JPC SYSTEMIC PATHOLOGY

HEMOLYMPHATIC SYSTEM

February 2024

H-B04

 

Signalment (JPC#1577423): Three-year-old blesbok.

 

HISTORY: Tissue from a three-year-old blesbok (African ruminant) that developed an acute illness and died.

 

HISTOPATHOLOGIC DESCRIPTION: Lymph node: Approximately 80% of nodal architecture is replaced by multifocal to coalescing areas of lytic necrosis, characterized by loss of tissue architecture, and replacement by abundant eosinophilic cellular and karyorrhectic debris, admixed with numerous necrotic neutrophils, abundant eosinophilic beaded material (fibrin), and numerous large, up to 250 µm diameter, botryoid colonies of densely packed, 1 x 2 µm, basophilic coccobacilli. Diffusely, remaining medullary cords and sinuses are expanded by moderate numbers of foamy macrophages, which often contain phagocytized cellular debris and erythrocytes (erythrophagocytosis), and fewer plasma cells.  Multifocally, there are large areas of hemorrhage, and diffusely, there is moderate congestion of blood vessels. The previously described inflammatory cells, hemorrhage, and fibrin multifocally extend into and expand the capsule and perinodal adipose tissue.

 

MORPHOLOGICAL DIAGNOSIS: Lymph node: Lymphadenitis, necrosuppurative, subacute, diffuse, severe, with hemorrhage and numerous large colonies of coccobacilli, blesbok (Damaliscus dorcas), artiodactyl.

 

ETIOLOGIC DIAGNOSIS: Yersinial lymphadenitis

 

CAUSE: Yersinia pseudotuberculosis 

 

GENERAL DISCUSSION:

• Facultative intracellular, oxidase-negative, gram negative, coccobacillus

• Pathogenic species of the genus Yersinia include Yersinia pestis (causative agent of plague; H-B05), Y. pseudotuberculosis, and Y. enterocolitica
  • Y. pseudotuberculosis & Y. enterocolitica lesions are identical grossly and histologically; culture or PCR required to differentiate
  • Biochemical differences: Y. enterocolitica produces acid in sucrolose and is ornithine decarboxylase positive; Y. pseudotuberculosis produces acid in rhamnose and is ornithine decarboxylase negative
  • Yersinia spp. grow best at cooler temperatures; inactivated by heat
• Yersinia pseudotuberculosis (YPT) is a zoonotic agent; occurs worldwide and causes disease in a wide variety of wild, laboratory, and domestic mammals, as well as birds; also widely distributed in soil, water, and food (milk/meat products, vegetables)
  • YPT has been classified into serotypes O1-O15 based on expression of the O-antigen
  • More severe disease in chital & red deer, water buffalo & exotic ungulates
• Can survive and replicate in the soil and in aquatic environments outside of host for months to years 
• Latent infections common; asymptomatic carriers can break with disease during periods of stress (cold and wet weather, overcrowding, capture, etc.), resulting in herd or flock outbreaks

 

PATHOGENESIS:

