JPC SYSTEMIC PATHOLOGY

RESPIRATORY SYSTEM

September 2017

P-B06

 

SIGNALMENT (JPC# 4069782): 3-month-old miniature horse filly

HISTORY: This filly presented with a one week history of non-resolving respiratory congestion.  High fever and increased respiratory rate were noted and (unspecified) treatment was initiated.  The patient was initially responsive to care, but subsequently had two seizures and died

HISTOPATHOLOGIC DESCRIPTION: Effacing approximately 40% of the normal pulmonary parenchyma there are multiple pyogranulomas (up to 11mm) composed of a central core of necrosis with numerous degenerate neutrophils and macrophages, admixed with necrotic cellular debris, fibrin and scattered mineral, surrounded by epithelioid macrophages, fewer multinucleated giant cells, and low numbers of lymphocytes and plasma cells.  Macrophages and multinucleated giant cells are often packed with numerous 1-2um basophilic coccobacilli. Similar inflammatory cells (including macrophages packed with coccobacilli), necrotic debris and fibrin fill remaining bronchioles, infiltrating through the bronchiolar epithelium/wall to fill adjacent alveoli and efface alveolar septa (necrosis). There is multifocal type II pneumocyte hyperplasia.  Bronchiolar epithelial cells are multifocally necrotic with sloughing into the lumen. In less affected areas, alveolar septa are expanded up to 4 times normal by fibrin, edema and low numbers of macrophages.  There are multifocal areas of mild hemorrhage and a few hemosiderin-laden macrophages are present.  The pleura and interlobular septa are expanded up to 5 times normal by fibrin and edema.  Multifocally, vascular walls contain mild neutrophilic infiltrate and are rimmed by moderate perivascular edema.

MORPHOLOGIC DIAGNOSIS: Lung: Pneumonia, pyogranulomatous and necrotizing, multifocal-to-coalescing, chronic-active, severe, with numerous intrahistiocytic coccobacilli, miniature horse, equine.

ETIOLOGIC DIAGNOSIS:  Rhodococcal pneumonia

CAUSERhodococcus equi

GENERAL DISCUSSION:  

PATHOGENESIS: 

TYPICAL CLINICAL FINDINGS: 

TYPICAL GROSS FINDINGS: 

TYPICAL LIGHT MICROSCOPIC FINDINGS: 

ADDITIONAL DIAGNOSTIC TESTS: 

DIFFERENTIAL DIAGNOSIS:

Granulomatous pneumonia

Foal pneumonia:
Bacterial

Viral

Fungal

COMPARATIVE PATHOLOGY: 

References:

  1. Bryan, LK, Clark, SD, Díaz-Delgado J, et al. Rhodococcus equi infections in dogs.  Vet Pathol.  2017;54(1):159-163.
  2. Caswell JL, Williams KJ. Respiratory system. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 2. 6th ed. Philadelphia, PA: Elsevier; 2016:569-571.
  3. Chaffin MK, Cohen ND, Martens RJ, Edwards RF. Foal-related risks factors associated with development of Rhodococcus equi pneumonia on farms with endemic infection. J Am Vet Med Assoc. 2003;223(12):1791-1799.
  4. Cohen, ND, Chaffin MK, Kuskie KR, et al. Association of perinatal exposure to airborne Rhodococcus equi with risk of pneumonia caused by R equi in foals. Am J Vet Res. 2013;74(1):102-9.
  5. Davis WP, Stefick BA, Watson GL, et al. Disseminated Rhodococcus equi infection in two goats. Vet Pathol. 1999;36(4):336-339.
  6. Dawson DR, Nydam DV, Price CT, et al. Effects of opsonization of Rhodococcus equi on bacterial viability and phagocyte activation. Am J Vet Res. 2011;72(11):1465-75.
  7. Giguere S. Rhodococcus equi In: Smith BP, ed. Large Animal Internal Medicine. 5th ed. St Louis, MO: Mosby; 2015:481-488.
  8. Giguere S, Cohen ND, Chaffin MK, et al. Rhodococcus equi: clinical manifestations, virulence, and immunity. J Vet Intern Med. 2011;25(6):1221-1230.
  9. Jeckel S, Holmes P, King S, et al. Disseminated Rhodococcus equi infection in goats in the UK. Vet Rec. 2011;169(2):56.
  10. Lopez A, Martinson SA. Respiratory system, mediastinum, and pleurae. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 6th ed. St. Louis, MO: Elsevier Mosby; 2017:526-527.
  11. Patel A. Pyogranulomatous skin disease and cellulitis in a cat caused by Rhodococcus equi. J Small Anim Pract. 2002;43(3):129-132.
  12. Petry S, Sèvin C, Fleury MA, et al. Differential distribution of vapA-positive Rhodococcus equi in affected and unaffected horse breeding farms.  Vet Rec. 2017;181(6):145.
  13. Sakai M, Ohno R, Higuchi C, et al. Isolation of Rhodococcus equi from wild boars.  J Wildlife Dis. 2012; 48(3):815-7.
  14. Uzal FA, Plattner BL, Hostetter JM. Alimentary system. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 2. 6th ed. Philadelphia, PA: Elsevier; 2016:197-198.
  15. Zachary JF. Mechanisms of microbial infections. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 6th ed. St. Louis, MO: Elsevier Mosby; 2017:168-169.


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