JPC SYSTEMIC PATHOLOGY

RESPIRATORY SYSTEM

September 2023

P-P06 

 

Signalment (JPC #2133906): Cow

 

HISTORY: None

 

HISTOPATHOLOGIC DESCRIPTION: Lung: Approximately 75% of this section is characterized by multifocal to coalescing areas of either coagulative necrosis characterized by retention of cellular architecture and loss of differential staining or lytic necrosis characterized by loss of architecture with replacement by eosinophilic cellular and karryorhectic debris as well as fragmented alveolar septa (septal necrosis). Multifocally, bronchiolar and alveolar lumina are filled and expanded by a dense inflammatory exudate composed of abundant viable and necrotic neutrophils and macrophages and few eosinophils admixed with abundant fibrin, edema, hemorrhage, and necrotic debris. Similar inflammation, hemorrhage, fibrin, edema, and necrotic debris also surrounds and infiltrates bronchiolar walls. Alveolar septa are thickened up to 3 times normal by macrophages, neutrophils, and fibrous connective tissue (fibrosis).   In areas of necrosis, alveoli, alveolar septa, and bronchiolar lumina contain numerous, often pale staining, amoebic trophozoites and cysts. Trophozoites are up to 25µm and have vacuolated cytoplasm and a 4-7µm karyosome with a single endosome. Cysts are up to 20µm with a clear halo separating an outer ectocyst and inner endocyst. Bronchiolar epithelium is multifocally hyperplastic with folds extending into the lumen. Multifocally, the tunica media and tunica adventitia of blood vessels are expanded and infiltrated by amoebic cysts and trophozoites, neutrophils, macrophages, fibrin, hemorrhage, and karyorrhectic debris (necrotizing vasculitis). There is perivascular hemorrhage with low to moderate numbers of macrophages, plasma cells and lymphocytes. The pleura is expanded by fibrin and edema. 

 

MORPHOLOGIC DIAGNOSIS: Lung: Pneumonia, fibrinonecrotizing and pyogranulomatous, chronic-active, multifocal to coalescing, severe, with amoebic trophozoites and cysts, breed unspecified, bovine.

 

ETIOLOGIC DIAGNOSIS: Pulmonary amebiasis

 

CAUSE: Acanthamoeba sp.

 

CONDITION: Acanthamebiasis

 

GENERAL DISCUSSION: 

• Amoebae (subphylum Sarcodina, superclass Rhizopodea) belonging to genera Acanthamoeba, Sappinia, Balamuthia, and Naegleria are free-living, opportunistic, saprophytic organisms found in soil and water that are occasionally pathogenic for animals and man 
• Amoebae can cause two types of CNS disease: primary amoebic meningoencephalitis by N. fowleri and chronic granulomatous amoebic encephalitis by Acanthamoeba sp. or B. mandrillaris
• For Acanthamoeba spp. primary sites of infection include respiratory tract and skin
• Immunosuppression is a common predisposing condition in amoebic infections 

 

PATHOGENESIS:

• Pulmonary infection by Acanthamoeba: Proposed routes of infection include inhalation of organisms from air or soil or exposure of nasal cavity to contaminated water, followed by colonization of nasal passages, subsequent organism replication, and descent into lower respiratory tract   
• Encephalitis due to Acanthamoeba: Most frequently caused by hematogenous infection from the lung or cutaneous lesions; alternatively, infection of the nasal passages can lead to retrograde spread to the CNS via olfactory nerves or penetration through cribriform plate, but this route is most frequently described for Naegleria fowleri  

 

LIFE CYCLE:

• Two stage life cycle: Dormant free-living cyst in environment and vegetative feeding form (trophozoites) in host tissues
• Cyst inhaled or ingested > excystation to amoeba form (trophozoite) > invade other tissues > binary fission > cyst formation

 

TYPICAL CLINICAL FINDINGS:

• Signs are dependent upon organs involved and reflect chronic granulomatous disease
• In dogs, clinical manifestations of acanthamebiasis are similar to canine distemper: fever, oculonasal discharge, anorexia, lethargy, respiratory distress (coughing and dyspnea), and CNS signs (dysmetria, head tilt, seizures, etc.)
• Clinical laboratory findings are non-specific

 

TYPICAL GROSS FINDINGS: 

• Lung: Pale tan to deep-red, raised, semisolid nodules distributed in all lung lobes; nodules may coalesce, with central cavitation  
• Brain: Large, multifocal, and vary from red to tan-brown due to hemorrhage and necrosis of parenchyma
• Other organs affected include skin, heart, liver, kidney, adrenal gland, and pancreas 

 

TYPICAL LIGHT MICROSCOPIC FINDINGS:

• Necrohemorrhagic lesions with purulent pyogranulomatous or granulomatous inflammation and intralesional amoebic trophozoites and cysts, sometimes within macrophages; in brain often seen in perivascular and subarachnoid spaces
• Trophozoites measure 15-50 µm in diameter and have a round, eccentric karyosome (nucleus) and a single, centrally located, prominent endosome (nucleolus) surrounded by a thin, clear rim; the cytoplasm is eosinophilic and contains glycogen vacuoles 
• Trophozoites can be mistaken for macrophages, but are differentiated by the presence of the karyosome, endosome, and vacuolated cytoplasm
• Cysts (ectocyst) are 15-25µm with a wrinkled outer wall and PAS-positive inner wall (endocyst) separated by a clear space

