AFIP Wednesday Slide Conference - No. 14
22 January 1997

Conference Moderator: Dr. F. M. Garner
Diplomate, ACVP
4416 Oak Hill Road
Rockville, Maryland 20853

Return to WSC Case Menu

Case I - 952287 (AFIP 2554549)

Signalment: Tissue from a juvenile male cynomolgus monkey (Macaca fascicularis).

History: This monkey was euthanized in extremis following experimental aerosol exposure to monkeypox virus.

Gross Pathology: At necropsy, there were approximately 5, 2 - 4 mm, slightly raised, white to tan, round vesicles/papules widely scattered over the skin of the inguinal, ventral abdominal, and ventral thoracic regions. On the lips at the commissures of the mouth there were several 3 - 4 mm ulcers with white, slightly raised borders. On the soft and hard palates, dorsal surface of the tongue, and buccal surface of the gingiva, there were numerous 2 - 4 mm round ulcers with slightly raised white borders. Middle lung lobes were uniformly dark red and edematous. Cranial and caudal lung lobes were variably affected (25 - 40%) by patchy, dark red areas of atelectasis and edema.

Laboratory Results: Virus was isolated from the buffy coat of febrile animals, and high titers of virus were isolated from lung and spleen samples collected at necropsy.

Contributor's Diagnosis and Comments: Tongue: Glossitis, necrotizing, subacute, multifocal, moderate, with ballooning degeneration, intraepithelial vesicopustules, epithelial hyperplasia, and intraepithelial cytoplasmic inclusions.

Etiology: Monkeypox virus

Outbreaks of monkeypox have been reported in laboratory and zoological colonies of macaques and New World primates in North America and Europe. The disease also occurs sporadically as a zoonosis in West and Central Africa. Monkeypox virus is a member of the genus Orthopoxvirus, which includes variola and vaccinia. In humans, the clinical picture is very similar to that of smallpox, differing only in the occurrence of lymphadenopathy in monkeypox cases. The human case fatality rate is approximately 10-15% for non-vaccinated individuals, with most deaths occurring among young children.

In rhesus and cynomolgus monkeys, naturally-acquired infection usually results in a non-fatal illness with spontaneous regression. Clinically, the disease is characterized by a generalized rash that progresses through successive stages of macules, papules, vesicles, and pustules. Cutaneous lesions can occur over the entire body, but they are reported to be most frequent on the face, limbs, palms of the hands, soles of the feet, and tail. Histologically, lesions of the skin and mucus membranes consist of thickened, hyperplastic epithelium with ballooning degeneration, vesicle formation, necrosis, mononuclear and polymorphonuclear inflammatory infiltrates, and intraepithelial cytoplasmic inclusions.

The pathogenesis of monkeypox is believed to be similar to that of smallpox. Transmission of the virus occurs through aerosols, with entry via the mucosa of the upper respiratory tract, or through contact with abraded skin. Initial virus replication takes place in the tonsils or regional lymph nodes. Subsequent viremia results in dissemination of the virus to secondary sites such as the skin, spleen, gastrointestinal, and reproductive tracts.

AFIP Diagnosis: Tongue: Glossitis, necroulcerative, subacute, with vesicles, pustules, and intracytoplasmic inclusions, cynomolgus monkey (Macaca fascicularis), primate.

Conference Note: Some of the participants had difficulty visualizing the numerous, small, amphophilic to eosinophilic intracytoplasmic inclusions within swollen and degenerate epithelial cells. These inclusions appeared to be somewhat smaller than those of other orthopoxviral infections. Please note that there may be slight variation of the lesion in different sections; some sections did not contain vesicles or pustules. The differential diagnosis for this lesion might include tanapox (benign epidermal monkeypox), Yabapox, marmoset pox, and molluscum contagiosum. Grossly, the differential diagnosis would also include tuberculosis, melioidosis, mycotic granulomas, and papillomatosis.

Contributor: U.S. Army Medical Research Institute of Infectious Diseases, Fort Detrick, Frederick, MD 21702-5011.

