AFIP Wednesday Slide Conference - No. 22
March 3, 1999

Conference Moderator:
LTC Denzil Frost
Walter Reed Army Institute of Research
Division of Pathology
Washington, D.C. 20307-5100
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Case I - 98-0333 (AFIP 2663367)

Signalment: Two to three-year-old, male, rhesus monkey (Macaca mulatta).
History: This animal had been infected intravenously with chimeric simian/human immunodeficiency 89.6 (SHIV 89.6) virus twelve weeks prior to euthanasia. He had severe weight loss, diarrhea, and dyspnea at euthanasia. Prior to SHIV infection, the monkey was seronegative for SIV, SRV, STLV, and Herpes B. He also consistently tested negative for tuberculosis on intradermal skin tests.
Gross Pathology: The monkey was in poor nutritional condition, with minimal subcutaneous and abdominal fat. The lungs were multifocally reddened (congestion) and contained multifocal to coalescing, red-brown, consolidated areas that completely involved the apical lobe.
Laboratory Results: Bordetella bronchiseptica was isolated from the lungs at necropsy.
Contributor's Diagnoses and Comments:
1. Lung: Pneumonia, interstitial and perivascular, subacute, histiocytic, multifocal, moderate, with multinucleate syncytial giant cells, rhesus monkey (Macaca mulatta), non-human primate.
2. Lung: Pneumonia, interstitial, fibrinosuppurative, subacute, multifocal, moderate, with type II pneumocyte hyperplasia, karyomegaly and intranuclear inclusion bodies.
3. Lung: Bronchopneumonia, fibrinonecrotic, suppurative, multifocal to coalescing, moderate.
Microscopic diagnoses in other organs not submitted included:
1. Spleen: Lymphoid depletion, diffuse, moderate, with scattered periarteriolar lymphoid hyperplasia.
2. Thymus: Lymphoid depletion, diffuse, severe.
3. Lymph nodes, multiple: Follicular depletion and subinvolution, multifocal-coalescing, moderate, with scattered follicular hyperplasia, fibrosis, sinus histiocytosis, edema, subacute inflammation, and erythrophagocytosis.
4. Small intestine, jejunum, ileum: Enteritis, subacute, diffuse, mild, with crypt abscesses and Cryptosporidium organisms.
5. Colon: Colitis, subacute, multifocal, mild, with Cryptosporidium organisms.
6. Bone marrow: Hyperplasia, myeloid, diffuse, moderate.
7. Tongue: Intraepithelial yeast and pseudohyphae, many, etiology consistent with Candida sp.
8. Skeletal muscle, multiple: Sarcocysts, multifocal, moderate, with perimysial hemorrhage.
Simian immunodeficiency virus (SIV) infection of Asian macaques has been used extensively to study the pathogenesis of AIDS in human immunodeficiency virus type 1 (HIV-1)-infected humans. The SIVmac model is limited, however, due to the divergence of the envelope glycoproteins from HIV-1. Chimeric simian-human immunodeficiency viruses (SHIV) containing the tat, rev, vpu, and env genes of HIV-1 have been constructed and found to infect a number of macaque species causing an AIDS-like illness. These chimeric SHIV viruses will induce immune responses directed against the HIV-1 envelope glycoproteins. This model is currently being utilized for development of vaccine and therapy regimens for HIV-1.
The giant cell pneumonia seen in this case is typical of SIVmac-induced giant cell pneumonia and is characterized by extensive infiltration of alveolar septa and spaces by numerous macrophages with abundant foamy cytoplasm and multinucleate giant cells of macrophage-monocyte origin. The interstitial pneumonia with karyomegaly and intranuclear inclusions is characteristic of cytomegalovirus, a common secondary infection in SIVmac-infected animals. On transmission electron microscopy, an unidentified cell in the lung was found to contain an intranuclear inclusion body with peripheral clearing of the nuclear chromatin. Dispersing the nuclear chromatin were viral particles measuring 100 to 110 nm. The viral particle size and morphology were consistent with those of the herpesviridae group.
