JPC SYSTEMIC PATHOLOGY

HEMOLYMPHATIC SYSTEM

February 2024

H-B05

 

SIGNALMENT (JPC 2131320): White-tailed prairie dog (Cynomys leucurus)

 

HISTORY: Tissue from an adult female white-tailed prairie dog (Cynomys leucurus) experimentally infected with an organism isolated from free ranging animals. 

 

HISTOPATHOLOGIC DESCRIPTION: 1. Lymph node and perinodal adipose tissue:  There is an overall loss of lymphocytes and diffusely, normal lymph node architecture (including capsule, cortex, paracortex, and medulla) is lost and replaced by necrotic debris, edema, fibrin, minimal hemorrhage, numerous degenerate and viable neutrophils, and fewer macrophages. There are numerous perivascular and, to a lesser extent, intravascular large colonies of pale basophilic to amphophilic, 1 x 2 µm coccobacilli. Multifocally, both peri- and intranodal vessels exhibit marked fibrinoid vasculitis characterized by discontinuous endothelium, expansion of the tunica media by fibrin, hemorrhage, edema, neutrophils and fewer macrophages and edema in the tunica adventitia. Multifocally and predominantly perivascularly, the previously mentioned inflammatory cells, fibrin, edema, necrotic debris, and bacterial colonies extend into and replace perinodal adipose tissue.

 

2.  Lung: There is diffuse fibrinoid vasculitis characterized by disruption and expansion of the tunica media by fibrin, hemorrhage, edema, neutrophils, and fewer macrophages, often associated with and intraluminal thrombi and occasionally containing large colonies of previously described coccobacilli. The perivascular connective tissue is expanded by fibrin, hemorrhage, and edema. Diffusely, alveolar septa are congested and minimally to moderately expanded up to 35µm by hemorrhage, fibrin, edema, thrombosed capillaries, neutrophils and lymphocytes admixed with small amounts of eosinophilic cellular and karyorrhectic debris (necrosis). Alveolar lumina occasionally contain fibrin, edema, and few alveolar macrophages. Multifocally, bronchioles contain small amounts of sloughed respiratory epithelium, debris and erythrocytes.

 

MORPHOLOGIC DIAGNOSIS: 1. Lymph node: Lymphadenitis, necrosuppurative, diffuse, severe, with fibrinoid vasculitis, multifocal perinodal steatitis, and numerous intra and extravascular coccobacilli, white-tailed prairie dog (Cynomys leucurus), rodent.

2. Lung: Vasculitis, fibrinoid, subacute, diffuse, marked, with necrotizing neutrophilic interstitial pneumonia, fibrin thrombi, and numerous intravascular coccobacilli.

 

ETIOLOGIC DIAGNOSIS: Yersinial lymphadenitis and pneumonia

 

CAUSE: Yersinia pestis

 

CONDITION: Plague, Sylvatic Plague, Yersiniosis

 

GENERAL DISCUSSION:

• Y. pestis is a gram negative, facultative anaerobic, non-spore forming, intracellular, 0.5-0.8 x 1-3 µm, bipolar-staining coccobacillus
• Plague is a reportable zoonotic disease caused by Yersinia pestis; it is infectious and often fatal in susceptible mammals (e.g. felids, black-footed ferrets); morbidity and mortality approach 100%  
• Rodent reservoirs include prairie dogs, ground squirrels, antelope ground squirrels, chipmunks, wood rats, and mice; also seen among wild rabbits

• Domestic ferrets are generally resistant to plague, while the endangered black-footed ferret is highly susceptible
• Enzootic reservoirs include voles and deer mice; epizootic reservoirs include prairie dogs, rats, and squirrels

• Plague is endemic in the western United States; focally extensive in parts of Asia, Africa, and South America as well

 

PATHOGENESIS:

