Experimental infection of cynomolgus macaques (Macaca fascicularis) with aerosolized monkeypox virus

Mpox virus Clade IIb infected Cynomolgus macaques via mimic natural infection routes closely resembled human mpox infection

Generating an infectious non-human primate (NHP) model using a prevalent monkeypox virus (MPXV) strain has emerged as a crucial strategy for assessing the efficacy of vaccines and antiviral drugs against human MPXV infection. Here, we established an animal model by infecting cynomolgus macaques with the prevalent MPXV strain, WIBP-MPXV-001, and simulating its natural routes of infection. A comprehensive analysis and evaluation were conducted on three animals, including monitoring clinical symptoms, collecting hematology data, measuring viral loads, evaluating cellular and humoral immune responses, and examining histopathology. Our findings revealed that initial skin lesions appeared at the inoculation sites and subsequently spread to the limbs and back, and all infected animals exhibited bilateral inguinal lymphadenopathy, eventually leading to a self-limiting disease course. Viral DNA was detected in post-infection blood, nasal, throat, rectal and blister fluid swabs. These observations indicate that the NHP model accurately reflects critical clinical features observed in human MPXV infection. Notably, the animals displayed clinical symptoms and disease progression similar to those of humans, rather than a lethal outcome as observed in previous studies. Historically, MPXV was utilized as a surrogate model for smallpox. However, our study contributes to a better understanding of the dynamics of current MPXV infections while providing a potential infectious NHP model for further evaluation of vaccines and antiviral drugs against mpox infection. Furthermore, the challenge model closely mimics the primary natural routes of transmission for human MPXV infections. This approach enhances our understanding of the precise mechanisms underlying the interhuman transmission of MPXV.

Experimental inoculation of pigs with monkeypox virus results in productive infection and transmission to sentinels

Monkeypox virus (MPXV) is a re-emerging zoonotic poxvirus responsible for producing skin lesions in humans. Endemic in sub-Saharan Africa, the 2022 outbreak with a clade IIb strain has resulted in ongoing sustained transmission of the virus worldwide. MPXV has a relatively wide host range, with infections reported in rodent and non-human primate species. However, the susceptibility of many domestic livestock species remains unknown. Here, we report on a susceptibility/transmission study in domestic pigs that were experimentally inoculated with a 2022 MPXV clade IIb isolate or served as sentinel contact control animals. Several principal-infected and sentinel contact control pigs developed minor lesions near the lips and nose starting at 12 through 18 days post-challenge (DPC). No virus was isolated and no viral DNA was detected from the lesions; however, MPXV antigen was detected by IHC in tissue from a pustule of a principal infected pig. Viral DNA and infectious virus were detected in nasal and oral swabs up to 14 DPC, with peak titers observed at 7 DPC. Viral DNA was also detected in nasal tissues or skin collected from two principal-infected animals at 7 DPC post-mortem. Furthermore, all principal-infected and sentinel control animals enrolled in the study seroconverted. In conclusion, we provide the first evidence that domestic pigs are susceptible to experimental MPXV infection and can transmit the virus to contact animals.

Mpox infection of stromal cells and macrophages of macaque with endometriosis

The mpox outbreak of 2022-2023 represented a new global health challenge and recognition of mpox as a sexually transmitted disease. The majority of cases were reported in men who have sex with men (MSM), but women are also susceptible, especially during pregnancy. We evaluated the reproductive tracts of a subset of macaques from a large rechallenge study of mpox infection with virus from the 2022 outbreak and identified intraabdominal mpox replication associated with endometriosis. Mpox virus (MPXV) was found not only in skin, but in the cervix, the uterus, and periovarian endometriotic lesions of the affected macaque. Mpox replication preferentially targeted vimentin-positive poorly differentiated endometriotic stromal tissue and infiltrating macrophages in the reproductive tract. Mpox tropism for stromal cells and macrophages has broad implications for mpox pathogenesis and associated clinical syndromes. In addition, women with endometriosis may be at heightened risk for adverse outcomes associated with mpox infection. The rhesus macaque provides rare insight into this disease and the potential complications of mpox infection in the context of genitourinary tract disease.

Orthopox viruses: is the threat growing?

BACKGROUND

Smallpox was a major cause of human mortality until its eradication, but the threat of orthopox viruses has not disappeared. Since the eradication of smallpox and the cessation of the related vaccination campaigns, the threat has been growing, as evidenced by the currently ongoing worldwide Mpox outbreak. In addition to threats of an evolving Mpox, we must also be aware of a myriad of other threats that remain. Many countries still lack biosecurity regulations reflecting the recent technological advances, and the threat of bioterrorism remains ever present. Reconstruction of smallpox is a distinct possibility, as are other scenarios whereby other orthopox viruses may be made more fit for transmission in humans.

OBJECTIVES

To outline and discuss potential biosafety and biosecurity threats posed by orthopox viruses.

SOURCES

Published scientific literature, news articles, and international agreements.

CONTENT AND IMPLICATIONS

It would be wise to take steps to mitigate these threats now. Vaccination campaigns should be considered in areas with frequent orthopox outbreaks, and more efforts must be made to put a final end to the Mpox outbreak. In many countries, national biosafety and biosecurity regulations may need to be revised and strengthened to better reflect the threats posed by new technologies, including controls on synthesis of smallpox sequences. Furthermore, more international cooperation and aid is needed. The present global Mpox outbreak could likely have been prevented had areas where Mpox is endemic not been neglected. Future outbreaks could be much worse.

Insights into the emergence and evolution of monkeypox virus: Historical perspectives, epidemiology, genetic diversity, transmission, and preventative measures

In 2022, just before the COVID-19 pandemic ended, many countries noticed a viral monkeypox outbreak. Monkeypox virus, a zoonotic pathogen, causes a febrile illness in humans and resembles smallpox. Prevention strategies encompass vaccination, strict infection control measures, and avoiding contact with infected persons. As monkeypox and related poxviruses continue to pose challenges, ongoing surveillance, early diagnosis, prompt isolation, and effective control measures are crucial for limiting transmission and mitigating the impact of outbreaks on public health. This review provides valuable insights into the evolution of the monkeypox virus and its various modes of transmission, including postmortem transmission, and offers an overall perspective on the guidelines issued by the Government of India to prevent and effectively control the spread of this disease.

Utilizing non-human primate models to combat recent COVID-19/SARS-CoV-2 and viral infectious disease outbreaks

In recent times, global viral outbreaks and diseases, such as COVID-19 (SARS-CoV-2), Zika (ZIKV), monkeypox (MPOX), Ebola (EBOV), and Marburg (MARV), have been extensively documented. Swiftly deciphering the mechanisms underlying disease pathogenesis and devising vaccines or therapeutic interventions to curtail these outbreaks stand as paramount imperatives. Amidst these endeavors, animal models emerge as pivotal tools. Among these models, non-human primates (NHPs) hold a position of particular importance. Their proximity in evolutionary lineage and physiological resemblances to humans render them a primary model for comprehending human viral infections. This review encapsulates the pivotal role of various NHP species-such as rhesus macaques (Macaca mulatta), cynomolgus macaques (Macaca fascicularis), african green monkeys (Chlorocebus sabaeus/aethiops), pigtailed macaques (Macaca nemestrina/Macaca leonina), baboons (Papio hamadryas/Papio anubis), and common marmosets (Callithrix jacchus)-in investigations pertaining to the abovementioned viral outbreaks. These NHP models play a pivotal role in illuminating key aspects of disease dynamics, facilitating the development of effective countermeasures, and contributing significantly to our overall understanding of viral pathogenesis.

