Smallpox lesion characterization in placebo-treated and tecovirimat-treated macaques using traditional and novel methods.

Smallpox was the most rampant infectious disease killer of the 20th century, yet much remains unknown about the pathogenesis of the variola virus. Using archived tissue from a study conducted at the Centers for Disease Control and Prevention we characterized pathology in 18 cynomolgus macaques intravenously infected with the Harper strain of variola virus. Six macaques were placebo-treated controls, six were tecovirimat-treated beginning at 2 days post-infection, and six were tecovirimat-treated beginning at 4 days post-infection. All macaques were treated daily until day 17. Archived tissues were interrogated using immunohistochemistry, in situ hybridization, immunofluorescence, and electron microscopy. Gross lesions in three placebo-treated animals that succumbed to infection primarily consisted of cutaneous vesicles, pustules, or crusts with lymphadenopathy. The only gross lesions noted at the conclusion of the study in the three surviving placebo-treated and the Day 4 treated animals consisted of resolving cutaneous pox lesions. No gross lesions attributable to poxviral infection were present in the Day 2 treated macaques. Histologic lesions in three placebo-treated macaques that succumbed to infection consisted of proliferative and necrotizing dermatitis with intracytoplasmic inclusion bodies and lymphoid depletion. The only notable histologic lesion in the Day 4 treated macaques was resolving dermatitis; no notable lesions were seen in the Day 2 treated macaques. Variola virus was detected in all three placebo-treated animals that succumbed to infection prior to the study's conclusion by all utilized methods (IHC, ISH, IFA, EM). None of the three placebo-treated animals that survived to the end of the study nor the animals in the two tecovirimat treatment groups showed evidence of variola virus by these methods. Our findings further characterize variola lesions in the macaque model and describe new molecular methods for variola detection.

Temporal changes in pathology and viral RNA distribution in guinea pigs following separate infection with two New World Arenaviruses.

Numerous arenaviruses have been identified throughout the Americas and a subset of these viruses cause viral hemorrhagic fever in humans. This study compared the pathology and viral RNA distribution in Hartley guinea pigs challenged with two human-disease causing New World arenaviruses, Junin virus (JUNV) or Guanarito virus (GTOV). Histopathologic analysis and RNA in situ hybridization revealed similar pathology and viral RNA distribution for both groups of animals challenged with either JUNV or GTOV on days 3, 7, 10 and 12 post exposure (PE). Gross lesions were first observed on day 7 and primarily involved the lungs and liver. The most severe histologic lesions occurred in the lymph nodes, spleen, and thymus and included lymphoid depletion and necrosis which increased in severity over time. Extensive necrosis was also observed in the bone marrow on day 12. Minimal to mild inflammation with and without necrosis was observed in the choroid plexus of the brain, choroid of the eye, intestinal tract, lung and adrenal gland. Significant liver lesions were rare, consisting predominantly of hepatocyte vacuolation. Viral RNA labeling was identified in nearly all organs examined, was often extensive in certain organs and generally increased over time starting on day 7. Our data demonstrate the guinea pig may serve as a useful model to study New World arenavirus infection in humans and for the evaluation and development of medical countermeasures.

Retrospective detection of monkeypox virus in the testes of nonhuman primate survivors.

Close contact through sexual activity has been associated with the spread of monkeypox virus (MPXV) in the ongoing, global 2022 epidemic. However, it remains unclear whether MPXV replicates in the testes or is transmitted via semen to produce an active infection. We carried out a retrospective analysis of MPXV-infected crab-eating macaque archival tissue samples from acute and convalescent phases of infection of clade I or clade II MPXV using immunostaining and RNA in situ hybridization. We detected MPXV in interstitial cells and seminiferous tubules of testes as well as epididymal lumina, which are the sites of sperm production and maturation. We also detected inflammation and necrosis during the acute phase of the disease by histological analysis. Finally, we found that MPXV was cleared from most organs during convalescence, including healed skin lesions, but could be detected for up to 37 d post-exposure in the testes of convalescent macaques. Our findings highlight the potential for sexual transmission of MPXV in humans.

