JPC SYSTEMIC PATHOLOGY

INTEGUMENTARY SYSTEM

November 2022

I-P17 (NP)

 

Signalment (JPC# 2185344):  Spayed female, breed and age unspecified, dog

 

HISTORY:  This dog presented with rapidly spreading pruritic, ulcerative, and fistulous cutaneous lesions.

 

MICROSCOPIC DESCRIPTION:  Haired skin and subcutis: Focally extensively within the dermis and subcutis; surrounding, separating, and replacing collagen bundles and adipocytes; surrounding and separating adnexa; and elevating the multifocally eroded, ulcerated, or hyperplastic epidermis are dense infiltrates of neutrophils and macrophages with fewer lymphocytes, plasma cells, eosinophils, and reactive fibroblasts admixed with diffuse edema and scattered hemorrhage and fibrin. Moderate numbers of macrophages contain intracytoplasmic, 2x4µm, round to oval, protozoal tachyzoites that peripheralize the nucleus. Vascular endothelium is often reactive with variable numbers of macrophages and neutrophils within the tunica media and tunica adventitia (vasculitis). The epidermis is multifocally eroded and ulcerated with replacement by viable and degenerate neutrophils, serum and keratin debris (serocellular crust); in less affected areas, the epidermis is moderately hyperplastic characterized by acanthosis and spongiosis with few multifocal subcorneal pustules and a moderate parakeratotic hyperkeratosis. Hair follicles are lined by hyperplastic epithelium; occasionally the follicular epithelium and lumina is infiltrated by neutrophils (folliculitis) and infundibula are dilated and filled with abundant keratin debris (follicular keratosis). 

 

MORPHOLOGIC DIAGNOSIS:  Haired skin and subcutis: Dermatitis and panniculitis, neutrophilic and histiocytic, focally extensive, marked, with vasculitis, erosion and ulceration, and intrahistiocytic protozoal tachyzoites, breed not specified, canine.

 

ETIOLOGY:  Neospora caninum 

 

ETIOLOGIC DIAGNOSIS:  Cutaneous neosporosis

 

GENERAL

• Neospora is a cyst‑forming coccidian parasite in the phylum Apicomplexa (includes the genera Toxoplasma, Hammondia, Besnoitia, Isospora, Sarcocystis, and Frenkelia)
• Cutaneous form rarely seen in older immunosuppressed dogs, may represent recrudescence of juvenile infection or newly acquired infection
• Tissue cysts containing only tachyzoites; bradyzoites are NOT present in cutaneous disease

 

LIFE CYCLE

• Similar life cycle to that of Toxoplasma gondii (P-P01)
• Domestic and wild dogs - definitive host; can also be intermediate host
• Cattle, sheep, horses, goats, and deer  - intermediate hosts; infected by ingesting oocysts shed by the definitive host or, more commonly, transplacental transmission leading to abortion or subclinical congenital infection 
• Three infectious stages- tachyzoites and tissue cysts (intermediate and definitive hosts), and oocysts (only in definitive host)

 

PATHOGENESIS

• Dog – ingestion of tissues contaminated with tissue cysts, transplacental or postnatal infection (uncommon) > zoite penetration of cells > proliferation by endodyogeny as tachyzoites > encyst in CNS and other tissues as bradyzoites > fecal contamination with oocysts 
• Infected bitch - parasitemia develops during gestation with transplacental transmission to the fetus
• Pups may be subclinically infected with reactivation in later life associated with immunosuppressive illnesses, administration of modified live-virus vaccines, or glucocorticoids

 

TYPICAL CLINICAL FINDINGS

• Clinical disease is most commonly seen in puppies older than 5 weeks; infection in adults is typically subclinical
• Encephalomyelitis, polyradiculoneuritis, and polymyositis resulting in an ascending paralysis or posterior paresis
• Recent report of associated necrosuppurative, ulcerative colitis with intra- and extracellular protozoal zoites (Curtis, J Vet Diag Invest 2020)
• Abortion (ruminants, horses, dogs) – neonatal CNS disease or death

 

TYPICAL GROSS FINDINGS

• Multifocal to generalized, ulcerative papulonodular dermatitis; draining nodules or progressive lesions involving the eyelids, neck, thorax or perineum
• Acute disseminated infection
  • Liver - hepatomegaly with coalescing pale areas
  • Skeletal muscle - linear pallor; diaphragm - pale streaks of myonecrosis and fibrosis
  • Lungs - pulmonary congestion and edema

 

TYPICAL MICROSCOPIC FINDINGS

• Cutaneous lesions:  Dermatitis – pyogranulomatous, sometimes eosinophilic, necrotizing and hemorrhagic;
• Tachyzoites (4-7um x 1.5-5um), crescentic, pointed anterior end and rounded posterior end, within macrophages, neutrophils, keratinocytes, and rarely, endothelial cells and fibroblasts
• Other lesions:  Necrotizing, granulomatous, lymphoplasmacytic, occasionally eosinophilic meningoencephalomyelitis; myonecrosis; random, purulent and histiocytic hepatitis; pyogranulomatous and eosinophilic interstitial pneumonia

 