Zoonotic and Zooanthroponotic Potential of Monkeypox

The current multicounty outbreak of monkeypox virus (MPXV) posed an emerging and continued challenge to already strained public healthcare sector, around the globe. Since its first identification, monkeypox disease (mpox) remained enzootic in Central and West African countries where reports of human cases are sporadically described. Recent trends in mpox spread outside the Africa have highlighted increased incidence of spillover of the MPXV from animal to humans. While nature of established animal reservoirs remained undefined, several small mammals including rodents, carnivores, lagomorphs, insectivores, non-human primates, domestic/farm animals, and several species of wildlife are proposed to be carrier of the MPXV infection. There are established records of animal-to-human (zoonotic) spread of MPXV through close interaction of humans with animals by eating bushmeat, contracting bodily fluids or trading possibly infected animals. In contrast, there are reports and increasing possibilities of human-to-animal (zooanthroponotic) spread of the MPXV through petting and close interaction with pet owners and animal care workers. We describe here the rationales and molecular factors which predispose the spread of MPXV not only amongst humans but also from animals to humans. A range of continuing opportunities for the spread and evolution of MPXV are discussed to consider risks beyond the currently identified groups. With the possibility of MPXV establishing itself in animal reservoirs, continued and broad surveillance, investigation into unconventional transmissions, and exploration of spillover events are warranted.

Monkeypox Virus (MPXV) Infection: A Review

Monkeypox is a viral disease; its outbreak was recently declared a global emergency by the World Health Organization. For the first time, a monkeypox virus (MPXV)-infected patient was found in India. Various researchers back-to-back tried to find the solution to this health emergency just after COVID-19. In this review, we discuss the current outbreak status of India, its transmission, virulence factors, symptoms, treatment, and the preventive guidelines generated by the Indian Health Ministry. We found that monkeypox virus (MPXV) disease is different from smallpox, and the age group between 30-40 years old is more prone to MPXV disease. We also found that, besides homosexuals, gays, bisexuals, and non-vegetarians, it also affects normal straight men and women who have no history of travel. Close contact should be avoided from rats, monkeys and sick people who are affected by monkeypox. To date, there are no monkeypox drugs, but Tecovirimat is more effective than other drugs that are used for other viral diseases like smallpox. Therefore, we need to develop an effective antiviral agent against the virulence factor of MXPV.

Poxviridae Pneumonia

Poxviridae family includes several viruses that infecting humans usually causes skin lesions only, but in some cases their clinical course is complicated by viral pneumonia (with or without bacterial superinfections). Historically variola virus has been the poxviridae most frequently associated with the development of pneumonia with many large outbreaks worldwide before its eradication in 1980. It is still considered a biological threat for its potential in biological warfare and bioterrorism. Smallpox pneumonia can be severe with the onset of acute respiratory distress syndrome (ARDS) and death. Vaccinia virus, used for vaccination against smallpox exceptionally, in immunocompromised patients, can induce generalized (with also lung involvement) severe disease after vaccination. MPXV virus occasionally can cause pneumonia particularly in immunocompromised patients. The pathophysiology of poxviridae pneumonia is still an area of active research; however, in animal models these viruses can cause both direct damage to the lower airways epithelium and a hyperinflammatory syndrome, like a cytokine storm. Multiple mechanisms of immune evasion have also been described. The treatment of poxviridae pneumonia is mainly based on careful supportive care. Despite the absence of randomized clinical trials in patients with poxviridae pneumonia there are antiviral drugs, such as tecovirimat, cidofovir and brincidofovir, FDA-approved for use in smallpox and also available under an expanded access protocol for treatment of MPXV. There are 2 (replication-deficient modified vaccinia Ankara and replication-competent vaccinia virus) smallpox vaccines FDA-approved with the first one also approved for prevention of MPXV in adults that are at high risk of infection.

Mpox and healthcare workers — a minireview of our present knowledge

Introduction

Workers in the healthcare industry form the backbone of health systems everywhere. In the face of global health crises like the current monkeypox (mpox) outbreak, healthcare workers like doctors, dentists, pharmacists, nurses, midwives, paramedics, administrators, support staff, laboratory technicians, and community health workers all play crucial roles in providing care and containing the spread of the disease.

Aim

Therefore, in the wake of concerns about mpox recurrence, we seek to shed light on the occupational transmission of mpox infection and the possible risk to healthcare personnel.

Results

Contamination of the environment of the household of cases of mpox and environment of the patient care units with the viral DNA has been reported besides asymptomatic cases and detection of viral DNA in air samples; therefore, more research on non-lesion-based testing for human mpox infection for screening asymptomatic people, particularly among populations at high risk of infection, in the event of asymptomatic transmission and potential transmission via aerosols is necessary. Monitoring efforts can be aided by incorporating mpox testing into locations where people are more likely to contract illnesses and seek medical attention. We must take a precautionary infection control approach to control the spread of the virus while completing urgent research to understand better the human-to-human mpox transmission process.

Conclusions

In this minireview, we discuss the potential routes of mpox transmission to healthcare and preventative strategies and measures that should be taken and considered.

Graphical Abstract

Human monkeypox virus in the shadow of the COVID-19 pandemic

BACKGROUND

The end of smallpox in 1980 and the subsequent stopping of vaccination against smallpox was followed by the emergence of monkeypox (mpox), a viral disease of animal origin, meaning that it is transmitted from animal to human. The symptoms of mpox are similar to smallpox, except that they are less severe in terms of clinical features. In the case of public health, the mpox virus is one of the most important orthopoxviruses (such as variola, cowpox, and vaccinia) that come from the family Poxviridae. Mpox occurs mostly in central Africa and sometimes in tropical rainforests or some urban areas. Also, there are threats other than COVID-19, that must be addressed and prevented from spreading, as there has been an outbreak of mpox cases since May 7, 2022, throughout the USA, Europe, Australia, and part of Africa.

OBJECTIVES

In this review, we will discuss mpox between the past, the present and during the COVID-19 pandemic. Also, it offers an updated summary of the taxonomy, etiology, transmission, and epidemiology of mpox illness. In addition, the current review aims to highlight the importance of emerging pandemics in the same era such as mpox and COVID-19.

METHODS

A literature search was done for the study using online sources like PubMed and Google Scholar. Publications in English were included. Data for study variables were extracted. After the duplicate articles were eliminated, full-text screening was performed on the papers' titles and abstracts.

