JPC SYSTEMIC PATHOLOGY

NERVOUS SYSTEM

February 2026

N-P11

Slide A: Signalment (JPC #1856158): A 14-week-old dog

HISTORY: None

HISTOPATHOLOGIC DESCRIPTION: Cerebellum with choroid plexus: Focally, the leptomeninges are expanded up to 1 mm by multiple tangential and cross sections of viable and degenerate larval nematodes that are surrounded by an inflammatory infiltrate composed of numerous epithelioid macrophages, moderate numbers of viable and degenerate eosinophils, fewer lymphocytes, plasma cells, reactive fibroblasts, collagen bundles, neutrophils, minimal eosinophilic cellular and karyorrhectic debris (necrosis), hemorrhage, fibrin, and edema. Larval nematodes are 125 μm in diameter with a 5 μm to 8 μm wide eosinophilic, hyalinized, smooth cuticle lined by coelomyarian-polymyarian musculature. The pseudocoelom contains an intestinal tract lined by few multinucleated cells with an indistinct brush border, lateral chords, and often a developing gonad. Multifocally, the less affected meninges are mildly expanded by macrophages, plasma cells, and lymphocytes. Adjacent to the larval nematodes there is multifocal loss of the cerebellar molecular, Purkinje cell, and granular cell layers with replacement by numerous gitter cells, plasma cells, edema, fibrin, and hemorrhage (liquefactive necrosis).

 

MORPHOLOGIC DIAGNOSIS: Cerebellum: Meningoencephalitis, granulomatous and eosinophilic, multifocal, moderate, with few leptomeningeal larval metastrongyle nematodes and multifocal liquefactive necrosis, breed unspecified, canine.

Slide B: Signalment (JPC #1562195): A rat

HISTORY: This rat was from Southeast Asia.

HISTOPATHOLOGIC DESCRIPTION: Head, coronal section, cerebrum and cerebellum: Multifocally, the leptomeninges are expanded up to 0.5 mm with multiple cross and tangential sections of larval nematodes admixed with numerous eosinophils, neutrophils, fewer macrophages, multinucleated giant cells, lymphocytes, plasma cells, minimal eosinophilic cellular and karyorrhectic debris (necrosis), and hemorrhage, fibrin, and edema. Focally, there is also a cross section of a larval nematode adhered to the ependyma of the fourth ventricle. Larval nematodes are 125 μm in diameter with a 5 to 8 μm wide eosinophilic, hyalinized, smooth cuticle lined by coelomyarian-polymyarian musculature. The pseudocoelom contains an intestine lined by few multinucleated cells with an indistinct brush border, paired excretory glands, lateral chords, and often a developing gonad. Within the adjacent cerebrum (including hippocampus) and cerebellum, affecting both grey and white matter, there are multiple, focally extensive areas of pallor (rarefaction) characterized by architectural loss (liquefactive necrosis), spongiosis, occasional neuronal necrosis, gemistocytic astrocytes, reactive microglial cells, moderate numbers of gitter cells, and rare lymphocytes and plasma cells. Foci of necrosis in the hippocampus also contain few aggregates of neutrophils. Focally, the bone of the calvaria is thinned and irregular with few osteoclasts within Howship’s lacunae (osteolysis).

MORPHOLOGIC DIAGNOSIS: Cerebrum and cerebellum: Meningoencephalitis, granulomatous and eosinophilic, multifocal, moderate, with larval metastrongyle nematodes, multifocal liquefactive necrosis, neuronal necrosis, and gliosis, breed unspecified rat, rodent.

ETIOLOGICAL DIAGNOSIS: Meningeal parastrongylosis

CAUSE: Parastrongylus cantonensis (formerly Angiostrongylus cantonensis)

GENERAL DISCUSSION:

• Neurotropic metastrongylid lungworm of rats found in Australia, South Pacific, Southeast Asia, Hawaii, the Caribbean, and southern United States (Louisiana, Mississippi, Florida)
• Causes eosinophilic meningoencephalitis in aberrant hosts (dogs and humans)

PATHOGENESIS:

• Definitive host: rat; adults live in pulmonary arteries, rarely cause clinical disease
• Intermediate hosts: gastropods (snails, slugs), giant African snail
• Paratenic hosts: crabs and frogs; substitute intermediate or transport
• Aberrant hosts: dogs and humans; migration of larval nematodes in neural parenchyma and thrombosis and occlusion of vessels leading to infarction; spectrum of disease varies with strain of parasite, severity of infection, and host response
  • In immunosuppressed individuals, parasites may migrate back to the lungs, causing fatal pulmonary edema and pneumonia +/- proliferative endarteritis

LIFE CYCLE:

• In definitive host (rat), adult lays eggs in pulmonary arteries > migrate and lodge in alveolar capillaries > larvae hatch in about 6 days > tracheal-intestinal route to environment > L1 larvae penetrate intermediate host (gastropod) and develop to L3 > ingestion of intermediate or paratenic host by definitive or aberrant host > migration from gastrointestinal tract to the brain, kidney, and muscle > additional molts in CNS to L5 > migrate to the subarachnoid space for two weeks > young adults invade cerebral vein > migrate to heart and pulmonary arteries to complete maturation

