Conference 14 - 2015 Case: 03 20160120

Signalment:

11-year-old male Indian rhesus macaque (Macaca mulatta).This animal was born at ONPRC and housed outdoors until 3 years of age, then kept indoors for the remainder of his life. He received two mucosal doses of SIV Mac239 approximately 5 years before his death. He was found deceased in the cage and was presented for necropsy the following day. He had been sedated multiple times for bronchoalveolar lavage over the course of the protocol. The most recent was performed 9 months prior to death. He had a history of intermittent epistaxis with the first report 10 months prior to death. On 12/29/2012 he was reported for epistaxis, not looking well, and hesitancy to stand. A cage side evaluation by a technician revealed a mild right head tilt and epistaxis. He took and ate treats readily when offered and was bright and interactive with the observer. He appeared slow-moving and hunched when ambulating. He was found dead in his cage the following day (12/30).

Gross Description:

At necropsy, the animal was overweight (BCS 4/5). He had cyanotic oral mucous membranes, and epistaxis of the right naris was evident. There was marked edema and congestion of all lung lobes with greater severity on the left side (found in left lateral recumbency). Sectioned surfaces of lung oozed blood-tinged fluid on palpation. Femoral bone marrow was diffusely dark red. Liver was rubbery, congested, enlarged, mottled dark red-brown with an enhanced reticular pattern. Gallbladder, cystic duct, and common bile duct were thickened and contained scant pale yellow bile. Renal cortices exhibited swelling and streaked pallor and renal medullae were streaked and congested. There was mild meningeal hemorrhage and congestion. Post-fixation, sections of the cerebellar peduncles have multiple, irregular foci of pale tan discoloration and are softer than the surrounding tissue.

Histopathologic Description:

Within the cerebral white matter and extending into the white-gray matter junction are multifocal, irregular regions characterized by loss of neuropil and gliosis with prominent gemistocytic astrocytes that rarely contain glassy, intranuclear, amphophilic or granular, basophilic viral inclusions that marginate the chromatin. Astrocytes are cyto- and karyomegalic, many with misshapen or bizarre nuclei and large or bizarre nucleoli. Affected areas are infiltrated by foamy gitter cells and fewer lymphocytes. In and around affected regions, Virchow-Robbins space of vessels is markedly expanded by clear space (edema) with variable numbers of lymphocytes, macrophages, and rare eosinophils. There is multifocal, minimal to mild extravasation of red blood cells into Virchow-Robbins space and rarely into surrounding parenchyma.

Morphologic Diagnosis:

Cerebrum: Leukoencephalitis, multifocal, chronic, severe with demyelination, gliosis, gitter cells, gemistocytic astrocytosis, and intranuclear viral inclusions within oligodendroglia and bizarre astrocytes.

Lab Results:

Culture of the right naris grew Pseudomonas and Staphylococcus aureus. Culture of the lung grew Gram positive Bacillus spp. and α-hemolytic Streptococcus spp. His most recent complete blood count (1 month prior to necropsy) had only a minimal basophilia and the most recent serum chemistry (4 months prior to necropsy) was within normal limits.

Immunohistochemistry of brain sections for SV40 antigen revealed moderate to strong staining of astrocyte nuclei and nuclei of (presumably) oligodendroglia within the white matter of the cerebrum and the cerebellum. Luxol fast blue staining of cerebrum and cerebellum highlighted loss of myelin with minimal myelin particulates in gitter cells.

Condition:

SV40, rhesus macaque

Contributor Comment:

This case represents one manifestation of SV40 infection in immunosuppressed macaques. In this case, immunosuppression was due to experimental inoculation with SIV. The head tilt, posture, ambulation abnormalities, and death are attributable to brain lesions of SV40, while the epistaxis was unrelated and due to bacterial infection. Initial examination of the brain did not have grossly evident malacia, but multiple recuts of fixed tissue revealed discolored foci in the white matter. In addition to the charac-teristic histopathology, immunohistochemistry confirmed the presence of viral antigen within brain lesions.

Polyomaviruses are small, double-stranded DNA viruses and have been identified in birds, rodents, nonhuman primates, and humans. They were named for their propensity to cause tumors in either their natural host or atypical host(s), typically in differentiated cells. Much like herpesviruses, infection by polyomaviruses in their natural hosts typically causes an asymptomatic, life-long infection. The polyoma virion is divided into early and late-coding regions. The early region codes T antigens, the late codes capsid proteins. Small (t) and large (T) transforming/tumor antigens are conserved across all polyomavirus species and these proteins are fairly well-characterized. The small t antigen is not necessary for productive infection in cell culture, but the large T antigen is essential for production of progeny virions. T antigen plays a role in DNA replication as well as tumorigenesis. Some polyomaviruses, including SV40, have additional T antigens.1

Simian virus 40 (SV40) is an endemic polyomavirus in captive and free-ranging macaques. Seroprevalence increases with age in socially-housed animals, and the majority of animals are seropositive by 1 year of age.(9) Infection does not cause lesions in immunocompetent animals, but immune-suppression, such as SIV infection or immunosuppressive drug regimens, allows reactivation of latent infections or primary infections to cause disease. Disease in immunosuppressed macaques can manifest as progressive multifocal leukoenceph-alopathy (PML), nephritis, or pneumonia.(6)

SV40 is of particular utility in research due to its comparative ease to grow in culture as well as it causing PML in SIV or SHIV-infected macaques similar to disease in human AIDS patients infected with JC virus. SV40 is potentially zoonotic, identified as a contaminant in early polio vaccines and is seroprevalent in people working with macaques.(3,4) There is public concern over SV40 vaccine contamination, and there has been extensive research into oncogenicity of SV40 in people as it is known to cause a host of neoplasms in hamsters.(7)