• Rodents and various species of wild birds are the principal reservoirs

• Ingestion of contaminated food or water (or infected prey by carnivores)> bacteria adhere to distal small intestinal mucosal epithelial cells> enter GALT via uptake by M-cells, facilitated by expression of invasin which binds to β1 integrins and induces production of IL-8 > replicate in Peyer’s patches > local invasion of lamina propria or spread to the regional lymph nodes, causing lymphadenitis, and into the circulatory system leading to septicemia with spread to the liver, spleen, nervous system and lungs
• The intracellular environment of the phagocyte (37˚C, low calcium) activates the low calcium response (lcr) plasmid which leads to the production of surface proteins: V antigen and Yersinia outer membrane proteins (Yops)
• Virulence determinants:
  • Yersinia adhesion A protein (YadA, encoded on the pYV virulence plasmid), invasin (encoded by the chromosomal inv locus) and Ail (coded for by attachment invasion locus ail) facilitate bacterial contact for invasion of host small intestinal M-cells
    • YadA downregulates expression of invasion and inhibits phagocytosis, adheres to extracellular matrix proteins such as fibronectin, collagen and laminin; also inhibits classic complement & lectin pathway
    • Invasin and Ail bind to M-cell beta-1 integrins, promoting uptake
  • Yops: YopB & YopD form a pore in the host cell membrane which allows the type three secretion system (T3SS) injectisome (structure similar to flagella) to inject effector Yops into the host cell (Yop proteins inhibit the host inflammatory response via alteration of phagocyte function/resistance to phagocytosis, inhibition of oxidative burst, interference with signal transduction and disruption of the cytoskeleton)  
    • YopH encodes a tyrosine kinase that blocks activation of T and B cells
    • YopE, YopH, YopT block phagocytosis
    • YopM sequesters caspase-1, which blocks activation of pro-inflammatory cytokines 
    • YopP (Y. enterocolitica) / YopJ (Y. pseudotuberculosis) induces apoptosis of host cells by inhibiting the inflammatory and pro-survival actions of LPS and directly activating caspases  
    • YopK helps inhibit host recognition of type III secretion system
      • RNA chaperone protein Hfq is important in production of T3SS effectors and intracellular survival
      • PhoP/Q system (chromosomally encoded) stimulates growth and survival in macrophages as well as delayed macrophage activation via reduction in the stimulatory capacity of LPS
      • Superantigenic toxin YPM induces T-cell proliferation and cytokine production
      • Chromosomal high-pathogenicity island (HPI) for the siderophore yersiniabactin
• Abortion can occur after localization of bacteria in maternal caruncle, followed by passage to the chorioallantois and the fetus

 

TYPICAL CLINICAL FINDINGS:

• In acute infections, animals may be found dead without showing clinical signs
• Clinical signs: Malaise, depression, anorexia, vomiting, abdominal discomfort, diarrhea, icterus, lymphadenopathy, dyspnea, emaciation, and sudden death
• May cause abortion in cattle, sheep and goats (and NHPs)

 

TYPICAL GROSS FINDINGS:

• Caseonecrotic foci in mesenteric nodes, spleen, liver, occasionally lungs, kidneys, and bone marrow
• Multifocal to diffuse, often transmural, hemorrhage and necrosis of the small and large intestine (ulcerative enterocolitis)
• With abortion, fetus is well preserved and cotyledons are tan-red and thickened; some caruncles may still be attached with fibrin and fibrosis surrounding affected cotyledons

 

TYPICAL LIGHT MICROSCOPIC FINDINGS: 

• Lymphoid hyperplasia and histiocytosis in spleen and lymph nodes

• Necrosis with large gram negative microcolonies of coccobacilli with microabscesses, often seen first in ileum and colon and extending into regional lymph nodes
• Aberrant bacterial morphologies possible: Globular bodies, spherules, filaments
• Epithelioid macrophages in more chronic lesions, along with a fibrous capsule; conflicting reports on the presence or absence of multinucleated giant cells
• Necrotic placental villi with infiltrates of granulocytes, macrophages, and mononuclear cells in the interstitium of the chorioallantois with fibrinoid necrosis of placental vessels 
• Fetus: Numerous large bacterial colonies and multifocal areas of necrosis with infiltration of mononuclear cells and neutrophils, fibrin and edema in the lungs; also hepatic, myocardial and lymph node necrosis

 

ULTRASTRUCTURAL FINDINGS:

 

ADDITIONAL DIAGNOSTIC TESTS:

• Cold enrichment and culture (from blood, lesions, or feces) at temps below 37ºC (Yersinia spp. are psychrophiles)
• PCR

 

DIFFERENTIAL DIAGNOSIS:

Bacteria that appear histologically as large colonies: 

• Yersinia enterocolitica and pestis: Differentiate by culture and PCR
• Actinomyces sp. gram (+)
• Actinobacillus sp. gram (-)
• Corynebacterium sp. gram (+)
• Staphylococcus sp. gram (+)
• Streptococcus sp. gram (+)
• Trueperella pyogenes gram (+)
• Nocardia sp. gram (+)

*Francisella tuarensis is an important clinical differential but large bacterial lesions are not observed histologically

 

COMPARATIVE PATHOLOGY:

• Hamsters, Guinea pigs, rabbits: Necrotic caseous nodules in intestine, mesenteric lymph nodes, liver, spleen, and lungs; large colonies of bacteria usually readily apparent, often surrounded by microabscesses 
  • Caseous necrosis may also affect reproductive tract in rabbits
• Dogs, cats: Cats more likely to be infected due to predation of birds & rodents
  • May be asymptomatic carriers
• Rodents: Mice, voles, beavers, muskrats, and agoutis (in captivity) susceptible to acutely fatal disease; other species may act as carriers
  • Lesions include necrotizing hepatitis and splenitis and/or fibrinonecrotizing and ulcerative enterocolitis
  • Beavers: Acute necrotizing hepatitis and splenitis, intravascular septic emboli in lungs, small intestine, and kidneys, ulcers of tail and hind feet
  • Rats: Scattered raised nodules in liver, spleen, and other organs; produces epidemic disease
• Birds:
  • Clinical disease in birds includes acute sepicemia followed by chronic focal infection with caseous nodules; resembles avian tuberculosis
  • Village weaver birds: Three birds developed injection-site sarcomas after autogenous Yersinia pseudotuberculosis vaccination.
    • First report of presumptive vaccine-associated sarcoma in a non-mammalian species
  • Galliformes and Columbiformes: Clinical signs and lesions depend on chronicity; chronic disease more common than acute; lesions range from acute coagulative hepatic necrosis to giant cell granulomas (liver), similar lesions in spleen and kidneys
  • Psittacines: Infections in is rare; multifocal (miliary) caseous lesions in liver and other organs; presentation is typically hepatosplenomegaly +/- enteritis
  • Passerines and toucans: infections reported in zoo settings, toucans reported to be highly susceptible
  • Reported in Europe in passerines, ramphastids, turacos but rarely isolated from these birds as a pathogen in the U.S.
  • Likely responsible for epornitics in canaries, lorikeets, and mynahs 
    • Postmortem lesions in canaries and related species include significant splenomegaly
• Fish: In freshwater fish, especially rainbow trout, Y. ruckeri causes “red mouth disease” or “enteric redmouth”, a hemorrhagic inflammation of the perioral subcutis
• Bats: Reported in captive Pteropus rodicensis and Rousettus egypticus, and free-ranging Myotis myotis; necrosuppurative splenitis, hepatitits, nephritis, and pneumonia, and bone marrow necrosis
• Non-human primates: Triad of lesions usually seen at necropsy - Multifocal hepatic and splenic necrosis or abscess formation, mesenteric lymphadenopathy, ulcerative enterocolitis
  • Reported cause of abortion in squirrel monkeys and owl monkeys
  • Recognized as cause of enteric disease in captive prosimians
• Cattle: Enterocolitis; mesenteric lymphadenitis; septicemia with foci of necrosis in liver, spleen, lungs; abortion; and pneumonia  
• Sheep and Goats: A recent study in California identified goats as one of the most common mammals with YPT; enterocolitis was the most common manifestation; also mesenteric lymphadenitis & necrosis in liver (ovine yersiniosis known as “pyemic hepatitis”), spleen, lungs; placentitis with abortion or perinatal mortality; epididymitis/orchitis; oculoglandular syndrome/conjunctivitis (goats); and mastitis
• Swine: Necrotic foci surrounded by a thin layer of granulation tissue in lung, liver, spleen, mesenteric lymph nodes, and lymphoid follicles in large intestine; swine considered the major source of human food-borne disease due to Y. enterocolitica
• Meerkats: Necrotizing enteritis, hepatitis, splenitis (primarily neutrophilic); Morphology: bacilli and aberrant globular bodies strongly positive for the Y. pseudotuberculosis O4 antigen (IHC)
• Anteaters, tenrec, hedgehogs, armadillo: enteritis often associated with poor husbandry or contaminated feed, or immunocompromise
• Captive African lions: Outbreak reported in three animals (two died)
  • Second report of aberrant morphology: pleomorphic rod and filamentous morphologies in bacterial colonies found in tissues of one animal (typical colonies of coccobacilli found in other animal)

 

REFERENCES:

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