March 2017



Signalment (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:  Within the subependymal neuroparenchyma and compressing adjacent neuropil is a focal 2.5 x 1.0 mm area of rarefaction which is centered on multiple tangential and cross-sections of adult nematodes with a 2-4 um thick 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 neuropil is spongiotic or lost (necrosis) with hemorrhage.  There is a focal area of necrosis with hemorrhage and numerous foamy histiocytes (gitter cells), hemosiderophages, and histiocytes with phagocytosed erythrocytes.  Adjacent to this area and multifocally throughout the section 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, peripheral nuclei, and marginated Nissl substance (central chromatolysis).  Capillaries are diffusely occasionally lined by hypertrophic endothelial cells (reactive). 


Cerebellum:  Within normal limits.


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


ETIOLOGIC DIAGNOSIS:  Brainstem parelaphostrongylosis


CAUSE:  Parelaphostrongylus tenuis 


SYNONYMS:  Meningeal worm, brain worm



·         Parelaphostrongylus tenuis, superfamily Metastrongyloidea, family Protostrongylidae, is the common, predominantly nonpathogenic parasite of white-tailed deer (WTD)

·         Aberrant migration causes neurologic disease in cloven-hoofed animals and horses; most commonly reported in the goat



·         WTD are the definitive host and gastropods (snails & slugs) are the intermediate host

·         Infected by ingestion of infected gastropods

·         Larvae penetrate 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



·         CSF will have elevated protein levels, erythrocytes and pleocytosis of mononuclear cells and eosinophils

·         From a recent article on P. tenuis in calves: Acute cases had eosinophilic pleocytosis & chronic cases had lymphocytic pleocytosis while all had elevated protein

·         Asymetric pelvic limb deficits which progresses cranially; scoliosis and CN deficits also reported

·         A stiff or lame gait progresses to paraparesis or tetraparesis



·         CNS lesions: Random pinpoint hemorrhages in the parenchyma and leptomeninges

·         Occasionally palpable softening with a grayish discoloration of spinal cord

·         Abomasal hyperemia with pinpoint hemorrhages

·         Mild peritoneal fibrous adhesions

·         Mild pneumonia

·         Goats can develop a fibrosing dermatitison the trunk with basal keratinocyte hydropic degeneration



·         Most commonly affects the white matter of the spinal cord, but also the gray matter, cerebrum and cerebellum

·         Random, asymmetric foci of rarefaction and/or neuroparenchymal loss with variable inflammation and hemorrhage

·         Identification of the nematode is difficult; very few can cause severe disease

·         Nematode: 2-4 um eosinophilic cuticle, polymarian-coelomyarian musculature, accessory hypodermal cords, a pseudocoelom, intesting lined by multinucleate cells, and a reproductive tract



·         Fecal exam via Baermann technique for dorsal-spined L1 larvae suggestive but not definitive












(Table 14-4 from PBVD, 5th ed., pg 811)

Parasites causing CNS disease in aberrant hosts


Normal Host

Aberrant Host

Angiostrongylus cantonensis



Baylisascaris procyonis


Dog, man

Elaphostrongylus rangiferi


Sheep, goat (Europe)

Parelaphostrongylus tenuis


Sheep, goat, ox, horse

Setaria digitatum


Sheep, goat, horse


Aberrant parasite migration in definitive host

Angiostrongylus vasorum

Dog (coyote)

Dirofilaria immitis

Dog (cat)

Stephanurus dentatus


Strongylus sp. (vulgaris)


Halicephalobus gingivalis

Horse (free living parasite)

Cysticercus cellulosae




·         Aberrant hosts: Ox, llama, goat, sheep, horse, moose, black-tailed deer, caribou, wapiti, red deer, reindeer, sable antelope, mule deer and other native cervids and several exotic ruminants

·         Reported in a guinea pig fed grass from a backyard frequented by WTD



1.     Bowman DD. Georgis’ Parasitology for Veterinarians. 10th ed. St. Louis, MO: Saunders Elsevier; 2014:186, 423.

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.     Dobey CL, Grunenwald C, Newman SJ, Muller L, Gerhold RW. Retrospective study of central nervous system lesions and association with Parelaphostrongylus species by histology and specific nestered polymerase chain reaction in domestic camelids and wild ungulates. J Vet Diagn Invest. 2014;26(6):748-754.

4.     Jacques CN, Jenks JA, Klaver RW, Dubay SA. Associations among habitat characteristics and meningeal worm prevalence in eastern South Dakota, USA. Journal of Wildlife Diseases. 2017;53(1):131-135.

5.     Jacques CN, Jenks JA, Grovenburg TW, Klaver RW, Dubay SA. Influence of ecologic factors on prevalence of meningeal worm (Parelaphostrongylus tenuis) infection in South Dakota, USA. Journal of Wildlife Diseases. 2015;51(2):332-340.

6.     Maskey JJ, Sweitzer RA, Goodwin BJ. Climate and habitat influence prevalence of meningeal worm infection in North Dakota, USA. Journal of Wildlife Diseases. 2015;51(3):670-679.

7.     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.

8.     Miller AD, Zachary JF. Nervous system. In: McGavin MD, Zachary JF, eds. Pathologic Basis of Veterinary Disease. 6th ed. St. Louis, MO: Mosby Elsevier; 2017:846.

9.     Mitchell KJ, Peters-Kennedy J, Stokol T, et. al. Diagnosis of Parelaphostrongylus spp. infection as a cause of meningomyelitis in calves. J Vet Diagn Invest. 2011;23(6):1097-1103.

10.  Pinn TL, Bender HS, Stokol T, et. al. Cerebrospinal fluid eosinophilia is a sensitive and specific test for the diagnosis of Parelaphostrongylus tenuis in camelids in the northeastern United States. J Vet Diagn Invest. 2013;25(1):54-60.

11.  Southard T, Bender H, Wade SE, et al. Naturally occurring Parelaphostrongylus tenuis-associated choriomeningitis in a guinea pig with neurologic signs. Vet Pathol. 2013;50(3):560-562.

12.  Summers BA, Cummings JF, deLahunta A. Veterinary Neuropathology. St. Louis, MO: Mosby; 1995:159-162.

13.  Tanabe M, Gerhold RW, Beckstead RB, et. al. Molecular confirmation of Parelaphostrongylus tenuis infection in a horse with verminous encephalitis. Vet Pathol. 2010;47(4):759.

14.  Tanabe M, Kelly R, de Lahunta A, et. al. Verminous encephalitis in a horse produced by nematodes in the family protostrongylidae. Vet Pathol. 2007;44:119-122.

15.  Wunschmann A, Armien AG, Butler E, et al. Necropsy findings in 62 opportunistically collected free-ranging moose (Alces alces) from Minnesota, USA. Journal of Wildlife Diseases. 2015;51(1):157-165.



Click the slide to view.

Click on image for diagnostic series.

Back | Home | Contact Us | Links | Help |