The bronchopneumonia was thought to be due to secondary infection with Bordetella bronchiseptica. Areas with intra-alveolar foamy material suggestive of Pneumocystis carinii organisms were present in some sections; however, special stains failed to confirm the presence of these organisms. Findings in the lymphoid organs and other tissues are typical of an advanced infection with pathogenic SHIV and common secondary infections.
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Case 22-1. Lung. Exudate fills an ulcerated bronchus and extends into the surrounding parenchyma, obscuring normal alveolar architecture.
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Case 22-1. Lung. Alveoli are filled with neutrophils and lined by type II pneumocytes which occasionally contain eosinophilic intranuclear inclusions bodies.
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Case 22-1. Lung. A syncytial giant cell is accompanied by abundant foamy alveolar macrophages within and thickening the septal walls (interstitial pneumonia).
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Case 22-1.Lung. Immunohistochemistry demonstrates positive cells (red) stained for Rhesus cytomegalovirus antigen occuring multifocally within alveolar septa. Note scattered alveolar multinucleated giant (syncytial) cells.
AFIP Diagnoses:
1. Lung: Bronchopneumonia, necrotizing and suppurative, acute, focally extensive, severe, with pleuritis, hemorrhage, and bacilli, rhesus monkey (Macaca mulatta), nonhuman primate.
2. Lung: Pneumonia, interstitial, subacute, focally extensive, moderate, with multinucleate giant cells and few eosinophilic and basophilic intranuclear inclusions.
Conference Note: Variably affecting the sections of lung, there are multifocal to coalescing areas of atelectasis and consolidation. Bronchioles are partially or completely filled by numerous viable and degenerate neutrophils admixed with fewer macrophages, necrotic respiratory epithelial cells, abundant cellular debris, few bacilli, and mucin. There is occasional segmental attenuation and loss of the bronchiolar epithelium. Similar inflammatory cells partially or completely fill adjacent alveoli.
Additionally, there is multifocal thickening of alveolar septa by neutrophils, macrophages, and type II pneumocytes. Pneumocytes sometimes contain eosinophilic intranuclear inclusions that marginate the chromatin, or large, basophilic inclusions that completely fill the enlarged the nuclei. Alveoli sometimes contain large multinucleate cells with abundant eosinophilic cytoplasm and up to 15 peripheral nuclei. In addition, there are fewer multinucleate cells with less cytoplasm and fewer, centrally located, nuclei. The interstitial changes and multinucleate cells are most readily observed at the interface of less affected lung parenchyma and areas of consolidation.
Several concurrent infectious agents complicate the histologic lesions of the lung. The presence of bacilli in bronchioles and bacterial culture results suggest that the bronchopneumonia was primarily caused by infection with Bordetella bronchiseptica. The interstitial pneumonia, with characteristic multinucleate giant cells, was attributed to infection with SIVmac. Concurrent infection with cytomegalovirus also contributed to the interstitial pneumonia. These oppurtunistic pulmonary infections are common in SIV/SHIV infected macaques.
Contributor: Division of Pathology, Walter Reed Army Institute of Research, Washington DC 20307-5100.
1. King NW: Simian immunodeficiency virus infections. In: ILSI's Monographs on Pathology of Laboratory Animals: Nonhuman Primates I, Jones TC, Mohr U, Hunt RD, eds., pp. 5-20, Springer-Verlag, 1993.
2. Reimann KA, et al: A chimeric simian/human immunodeficiency virus expressing a primary patient human immunodeficiency virus type 1 isolate env causes an AIDS-like disease after in vivo passage in rhesus monkeys. J Virol 70:6922-6928, 1996.
3. Reimann KA, et al.: An env gene derived from a primary human immunodeficiency virus type 1 isolate confers high in vivo replicative capacity to a chimeric simian/human immunodeficiency virus in rhesus monkeys. J Virol 70:3198-206, 1996.