RESULTS

The evaluation included a series documenting mpox virus outbreaks, and both prospective and retrospectiveinvestigations.

CONCLUSIONS

monkeypox is a viral disease caused by the monkeypox virus (MPXV), which is primarily found in central and western Africa. The disease is transmitted from animals to humans and presents symptoms similar to those of smallpox, including fever, headache, muscle aches, and a rash. Monkeypox can lead to complications such as secondary integument infection, bronchopneumonia, sepsis, and encephalitis, as well as corneal infection that can result in blindness. There is no specific clinically proven treatment for monkeypox, and treatment is primarily supportive. However, antiviral drugs and vaccines are available for cross-protection against the virus, and strict infection control measures and vaccination of close contacts of affected individuals can help prevent and control outbreaks.

Mpox virus Clade IIb detection in the air

Mpox is a viral zoonotic disease endemic in Central and West Africa that is caused by the Mpox virus, which belongs to the Orthopoxvirus genus and Poxviridae family. The clinical manifestations of mpox infection are milder than those of smallpox, and the incubation time of mpox varies from 5 to 21 days. Since May 2022, the mpox outbreak (formerly known as monkeypox) has suddenly and unexpectedly spread in non-endemic countries, suggesting that there may have been some undetected transmissions. Based on molecular analysis, there are two major genetic clades that represent the mpox virus: Clade I (formerly the Congo Basin clade OR the Central African clade) and Clade II (formerly the West African clade). It is believed that people who are asymptomatic or paucisymptomatic may spread the mpox virus. Infectious viruses cannot be distinguished by PCR testing; therefore, virus culture should be carried out. Recent evidence regarding the detection of the mpox virus (Clade IIb) in air samples collected from the patient's environment during the 2022 mpox outbreak was reviewed. Further studies are needed to evaluate the extent to which the presence of mpox virus DNA in the air could affect immunocompromised patients in healthcare facilities, and further epidemiological studies are crucial, especially in Africa.

Mpox respiratory transmission: the state of the evidence

The relative contribution of the respiratory route to transmission of mpox (formerly known as monkeypox) is unclear. We review the evidence for respiratory transmission of monkeypox virus (MPXV), examining key works from animal models, human outbreaks and case reports, and environmental studies. Laboratory experiments have initiated MPXV infection in animals via respiratory routes. Some animal-to-animal respiratory transmission has been shown in controlled studies, and environmental sampling studies have detected airborne MPXV. Reports from real-life outbreaks demonstrate that transmission is associated with close contact, and although it is difficult to infer the route of MPXV acquisition in individual case reports, so far respiratory transmission has not been specifically implicated. Based on the available evidence, the likelihood of human-to-human MPXV respiratory transmission appears to be low; however, studies should continue to assess this possibility.

Transmission of monkeypox/mpox virus: A narrative review of environmental, viral, host, and population factors in relation to the 2022 international outbreak

Monkeypox virus (MPXV) has spread globally. Emerging studies have now provided evidence regarding MPXV transmission, that can inform rational evidence-based policies and reduce misinformation on this topic. We aimed to review the evidence on transmission of the virus. Real-world studies have isolated viable viruses from high-touch surfaces for as long as 15 days. Strong evidence suggests that the current circulating monkeypox (mpox) has evolved from previous outbreaks outside of Africa, but it is yet unknown whether these mutations may lead to an inherently increased infectivity of the virus. Strong evidence also suggests that the main route of current MPXV transmission is sexual; through either close contact or directly, with detection of culturable virus in saliva, nasopharynx, and sperm for prolonged periods and the presence of rashes mainly in genital areas. The milder clinical presentations and the potential presence of presymptomatic transmission in the current circulating variant compared to previous clades, as well as the dominance of spread amongst men who have sex with men (MSMs) suggests that mpox has a developed distinct clinical phenotype that has increased its transmissibility. Increased public awareness of MPXV transmission modalities may lead to earlier detection of the spillover of new cases into other groups.

In vitro and in vivo models for monkeypox

The emergence and rapid spread outside of monkeypox virus (MPXV) to non-endemic areas has led to another global health emergency in the midst of the COVID-19 pandemic. The scientific community has sought to rapidly develop in vitro and in vivo models that could be applied in research with MPXV. In vitro models include two-dimensional (2D) cultures of immortalized cell lines or primary cells and three-dimensional (3D) cultures. In vitro models are considered cost-effective and can be done in highly controlled conditions; however, they do not always resemble physiological conditions. In this way, several in vivo models are being characterized to meet the growing demand for new studies related to MPXV. In this review, we summarize the main MPXV models that have already been developed and discuss how they can contribute to advance the understanding of its pathogenesis, replication, and transmission, as well as identifying antivirals to treat infected patients.

Monkeypox Virus Infections in Humans

Human monkeypox is a viral zoonosis endemic to West and Central Africa that has recently generated increased interest and concern on a global scale as an emerging infectious disease threat in the midst of the slowly relenting COVID-2019 disease pandemic. The hallmark of infection is the development of a flu-like prodrome followed by the appearance of a smallpox-like exanthem. Precipitous person-to-person transmission of the virus among residents of 100 countries where it is nonendemic has motivated the immediate and widespread implementation of public health countermeasures. In this review, we discuss the origins and virology of monkeypox virus, its link with smallpox eradication, its record of causing outbreaks of human disease in regions where it is endemic in wildlife, its association with outbreaks in areas where it is nonendemic, the clinical manifestations of disease, laboratory diagnostic methods, case management, public health interventions, and future directions.

Human Monkeypox: Oral Implications and Recommendations for Oral Screening and Infection Control in Dental Practice

The World Health Organization declared the spread of the human monkeypox virus (MPXV) an "emerging threat of moderate health concern" on 23 June 2022. Although about 20,000 cases of Monkeypox (MPX) were recorded in Europe and more than 28,000 in the United States from May to October 2022, their number is still small compared to the number of dental patients treated annually. Therefore, the likelihood of oral healthcare workers encountering an MPX case is relatively low in not endemic regions. In addition, MPX-positive individuals are considered contagious only during the prodromal or acute phase. However, the exact shedding and transmission routes of MPX and the associated risk of transmission in the dental setting remain unclear. Moreover, infected subjects whose disease is confined to the head and neck may require oral and dental care because they complain of lymphadenopathy involving the cervical lymph nodes. Furthermore, MPX lesions may first appear in the oral cavity or perioral area. Therefore, given the recent spread of MPXV in non-endemic areas where dentists are not used to considering this disease in the differential diagnosis and taking appropriate preventive measures, all oral healthcare providers nowadays should be aware of the oral presentation of MPX for adequate oral screening and appropriate preventive measures for infection control in the dental practice.

Air and surface sampling for monkeypox virus in a UK hospital: an observational study

BACKGROUND

An outbreak of monkeypox virus infections in non-endemic countries was recognised on May 12, 2022. As of September 29, more than 67 000 infections have been reported globally, with more than 3400 confirmed cases in the UK by September 26. Monkeypox virus is believed to be predominantly transmitted through direct contact with lesions or infected body fluids, with possible involvement of fomites and large respiratory droplets. A case of monkeypox in a health-care worker in the UK in 2018 was suspected to be due to virus exposure while changing bedding. We aimed to measure the extent of environmental contamination in the isolation rooms of patients with symptomatic monkeypox.

