteric lymphadenopathy
- Stomach and duodenum most common sites; invasion to pancreas, mesenteric lymph nodes or bile ducts possible
- Peripheral absolute eosinophilia
TYPICAL GROSS FINDINGS:
- Cutaneous form (limbs; distal to carpus and hock is most common and ventral thorax and abdomen, tail head)
- Rapidly progresses from poorly circumscribed nodule to multiple ulcerative nodules with fistulous tracts draining purulent exudates
- Characteristic gray-white to pale yellow coral-like concretions found in sinus tracts and may extrude from skin surface, unique to horses, known as “kunkers”
- Two patterns:
- Necro-eosinophilic: broad zones of eosinophilic necrosis, cell debris, and variable numbers of eosinophils
- Granulomatous: epithelioid macrophages and Langerhans giant cells surrounded by connective tissue
- Enteric form
- Segmental thickening of GIT (anywhere) with irregular mucosal ulceration
- Transmural granulomatous inflammation +/- perforation with granulomatous peritonitis, +/- omental adhesions, +/- obstruction/infarction
- Enlarged mesenteric lymph nodes, thickened lymphovascular channels
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- Granulomatous to pyogranulomatous lesions consisting of necrotic foci with neutrophils, eosinophils, epithelioid macrophages, plasma cell and multinucleated giant cell infiltrates and fibrosis
- Difficult to see hyphae on H&E, may see clear spaces outlined by eosinophilic material
- Large focal eosinophilic areas with necrotic eosinophils and neutrophils, collagenolysis and fungal hyphae within the necrotic core
- Hyphae surrounded by eosinophils; resembles a Splendore-Hoeppli reaction
- Irregularly branching, non-dichotamous, rarely septate hyphae with 2-9µm diameter nonparallel walls
ADDITIONAL DIAGNOSTIC TESTS:
- Difficult to impossible to distinguish from Lagenidium and Entomophthoromycosis (Basidiobolus and Conidiobolus) on histologic sections
- Staining: H&E, GMS, Gridley’s
- PCR, IHC, culture (lacks specificity)
- Serological assays (ELISA, immunoblot) – high sensitivity and specificity
- Hemagglutination test – sheep RBCs coated with insidiosum extract
- Infectious granulomas: Deep pyoderma, opportunistic mycobacterial infections, actinomycosis, nocardiosis
- Zygomycosis: Basidiobolus, Conidiobolus, Mucor
- Lagenidium (dogs)
- Fungal infections: Cryptococcosis, blastomycosis, histoplasmosis
- Demodicosis, habronemiasis
- Acral lick dermatitis
- Foreign body granulomas
- Idiopathic nodular dermatoses
- Neoplasia: Squamous cell carcinoma, equine sarcoid
- Horses (pythiosis also called Florida horse leech, bursattee swamp cancer)
- Predominantly cutaneous form - lesions on areas likely to touch water- lower limbs distal to carpus & hock (often circumferential), ventral abdomen, and chest that rarely disseminate to internal organs (may invade bone)
- Subcutaneous nodules or masses up to 45cm in diameter; ulcerated, scarred surface with multiple draining tracts; kunkers/leeches; often pruritic
- Less commonly, infection of the small intestine causes eosinophilic enteritis and granulomas and may result in colic
- Cattle - uncommonly in beef cattle <12 months old; predominantly cutaneous/subcutaneous form; lesions on lower limbs (do not form leeches/kunkers)
- Cats - rare; cutaneous/subcutaneous lesions affecting inguinal, tailhead, or periorbital regions; draining lesions on extremities; rare gastrointestinal pythiosis
- Sheep - predominantly cutaneous/subcutaneous form over limbs, abdomen, and prescapular regions with rare lung and lymph node dissemination; recent report of an outbreak of granulomatous rhinitis due to insidiosum
- Individual case reports in many other species
- do Carmo PM, Portela RA, Silva TR, et al. Cutaneous pythiosis in a goat. J Comp Pathol. 2015;152(2-3):103-5.
- Gaastra W, Lipman, LJ, De Cock AW, et. al. Pythium insidiosum: An Overview. Vet Microbiol. 2010;146:1-16.
- Mauldin EA, Peters-Kennedy, J. Integumentary system. In: Maxie MG. ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 1. 6th ed. Philadelphia, PA: Elsevier Saunders; 2015:657-659.
- Grooters AM, Foil CS: Miscellaneous fungal diseases. In: Greene CE ed. Infectious Diseases of the Dog and Cat. 4th ed. St. Louis, MO: Saunders Elsevier; 2012:677-681.
- Gross TL, Ihrke PJ, Walder EJ, et. al. Infectious nodular and diffuse granulomatous and pyogranulomatous diseases of the dermis. In: Skin Diseases of the Dog and Cat. 2nd ed. Oxford, UK: Blackwell Science; 2005:303-309.
- Maia LA, Olinda RG, Araújo TF, Firmino PR, et al Cutaneous pythiosis in a donkey (Equus asinus) in Brazil. J Vet Diagn Invest. 2016;28(4):436-9.
- Miller WH, Griffin CE, Campbell KL.: Fungal and algal skin diseases. In: Muller & Kirk’s Small Animal Dermatology. 7th ed. Philadelphia, PA: Saunders Co; 2012:257-259.
- Pesavento PA, Barr B, Riggs SM, et al. Cutaneous pythiosis in a nestling white-faced ibis. Vet Pathol. 2008;45(4):538-41.
- Souto EP, Maia LA, Olinda RG, et al. Pythiosis in the nasal cavity of horses [published online ahead of print July 9, 2016]. J Comp Pathol. 2016. pii: S0021-9975(16)30060-3. doi: 10.1016/j.jcpa.2016.06.005.