AFIP SYSTEMIC PATHOLOGY

JPC SYSTEMIC PATHOLOGY

NERVOUS SYSTEM

April 2014

N-P12

 

Slide A

Signalment (JPC #1652892):  Military working dog

 

HISTORY:  This dog developed convulsions and ataxia.

 

HISTOPATHOLOGIC DESCRIPTION:  Cerebrum, meninges:  Focally elevating and expanding the meninges and compressing the adjacent gray and white matter, is an up to 5 mm diameter connective tissue capsule that surrounds a single up to 5 mm diameter larval cestode with a invaginated scolex and a large bladder (cysticercus).  The capsule is composed of multiple layers of fibroblasts and collagen with rare lymphocytes, and blends with the meninges.  The bladder wall is characterized by an up to 30 um eosinophilic tegument composed of parenchyma with many embedded oval 10 x 30 um basophilic to clear calcareous corpuscles.  Multiple sections of sucker are visible within the scolex.  In the adjacent compressed gray matter, there is mild vacuolation and dissolution of the neuropil (spongiosis), few neurons with hypereosinophilic shrunken angular cytoplasm and pyknotic nuclei (neuronal necrosis), few reactive astrocytes with abundant eosinophilic cytoplasm (gemistocytes), and few swollen degenerate axons (spheroids).

 

MORPHOLOGIC DIAGNOSIS:  Cerebrum, meninges:  Cysticercus, focal, with gray and white matter spongiosis, neuronal necrosis, and gemistocytosis, breed not specified, canine.

 

ETIOLOGIC DIAGNOSIS:  Cerebral cysticercosis

 

ETIOLOGY:  Cysticercus cellulosae (larval stage of Taenia solium)

 

CONDITION:  Cysticercosis

 

Slide B

Signalment (JPC #2026219):  2-year-old Corriedale ram

 

HISTORY:  This ram was circling, with a head tilt, had a peculiar high-stepping gait, was grinding its teeth, and had an aversion to flocking behavior.  He was one of several similarly affected sheep examined in Peru.

 

HISTOPATHOLOGIC DESCRIPTION:  Brain stem:  Multifocally elevating and expanding the meninges and minimally compressing the subjacent white matter, are few variably sized connective tissue capsules that are infiltrated by numerous nodular aggregates and scattered inflammatory cells composed of varying numbers  of neutrophils, lymphocytes, plasma cells, eosinophils, macrophages, multinucleate giant cells of the foreign body and Langhans type, abundant eosinophilic cellular and karyorrhectic debris (necrosis), and many congested blood vessels.  Focally, there is a granuloma characterized by a central zone of necrosis surrounded by a concentric rim of epithelioid macrophages, bounded by a layer of numerous lymphocytes, plasma cells, and scattered eosinophils, which is further bounded by few fibroblasts on a thin collagenous matrix, and few multinucleate giant cells.  Each capsule contains multiple larval cestodes with up to 700 um diameter invaginated scolices surrounded by a single fluid-filled bladder (coenurus).  The bladder wall is characterized by an up to 400 um thick eosinophilic tegument composed of parenchyma with many embedded oval 10 x 30 um basophilic to clear calcareous corpuscles.  The scolices often contain one or two suckers and a rostellum with refractile chitinized hooks.  Focally, a nerve rootlet is minimally infiltrated by few lymphocytes and plasma cells.  Scattered macrophages and multinucleate giant cells frequently contain an intracytoplasmic brown globular pigment (hemosiderin).  Multifocally, in areas of compressed white matter, lymphocytes and plasma cells expand Virchow-Robin space (perivascular cuffing) and affected blood vessels have hypertrophic endothelium (reactive).  Multifocally, there is mild vacuolation of the parenchyma (spongiosis), and gliosis.

 

MORPHOLOGIC DIAGNOSIS:  Brain stem:  Meningitis, granulomatous, and lymphoplasmacytic, diffuse, severe, with spongiosis, gliosis, perivascular cuffing, and multiple meningeal coenuri, Corriedale, ovine.

