Cytomegalovirus-associated Discrete Gastrointestinal Masses in Macaques Infected with the Simian Immunodeficiency Virus

Common and Not-So-Common Pathologic Findings of the Gastrointestinal Tract of Rhesus and Cynomolgus Macaques

Rhesus and cynomolgus macaques are the most frequently used nonhuman primate (NHP) species for biomedical research and toxicology studies of novel therapeutics. In recent years, there has been a shortage of laboratory macaques due to a variety of competing factors. This was most recently exacerbated by the surge in NHP research required to address the severe acute respiratory syndrome (SARS)-coronavirus 2 pandemic. Continued support of these important studies has required the use of more varied cohorts of macaques, including animals with different origins, increased exposure to naturally occurring pathogens, and a wider age range. Diarrhea and diseases of the gastrointestinal tract are the most frequently occurring spontaneous findings in macaques of all origins and ages. The purpose of this review is to alert pathologists and scientists involved in NHP research to these findings and their impact on animal health and study endpoints, which may otherwise confound the interpretation of data generated using macaques.

Research Relevant Conditions and Pathology in Nonhuman Primates

Biomedical research involving animal models continues to provide important insights into disease pathogenesis and treatment of diseases that impact human health. In particular, nonhuman primates (NHPs) have been used extensively in translational research due to their phylogenetic proximity to humans and similarities to disease pathogenesis and treatment responses as assessed in clinical trials. Microscopic changes in tissues remain a significant endpoint in studies involving these models. Spontaneous, expected (ie, incidental or background) histopathologic changes are commonly encountered and influenced by species, genetic variations, age, and geographical origin of animals, including exposure to infectious or parasitic agents. Often, the background findings confound study-related changes, because numbers of NHPs used in research are limited by animal welfare and other considerations. Moreover, background findings in NHPs can be exacerbated by experimental conditions such as treatment with xenobiotics (eg, infectious morphological changes related to immunosuppressive therapy). This review and summary of research-relevant conditions and pathology in rhesus and cynomolgus macaques, baboons, African green monkeys, common marmosets, tamarins, and squirrel and owl monkeys aims to improve the interpretation and validity of NHP studies.

Pseudotumor presentation of CMV disease: Diagnostic dilemma and association with immunomodulating therapy

Cytomegalovirus (CMV) is a significant cause of morbidity and mortality in the immunocompromised host. Atypical presentations which include pseudotumors or "cancer mimics" have been described. The etiology of these lesions remains unclear. The authors describe two previously unpublished cases that have arisen in the context of newer immunomodulating therapy and review the existing non-HIV-associated CMV pseudotumors described in the literature.

Cytomegaloviral hypophysitis in a simian immunodeficiency virus-infected rhesus macaque (Macacca mulatta)

Rhesus macaques experimentally infected with Simian Immunodeficiency Virus (SIV) experience immunosuppression and often opportunistic infection. Among the most common opportunistic infections are rhesus cytomegalovirus (RhCMV), a ubiquitous betaherpesvirus that undergoes continuous low-level replication in immunocompetent monkeys. Upon SIV-mediated immunodeficiency, RhCMV reactivates and results in lesions in numerous organ systems including the nervous and reproductive systems. We report the first case of cytomegaloviral hypophysitis in a SIV-immunocompromised rhesus macaque.

Ménétrier's disease-like hypertrophic gastritis in two red-capped mangabeys (Cercocebus torquatus)

Chronic lymphoplasmacytic gastritis in two red-capped mangabeys (Cercocebus torquatus) at a zoological facility progressed to severe hypertrophic gastropathy similar to Ménétrier's disease that affects humans. Clinical signs included emesis, diarrhea, hunched posture consistent with abdominal pain, anemia, and hypoproteinemia. Large gastric masses were present and in one case created a gastric outflow obstruction. Both cases were positive for simian immunodeficiency virus and Helicobacter spp. were variably isolated, although the association with the hypertrophic gastropathy is unclear. Medical treatment had varying success and included sucralfate, H2 receptor antagonists, proton pump inhibitors, diet manipulations, and antibiotic therapies targeting Helicobacter spp. Surgical resection of a large portion of the stomach resulted in some palliative improvement in one case. Overall, this disease presented many challenges regarding identification, confirmation of diagnosis, and clinical management. Both aggressive medical and surgical treatments were unrewarding for long-term management of hypertrophic gastropathy in this pair of red-capped mangabeys and resulted in a poor prognosis in these cases.