TYPICAL CLINICAL FINDINGS:

• Dogs:
  • Paraparesis, paraplegia, ataxia, urinary and fecal incontinence, and tail paralysis
  • Extreme pain during lumbar palpation or manipulation
• Rats:
  • Minor infections: Asymptomatic
  • Heavy infections: Weakness, ataxia, circling, paraplegia, upper respiratory disease, coma, or death

TYPICAL GROSS FINDINGS:

• Brain: Meningeal congestion
• Lungs: Mottled, atelectatic, consolidated, pleural adhesions
• Rat lung: Adult nematodes within pulmonary arteries

TYPICAL LIGHT MICROSCOPIC FINDINGS:

• Molting larvae in brain produce a mild to severe inflammatory reaction
• Eosinophilic to granulomatous meningoencephalitis in aberrant hosts
• Immature adults: Smooth, 3 to 5 μm diameter cuticle; coelomyarian-polymyarian somatic musculature; lateral cords, four accessory hypodermal chords; intestine composed of few, large multinucleate cells

ADDITIONAL DIAGNOSTIC TESTS:

• Fecal examination for eggs or larvae
• CSF: Eosinophilic pleocytosis

DIFFERENTIAL DIAGNOSIS:

• Other causes of cerebrospinal nematodiasis in animals:
  • Setaria digitata: Filarid parasite of peritoneal cavity of cattle in Far East; causes cerebrospinal nematodiasis in aberrant infections of sheep, goats and horses
  • Parelaphostrongylus tenuis (N-P09): Parasite inhabits subdural space and venous sinuses of white-tailed deer with little disease; infection in aberrant species (moose, elk, caribou, sheep, llama and horse) causes destructive lesions in brain due to migrating parasites; Elpahastrongylus cervi and E. Rangiferi affect sheep and goats
  • Halicephalobus gingivalis (N-P11, formerly Micronema deletrix): Saprophytic filarid nematode causing encephalitis and inflammation of multiple tissues in horses and man
  • Gurltia paralysans: in spinal veins of cats; paralysis
  • Angiostrongylus vasorum: hemorrhagic malacia in brains of dogs
  • Baylisacaris procyonis (racoon ascarid) or B. columnaris (skunk ascarid) in aberrant hosts (N-P14)
  • Other nematodes: Strongylus vulgaris in horses (C-P02, migrating larvae), Draschia megastoma (horses), Toxocara sp., Dirofilaria immitis (adult nematode) in dogs and cats, Meningonema peruzzi and Dipetalonema perstans in monkeys
• Other causes of verminous encephalomyelitis:
  • Coenurus cerebralis, various Cysticerci sp., Echinococcus sp., Troglotrema sp., Oestrus ovis, Hypoderma bovis and Cuterebra sp. (associated with feline ischemic encephalopathy, N-M23)

COMPARATIVE PATHOLOGY:

Parastrongylus cantonensis in other species:

• Nonhuman primates (gibbons, orangutan, owl monkeys, callitrichids): Eosinophilic meningitis or meningoencephalitis
• Aberrant infections also reported in horses, macropods (there is a recent report in a red kangaroo (Patial et al., 2022))

Other Angiostrongylus sp.:

• Dogs and wild carnivores: Angiostrongylus (Parastrongylus) vasorum (P-P02), pulmonary artery and right ventricle; causes obstruction, endarteritis and thrombosis
• Parastrongylus costaricensis causes abdominal angiostrongyliasis in NHPs

References:

1. Barthold SW and Imai DM. Pathology of Laboratory Rodents and Rabbits. 5th ed. John Wiley & Sons; 2026:194.
2. Cantile C, Miller AD, Youssef S. Nervous System. In: Maxie MG, ed. Jubb, Kennedy & Palmer's Pathology of Domestic Animals. Vol 1. 7th ed. St. Louis, MO: Elsevier; 2026:387. Gardiner CH, Poynton SL. Strongyles. In Gardiner CH, Poynton SL, eds. An Atlas of Metazoan Parasites in Animal Tissues. Washington, DC: Armed Forces Institute of Pathology; 1999:22-29.
3. Lowenstine LJ, McManamon R, Terio KA. Apes. In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. London, UK: Academic Press; 2018:399-400.
4. Patial S, Delcambre BA, DiGeronimo PM, Conboy G, Vatta AF, Bauer R. Verminous meningoencephalomyelitis in a red kangaroo associated with Angiostrongylus cantonensis infection. J Vet Diagn Invest. 2022;34(1):107-111.
5. Strait K, Else JG, Eberhard ML. Parasitic diseases of nonhuman primates. In: Abee CR, Mansfield K, Tardif S, et al., eds. Nonhuman Primates in Biomedical Research: Diseases. Vol 2. 2nd ed. London, UK: Elsevier; 2012:235-236.
6. Miller AD, Porter BF. Nervous system. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 7th ed. St. Louis, MO: Elsevier; 2022:931.

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