AFIP SYSTEMIC PATHOLOGY

JPC SYSTEMIC PATHOLOGY

INTEGUMENT SYSTEM

October 2019

I-P18

 

Signalment (JPC# 2416085): Adult female African clawed frog (Xenopus laevis)

 

HISTORY: This frog was submitted for necropsy. The frog had become thin and lethargic and had an area of brown discoloration on its dorsum.

 

MICROSCOPIC DESCRIPTION: Skin: The epidermis is diffusely thickened up to four times normal with acanthosis and spongiosis. Multifocally within the epidermis there are numerous adult aphasmid nematodes that are often degenerate surrounded by a cystic space (tunnel) admixed with cellular debris; occasional viable nematodes measure up to 100 um in diameter with a thin eosinophilic cuticle, a stichosome, inapparent musculature and bacillary bands, a uterus containing many eggs or testis with sperm, and an intestine lined by multiple cuboidal cells. Occasionally basal keratinocytes are swollen with a clear vacuole (hydropic degeneration) and rarely cells within the stratum spinosum are rounded with intensely eosinophilic cytoplasm (dyskeratosis). Occasionally, granulocytes transmigrate the epidermis, and there are a few lymphocytes and plasma cells in the dermis. There is orthokeratotic hyperkeratosis with few degenerating nematode fragments within the stratum corneum. There is a focal area of sub-basilar erosion with clefting at the basement membrane zone; the cleft contains a moderate amount of homogenous eosinophilic to fibrillar fluid (serum, fibrin).

MORPHOLOGIC DIAGNOSIS: Skin: Hyperplasia, epidermal, diffuse, moderate, with viable and degenerate intraepithelial aphasmid nematodes, and orthokeratotic hyperkeratosis, African clawed frog (Xenopus laevis), amphibian.

 

ETIOLOGIC DIAGNOSIS: Cutaneous capillariasis

 

ETIOLOGY: Pseudocapillaroides xenopi

 

ETIOLOGY SYNONYMS: Capillaria xenopodis

 

CONDITION: Capillariasis

 

CONDITION SYNONYMS: Flaky skin disease, gray skin disease

 

GENERAL:

·      Common parasite of wild caught and captive bred clawed frogs, including those in research colonies

·      Causes a wasting syndrome characterized by anorexia, changes to skin color, and excessive epidermal desquamation which often results in death

·      May be asymptomatic until stressed

·      Parasites typically found in dorsal skin; ventral lesions usually associated with bacterial infection from secondary invaders

 

LIFE CYCLE:

·      Not completely understood but thought to be direct, and completed within the epidermis

·      Transmission via ingestion of eggs in desquamated skin or through autoinfection

 

PATHOGENESIS:

·      Epithelial damage predisposes to secondary bacterial infection, which may progress to septicemia

·      In amphibians, the skin is important in maintaining hydration, osmoregulation, thermoregulation, and respiration; therefore, excessive epidermal desquamation can result in death

·      Dependent on thymus-mediated immune response

 

TYPICAL CLINICAL AND GROSS FINDINGS:

·      Dry, rough, flaky, dull gray skin usually over the dorsum with varying degrees of ventral erythema

·      Excess mucus, ulceration, and sloughing of the skin

·      Small (2-4mm x 1mm) white, sigmoid shaped nematodes in mucus overlying epidermis

·      Anorexia and emaciation

·      Gradual onset, may take up to 12-18 months after infection for clinical signs to develop

 

TYPICAL MICROSCOPIC FINDINGS:

·      Nematodes:

·      Nematode adults and larvated eggs within epidermal tunnels and subepidermal clefts; degenerate parasites within the superficial epidermis, viable adults within the deeper layers

·      Adults: 100-200um diameter, thin cuticle, inapparant musculature, esophagus with stichosome glands, hypodermal/bacillary bands, lacks sensory papillae

·      Females are twice as large as males, and contain embryonated and larvated eggs within uteri

·      Males have a caudal spicule

·      Eggs are thin-walled with bipolar plugs and contain embryonated larvae

·      Epidermis: Acanthosis, parakeratosis, dyskeratosis, epidermal ulcerations and erosions, variable granulocytic and monocytic inflammation surrounding parasites

·      Dermis: Variable granulocytic and monocytic inflammation within the superficial dermis; granular degeneration of dermal glands in severe cases

 

ADDITIONAL DIAGNOSTIC TESTS:

·      Direct examination of the skin of a live frog under dissecting microscope

·      Microscopic examination of skin scrape or wet smear of desquamated skin

 

DIFFERENTIAL DIAGNOSIS:

Gross:

·      Aeromonas hydrophila (Red-leg)causes acute septicemia, cutaneous hemorrhages and death; common secondary invader

·      Basidiobolus ranarum—broad, irregular, rarely septate Zygomycete

·      Batrachochytrium dendrobatidis (I-F10, chytridiomycosis)—causes cutaneous erythema and orthokeratotic hyperkeratosis; fungal thalli have distinct discharge papillae

·      Chromomycosis—dematiaceous fungi of the genera Fonsecaea, Phialophora, Cladosproium, Rhinocladiella and Scolecosbasidium cause disseminated disease in amphibians and have dark-brown hyphae or thick walled muriform cells (sclerotic bodies)

 

Histologic:

·      None (Pseudocapillaroides xenopi is the only epidermal nematode of South African clawed frogs)

 

COMPARATIVE PATHOLOGY:

Other nematodes that localize in the epithelium include:

·      Trichosomoides crassicauda (U-P10) in urothelium of rats

·      Pearsonema sp. in the urothelium of cats, mink, dogs

·      Gongylonema sp. in the esophagus of ruminants, does not elicit an inflammatory response; in the tongue and infrequently the esophagus of nonhuman primates and small mammals where it often elicits considerable inflammation

·      Anatrichosoma sp. (I-P05) in the nasal mucosa of nonhuman primates

·      Eucoleus boehmi in the nasal mucosa of dogs

·      Eucoleus aerophila (P-P15) in the tracheal and bronchial mucosa of wild canids, domestic dogs, and cats

 

REFERENCES:

1.    Pessier AP. Amphibia. In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. Cambridge, MA: Elsevier; 2018: 936.


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