Potential use of cidofovir, brincidofovir, and tecovirimat drugs in fighting monkeypox infection: recent trends and advancements

Recent years have witnessed the rise of more recent pandemic outbreaks including COVID-19 and monkeypox. A multinational monkeypox outbreak creates a complex situation that necessitates countermeasures to the existing quo. The first incidence of monkeypox was documented in the 1970s, and further outbreaks led to a public health emergency of international concern. Yet as of right now, neither vaccines nor medicines are certain to treat monkeypox. Even the inability of conducting human clinical trials has prevented thousands of patients from receiving effective disease management. The current state of the disease's understanding, the treatment options available, financial resources, and lastly international policies to control an epidemic state are the major obstacles to controlling epidemics. The current review focuses on the epidemiology of monkeypox, scientific ideas, and available treatments, including potential monkeypox therapeutic methods. As a result, a thorough understanding of monkeypox literature will facilitate in the development of new therapeutic medications for the prevention and treatment of monkeypox.

Monkeypox and oral lesions associated with its occurrence: a systematic review and meta-analysis

Background

A zoonotic, double-stranded DNA virus belonging to the genus Orthopoxvirus, the mpox virus (MPXV) is most common in tropical regions of Central and West Africa. The frequency of monkeypox (mpox) cases, however, has sharply climbed globally since May 2022.

Objectives

To establish the threat of mpox in terms of the oral lesions caused in sufferers.

Materials and methods

After a thorough study of the literature identified in the PubMed, Web of Science, and Cochrane library databases using the PRISMA framework, 103 papers were found. Using inclusion and exclusion criteria, we chose research that was relevant for our review before shortlisting 14 papers that conformed to the review's guidelines.

Results

In the 14 selected studies, it was found that oral lesions were among the first clinical signs of a mpox affliction, with ulcers on the dorsal surface of tongue lips being the most common areas affected.

Conclusion

The rarely observed oral lesions of mpox infection may help in the diagnosis and management of this condition. It is critical to keep in mind that recognising and detecting oral lesions in mpox patients opens the door to more research and efficient patient management.

Marmosets as models of infectious diseases

Animal models of infectious disease often serve a crucial purpose in obtaining licensure of therapeutics and medical countermeasures, particularly in situations where human trials are not feasible, i.e., for those diseases that occur infrequently in the human population. The common marmoset (Callithrix jacchus), a Neotropical new-world (platyrrhines) non-human primate, has gained increasing attention as an animal model for a number of diseases given its small size, availability and evolutionary proximity to humans. This review aims to (i) discuss the pros and cons of the common marmoset as an animal model by providing a brief snapshot of how marmosets are currently utilized in biomedical research, (ii) summarize and evaluate relevant aspects of the marmoset immune system to the study of infectious diseases, (iii) provide a historical backdrop, outlining the significance of infectious diseases and the importance of developing reliable animal models to test novel therapeutics, and (iv) provide a summary of infectious diseases for which a marmoset model exists, followed by an in-depth discussion of the marmoset models of two studied bacterial infectious diseases (tularemia and melioidosis) and one viral infectious disease (viral hepatitis C).

Clinical considerations on monkeypox antiviral medications: An overview

Monkeypox (mpox), a virus belonging to the orthopoxvirus family, can cause a zoonotic infectious disease with morbidity and cosmetic complications. Therefore, effective antiviral drugs with appropriate safety profiles are important for the treatment of patients with mpox. To date, there is no FDA-approved drug for the treatment of mpox. However, tecovirimat, brincidofovir, and cidofovir are the candidate therapies for the management of mpox. Given the safety concerns following the use of these medications, we aimed to review evidence on the clinical considerations of mpox antiviral medications that will be useful to guide clinicians in the treatment approach. Based on the current evidence, tecovirimat has favorable clinical efficacy, safety, and side effect profile and it can be considered as first-line treatment for mpox.

Recent advances in targeting the "undruggable" proteins: from drug discovery to clinical trials

Undruggable proteins are a class of proteins that are often characterized by large, complex structures or functions that are difficult to interfere with using conventional drug design strategies. Targeting such undruggable targets has been considered also a great opportunity for treatment of human diseases and has attracted substantial efforts in the field of medicine. Therefore, in this review, we focus on the recent development of drug discovery targeting "undruggable" proteins and their application in clinic. To make this review well organized, we discuss the design strategies targeting the undruggable proteins, including covalent regulation, allosteric inhibition, protein-protein/DNA interaction inhibition, targeted proteins regulation, nucleic acid-based approach, immunotherapy and others.

