JPC SYSTEMIC PATHOLOGY
NERVOUS SYSTEM
March 2023
N-P13 (NP)
Signalment (JPC #1579146): Bottlenose dolphin.
HISTORY: This dolphin stranded on the southern California coast. The animal was transported to a local aquarium where it had trouble maintaining equilibrium, was dyspneic, and died.
HISTOPATHOLOGIC DESCRIPTION: Cerebrum: Multifocally, there is disruption of the gray and white matter architecture with extensive areas of liquefactive necrosis and cavitation (linear migration tracts) with replacement by hemorrhage, fibrin, edema, numerous gitter cells, degenerate neutrophils, eosinophils, lymphocytes, plasma cells, moderate amounts of black birefringent material (fluke pigment), a tangential section of an adult trematode, and triangular trematode eggs occasionally surrounded by multinucleated giant cells. The trematode is 500 µm wide with a 15 µm thick spiny tegument surrounding spongy parenchyma that contains numerous vitellaria, paired ceca, and testes. Eggs are 50 µm diameter, have a 5 um thick, golden brown, refractile shell, contain granular basophilic material. Within the adjacent neuroparenchyma, there is rarefaction, spongiosis, hemorrhage and a mild gliosis. Multifocally the leptomeninges and perivascular spaces are expanded by edema, fibrin, moderate numbers of lymphocytes, plasma cells, and eosinophils, fewer neutrophils, and hemosiderin-laden macrophages.
MORPHOLOGIC DIAGNOSIS: Cerebrum: Meningoencephalitis, necrotizing and granulomatous, multifocal, severe, with adult trematodes and eggs, bottlenose dolphin (Tursiops truncatus), cetacean.
ETIOLOGIC DIAGNOSIS: Cerebral nasitremiasis
CAUSE: Nasitrema sp.
ETIOLOGY SYNONYMS: Air sinus fluke, brain fluke
GENERAL DISCUSSION:
- Relatively common trematode found in numerous odontocete cetaceans (whales, porpoises, and dolphins); N. globicephae and other Nasitrema spp. are primarily found within the pterygoid sinuses and tympanic cavities
- Reportedly high prevalence of Nasitrema sp. on the southern California coast, thought to be an important cause of marine mammal strandings (study published in 1980s); since the 2000s stranded cetaceans have had a low incidence of Nasitrema sp. infection; shifting prevalence may be due to change in dietary preferences or prey availability in the region
PATHOGENESIS:
- Infection most likely acquired when host eats infected fish containing larval stages
- Aberrant migration can result in neuritis of the eighth cranial nerves, otitis media, and marked meningoencephalitis
LIFE CYCLE:
- Unknown
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- Migration tracts are seen in white and grey matter and are associated with necrosis and cavitations, extensive areas of hemorrhage, edema, and an influx of gitter cells, degenerate neutrophils and eosinophilic, lymphocytes, and plasma cells
- Intralesional black birefringent material (fluke pigment)
- Adult trematodes: 500 µm wide with a 15 µm thick, spiny tegument and contain numerous vitellaria, paired ceca, and testes all of which are surrounded by parenchyma
- Eggs: 50 µm triangular, thick walled, golden-brown shell
- Adjacent neural tissue may have spongiosis and gliosis; meninges and perivascular spaces are expanded by edema, fibrin, lymphocytes, plasma cells, eosinophils, and fewer neutrophils and hemosiderin-laden macrophages
DIFFERENTIAL DIAGNOSIS:
Encephalitis due to aberrant migration in cetaceans:
- Hunterotrema sp. – Large fluke that causes mucoid bronchitis and bronchiectasis in Amazon River dolphins; eggs identical to Nasitrema sp.
- Cyclorchis campula – Fluke that causes fibrosing hepatitis and pancreatitis; eggs identical to Nasitrema sp.
- Crassicauda sp.- Nematode located in pterygoid air sinus; mammary tissue, kidneys, urogenital system; associated disease includes sinusitis, osteitis, erosive bone lesions, and decreased milk production
- Arterial and renal crassicaudiasis recently reported in stranded Cuvier’s beaked whales; mesenteric arteries, gastroepiploic arteries, thoracic and abdominal aorta contained severe, extensive, chronic fibrosing arteritis with hemorrhage, thrombosis, and aneurysms, often associated with nematode larva; adult nematodes within renal arteries, veins, parenchyma, and/or ureter (Diaz-Delgado, Vet Pathol. 2016)
References:
- Diaz-Delgado J, et al. Verminous arteritis due to Crassicauda sp. in Cuvier’s beaked whales (Ziphius cavirostris). Vet Pathol. 2016; 56(6): 1233-1240.
- St. Leger J, Raverty S, Mena A. Cetacea. In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. San Diego, CA: Elsevier; 2018: 562-563, 564.e6-7.