Eastern equine encephalitis virus rapidly infects and disseminates in the brain and spinal cord of cynomolgus macaques following aerosol challenge.

Eastern equine encephalitis virus (EEEV) is mosquito-borne virus that produces fatal encephalitis in humans. We recently conducted a first of its kind study to investigate EEEV clinical disease course following aerosol challenge in a cynomolgus macaque model utilizing the state-of-the-art telemetry to measure critical physiological parameters. Here, we report the results of a comprehensive pathology study of NHP tissues collected at euthanasia to gain insights into EEEV pathogenesis. Viral RNA and proteins as well as microscopic lesions were absent in the visceral organs. In contrast, viral RNA and proteins were readily detected throughout the brain including autonomic nervous system (ANS) control centers and spinal cord. However, despite presence of viral RNA and proteins, majority of the brain and spinal cord tissues exhibited minimal or no microscopic lesions. The virus tropism was restricted primarily to neurons, and virus particles (~61-68 nm) were present within axons of neurons and throughout the extracellular spaces. However, active virus replication was absent or minimal in majority of the brain and was limited to regions proximal to the olfactory tract. These data suggest that EEEV initially replicates in/near the olfactory bulb following aerosol challenge and is rapidly transported to distal regions of the brain by exploiting the neuronal axonal transport system to facilitate neuron-to-neuron spread. Once within the brain, the virus gains access to the ANS control centers likely leading to disruption and/or dysregulation of critical physiological parameters to produce severe disease. Moreover, the absence of microscopic lesions strongly suggests that the underlying mechanism of EEEV pathogenesis is due to neuronal dysfunction rather than neuronal death. This study is the first comprehensive investigation into EEEV pathology in a NHP model and will provide significant insights into the evaluation of countermeasure.

Ebola virus persistence and disease recrudescence in the brains of antibody-treated nonhuman primate survivors.

Effective therapeutics have been developed against acute Ebola virus disease (EVD) in both humans and experimentally infected nonhuman primates. However, the risk of viral persistence and associated disease recrudescence in survivors receiving these therapeutics remains unclear. In contrast to rhesus macaques that survived Ebola virus (EBOV) exposure in the absence of treatment, we discovered that EBOV, despite being cleared from all other organs, persisted in the brain ventricular system of rhesus macaque survivors that had received monoclonal antibody (mAb) treatment. In mAb-treated macaque survivors, EBOV persisted in macrophages infiltrating the brain ventricular system, including the choroid plexuses. This macrophage infiltration was accompanied by severe tissue damage, including ventriculitis, choroid plexitis, and meningoencephalitis. Specifically, choroid plexus endothelium-derived EBOV infection led to viral persistence in the macaque brain ventricular system. This resulted in apoptosis of ependymal cells, which constitute the blood-cerebrospinal fluid barrier of the choroid plexuses. Fatal brain-confined recrudescence of EBOV infection manifested as severe inflammation, local pathology, and widespread infection of the ventricular system and adjacent neuropil in some of the mAb-treated macaque survivors. This study highlights organ-specific EBOV persistence and fatal recrudescent disease in rhesus macaque survivors after therapeutic treatment and has implications for the long-term follow-up of human survivors of EVD.

Detailed analysis of the pathologic hallmarks of Nipah virus (Malaysia) disease in the African green monkey infected by the intratracheal route.

Disease associated with Nipah virus infection causes a devastating and often fatal spectrum of syndromes predominated by both respiratory and neurologic conditions. Additionally, neurologic sequelae may manifest months to years later after virus exposure or apparent recovery. In the two decades since this disease emerged, much work has been completed in an attempt to understand the pathogenesis and facilitate development of medical countermeasures. Here we provide detailed organ system-specific pathologic findings following exposure of four African green monkeys to 2.41×105 pfu of the Malaysian strain of Nipah virus. Our results further substantiate the African green monkey as a model of human Nipah virus disease, by demonstrating both the respiratory and neurologic components of disease. Additionally, we demonstrate that a chronic phase of disease exists in this model, that may provide an important opportunity to study the enigmatic late onset and relapse encephalitis as it is described in human disease.