The Global Monkeypox (Mpox) Outbreak: A Comprehensive Review

Monkeypox (Mpox) is a contagious illness that is caused by the monkeypox virus, which is part of the same family of viruses as variola, vaccinia, and cowpox. It was first detected in the Democratic Republic of the Congo in 1970 and has since caused sporadic cases and outbreaks in a few countries in West and Central Africa. In July 2022, the World Health Organization (WHO) declared a public-health emergency of international concern due to the unprecedented global spread of the disease. Despite breakthroughs in medical treatments, vaccines, and diagnostics, diseases like monkeypox still cause death and suffering around the world and have a heavy economic impact. The 85,189 reported cases of Mpox as of 29 January 2023 have raised alarm bells. Vaccines for the vaccinia virus can protect against monkeypox, but these immunizations were stopped after smallpox was eradicated. There are, however, treatments available once the illness has taken hold. During the 2022 outbreak, most cases occurred among men who had sex with men, and there was a range of 7-10 days between exposure and the onset of symptoms. Three vaccines are currently used against the Monkeypox virus. Two of these vaccines were initially developed for smallpox, and the third is specifically designed for biological-terrorism protection. The first vaccine is an attenuated, nonreplicating smallpox vaccine that can also be used for immunocompromised individuals, marketed under different names in different regions. The second vaccine, ACAM2000, is a recombinant second-generation vaccine initially developed for smallpox. It is recommended for use in preventing monkeypox infection but is not recommended for individuals with certain health conditions or during pregnancy. The third vaccine, LC16m8, is a licensed attenuated smallpox vaccine designed to lack the B5R envelope-protein gene to reduce neurotoxicity. It generates neutralizing antibodies to multiple poxviruses and broad T-cell responses. The immune response takes 14 days after the second dose of the first two vaccines and 4 weeks after the ACAM2000 dose for maximal immunity development. The efficacy of these vaccines in the current outbreak of monkeypox is uncertain. Adverse events have been reported, and a next generation of safer and specific vaccines is needed. Although some experts claim that developing vaccines with a large spectrum of specificity can be advantageous, epitope-focused immunogens are often more effective in enhancing neutralization.

Nasal monkeypox virus infection successfully treated with cidofovir in a patient newly diagnosed with HIV

Monkeypox (MPXV) usually causes a mild and self-limited infection. To date there are no data about cidofovir for the treatment for MPXV in humans. We report a case of a 25 years-old Brazilian man with a concurrent diagnosis of acute HIV (human immunodeficiency virus) infection, primary syphilis and MPXV infection with a nasal lesion successfully treated with intravenous cidofovir.

Use of cidofovir in a patient with severe mpox and uncontrolled HIV infection

A 48-year-old man with poorly controlled HIV presented with severe human monkeypox virus (hMPXV) infection, having completed 2 weeks of tecovirimat at another hospital. He had painful, ulcerating skin lesions on most of his body and oropharyngeal cavity, with subsequent Ludwig's angina requiring repeated surgical interventions. Despite commencing a second, prolonged course of tecovirimat, he did not objectively improve, and new lesions were still noted at day 24. Discussion at the UK National Health Service England High Consequence Infectious Diseases Network recommended the use of 3% topical and then intravenous cidofovir, which was given at 5 mg/kg; the patient made a noticeable improvement after the first intravenous dose. He received further intravenous doses at 7 days and 21 days after the dose and was discharged at day 52. Cidofovir is not licensed for use in treatment of hMPXV infection. Data for cidofovir use in hMPXV are restricted to studies in animals. Four other documented cases of cidofovir use against hMPXV have been reported in the USA in 2022, but we present its first use in the UK. The scarcity of studies into the use of cidofovir in this condition clearly shows the need for robust studies to assess efficacy, optimum dosage, timing, and route of administration.

Current Insights into Diagnosis, Prevention Strategies, Treatment, Therapeutic Targets, and Challenges of Monkeypox (Mpox) Infections in Human Populations

In the wake of the emergence and worldwide respread of a viral infection called Monkeypox (Mpox), there is a serious threat to the health and safety of the global population. This viral infection was endemic to the western and central parts of Africa, but has recently spread out of this endemic area to various countries, including the United Kingdom (UK), Portugal, Spain, the United States of America (USA), Canada, Sweden, Belgium, Italy, Australia, Germany, France, the Netherlands, Israel, and Mexico. This is a timely review focusing on recent findings and developments in the epidemiology, clinical features, therapeutic targets, diagnosis, prevention mechanisms, research challenges and possible treatment for Mpox. To date (29 November 2022), there have been around 81,225 reported cases of Mpox. In most cases, this illness is mild; however, there is a fatality rate ranging from 1 to 10%, which might be increased due to associated complications and/or secondary infections. There is a real challenge in the diagnosis of Mpox, since its symptoms are very similar to those of other infections, including smallpox and chickenpox. Generally, to prevent/limit the risk and transmission of Mpox, the detection and isolation of infected individuals, as well as hand hygiene and cleanliness, are essential and effective approaches to control/combat this viral infection. Nevertheless, updated information about Mpox from different angles is lacking. Thus, this review provides updated and comprehensive information about the Mpox illness, which should highlight the global burden, pathogenicity, symptoms, diagnosis, prevention measures and possible treatment of this emerging disease.

Safety and Pharmacokinetics of the Substance of the Anti-Smallpox Drug NIOCH-14 after Oral Administration to Laboratory Animals

BACKGROUND

Since most of the modern human population has no anti-smallpox immunity, it is extremely important to develop and implement effective drugs for the treatment of smallpox and other orthopoxvirus infections. The objective of this study is to determine the main characteristics of the chemical substance NIOCH-14 and its safety and bioavailability in the body of laboratory animals.

METHODS

The safety of NIOCH-14 upon single- or multiple-dose intragastric administration was assessed according to its effect on the main hematological and pathomorphological parameters of laboratory mice and rats. In order to evaluate the pharmacokinetic parameters of NIOCH-14 administered orally, a concentration of ST-246, the active metabolite of NIOCH-14, in mouse blood and organs was determined by tandem mass spectrometry and liquid chromatography.

