JPC SYSTEMIC PATHOLOGY

Hemolymphatic System

February 2024

H-B10

 

SIGNALMENT (JPC Accession #3134342): 7-month-old spayed female Maltese mix dog.

 

HISTORY: This dog presented with a 5-day history of lethargy and 2-day history of anorexia and vomiting. The dog was obtunded and laterally recumbent on physical exam. The dog was hypothermic (96.8F), with 8-10% dehydration. Following rehydration, the dog developed watery melena and vomited frank blood.

 

HISTOPATHOLOGIC DESCRIPTION: 

SLIDE A: Lymph node: Diffusely, there is lymphocyte loss and lymph node follicular and parafollicular architecture is effaced by numerous macrophages, low to moderate numbers of neutrophils, scattered hemorrhage with fibrin, increased clear space (edema), and necrotic cellular debris. Macrophages have abundant eosinophilic cytoplasm and often contain amphophilic 1µm coccoid rickettsiae, erythrocytes, or cellular debris. The subcapsular, cortical, and medullary sinuses and are diffusely expanded by a similar population of macrophages admixed with edema and hemorrhage. Sinus macrophages often demonstrate erythrophagocytosis.

 

Duodenum: Embedded within a mucosal crypt, there is a 400µm diameter adult trematode with spiny eosinophilic tegument, a muscular oral sucker, spongy parenchyma, vitellaria, testes with germ cells and sperm, and thin-walled, 3-5µm, refractile eggs that contain a miracidium. The adjacent mucosa is thickened with an infiltrate of lymphocytes, plasma cells, and macrophages that expand the lamina propria. Crypt epithelium is moderately proliferative with increased basophilia, vesiculate nuclei, and occasional pluristratification and crypts are occasionally mildly expanded by eosinophilic cellular and karyorrhectic debris (necrosis). There is mild villar blunting and fusion with loss of mucosal epithelium and scant hemorrhage. Remaining mucosal epithelium is occasionally degenerate with occasional swollen, vesiculate nuclei. Within scattered macrophages are intracellular 1µm amphophilic coccoid rickettsiae 

 

MORPHOLOGIC DIAGNOSIS:  

1. Lymph node: Lymphadenitis, granulomatous and necrotizing, diffuse, severe, with lymphocyte loss and intrahistiocytic rickettsiae, Maltese mix, canine.

 

2. Duodenum: Enteritis, granulomatous and lymphoplasmacytic, multifocal, moderate, with adult trematode and intrahistiocytic rickettsiae.

 

SLIDE B: (Giemsa) Lymph node: Diffusely, there are metachromatically staining (purple) 1µm cocci filling the cytoplasm of macrophages.

 

Duodenum: Multifocally, there are metachromatically staining 1µm coccoid organisms within the cytoplasm of epithelial cells and macrophages within the lamina propria.

 

SLIDE C: Cranial section of salmon fingerling: Multifocally expanding skeletal muscle, gill lamellae, and splenic parenchyma are numerous up to 125µm diameter cross sections of trematode metacercariae which compress adjacent parenchyma, characterized by a 3µm brightly eosinophilic cyst wall, spongy parenchyma, and an oral sucker.

 

MORPHOLOGIC DIAGNOSIS: Skeletal muscle; gill lamellae; kidney: Trematode metacercariae, multifocal, salmon, piscine.

 

ETIOLOGIC DIAGNOSIS: Neorickettsial lymphadenitis and enteritis

 

ETIOLOGY: Neorickettsia helminthoeca

 

CONDITION: Salmon poisoning disease (SPD); canine neorickettsiosis

 

GENERAL: 

· The genus Neorickettsia, along with three other genera (Anaplasma, Ehrlichia, and Aegyptianella) comprise the family Anaplasmatacea, within the order Rickettsiales. Anaplasmatacea organisms are minute, non-motile Gram-negative obligate intracellular bacteria that lack cell walls and infect cells of hematopoietic origin. Generally, they cause arthropod-borne systemic disease in animals as well as humans.  