Natural History of Aerosol-Induced Ebola Virus Disease in Rhesus Macaques.

Ebola virus disease (EVD) is a serious global health concern because case fatality rates are approximately 50% due to recent widespread outbreaks in Africa. Well-defined nonhuman primate (NHP) models for different routes of Ebola virus exposure are needed to test the efficacy of candidate countermeasures. In this natural history study, four rhesus macaques were challenged via aerosol with a target titer of 1000 plaque-forming units per milliliter of Ebola virus. The course of disease was split into the following stages for descriptive purposes: subclinical, clinical, and decompensated. During the subclinical stage, high levels of venous partial pressure of carbon dioxide led to respiratory acidemia in three of four of the NHPs, and all developed lymphopenia. During the clinical stage, all animals had fever, viremia, and respiratory alkalosis. The decompensatory stage involved coagulopathy, cytokine storm, and liver and renal injury. These events were followed by hypotension, elevated lactate, metabolic acidemia, shock and mortality similar to historic intramuscular challenge studies. Viral loads in the lungs of aerosol-exposed animals were not distinctly different compared to previous intramuscularly challenged studies. Differences in the aerosol model, compared to intramuscular model, include an extended subclinical stage, shortened clinical stage, and general decompensated stage. Therefore, the shortened timeframe for clinical detection of the aerosol-induced disease can impair timely therapeutic administration. In summary, this nonhuman primate model of aerosol-induced EVD characterizes early disease markers and additional details to enable countermeasure development.

The Natural History of Aerosolized Francisella tularensis Infection in Cynomolgus Macaques.

Tularemia is a severe, zoonotic infection caused by the Gram-negative bacterium Francisella tularensis. Inhalation results in a rapid, severe bacterial pneumonia and sepsis, which can be lethal. Because the cynomolgus macaque is the accepted nonhuman primate model for tularemia, we conducted a natural history study of pneumonic tularemia by exposing macaques to target inhaled doses of 50, 500, or 5000 colony forming units (CFU) of F. tularensis subsp. tularensis SCHU S4. Two animals within the 50 CFU group (calculated doses of 10 and 11 CFU) survived the challenge, while the remainder succumbed to infection. Exposure of cynomolgus macaques to aerosolized SCHU S4 resulted in fever, anorexia, increased white blood cell counts, lymphopenia, thrombocytopenia, increased liver enzymes, alterations in electrocardiogram (ECG), and pathological changes typical of infection with F. tularensis, regardless of the challenge dose. Blood pressure dropped during the febrile phase, particularly as temperature began to drop and macaques succumbed to the disease. ECG analysis indicated that in 33% of the macaques, heart rate was not elevated during the febrile phase (Faget's sign; pulse-temperature disassociation), which has been reported in a similar percentage of human cases. These results indicated that infection of cynomolgus macaques with aerosolized F. tularensis results in similar disease progression and outcome as seen in humans, and that cynomolgus macaques are a reliable animal model to test medical countermeasures against aerosolized F. tularensis.

Immune-Mediated Systemic Vasculitis as the Proposed Cause of Sudden-Onset Sensorineural Hearing Loss following Lassa Virus Exposure in Cynomolgus Macaques.