RESULTS

The intragastric administration of NIOCH-14 at a dose of 5 g/kg body weight caused neither death nor signs of intoxication in mice. The intragastric administration of NIOCH-14 to mice and rats at doses of 50 and 150 µg/g body weight either as a single dose or once daily during 30 days did not cause animal death or critical changes in hematological parameters and the microstructure of internal organs. The tissue availability of NIOCH-14 administered orally to the mice at a dose of 50 µg/g body weight, which was calculated according to concentrations of its active metabolite ST-246 for the lungs, liver, kidney, brain, and spleen, was 100, 69.6, 63.3, 26.8 and 20.3%, respectively. The absolute bioavailability of the NIOCH-14 administered orally to mice at a dose of 50 µg/g body weight was 22.8%.

CONCLUSION

Along with the previously determined efficacy against orthopoxviruses, including the smallpox virus, the substance NIOCH-14 was shown to be safe and bioavailable in laboratory animal experiments.

Insights into monkeypox pathophysiology, global prevalence, clinical manifestation and treatments

On 23rd July 2022, the World Health Organization (WHO) recognized the ongoing monkeypox outbreak as a public medical crisis. Monkeypox virus (MPV), the etiological agent of monkeypox, is a zoonotic, linear, double-stranded DNA virus. In 1970, the Democratic Republic of the Congo reported the first case of MPV infection. Human-to-human transmission can happen through sexual contact, inhaled droplets, or skin-to-skin contact. Once inoculated, the viruses multiply rapidly and spread into the bloodstream to cause viremia, which then affect multiple organs, including the skin, gastrointestinal tract, genitals, lungs, and liver. By September 9, 2022, more than 57,000 cases had been reported in 103 locations, especially in Europe and the United States. Infected patients are characterized by physical symptoms such as red rash, fatigue, backache, muscle aches, headache, and fever. A variety of medical strategies are available for orthopoxviruses, including monkeypox. Monkeypox prevention following the smallpox vaccine has shown up to 85% efficacy, and several antiviral drugs, such as Cidofovir and Brincidofovir, may slow the viral spread. In this article, we review the origin, pathophysiology, global epidemiology, clinical manifestation, and possible treatments of MPV to prevent the propagation of the virus and provide cues to generate specific drugs.

Potential therapeutic targets for Mpox: the evidence to date

INTRODUCTION

The global Mpox (MPX) disease outbreak caused by the Mpox virus (MPXV) in 2022 alarmed the World Health Organization (WHO) and health regulation agencies of individual countries leading to the declaration of MPX as a Public Health Emergency. Owing to the genetic similarities between smallpox-causing poxvirus and MPXV, vaccine JYNNEOS, and anti-smallpox drugs Brincidofovir and Tecovirimat were granted emergency use authorization by the United States Food and Drug Administration. The WHO also included cidofovir, NIOCH-14, and other vaccines as treatment options.

AREAS COVERED

This article covers the historical development of EUA-granted antivirals, resistance to these antivirals, and the projected impact of signature mutations on the potency of antivirals against currently circulating MPXV. Since a high prevalence of MPXV infections in individuals coinfected with HIV and MPXV, the treatment results among these individuals have been included.

EXPERT OPINION

All EUA-granted drugs have been approved for smallpox treatment. These antivirals show good potency against Mpox. However, conserved resistance mutation positions in MPXV and related poxviruses, and the signature mutations in the 2022 MPXV can potentially compromise the efficacy of the EUA-granted treatments. Therefore, MPXV-specific medications are required not only for the current but also for possible future outbreaks.

Smallpox, Monkeypox and Other Human Orthopoxvirus Infections

Considering that vaccination against smallpox with live vaccinia virus led to serious adverse effects in some cases, the WHO, after declaration of the global eradication of smallpox in 1980, strongly recommended to discontinue the vaccination in all countries. This led to the loss of immunity against not only smallpox but also other zoonotic orthopoxvirus infections in humans over the past years. An increasing number of human infections with zoonotic orthopoxviruses and, first of all, monkeypox, force us to reconsider a possible re-emergence of smallpox or a similar disease as a result of natural evolution of these viruses. The review contains a brief analysis of the results of studies on genomic organization and evolution of human pathogenic orthopoxviruses, development of modern methods for diagnosis, vaccination, and chemotherapy of smallpox, monkeypox, and other zoonotic human orthopoxvirus infections.

Therapeutic strategies for human poxvirus infections: Monkeypox (mpox), smallpox, molluscipox, and orf

Therapeutic and vaccine development for human poxvirus infections (e.g., monkeypox (mpox) virus, variola virus, molluscum contagiosum virus, orf virus) has been largely deserted, especially after the eradication of smallpox by 1980. Human mpox is a self-limited disease confined to Central and West Africa for decades. However, since April 2022, mpox has quickly emerged as a multi-country outbreak, urgently calling for effective antiviral agents and vaccines to control mpox. Here, this review highlights possible therapeutic options (e.g., tecovirimat, brincidofovir, cidofovir) and other strategies (e.g., vaccines, intravenous vaccinia immune globulin) for the management of human poxvirus infections worldwide.

Monkeypox-What Pediatricians Need to Know

Monkeypox is a zoonotic disease, presenting with fever, lymphadenopathy and vesicular-pustular skin lesions, that historically has rarely been reported outside the endemic regions of Central and West Africa. It was previously thought that human-to-human transmission was too low to sustain spread. During 2022, the number of cases of monkeypox, caused by clade II, rose rapidly globally, predominantly among men who have sex with men. In previous outbreaks with monkeypox clade 1 in endemic areas, children were disproportionately more affected with higher morbidity and mortality. It is unclear whether children are at similarly higher risk from monkeypox clade II. Nonetheless, children and pregnant women are considered high-risk groups and antiviral treatment should be considered for those affected. While smallpox vaccination offers good protection against monkeypox, the duration of protection is unknown, and infection occurs in vaccinated individuals. Should the current outbreak spread to children, authorities should be prepared to rapidly implement vaccination for children. In this review, we summarize epidemiological and clinical features, as well as the pathogenesis, treatment, and prevention options for monkeypox with a focus on considerations for children.