· Salmon poisoning disease: acute, febrile, often fatal disease of canids (dog, fox, coyote) caused by the rickettsial organism Neorickettsia helminthoeca

·  Neorickettsia helminthoeca is a gram-negative cocci or pleomorphic bacterium, obligate intracellular and resides within macrophage vacuoles 

·   Occurs in the northwestern United States as well as eastern Siberia and Vancouver Island, Canada; this is the range of the 1st intermediate host: snail (Oxytrema silicula) 

 

PATHOGENESIS:

·  Nanophyetus salmincola adult trematode attaches to definitive host: fish eating mammal or bird intestinal mucosa > sheds eggs in feces > in water develop into ciliated larvae (miracidia) > enter 1st intermediate host: snail (Oxytrema silicula) > develop into free-swimming larvae (cercariae) > enter 2nd intermediate host: salmon/trout > develop into metacercariae in salmon/trout and encyst mostly in kidney but also in eyes, liver, intestinal wall, musculature, and fin > ingested by definitive host > develop into adult trematode in intestinal mucosa

·  If adult fluke harbors N. helminthoeca > rickettsiae released in intestine and inoculates definitive host via unknown mechanism > 1st replication in enterocytes > disseminated by histiocytic cells > lymph nodes, spleen, tonsils, thymus, liver, lungs, and brain 

·   The incubation period after ingestion in the DH is generally 5-7 days

·   The cause of death in SPD is unknown; mortality is low with antibiotic therapy and N. helminthoeca is not pathogenic in the 1^st or 2^nd intermediate host

 

TYPICAL CLINICAL FINDINGS:

·  Characterized by lethargy, pyrexia with splenomegaly, generalized lymphadenopathy, vomiting, and diarrhea

·   Serous nasal discharge 

·   Untreated cases of SPD have high mortality (up to 90%) within 6-10 days

 

TYPICAL GROSS FINDINGS:

·  Severe generalized lymphadenopathy (especially in abdominal cavity) and splenomegaly

·   Peyer’s patches elevated above mucosal surface

·  Thymic hemorrhage 

·   Flukes, primarily the duodenum; may cause tissue damage

·  Pale, swollen liver with exaggerated lobular pattern

·   Small intestinal intussusception, hemoabdomen

 

TYPICAL LIGHT MICROSCOPIC FINDINGS:

· Lymphocyte depletion with histiocytosis in lymph nodes and thymus; +/- splenic follicle necrosis

• Gram-negative, 0.3-2.0 µm, coccoid to pleomorphic organisms (“elementary bodies”) within macrophages and reticuloendothelial cells of lymphoid tissues, GI tract, and brain

• Lymphohistiocytic meningitis +/- elementary bodies in reticuloendothelial cells in the CNS

 

ADDITIONAL DIAGNOSTIC TESTS:

·  Gram-negative; stain purple with Giemsa; bright red rickettsia w/ blue nuclei with Macchiavello’s; black or dark brown with Levaditi’s

·  Fecal: Operculated trematode eggs appear in dog feces 5 to 8 days after ingestion of infected fish

· Lymph node aspirate or impression smears: Giemsa (purple) or Macchiavellos (red); Intra-cytoplasmic neoreckettsial bodies within macrophages

 

DIFFERENTIAL DIAGNOSIS:

·  Lymphadenopathy: Lymphoma, leishmaniasis, yersiniosis

·  Hemorrhagic enteritis: Canine parvovirus

·   Intracytoplasmic organisms in monocytes: Canine ehrlichiosis (E. canis)

• Stellanchatus falcatus: Canine disease clinically identical to SPD in Pacific Northwest from related neorickettsial organism harbored by N. salmincola (Pastenkos, Vet Pathol. 2020)
• Neorickettsia elokominica: Elokomin fluke fever, dog/bear/raccoon in Pacific Northwest, high morbidity but lower mortality than SPD; similar but less severe lesions