1. Arita I, Jezek A, Khodakevich L, Ruti K: Human monkeypox: A newly emerged orthopoxvirus zoonosis in the tropical rain forests of Africa. Am J Trop Med 1985;34:781-789.
2. Casey HW, Woodruff JM, Butcher WI: Electron microscopy of a benign epidermal pox disease of rhesus monkeys. Am J Pathol 1967;51:431-446.
3. Crandell RA, Casey HW, Brumlow WB: Studies of a newly recognized poxvirus of monkeys. J Infect Dis 1969;119:80-88.
4. Gispen R, Verlinde JD, Zwart P: Histopathological and virological studies on monkeypox. Arch Gesamte Virusforsch 1967;21:205-216.
5. Gough AW, Barsoum NJ, Gracon SI, Mitchell L, Sturgess JM: Poxvirus infection in a colony of common marmosets (Callithrix jacchus). Lab Anim Sci 1982;32:87-90.
6. Jezek Z, Szczeniowski M, Paluku KM: Human monkeypox: Clinical features of 282 patients. J Infect Dis 1987;156:293-298.
7. von Magnus P, Andersen EK, Peterson KB, Birch-Andersen A: A pox-like disease in cynomolgus monkeys. Acta Pathol Microbiol Scand 1959;46:156-176.
8. Stagles MJ, Watson AA, Boyd JF, More IAR McSeveney: The histopathology and electron microscopy of human monkey lesion. Trans R Soc Trop Med Hyg 1985;79:192-202.
9. Wenner HA, Bolano CR, Cho Ct, Kamitsuka PS: Studies on the pathogenesis of monkeypox. 3. Histopathological lesions and sites of immunofluorescence. Arch Gesamte Virusforsch 1969;27:179-197.

International Veterinary Pathology Slide Bank:
Laser disc frame #4479, 4480.


Case II - CP96-384 (AFIP 2548994)

Signalment: 10-week-old athymic nu/nu BALB/c mouse (Mus musculus).

History: Forty BALB/c nu/nu mice were used in a research experiment involving the subcutaneous injection of a neuroblastoma cell line in which a gene designed to initiate secretion of gamma interferon was inserted. Seven mice exhibited clinical signs of weight loss and three mice died unexpectedly. All 40 of the mice were injected with the neuroblastoma cell line approximately 6 weeks prior to the observation of clinical signs of disease.

Gross Pathology: No gross lesions were observed.

Laboratory Results: Aerobic culture of lung did not yield any bacterial growth.

Sentinel mouse serology obtained from this room was positive for mouse hepatitis virus (MHV) and serologically negative for Mycoplasma pulmonis, Sendai virus, epizootic diarrhea of infant mice (EDIM), pneumonia virus of mice (PVM), ectromelia, lymphocytic choriomeningitis virus (LCM), reovirus type 3, parvovirus, and Theiler's murine encephalomyelitis virus.

Because MHV is a common contaminant of cell lines, mouse antibody production (MAP) testing was completed on the neuroblastoma cell line and the results were negative for MHV, Sendai virus, PVM, minute virus of mice, Theiler's murine encephalomyelitis virus (GD-VII), reovirus type 3, LCM, ectromelia, K virus, polyoma virus, mouse adenovirus, EDIM, mouse cytomegalovirus, mouse thymic necrosis virus, Hantaan, and lactate dehydrogenase-elevating virus.

Contributor's Diagnosis and Comments:

1. Liver, Hepatitis, marked, random, multifocal, necrotizing, with numerous syncytial cells.
2. Lung, Vascular endothelium syncytial cell formation.

Etiology: Mouse Hepatitis Virus

MHV is a coronavirus with numerous antigenically related strains that have great variability in their tissue tropism and in their virulence. Susceptibility to MHV can be influenced by many factors, including genotype, age, strain of virus, route of inoculation, immune status, diet, and concurrent infections. MHV can be loosely classified in two groups according to their primary target organ; enterotropic and pneumotropic. Enterotropic strains selectively infect intestinal mucosa with little, if any, dissemination to other target tissues. This is in contrast to the respiratory strains, which are considered polytropic, replicating in the nasal mucosa followed by secondary dissemination to multiple organs.

The majority of MHV strains, including the prototype strains MHV-S, MHV-A59, MHV-JMH, MHV-1, MHV-3, have primary tropism for the respiratory system rather than the gastrointestinal system. Following infection with a respiratory MHV strain, the virus replicates in the nasal epithelium and disseminates via the blood stream to other target tissues including liver, vascular endothelium, lymphoreticular tissues, and brain in susceptible hosts. Pulmonary involvement is restricted to vascular endothelium and does not involve respiratory mucosa. The route of dissemination of infection to the brain is somewhat dependent on the age of the mouse. In the young mouse, infection is generally via the blood stream while in adult mice, infection tends to occur by extension of virus along the olfactory neural pathway.

Athymic or SCID mice infected with virulent respiratory strains of MHV may develop progressively fatal, multi-systemic infections with severe necrotizing lesions in nasal epithelium, vascular endothelium, brain, liver, bone marrow, lymphoid tissue and other sites. Virulent MHV strains kill these mice rapidly, but disease can be chronic with wasting in mice exposed to natural, avirulent strains of virus. In contrast to mice infected with respiratory strains, immunocompromised mice infected with enterotropic MHV develop enteric infections which are chronic but may not manifest overt clinical disease.