Antiviral Treatment against Monkeypox: A Scoping Review

During the COVID-19 pandemic, the increase in reports of human monkeypox virus infection cases spreading in many countries outside Africa is a major cause for concern. Therefore, this study aimed to explore the evidence of antiviral pharmacotherapy available for the treatment of adult patients with monkeypox. A scoping review of the literature was conducted using PubMed, Scopus, Web of Science, Embase, and CENTRAL databases until 12 September 2022. The key search terms used were "monkeypox" and "treatment". A total of 1927 articles were retrieved using the search strategy. After removing duplicates (n = 1007) and examining by title, abstract, and full text, 11 studies reporting case reports of monkeypox with antiviral treatment were included, detailing the number of monkeypox cases, clinical manifestations, number of participants with antiviral treatment, history of sexually transmitted diseases, method of diagnosis, location of skin lesions, drugs used in antiviral treatment, route of administration, and outcome. A total of 1281 confirmed cases of monkeypox have been reported, of which 65 monkeypox cases had antiviral treatment distributed most frequently in the United States (n = 30), the United Kingdom (n = 6), and Spain (n = 6). Of the total cases, 1269 (99.1%) were male with an age range of 18 to 76 years, and 1226 (95.7%) had a sexual behavior of being men who have sex with men. All confirmed cases of monkeypox were diagnosed by reverse transcriptase polymerase chain reaction (RT-PCR). The most frequent clinical manifestations were skin lesions, fever, lymphadenopathy, headache, fatigue, and myalgia. The most frequent locations of the lesions were perianal, genital, facial, and upper and lower extremities. The most commonly used drugs for antiviral treatment of monkeypox were: tecovirimat, cidofovir, and brincidofovir. All patients had a complete recovery. According to current evidence, the efficacy and safety of antiviral drugs against monkeypox is of low quality and scarce.

Comprehensive Literature Review of Monkeypox

The current outbreak of monkeypox (MPX) infection has emerged as a global matter of concern in the last few months. MPX is a zoonosis caused by the MPX virus (MPXV), which is one of the Orthopoxvirus species. Thus, it is similar to smallpox caused by the variola virus, and smallpox vaccines and drugs have been shown to be protective against MPX. Although MPX is not a new disease and is rarely fatal, the current multi-country MPX outbreak is unusual because it is occurring in countries that are not endemic for MPXV. In this work, we reviewed the extensive literature available on MPXV to summarize the available data on the major biological, clinical and epidemiological aspects of the virus and the important scientific findings. This review may be helpful in raising awareness of MPXV transmission, symptoms and signs, prevention and protective measures. It may also be of interest as a basis for performance of studies to further understand MPXV, with the goal of combating the current outbreak and boosting healthcare services and hygiene practices.Trial registration: ClinicalTrials.gov identifier: NCT02977715..Trial registration: ClinicalTrials.gov identifier: NCT03745131..Trial registration: ClinicalTrials.gov identifier: NCT00728689..Trial registration: ClinicalTrials.gov identifier: NCT02080767..

Repositioning potentials of smallpox vaccines and antiviral agents in monkeypox outbreak: A rapid review on comparative benefits and risks

Background and aims

There is a sought for vaccines and antiviral agents as countermeasures for the recent monkeypox outbreak. Here, we aimed to review and discuss the repurposing potentials of smallpox vaccines and drugs in monkeypox outbreaks based on their comparative benefits and risks. Therefore, we conducted this rapid review and discussed the repurposing potentials of smallpox vaccines and drugs in monkeypox infection.

Methods

Here, we searched Google Scholar and PubMed for relevant information and data. We found many articles that have suggested the use of smallpox vaccines and antiviral drugs in monkeypox outbreaks according to the study findings. We read the relevant articles to extract information.

Results

According to the available documents, we found two replication‐competent and one replication‐deficient vaccinia vaccines were effective against Orthopoxvirus. However, the healthcare authorities have authorized second‐generation live vaccina virus vaccines against Orthopoxvirus in many countries. Smallpox vaccine is almost 85% effective in preventing monkeypox infection as monkeypox virus, variola virus, and vaccinia virus are similar. The United States and Canada have approved a replication‐deficient third‐generation smallpox vaccine for the prevention of monkeypox infection. However, the widely used second‐generation smallpox vaccines contain a live virus and replicate it into the human cell. Therefore, there is a chance to cause virus‐induced complications among the vaccinated subjects. In those circumstances, the available Orthopoxvirus inhibitors might be a good choice for treating monkeypox infections as they showed similar efficacy in monkeypox infection in different animal model clinical trials. Also, the combined use of antiviral drugs and vaccinia immune globulin can enhance significant effectiveness in immunocompromised subjects.

Conclusion

Repurposing of these smallpox vaccines and antiviral agents might be weapons to fight monkeypox infection. Also, we recommend further investigations of smallpox vaccines and Orthopoxvirus inhibitors in a human model study to explore their exact role in human monkeypox infections.

