Adult male cynomolgus macaque (Macaca fascicularis).This macaque was in a study to determine the efficacy of a novel therapeutic drug for treating Marburg virus (MARV) infection.  All of the monkeys in this study were inoculated subcutaneously with MARV and then once daily intramuscular treatments with either saline (control group) or different doses of the therapeutic drug (experimental groups) began.  This animal was in one of the experimental groups and it was found dead on Day 11 after viral challenge.
This monkey was part of a research project conducted under an IACUC approved protocol in compliance with the Animal Welfare Act, PHS Policy, and other federal statutes and regulations relating to animals and experiments involving animals. The facility where this research was conducted is accredited by the Association for Assessment and Accreditation of Laboratory Animal Care, International and adheres to principles stated in the 8th edition of the Guide for the Care and Use of Laboratory Animals, National Research Council, 2011.

Gross Description:  

The mucosa of the rectum and distal 20 cm of the colon was diffusely hemorrhagic.  The liver was enlarged (~1.5 X), pale tan, and markedly friable. The spleen was also friable.  Other organs were unremarkable.

Histopathologic Description:

Lung (right inferior lobe):  Multifocally within alveoli and often attached to the alveolar septa, there are low numbers of multinucleated giant cells, measuring up to 100 µm in diameter, most of which contain intra-cytoplasmic aggregates of pale blue-gray amorphous to spicular refractile material.  The interstitium also contains scattered aggregates of low numbers of histiocytes containing intracytoplasmic brown-black finely-granular material.  Many blood vessels contain numerous intraluminal mononuclear leukocytes (monocytes).

Morphologic Diagnosis:  

1. Lung; intravascular leukocytosis (monocytic), moderate
2. Lung; multifocal histiocytic (multinucleated giant cell) alveolitis, mild, with intracytoplasmic crystalline foreign bodies 3. Lung; multifocal interstitial anthracosilicosis, minimal

Lab Results:  



Histiocytic alveolitis with intracytoplasmic crystalline protein

Contributor Comment:  

The timing of this monkey’s death is within the usual interval (i.e. 7-11 days) that cynomolgus macaques die after experimental exposure to a lethal dose of MARV.  There were histologic lesions in the liver, spleen, adrenal glands, tonsils, and lymph nodes of this monkey that were caused by MARV infection; these organs are considered “target organs” for the virus.7 Immuno-histochemistry (IHC) revealed MARV antigen in every organ examined from this animal.  The histologic findings and IHC results confirmed that this macaque died from a disseminated MARV infection.  Although the exact cause of the intestinal bleeding noted at necropsy was not determined, this was most likely associated with MARV-induced coagulopathy; disseminated intravascular coagulopathy (DIC) occurs commonly in primates (including humans) infected with viruses in the family Filoviridae (i.e. ebolaviruses and MARV).6,7
The monocytic leukocytosis noted within pulmonary blood vessels of this monkey is attributable to the viral infection.  IHC revealed abundant MARV antigen in many of these monocytes.  Cells of the monocyte-macrophage system are infected very early during the course of filovirus infection and are primarily responsible for disseminating the viruses throughout the body.5,7
The presence of multinucleated giant cells within alveoli and/or attached to alveolar septa of this monkey was an unexpected finding and was unrelated to the MARV infection.  This lesion was seen in the right inferior lung lobe but not in the other lung lobes that were examined histologically. These giant cells were an inflammatory response to the presence of intra-alveolar crystalline foreign material; the foreign material was initially phagocytized by macrophages that then fused to form large multinucleated cells.1 IHC revealed that some of the giant cells also contained intracytoplasmic MARV antigen.
The composition of the crystalline foreign material, which is anisotropic in polarized light, is unknown.  However, a review of the medical records for this monkey revealed that approximately one month before the initiation of the MARV study, this animal had been administered an oral suspension of Pepcid® once a day for three consecutive days. It is possible that some of the suspension was aspirated into the right inferior lung lobe (which is a dependent lung lobe in a primate).  The active ingredient in the Pepcid® suspension is famotidine, which is a crystalline compound, and inactive ingredients include microcrystalline cellulose.2 Overall, the foreign-body alveolitis was a very mild and clinically insignificant lesion that did not affect the pathogenesis or outcome of the MARV challenge. Anthracosilicosis is a common finding in adult macaques and is usually an incidental lesion (as in this case). Note: Opinions, interpretations, conclusions, and recommendations are those of the author and are not necessarily endorsed by the U.S. Army.