Lassa virus (LASV) causes a severe, often fatal hemorrhagic disease in regions in Africa where the disease is endemic, and approximately 30% of patients develop sudden-onset sensorineural hearing loss after recovering from acute disease. The causal mechanism of hearing loss in LASV-infected patients remains elusive. Here, we report findings after closely examining the chronic disease experienced by surviving macaques assigned to LASV exposure control groups in two different studies. All nonhuman primates (NHPs) developed typical signs and symptoms of Lassa fever, and seven succumbed during the acute phase of disease. Three NHPs survived beyond the acute phase and became chronically ill but survived to the study endpoint, 45 days postexposure. All three of these survivors displayed continuous disease symptoms, and apparent hearing loss was observed using daily subjective measurements, including response to auditory stimulation and tuning fork tests. Objective measurements of profound unilateral or bilateral sensorineural hearing loss were confirmed for two of the survivors by brainstem auditory evoked response (BAER) analysis. Histologic examination of inner ear structures and other tissues revealed the presence of severe vascular lesions consistent with systemic vasculitides. These systemic immune-mediated vascular disorders have been associated with sudden hearing loss. Other vascular-specific damage was also observed to be present in many of the sampled tissues, and we were able to identify persistent virus in the perivascular tissues in the brain tissue of survivors. Serological analyses of two of the three survivors revealed the presence of autoimmune disease markers. Our findings point toward an immune-mediated etiology for Lassa fever-associated sudden-onset hearing loss and lay the foundation for developing potential therapies to prevent and/or cure Lassa fever-associated sudden-onset hearing loss.IMPORTANCE Lassa virus is one of the most common causes of viral hemorrhagic fever. A frequent, but as yet unexplained, consequence of infection with Lassa virus is acute, sudden-onset sensorineural hearing loss in one or both ears. Deafness is observed in approximately 30% of surviving Lassa fever patients, an attack rate that is approximately 300% higher than mumps virus infection, which was previously thought to be the most common cause of virus-induced deafness. Here, we provide evidence from Lassa virus-infected cynomolgus macaques implicating an immune-mediated vasculitis syndrome underlying the pathology of Lassa fever-associated deafness. These findings could change the way human Lassa fever patients are medically managed in order to prevent deafness by including diagnostic monitoring of human survivors for onset of vasculitides via available imaging methods and/or other diagnostic markers of immune-mediated vascular disease.

A DNA vaccine delivered by dermal electroporation fully protects cynomolgus macaques against Lassa fever.

Lassa virus (LASV) is an ambisense RNA virus in the Arenaviridae family and is the etiological agent of Lassa fever, a severe hemorrhagic disease endemic to West and Central Africa. 1,2 There are no US Food and Drug Administration (FDA)-licensed vaccines available to prevent Lassa fever. 1,2 in our previous studies, we developed a gene-optimized DNA vaccine that encodes the glycoprotein precursor gene of LASV (Josiah strain) and demonstrated that 3 vaccinations accompanied by dermal electroporation protected guinea pigs from LASV-associated illness and death. Here, we describe an initial efficacy experiment in cynomolgus macaque nonhuman primates (NHPs) in which we followed an identical 3-dose vaccine schedule that was successful in guinea pigs, and a follow-on experiment in which we used an accelerated vaccination strategy consisting of 2 administrations, spaced 4 weeks apart. In both studies, all of the LASV DNA-vaccinated NHPs survived challenge and none of them had measureable, sustained viremia or displayed weight loss or other disease signs post-exposure. Three of 10 mock-vaccinates survived exposure to LASV, but all of them became acutely ill post-exposure and remained chronically ill to the study end point (45 d post-exposure). Two of the 3 survivors experienced sensorineural hearing loss (described elsewhere). These results clearly demonstrate that the LASV DNA vaccine combined with dermal electroporation is a highly effective candidate for eventual use in humans.

Infusion of solutions of pre-irradiated components in rats.

INTRODUCTION: The objective of this study was to conduct a 14-day toxicology assessment for intravenous solutions prepared from irradiated resuscitation fluid components and sterile water. METHODS: Healthy Sprague Dawley rats (7-10/group) were instrumented and randomized to receive one of the following Field IntraVenous Resuscitation (FIVR) or commercial fluids; Normal Saline (NS), Lactated Ringer's, 5% Dextrose in NS. Daily clinical observation, chemistry and hematology on days 1,7,14, and urinalysis on day 14 were evaluated for equivalence using a two sample t-test (p<0.05). A board-certified pathologist evaluated organ histopathology on day 14. RESULTS: Equivalence was established for all observation parameters, lactate, sodium, liver enzymes, creatinine, WBC and differential, and urinalysis values. Lack of equivalence for hemoglobin (p=0.055), pH (p=0.0955), glucose (p=0.0889), Alanine-Aminotransferase (p=0.1938), albumin (p=0.1311), and weight (p=0.0555, p=0.1896), was deemed not clinically relevant due to means within physiologically normal ranges. Common microscopic findings randomly distributed among animals of all groups were endocarditis/myocarditis and pulmonary lesions. DISCUSSION: These findings are consistent with complications due to long-term catheter use and suggest no clinically relevant differences in end-organ toxicity between animals infused with FIVR versus commercial fluids.