Lesions associated with enterotropic strains include necrotizing enterocolitis resulting in lesions similar to coronaviral enteric syndromes of other species. As in other species, the most severe clinical signs of disease are found in neonates although all ages and strains of mice are susceptible to infection. Mortality and severity of lesions decrease with age. The immaturity of the immune system and the related inability of intestinal mucosa to quickly respond to a severe insult have been proposed as primary reasons why the immature animal is much more susceptible to clinical disease from MHV. Neonatal mice have poorly developed intestinal mucosal crypts, relatively short villi, and slow turnover of mucosal cells. These immature intestinal mucosal cells are unable to adequately respond to severe mucosal injury. By two weeks of age the intestinal mucosa is better prepared to combat damage caused by MHV. At this time, villi are much longer and the crypts have developed proliferative cell pools from which new cells can rapidly migrate onto villi. In the older mouse, MHV can still cause mucosal damage, which is often segmental, but the repair process is capable of rapidly replacing the damaged cells. Histologically, infection in an older mouse is characterized by epithelial cell hyperplasia of both crypts and villi. Multinucleated syncytial cells may be observed; however, these cells are often difficult to identify in the hyperplastic mucosa. The mucosal hyperplasia may result in temporary malabsorption and resulting diarrhea, which is typically self limiting and old of minor clinical significance.

AFIP Diagnosis:

1. Liver: Hepatitis, subacute, multifocal to coalescing, moderate, with hepatocellular degeneration, necrosis and loss, and endothelial syncytial cell formation, BALB/c mouse (Mus musculus), rodent.
2. Lung, vascular endothelium: Syncytial cells.

Conference Note: This is a classic example of mouse hepatitis virus infection with the hallmark lesion: virus-induced syncytia arising from the endothelium of target organs. Viral syncytia also can frequently be seen within leukocytes and parenchymal cells of affected organs, including the central nervous system.

Contributor: University of Texas Southwestern Medical Center at Dallas, 5323 Harry Hines Blvd. Dallas, TX 75235-9037.

1. Percy DH, and Barthold SW: Mouse Viral Infections, p. 13-27, In Pathology of Laboratory Rodents and Rabbits, Iowa State University Press, 1993.
2. Barthold SW: Mouse hepatitis virus biology and epizootiology, 571-601. In PN Bhatt, RO Jacoby, AC Morse, III and AE New (eds)., Viral and mycoplasmal infection of laboratory rodents: effects on biomedical research. Academic Press, 1986.
3. Compton SR, Barthold SW, Smith AL: The cellular and molecular pathogenesis of coronaviruses. Lab. Anim. Sci. 43:12-28, 1993.
4. Kraft L: Viral Diseases of the Digestive System, pp. 173-191, In H.L. Foster, JD Small, and JG Fox (eds), The Mouse in Biomedical Research, Vol II: Diseases. Academic Press, 1982.

International Veterinary Pathology Slide Bank: None.


Case III - HB 1731 (AFIP 2554542), 1 photo

Signalment: 13-year-old male Shetland Sheepdog.

History: This dog underwent unilateral enucleation of the left eye after a one year history of slowly progressive exophthalmos. The medical record of this dog indicated the excision of a left eyelid tumor eighteen months prior to enucleation.

Gross Pathology: The maximum cut surface of the tumor including ocular adnexa and globe measured 2.7 x 3.3 cm. Tumor of the ocular adnexa was partly ill- defined and light gray or gray-tan in color. Most of the globe tissues were replaced by the tumor.

Laboratory Results: None.

Contributor's Diagnosis and Comments: The tumor in the ocular adnexa was diagnosed as a compound apocrine adenocarcinoma, originating from the apocrine glands of the eyelid. The infiltrating intraocular neoplasm was diagnosed as a malignant mixed sweat gland tumor.

The tumor of the ocular adnexa is composed of duct-forming epithelial cells with decapitation luminal secretion and spindle-shaped myoepithelial cells. Tumor cells invaded the globe through the tunica conjunctiva and replaced the vitreous body. Cornea, iris, ciliary body and retina were extensively destroyed. In the globe, both neoplastic epithelial and spindle-shaped cells showed nuclear atypia and mitotic activity. Osseous and cartilagineous metaplasia was recognized in the tumorous tissue of the vitreous body.

