JPC SYSTEMIC PATHOLOGY
SIGNALMENT (JPC #2550908): Adult female Barbary ape (Macaca sylvana)
HISTORY: This animal was kept in a zoo.
HISTOPATHOLOGIC DESCRIPTION: Liver: Expanding and replacing approximately 50% of the hepatic parenchyma in this section and compressing adjacent hepatocytes is a multilocular alveolar hydatid cyst composed of round to oval to irregular intact and ruptured 2-6 mm diameter cysts surrounded and separated by variably thick bands of fibrous connective tissue that extend into and replace adjacent hepatic parenchyma. Fibrous connective tissue contains moderate numbers of lymphocytes, plasma cells, macrophages and eosinophils, and many entrapped bile ductules. Cysts are lined by a 10-50 um thick eosinophilic hyaline outer laminated membrane and a 50-150um inner germinal epithelial layer containing basophilic nuclei, eosinophilic flocculant to granular material, and numerous 5-20 um basophilic calcareous corpuscles. Budding from the germinal epithelium or free within the cyst lumen are many thin-walled brood capsules containing multiple 100-150 um diameter protoscolices. Protoscolices have a 5 um thick tegument enclosing spongy parenchyma which contains calcareous corpuscles, a sucker and a rostellum armed with birefringent hooks. Ruptured cysts are collapsed and contain variable amounts of eosinophilic necrotic debris admixed with degenerate neutrophils, eosinophils, lymphocytes, plasma cells, foamy macrophages and multinucleated giant cells, which extend into the adjacent fibrous connective tissue. Multifocally, throughtout the adjacent hepatic parenchyma, hepatocytes are necrotic with shrunken hypereosinophilic cytoplasm and pyknosis, are individualized and surrounded by hemorrhage, are degenerate, with swollen, pale, vacuolated cytoplasm or are lost and replaced by necrotic debris, hemorrhage and/or fibrosis. Portal areas adjacent to the hydatid cyst and areas of hepatocellular necrosis have increased numbers of small bile duct profiles (biliary ductal reaction).
MORPHOLOGIC DIAGNOSIS: Liver: Hydatid cyst, multiloculated, with multifocal fibrosis, necrotizing hepatitis and biliary hyperplasia, etiology consistent with Echinococcus multilocularis, Barbary ape (Macaca sylvana), primate.
ETIOLOGIC DIAGNOSIS: Hepatic echinococcosis
CAUSE: Echinococcus multilocularis
CONDITION: Alveolar or multilocular hydatid disease
- The genus Echinococcus, a member of the Taeniidae family, includes multilocularis and E. granulosus
- Sylvatic life cycle and red and artic foxes are the most important definitive hosts, with other hosts (coyotes, raccoon-dogs, wolves) also being common
- Intermediate hosts are rodents (voles, lemmings, deer mice) in temperate climates
- Aberrent intermediate hosts include pigs, horses, nonhuman primates, humans, among others
- Human alveolar echinococcosis is a serious zoonosis
- Dogs can act as simultaneous intermediate and definite hosts
- Dogs become aberrant intermediate hosts and develop alveolar echinococcosis via coprophagia or autoinfection from adult tapeworm intestinal infection
- Cyst growth and exogenous budding compress and replace parenchyma, causing progressive hepatic loss and bile stasis
- Cysts spread by infiltration of germinal epithelium into surrounding tissue; germinal cells reaching vessels can become disseminated
- Host reaction: Lymphoplasmacytic to granulomatous inflammation with extensive fibrosis > progressive disease is fatal
- Definitive hosts such as canids and other carnivores with adults in their intestinal tract sheds eggs as gravid segments > ingested by intermediate host > oncosphere (L1) hatches and penetrates the gut wall > travels via portal circulation to the liver (or other aberrant location) > develops to L2 stage (hydatid cyst or metacestode) containing internal brood capsules and protoscolices (also called scolices)
- Intermediate host is ingested by the definitive host
TYPICAL CLINICAL FINDINGS:
- Definitive host: Asymptomatic
- Intermediate host: Signs depend on the organ involved; relentless proliferation of the parasite makes the condition invariably fatal
TYPICAL GROSS FINDINGS:
- Definitive host: Adult tapeworm is 5mm long with a scolex and approximately five segments
- Intermediate host:
- Multiloculated, encapsulated, white to grey, spongy, clear to flocculent fluid-filled hepatic cysts (brood capsules floating free in cyst fluid form “hydatid sand”)
- May be referred to as alveolar echinococcosis as budding cysts resemble alveoli
- Large cysts may have central areas of necrosis surrounded by a thin rim of viable proliferating parasites
- Hydatid cysts most commonly occur in the liver and lung, but may be found in the peritoneum, heart, bone, subcutis, brain, retrobulbar and other areas throughout the body
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- Multiple variably sized cysts surrounded by fibrosis; +/- mineralization
- Cysts are lined by an inner germinal epithelium and prominent outer PAS-positive lamellar hyaline membrane; both are of parasitic origin
- Brood capsules budding from the inner germinal layer and free in the lumen containing variable numbers of invaginated protoscolices
- Protoscolices have birefringent, clear to golden-brown hooklets surrounded by parenchyma that occasionally contains calcareous corpuscles
- Echinococcus granulosus: Unilocular hydatid cyst; usually not invasive; confined to the connective tissue capsule; endogenous budding; expansile growth; sheep-dog cycle
- Taeniid forms:
- Cysticercus – fluid-filled cyst with invaginated scolex of single larva
- Strobilicercus – same as cysticercus but it begins to elongate like an adult while still in the intermediate host, and scolex evaginates
- Coenurus – single or loculated fluid-filled cyst with numerous invaginated scolices
- Hydatid cyst – uni- or mulitloculated with brood capsule which contain invaginated protoscolices
- Other taeniid tapeworms and associated metacestodes:
- Taenia taeniaformis – cats, wild felids; Cysticercus fasciolaris – liver of small rodents, may form fibrosarcoma
- T. pisiformis – dogs, wild canids; C. pisiformis – liver of intermediate host
- T. hydatigena – dog; C. tenuicollis – peritoneum of sheep, cattle, swine
- T. ovis – dogs, wild canids; C. ovis – muscle of sheep (“sheep measles”)
- T. saginata – dog; C. bovis – cattle (“measley beef”)
- T. solium – dog; C. cellulosae – swine
- T. multiceps – dogs, wild canids; Coenurus cerebralis – brain, spinal cord of sheep (“gid”), ungulates
- Echinococcus canadensis – gray wolves and cervids in Idaho, US
- Echinococcus granulosus – wild boars in central Italy
- Echinococcus multilocularis – zoo kept Goeldi’s monkey in British Columbia
- Echinococcus multilocularis – old world monkeys (guenons, colobus monkeys, mangabeys, mandrills, rhesus monkeys); new world monkeys (marmosets); great apes (chimpanzee, gorilla, orangutan); prosimians (galagos, lemurs)
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