 

CAUSE:  Coenurus cerebralis (larval stage of Taenia multiceps)

 

ETIOLOGIC DIAGNOSIS:  Meningeal coenurosis

 

CONDITION:  "Gid" or "Sturdy"

 

GENERAL DISCUSSION:

·         Tapeworms belong to the class Cestoda of the phylum Platyhelminthes; the two orders of veterinary interest are Pseudophyllidea and the Cyclophyllidea

·         The order Pseudophyllidea has two genera of veterinary interest:  Diphyllobothrium and Spirometra; most require two intermediate hosts and are associated with aquatic food chains

·         The order Cyclophyllidea has five families of veterinary interest Taeniidae, Mesocestoididae, Anoplocephalida, Dipylidiida, and Hymenolepididae; most only require one intermediate host and are associated with terrestrial food chains

·         Fully developed second stage larvae in the family Taeniidae consist of a fluid filled bladder with one or more scolices (often called a bladderworm) surrounded by a connective tissue capsule formed by the vertebrate intermediate host

·         The larvae (Cysticercus cellulosae) of the human tapeworm, Taenia solium occur primarily within cardiac and skeletal muscle (masseter muscle, tongue, shoulder muscle) of pigs and may cause neurological disease in swine, humans, and occasionally dogs

·         The larvae (Coenurus cerebralis) of the canine tapeworm, Taenia multiceps, produce neurological disease in sheep and other animals

·         Cysticercus:  A single bladder with one scolex

·         Coenurus:  A single bladder with many scolices

 

PATHOGENESIS:

Cysticercus cellulosae/Taenia solium:

·         Cysticerci encyst within striated muscle > avoidance of immune-mediated destruction by inactivating elements of the complement system > release enzymes that cause lysis to allow room for the growing connective tissue capsule

Coenurus cerebralis/Taenia multiceps:

·         The pathology is twofold: (1) larval migration causes necrosis and inflammation within the CNS > (2) capsule expansion compresses neural tissue, and may even perforate the overlying skull > can lead to increased intracranial pressure, hydrocephalus, and necrosis of the adjacent brain

 

LIFE CYCLE:

Cysticercus cellulosae/Taenia solium:

·         Taenia solium (adult tapeworm) resides in the human small intestine (definitive host); larval forms most likely in dogs, sheep and pigs

·         Swine become infected by ingestion of tapeworm eggs from human feces

·         In the pig, the outer shell of the egg is digested within the stomach and an oncosphere hatches; oncosphere penetrates the pig's intestinal blood vessels and enters the systemic circulation

·         Most cysticerci (larvae) migrate to skeletal and cardiac muscle of the pig (intermediate host) but may migrate to CNS (i.e. neurocysticercosis); humans may act as intermediate hosts if they ingest eggs and then cysticerci can form within the brain, viscera, and connective tissue

·         Adult tapeworms develop when humans are infected by eating inadequately cooked pork containing cysticerci

Coenurus cerebralis/Taenia multiceps:

·         Similar to above, but the dog (definitive host) carries the adult tapeworm, and coenuri develop within the CNS of sheep (intermediate host)

 

TYPICAL CLINICAL FINDINGS:

Cysticercus cellulosae/Taenia solium:

·         No clinical signs in swine if located within striated muscle

·         Neurological signs if located within the CNS

Coenurus cerebralis/Taenia multiceps:

·         Neurological signs in sheep (blindness, incoordination, circling, head pressing)

 

TYPICAL GROSS FINDINGS:

Cysticercus cellulosae/Taenia solium:

·         Multiple small translucent vesicles filled with clear fluid in striated muscle (heart, masseter, tongue and shoulder muscles) and occasionally meninges and brain

Coenurus cerebralis/ Taenia multiceps:

·         Purulent meningoencephalitis, and tortuous yellow to red tracts within CNS parenchyma during the migratory phase

·         Expansile coenuri may develop anywhere in the brain and spinal cord

·         Space occupying 4-5 cm diameter cysts but may be larger, with translucent wall and thick clear fluid, in the CNS later in infection (referred to as “gid” at that point) most commonly present near the surface of parietal cortex of cerebrum but may be anywhere in brain or spinal cord; atrophy of adjacent neuroparenchyma

 

TYPICAL LIGHT MICROSCOPIC FINDINGS:

Cysticercus cellulosae/Taenia solium:

·         Cysticercus (larva) has a single bladder with one scolex

·         The cysticercus has a tegument, parenchyma, calcareous corpuscles, suckers on the scolex and rostellar hooks

·         Little to no inflammation in striated muscle of pigs if cysticercus is alive

·         Granulomatous inflammation and mineral if dead; then absorbed by the body

·         Cysticerci are primarily found within the striated muscle of pigs and less commonly in the CNS

Coenurus cerebralis/Taenia multiceps:

·         Coenurus has a single bladder with multiple scolices

·         The coenurus has a tegument, parenchyma, calcareous corpuscles, suckers on the scolex and a rostellum with chitinized hooks

·         During migration, there is coagulative and lytic necrosis / malacia, hemorrhage, degenerate granulocytes, histiocytes including giant cells, mononuclear cells, and a fibroblastic capsule contributed by the host; reaction / inflammation may be minimal

·         Disruption and destruction of tissue leads to microcavitation and gemistocytes may be present in older lesions

·         Later, expansion of the coenurus causes neural tissue compression to the point of obliteration and overlying bone may be thin or perforated

 

DIFFERENTIAL DIAGNOSIS:

Cestode larvae in the CNS of cattle/small ruminants:

·         Cysticercus bovis rarely invades the nervous system

·         Echinococcus granulosus is differentiated by the presence of a unilocular cyst with a brood capsule and hydatid sand; dog-sheep life cycle

 

COMPARATIVE PATHOLOGY:

·         Goats:  Coenuri also occur in other organs, beneath the skin and within muscle

·         Cats:  Accidental intermediate host for Taenia serialis; cerebral coenuri

·         Rats:  Fibrosarcomas develop from hepatic cysts of Cysticercus fasciolaris, larval stage of Taenia taeniaeformis (cat tapeworm)

 

 

 

 

ADULT

TAPEWORM

DEFINITIVE HOST

LARVAL FORM

INTERMEDIATE HOST

SITE

Taenia saginata

man

Cysticercus bovis

cattle

muscle

Taenia solium

man

Cysticercus cellulosae

pig, dog, sheep

Muscle, CNS

Taenia(Multiceps) multiceps

dog

Coenurus cerebralis

sheep, cattle

CNS

Taenia hydatigena

dog

Cysticercus tenuicollis

sheep, cattle, pig

peritoneum

Taenia ovis

dog

Cysticercus ovis

sheep

muscle

Taenia pisiformis

dog

Cysticercus pisiformis

rabbit

peritoneum, liver

Taenia serialis

dog

Coenurus serialis

rabbit

connective tissue

Taenia taeniaeformis

cat

Cysticercus fasciolaris (strobilocercus)

mouse, rat

liver

Taenia krabbei

dog

Cysticercus tarandi

reindeer

muscle

Taenia mustelae

wild felids

 

rodents

liver

Diphyllobothrium latum

bear, man

sparganum

fish

muscle

Diphyllobothrium pacificum

seal, sea lion

sparganum

marine birds

muscle

 

 

REFERENCES:

1.     Bowman DD. Georgi's Parasitology for Veterinarians. 10th ed. St. Louis, MO: Elsevier Saunders; 2014:143-150; 413-417.

2.     Cantile C, Youssef S. Nervous system. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 1. 6th ed. St. Louis, MO: Saunders Elsevier; 2016: 389-390.

3.     Cooper BJ, Valentine BA. Muscle and tendon. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 1. 6th ed. St. Louis, MO: Saunders Elsevier; 2016:239-240.

4.     Gardiner CH, Poynton SL. An Atlas of Metazoan Parasites in Animal Tissues. Washington, DC: Armed Forces Institute of Pathology; 1999:50-53.

5.     Miller AD, Zachary JF. Nervous system. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 6th ed. St. Louis, MO: Elsevier; 2017: 845-846.

6.     Summers BA, Cummings JF, de Lahunta A. Veterinary Neuropathology. St. Louis, MO: Mosby; 1995:161.

7.     Uzal FA, Plattner BL, Hostetter JM. Alimentary system. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 2. 6th ed. St. Louis, MO: Saunders Elsevier; 2016:222-225.

 

 

 


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