JPC SYSTEMIC PATHOLOGY

NERVOUS SYSTEM

February 2023

N-P09

 

Signalment (JPC #84-644): 4‑month‑old sable antelope (Hippotragus niger)

 

HISTORY: This antelope exhibited progressive ataxia and paresis of the hind limbs.

                                     

HISTOPATHOLOGIC DESCRIPTION: Medulla oblongata: Unilaterally within the nucleus of the spinal tract of the trigeminal nerve and mildly compressing adjacent neuroparenchyma is a focal 2.5 x 1.0 mm area of neuroparenchymal loss and rarefaction (liquefactive necrosis) admixed with scant hemorrhage, fibrin, and edema. This focus of necrosis is centered on multiple tangential and cross-sections of adult nematodes with a 2-4 µm thick smooth eosinophilic cuticle, polymyarian-coelomyarian musculature, accessory hypodermal chords, a pseudocoelom, an intestine lined by few multinucleate cells, and either an ovary or testis. The surrounding neuroparenchyma is spongiotic or lost (necrosis) with hemorrhage. On the contralateral side of the medulla oblongata at the area of the medial cuneate nucleus there is a 100x500µm focus of liquefactive necrosis with replacement hemorrhage, fibrin, edema, and numerous foamy histiocytes (gitter cells), hemosiderophages, hematoidin, and histiocytes with phagocytosed erythrocytes. Adjacent to this area and multifocally there are occasional dilated myelin sheaths with swollen axons (spheroids) and mild gliosis. There are rare scattered degenerate neurons that are swollen with abundant pale eosinophilic cytoplasm, peripheralized nuclei, and marginated Nissl substance (central chromatolysis).   Capillaries are occasionally lined by hypertrophic endothelial cells (reactive).  

 

Cerebellum: Essentially normal tissue.

 

MORPHOLOGIC DIAGNOSIS: Medulla oblongata: Necrosis, focally extensive, subacute, with neuronal degeneration, multifocal mild hemorrhage, gliosis, spheroids, and few adult Strongylid nematodes, sable antelope (Hippotragus niger), artiodactyl. 

 

ETIOLOGIC DIAGNOSIS: Brainstem parelaphostrongylosis

 

CAUSE: Parelaphostrongylus tenuis  

 

SYNONYMS: Meningeal worm, brain worm

 

GENERAL DISCUSSION:

• Parelaphostrongylus tenuis, superfamily Metastrongyloidea, family Protostrongylidae, is the most common, predominantly non-pathogenic parasite of white-tailed deer (WTD)
• Aberrant migration causes neurologic disease in non-WTD cloven-hoofed animals and horses; most commonly reported in the goat

 

PATHOGENESIS:

• WTD are the definitive host and gastropods (snails & slugs) are the intermediate host 
• Deer are infected by ingestion of infected gastropods
• Larvae penetrate the gastrointestinal tract wall, migrate along spinal nerves to the dorsal horn of the spinal cord and then to subdural space of WTD
• Infection in WTD is asymptomatic unless heavy parasite burden or debilitated

 

TYPICAL CLINICAL FINDINGS:

• CSF will have elevated protein levels, erythrocytes, and pleocytosis of mononuclear cells and eosinophils
• Asymmetric pelvic limb deficits which progresses cranially; scoliosis and CN deficits also reported
• A stiff or lame gait progresses to paraparesis or tetraparesis
• P. tenuis in calves: Acute cases had eosinophilic pleocytosis, chronic cases had lymphocytic pleocytosis, all cases had elevated protein

 

TYPICAL GROSS FINDINGS:

• CNS lesions: 
  • Random pinpoint hemorrhages in the parenchyma and leptomeninges
  • Occasionally palpable softening with a gray discoloration of spinal cord
• Abomasal hyperemia with pinpoint hemorrhages
• Mild peritoneal fibrous adhesions
• Mild pneumonia
• Goats can develop a fibrosing dermatitis often restricted to one side of the body, and characterized by vertically oriented areas of alopecia, ulceration, crusting, and/or scarring over the shoulders, thorax, or flanks

 

TYPICAL LIGHT MICROSCOPIC FINDINGS:

• Random, asymmetric foci of rarefaction and/or neuroparenchymal loss with variable inflammation and hemorrhage 
• Can affect both the gray and white matter of the spinal cord; the cerebrum and cerebellum are affected less often; there is some evidence that myelinated tissue may be preferentially affected
• Identification of the nematode is difficult; very few can cause severe disease in aberrant hosts
• Nematode: 2-4 µm smooth eosinophilic cuticle, polymarian-coelomyarian musculature, accessory hypodermal cords, a pseudocoelom, intestine lined by multinucleate cells, and a reproductive tract

 

ADDITIONAL DIAGNOSTIC TESTS:

 

DIFFERENTIAL DIAGNOSIS:

Nematodes causing CNS disease in domestic animals
Parasite	Normal Host	Aberrant Host
Nematode migration in aberrant host
Angiostrongylus cantonensis	Rat	Dog
Baylisascaris procyonis	Raccoon	Dog
Elaphostrongylus cervi	Red deer	Sheep, goat
Elaphostrongylus rangiferi	Reindeer	Sheep, goat
Halicephalobus gingivalis	Unknown	Horse
Parelaphostrongylus tenuis	Deer	Sheep, goat
Setaria digitate	Cattle	Sheep, goat, horse
Abberant nematode migration in normal host
Angiostrongylus vasorum	Dog (coyote)
Dirofilaria immitis	Dog (cat)
Stephanurus dentatus	Pig
Strongylus spp.	Horse

Table 14-4; Miller AD, Zachary JF. Nervous system. In: McGavin MD, Zachary JF, eds. Pathologic Basis of Veterinary Disease. 7th ed. St. Louis, MO: Mosby Elsevier; 2022:931.

 

COMPARATIVE PATHOLOGY:

• Aberrant hosts: Ox, llama, goat, sheep, horse, moose, black-tailed deer, caribou, wapiti, red deer, reindeer, sable antelope, mule deer, elk, and other native cervids and several exotic ruminants
  1. Case report of cerebrospinal nematodosis caused by Parelaphostrongylus species in an adult bull

 

References:

1. Agnew D. Camelidae. In:   Terio, KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. San Diego, CA: Academic Press Elsevier; 2018:200.
2. Cantile C, Youssef S. Nervous system. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 1. 6th ed. Philadelphia, PA: Saunders Elsevier; 2016:390.
3. 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; 2018:168.
4. Jones MEB, Gasper DJ, Mitchell E. Bovidae, antilocapridae, giraffidae, tragulidae, hippopotamidae. In:  Terio, KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. San Diego, CA: Academic Press Elsevier; 2018:138.
5. MacKay EE, Fratzke AP, Gerhold RW, Porter BF, Washburn KE. Cerebrospinal nematodosis caused by Parelaphostrongylus species in an adult bull. J Vet Diagn Invest. 2020 May;32(3):486-489.
6. Mauldin EA, Peters-Kennedy J. Skin and appendages. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 1. 6th ed. Philadelphia, PA: Saunders Elsevier; 2016:689-690.
7. Miller AD, Zachary JF. Nervous system. In: McGavin MD, Zachary JF, eds. Pathologic Basis of Veterinary Disease. 7th ed. St. Louis, MO: Mosby Elsevier; 2022:931.

 

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