Cercopithecine Herpesvirus 9 (Simian Varicella Virus) Infection after Total-Body Irradiation in a Rhesus Macaque (Macaca mulatta).

This case report describes a rhesus macaque (Macaca mulatta; male; age, 5 y; weight, 6.7 kg) with anorexia, dehydration, lethargy, ataxia, and generalized skin rashes that occurred 30 d after total-body irradiation at 6.5 Gy ((60)Co γ-rays). Physical examination revealed pale mucus membranes, a capillary refill time of 4 s, heart rate of 180 bpm. and respirations at 50 breaths per minute. Diffuse multifocal maculopapulovesicular rashes were present on the body, including mucocutaneous junctions. The CBC analysis revealed a Hct of 48%, RBC count of 6.2 × 10(6)/µL, platelet count of 44 × 10(3)/µL, and WBC count of 25 × 10(3)/µL of WBC. The macaque was euthanized in light of a grave prognosis. Gross examination revealed white foci on the liver, multifocal generalized petechiation on serosal and mucosal surfaces of the gastrointestinal tract, hemorrhagic lymph nodes, and hemorrhagic fluid in the thoracic cavity. Microscopic examination revealed cutaneous vesicular lesions with intranuclear eosinophilic viral inclusions within the epithelial cells, consistent with herpesvirus. Immunohistochemistry was positive for herpesvirus. The serum sample was negative for antibodies against Macacine herpesvirus 1 and Cercopithecine herpesvirus 9 (simian varicella virus, SVV). Samples submitted for PCR-based identification of the etiologic agent confirmed the presence of SVV DNA. PCR analysis, immunohistochemistry, and histology confirmed that lesions were attributed to an active SVV infection in this macaque. This case illustrates the importance of screening for SVV in rhesus macaques, especially those used in studies that involve immunosuppressive procedures.

Pathological findings and diagnostic implications of a rhesus macaque (Macacca mulatta) model of aerosol exposure to Burkholderia mallei (glanders).

Burkholderia mallei is a Gram-negative bacillus that causes a pneumonic disease known as glanders in equids and humans, and a lymphatic infection known as farcy, primarily in equids. With the potential to infect humans by the respiratory route, aerosol exposure can result in severe, occasionally fatal, pneumonia. Today, glanders infections in humans are rare, likely due to less frequent contact with infected equids than in the past. Acutely ill humans often have non-specific clinical signs and in order to diagnose cases, especially in scenarios of multiple cases in an unexpected setting, rapid diagnostics for B. mallei may be critical. The pathogenesis of acute glanders in the rhesus macaque (Macaca mulatta) was studied as an initial effort to improve diagnostic methods. In the study described here, the diagnostic techniques of PCR, culture and histopathology were compared. The results indicated that PCR may provide rapid, non-invasive diagnosis of glanders in some cases. As expected, PCR results were positive in lung tissue in 11/12 acutely infected rhesus macaques, but more importantly in terms of diagnostic algorithm development, PCR results were frequently positive in non-invasive samples such as broncho-alveolar lavage or nasal swabs (7/12) and occasionally in blood (3/12). However, conventional bacterial culture failed to recover bacteria in many of these samples. The study showed that the clinical presentation of aerosol-exposed rhesus macaques is similar to descriptions of human glanders and that PCR has potential for rapid diagnosis of outbreaks, if not individual cases.

Pathological findings and diagnostic implications of a rhesus macaque (Macaca mulatta) model of aerosol-exposure melioidosis (Burkholderia pseudomallei).