4. Lu Y, Pauza CD, Lu X, Montefiori DC, Miller CJ: Rhesus macaques that become systemically infected with pathogenic SHIV 89.6-PD after intravenous, rectal, or vaginal inoculation and fail to make an antiviral antibody response rapidly develop AIDS. J Acquir Immune Defic Syndr Hum Retrovirol 19:6-18, 1998.

Case II - Labeled "B" (AFIP 2639067)

Signalment: Five-month-old, Thoroughbred, male, equine.
History: The weanling presented with a three-day history of watery diarrhea, dehydration, dependent edema and signs of endotoxemia. The diarrhea resolved within 24 hours of initiating therapy (IV fluids, banamine, bacitracin, and pentoxifylline), but hypoproteinemia persisted. The animal collapsed and was euthanized.
Gross Pathology: There was moderate edema of hind legs and scrotum. The intestinal contents were grossly unremarkable, and formed feces were pres-ent within the small colon. The mucosa of the distal meter of the ileum was thickened and rugose. The cecum and pelvic flexure of the large colon were markedly edematous.
Laboratory Results: Bacterial cultures were negative for significant pathogens, including Rhodococcus equi and multiple cultures for Salmonella spp. and Clostridium spp. Parasitology was negative for Cryptosporidium, Giardia, and other parasites.
Contributor's Diagnosis and Comments: Ileum: Proliferative enteropathy - Lawsonia intracellularis-like bacterium.
On histopathologic examination, the ileal mucosa is diffusely thickened by elongated, branching, hyperplastic crypts lined by immature enterocytes. Warthin-Starry stained sections reveal large numbers of small curved bacteria within the apical cytoplasm of crypt and villar enterocytes. Sections of ileum sent for PCR analysis using primers for porcine Lawsonia intracellularis were positive.
Proliferative enteropathy has been reported in several animal species, including the pig, horse, dog, white-tail-ed deer, blue fox, guinea pig, ferret, hamster, rat and rabbit. Gross and histological findings in this case are similar to previously published cases in foals, thought to be caused by Lawsonia intracellularis, or a closely related organism.
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Case 22-2. Small intestine. Crypts are tortuous and crypt epithelium is piled up and contains frequent mitotic figures. Low numbers of macrophages and lymphocytes expand the lamina propria.
Warthin Starry stain, 40x obj.
Case 22-2. Small intestine. There are numerous silver-positive curved bacilli within the apical zone of crypt epithelial cells.
AFIP Diagnosis: Small intestine: Enteritis, proliferative, subacute, diffuse, severe, with mild diffuse submucosal edema, and multifocal villar fusion, crypt herniation, and crypt abscesses, Thoroughbred, equine.
Conference Note: Proliferative enteritis or enteropathy occurs in a number of animal species. Among domestic animals, the disease is economically important in swine. In laboratory animals, the condition is an important cause of enteritis in hamsters. The etiology of the proliferative enteropathy in swine remained unknown until recently when it was identified as Lawsonia intracellularis. An organism nearly indistinguishable from L. intracellularis has also been isolated from hamsters. Organisms similar to L. intracellularis have been identified in lesions of proliferative enteritis/colitis in rabbits, deer, ostriches, horses, and ferrets; the organisms are closely related to L. intracellularis.
There is some variation among affected species in the location of gross lesions. Lesions have been reported in the ileum of horses, sheep, ostriches, guinea pigs, rabbits, hamsters, and swine; in the stomach and ileum of dogs; in the cloaca of emus; and in the colon of foxes, rats, and ferrets. Histologically, the disease is characterized by crypt hyperplasia and numerous small, curved, intracellular bacteria in the apical cytoplasm of infected enterocytes, usually only visible with silver stains (such as Steiner's or Warthin-Starry methods). Thus, despite the variability in location of gross lesions, enterocyte proliferation and intracellular organisms are the two common histologic features of proliferative enteropathy in animals.