METHODS

We investigated environmental contamination with monkeypox virus from infected patients admitted to isolation rooms at the Royal Free Hospital (London, UK) between May 24 and June 17, 2022. Surface swabs of high-touch areas in five isolation rooms, of the personal protective equipment (PPE) of health-care workers in doffing areas in three rooms, and from air samples collected before and during bedding changes in five rooms were analysed using quantitative PCR to assess monkeypox virus contamination levels. Virus isolation was performed to confirm presence of infectious virus in selected positive samples.

FINDINGS

We identified widespread surface contamination (56 [93%] of 60 samples were positive) in occupied patient rooms (monkeypox DNA cycle threshold [Ct] values 24·7-37·4), on health-care worker PPE after use (Ct 26·1-35·6), and in PPE doffing areas (Ct 26·3-36·8). Of 20 air samples taken, five (25%) were positive. Three (75%) of four air samples collected before and during a bedding change in one patient's room were positive (Ct 32·7-36·2). Replication-competent virus was identified in two (50%) of four samples selected for viral isolation, including from air samples collected during bedding change.

INTERPRETATION

These data show contamination in isolation facilities and potential for suspension of monkeypox virus into the air during specific activities. PPE contamination was observed after clinical contact and changing of bedding. Contamination of hard surfaces in doffing areas supports the importance of cleaning protocols, PPE use, and doffing procedures.

FUNDING

None.

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.

Atypical and Unique Transmission of Monkeypox Virus during the 2022 Outbreak: An Overview of the Current State of Knowledge

An ongoing monkeypox outbreak in non-endemic countries has resulted in the declaration of a public health emergency of international concern by the World Health Organization (WHO). Though monkeypox has long been endemic in regions of sub-Saharan Africa, relatively little is known about its ecology, epidemiology, and transmission. Here, we consider the relevant research on both monkeypox and smallpox, a close relative, to make inferences about the current outbreak. Undetected circulation combined with atypical transmission and case presentation, including mild and asymptomatic disease, have facilitated the spread of monkeypox in non-endemic regions. A broader availability of diagnostics, enhanced surveillance, and targeted education, combined with a better understanding of the routes of transmission, are critical to identify at-risk populations and design science-based countermeasures to control the current outbreak.

Evaluation of Virulence in Cynomolgus Macaques Using a Virus Preparation Enriched for the Extracellular Form of Monkeypox Virus

The 2022 global human monkeypox outbreak emphasizes the importance of maintaining poxvirus research, including enriching a basic understanding of animal models for developing and advancing therapeutics and vaccines. Intravenous administration of monkeypox virus in macaques is arguably one of the best animal models for evaluating the efficacy of medical countermeasures. Here we addressed one criticism of the model, a requirement for a high-titer administration of virus, as well as improving our understanding of monkeypox virus pathogenesis. To do so, we infected macaques with a challenge dose containing a characterized inoculum enriched for the extracellular form of monkeypox virus. Although there were some differences between diseases caused by the enriched preparation compared with a relatively similar unpurified preparation, we were unable to reduce the viral input with the enriched preparation and maintain severe disease. We found that inherent factors contained within the serum of nonhuman primate blood affect the stability of the monkeypox extracellular virions. As a first step to study a role of the extracellular form in transmission, we also showed the presence of this form in the oropharyngeal swabs from nonhuman primates exposed to monkeypox virus.

Human monkeypox disease (MPX)

Monkeypox is a rare viral infection, endemic in many central and western African countries. The last international outbreak of monkeypox reported outside Africa occurred back in 2003. However, monkeypox has reemerged at a global scale with numerous confirmed cases across the globe in 2022. The rapid spread of cases through different countries has raised serious concerns among public health officials worldwide prompting accelerated investigations aimed to identify the origins and cause of the rapid expansion of cases. The current situation is reminiscent of the very early stages of the still ongoing COVID-19 pandemic. Overlapping features between these, two seemingly alike viral entities include the possibility for airborne transmission and the currently unexplained and rapid spread across borders. Early recognition of cases and timely intervention of potential transmission chains are necessary to contain further outbreaks. Measures should include rapid and accurate diagnosis of cases meeting case definitions, active surveillance efforts, and appropriate containment of confirmed cases. Governments and health policymakers must apply lessons learned from previous outbreaks and start taking active steps toward limiting the recent global spread of monkeypox. Herein, we discuss the status of the current monkeypox outbreaks worldwide, the epidemiological and public health situation at a global scale and what can be done to keep at bay its further expansion and future global implications.

Monkeypox: Some Keys to Understand This Emerging Disease

In 1958, several monkeys in a Copenhagen laboratory developed a skin rash from which an orthopoxvirus could be isolated, which was named monkeypox virus (MPXV). However, the natural animal reservoir for MPXV is thought to be a rodent. The first human case occurred in 1970, and the incidence has increased progressively throughout the years. Starting May 2022, the number of cases outside Africa has soared, especially in Western Europe. There are two clades of MPXV, Congo Basin, with higher virulence and mortality, and Western Africa (WA). MPXV from the present outbreak has been proposed to be classified as Clade 3, distinct from the WA clade by at least 50 substitutions, which may increase human-to-human transmissibility. Most cases correspond to men in their 30s who have sex with men, and the possibility of sexual transmission is under investigation. Though there is no evidence of human-to-animal transmission, pets of positive human cases may be classified as low risk, including dogs, cats, and birds, who can be quarantined at home, and high risk, such as pet rabbits or mice, who should be isolated in official laboratories for observation. The current epidemiological data do not support the risk of a pandemic.

Monkeypox virus: a re-emergent threat to humans

Human monkeypox (MPX) is a rare zoonotic infection characterized by smallpox-like signs and symptoms. It is caused by monkeypox virus (MPXV), a double stranded DNA virus belonging to the genus Orthopoxvirus. MPX was first identified in 1970 and mostly prevailed in the rural rainforests of Central and West Africa in the past. Outside Africa, MPX was reported in the United Kingdom, the USA, Israel, and Singapore. In 2022, the resurgence of MPX in Europe and elsewhere posed a potential threat to humans. MPXV was transmitted by the animals-human or human-human pathway, and the symptoms of MPXV infection are similar to that of smallpox, but in a milder form and with lower mortality (1%-10%). Although the smallpox vaccination has been shown to provide 85% protection against MPXV infection, and two anti-smallpox virus drugs have been approved to treat MPXV, there are still no specific vaccines and drugs against MPXV infection. Therefore it is urgent to take active measures including the adoption of novel anti-MPXV strategies to control the spread of MPXV and prevent MPX epidemic. In this review, we summarize the biological features, epidemiology, pathogenicity, laboratory diagnosis, and prevention and treatment strategies on MPXV. This review provides the basic knowledge for prevention and control of future outbreaks of this emerging infection.