Mesenchymoproliferative enteropathy associated with dual simian polyomavirus and rhesus cytomegalovirus infection in a simian immunodeficiency virus-infected rhesus macaque (Macaca mulatta)

Opportunistic viral infections are common in simian immunodeficiency virus-infected rhesus macaques and include simian polyomavirus 40 (SV40), which causes interstitial nephritis, pneumonia, meningoencephalitis, and progressive multifocal leukoencephalopathy and rhesus cytomegalovirus (Macacine herpesvirus-3), which is associated with many pathologic manifestations, including the formation of neutrophil-rich gastrointestinal masses. Herein we report the findings of a simian immunodeficiency virus-infected rhesus macaque that presented to necropsy with multiple nodular masses restricted to the proximal jejunum. Histologically, the masses within the lamina propria were composed of abundant, loosely organized, mesenchymal tissue forming broad interlacing whorls and sheets admixed with variable numbers of neutrophils. Cells within the mesenchymoproliferative nodules contained numerous basophilic, intranuclear inclusion bodies with only scattered cytomegalic cells. Immunohistochemistry for rhesus cytomegalovirus and SV40 demonstrated variable numbers of immunopositive cells within the affected nodules. This report is the first description of SV40-associated pathology in the small intestine of a rhesus macaque and highlights the role that opportunistic viral infections can have on gastrointestinal pathology in immunosuppressed rhesus macaques.

Cytomegalovirus pseudotumor of the duodenum in a patient with AIDS: an unrecognized and potentially treatable clinical entity

BACKGROUND

Cytomegalovirus (CMV) is a common pathogen affecting the gastrointestinal tract in patients with AIDS. We report a case of CMV-induced pseudotumor of the duodenum in a patient with AIDS and review other reported cases of CMV-induced pseudotumors in the gastrointestinal tract. CMV-induced pseudotumor in patients with AIDS is an exceptionally rare clinical entity, and to our knowledge no reports have previously summarized this clinical entity.

METHODS

All previous cases included in our literature review were found using a PubMed search (1980-November 2008) of the English-language medical literature applying the terms 'CMV infection', 'inflammatory mass', 'pseudotumor', and 'gastrointestinal tract'. The references cited in these articles were examined to identify additional reports.

RESULTS

Although CMV-induced duodenitis has been described in patients with HIV infection, to our knowledge CMV-induced pseudotumor of the duodenum has not been previously reported in the literature. We describe the first case of an AIDS patient with CMV pseudotumor responding to oral treatment with valganciclovir with complete resolution of the CMV mass. Among reports of non-duodenal pseudotumor reported in the English literature, we found only 14 cases of CMV-induced gastrointestinal pseudotumors in HIV-positive patients. The clinical manifestations, pathologic findings of the CMV pseudotumors, as well as the treatment and outcome of these HIV patients are reviewed.

CONCLUSION

CMV pseudotumor should be included in the differential diagnosis of gastrointestinal mass lesions in AIDS patients and in other immunocompromised patients. The tumor often responds to antiviral therapy, but resolution of a CMV mass as a result of oral antiviral therapy has not been previously described. Since pseudotumors secondary to CMV often respond to medical treatment, it is important that the physicians treating severely immunocompromised patients are aware of this entity.

Expanded tissue targets for foamy virus replication with simian immunodeficiency virus-induced immunosuppression

Foamy viruses (FV) are the oldest known genus of retroviruses and have persisted in nonhuman primates for over 60 million years. FV are efficiently transmitted, leading to a lifelong nonpathogenic infection. Transmission is thought to occur through saliva, but the detailed mechanism is unknown. Interestingly, this persistent infection contrasts with the rapid cytopathicity caused by FV in vitro, suggesting a host defense against FV. To better understand the tissue specificity of FV replication and host immunologic defense against FV cytopathicity, we quantified FV in tissues of healthy rhesus macaques (RM) and those severely immunosuppressed by simian immunodeficiency virus (SIV). Contrary to earlier findings, we find that all immunocompetent animals consistently have high levels of viral RNA in oral tissues but not in other tissues examined, including the small intestine. Strikingly, abundant viral transcripts were detected in the small intestine of all of the SIV-infected RM, which has been shown to be a major site of SIV (and human immunodeficiency virus)-induced CD4+ T-cell depletion. In contrast, there was a trend to lower viral RNA levels in oropharyngeal tissues of SIV-infected animals. The expansion of FV replication to the small intestine but not to other CD4+ T-cell-depleted tissues suggests that factors other than T-cell depletion, such as dysregulation of the jejunal microenvironment after SIV infection, likely account for the expanded tissue tropism of FV replication.

Malignancy after transplantation

As newer immunosuppressive regimens have steadily reduced the incidence of acute rejection and have extended the life expectancy of allograft recipients, posttransplant malignancy has become an important cause of mortality. In fact, it is expected that cancer will surpass cardiovascular complications as the leading cause of death in transplant patients within the next 2 decades. An understanding of the underlying pathobiology and how to minimize cancer risks in transplant recipients are essential. The etiology of posttransplant malignancy is believed to be multifactorial and likely involves impaired immunosurveillance of neoplastic cells as well as depressed antiviral immune activity with a number of common posttransplant malignancies being viral-related. Although calcineurin inhibitors and azathioprine have been linked with posttransplant malignancies, newer agents such as mycophenolate mofetil and sirolimus have not and indeed may have antitumor properties. Long-term data are needed to determine if the use of these agents will ultimately lower the mortality due to malignancy for transplant recipients.