JPC Diagnosis:  

Lung: Alveolitis, histiocytic, multifocal, mild with low numbers of multinucleated giant cell macrophages and abundant intracytoplasmic crystalline protein, cynomolgus macaque, Macaca fascicularis.

Conference Comment:  

This interesting case was submitted by the conference moderator and presented participants with a diagnostic challenge to identify the origin of the amphophilic, anisotropic, and crystalline material within macrophages and multi-nucleated giant cells in this section of lung. Most favored the diagnosis of pneumo-coniosis, which is a lung disease secondary to inhalation of inorganic particulate material, such as asbestos or silica.4 Readers are encouraged to review Wednesday Slide Conference 2015 Conference 3 Case 4 for a review and fascinating discussion of silicate pneumoconiosis in a horse from California. Silica dusts typically generate a granulo-matous inflammatory response with fibrosis, not seen in this case. Additionally, asbestos fibers in the lung are linear and beaded with globoid ends, also not a feature of this case.4
There have been sporadic reports of kaolin aspiration in nonhuman primates causing similar lesions to this case.3,8,9 Kaolin is a common crystalline compound found in antidiarrheal medication as well as a variety of other products, such as toothpaste, ceramics, soap, and paint. Initially, the terminal bronchioles and alveoli of animals exposed to aspirated or inhaled kaolin are acutely inflamed, but by day seven post exposure, there is only mild mononuclear inflammation, type II pneumocyte hyper-plasia, and aggregates of anisotropic dust-laden macrophages and multinucleated cells.9 This is in contrast to silica inhalation, which induces a progressive granulomatous and fibrotic response.4,9 The route of exposure of most reported cases in nonhuman primates is aspiration of oral antidiarrheal medication.8 Kaolin can also cause granulomas containing numerous macrophages filled with birefringent crystals if delivered subcutaneously.3
To this author’s knowledge, there have been no reported cases of famotidine aspiration causing aspiration alveolitis in humans or animals; although the pathogenesis posited by the contributor is plausible. Unfortunately, given strict regulations on tissue handling of Marburg (MARV)-infected animals, a tissue block was unable to be submitted for further chemical analysis. Regardless of the origin of the crystalline proteinaceous material, conference participants agreed that this lesion is likely unrelated to MARV infection and is an incidental finding.


1. Ackermann MR. Inflammation and healing. In: Zachary JF and McGavin MD, ed. Pathologic Basis of Veterinary Disease. 5th ed. St Louis, Mo: Elsevier, 2012:89-146.
2. Anonymous. Pepcid oral suspension.  Retrieved from:
3. Baskin GB. Pathology of nonhuman primates. 1993. New Orleans: Tulane Regional Primate Research Center.
4. Caswell JL, Willims KJ. Respiratory system. In: Maxie MG ed. Jubb, Kennedy, and Palmer’s pathology of domestic animals. Vol 2. 6th ed. St. Louis, Missouri: Elsevier; 2016:518.
5. Geisbert TW, Hensley LE, Larsen T, et al. Pathogenesis of ebola hemorrhagic fever in cynomologus macaques.  Evidence that dendritic cells are early and sustained targets of infection. Am J Path. 2003; 163(6):2347-2370.
6. Geisbert TW, Young HA, Jahrling PB, et al. Pathogenesis of ebola hemorrhagic fever in primate models.  Evidence that hemorrhage is not a direct effect of virus-induced cytolysis of endothelial cells. Am J Path. 2003; 163(6): 2371-2382.
7. Hensley LE, Alves DA, Geisbert JB, et al. Pathogenesis of Marburg hemorrhagic fever in cynomolgus macaques. J Inf Dis. 2011; 204 (Suppl 3): S1021-S1031.
8. Herman SJ, Olscamp GC, Weisbrod GL. Pulmonary kaolin granulomas. J Can Assoc Radiol. 1982; 33(4):279-280.
9. Vallyathan V, Schwegler D, et al. Comparative in vitro cytotoxicity and relative pathogenicity of mineral dusts. Ann Occup Hyg. 1988; 32:279-289

Click the slide to view.

4-1. Lung, cynomolgus macaque.

4-2. Lung, cynomolgus macaque.

4-3. Lung, cynomolgus macaque.

4-4. Lung, cynomolgus macaque.

4-5. Lung, cynomolgus macaque.

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