Contributor: Animal Health Laboratory, Laboratory Services Division, University of Guelph, Box 3612, Guelph, Ontario, CANADA N1H 6R8.
1. Williams NM, Harrison LR, Gebhart CJ: Proliferative enteropathy in a foal caused by Lawsonia intracellularis-like bacterium. J Vet Diagn Invest 8:254-256,1996.
2. Duhamel GE, Wheeldon EB: Intestinal adenomatosis in a foal. Vet Pathol 19:447-450, 1982.
3. Cooper DM, Gebhart CJ: Comparative aspects of proliferative enteritis. J Amer Vet Med Assoc 212:1446-1450, 1998.

Case III - B98-5016 (AFIP 2639016)

Signalment: Ten-year-old, captive-born, female, Indochinese tiger (Panthera tigris corbetti).
History: The animal, housed in a zoo, presented with mild neurologic signs. Eleven days later, marked ataxia and paraparesis were observed, with forelimbs more severely affected than hind limbs. Neurologic signs were unchanged on day sixteen. Physical examination revealed normal muscle mass and tone, and normal to hyper-reflexia in all limbs. On day 17, the animal was eating well but had developed mild head tremors which persisted for two days. By day 27, the paraparesis had worsened. On day 30, analysis of cerebrospinal fluid showed a mild pleocytosis, but was otherwise unremarkable. The animal was euthanatized on day 38.
Gross Pathology: Gross postmortem examination revealed healing fractures of the dorsal spinous processes of C7, T1, T3 and T4. No other significant lesions were noted.
Laboratory Results: Hematology, serum chemistries, and urinalysis were unremarkable. Titers for feline leukemia virus, feline infectious peritonitis virus, feline immunodeficiency virus and toxoplasmosis were negative.
Contributor's Diagnosis and Comments: Nonsuppurative and demyelinating meningomyelitis, cervical spinal cord.

Etiology: Canine distemper virus.
Histopathologic findings were most pronounced in the brain stem and cervical spinal cord. Alterations included nonsuppurative meningo-encephalomyelitis, gliosis, and irregular parenchymal necrosis that was most pronounced in sections of cervical spinal cord. Descending tracts in the spinal cord white matter exhibited demyelination and axon swelling. Astrocytes in sections of brain stem contained eosinophilic intranuclear inclusion bodies that were confirmed to be canine distemper virus by immunohistochemistry (courtesy of Dr. Brian Summers, Cornell University). No significant lesions were noted in other tissues. Just after canine distemper was diagnosed in this tiger, two wild raccoons showing neurologic signs were captured on zoo grounds and confirmed to have canine distemper.
In the past several years, canine distemper virus (CDV) infection has been reported in several species of exotic cats, including snow leopards and lions (Fix et al., 1989, Roelke-Parker et al., 1996). Although many believe that this is a relatively recent phenomena, a retrospective survey of archived tissues from a zoo in Switzerland demonstrated positive immunoreactivity to CDV in 12 of 42 lions and tigers necropsied from 1972 to 1992 (Myers et al., 1997). Some molecular evidence indicates that outbreaks in felids likely originate from feral non-felid carnivores (Harder et al., 1996). These events continue to build evidence for the ability of morbilliviruses to expand their host range, as is also known for several species of cetaceans and phocids.
Case 22-3. Spinal cord. Numerous punched out areas represent necrosis and loss of white matter. Note the macrophages in the center of the field (Gitter cells). There is a mild perivascular infiltrate of lymphocytes.
Case 22-3. Spinal cord. There is diffuse degeneration and loss of myelin in axonal tracts (spongiosis). A single glial cell in the center contains an eosinophilic intranuclear inclusion (arrow).
AFIP Diagnosis: Spinal cord: Demyelination, multifocal, severe, and moderate nonsuppurative meningomyelitis and few glial eosinophilic intranuclear inclusions, Indochinese tiger (Panthera tigris corbetti), feline.