Effects of Treatment Delay on Efficacy of Tecovirimat Following Lethal Aerosol Monkeypox Virus Challenge in Cynomolgus Macaques

Background

Tecovirimat (ST-246) is being developed as an antiviral therapeutic for smallpox for use in the event of an accidental or intentional release. The last reported case of smallpox was 1978 but the potential for use of variola virus for biowarfare has renewed interest in smallpox antiviral therapeutics.

Methods

Cynomolgus macaques were challenged with a lethal dose of monkeypox virus (MPXV) by aerosol as a model for human smallpox and treated orally with 10 mg/kg tecovirimat once daily starting up to 8 days following challenge. Monkeys were monitored for survival, lesions, and clinical signs of disease. Samples were collected for measurement of viremia by quantitative real-time polymerase chain reaction, and for white blood cell counts.

Results

Survival in animals initiating treatment up to 5 days postchallenge was 100%. In animals treated starting 6, 7, or 8 days following challenge, survival was 67%, 100%, and 50%, respectively. Treatment initiation up to 4 days following challenge reduced severity of clinical manifestations of infection.

Conclusions

Tecovirimat treatment initiated up to 8 days following a lethal aerosol MPXV challenge improves survival and, when initiated earlier than 5 days after challenge, provides protection from clinical effects of disease, supporting the conclusion that it is a promising smallpox antiviral therapeutic candidate.

Improving the Care and Treatment of Monkeypox Patients in Low-Resource Settings: Applying Evidence from Contemporary Biomedical and Smallpox Biodefense Research

Monkeypox is a smallpox-like illness that can be accompanied by a range of significant medical complications. To date there are no standard or optimized guidelines for the clinical management of monkeypox (MPX) patients, particularly in low-resource settings. Consequently, patients can experience protracted illness and poor outcomes. Improving care necessitates developing a better understanding of the range of clinical manifestations-including complications and sequelae-as well as of features of illness that may be predictive of illness severity and poor outcomes. Experimental and natural infection of non-human primates with monkeypox virus can inform the approach to improving patient care, and may suggest options for pharmaceutical intervention. These studies have traditionally been performed to address the threat of smallpox bioterrorism and were designed with the intent of using MPX as a disease surrogate for smallpox. In many cases this necessitated employing high-dose, inhalational or intravenous challenge to recapitulate the severe manifestations of illness seen with smallpox. Overall, these data-and data from biomedical research involving burns, superficial wounds, herpes, eczema vaccinatum, and so forth-suggest that MPX patients could benefit from clinical support to mitigate the consequences of compromised skin and mucosa. This should include prevention and treatment of secondary bacterial infections (and other complications), ensuring adequate hydration and nutrition, and protecting vulnerable anatomical locations such as the eyes and genitals. A standard of care that considers these factors should be developed and assessed in different settings, using clinical metrics specific for MPX alongside consideration of antiviral therapies.

Dynamics of Pathological and Virological Findings During Experimental Calpox Virus Infection of Common Marmosets (Callithrix jacchus)

Experimental intranasal infection of marmosets (Callithrix jacchus) with calpox virus results in fatal disease. Route and dose used for viral inoculation of the test animals mimics the natural transmission of smallpox, thus representing a suitable model to study pathogenesis and to evaluate new vaccines against orthopoxvirus infection. However, the pathogenic mechanisms leading to death are still unclear. Therefore, our study aimed at investigating the kinetics of pathological alterations to clarify the pathogenesis in calpox virus infection. Following intranasal inoculation with two different viral doses, common marmosets were sacrificed on days 3, 5, 7, 10 and 12 post inoculation. Collected tissue was screened using histopathology, immunohistochemistry, transmission electron microscopy, and virological assays. Our data suggest that primary replication took place in nasal and bronchial epithelia followed by secondary replication in submandibular lymph nodes and spleen. Parallel to viremia at day 7, virus was detectable in many organs, mainly located in epithelial cells and macrophages, as well as in endothelial cells. Based on the onset of clinical signs, the histological and ultrastructural lesions and the immunohistochemical distribution pattern of the virus, the incubation period was defined to last 11 days, which resembles human smallpox. In conclusion, the data indicate that the calpox model is highly suitable for studying orthopoxvirus-induced disease.

Evaluation of Taterapox Virus in Small Animals

Taterapox virus (TATV), which was isolated from an African gerbil (Tatera kempi) in 1975, is the most closely related virus to variola; however, only the original report has examined its virology. We have evaluated the tropism of TATV in vivo in small animals. We found that TATV does not infect Graphiurus kelleni, a species of African dormouse, but does induce seroconversion in the Mongolian gerbil (Meriones unguiculatus) and in mice; however, in wild-type mice and gerbils, the virus produces an unapparent infection. Following intranasal and footpad inoculations with 1 × 10⁶ plaque forming units (PFU) of TATV, immunocompromised stat1^−/− mice showed signs of disease but did not die; however, SCID mice were susceptible to intranasal and footpad infections with 100% mortality observed by Day 35 and Day 54, respectively. We show that death is unlikely to be a result of the virus mutating to have increased virulence and that SCID mice are capable of transmitting TATV to C57BL/6 and C57BL/6 stat1^−/− animals; however, transmission did not occur from TATV inoculated wild-type or stat1^−/− mice. Comparisons with ectromelia (the etiological agent of mousepox) suggest that TATV behaves differently both at the site of inoculation and in the immune response that it triggers.

Using the Ground Squirrel (Marmota bobak) as an Animal Model to Assess Monkeypox Drug Efficacy

In experiments to study the sensitivity of ground squirrels (Marmota bobak) to monkeypox virus (MPXV) at intranasal challenge, expressed pox-like clinical symptoms (hyperthermia, lymphadenitis, skin rash all over the body and mucous membranes and others) were observed 7-9 days post-infection. The 50% infective dose (ID50 ) of MPXV for these marmots determined by the presence of clinical signs of the disease was 2.2 log10 PFU. Some diseased marmots (about 40%) died 13-22 days post-infection, and the mortality rate was weakly dependent on MPXV infective dose. Lungs with trachea were primary target organs of marmots challenged intranasally (with ~30 ID50 ). The pathogen got to secondary target organs of the animals mainly via the lymphatic way (with replication in bifurcation lymph nodes). Lungs with trachea, nasal mucosa and skin were the organs where the maximum MPXV amounts accumulated in these animals. Evidences of the pathogen presence and replication were revealed in these and subcutaneously infected marmots in the traditional primary target cells for MPXV (macrophages and respiratory tract epitheliocytes), as well as in some other cells (endotheliocytes, plasmocytes, fibroblasts, reticular and smooth muscle cells). Our use of this animal species to assess the antiviral efficacy of some drugs demonstrated the agreement of the obtained results with those described in scientific literature, which opens up the prospects of using marmots as animal models for monkeypox to develop therapeutic and preventive anti-smallpox drugs.