Prevention and Treatment of Monkeypox: A Step-by-Step Guide for Healthcare Professionals and General Population

The World Health Organization (WHO) recently declared the monkeypox virus a Public Health Emergency of International Concern (PHEIC). As the cases of the COVID-19 pandemic start to get under control, we have seen the monkeypox virus, found predominantly in Africa, spread in non-endemic countries worldwide. In the 1970s, after the smallpox virus eradication and the vaccine's discontinuation, the monkeypox virus infection started to gain attention. The first United States outbreak happened in 2003; since then, more sporadic cases of monkeypox have gained media attention. With cases spreading worldwide, without epidemiological links with outbreaks among men who have sex with men (MSM), it warrants urgent public health control measures to contain the spread of the monkeypox virus and investigate the underlying pathophysiology, including genetic modification of the virus. This review highlights the epidemiology, transmission, pathogenesis, clinical manifestation, diagnosis, prevention, and management of the current human monkeypox virus infection.

Prevention and Treatment of Monkeypox

Human monkeypox is a zoonotic orthopoxvirus with presentation similar to smallpox. Monkeypox is transmitted incidentally to humans when they encounter infected animals. Reports have shown that the virus can also be transmitted through direct contact (sexual or skin-to-skin), respiratory droplets, and via fomites such as towels and bedding. Multiple medical countermeasures are stockpiled for orthopoxviruses such as monkeypox. Two vaccines are currently available, JYNNEOSTM (live, replication incompetent vaccinia virus) and ACAM2000® (live, replication competent vaccinia virus). While most cases of monkeypox will have mild and self-limited disease, with supportive care being typically sufficient, antivirals (e.g. tecovirimat, brincidofovir, cidofovir) and vaccinia immune globulin intravenous (VIGIV) are available as treatments. Antivirals can be considered in severe disease, immunocompromised patients, pediatrics, pregnant and breastfeeding women, complicated lesions, and when lesions appear near the mouth, eyes, and genitals. The purpose of this short review is to describe each of these countermeasures.

[We should be prepared to smallpox re-emergence.]

The review contains a brief analysis of the results of investigations conducted during 40 years after smallpox eradication and directed to study genomic organization and evolution of variola virus (VARV) and development of modern diagnostics, vaccines and chemotherapies of smallpox and other zoonotic orthopoxviral infections of humans. Taking into account that smallpox vaccination in several cases had adverse side effects, WHO recommended ceasing this vaccination after 1980 in all countries of the world. The result of this decision is that the mankind lost the collective immunity not only to smallpox, but also to other zoonotic orthopoxvirus infections. The ever more frequently recorded human cases of zoonotic orthopoxvirus infections force to renew consideration of the problem of possible smallpox reemergence resulting from natural evolution of these viruses. Analysis of the available archive data on smallpox epidemics, the history of ancient civilizations, and the newest data on the evolutionary relationship of orthopoxviruses has allowed us to hypothesize that VARV could have repeatedly reemerged via evolutionary changes in a zoonotic ancestor virus and then disappeared because of insufficient population size of isolated ancient civilizations. Only the historically last smallpox pandemic continued for a long time and was contained and stopped in the 20th century thanks to the joint efforts of medics and scientists from many countries under the aegis of WHO. Thus, there is no fundamental prohibition on potential reemergence of smallpox or a similar human disease in future in the course of natural evolution of the currently existing zoonotic orthopoxviruses. Correspondingly, it is of the utmost importance to develop and widely adopt state-of-the-art methods for efficient and rapid species-specific diagnosis of all orthopoxvirus species pathogenic for humans, VARV included. It is also most important to develop new safe methods for prevention and therapy of human orthopoxvirus infections.

Drug Development against Smallpox: Present and Future

Forty years after the last endemic smallpox case, variola virus (VARV) is still considered a major threat to humans due to its possible use as a bioterrorism agent. For many years, the risk of disease reemergence was thought to solely be through deliberate misuse of VARV strains kept in clandestine laboratories. However, recent experiments using synthetic biology have proven the feasibility of recreating a poxvirus de novo, implying that VARV could, in theory, be resurrected. Because of this new perspective, the WHO Advisory Committee on VARV Research released new recommendations concerning research on poxviruses that strongly encourages pursuing the development of new antiviral drugs against orthopoxviruses. In 2018, the U.S. FDA advised in favor of two molecules for smallpox treatment, tecovirimat and brincidofovir. This review highlights the difficulties to develop new drugs targeting an eradicated disease, especially as it requires working under the FDA "animal efficacy rule" with the few, and imperfect, animal models available.

Nonclinical data supporting orphan medicinal product designations in the area of rare infectious diseases

This review provides an overview of nonclinical in vivo models that can be used to support orphan designation in selected rare infectious diseases in Europe, with the aim to inform and stimulate the planning of nonclinical development in this area of often neglected diseases.

Preclinical pharmacokinetic evaluation to facilitate repurposing of tyrosine kinase inhibitors nilotinib and imatinib as antiviral agents

Background

Several tyrosine kinase inhibitors (TKIs) developed as anti-cancer drugs, also have anti-viral activity due to their ability to disrupt productive replication and dissemination in infected cells. Consequently, such drugs are attractive candidates for “repurposing” as anti-viral agents. However, clinical evaluation of therapeutics against infectious agents associated with high mortality, but low or infrequent incidence, is often unfeasible. The United States Food and Drug Administration formulated the “Animal Rule” to facilitate use of validated animal models for conducting anti-viral efficacy studies.