Conference Note: Canine distemper virus (CDV) is a morbillivirus, as are measles virus, rinderpest virus, peste des petits ruminants virus and recently recognized phocine and cetacean viruses. Morbilliviruses, members of the family Paramyxoviridae, are enveloped, single-stranded, RNA viruses that measure between 150-300 nm in diameter. There is one serotype of CDV, but multiple strains occur which differ in virulence and neurotropism.
Conference participants favored canine distemper virus infection based upon the histopathologic findings of nonsuppurative meningomyelitis with demyelination and intranuclear inclusions. Differential diagnosis considered by attendees included pseudorabies virus (Herpesvirus suis) and feline rhinotracheitis virus (feline herpesvirus type 1).
Contributor: The Procter & Gamble Company, Miami Valley Laboratories, PO Box 398707, Cincinnati, Ohio 45239-8707.
1. Fix AS, et al.: Feline panleukopenia virus and subsequent canine distemper virus infection in two snow leopards (Panthera uncia). J Zoo Wildl Med 20:273-281, 1989.
2. Harder TC, et al.: Canine distemper virus from disease large felids: Biological properties and phylogenetic relationships. J Gen Virol 77:397-405, 1996.
3. Myers DL, et al.: Distemper - not a new disease in lions and tigers. Clin Diagn Lab Immunol 4:180-4, 1997.
4. Roelke-Parker ME, et al.: A canine distemper virus epidemic in Serengeti lions (Pantera leo). Nature 379:441-5, 1996.
5. Fenner F, et al.: Paramyxoviridae. In: Veterinary Virology, Fenner F, et al., eds., pp. 485-501, Academic Press, San Diego, CA, 1987.
6. Summers BA, Cummings JF, de Lahunta A: Inflammatory diseases of the central nervous system. In: Veterinary Neuropathology, Summers BA, Cummings JF, de Lahunta A, eds., pp. 103-110, Mosby Yearbook, Saint Louis, MO, 1995.
7. Dungworth DL: The respiratory system. In: Pathology of Domestic Animals, Jubb KVF, Kennedy PC, Palmer N, eds., 4th edition, vol. 2, pp. 558, Academic Press, San Diego, CA, 1993.
8. Jones TC, RD Hunt, NW King: Diseases caused by viruses. In: Veterinary Pathology, 6th edition, pp. 233-234, Williams and Wilkins, Baltimore, MD, 1997.

Case IV - 98A-25996 (AFIP 2641596)

Signalment: Five-month-old, Angus heifer, bovine.
History: This heifer had been pastured alone and was found dead without prior signs of illness.
Gross Pathology: The carcass was well-fleshed. The tissues were icteric and pale. The urine was red and clear. The spleen was mildly enlarged, and the liver was diffusely pale tan.
Laboratory Results: Fluorescent immunostains on frozen sections of kidney and liver were positive for Leptospira sp.
Contributor's Diagnoses and Comments:
1. Liver: Erythrophagocytosis, canalicular bile plugs, multifocal acute hepatocellular necrosis and intralesional leptospiral bacteria.
2. Kidney: Mild acute purulent tubular nephritis with intralesional leptospiral bacteria.
Animals infected by Leptospira sp. have an initial bacteremia followed by localization in the kidney, where organisms multiply in proximal convoluted tubule lumens and are excreted in urine. Clinicopathological manifestations of bovine leptospirosis include hemolytic anemia, hemoglobinuria, icterus, abortion, mastitis, and nephritis. Many serovars may be responsible for disease, including Leptospira hardjo (for which cattle are reservoir hosts), L. pomona, L. icterohemorrhagiae, L. canicola, L. grippotyphosa, L. szwajizak, L. balcanica. The specific serovar responsible for illness in the present case was not determined.
