Meeting Report

Abstract

A workshop on Emerging Respiratory Viral Infections and Spontaneous Diseases in nonhuman primates was sponsored by the concurrent Annual Meetings of the American College of Veterinary Pathologists and the American Society for Veterinary Clinical Pathology, held December 1–5, 2012, in Seattle, Washington. The session had platform presentations from Drs Karen Terio, Thijs Kuiken, Guy Boivin, and Robert Palermo that focused on naturally occurring influenza, human respiratory syncytial virus, and metapneumovirus in wild and zoo-housed great apes; the molecular biology and pathology of these viral respiratory diseases in nonhuman primate (NHP) models; and the therapeutic and vaccine approaches to prevention and control of these emerging respiratory viral infections. These formal presentations were followed by presentations of 14 unique case studies of rare or newly observed spontaneous lesions in NHPs (see online files for access to digital whole-slide images corresponding to each case report at http://scanscope.com/ACVP%20Slide%20Seminars/2012/Primate%20Pathology/view.apml). The session was attended by meeting participants that included students, pathology trainees, and experienced pathologists from academia and industry with an interest in respiratory and spontaneous diseases of NHPs.

Meeting Platform Presentations: Drs Terio, Kuiken, Boivin, and Palermo

Dr Terio, Clinical Associate Professor, University of Illinois, Zoological Pathology Program, provided an overview of respiratory diseases in wild and zoo-housed great apes. Dr Terio observed that respiratory disease has been a long-term concern for the conservation of great ape populations. Dr Terio described the impact of influenza, human respiratory syncytial virus, and metapneumovirus (hMPV) on both captive and wild populations of great apes and highlighting the importance of these anthropozoonotic infections. Although modifications and improved enclosure design have greatly decreased the risk of transmission between apes and the viewing public in zoological settings, multiple episodes of viral transmission from humans to wild apes have emphasized the need for improved biosecurity protocols for ecotourism and behavioral research.

Dr Thijs Kuiken, Professor of Comparative Pathology, Erasmus MC Department of Virology, the Netherlands, presented research on the pathogenesis of influenza and hMPV using nonhuman primate (NHP) models. Research presented used a variety of in vivo and ex vivo models to elucidate the pathogenesis of these infections. He described the histopathologic lesions noted in experimental infections and presented studies into tissue tropism of various viral strains and host immune responses that have contributed to our understanding of these pathogens. Dr Kuiken finished by presenting the lesions and findings of recent research into the pathogenesis of respiratory coronaviruses, as well as the association with severe acute respiratory syndrome and the ongoing outbreak in Saudi Arabia.

Dr Guy Boivin, holder of the Canada Research Chair on emerging viruses and antiviral resistance, Infectious Disease Research Center, University of Laval and Center Hospital University of Quebec, Quebec, Canada, gave a presentation entitled “Ten Years of Human Metapneumovirus Research.” In this presentation, Dr Boivin mentioned that since first being described in 2001, hMPV has become one of the main viral pathogens responsible for acute respiratory tract infections in children but also in the elderly and in immunocompromised patients. Dr Boivin stated that there currently exists no approved therapeutic or prophylactic treatment modality in the management of hMPV infection. He then described some innovative approaches based on RNA interference and on fusion inhibitors, which have shown efficacy in vitro and in animal studies. Dr Boivin described several new strategies, such as the use of live-attenuated viruses generated by reverse genetics or recombinant proteins that are currently in preclinical development.

Dr Robert Palermo, Assistant Professor of Microbiology, Department of Microbiology, Washington National Primate Research Center, University of Washington, Seattle, presented a talk entitled “Systems Biology Approaches to Characterize the Host Immune Response to Influenza Infection.” Dr Palermo stated that although targeted molecular approaches that focus on individual genes and proteins have led to considerable progress in our understanding of viral infectious diseases and subsequently in the development of effective pharmacological therapies and disease/infection management, the rapid emergence of resistance viruses remains a concern. Dr Palermo described his group’s application of systems biology approaches to understand the host response to influenza infection. They have employed infection models at differing scales of complexity, using in vitro cell lines, marine systems, and NHPs.