• Transmission: Disease is primarily acquired via the bite of infected rodent fleas (e.g. Xenopsylla cheopsis), but may be horizontally transmitted, or via ingestion of water and food contaminated with rodent feces, or ingestion of infected rodents (i.e. as prey, cannibalism, or scavenging)
• Plasmids have contributed to the evolution of the Yersinia genus: Y. pestis has acquired two plasmids that differentiate it from other Yersinia spp., and has lost a number of enteropathogenic virulence genes

• One plasmid encodes a toxin as well as a capsule that allows it to survive within the flea, which the other Yersinia spp. cannot
• The second plasmid encodes a plasminogen activator that facilitates dissemination into the host following the flea bite

• Yersinia spp. pathogenesis is determined by a plasmid known as the Yop virulon, which encodes for a type III secretion system and the effector Yersinia outer proteins (Yops); expression is blocked in the flea but is active at 37^o C in the host

• YopH encodes a tyrosine kinase that blocks activation of T and B lymphocytes by dephosphorylating signaling proteins; prevents phagocytosis and oxidative burst
• YopK and others help inhibit host immune recognition of the type III secretion system, contributing to survival
• Other Yersinia spp. have additional Yops (YopJ, YopP)

• Other factors such as LcrV (low calcium response virulence) decrease anti-inflammatory signalling and neutrophil chemotaxis to tamp down host response

• Not surprisingly, Yops, LcrV, and T3SS genes are co-expressed as they are all on the same plasmid

• Expression of a capsule and iron sequestration (yersiniabactin) also aid extracellular multiplication

 

TYPICAL CLINICAL FINDINGS:  

1. Bubonic plague – Swollen, painful, draining lymph nodes, fever, anorexia, dehydration; possible septicemia

1. Pneumonic plague – Results from hematogenous or lymphogenous spread of organisms as a sequela to bubonic or septic plague
   • Primary pneumonic plague is contracted via inhalation

3. Septicemic plague – Bacteremia without palpable lymphadenopathy; systemic signs of fever, endotoxic shock and DIC

• A history of exposure to or consumption of rodents or prairie dogs would increase the index of suspicion, as would location in plague-endemic area
• In rodents, disease is usually peracute, and symptoms include lymphadenomegaly and subcutaneous hemorrhages

 

TYPICAL GROSS FINDINGS:

• Bubonic: Lymphadenomegaly (bubo), soft, pulpy, and plum colored with abscesses
• Pneumonic: Necrotizing pneumonia, fibrinous pleuritis
• Septicemic: Multifocal necrosis of many organs (liver, kidney, spleen, brain, lung, eye)

 

TYPICAL LIGHT MICROSCOPIC FINDINGS:  

• Histologic diagnosis is definitive: Large colonies of extracellular and intracellular bacteria with the following findings:

• Bubonic: Necrosuppurative lymphadenitis with numerous characteristic organisms, marked tissue swelling, necrosis, vasculitis, thrombosis, and hemorrhage
• Pneumonic: Necrotizing pneumonia with edema
• Septicemic: Multiorgan, multifocal abscessation and necrosis

 

ADDITIONAL DIAGNOSTIC TESTS:  

• Cytology: Bipolar-staining, gram-negative coccobacilli on lymph node aspirates, especially visible with Wright-Geimsa stains
• Culture: Growth on blood agar at tandem 37C and 28C temperatures; Y. pestis will grow faster at the lower temperature, but does not express the diagnostic marker F1 antigen at the lower temperature
• Immunohistochemistry

 

DIFFERENTIAL DIAGNOSIS:

Gross

• Francisella tularensis (tularemia): Acute, severe, febrile disease that causes pneumonia, septicemia, and death in rodents and humans; multifocal necrosis of liver, spleen, and lymph nodes that grossly resembles plague 
• Pasteurella spp.: Causes septicemia, pneumonia, and lymphadenitis in rodents; causes lymphadenitis in carnivores, which can grossly resemble plague lymphadenomegaly
• Tyzzer’s disease (Clostridium piliforme): Affected animals can also grossly present with miliary foci (especially on liver), petechiae/ecchymoses, and rapid, sudden death that can mimic some of the features of Y. pestis in the bubonic and/or septicemic form

