Conference 17 - 2016 Case: 1 20170201

Signalment:

Three-year-old, male, pigtail macaque, (Macaca nemestrina).This animal was inoculated intravenously with SIVmac239, 177 days prior to humane sacrifice. It had a history of intermittent diarrhea, weight loss, mild dehydration, and upper respiratory signs (sneezing and nasal discharge). The day before sacrifice the animal began vocalizing and became progressively ataxic.

Gross Description:

The animal was thin with atrophic thymus and peripheral nodes but enlarged mesenteric and internal iliac nodes. Distal esophageal mucosa was covered with a proliferative growth of Candida sp. The colon had a thickened mucosa and was dilated with fluid feces.

Histopathologic Description:

The section of testis includes edematous rete testis with canaliculi, lobules made up of immature seminiferous tubules with multiple zones of necrosis, and thickened, inflamed, and partially fused tunica albuginea and vaginalis. Complete and partial lobules are destroyed by multifocal to coalescing coagulative necrosis involving seminiferous tubules and interstitium. Segments of small and medium-sized vessels are necrotic with hyalinized walls, fibrin thrombi and infiltration of neutrophils. Sertoli cells within the tubules, numerous Leydig cells, fibrocytes and myoid cells adjacent to the basal lamina of the tubules, and fibroblasts and endothelium lining interstitial vessels contain large round, oval, tear-drop and occasionally lobulated and multiple eosinophilic intranuclear inclusions usually surrounded by a clear halo. Some enlarged cells have additional amorphous granular eosinophilic aggregates within the cytoplasm. Interstitial stroma of the mediastinum, lobules, and both tunics is severely edematous with fibrin deposition, microhemorrhages, microthrombi, and predominantly neutrophilic infiltration, especially around small vessels. Neutrophils are necrotic, fragmented and mixed with small numbers of eosinophils.

Morphologic Diagnosis:

Acute orchitis with multifocal to coalescing, coagulative and fibrinoid necrosis, intra-vascular fibrin thrombi and intranuclear inclusions, Cytomegalovirus, Testis

Lab Results:

Moraxella sp. and hemolytic staphylococcus were cultured from the nasal cavity. Balantidium coli and Trichuris trichiura were identified by fecal flotation. Cytomegalovirus was identified by PCR in paraffin sections of testis.

Condition:

Necrotizing periorchitis/Rhesus cytomegalovirus

Contributor Comment:

Cytomegalovirus (CMV) is a betaherpesvirus comparable in sequence and pathogenesis to species-specific CMV of monkeys, humans, and other animals. CMV of Rhesus and Japanese macaques, African green monkeys (AGM), and chimps have distinct restriction fragment profiles.^1,6 Uncomplicated infections rarely cause disease, even in infants, usually become latent, and may reactivate later in life due to the immunosuppression of viral infection, cancer treatment, or organ transplantation. In breeding colonies, 50% of infants become seropositive by six months and nearly 100% by one year.³ Transmission via breast milk, saliva, and possibly urine² seem likely routes of transmission; transplacental infection is possible but rare²; trans-plantation of infected organs is a documented risk.¹²

The incidence of CMV disease in monkeys with SAIDS is variable but can be as high as 30-50% of seropositive animals.^12,15 Tissues displaying cytomegalic cells containing intranuclear inclusions include central and peripheral nervous system, lung, lymph nodes, liver, GI tract, testis, and arteries⁴. CMV disease in SIV-infected monkeys can be predicted by prolonged detection of CMV DNA in plasma and a decrease in anti-CMV titer and avidity¹⁴. Profound depletion of CD8 T cells (once thought linked⁹) is less important than the expanded target cell pool of activated CD4 cells.⁴

Genomes for rhesus and chimp CMV are sequenced and partial sequences for AGM and baboon CMV are reported.^6,7 There is a strong conservation of coding content between human and simian CMV, with even closer homologies among CMV of closely related primate hosts. While estimates of open reading frames in rhesus CMV vary from 230-258 genes, it is clear that evolution has produced extra coding capacity in rhesus compared to human and chimp CMV.³ Sequence homology demonstrates codes for proteins critical for neutrophil activation by CXC chemokines, TNF receptor, B-chemokine receptor, and IL-10 in rhesus CMV. In human fibroblasts, CMV can change levels of more than 250 cellular genes including cyclooxygenase 2 (COX-2)¹⁷, which converts arachidonic acid (AA) to prostaglandin endoperoxide H. Rhesus CMV does not increase cellular COX-2 but produces a homologue protein⁶ that could be used to modulate the host inflammatory process.