Detection of Vaccinia Virus in Milk: Evidence of a Systemic and Persistent Infection in Experimentally Infected Cows

Bovine vaccinia (BV) is a zoonosis caused by Vaccinia virus (VACV), which affects lactating cows and milkers. VACV DNA and infectious particles have been detected in milk of naturally infected cows. However, the period and pattern of VACV shedding in milk is unknown, as is whether the presence of VACV in milk is due to a localized or a systemic infection. To address those questions, eight lactating cows were inoculated with VACV in previously scarified teats. The experiment was divided in two phases. In Phase 1, milk samples were collected daily for 33 days, and in Phase 2, four animals from the first phase were immunosuppressed. In both phases, milk was collected with a sterile catheter on even days and by hand milking on odd days. All animals showed typical BV lesions in the inoculated teats. All milk samples were subjected to nested polymerase chain reaction (PCR) and real-time quantitative PCR to detect VACV DNA. PCR-positive samples were subjected to virus isolation. VACV DNA was intermittently detected in milk in both phases and infectious viral particles could be detected only in phase 2, on the 69th, 73rd, 74th, 77th, 79th, and 81st days postinfection. Despite the possibility of propagation of VACV through milk, it is known that milk continues to be drawn and marketed normally during outbreaks of the disease. The detection of both VACV DNA and infectious particles in milk samples draws attention to the potential public health risk associated with the consumption of milk from BV outbreaks. Detection of VACV in the milk from noninfected teats demonstrated that VACV shedding in milk might be related to a systemic infection. Moreover, it was shown that VACV DNA and viral infectious particles could be detected in milk even after healing of the lesions, demonstrating that VACV may cause a persistent infection in cattle.

Exposure of rhesus monkeys to cowpox virus Brighton Red by large-particle aerosol droplets results in an upper respiratory tract disease

We previously demonstrated that small-particle (0.5-3.0 µm) aerosol infection of rhesus monkeys (Macaca mulatta) with cowpox virus (CPXV)-Brighton Red (BR) results in fulminant respiratory tract disease characterized by severe lung parenchymal pathology but only limited systemic virus dissemination and limited classic epidermal pox-like lesion development (Johnson et al., 2015). Based on these results, and to further develop CPXV as an improved model of human smallpox, we evaluated a novel large-particle aerosol (7.0-9.0 µm) exposure of rhesus monkeys to CPXV-BR and monitored for respiratory tract disease by serial computed tomography (CT). As expected, the upper respiratory tract and large airways were the major sites of virus-induced pathology following large-particle aerosol exposure. Large-particle aerosol CPXV exposure of rhesus macaques resulted in severe upper airway and large airway pathology with limited systemic dissemination.

Modified Vaccinia Ankara Virus Vaccination Provides Long-Term Protection against Nasal Rabbitpox Virus Challenge

Modified vaccinia Ankara virus (MVA) is a smallpox vaccine candidate. This study was performed to determine if MVA vaccination provides long-term protection against rabbitpox virus (RPXV) challenge, an animal model of smallpox. Two doses of MVA provided 100% protection against a lethal intranasal RPXV challenge administered 9 months after vaccination.

Further Assessment of Monkeypox Virus Infection in Gambian Pouched Rats (Cricetomys gambianus) Using In Vivo Bioluminescent Imaging

Monkeypox is a zoonosis clinically similar to smallpox in humans. Recent evidence has shown a potential risk of increased incidence in central Africa. Despite attempts to isolate the virus from wild rodents and other small mammals, no reservoir host has been identified. In 2003, Monkeypox virus (MPXV) was accidentally introduced into the U.S. via the pet trade and was associated with the Gambian pouched rat (Cricetomys gambianus). Therefore, we investigated the potential reservoir competence of the Gambian pouched rat for MPXV by utilizing a combination of in vivo and in vitro methods. We inoculated three animals by the intradermal route and three animals by the intranasal route, with one mock-infected control for each route. Bioluminescent imaging (BLI) was used to track replicating virus in infected animals and virological assays (e.g. real time PCR, cell culture) were used to determine viral load in blood, urine, ocular, nasal, oral, and rectal swabs. Intradermal inoculation resulted in clinical signs of monkeypox infection in two of three animals. One severely ill animal was euthanized and the other affected animal recovered. In contrast, intranasal inoculation resulted in subclinical infection in all three animals. All animals, regardless of apparent or inapparent infection, shed virus in oral and nasal secretions. Additionally, BLI identified viral replication in the skin without grossly visible lesions. These results suggest that Gambian pouched rats may play an important role in transmission of the virus to humans, as they are hunted for consumption and it is possible for MPXV-infected pouched rats to shed infectious virus without displaying overt clinical signs.

Susceptibility of Marmosets (Callithrix jacchus) to Monkeypox Virus: A Low Dose Prospective Model for Monkeypox and Smallpox Disease

Although current nonhuman primate models of monkeypox and smallpox diseases provide some insight into disease pathogenesis, they require a high titer inoculum, use an unnatural route of infection, and/or do not accurately represent the entire disease course. This is a concern when developing smallpox and/or monkeypox countermeasures or trying to understand host pathogen relationships. In our studies, we altered half of the test system by using a New World nonhuman primate host, the common marmoset. Based on dose finding studies, we found that marmosets are susceptible to monkeypox virus infection, produce a high viremia, and have pathological features consistent with smallpox and monkeypox in humans. The low dose (48 plaque forming units) required to elicit a uniformly lethal disease and the extended incubation (preclinical signs) are unique features among nonhuman primate models utilizing monkeypox virus. The uniform lethality, hemorrhagic rash, high viremia, decrease in platelets, pathology, and abbreviated acute phase are reflective of early-type hemorrhagic smallpox.

Small particle aerosol inoculation of cowpox Brighton Red in rhesus monkeys results in a severe respiratory disease

Cowpox virus (CPXV) inoculation of nonhuman primates (NHPs) has been suggested as an alternate model for smallpox (Kramski et al., 2010, PLoS One, 5, e10412). Previously, we have demonstrated that intrabronchial inoculation of CPXV-Brighton Red (CPXV-BR) into cynomolgus monkeys resulted in a disease that shared many similarities to smallpox; however, severe respiratory tract disease was observed (Smith et al., 2011, J. Gen. Virol.). Here we describe the course of disease after small particle aerosol exposure of rhesus monkeys using computed tomography (CT) to monitor respiratory disease progression. Subjects developed a severe respiratory disease that was uniformly lethal at 5.7 log10 PFU of CPXV-BR. CT indicated changes in lung architecture that correlated with changes in peripheral blood monocytes and peripheral oxygen saturation. While the small particle aerosol inoculation route does not accurately mimic human smallpox, the data suggest that CT can be used as a tool to monitor real-time disease progression for evaluation of animal models for human diseases.