SV40 is of particular utility in research due to its comparative ease to grow in culture as well as it causing PML in SIV or SHIV-infected macaques similar to disease in human AIDS patients infected with JC virus. SV40 is potentially zoonotic, identified as a contaminant in early polio vaccines and is seroprevalent in people working with macaques.(3,4) There is public concern over SV40 vaccine contamination, and there has been extensive research into oncogenicity of SV40 in people as it is known to cause a host of neoplasms in hamsters.(7)

Neuropathology of SV40 can be PML or meningoencephalitis, though some overlap does occur.(2) PML is hypothesized to occur in animals with underlying SV40 infection that subsequently are immunosuppressed, while macaques with more inflammatory than demyelinating lesions were SV40-negative at the time of SIV infection with subsequent experimental SV40 infection.(8,2) PML occurs due to infection and subsequent loss or dysfunction of myelin-producing oligodendroglia. In addition to the demyelination, a unique histopathologic feature of PML in macaques are the gemistocytic astrocytes with abundant eosinophilic cytoplasm and bizarre nuclei.(6) The gitter cell infiltration and gliosis are a secondary reaction to the breakdown of myelin. The more inflammatory manifest-tation of neurologic SV40 is characterized by leptomeningeal edema and perivascular and multifocal plaque-like infiltrates of lymphocytes and macrophages with extension of inflammatory cells into cortical gray matter.(2)

JPC Diagnosis:

Cerebrum, subcortical white matter: Leukoencephalomalacia, multifocal, marked with demyelination, numerous pleomorphic gemistocytic astrocytes, and glial intranuclear inclusion bodies.

Conference Comment:

The contributor provides an excellent review of SV40 infection and corresponding lesions above. There are seven polyomaviruses that have been identified in non-human primates. In addition to SV40 in macaques, these include SV12 in baboons, B-lymphocyte papovavirus (LPV) in African green monkeys, Polyomavirus papionis 2 in baboons, cynomolgus polyomavirus (CPV), SV40-CAL in macaques, and chimpanzee polyomavirus. These viruses are common as latent infections as seen with SV40 and discussed above.5 Renal lesions are associated with initial SV40 infection and the characterization of renal lesions and their relationship to the sequence of infection and immunosuppression vary between different polyomaviruses in non-human primates and humans.2 With SV40 infection lesions include nonsuppurative tubulointerstitial nephritis with basophilic intranuclear inclusion bodies in tubule epithelial cells. Sloughed epithelial cells are present in tubule lumina and evidence of regeneration may be present. Pulmonary lesions secondary to SV40 infection may include interstitial pneumonia; other pulmonary lesions may be also present and associated with immunosuppression, not secondary to SV40 infection.(6)

The pathogenesis of infection and corresponding CNS lesions in this case was also discussed. Recrudescence of the virus secondary to immunosuppression results in infection of oligodendrocytes and astrocytes, with loss of oligodendrocytes resulting in the demyelinating lesion seen histologically.

Multifocal to coalescing areas of necrosis and loss of the white matter constitute approximately 10% of the section, and are located primarily at the junction of the grey and white matter which contain numerous gemistocytic astrocytes and gitter cells. Additional characteristics include mild spongiosis and multifocal dilation of axon sheaths. There was a discussion regarding the chronicity of these lesions with some participants interpreting areas of pallor as having abundant astrocytic fibers, less debris and fewer gitter cells, indicating a developing astrocytic scar. Immuno-histochemistry for glial fibrillary acidic protein proved that many of the filaments traversing these areas are indeed astrocytic processes.

References:

1. An P, S+â-íenz Robles MT, Pipas JM. Large T antigens of polyomaviruses: amazing molecular machines. Annu Rev Microbiol. 2012. 66:213-236.

2. Axthelm MK, Koralnik IJ, Dang X, et al. Meningoencephalitis and demyelination are pathologic manifestations of primary polyomavirus infection in immunosuppressed rhesus monkeys. J Neuropath Exp Neurol. 2004. 63 (7): 750-758.

3. Engels EA. Cancer risk associated with receipt of vaccines contaminated with simian virus 40: epidemiologic research. Expert Rev Vaccines. 2005 Apr; 4(2):197-206.

4. Engels EA, Switzer WM, Heneine W, Viscidi RP. Serologic evidence for exposure to simian virus 40 in North American zoo workers. J Infect Dis. 2004 Dec 15; 190(12):2065-9.

5. Fahey MA, Westmoreland SV. Nervous system disorders of nonhuman primates and research models. In: Abee CR, Mansfield K, Tardif S, Morris T. eds. Nonhuman Primates in Biomedical Research: Diseases. 2nd ed. Vol 2. Waltham, MA: Elsevier; 2012: 739-741.

6. Horvath CJ, Simon MA, Bergsagel DJ et al. Simian Virus 40-induced disease in rhesus monkeys with simian acquired immunodeficiency syndrome. Am J Path.1192 140(6): 1431-1440.

7. Qi F, Carbone M, Yang H, Gaudino G. Simian virus 40 transformation, malignant mesothelioma and brain tumors. Expert Rev Respir Med. 2011; 5(5):683-97. doi: 10.1586/ers.11.51.

8. Simon MA, Ilyinskii PO, Baskin GB, Knight HY, Pauley DR, Lackner AA. Association of simian virus 40 with central nervous system lesion distinct from progressive multifocal leukoencephalopathy in macaques with AIDS. Am J Pathol. 1992; 154: 437-446.

9. Verschoor EJ, Niphuis H, Fagrouch Z, et al. Seroprevalence of SV40-like polyomavirus infections in captive and free-ranging macaque species. J Med Primatol. 2008 Aug;37(4):196-201. doi: 10.1111/j.1600-0684.2007.00276.x. Epub 2008 Jan 9.