CMV establishes life-long infection in immunocompetent hosts in sites of latency and persistent infection. During latency, infected cells demonstrate limited viral gene expression, while in persistently infected cells; virions are continuously produced with minimal cytopathic effect. Endothelial cells, myeloid cells (particularly CD14+ monocytes) and possibly smooth muscle cells in large arteries are the likely sites of infection and latency.⁹ CMV infection of endothelial cells increases expression of cell adhesion molecules (ICAM-1) which interacts with monocytes and could provide a means for distribution. Infected cells induce a vigorous immune response releasing pro-inflammatory cytokines (like gamma IFN and TNF-alpha) that play a role in reactivation¹⁵. Monocyte differentiation driven by con-A-stimulated T-cells has been shown to reactivate non-lytic infection in monocyte-derived macrophages as well as other myeloid precursors⁷. The precise combination of cells and mediators may vary depending on the system but inflammatory cytokines, chemokines, and even some anti-inflammatory cytokines like IL-10 play a role in reactivation. The ability of CMV to bind to Fc-domains of neutralizing antibody and use it to infect naïve cells¹³ enhances viral persistence. In one study all SIV-infected rhesus monkeys were latently infected with CMV, seven of eleven had productive infections demonstrated by immunohistochemistry in the gut, liver, lungs, and testicles, and two of these seven had typical inflammatory lesions.¹¹

Our case demonstrates reactivation of CMV in the testis. Large numbers of classic owls-eye cells are noted in the endothelium and interstitial cells extending Baskins earlier observations.⁵ Evidence of vascular thrombosis could have contributed to the extensive necrosis observed in this tissue.

JPC Diagnosis:

Testis: Coagulative necrosis (infarct), focally extensive, with vascular thrombosis, fibrinoid necrosis, chronic periorchitis with adhesions, and intranuclear viral inclusions, pigtail macaque, Macaca nemestrina.

Conference Comment:

Rhesus cytomegalovirus (CMV), also known as macacine herpesvirus-3, is the most common opportunistic pathogen in SIV-infected rhesus macaques with a seroprevalence approaching 100% within the first year of life. Other nonhuman primates with host-adapted CMVs include chimpanzees, African green monkeys, sooty mangabeys, and owl monkeys.^2,3,4,6

These highly host-specific dsDNA viruses of the subfamily betaherpesvirinae have tropism for multiple organs producing interstitial pneumonia, gastroenteritis, poly-radiculoneuritis, encephalitis, and lymphadenitis, in addition to orchitis and periorchitis present in this case.² Lesions may also be in the liver, spleen, salivary gland, lymph node, and kidney. Both human and rhesus CMV are unique in that they encode a CXC chemokine, interleukin 8 (IL-8), which induces neutrophil chemotaxis, a prominent feature in this case.² This tissue section has marked karyomegaly and cytomegaly with prominent magenta intranuclear inclusions, typical for CMV. Necrotizing and proliferative vasculitis has also been reported in affected tissues.^2,3 In this case, there is fibrinoid vascular necrosis with thrombosis, which likely caused a focally extensive area of coagulative necrosis (infarct) in this testis.

Additionally, a recent report in Veterinary Pathology² reported peripheral neuropathy in the facial nerve associated with systemic CMV infection in a group of SIV-positive rhesus macaques. Interestingly, the pathogenesis of the nerve damage is likely due to the bystander effect secondary to CMV-induced inflammation rather than direct viral infection of Schwann cells.² Readers are encouraged to review for a great example of CMV-induced radiculitis within lumbar spinal roots of a rhesus macaque.

Conference participants discussed other cytomegaloviruses of veterinary importance. Guinea pig cytomegalovirus, also known as Cavid herpesvirus 1, is a common incidental finding in immunocompetent guinea pigs. Similar to CMV of other species, the salivary glands are the primary target tissue in the guinea pig.¹⁵ Additionally, suid herpesvirus 2 is a CMV that affects pigs causing inclusion body rhinitis in suckling pigs and severe generalized disease in neonates (>3 weeks old).¹⁸ Hamster, mice, and rats also have their own host adapted CMVs typically affecting the salivary and lacrimal glands.¹⁵

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