Methods

To enable such efficacy studies of two clinically approved TKIs, nilotinib, and imatinib, we first conducted comprehensive pharmacokinetic (PK) studies in relevant rodent and non-rodent animal models. PK of these agents following intravenous and oral dosing were evaluated in C57BL/6 mice, prairie dogs, guinea pigs and Cynomolgus monkeys. Plasma samples were analyzed using an LC-MS/MS method. Secondarily, we evaluated the utility of allometry-based inter-species scaling derived from previously published data to predict the PK parameters, systemic clearance (CL) and the steady state volume of distribution (Vss) of these two drugs in prairie dogs, an animal model not tested thus far.

Results

Marked inter-species variability in PK parameters and resulting oral bioavailability was observed. In general, elimination half-lives of these agents in mice and guinea pigs were much shorter (1–3 h) relative to those in larger species such as prairie dogs and monkeys. The longer nilotinib elimination half-life in prairie dogs (i.v., 6.5 h and oral, 7.5 h), facilitated multiple dosing PK and safety assessment. The allometry-based predicted values of the Vss and CL were within 2.0 and 2.5-fold, respectively, of the observed values.

Conclusions

Our results suggest that prairie dogs and monkeys may be suitable rodent and non-rodent species to perform further efficacy testing of these TKIs against orthopoxvirus infections. The use of rodent models such as C57BL/6 mice and guinea pigs for assessing pre-clinical anti-viral efficacy of these two TKIs may be limited due to short elimination and/or low oral bioavailability. Allometry-based correlations, derived from existing literature data, may provide initial estimates, which may serve as a useful guide for pre-clinical PK studies in untested animal models.

Challenges and Achievements in Prevention and Treatment of Smallpox

Declaration of smallpox eradication by the WHO in 1980 led to discontinuation of the worldwide vaccination campaign. The increasing percentage of unvaccinated individuals, the existence of its causative infectious agent variola virus (VARV), and the recent synthetic achievements increase the threat of intentional or accidental release and reemergence of smallpox. Control of smallpox would require an emergency vaccination campaign, as no other protective measure has been approved to achieve eradication and ensure worldwide protection. Experimental data in surrogate animal models support the assumption, based on anecdotal, uncontrolled historical data, that vaccination up to 4 days postexposure confers effective protection. The long incubation period, and the uncertainty of the exposure status in the surrounding population, call for the development and evaluation of safe and effective methods enabling extension of the therapeutic window, and to reduce the disease manifestations and vaccine adverse reactions. To achieve these goals, we need to evaluate the efficacy of novel and already licensed vaccines as a sole treatment, or in conjunction with immune modulators and antiviral drugs. In this review, we address the available data, recent achievements, and open questions.

Are We Prepared in Case of a Possible Smallpox-Like Disease Emergence?

Smallpox was the first human disease to be eradicated, through a concerted vaccination campaign led by the World Health Organization. Since its eradication, routine vaccination against smallpox has ceased, leaving the world population susceptible to disease caused by orthopoxviruses. In recent decades, reports of human disease from zoonotic orthopoxviruses have increased. Furthermore, multiple reports of newly identified poxviruses capable of causing human disease have occurred. These facts raise concerns regarding both the opportunity for these zoonotic orthopoxviruses to evolve and become a more severe public health issue, as well as the risk of Variola virus (the causative agent of smallpox) to be utilized as a bioterrorist weapon. The eradication of smallpox occurred prior to the development of the majority of modern virological and molecular biological techniques. Therefore, there is a considerable amount that is not understood regarding how this solely human pathogen interacts with its host. This paper briefly recounts the history and current status of diagnostic tools, vaccines, and anti-viral therapeutics for treatment of smallpox disease. The authors discuss the importance of further research to prepare the global community should a smallpox-like virus emerge.

Enhanced efficacy of cidofovir combined with vaccinia immune globulin in treating progressive cutaneous vaccinia virus infections in immunosuppressed hairless mice

The treatment of progressive vaccinia in individuals has involved antiviral drugs, such as cidofovir (CDV), brincidofovir, and/or tecovirimat, combined with vaccinia immune globulin (VIG). VIG is costly, and its supply is limited, so sparing the use of VIG during treatment is an important objective. VIG sparing was modeled in immunosuppressed mice by maximizing the treatment benefits of CDV combined with VIG to determine the effective treatments that delayed the time to death, reduced cutaneous lesion severity, and/or decreased tissue viral titers. SKH-1 hairless mice immunosuppressed with cyclophosphamide and hairless SCID mice (SHO strain) were infected cutaneously with vaccinia virus. Monotherapy, dual combinations (CDV plus VIG), or triple therapy (topical CDV, parenteral CDV, and VIG) were initiated 2 days postinfection and were given every 3 to 4 days through day 11. The efficacy assessment included survival rate, cutaneous lesion severity, and viral titers. Delays in the time to death and the reduction in lesion severity occurred in the following order of efficacy: triple therapy had greater efficacy than double combinations (CDV plus VIG or topical plus parenteral CDV), which had greater efficacy than VIG alone. Parenteral administration of CDV or VIG was necessary to suppress virus titers in internal organs (liver, lung, and spleen). The skin viral titers were significantly reduced by triple therapy only. The greatest efficacy was achieved by triple therapy. In humans, this regimen should translate to a faster cure rate, thus sparing the amount of VIG used for treatment.