Acute leptospirosis is most severe in calves and usually manifests as hemolytic anemia. The gross lesions noted in this case are typical of the acute septicemic form of disease. Histologic lesions are often mild and non-specific. In the kidney, there is edema, degeneration and necrosis of tubular epithelial cells, and intratubular neutrophilic exudate. After a day or two, hemoglobin pigment may accumulate within tubules. In the liver, there may be disaggregation of hepatic cords and necrosis of individual hepatocytes, or a more zonal pattern attributable to hypoxia. In subacute (or post-subclinical) phases, the organisms localize in kidneys and cause interstitial nephritis.
Case 22-4. Kidney. There is tubular degeneration and necrosis (vacuolation, karyorrhexis), multifocal neutrophilic infiltrates in tubular lumens, and mononuclear cells within the interstitium.
Case 22-4. Liver. There is periportal infiltration by lymphocytes, and focal degeneration and necrosis of hepatocytes. Several Kupffer cells contain erythrocytes (erythrophagocytosis).
AFIP Diagnoses:
1. Kidney: Nephritis, tubulo-interstitial, neutrophilic and lymphoplasmacytic, multifocal, mild, with erythrophagocytosis, Angus, bovine.
2. Liver: Hepatitis, portal, lymphoplasmacytic, diffuse, mild, with multifocal and centrilobular hepatocellular degeneration and necrosis, and erythrophagocytosis.
Conference Note: Rare argyrophilic spirochetal bacteria were identified within hepatic sinusoids and renal tubules by Steiner's method. Conference participants did not observe evidence of bile stasis in the examined sections.
Leptospira sp. bacteria are commonly referred to as spirochetes. The organisms are slender, helically-coiled, single-celled, aerobic, and motile by means of periplasmic flagellae. The bacteria are not visible in standard hematoxylin and eosin stained tissue sections, but may be seen by darkfield microscopy, electron microscopy, tissue silver stains, fluorescent antibody methods, and immunohistochemical stains.
Leptospirosis is a zoonotic disease found worldwide, and infection is caused by antigenically distinct serovars of the species Leptospira interrogans. The bacteria are maintained in the environment by infected domestic animal and wildlife reservoir hosts. Transmission may occur by direct contact with infected urine, venereal or placental transfer, bite wounds, or ingestion of infected tissues. Indirect transmission can occur under favorable environmental conditions, such as contact with contaminated stagnant or slow-moving water.
The liver and kidney are the two primary parenchymatous organs affected by leptospiral bacteremia. In dogs, icterus is attributed to hepatic dysfunction induced by leptospiral toxins, which cause hepatocellular degeneration and necrosis. In severely affected calves, acute leptospiremia causes hemolytic anemia, hemoglobinuria, jaundice, pulmonary congestion, and occasionally meningitis. Icterus in calves occurs as a result of hemolysis due to hemolysin from the bacteria, and from hepatocellular injury of both ischemic and toxin origin. Hemolytic anemia is initially attributed to bacterial hemolysins, but may later be due to antibodies reacting with bacterial products coating red blood cells.
Contributor: Pathology Department, University of Georgia, College of Veterinary Medicine, University of Georgia, Athens, Georgia 30602-7388.
1. Jones TC, RD Hunt, NW King: Diseases caused by bacteria. In: Veterinary Pathology, 6th edition, pp. 467-472, Williams and Wilkins, Baltimore, MD, 1997.
2. Miller DA, Wilson MA, Beran GW: Relationships between prevalence of Leptospira interrogans in cattle, and regional, climatic and seasonal factors. Amer J Vet Res 52:1766-1768, 1991.
3. Greene CE, Miller MA, Brown CA: Leptospirosis. In: Infectious Diseases of the Dog and Cat, Greene CE, ed., 2nd ed., pp. 273-282, WB Saunders, Philadelphia, PA, 1998.
4. Maxie MG: The kidney. In: Pathology of Domestic Animals, Jubb KVF, Kennedy PC, Palmer N, eds., 4th edition, vol. 2, pp. 503-511, Academic Press, San Diego, CA, 1993.
Conference Coordinator:
Ed Stevens, DVM
Captain, United States Army
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
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