The tumor was considered to be of apocrine origin based upon the following criteria: eosinophilic cytoplasm of tumor cells, decapitation luminal secretion, intracellular PAS positive and diastase resistant granules, and the presence of intracellular iron- positive granules. The possibility of remote metastasis of other sweat gland tumors or mammary gland tumors was excluded as there was no clinical sign or medical record of previous malignancy. Accordingly, the origin of the present tumors appears to be apocrine glands in the eyelid. However, since there are two sweat glands in the eyelid; apocrine sweat glands in the skin surface of the eyelid and Moll glands (ciliary glands), the exact origin could not be determined.

Apocrine sweat gland tumors in dogs occur at any cutaneous site with no predilection and represent 2.2% of the canine skin tumors. However, to the best of our knowledge, there is no published report of apocrine gland tumor in the canine eyelid with invasive intraocular growth. The tumor was considered to be highly malignant.

AFIP Diagnosis: Eye and adjacent tissue: Malignant mixed tumor of apocrine gland, Shetland Sheepdog, canine.

Conference Note: Only a small area of extraocular neoplasia is present in the section examined during the conference, and it appears generally similar to the intraocular neoplasm; thus, only one diagnosis was made based on the features of both the intraocular and extraocular neoplastic tissue. All components of the neoplasm may not be present in all sections. In addition to the evidence of apocrine gland origin noted by the contributor, the glandular epithelial component of the neoplasm stained positively for S-100 protein by immunohistochemistry, as is characteristic of apocrine epithelium. Many of the malignant appearing spindle cells stained positively for smooth muscle actin consistent with myoepithelial origin. Additionally, a small area of osseous and cartilaginous tissue is present within the neoplasm in the section examined during the conference. Apocrine gland neoplasms with such features are uncommon.

Contributor: Laboratory of Comparative Pathology, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo 060, Japan.

1. Aurora AL, Luxenberg MN: Case report of adenocarcinoma of glands of Moll. Am J Opthalmol 70:984-990, 1970.
2. Gross TL, Ihrke PH, Walder EJ: Sweat gland tumors. In: Veterinary Dermatopathology, pp. 392-395. Mosby-Year Book, St. Louis, 1992.
3. Moulton JE: Tumors in Domestic Animals, 3rd ed., pp. 66-68. University of California Press, Berkeley, 1990.
4. Seregard S: Apocrine adenocarcinoma arising in Moll gland cystadenoma. Ophthalmology 100:1716-1719, 1993.

International Veterinary Pathology Slide Bank: None.


Case IV - 96-02 (AFIP 2551108)

Signalment: Rat, Tif:Ralf(SPF), Sprague-Dawley derived, male, approximately 6-months-old.

History: The animal was part of an evaluation study for a urine electrophoresis method. It received hexachloro-1,3-butadiene (HMBD) as daily oral doses of 50 mg/kg for seven days. The rat showed signs of poor general condition (muscular hypotonia, reduced motility, rough coat) and was euthanized on day 8 (approx. 24 hours after the last dose).

Gross Pathology: The renal cortex showed gray-white discoloration, whereas the medulla was dark red.

Laboratory Results: Clinical pathology: Blood: marked increases in creatinine, urea, alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase and plasma cholinesterase activities, bilirubin, cholesterol and triglycerides. Urine: marked increases in protein, glucose, and ketone bodies.

Contributor's Diagnosis and Comments: Tubular necrosis, acute-subacute, marked, mainly affecting proximal tubules, especially the pars recta.

Etiology: Toxicity of hexachloro-1,3-butadiene.

Marked tubular basophilia was observed in the outer stripe of the outer medulla and in medullary rays. The affected tubules corresponded to the pars recta of the proximal tubules. Mitotic figures in tubular epithelial cells were frequent. There was also some extent of tubular dilation. In addition, vacuolation of epithelial cells, hyaline droplets, necrosis of epithelial cells and casts and cellular debris in the tubular lumen were seen. In the other parts of the medulla, dilation and casts were frequent. In cortical areas proximal convoluted tubules showed degenerative changes which progressed to necrosis (loss of brush borders, vacuolation, necrosis, casts). The tubular basement membrane appeared to be intact. Distal tubules were slightly dilated, partially with casts. Glomeruli were not affected.

The necrosis represented an acute lesion whereas the tubular basophilia was indicative of regeneration following necrosis. Tubules of the pars recta were the most vulnerable segments of the nephron to the toxic effects of HCBD and the damage occurred early during the treatment. After one week, most of the tubules had regenerated. Before these cells are fully differentiated, they are protected to a certain extent from further toxic insults. Proximal convoluted tubules were less sensitive to the toxic effect of HCBD. They were apparently only affected after several days of repeated doses and showed more acute lesions with little evidence of regeneration. Dilation of distal tubules and casts were considered secondary to the lesions in the proximal segments of the nephron.