Case Reports

Fourteen case reports in various species of NHPs were presented. Nine of the 14 cases involved respiratory pathology, including bacterial, viral, fungal and parasitic, degenerative, proliferative, and neoplastic diseases in the lung. The remaining 5 cases included some rare or newly observed pathogens in NHPs. Brief case histories, morphologic diagnosis, etiology, and short discussions are listed below. All cases were digitally scanned (20× objective). For digital whole-slide images corresponding to each case report, see supplemental files at http://scanscope.com/ACVP%20Slide%20Seminars/2012/Primate%20Pathology/view.apml.

This supplement will serve as a unique resource for training and continuing education in primate pathology.

Case 1. Audrey Baldessari (University of Washington, National Primate Research Center)

History

A domestic-bred, 1.5-year-old female pig-tailed macaque (Macaca nemestrina) presented for dehydration, with a cough and purulent nasal discharge. She had loose stools and poor body condition with recent weight loss. There was an initial response to antibiotic and symptomatic therapy, but clinical signs returned. Thoracic radiographs were consistent with diffuse interstitial pneumonia and enlarged pulmonary lymph nodes. Coccidioides titer was 1:256. Euthanasia was elected due to poor prognosis.

Morphologic diagnosis

Lung: pyogranulomatous pneumonia, multifocal to coalescing, severe, with intralesional fungal spherules

Etiology

Coccidioides sp

Discussion

This animal was one of several that presented with similar clinical signs of coughing, weight loss, and lack of response to symptomatic therapy. Fungal titers were positive for Coccidioides, with the majority of titers being 1:256. Organisms were seen in cytology samples on some of the animals. The distribution of lesions varied from localized skin lesions, more commonly hilar lymph node and lung involvement, and disseminated disease in a subset of animals. Coccidioidomycosis is endemic to the southwestern United States and is caused by Coccidioides immitis and Coccidioides posadasii.^15,38,41 There has been a recent increase in cases reported in the southwestern United States that are thought to be associated with weather patterns, including draught following a rainy period, with wind-blown organisms inhaled by the host. Most human and canine infections are subclinical but when present usually begin with respiratory or skin lesions, with occasional dissemination to other organs, including eyes and bone. There is a canine case series of 17 dogs that presented for right-sided heart failure and pericardial effusion with pericarditis. ¹⁵ A cell-mediated immune response is reported to be required for a successful clinical outcome. It is reported that mice with higher amounts of T lymphocytes are more resistant to infection, and vaccinated mice mount a significantly increased T-cell response. Canine cases of coccidioidomycosis have been shown to involve T-cell predominance regardless of severity of infection. ³⁸ Lymphocytes are seen in this case throughout the lesion, often concentrated around the granulomas.

Case 2. Carole Harbison (Harvard Medical School, New England Primate Research Center)

History

A 2-year-old female rhesus macaque (Macaca mulatta) enrolled in a simian immunodeficiency virus (SIV) study was inoculated with SIVmac239 seven months prior to euthanasia. The animal developed chronic intermittent diarrhea with loss of body condition following inoculation. Prior to euthanasia, the animal had a 1-day history of dyspnea, hypothermia, and anorexia that progressed to severe weakness with recumbency.

Morphologic diagnosis

Lung: necrotizing and suppurative pleuropneumonia, diffuse, with chronic abscessation and intralesional cocci bacteria

Etiology

Staphylococcus aureus (via culture)

Discussion

In NHPs, bacterial pneumonias occur as both primary and secondary infections and can include overgrowth of flora found in the upper respiratory tract of healthy animals. Immunosuppression by experimental SIV infection and/or the disturbance of normal defense mechanisms by viral infections frequently precede bacterial infection by agents such as Corynebacterium ulcerans, Staphylococcus spp and Streptococcus spp, Escherichia coli, and Klebsiella pneumonia. As seen with this case, bacterial culture is frequently required to identify the specific agent(s) responsible for clinical signs.^14,35 S. aureus is a commensal of primate skin and nasopharynx but is also a common cause of secondary pneumonia, dermatitis, bite wound abscesses, and other infections in macaques. Demonstration of pyogranulomatous inflammation with intracellular bacteria is required to differentiate from contamination of culture swabs by bystander commensals. ³⁶ In this case, SIV infection with immunosuppression was likely the predisposing factor for dissemination and proliferation of S. aureus. Tuberculosis (Mycobacterium tuberculosis or Mycobacterium bovis) is an important differential for multinodular pulmonary disease. Miliary pulmonary lesions may occur early in the course of infection, developing later into classic granulomatous disease with caseation and regional lymph node involvement. Rhesus macaques appear to be particularly sensitive to infection, necessitating strict quarantine and testing regimens of animals and human caretakers to prevent devastating outbreaks. Nocardia spp infection is a primary differential for tuberculosis, but the gross lesions differ slightly and include abscessation, cavitation, and pulmonary consolidation with occasional sulfur granule formation. ²⁵