 

COMPARATIVE PATHOLOGY:

· SPD seen in sun bears (eosinophilic gastritis and enteritis) and coyotes 

· Rickettsiales order (Rickettsiaceae and Anaplasmataceae family) species of importance in veterinary medicine:

Pathogen	Host	Vector	Target cells	Disease
Aegyptianella pullorum	Poultry	Ticks	Erythrocytes, monocytes, macrophages	Aegyptianellosis
Anaplasma bovis	Cattle	Ticks	Erythrocytes	Bovine anaplasmosis
Anaplasma marginale	Ruminants	Ticks	Erythrocytes	Anaplasmosis
Anaplasma ovis	Sheep, goats	Ticks	Erythrocytes	Anaplasmosis
Anaplasma phagocytophilum   *formerly Ehrlichia equi and Ehrlichia phagocytophila	Ruminants, horses, humans	Ticks	Granulocytes	Tick-borne fever, equine and human granulocytic ehrlichiosis
Ehrlichia ruminantium    *formerly Cowdria ruminantium	Ruminants	Ticks	Granulocytes	Heartwater
Ehrlichia ondiri	Cattle	Ticks?	Granulocytes, monocytes	Bovine petechial fever
Ehrlichia ovina	Sheep	Ticks	Monocytes, macrophages	Ovine ehrlichiosis
Anaplasma platys	Dogs	Ticks?	Platelets	Canine cyclic thrombocytopenia
Ehrlichia canis	Dogs	Ticks	Monocytes, macrophages	Canine monocytic ehrlichiosis
Ehrlichia ewingii	Dogs	Ticks	Granulocytes	Canine granulocytic ehrlichiosis
Rickettsia ricketsii	Dogs	Ticks	Endothelial cells	Rocky Mountain spotted fever
Neorickettsia elokominica	Dogs, bears, raccoons	Flukes	Monocytes, macrophages, lymphoid cells	Elokomin fluke fever
Neorickettsia helminthoeca	Dogs, bears	Flukes	Monocytes, macrophages, lymphoid cells	Salmon poisoning disease
Neorickettsia risticii	Horses	Flukes	Monocytes, intestinal epithelial cells, mast cells	Potomac horse fever

 

 

REFERENCES:

1. Blauvelt M, Messick JB. The Lymph Nodes. In: Valenciano AC, Cowell RL, eds. Diagnostic Cytology and Hematology of the Dog and Cat. 5th ed. St. Louis, MO: Elsevier Mosby; 2014:174, 177.

2. Haddad JL, Marks Stowe DA, Neel JA. The Gastrointestinal Tract. In: Valenciano AC, Cowell RL, eds. Diagnostic Cytology and Hematology of the Dog and Cat. 5th ed. St. Louis, MO: Elsevier Mosby; 2014:305.

3. Keel MK, Terio KA, McAloose D. Canidae, Ursidae, and Ailuridae. In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. London, UK: Academic Press; 2018:244. 

4. Pastenkos G, Snekvik K, Bradway D, et al. A Novel Neorickettsial Infection in 3 Dogs in the Pacific Northwest. Vet Pathol. 2020;57(2):286-289.

5. Raskin RE. Chapter 4: Hemolymphatic System. In: Raskin RE, Meyer DJ, & Boes KM eds. Canine and Feline Cytopathology: A Color Atlas and Interpretation Guide. 4th ed. St. Louis, MO: Elsevier; 2022:134, 700. 

6. 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; 2022:482.

7. Uzal FA, Plattner BL, Hostetter JM. Alimentary System. In: Maxie MG, ed. Jubb, Kennedy & Palmer's Pathology of Domestic Animals. Vol 2. 6th ed. St. Louis, MO: Elsevier; 2016:117, 225-226. 

8. Valli VEO, Kiupel M, Bienzle D. Hemopoietic system. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 3. 6th ed. St. Louis, MO: Elsevier; 2016:148-149.

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