August 2019

Signalment (JPC# 1662297):  6-year-old male chimpanzee (Pan troglodytes)

HISTOPATHOLOGIC DESCRIPTION:  Slide A:  Haired skin:  Diffusely expanding the dermis, elevating the epidermis, widely separating collagen bundles, and extending to surgical margins are numerous histiocytes and fewer lymphocytes, plasma cells, and reactive fibroblasts arranged in variably sized nodular aggregates and multifocally infiltrating peripheral nerves.  Histiocytes either have abundant, microvacuolated, eosinophilic cytoplasm or a variably sized (up to 50µm in diameter), clear, cytoplasmic vacuole with clumped aggregates of intracytoplasmic, amphophilic to lightly basophilic, fibrillar material (lepra cells).  Dermal collagen is often fragmented and hypereosinophilic (collagenolysis).  Small vessels within the granulomatous nodules are lined by hypertrophied, reactive endothelium.  Multifocally, the epidermis is mildly hyperplastic with acanthosis and there is diffuse moderate orthokeratotic hyperkeratosis.

Peripheral nerve:  Diffusely expanding and infiltrating into the nerve fascicles and expanding and elevating the perineurium and epineurium are abundant inflammatory infiltrates as previously described.  Cytoplasmic vacuoles within lepra cells are up to 100um in diameter.  There are multifocal areas of mild perineural fibrosis admixed with numerous lymphocytes and fewer plasma cells.

Liver:  Multifocally and randomly, there are variably sized nodular aggregates of the previously described histiocytes with large, clear cytoplasmic vacuoles (lepra cells) multifocally admixed with few to many viable and degenerate neutrophils.  Diffusely, hepatocytes contain numerous, variably sized, intracytoplasmic, clear vacuoles (vacuolar change). Multifocally, there are few periportal lymphocytes and fewer macrophages and plasma cells.

Slide B:  Acid-fast stain:  Haired skin, liver, and peripheral nerve:  Vacuoles within histiocytes contain numerous acid-fast, 2-3 µm x 1 µm bacilli, occurring singly and in long, beaded chains up to 8-10 µm in length.


  1. Haired skin:  Dermatitis, granulomatous, diffuse, severe, with granulomatous neuritis, moderate orthokeratotic hyperkeratosis, and intrahistiocytic acid-fast bacilli, chimpanzee (Pan troglodytes), nonhuman primate.
  2. Peripheral nerve: Neuritis, granulomatous, diffuse, severe, with mild perineural fibrosis, and intrahistiocytic acid-fast bacilli.
  3. Liver: Hepatitis, histiocytic and neutrophilic, random, mild, with intrahistiocytic acid-fast bacilli. 

ETIOLOGIC DIAGNOSIS:  Mycobacterial dermatitis, neuritis, and hepatitis

CAUSE:  Mycobacterium leprae

CONDITION:  Lepromatous leprosy

SYNONYMS:  Leprosy; Hansen’s disease











  1. Ackermann MR. Inflammation and healing. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 6th ed., St. Louis, MO: Elsevier; 2017:110-111.
  2. Avansi C, et al. Red squirrels in the British Isles are infected with leprosy bacilli. 2016; 354(6313):744-747.
  3. Further evidence of leprosy in Isle of Wright red squirrels. Vet Rec. 2017; 180(16): 407.
  4. Hargis AM, Myers S. The integument. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 6th ed., St. Louis, MO: Elsevier; 2017:1032-1033, 1143.
  5. Magden ER, Mansfield KG, Simmons JH, Abee CR. Nonhuman primates. In: Fox JG, Anderson LC, Otto GM, Whary MT, eds. Laboratory Animal Medicine. 3rd ed. San Diego, CA: Elsevier; 2015:858-859.
  6. Malik R, Smits B, Reppas G, et al. Ulcerated and nonulcerated nontuberculous cutaneous mycobacterial granulomas in cats and dogs. Vet Dermatol. 2013; 24(1):146-153.
  7. Mauldin EA, Peters-Kennedy J. Integumentary system. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 1. 6th ed. St. Louis, MO: Elsevier; 2016: 640-641.
  8. McAdam AJ, Milner DA, Sharpe AH. Infectious diseases. In: Kumar V, Abbas AK, Aster JC, eds. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Philedelphia, PA: Elsevier Saunders; 2015:377-378.
  9. Njaa BL. The ear. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 6th ed. St. Louis, MO: Elsevier; 2017:1259-1260.
  10. Perez-Heydrick C, Loughry WJ, Anderson CD, Oli MK. Patterns of Mycobacterium leprae infection in wild nine-banded armadillos (Dasypus novemcinctus) in Mississippi, USA. J Wildl Dis. 2016; 52(3):524-532.
  11. Shilling AK, et al. Leprosy in red squirrels in the UK. Rec. 2019; 184(13):416.
  12. Simmons J, Gibson S. Bacterial and Mycotic Diseases of Nonhuman Primates. In: Abee CR, Mansfield K, Tardif S, et al. Nonhuman primates in biomedical research: Diseases. Vol 2.  San Diego, CA: Academic Press; 2012: 136-138.
  13. Truman RW, Singh P, Sharma R, et al. Probable zoonotic leprosy in the Southern United States. N Engl J Med. 2011; 364(17):1626-1633.

Click the slide to view.

Click on image for diagnostic series.

Back | Home | Contact Us | Links | Help |