Case 3. Steven Laing (University of California, California National Primate Research Center)

History

A 7-day-old, male, 205-g rhesus macaque (M. mulatta) was born in captivity to a 5-year-old primiparous female in an outdoor corral. The infant was found dead with no observed premonitory signs.

Morphologic diagnosis

Lung: necrotizing bronchointerstitial pneumonia, severe, with intralesional bacteria and amphophilic intranuclear viral inclusions

Etiology

Macacine herpesvirus 1 (MHV-1)

Discussion

In addition to the MHV-1–associated severe necrotizing bronchointerstitial pneumonia, multifocal random acute necrosis with numerous amphophilic intranuclear viral inclusions in the bone marrow, thymus, adrenal glands, and liver was observed. In addition, there was multifocal acute vasculitis with fibrinoid vascular necrosis and multifocal acute necrosis in the spleen and multifocal lymphocytic meningoencephalitis with rare amphophilic intranuclear viral inclusions. MHV-1, also known as Cercopithecine herpesvirus 1, herpes B, Herpes simiae, and B virus, is enzootic in macaques with a reported seroprevalence of up to 97% in housed animals older than 2.5 years. ⁴⁶ Clinical disease is infrequent in rhesus macaques and, when present, is typically limited to mucocutaneous erosions and ulcers. ⁴⁵ Disseminated disease and mortality, as in this case, are rare and are usually found in young, stressed, or immunosuppressed animals.^29,45 MHV-1 is an important zoonosis. The rate of human infection, typically by direct inoculation of macaque tissue or fluids, is low, but mortality rates of more than 70% in untreated individuals are reported. ¹⁹ In addition, fatalities in several other NHP species have been reported. ¹⁸ MHV-1 is an alphaherpesvirus that typically results in acute necrosis with or without syncytium formation and intranuclear, Cowdry type A viral inclusions. ⁴⁵ Although multiple organs may be affected in disseminated disease, the virus has tropism for neural tissues. Trigeminal and lumbosacral ganglia are sites of latency in macaques, and encephalomyelitis results in mortality in other species, including humans. ⁴⁵ The major differential diagnosis in this case was rhesus cytomegalovirus (CMV), which can produce a similar spectrum of lesions in immunosuppressed macaques. However, the presence of syncytia in this case and the lack of intracytoplasmic inclusions, in addition to intranuclear inclusions, are inconsistent with CMV.

Case 4. Saravanan Kaliyaperumal (Harvard Medical School, New England Primate Research Center)

History

A 2.5-year-old male rhesus macaque (M. mulatta) enrolled in an SIV study. Following infection with SIV, the animal developed protracted diarrhea and was found to be fecal positive for Entamoeba. Treatment included varying regimens of baytril, metronidazole, and tinidazole. Four months following treatment for gastrointestinal disease, the animal was euthanized due to failing health and markedly increased respiratory effort.

Morphologic diagnosis

Lung: histiocytic and neutrophilic bronchointersitial pneumonia with type II pneumocyte hyperplasia, diffuse, severe, with intralesional fungal organisms (Pneumocystis sp), bronchial-associated Cryptosporidium, and SIV-associated giant cells