Generation and characterization of large-particle aerosols using a center flow tangential aerosol generator with a non-human-primate, head-only aerosol chamber

Aerosol droplets or particles produced from infected respiratory secretions have the potential to infect another host through inhalation. These respiratory particles can be polydisperse and range from 0.05 to 500 µm in diameter. Animal models of infection are generally established to facilitate the potential licensure of candidate prophylactics and/or therapeutics. Consequently, aerosol-based animal infection models are needed to properly study and counter airborne infections. Ideally, experimental aerosol exposure should reliably result in animal disease that faithfully reproduces the modeled human disease. Few studies have been performed to explore the relationship between exposure particle size and induced disease course for infectious aerosol particles. The center flow tangential aerosol generator (CenTAG™) produces large-particle aerosols capable of safely delivering a variety of infectious aerosols to non-human primates (NHPs) within a Class III Biological Safety Cabinet (BSC) for establishment or refinement of NHP infectious disease models. Here, we report the adaptation of this technology to the Animal Biosafety Level 4 (ABSL-4) environment for the future study of high-consequence viral pathogens and the characterization of CenTAG™-created sham (no animal, no virus) aerosols using a variety of viral growth media and media supplements.

Sequence of pathogenic events in cynomolgus macaques infected with aerosolized monkeypox virus

To evaluate new vaccines when human efficacy studies are not possible, the FDA's "Animal Rule" requires well-characterized models of infection. Thus, in the present study, the early pathogenic events of monkeypox infection in nonhuman primates, a surrogate for variola virus infection, were characterized. Cynomolgus macaques were exposed to aerosolized monkeypox virus (10(5) PFU). Clinical observations, viral loads, immune responses, and pathological changes were examined on days 2, 4, 6, 8, 10, and 12 postchallenge. Viral DNA (vDNA) was detected in the lungs on day 2 postchallenge, and viral antigen was detected, by immunostaining, in the epithelium of bronchi, bronchioles, and alveolar walls. Lesions comprised rare foci of dysplastic and sloughed cells in respiratory bronchioles. By day 4, vDNA was detected in the throat, tonsil, and spleen, and monkeypox antigen was detected in the lung, hilar and submandibular lymph nodes, spleen, and colon. Lung lesions comprised focal epithelial necrosis and inflammation. Body temperature peaked on day 6, pox lesions appeared on the skin, and lesions, with positive immunostaining, were present in the lung, tonsil, spleen, lymph nodes, and colon. By day 8, vDNA was present in 9/13 tissues. Blood concentrations of interleukin 1ra (IL-1ra), IL-6, and gamma interferon (IFN-γ) increased markedly. By day 10, circulating IgG antibody concentrations increased, and on day 12, animals showed early signs of recovery. These results define early events occurring in an inhalational macaque monkeypox infection model, supporting its use as a surrogate model for human smallpox.

IMPORTANCE

Bioterrorism poses a major threat to public health, as the deliberate release of infectious agents, such smallpox or a related virus, monkeypox, would have catastrophic consequences. The development and testing of new medical countermeasures, e.g., vaccines, are thus priorities; however, tests for efficacy in humans cannot be performed because it would be unethical and field trials are not feasible. To overcome this, the FDA may grant marketing approval of a new product based upon the "Animal Rule," in which interventions are tested for efficacy in well-characterized animal models. Monkeypox virus infection of nonhuman primates (NHPs) presents a potential surrogate disease model for smallpox. Previously, the later stages of monkeypox infection were defined, but the early course of infection remains unstudied. Here, the early pathogenic events of inhalational monkeypox infection in NHPs were characterized, and the results support the use of this surrogate model for testing human smallpox interventions.

Pathogenesis of fulminant monkeypox with bacterial sepsis after experimental infection with West African monkeypox virus in a cynomolgus monkey

The pathogenesis of severe human monkeypox, which causes systemic and fulminant infections, is not clear. This study presents a case repot of fulminant monkeypox with bacterial sepsis after experimental infection with monkeypox virus in a cynomolgus monkey (Macaca fascicularis). In our previous study (Saijo et al., 2009, J Gen Virol), two cynomolgus monkeys became moribund after experimental infection with monkeypox virus Liberia strain, West African strain. One exhibited typical monkeypox-related papulovesicular lesions. The other monkey presented fulminant clinical symptoms with a characteristic flat red rash similar to that found in smallpox, which is associated with extremely high fatality rates. In this study, we found that the monkey with flat red rash had high levels of viremia and neutropenia, as well as high plasma levels of pro-inflammatory cytokines and chemokines compared with the other monkey. Monkeypox virus replicates in epithelial cells and macrophages in various organs. Sepsis due to Gram-positive cocci was confirmed histopathologically in the monkey with flat red rash. The lack of inflammatory response in the lesion suggested that the monkey with sepsis experienced strong immune suppression during the viral infection. The neutropenia and excessive inflammatory cytokine responses indicate that neutrophils play key roles in the pathogenesis of systemic and fulminant human monkeypox virus infections with sepsis.

Identification and characterization of microRNAs in the crab-eating macaque (Macaca fascicularis) using transcriptome analysis

MicroRNAs (miRNAs), with an average length between 16 nt and 26 nt, are small non-coding RNAs that can repress gene expression on the post-transcriptional level. Macaca fascicularis (M. fascicularis), one of the most important nonhuman primate animal models, is widely used in basic and applied preclinical research, especially in studies that involve neuroscience and disease. However, due to the lack of a complete genome sequence, the miRNAs in M. fascicularis have not been completely characterized. In this study, 86 putative M. fascicularis miRNAs were identified using a strategy of our design. The expression of some of these miRNAs in the tissue was confirmed by qRT-PCR. The function and pathway of their targeted genes were analyzed to reveal the potential relevance of miRNA regulation on diseases and physiological processes. The current study provides insight into potential miRNAs and forms a useful knowledge base for the future understanding of the function of miRNAs in M. fascicularis.

Molecular Localization Techniques in the Diagnosis and Characterization of Nonhuman Primate Infectious Diseases

Molecular localization techniques remain important diagnostic and research tools for the pathologist evaluating nonhuman primate tissues. In situ hybridization and immunohistochemistry protocols have been developed for many important pathogens of nonhuman primates, including RNA and DNA viruses, prions, and bacterial, protozoal, and fungal pathogens. Such techniques will remain critical in defining the impact and relevance of novel agents on animal health and disease. A comparative pathology perspective often provides valuable insight to the best strategy for reagent development and can also facilitate interpretation of molecular localization patterns. Such a perspective is grounded in a firm understanding of microbe-host pathobiology. This review summarizes current molecular localization protocols used in the diagnosis of selected primate infectious diseases.

Orthopoxvirus variola infection of Cynomys ludovicianus (North American Black tailed prairie dog)

Since the eradication of Smallpox, researchers have attempted to study Orthopoxvirus pathogenesis and immunity in animal models in order to correlate results human smallpox. A solely human pathogen, Orthopoxvirus variola fails to produce authentic smallpox illness in any other animal species tested to date. In 2003, an outbreak in the USA of Orthopoxvirus monkeypox, revealed the susceptibility of the North American black-tailed prairie dog (Cynomys ludovicianus) to infection and fulminate disease. Prairie dogs infected with Orthopoxvirus monkeypox present with a clinical scenario similar to ordinary smallpox, including prodrome, rash, and high mortality. This study examines if Black-tailed prairie dogs can become infected with O. variola and serve as a surrogate model for the study of human smallpox disease. Substantive evidence of infection is found in immunological seroconversion of animals to either intranasal or intradermal challenges with O. variola, but in the absence of overt illness.