 

Microscopic

• Y. pseudotuberculosis or Y. enterocolitica: Ulcerative and abscessing ileitis, colitis, and mesenteric lymphadenitis; differentiate by culture
• Bacteria that appear histologically as large colonies:

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

 

COMPARATIVE PATHOLOGY:  

Y. pseudotuberculosis (H-B04), Y. enterocolitica (see D-B11)

• Normal gastrointestinal inhabitants that may cause mild to severe diarrhea, septicemia, or lymphadenitis primarily in ruminants, although pigs, cervids (especially farmed deer), horses, wild ungulates, poultry, birds, wild rodents, wild hares (especially in Europe), nonhuman primates, and humans are also susceptible 

• Yersinia spp. invade the intestine via M cells overlying GALT via bacterial invasins and cell-associated β1-integrins à systemic spread 

• Latent carrier states exist in many species due to the bacteria’s facultative intracellular nature
• Cool temperatures support bacterial growth (versus body temperature)
• Lesions include intestinal lamina propria and crypt microabscesses and granulomas, caseonecrotic foci in the mesenteric nodes, spleen, and liver with abundant intralesional bacteria; in sheep, this condition is called “pyemic hepatitis”
• Y. enterocolitica shares an antigen with Brucella abortus, which may result in false positive agglutination reactions in brucellosis serologic testing
• Y. pseudotuberculosis bacteria may present with aberrant morphologies in tissues, including spheroplasts (globular bodies) and filaments

 

 

REFERENCES:  

1. Barthold SW, Griffey SM, Percy DH. Pathology of Laboratory Rodents and Rabbits. 4th ed. Ames, IA: Blackwell Publishing; 2016: 186, 230-231, 288.
2. Brown DL, Van Wettere AJ.  Hepatobiliary system and exocrine pancreas.  In: Zachary JF, ed. Pathological Basis of Veterinary Disease. 7th ed. Philadelphia, PA: Mosby Elsevier Inc.; 2022:516.
3. Delaney, A. Martha, Treuting, M. Piper, Rothenburger, L., Jamie. Rodentia. In: Pathology of Wildlife and Zoo Animals. London, United Kingdom: Academic press, 2018: 508.
4. Spagnoli S, Gelburg HB.  Alimentary system and the peritoneum, omentum, mesentery, and peritoneal cavity.  In: Zachary JF, ed. Pathological Basis of Veterinary Disease. 7th ed. Philadelphia, PA: Mosby Elsevier Inc.; 2022:453.
5. Moxley R.  Enterobacteriaceae: Yersinia.  In: McVey DS, Kennedy M, Chengappa MM, eds.  Veterinary Microbiology.  3rd ed. Ames, IA: Wiley & Sons, Inc.; 2013:85-94.
6. Simmons J, Gibson S.  Bacterial and mycotic diseases of nonhuman primates.  In: Abee CR, Mansfield K, Tardiff S, Morris T, eds.   Nonhuman Primates in Biomedical Research: Diseases, Vol. 2.  2nd ed.  Waltham, MA: Academic Press; 2012:138-141.
7. Swennes AG, Fox JG.  Bacterial and mycoplasmal diseases. In: Fox JG, Marini RP. Biology and Diseases of the Ferret.  3rd ed.  Ames, IA: Wiley & Sons, Inc.; 2014:543-544.
8. Terio, K. A., McAloose, D., Mitchell, Emily. Felidae. In: Pathology of Wildlife and Zoo Animals. London, United Kingdom: Academic press, 2018: 278.
9. Valli VEO, Kiupel M, Bienzle D.  Hematopoietic system. In: Maxie MG, ed. Jubb, Kennedy and Palmer’s Pathology of Domestic Animals. Vol 3. 6th ed. Philadelphia, PA: Elsevier Saunders; 2016:209-210.
10. Williams BH, Huntington ABK, Miller M. Mustelids. In: Pathology of Wildlife and Zoo Animals. London, United Kingdom: Academic press, 2018: 299.

Click the slide to view.

---