 

ADDITIONAL DIAGNOSTIC TESTS: 

• Organisms are PAS and GMS positive
• Can be cultured using potato dextrose agar 
• Species may be identified by immunofluorescence and PCR
• Cytologic findings: Cysts are 10-25µm with a two layer wall (ectocyst and endocyst that converge at wall pores), trophozoites are 15-50µm in diameter

 

DIFFERENTIAL DIAGNOSIS:

• Balamuthia mandrillaris:  Difficult to distinguish from Acanthamoeba on H&E; reported veterinary cases have been in old world primates (gorilla, gibbon, mandrill baboon, colobus monkey)
• Naegleria fowleri:  Causes acute hemorrhagic necrosis of the cerebral cortex and/or olfactory bulbs; pockets of amoebic trophozoites are present within edematous and hemorrhagic neuropil or occur deep in Virchow-Robin spaces and around blood vessels; cyst forms do not occur in host tissue
• Entamoeba histolytica:  Less distinct or invisible endosome; clumped, marginated chromatin; and lesions bound by a variably thick fibrous capsule; causes amebic abscesses in liver, lung, and brain, with typical, flask-shaped ulcers in the intestine
• Blastomyces dermatitidis:  Budding forms are usually present in blastomycosis; amoebic cysts may resemble B. dermatitidis, but lack budding forms and lack thick, double-contoured cell wall
• Prototheca sp. and Chlorella:  Uninucleated forms of these algal organisms are similar to Acanthamoeba cysts but can be distinguished by presence of endosporulated forms (triangular or wedge-shaped endospores)

 

COMPARATIVE PATHOLOGY:

• Acanthamoeba infections have been described in multiple nonhuman primate species and other mammals
• Balamuthia mandrillaris infections have been described in Old World and New World nonhuman primates; also in a Siberian tiger (Niedringhaus et al, 2023)
• Naegleria fowleri has flagella when free-living in water; has caused disease in a South American tapir; intranasal injection of amoebae causes meningoencephalitis in mice and monkeys  
• Entamoeba invadens causes severe amebic dysentery in certain groups of snakes and reptiles; other groups of reptiles (e.g. garter snake, box turtles) carry the organism as a commensal, do not develop dysentery, and transmit to susceptible species

• Entamoeba histolytica causes amebic dysentery in humans, nonhuman primates (especially old world), and rarely in other species (dogs, cats, pigs); many infections are asymptomatic; erosive/ulcerative colitis that is classically flask-shaped

• Neoparamoeba spp. (N. perurans, N. branchiphila and N. pemaquidensis) cause “amoebic gill disease” (AGD) in salmonids

• Amoeba of the family Cochliopodidae cause “nodular gill disease” in rainbow trout from freshwater habitats

 

REFERENCES: 

1. Boes KM. Respiratory System. In: Raskin RE, Meyer DJ, eds. Canine and Feline Cytology: A Color Atlas and Interpretation Guide. 4th ed. St. Louis, MO: Elsevier; 2023:189, 224-225.
2. Caswell JL, Williams KJ. Respiratory system. In: Maxie MG ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. 6th ed. Vol 2. St. Louis, MO: Elsevier; 2016:513,574.
3. De Terlizzi R, English K, Cowell RL, Tyler RD, Meinkoth JH. Transtracheal and Bronchoalveolar Washes. In: Valenciano AC, Cowell RL, eds. Diagnostic Cytology and Hematology of the Dog and Cat. 5th ed. St. Louis, MO: Elsevier Mosby; 2020:280.
4. Frasca S, Wolf JC, Kinsel MJ, et al. Osteichthyes. In:   Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals, Cambridge, MA Academic Press; 2018: 991-992.
5. Gardiner CH, Fayer R, Dubey JP. An Atlas of Protozoan Parasites in Animal Tissues, 2nd ed. Washington, DC: Armed Forces Institute of Pathology;1998;10-11
6. Niedringhaus KD, Gordon M, Yabsley MJ, Gai J, Uzal FA, Woolard KD. Fatal balamuthosis in a Siberian tiger and a literature review of detection options for free-living amoebic infections in animals. J Vet Diagn Invest. 2023 May;35(3):311-316.
7. Ossiboff FJ. Serpentes. In:  Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals, Cambridge, MA Academic Press; 2018: 915-916.
8. Rodrigues CE, Duque AH, Steinberg J, Woodburn DB. Chelonia. In:  Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals, Cambridge, MA Academic Press; 2018: 848-849.
9. Spagnoli ST, Gelberg HB. Alimentary system and the peritoneum, omentum, mesentery, and peritoneal cavity. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 7th ed. St. Louis, MO: Elsevier; 2022:456-457.
10. Strait K, Else JG, Eberhard ML. Parasitic diseases of nonhuman primates. In: Abee CR, Mansfield K, Tardif S, Morris T, ed. Nonhuman Primates in Biomedical Research: Diseases. Vol 2. London, UK: Academic Press; 2012: 208-209.
11. Uzal FA, Plattner BL, Hostetter JM. Alimentary system. In: Maxie MG ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. 6th ed. Vol 2. St. Louis, MO: Elsevier; 2016:242.

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