Assessment of the protective effect of Imvamune and Acam2000 vaccines against aerosolized monkeypox virus in cynomolgus macaques

To support the licensure of a new and safer vaccine to protect people against smallpox, a monkeypox model of infection in cynomolgus macaques, which simulates smallpox in humans, was used to evaluate two vaccines, Acam2000 and Imvamune, for protection against disease. Animals vaccinated with a single immunization of Imvamune were not protected completely from severe and/or lethal infection, whereas those receiving either a prime and boost of Imvamune or a single immunization with Acam2000 were protected completely. Additional parameters, including clinical observations, radiographs, viral load in blood, throat swabs, and selected tissues, vaccinia virus-specific antibody responses, immunophenotyping, extracellular cytokine levels, and histopathology were assessed. There was no significant difference (P > 0.05) between the levels of neutralizing antibody in animals vaccinated with a single immunization of Acam2000 (132 U/ml) and the prime-boost Imvamune regime (69 U/ml) prior to challenge with monkeypox virus. After challenge, there was evidence of viral excretion from the throats of 2 of 6 animals in the prime-boost Imvamune group, whereas there was no confirmation of excreted live virus in the Acam2000 group. This evaluation of different human smallpox vaccines in cynomolgus macaques helps to provide information about optimal vaccine strategies in the absence of human challenge studies.

Poxvirus antigen staining of immune cells as a biomarker to predict disease outcome in monkeypox and cowpox virus infection in non-human primates

Infection of non-human primates (NHPs) such as rhesus and cynomolgus macaques with monkeypox virus (MPXV) or cowpox virus (CPXV) serve as models to study poxvirus pathogenesis and to evaluate vaccines and anti-orthopox therapeutics. Intravenous inoculation of macaques with high dose of MPXV (>1-2×10(7) PFU) or CPXV (>10(2) PFU) results in 80% to 100% mortality and 66 to 100% mortality respectively. Here we report that NHPs with positive detection of poxvirus antigens in immune cells by flow cytometric staining, especially in monocytes and granulocytes succumbed to virus infection and that early positive pox staining is a strong predictor for lethality. Samples from four independent studies were analyzed. Eighteen NHPs from three different experiments were inoculated with two different MPXV strains at lethal doses. Ten NHPs displayed positive pox-staining and all 10 NHPs reached moribund endpoint. In contrast, none of the three NHPs that survived anticipated lethal virus dose showed apparent virus staining in the monocytes and granulocytes. In addition, three NHPs that were challenged with a lethal dose of MPXV and received cidofovir treatment were pox-antigen negative and all three NHPs survived. Furthermore, data from a CPXV study also demonstrated that 6/9 NHPs were pox-antigen staining positive and all 6 NHPs reached euthanasia endpoint, while the three survivors were pox-antigen staining negative. Thus, we conclude that monitoring pox-antigen staining in immune cells can be used as a biomarker to predict the prognosis of virus infection. Future studies should focus on the mechanisms and implications of the pox-infection of immune cells and the correlation between pox-antigen detection in immune cells and disease progression in human poxviral infection.

Transmissibility of the monkeypox virus clades via respiratory transmission: investigation using the prairie dog-monkeypox virus challenge system

Monkeypox virus (MPXV) is endemic within Africa where it sporadically is reported to cause outbreaks of human disease. In 2003, an outbreak of human MPXV occurred in the US after the importation of infected African rodents. Since the eradication of smallpox (caused by an orthopoxvirus (OPXV) related to MPXV) and cessation of routine smallpox vaccination (with the live OPXV vaccinia), there is an increasing population of people susceptible to OPXV diseases. Previous studies have shown that the prairie dog MPXV model is a functional animal model for the study of systemic human OPXV illness. Studies with this model have demonstrated that infected animals are able to transmit the virus to naive animals through multiple routes of exposure causing subsequent infection, but were not able to prove that infected animals could transmit the virus exclusively via the respiratory route. Herein we used the model system to evaluate the hypothesis that the Congo Basin clade of MPXV is more easily transmitted, via respiratory route, than the West African clade. Using a small number of test animals, we show that transmission of viruses from each of the MPXV clade was minimal via respiratory transmission. However, transmissibility of the Congo Basin clade was slightly greater than West African MXPV clade (16.7% and 0% respectively). Based on these findings, respiratory transmission appears to be less efficient than those of previous studies assessing contact as a mechanism of transmission within the prairie dog MPXV animal model.

A review of experimental and natural infections of animals with monkeypox virus between 1958 and 2012

Monkeypox virus (MPXV) was discovered in 1958 during an outbreak in an animal facility in Copenhagen, Denmark. Since its discovery, MPXV has revealed a propensity to infect and induce disease in a large number of animals within the mammalia class from pan-geographical locations. This finding has impeded the elucidation of the natural host, although the strongest candidates are African squirrels and/or other rodents. Experimentally, MPXV can infect animals via a variety of multiple different inoculation routes; however, the natural route of transmission is unknown and is likely to be somewhat species specific. In this review we have attempted to compile and discuss all published articles that describe experimental or natural infections with MPXV, dating from the initial discovery of the virus through to the year 2012. We further discuss the comparative disease courses and pathologies of the host species.

Comparative pathology of smallpox and monkeypox in man and macaques

In the three decades since the eradication of smallpox and cessation of routine vaccination, the collective memory of the devastating epidemics caused by this orthopoxvirus has waned, and the human population has become increasingly susceptible to a disease that remains high on the list of possible bioterrorism agents. Research using surrogate orthopoxviruses in their natural hosts, as well as limited variola virus research in animal models, continues worldwide; however, interpretation of findings is often limited by our relative lack of knowledge about the naturally occurring disease. For modern comparative pathologists, many of whom have no first-hand knowledge of naturally occurring smallpox, this work provides a contemporary review of this historical disease, as well as discussion of how it compares with human monkeypox and the corresponding diseases in macaques.

Animal Models of Human Viral Diseases

As the threat of exposure to emerging and reemerging viruses within a naive population increases, it is vital that the basic mechanisms of pathogenesis and immune response be thoroughly investigated. By using animal models in this endeavor, the response to viruses can be studied in a more natural context to identify novel drug targets, and assess the efficacy and safety of new products. This is especially true in the advent of the Food and Drug Administration's animal rule. Although no one animal model is able to recapitulate all the aspects of human disease, understanding the current limitations allows for a more targeted experimental design. Important facets to be considered before an animal study are the route of challenge, species of animals, biomarkers of disease, and a humane endpoint. This chapter covers the current animal models for medically important human viruses, and demonstrates where the gaps in knowledge exist.