In vitro surrogate models to aid in the development of antivirals for the containment of foot-and-mouth disease outbreaks

Foot-and-mouth disease virus (FMDV) is a highly pathogenic member of the genus Aphthovirus (family Picornaviridae) that is only to be manipulated in high-containment facilities, thus complicating research on and discovery of antiviral strategies against the virus. Bovine rhinitis B virus (BRBV) and equine rhinitis A virus (ERAV), phylogenetically most closely related to FMDV, were explored as surrogates for FMDV in antiviral studies. Although no efficient cell culture system has been reported so far for BRBV, we demonstrate that infection of primary bovine kidney cells resulted in an extensive but rather poorly-reproducible induction of cytopathic effect (CPE). Madin-Darby bovine kidney cells on the other hand supported viral replication in the absence of CPE. Antiviral tests were developed for ERAV in Vero A cells employing a viral RNA-reduction assay and CPE-reduction assay; the latter having a Z' factor of 0.83±0.07. The BRBV and ERAV models were next used to assess the anti-aphthovirus activity of two broad-spectrum antiviral agents 2'-C-methylcytidine (2CMC) and ribavirin, as well as of the enterovirus-specific inhibitor enviroxime. The effects of the three compounds in the CPE-reduction (ERAV) and viral RNA-reduction assays (BRBV and ERAV) were comparable. Akin to 2CMC, compound A, a recently-discovered non-nucleoside pan-serotype FMDV inhibitor, also inhibited the replication of both BRBV and ERAV, whereas enviroxime was devoid of activity. The BRBV and ERAV surrogate models reported here can be manipulated in BSL-2 laboratories and may facilitate studies to unravel the mechanism of action of novel FMDV inhibitors.

Orthopoxvirus inhibitors that are active in animal models: an update from 2008 to 2012

Antiviral agents are being sought as countermeasures for the potential deliberate release of smallpox (variola) and monkeypox viruses, for the treatment of naturally acquired monkeypox virus infections, and as therapy for complications due to smallpox (live-attenuated vaccinia virus) vaccination or accidental infection after exposure to vaccinated persons. Reviews of the scientific literature spanning 1950-2008 have documented the progress made in developing small-animal models of poxvirus infection and identifying novel antiviral agents. Compounds of considerable interest include cidofovir, CMX001 and ST-246® (tecovirimat; SIGA Technologies, NY, USA). New inhibitors have been identified since 2008, most of which do not exhibit the kind of potency and selectivity required for drug development. Two promising agents include 4'-thioidoxuridine (a nucleoside analog) and mDEF201 (an adenovirus-vectored interferon). Compounds that have been effectively used in combination studies include vaccinia immune globulin, cidofovir, ST-246 and CMX001. In the future there may be an increase in experimental work using active compounds in combination.

Camelpox, an emerging orthopox viral disease

Camelpox is considered as emerging public health problem during this decade due to increased reported cases and outbreaks in camels. Camelpox is a contagious, often sporadic, and notifiable skin disease of camelids and is socio-economically significant as it incurs considerable loss in terms of morbidity, mortality, loss of weight and reduction in milk yield and confined to camel-rearing countries. The causative agent, camelpox virus (CMLV) is genetically closely related to variola virus and has gained much attention from researchers due to its recent emergence in human. The virus carrying genes responsible for host immune evasion mechanisms owing to the threat posed by potential bio-warfare agents. Although the disease can be diagnosed based on clinical features, the similar confounding skin lesions necessitate identification, detection and differentiation of the CMLV by molecular techniques. Vaccines are available in some countries and the available live attenuated vaccine provides long-lasting immunity. Further, novel highly sensitive and specific techniques would be useful in the identification of emerging and re-emerging virus, thereby therapeutic, prophylactic, preventive measures would be applied in time to curtail further spread of camelpox like other zoonotic diseases. This review provide overview of the camelpox particularly on its epidemiology, pathogenesis and biology of the disease, diagnostic approaches and control measures.

Mutations conferring resistance to viral DNA polymerase inhibitors in camelpox virus give different drug-susceptibility profiles in vaccinia virus

Cidofovir or (S)-HPMPC is one of the three antiviral drugs that might be used for the treatment of orthopoxvirus infections. (S)-HPMPC and its 2,6-diaminopurine counterpart, (S)-HPMPDAP, have been described to select, in vitro, for drug resistance mutations in the viral DNA polymerase (E9L) gene of vaccinia virus (VACV). Here, to extend our knowledge of drug resistance development among orthopoxviruses, we selected, in vitro, camelpox viruses (CMLV) resistant to (S)-HPMPDAP and identified a single amino acid change, T831I, and a double mutation, A314V+A684V, within E9L. The production of recombinant CMLV and VACV carrying these amino acid substitutions (T831I, A314V, or A314V+A684V) demonstrated clearly their involvement in conferring reduced sensitivity to viral DNA polymerase inhibitors, including (S)-HPMPDAP. Both CMLV and VACV harboring the A314V change showed comparable drug-susceptibility profiles to various antivirals and similar impairments in viral growth. In contrast, the single change T831I and the double change A314V+A684V in VACV were responsible for increased levels of drug resistance and for cross-resistance to viral DNA polymerase antivirals that were not observed with their CMLV counterparts. Each amino acid change accounted for an attenuated phenotype of VACV in vivo. Modeling of E9L suggested that the T→I change at position 831 might abolish hydrogen bonds between E9L and the DNA backbone and have a direct impact on the incorporation of the acyclic nucleoside phosphonates. Our findings demonstrate that drug-resistance development in two related orthopoxvirus species may impact drug-susceptibility profiles and viral fitness differently.