Etiology

Pneumocystis sp, Cryptosporidium sp, and SIV

Discussion

Of all the experimentally induced infections in NHPs, SIV (genus Lentivirus, family Retroviridae) is the single most thoroughly studied virus known to contribute and predispose to the development of opportunistic infections (OIs) in an immunocompromised individual. SIV infection is usually asymptomatic in large numbers of African species but leads to an immunodeficiency syndrome when inoculated in Asian macaques. ¹⁷ Among various OIs related to SIV-induced immunosuppression, many target the lungs. Pneumocystis carinii is an opportunistic fungal pathogen, which is usually host specific and causes multifocal to coalescing interstitial pneumonia with marked consolidation of lung parenchyma. There is often pronounced type II pneumocyte hyperplasia accompanied by numerous organisms in the alveoli. Gomori methenamine silver staining and immunohistochemistry may be useful in diagnosis. Cryptosporidium parvum is a protozoal parasite that induces persistent diarrhea with marked wasting. Infection can involve the gastrointestinal, pancreatic, respiratory, and hepatobiliary systems and is often seen in immunosuppressed individuals.^39,44 The transmission is usually by the fecal-oral route. Another OI that can commonly affect the lung of immunosuppressed rhesus animals is Cercopithecine herpesvirus 3 or rhesus CMV. CMV is slowly cytolytic, leading to nuclear and cytoplasmic enlargement with the presence of both intranuclear and intracytoplasmic inclusions. ³ The viral replication is usually accompanied by diffuse moderate to extensive necrosis and neutrophilic infiltration.

Case 5. Kerstin Mätz-Rensing (German Primate Center)

History

A chimpanzee (Pan troglodytes) from a community of wild chimpanzees living in the Taï National Park, Ivory Coast, was in apparent good health, exhibited no previous signs of illness, and died with signs of a peracute hemorrhagic disease.

Morphologic diagnosis

Lung, heart, lymph node, spleen, liver: septicemia, peracute anthrax-like disease with anthrax-like bacilli

Etiology

Bacillus cereus biovar anthracis (confirmed by culture and polymerase chain reaction [PCR])

Discussion

Anthrax is classically caused by Bacillus anthracis, a monophyletic group of bacilli within the B. cereus group. It is an acute disease that can infect all mammalian species. Species differ in susceptibility. Anthrax is a typical zoonotic disease, resulting from contact with infected animals, contaminated hides or wool, or uncooked meat. The case presented is an example of a peracute anthrax-like disease related to septicaemia induced by the novel B. anthracis–like bacterium, called B. cereus biovar anthracis.^22,23 The strain contains the plasmids pXO1 and pXO2, which are important for anthrax pathogenesis. This anthrax-like disease caused by an atypical B. anthracis strain has killed at least 13 chimpanzees in the study groups of wild chimpanzees living in Taï National Park, pointing toward an endemic presence of the bacillus in the region that may have important implications for great ape conservation as well as human health. ²⁴

Case 6. Andrew Miller (Harvard Medical School, New England Primate Research Center)

History

A 4-year-old female rhesus macaque (M. mulatta) that was enrolled in an SIV pathogenesis study was inoculated with SIVmac239 eight months prior to death. The animal presented with diarrhea, epistaxis, a heart murmur, and mildly harsh lung sounds 6 weeks prior to death. The animal was found dead in its cage following an episode of dyspnea.

Morphologic diagnosis

Lung: lymphoma

Etiology

Rhesus lymphocryptovirus (LCV)

Discussion

Lymphoma has been described in most NHP species, including immunosuppressed and non-immunosuppressed animals. Lymphoma is one of the few malignant conditions that is also an AIDS-defining lesion due to its association with rhesus LCV. ²¹ This virus is closely related to Epstein-Barr virus, and as such, immunohistochemical assays such as EBNA (Epstein-Barr nuclear antigen) and BZLF (immediate-early lytic protein) can be used to stain LCV-associated lymphoma in immunosuppressed macaques. ³¹ Many macaques are latently infected with LCV, and following immunosuppression, the virus recrudesces and leads to peripheral lymphadenopathy and multiorgan lymphoma. Lymphoma can be distributed throughout the body, but common sites include kidney, gastrointestinal tract, and lymph nodes. ³¹ Infection with LCV does not produce disease in immunologically competent macaques even though there is a high seropositivity rate. Not all cases of lymphoma in immunosuppressed rhesus macaques are immunopositive for or associated with rhesus LCV. Another virus that may be associated with the development of lymphoma in immunosuppressed macaques is rhadinovirus. There are 2 major rhadinovirus lineages in NHPs: those that belong to the RV1 lineage, which are homologs of Kaposi sarcoma–associated herpesvirus, and those that are in the RV2 lineage, of which the prototype virus is rhesus macaque rhadinovirus. ³¹ This latter virus has been associated with persistent B-lymphocyte hyperplasia and clinical lymphadenopathy in rhesus macaques. ³⁴ RV2 rhadinoviruses have recently been associated with the development of lymphoma in SIV-infected pig-tailed macaques. ³¹ Its role in lymphoma in the rhesus macaque remains to be elucidated; however, it likely plays a similar role in the rhesus macaque as it does in the pig-tailed macaque.

