March 2018


HISTORY:  Tissue from a 150 gm male rat inoculated intraperitoneally with an infectious agent and killed 72 hours later.

HISTOPATHOLOGIC DESCRIPTION:  Spleen: Effacing over 85% of the splenic white pulp are multifocal to coalescing nodules of lytic necrosis, up to 2 mm in diameter, that are composed of abundant eosinophilic cellular and karyorrhectic necrotic debris and variable amounts of eosinophilic finely beaded fibrillar fibrin admixed with few lymphocytes, macrophages, and erythrocytes. Nodules are surrounded by moderate amounts of fibrin and edema that extends into the adjacent red pulp. The remaining white pulp is hypocellular (lymphoid depletion). Multifocally, trabecular arteries contain fibrin thrombi and vessels are lined by hypertrophied, reactive endothelial cells. Multifocally, the capsule contains few lymphocytes and plasma cells and mesothelial cells are hypertrophic (reactive).

Lymph node: Expanding and replacing the cortical follicles and paracortical lympohocytes, and extending into subcapsular sinuses are multiple coalescing foci, up to 1 mm in diameter, of necrosis (lymphoid depletion), often surrounded by moderate numbers of macrophages.  Affected areas are composed of abundant eosinophilic cellular and karyorrhectic debris admixed with may individula necrotic cells, fibrin and edema. Medullary and subcapsular sinuses are expanded by numerous foamy macrophages, many with intracytoplasmic erythrocytes (erythrophagocytosis), and increased clear space (edema) and small amounts of fibrin. Vessels are often lined by hypertrophic epithelium and are diffusely congested and there is perivascular edema. 


  1. Spleen: Splenitis, necrotizing, subacute, multifocal to coalescing, severe, with lymphoid depletion, breed unspecified, rat, rodent.
  2. Lymph node: Lymphadenitis, necrotizing, subacute, multifocal, severe, with lymphoid depletion, sinus histiocytosis, erythrophagocytosis, edema, and diffuse congestion.

ETIOLOGIC DIAGNOSIS:  Splenic and lymphatic francisellosis

CAUSE:  Francisella tularensis

CONDITION:  Tularemia, Rabbit fever, deer fly fever, Ohara"s Disease








Multifocal necrotizing lymphadenitis, splenitis, and hepatitis in laboratory animals:



  1. Berman-Booty LD, Cui J, Horvath SJ, Premanandan C. Pathology in practice. J Am Vet Med Assoc. 2010;237(2):163-165.
  2. Brown VR, Adney DR, Bielefeldt-Ohmann H, et al. Serologic Survey of Snowshoe Hares (Lepus americanus) in the Greater Yellowstone Area for Brucellosis, Tularemia, and Snowshoe Hare Virus Full Access. J Wildl Dis. 2015:51(3):769-73.
  3. Gelberg HB. Alimentary System and the Peritoneum, Omentum, Mesentery, and Peritoneal Cavities. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 6th ed. St. Louis, MO: Mosby/Elsevier; 2017:444.
  4. Gyuranecz M, Fodor L, Makrai L, et al. Generalized tularemia in a vervet monkey (Chlorocebus aethiops) and a patas monkey (Erythrocebus patas) in a zoo. J Vet Diagn Invest. 2009;21(3):384-387.
  5. Gyuranecz M, Szeredi L, Makrai L, et al. Tularemia of European brown hare (Lepus europaeus): a pathological, histopathological, and immunohistochemical study. Vet Pathol. 2010;47(5):958-963.
  6. Hestvik G, Uhlhorn H, Sodersten F, et al. Tularaemia in European Brown Hares (Lepus europaeus) and Mountain Hares (Lepus timidus) Characterized by Histopathology and Immunohistochemistry: Organ Lesions and Suggestions of Routes of Infection and Shedding. J Comp Pathol. 2017:157(2-3):103-114.
  7. Larson MA, Fey PD, Hinrichs SH, Iwen PC. Francisella tularensis bacteria associated with feline tularemia in the United States. Emerg Infect Dis. 2014;20(12):2068-2071.
  8. Matz-Rensing K, Floto A, Schrod A, et al. Epizootic of tularemia in an outdoor housed group of cynomolgus monkeys (Macaca fascicularis). Vet Pathol. 2007;44(3):327-334.
  9. Nelson DD, Haldorson GJ, Stanton JB, et al. Francisella tularensis infection without lesions in gray tree squirrels (Sciurus griseus): a diagnostic challenge. J Vet Diag Invest. 2014;26(2):312-315.
  10. Origgi FC, Pilo P. Francisella tularensis Clades B.FTN002-00 and B.13 Are Associated With Distinct Pathology in the European Brown Hare (Lepus europaeus). Vet Pathol. 2016:53(6):1220-1232.
  11. Spagnoli ST, Kuroki K, Schommer SK, Reilly TJ, Fales WH. Pathology in practice. J Am Vet Med Assoc. 2011;238(10):1271-1273.
  12. Twenhafel NA, Alves DA, Purcell BK. Pathology of inhalational Francisella tularensis spp. tularensis SCHU S4 infection in African green monkeys (Chlorocebus aethiops). Vet Pathol. 2009;46(4):698-706.
  13. Tylers D, Zimmer J, Lewandowski K. Serologic Survey of Snowshoe Hares (Lepus americanus) in the Greater Yellowstone Area for Brucellosis, Tularemia, and Snowshoe Hare Virus. J Wildl Dis. 2015:51(3):769-73.
  14. Valli VEO, Kiupel M, Bienzle D. Hematopoietic system. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. 6th ed. Vol 3. Philadelphia, PA: Elsevier; 2016:184-186.


Click the slide to view.

Click on image for diagnostic series.

Back | Home | Contact Us | Links | Help |