ULTRASTRUCTURE

• Tachyzoites- loosely arranged; free in the host cell cytoplasm or within a parasitophorous vacuole
• Moderately electron dense cytoplasm; single plasmalemma and double inner membrane complex; a conoid consisting of 2 microtubules arranged in a helix; 11 or more rhoptries; micronemes arranged perpendicular to the pellicle; organelles include a Golgi complex; smooth and rough endoplasmic reticulum; ribosomes; one or two mitochondria
• Tissue cyst wall - 1 to 4 um thick, amorphous, non-septate
• Bradyzoites - 3.5 x1 um; periodic acid-Schiff (PAS) positive 

 

ADDITIONAL DIAGNOSTIC TESTS

• IHC, electron microscope, or PCR to differentiate from Toxoplasmosis
• Cerebrospinal fluid analysis 
• Cytology: Mixed inflammation composed of macrophages, neutrophils, lymphocytes, plasma cells, and eosinophils with extra- and intracellular tachyzoites (1-5µm x 5-7µm, oval to crescent-shaped with central metachromatic nucleus and lightly basophilic cytoplasm); indistinguishable from T. gondii tachyzoites; in acute disseminated disease, tachyzoites found in pleural or peritoneal fluid, CSF, blood, tissue aspirates, and bronchoalveolar lavage fluid

 

DIFFERENTIAL DIAGNOSIS

Gross 

• Similar to Toxoplasma gondii in all lesions (can also be in follicular, epidermal, and glandular epithelial cells)
• Caryospora spp.- pyogranulomatous dermatitis in puppies; immunosuppression and concurrent disease likely play a role; schizonts, gamonts, oocysts, and caryocysts in macrophages; caryocysts- thin cell wall enclosing host cell nucleus and up to 3 sporozoites
• Unidentified Sarcocystis-like protozoa: multiple cutaneous abscesses and disseminated visceral lesions; diffuse necrohemorrhagic and suppurative dermatitis; protozoa in macrophages, neutrophils, and occasionally endothelial cells and fibroblasts; +/- thrombi with epidermal and dermal infarction

Microscopic 

• T. gondii - cysts in numerous tissues; thin (£ 0.5 um) walls; zoites have few rhoptries; always within a parasitophorous vacuole
• N. caninum (this entity)- cysts observed only within CNS, retina, and muscles (tachyzoites in other tissues); up to 107um in diameter, 1‑4 um thick walls; zoites 
• Sarcocystis - cysts primarily in cardiac and skeletal muscle or in neural tissue, of herbivores; do not have rhoptries; not within parasitophorous vacuoles

 

COMPARATIVE PATHOLOGY

• Abortion – dairy and beef cattle (3-9 months of gestation), no gross lesions; sheep and goats (experimentally, natural disease is rare), horses, and dogs
  1. Almost pathognomonic CNS lesion in bovine fetuses is multifocal discrete foci of necrosis, ~100-300um in diameter, with clusters of microglial cells and zoites in or around these foci in the brain and spinal cord
• Mammals that may become naturally infected with disseminated Neospora include dogs, cats, cattle, horses, and deer
• Experimental infections – sheep, goats
• Red fox- report of concurrent cutaneous N. caninum and Toxoplasma gondii infection; severe hyperplastic dermatitis with parakeratosis, keratinocyte necrosis, extensive dermal necrosis, mineralization
• Pet and aviary birds- muscle cysts

 

REFERENCES

1. Boes KM. Respiratory System. In: Canine and Feline Cytology: A Color Atlas and Interpretation Guide, 4^rd ed. Raskin RE, Meyer, DJ, and Boes KM, eds. St. Louis, MO: Elsevier; 2023:224. 
2. Cantile C and Youssef S. Nervous System. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 1. 6th ed. Philadelphia, PA:Elsevier; 2016: 387-388. 
3. Curtis B, Harris A, Ullal T, et al. Disseminated Neospora caninum infection in a dog with severe colitis. J Vet Diag Invest. 2020;32(6):923-927.
4. Foster RA and Premanandan C. Female Reproductive System and Mammae. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 7th ed., St. Louis, MO: Elsevier; 2022: 1295.
5. Keel MK, Terio KA, and McAloose D. Canidae, Ursidae, and Ailuridae. In: Terio KA, McAloose D, and St. Leger J, eds. Pathology of Wildlife and Zoo Animals. San Diego, CA: Elsevier; 2018: 252.
6. Lane LV, Yang PJ, and Cowell RL. Selected Infectious Agents. In: Valenciano AC and Cowell RL, eds. Cowell and Tyler’s Diagnostic Cytology and Hematology of the Dog and Cat. 5^th ed. St. Louis, MO: Elsevier; 2020: 56. 
7. Mauldin A and, 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; 2016:664-665.
8. Schmidt RE, Reavill DR, and Phalen DN. Pathology of Pet and Aviary Birds. 2^nd ed. Ames, IA: Joh Wiley & Sons, Inc.; 2015: 204-205. 
9. Staton JB and Zachary JF. Mechanisms of Microbial Infections. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 7th ed., St. Louis, MO: Elsevier; 2022:289.

 

 

Click the slide to view.

---