Case 7. Lisa D. Schmidt and Jessica Kaplan-Kees (Wake Forest University School of Medicine)

History

A 6-year-old male Chinese rhesus macaque (M. mulatta) received 7.2-gray (Gy) whole-body irradiation and was part of a long-term observational study of late radiation effects. It was known to have a heart murmur and was found dead 2.75 years after irradiation.

Morphologic diagnosis

Lung: alveolar septal fibrosis, diffuse, moderate; congestion and edema, diffuse, chronic, moderate with hemosiderin-laden alveolar macrophages and erythrophagocytosis; type II pneumocyte hyperplasia and respiratory metaplasia, multifocal, mild

Etiology

Radiation-induced injury

Discussion

The lung is highly susceptible to radiation-induced injury and is often the dose-limiting organ in patients receiving whole-body irradiation. ⁴⁸ Radiation-induced lung injuries are divided into acute (1–6 months after irradiation) and chronic pneumonitis (>6 months after irradiation). ²⁶ Risk factors for the development of radiation pneumonitis include high radiation dose (as in this case), large radiation treatment volume, administration of chemotherapeutic agents, advanced age, and preexisting pulmonary disease. ⁴⁷ NHPs are the model of choice to study the effect of radiation on the lungs, despite a lack of well-defined dose-response curves. ⁴⁸ Radiation pneumonitis results from injury to type II pneumocytes and endothelial cells. Acute pneumonitis is characterized by the exudation of protein-rich edema fluid into the alveoli, desquamation of alveolar epithelial cells, and inflammation, all of which impair gas exchange and reduce lung compliance. With chronicity, the alveolar septa become progressively fibrotic. It is believed that radiation generates reactive oxygen species, which initiates a self-sustaining cycle of inflammation and fibrosis, perpetuated by hypoxia, macrophage accumulation and activation, and the generation of cytokines, which promote angiogenesis and fibrosis, eventually culminating in extensive alveolar septal fibrosis.^12,26 The hemosiderin-laden alveolar macrophages and pulmonary edema in this case are consistent with congestive heart failure, which may also have been initiated by radiation-induced vascular injury due to inflammation and oxidative stress, similar to the mechanism described for the lung. ²

Case 8. Edward J. Dick Jr. (Texas Biomedical Research Institute, Southwest National Primate Research Center)

History

A 16.5-year-old captive bred female baboon (Papio sp) with 1- to 2-mm diameter pale cystic lesions on the right medial and left caudal dorsal lung surfaces.

Morphologic diagnosis

Lung: pleuropulmonary endometriosis

Etiology

Unknown

Discussion

Endometriosis is one of the most common gynecologic disorders in humans, with up to 10% of reproductive age women ⁸ and 30% to 55% of infertile women being affected. ¹³ Pleuropulmonary endometriosis (PPE) or thoracic endometriosis is a rare but well-defined condition in humans. Our current knowledge of the pathogenesis of endometriosis in general and for the development of PPE remains unclear. Three major theories have been proposed: coelomic metaplasia, lymphatic or hematogenous embolization from the uterus or pelvis, and Sampson’s theory of retrograde menstruation with subsequent transperitoneal-transdiaphragmatic migration of endometrial tissue. ¹³ A case of pulmonary endometriosis has been reported in an aged rhesus macaque. ¹ The baboon is an excellent model for experimental studies on endometriosis. The pelvic anatomy of baboons is very similar to humans, and they have monthly menstrual cycles and spontaneous menses. ⁷ After more than 2 years in captivity, the prevalence of biopsy-proven endometriosis is as high as 27%. ⁷ In established multigenerational breeding colonies, the prevalence has been reported as high as 60% in infertile animals. Also, in large, established colonies, many cases of severe disease are encountered at the time of necropsy. Recently, 10 cases of PPE (3 with concurrent pelvic [uterine] endometriosis) in baboons were reported. ²⁰ PPE is observed in the absence of detected pelvic endometriosis, and pelvic endometriosis occurs without PPE. Gross lesions are typically composed of single to multiple, generally small, round, blue-gray cystic structures. These are generally in a subpleural location, descending slightly into the subjacent parenchyma. Deeper lesions are rarely observed. Histologic changes are typically as observed in this case, sometimes with more prominent columnar epithelium, denser stromal component, or more hemosiderin. In addition, aggregated stromal cells deep in the interstitium with peripherally located epithelial cells can be observed.

