JPC SYSTEMIC PATHOLOGY

INTEGUMENTARY SYSTEM

November 2022

I-P14

 

Signalment (JPC# 1957380):  18-month old Nguni bull

 

HISTORY:  Two out of 10 cattle had alopecia with chronic skin lesions. Skin scrapings were negative for parasites, and weekly dipping had no effect on the lesions.

 

HISTOPATHOLOGIC DESCRIPTION:  Haired skin: Multifocally expanding the superficial dermis and to a lesser extent the deep dermis are numerous, round to ovoid, up to 400µm protozoal tissue cysts that compress adjacent dermal collagen and adnexa. Tissue cysts have 30µm thick, pale eosinophilic, bilayered, outer and inner cell walls that surround a 10µm rim of compressed host cell cytoplasm with multiple enlarged nuclei and a large, 250µm, intracytoplasmic, parasitophorous vacuole that compresses the rim of host cytoplasm and contains numerous, densely packed, crescentic-shaped, 3-5µm bradyzoites. Multifocally surrounding the tissue cysts are low numbers of macrophages, lymphocytes, plasma cells, and fewer eosinophils as well as increased mature dermal collagen (fibrosis). The overlying epidermis is mildly hyperplastic with rete ridges and moderate orthokeratotic hyperkeratosis. 

 

MORPHOLOGIC DIAGNOSIS:  Haired skin: Dermatitis, histiocytic and eosinophilic, multifocal, moderate, with numerous protozoal cysts, Nguni, bovine.

 

ETIOLOGIC DIAGNOSIS:  Cutaneous besnoitiosis  

 

CAUSE:  Besnoitia besnoiti

 

CONDITION: Besnoitiosis

 

SYNONYMS:  Globidiosis, elephant skin disease

 

GENERAL DISCUSSION: 

• Besnoitia sp.: Host-specific coccidian parasite of family Sarcocystidae, phylum Apicomplexa with worldwide distribution in wild and domestic animals
• Besnoitia besnoiti is an emerging disease of cattle in Europe and in donkeys (typically young) in US; it is enzootic in cattle in Africa and Asia where it is of high economic importance, causing up to 80% morbidity and 10% mortality

 

PATHOGENESIS:

• Acute stage: Tachyzoites proliferate within vascular endothelial cells, monocytes, and neutrophils; clinical signs and lesions are mainly associated with vascular lesions (e.g. vasculitis, thrombosis)
• Subacute and chronic stage: Bradyzoite proliferation occurs within mesenchymal host cells resulting in enlargement of the host cell, multiple hypertrophied nuclei, enlargement of parasitophorous vacuole, formation of inner cyst wall, and eventual formation of outer cyst wall in a variety of tissues

 

LIFE CYCLE:  

• Life cycle of only four of 10 species is understood; pathogenesis, life cycle, and route of infection are poorly understood for the four Besnoitia spp. that affect ungulates
• Two-host life cycle:  Definitive carnivore host and an intermediate herbivore host
  • 4 days to 4 weeks prepatent period in definitive host
  • 1-3 weeks from ingestion by intermediate host to tissue cysts
• Definitive host (carnivore) ingests intermediate host tissue containing cysts > bradyzoites released in gastrointestinal tract and invade enterocytes and endothelial cells > merogony > merozoites enter enterocytes and develop into male or female gamonts (gametogony) > in situ fertilization of female > oocysts within enterocyte > enterocyte rupture > oocysts in feces > infection of intermediate host (herbivore) by sporulated oocyst via undetermined mode > sporozoites excyst > penetrate host tissues > merogony > tachyzoites proliferate in macrophages, fibroblasts, and endothelial cells with possible vasculitis and thrombosis > develop into bradyzoites in tissue cysts 
  • Exact mode of infection of intermediate host is not known, but ingestion of contaminated feces and mechanical transmission via direct contact, insects, or inanimate vectors between intermediate hosts are regarded as important natural modes

 

TYPICAL CLINICAL FINDINGS:

• Acute stage: Fever, generalized edema, weakness, anorexia, lymphadenopathy, abortion, orchitis/sterility; can be confused with bluetongue or MCF in acute stage
• Chronic stage (most often recognized during this stage): Alopecia, marked thickening and folding of the skin (neck, shoulders, rump), scaling, exudation, fissuring, decreased milk production, loss of body condition, permanent sterility in males, significant hide damage, up to 10% mortality

 

TYPICAL GROSS FINDINGS:  

• Firm cysts most concentrated around mucous membranes (nares, conjunctiva, vulva, perineum) and sclera (“scleral pearls”) but also occur commonly in dermis, subcutis, fascia, muscles, epididymis, testes, mucosa of pharynx, larynx, and trachea; less commonly in spleen, liver, lung, lymph nodes, periosteum, endosteum, and heart muscle
• Alopecia with thickening, exudation, and fissuring of skin; subcutaneous edema; generalized lymphadenopathy

 

TYPICAL LIGHT MICROSCOPIC FINDINGS:

• Acute stage: 
  • Tachyzoites proliferate in macrophages, fibrobasts, and endothelial cells; in cattle, rarely free in tissue spaces, arterioles and lymphatics; 
  • Tachyzoites are crescent-shaped with eosinophilic cytoplasm and round basophilic nucleus 
  • Vasculitis, thrombosis, dermal and epidermal necrosis
• Subacute stage: Early tissue cysts consist of hypertrophied host cells with eosinophilic cytoplasm and with enlarged nucleus; host cell surrounded by thin, circular, gray-bluish layer with irregular, lacerated borders (inner cyst wall)
• Chronic stage: The principle distinguishing morphologic characteristic is the large, bradyzoite-filled cyst (tissue cyst) that occurs in the connective tissues and sometimes within blood vessels (cattle and goats); these tissue cysts represent parasitized host cells (e.g., fibroblasts, myofibroblasts, endothelial cells, smooth muscle cells); there is little or no inflammatory reaction to intact cysts but granulomatous inflammation when cyst ruptures; tissue cysts surround the host cell, are 150-500um wide with 10-50um thick wall composed of 4 layers that are (from outside to inside):
  • Outer cell wall: Condensed, hyalinzed, laminated, eosinophilic to amphophilic collagen type I fibers
  • Inner cell wall: Elements of extracellular matrix
  • Small rim of host cell cytoplasm with flattened nuclei
  • Thin inner membrane forming large parasitophorous vacuole filled with myriad tightly-packed crescentic bradyzoites

 

ULTRASTRUCTURAL FINDINGS:  

• Typical apicomplexan organelles: Micronemes, rhoptries, conoid
• Bradyzoites within a parasitophorous vacuole

 

ADDITIONAL DIAGNOSTIC TESTS:  

• Giemsa & PAS positive
• Flourescent antibody test and immunoblot for bradyzoites and tachyzoites
• PCR has superior sensitivity in the acutely affected animal
• Anti-besnoitia IHC for bradyzoites and tachyzoites in acute stage
• Scleral conjunctival scraping

 

DIFFERENTIAL DIAGNOSIS:

• Hyperkeratotic and alopecic skin lesions in cattle:
  • Dermatophilus congolensis (I-B01):  Gram positive cocci; proliferative, exudative dermatitis of the dorsal midline that mats hair together
  • Dermatophytosis (I-F11):  Common fungal skin infection; usual etiology Trichophytum verrucosum; circular crusty lesion of the head, neck, dewlap
  • Lumpy skin disease:  Africa; caused by a capripoxvirus, (eosinophilic intracytoplasmic inclusion bodies); firm, flat, well circumscribed lesions of the neck, back, chest, legs, udder, scrotum, perineum
  • Demodex bovix, D. ghanensis (I-P07)
• Vasculitis, fever in cattle:
  • Bluetongue virus (D-V16)
  • Malignant catarrhal fever virus (D-V15, S-V01)

 

 

COMPARATIVE PATHOLOGY:

Intermediate Host	Besnoitia spp.	Definitive Host
Cattle	B. besnoiti	Unknown
Equids	B. bennetti	Unknown
Goats, sheep	B. caprae	Unknown
Reindeer, caribou	B. tarandi	Unknown
Rabbits	B. oryctofelis	Feline
N. American opossums	B. darlingi	Feline
Southern plain woodrat	B. neotomofelis	Feline
Rodents	B. wallacei	Feline

 

• Besnoitia sp. affects horses, zebra, and mules in Africa
• B. caprae in goats has only been reported in Iran and Kenya; typically older goats are affected
• B. darling has historically been considered common and nonpathogenic in opposums, but is now being recognized as a cause of disease and mortality in N. American opposums. Protozoal cysts may be accompanied by granulomatous inflammation and degenerative lesions.
• Cattle: Per PVD, the scrotum is a predilection site for B. besnoiti (and D. congolensis).

 

References:

1. Foster RA, Premanandan, C. Male Reproductive System. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 7th ed. St. Louis, MO: Elsevier; 2022:1317. 
2. Gardiner CH, Fayer R, Dubey JP. An Atlas of Protozoan Parasites in Animal Tissues, 2nd ed. Washington, DC: Armed Forces Institute of Pathology; 1998: 49-52.
3. Higgins D, Rose K, Spratt D.  Monotremes and marsupials. In: Terio, KA, McAloose, D, St. Leger, J, eds. Pathology of Wildlife and Zoo Animals. San Diego, CA: Academic Press Elsevier; 2018:475.
4. Howerth, EW, Nemeth, NM, Ryser-Degiorgis, MP. Cervidae. In: Terio, KA, McAloose, D, St. Leger, J, eds. Pathology of Wildlife and Zoo Animals. San Diego, CA: Academic Press Elsevier; 2018:172.
5. Langenmayer MC, Gollnick NS, Majzoub-Altweck M, Scharr JC, Schares G, Hermanns W. Naturally acquired bovine besnoitiosis: Histological and immunohistochemical findings in acute, subacute, and chronic disease.  Vet Pathol. 2015; 52(3): 476-488.
6. Lopez A, Martinson SA. Respiratory system, thoracic cavities, mediastinum and pleurae. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 7th ed. St. Louis, MO: Elsevier; 2022:570. 
7. Mauldin EA, Peters-Kennedy J. Integumentary system.  In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 1. 6th ed. St. Louis, MO: Elsevier; 2016: 661-663.

 

 

 

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