Aerosolized Burkholderia pseudomallei, the causative agent of melioidosis, can infect many species of mammals (including humans), causing rapid, severe pneumonia with high mortality. Diagnosis in humans is challenging, as few organisms can be detected in blood or other non-invasive samples. Although it cannot be said that the model is established, studies to date indicate that rhesus macaques may represent a good model of human melioidosis. This is supported by the results of this study. The early progression of meliodosis in the rhesus macaque was studied in an effort to better understand the disease and the application of rapid diagnostic methods. Results indicate that a PCR analysis of key diagnostic samples such as nasal swabs, throat swabs, tracheo bronchial lymph node aspirates and broncho-alveolar lavage may be a useful component of a rapid diagnostic algorithm in case of aerosol exposure.

Natural history of inhalation melioidosis in rhesus macaques (Macaca mulatta) and African green monkeys (Chlorocebus aethiops).

Burkholderia pseudomallei, the causative agent of melioidosis, is recognized as a serious health threat due to its involvement in septic and pulmonary infections in areas of endemicity and is recognized by the Centers for Disease Control and Prevention as a category B biothreat agent. An animal model is desirable to evaluate the pathogenesis of melioidosis and medical countermeasures. A model system that represents human melioidosis infections is essential in this process. A group of 10 rhesus macaques (RMs) and 10 African green monkeys (AGMs) was exposed to aerosolized B. pseudomallei 1026b. The first clinical signs were fever developing 24 to 40 h postexposure followed by leukocytosis resulting from a high percentage of neutrophils. Dyspnea manifested 2 to 4 days postexposure. In the AGMs, an increase in interleukin 1ß (IL-1ß), IL-6, IL-8, gamma interferon (IFN-γ), and tumor necrosis factor alpha (TNF-α) was observed. In the RMs, IL-1ß, IL-6, and TNF-α increased. All the RMs and AGMs had various degrees of bronchopneumonia, with inflammation consisting of numerous neutrophils and a moderate number of macrophages. Both the RMs and the AGMs appear to develop a melioidosis infection that closely resembles that seen in acute human melioidosis. However, for an evaluation of medical countermeasures, AGMs appear to be a more appropriate model.

Peripheral primitive neuroectodermal tumor in a two-year-old paint horse.

A 2-year-old gelding presented with a history of lethargy and anorexia. Physical examination revealed pleural and abdominal fluid, as well as several masses in the scrotum. The horse became acutely dyspneic despite 7 days of supportive care. Because of the poor prognosis, the owners elected euthanasia. Gross necropsy findings included multiple masses in the scrotum and inguinal canals and along the dorsal peritoneal cavity. The neoplasm infiltrated the kidneys, liver, spleen, mesenteric lymph nodes, mesentery, and abdominal surface of the diaphragm. Histologically, the neoplasm is composed of spindle to round cells arranged in densely cellular areas, vague streams, and rare rosettes. Neoplastic cells were immunoreactive for S-100 protein, glial fibrillary acidic protein, neuron-specific enolase, neurofilament protein, and synaptophysin. Based on gross, histological, and immunohistochemical findings, a diagnosis of peripheral primitive neuroectodermal tumor was made. Primitive neuroectodermal tumors are rarely described in horses that were associated with the eyes.

Congenital neuroglial heterotopia in a neonatal harbor seal (Phoca vitulina richardsi ) with evidence of recent exposure to polycyclic aromatic hydrocarbons.

A male neonatal Pacific harbor seal (Phoca vitulina richardsi) stranded off the coast of California, USA, was presented for rehabilitation with numerous partially haired, soft tissue masses around the mouth and in the oropharynx. Because of the extent of the lesions, the seal was humanely euthanized. Histologically, the masses consisted of subepithelial connective tissue and subcutis expanded by a proliferation of streams and bundles of spindle to stellate cells. Morphology of these cells suggested a neural origin, which was confirmed by positive immunohistochemistry for two neural markers, S-100 protein and glial fibrillary acidic protein, so the masses were diagnosed as neuroglial heterotopia. Heterotopic neuroglial tissue is a rare lesion comprised of benign mature neural tissue in an ectopic location with no connection to the central nervous system. Results of polycyclic aromatic hydrocarbon (PAH) metabolite analysis of bile indicated recent exposure to a petroleum source. Although fetal exposure to PAHs in utero can cause neurotoxicity and affect normal embryonic development, it is unknown whether gestational exposure occurred in this case.