Case 9. J. Rachel Reader (University of California, California National Primate Research Center)

History

A 2-year-old male rhesus macaque (M. mulatta) housed in the outdoor corn cribs presented in fair body condition, was mildly bloated with a temperature of 105.5°F, and had possible diarrhea. The mesenteric lymph nodes were palpably enlarged, and this was confirmed on ultrasound. The animal deteriorated further and was euthanized.

Morphologic diagnosis

Mesenteric lymph nodes: necrotizing lymphadenitis, extensive, severe; small intestine and mesentery: lymphangitis and steatitis

Etiology

Francisella tularensis confirmed by PCR and immunohistochemistry

Discussion

F. tularensis is a zoonotic Gram-negative bacterium. It is widespread throughout North America, Europe, and Asia. The organism can infect several species of mammals and even some birds and reptiles. Outbreaks of the disease in NHPs are fairly uncommon.^11,27 This case was one of a cluster of cases of tularemia diagnosed at the California National Primate Research Center in animals housed in the outdoor corn cribs in the fall of 2010. ¹¹ Seven cases in total came to pathology, while several other animals were successfully treated. The gross lesions this case were somewhat unusual compared with lesions found in other animals necropsied during the outbreak. The mesenteric lymph nodes were severely affected, but there was no involvement of oropharyngeal lymph nodes or tissues. The severely enlarged and compromised mesenteric lymph nodes resulted in obstruction to lymphatic drainage from the small intestine and free chyle within the abdomen. There were other minor lesions in the pancreatic and gastric lymph nodes but no involvement of other lymph nodes or lesions in any other organs.

Case 10. David Liu (Tulane University, Tulane National Primate Research Center)

History

A 7-year-old female rhesus macaque (M. mulatta) was originally imported from China through a vendor and tested negative for MHV-1, SIV, simian retrovirus (SRV), simian T-lymphotropic virus 1 (STLV-1), and M. tuberculosis. This animal was quarantined for 3 months, showed no physical signs of illness, and was assigned to a human immunodeficiency virus (HIV) vaccine study. The animal twice received SIV/HIV (SHIV) inoculations intravaginally. Chronic, mild to severe anemia, fever, and anorexia developed 2 weeks after the second SHIV inoculation. The red blood cells (RBCs) and the number of lymphocytes reached their lowest levels (RBCs, 3.24 × 10 ⁶ /μl; hemoglobin, 8.6 g/dl; hematocrit, 28.6% [reticulocyte index (RI), 37.2%–47.1%]; and total lymphocytes, 1.01 × 10 ³ /μl [RI, 2.3–13 × 10 ³ /μl]) 15 months after the second inoculation.

Morphological diagnosis

Peripheral blood: babesiosis with moderate regenerative anemia

Etiology

Babesia microti–like parasite

Discussion

Babesia is one of most common infectious protozoans in free-living animals worldwide, in which Ixodes ticks carry Babesia spp. In the NHP, Entopolypoides macaci was first described in macaques by Mayer in 1934. ⁴² Recent phylogenetic evidence showed the synonymy of Entopolypoides and Babesia with a 97.9% sequence similarity. ⁴ Severe babesiosis is typically associated with splenectomization, anti–lymphocyte antibody therapy, and SRV infections. Recently, a B. microti–like parasite was found in wild NHPs, African green monkeys, Syke’s monkeys, olive baboons, and Japanese macaques. However, these monkeys usually are asymptomatic, although parasitemia can reach 0.3% in blood smears. ¹⁶ Although the source of Babesia in this case was uncertain, it is possible that this animal was infected with B. microti–like parasite while in China.