Hexachloro-1,3-butadiene (HCBD) is a by-product of the manufacture of chlorinated hydrocarbons. There has been considerable interest in HCBD in the past, especially due to its intriguing mechanism of toxicity. The main target organ is the kidney. Single doses of 200 mg/kg in rats are reported to cause necrosis of the pars recta of the proximal tubules, which are situated in the outer stripe of the outer medulla. Necrotic tubules were observed eight hours after administration and evidence of tubular regeneration was apparent by day five.

Ultrastructurally, changes were detected as early as one hour after administration of 300 mg/kg (loss or thinning of microvillus brush border, cytoplasmic vacuoles, swollen mitochondria). Various studies for elucidation of the mechanisms of nephrotoxicity were carried out. In rats the principal route of excretion of HCBD was biliary (direct conjugate between glutathione and HCBD and cysteinylglycine conjugate of HCBD). There was evidence that biliary metabolites were reabsorbed and excreted via the kidneys. Studies of the metabolites showed that they were also nephrotoxic. Rats fitted with a biliary canula were protected from kidney damage. It was proposed that the hepatic glutathione conjugate of HCBD was degraded to its equivalent cysteine conjugate, which was cleaved by the renal cytosolic enzyme ß-lyase to give a toxic thiol which caused localized kidney damage. A more recent study has shown that cannulated bile ducts could not completely protect the animals from kidney damage; therefore, the authors have concluded that biliary metabolites are not solely responsible for the nephrotoxicity. Sinusoidal efflux of the HCBD conjugate from the liver was suggested as an additional factor.

AFIP Diagnosis: Kidney, proximal tubules: Degeneration, necrosis and regeneration, multifocal, moderate, Sprague-Dawley rat, rodent.

Conference Note: Hexachloro-1:3-butadiene (HCBD) is used commercially in small quantities as a vineyard fumigant and in the recovery of chlorine gas in the chemical industry. More significant amounts are found in industrial waste, generated mainly from the manufacture of tetra- and trichloroethylene and carbon tetrachloride.

The renal damage seen in the rat following HCBD is similar to that described with a number of other nephrotoxic agents such as mercuric chloride, dl-serine, dl- ethionine, lysinoalanine, and cis-platinum. All these compounds produce necrosis of the pars recta or S3 portion of the proximal tubule. The pars recta of the proximal convoluted tubule is especially rich in mixed function oxidase enzymes. As the contributor alluded, the reason for selective toxicity to the epithelium of the pars recta is probably local enzymatic cleavage of the toxin or one of its metabolites to a nephrotoxic agent. In the case of HCBD, the cytosolic enzyme -lyase cleaves HCBD into toxic thiols. It was also noted above regenerating tubular epithelial cells are resistant to the toxic effects of HCBD; these cells have an immature mixed-function oxidase system with reduced activity, and thus, decreased ability to convert compounds to nephrotoxic agents.

Contributor: Ciba-Geigy AG, Preclinical Safety, Pathology, K-135.2.26, CH- 4002, Basel, Switzerland.

1. Ishmael J, Pratt I, Lock EA: Necrosis of the pars recta (S3 segment) of the rat kidney produced by hexachloro 1:3 butadiene. J Pathol 138:99-113, 1982.
2. Ishmael J, Lock EA: Nephrotoxicity of hexachlorobutadiene and its glutathione-derived conjugates. Toxicol Pathol 14:258-262, 1986.
3. Nash JA, King LJ, Lock EA, Green T: The metabolism and disposition of hexachloro-1:3-butadiene in the rat and its relevance to nephrotoxicity. Toxicol Appl Pharmacol 73:124-137, 1984.
4. Payan JP, Beydon D, Fabry JP, Morel G, Brondeau MT, BanM, De Ceaurriz J: Partial contribution of biliary metabolites to nephrotoxicity, renal content and excretion of [14C]Hexachloro-1,3-butadiene in rats. J Appl Toxicol 13:19-24, 1993.
5. Yang RS: Hexachloro-1,3-butadiene: Toxicology, metabolism, and mechanisms of toxicity. Rev Environ Contam Toxicol 101:121-137, 1988.

International Veterinary Pathology Slide Bank: None.

Lance Batey
Captain, VC, USA
Registry of Veterinary Pathology*
Department of Veterinary Pathology
Armed Forces Institute of Pathology
(202)782-2615; DSN: 662-2615

* The American Veterinary Medical Association and the American College of Veterinary Pathologists are co-sponsors of the Registry of Veterinary Pathology. The C.L. Davis Foundation also provides substantial support for the Registry.

Return to WSC Case Menu