Case 11. LaTasha K. Crawford and Joseph L. Mankowski (Dept of Molecular and Comparative Pathobiology, Johns Hopkins University)

History

A 14-year-old male, wild-caught baboon (Papio sp) used in a research program had exposure to investigational drugs. There was a recent repair of an indwelling catheter. There were no signs of illness prior to sudden death.

Morphological diagnoses

Brain (frontal lobe): leukoencephalomalacia; subcortical, bilaterally symmetrical, multifocal, severe with mild multifocal encephalitis; gliosis; gemistocytosis; neuron necrosis; and accumulation of spheroids and Gitter cells

Cerebral blood vessels: cerebral vasculopathy, multifocal, moderate to severe with partial to complete occlusion

Etiology

Unknown

Discussion

There were bilaterally symmetrical subcortical ischemic infarcts of white matter accompanied by moderate to severe mural thickening of blood vessels. Trichrome stain demonstrated abundant collagen in the thickened vessel walls. Vessels were negative for amyloid with Congo red stains and negative for β-amyloid and amyloid A by immunohistochemistry, making cerebral amyloid angiopathy unlikely. ³² Vascular changes were not seen outside of the brain, and there were no lesions in other tissues to suggest systemic hypertension. Death was attributable to a hemothorax, unrelated to the neuropathology. The mural thickening and degeneration of cerebral blood vessels along with subcortical infarcts resemble a condition reported in humans known as cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL, http://www.ninds.nih.gov/disorders/cadasil/CADASIL.htm), a genetic form of vascular dementia that results from degeneration of arterial smooth muscle in the brain. Histologic hallmarks of CADASIL are periodic acid–Schiff (PAS)–positive, osmophilic granular deposits within the tunica media of arterioles, which are visible using electron microscopy. ⁴³ There are also arteriopathies with undefined genetics that do not exhibit the granular deposits seen in CADASIL. ³⁰ Electron microscopy was not done in this case. PAS staining to detect granular deposits in vessel walls was negative. Thus, this case likely represents a distinct, uncharacterized cerebral vasculopathy.

Case 12. Joan H. Lane (Biogen Idec, Inc)

History

A juvenile captive-bred male cynomolgus macaque (Macaca fascicularis) of Chinese origin was assigned to the vehicle control cohort of a 28-day toxicology study. Animals on test were obtained from 3 different vendors. At termination, gross examination, serum chemistry, and coagulation results were unremarkable. A mild lymphocytic/monocytic leukocytosis was noted on day 14. The white blood cell count returned to baseline levels by day 29. Large unstained cells increased in a time-dependent fashion, with day 29 counts showing an approximate 2.6-fold increase over the prestudy values.

Morphologic diagnosis

Spleen and lymph nodes: polytypic B-cell hyperplasia, multifocal, consistent with acute mononucleosis-like disease

Etiology

Presumptive acute LCV infection. Residual plasma samples submitted for serologic evidence of gammaherpesvirus infection demonstrated seroconversion and rising titers of LCV.

Discussion

In this case, multifocally, within the paracortices and medullary cords of the submitted lymph nodes and within periarterial lymphoid sheath of the spleen, there were expanded clusters of B cells that included immunoblasts, plasma cells, and occasional Reed-Sternberg–like cells; atypical B cells and mitotic figures were frequent, while normal T- and B-cell area architecture was preserved. A diagnosis of polytypic B-cell hyperplasia consistent with acute mononucleosis-like disease associated with acute infection with LCV was made. Naturally occurring LCV, closely related to Epstein-Barr virus, has been identified in New and Old World NHP species.^5,37 The genomic organization and pathobiology of these viruses are remarkably conserved; LCVs have the ability to immortalize host cells and express a similar complement of lytic and latent genes to those found in EBV infection. ³³ This case provides a rare opportunity to review the early histomorphologic changes associated with spontaneous LCV seroconversion during toxicology study conduct. In humans, posttransplant EBV seroconversion and immune suppression are well-known risk factors for the development of lymphoproliferative disease. It is likely that seroconversion during immunosuppression has similar implications in NHPs. Knowledge of the infection status of animals prior to and during study conduct and recognition of the often subtle histomorphologic changes associated with acute LCV infection may be critical in the interpretation of certain study outcomes. Currently, it is not standard practice to perform serologic tests for gammaherpesviruses prior to toxicology study placement.

Case 13. Sarah M. Corner (University of Illinois, Zoological Pathology Program)

History

A 44-year-old captive female chimpanzee (P. troglodytes) that was group-housed at a zoological institution had a slow-growing, clinically silent gingival mass associated with the right maxillary canine that was noted at least 1 year prior to necropsy. The mass was 3.2 × 2.0 × 0.7 cm, smooth, firm, pale pink, unencapsulated, and moderately well demarcated, without apparent involvement of the associated canine tooth.

Morphologic diagnosis

Gingival mass (right maxillary canine): periapical cemental dysplasia

Etiology

Unknown

Discussion

Periapical cemental dysplasia is a type of cemento-osseous dysplasia that is grouped under the category of fibrous dysplasias of the jaw or benign fibro-osseous lesions in the human literature. ⁹ This lesion is similar to cemento-ossifying fibromas but nonencapsulated with less well-defined margins. ⁴⁰ In humans, this lesion can affect periapical regions of one to several adjacent or distant teeth. ⁹ The lesion is often self-limiting and not associated with pathology of the involved teeth, and treatment is usually conservative. Although, to our knowledge, there are no reports in NHPs or other mammals of periapical/focal cemental dysplasia, cementifying fibromas have many similar characteristics. Interestingly, an adult male conspecific from the same institution had a similar gingival mass near the left maxillary canine that was biopsied and found to have identical histologic features.

Case 14. Ingrid D Pardo and Mark G Evans (Pfizer, Inc)

History

Healthy young male cynomolgus macaque (M. fascicularis) with no necropsy findings

Morphologic diagnosis

Heart: myocarditis and neuritis (ganglionitis), lymphoplasmacytic and histiocytic with intralesional Trypanosoma cruzi pseudocysts, multifocal to coalescing, marked

Etiology

T. cruzi

Discussion

T. cruzi, the etiologic agent of Chagas disease, is found in the southern United States and Central and South America, and it affects several domestic animals, NHPs, and people. It is transmitted to vertebrate hosts by insect bites of the Triatominae family (assassin bugs or kissing bugs). Trypomastigotes from insect feces enter the blood when the host scratches the bitten area. Cardiomyocytes become infected from the circulation; amastigotes then form pseudocysts in cardiomyocytes. ²⁸ The acute and chronic phases of this disease are dominated by cardiac and gastrointestinal manifestations. The exact mechanism of how the parasite causes tissue damage in the chronic phase is unknown. However, microvascular disturbances, direct parasite damage to the myocardium, immune-mediated myocardial injury, and destruction of the cardiac autonomic nervous system (neurologic theory) have been proposed.^6,10 In this case, there was remarkable inflammation of a ganglion near the heart. Inflammation was present in the interstitium of the heart and vasculature. Lack of inflammation in areas immediately adjacent to pseudocysts is common in Chagas disease.

Conclusion

The workshop on Emerging Respiratory Viral Infections and Spontaneous Diseases in NHPs incorporated lectures on naturally occurring influenza, hMPV, and RSV in wild and zoo-housed great apes; the molecular biology and pathology of these viral respiratory diseases in NHP animal models; and the therapeutic and vaccine approaches to prevent and control these emerging respiratory viral infections. These formal presentations were followed by presentations of 14 case studies in NHPs. Nine of the 14 cases involved bacterial (B. cereus biovar anthracis, S. aureus), viral (MHV-1), fungal (Coccidioides sp, Pneumocystis sp), or parasitic (Cryptosporidium sp) diseases or degenerative/proliferative/neoplastic (radiation induced, pleuropulmonary endometriosis, LCV-related lymphoma) processes in the lung. The remaining 5 cases included included uncommon pathogens (eg, T. cruzi, F. tularensis, B. microti–like parasite) or degenerative/proliferative processes (leukoencephalomalacia, LCV-associated polytypic B-cell hyperplasia, periapical cemental dysplasia) in NHPs. All cases were digitally scanned, and the whole-slide images corresponding to each case report are included as supplemental files at http://scanscope.com/ACVP%20Slide%20Seminars/2012/Primate%20Pathology/view.apml to serve as a unique resource for training and continuing education in primate pathology.