Zoonotic Poxviruses Associated with Companion Animals

Simple Summary

Contemporary enthusiasm for the ownership of exotic animals and hobby livestock has created an opportunity for the movement of poxviruses—such as monkeypox, cowpox, and orf—outside their traditional geographic range bringing them into contact with atypical animal hosts and groups of people not normally considered at risk. It is important that pet owners and practitioners of human and animal medicine develop a heightened awareness for poxvirus infections and understand the risks that can be associated with companion animals and livestock. This article reviews the epidemiology and clinical features of zoonotic poxviruses that are most likely to affect companion animals.

Abstract

Understanding the zoonotic risk posed by poxviruses in companion animals is important for protecting both human and animal health. The outbreak of monkeypox in the United States, as well as current reports of cowpox in Europe, point to the fact that companion animals are increasingly serving as sources of poxvirus transmission to people. In addition, the trend among hobbyists to keep livestock (such as goats) in urban and semi-urban areas has contributed to increased parapoxvirus exposures among people not traditionally considered at high risk. Despite the historic notoriety of poxviruses and the diseases they cause, poxvirus infections are often missed. Delays in diagnosing poxvirus-associated infections in companion animals can lead to inadvertent human exposures. Delays in confirming human infections can result in inappropriate treatment or prolonged recovery. Early recognition of poxvirus-associated infections and application of appropriate preventive measures can reduce the spread of virus between companion animals and their owners. This review will discuss the epidemiology and clinical features associated with the zoonotic poxvirus infections most commonly associated with companion animals.

Therapy and long-term prophylaxis of vaccinia virus respiratory infections in mice with an adenovirus-vectored interferon alpha (mDEF201)

An adenovirus 5 vector encoding for mouse interferon alpha, subtype 5 (mDEF201) was evaluated for efficacy against lethal vaccinia virus (WR strain) respiratory infections in mice. mDEF201 was administered as a single intranasal treatment either prophylactically or therapeutically at doses of 10⁶ to 10⁸ plaque forming units/mouse. When the prophylactic treatment was given at 56 days prior to infection, it protected 90% of animals from death (100% protection for treatments given between 1–49 days pre-infection), with minimal weight loss occurring during infection. Surviving animals re-challenged with virus 22 days after the primary infection were protected from death, indicating that mDEF201 did not compromise the immune response against the initial infection. Post-exposure therapy was given between 6–24 h after vaccinia virus exposure and protection was afforded by a 10⁸ dose of mDEF201 given at 24 h, whereas a 10⁷ dose was effective up to 12 h. Comparisons were made of the ability of mDEF201, given either 28 or 1 day prior to infection, to inhibit tissue virus titers and lung infection parameters. Lung, liver, and spleen virus titers were inhibited to nearly the same extent by either treatment, as were lung weights and lung hemorrhage scores (indicators of pneumonitis). Lung virus titers were significantly (>100-fold) lower than in the placebo group, and the other infection parameters in mDEF201 treated mice were nearly at baseline. In contrast, viral titers and lung infection parameters were high in the placebo group on day 5 of the infection. These results demonstrate the long-acting prophylactic and treatment capacity of mDEF201 to combat vaccinia virus infections.

Comparison of the safety and pharmacokinetics of ST-246® after i.v. infusion or oral administration in mice, rabbits and monkeys

BACKGROUND

ST-246® is an antiviral, orally bioavailable small molecule in clinical development for treatment of orthopoxvirus infections. An intravenous (i.v.) formulation may be required for some hospitalized patients who are unable to take oral medication. An i.v. formulation has been evaluated in three species previously used in evaluation of both efficacy and toxicology of the oral formulation.

METHODOLOGY/PRINCIPAL FINDINGS

The pharmacokinetics of ST-246 after i.v. infusions in mice, rabbits and nonhuman primates (NHP) were compared to those obtained after oral administration. Ten minute i.v. infusions of ST-246 at doses of 3, 10, 30, and 75 mg/kg in mice produced peak plasma concentrations ranging from 16.9 to 238 µg/mL. Elimination appeared predominately first-order and exposure dose-proportional up to 30 mg/kg. Short i.v. infusions (5 to 15 minutes) in rabbits resulted in rapid distribution followed by slower elimination. Intravenous infusions in NHP were conducted at doses of 1 to 30 mg/kg. The length of single infusions in NHP ranged from 4 to 6 hours. The pharmacokinetics and tolerability for the two highest doses were evaluated when administered as two equivalent 4 hour infusions initiated 12 hours apart. Terminal elimination half-lives in all species for oral and i.v. infusions were similar. Dose-limiting central nervous system effects were identified in all three species and appeared related to high C(max) plasma concentrations. These effects were eliminated using slower i.v. infusions.

CONCLUSIONS/SIGNIFICANCE

Pharmacokinetic profiles after i.v. infusion compared to those observed after oral administration demonstrated the necessity of longer i.v. infusions to (1) mimic the plasma exposure observed after oral administration and (2) avoid C(max) associated toxicity. Shorter infusions at higher doses in NHP resulted in decreased clearance, suggesting saturated distribution or elimination. Elimination half-lives in all species were similar between oral and i.v. administration. The administration of ST-246 was well tolerated as a slow i.v. infusion.

Developments in antivirals against influenza, smallpox and hemorrhagic fever viruses

INTRODUCTION

the search for effective inhibitors to multiple infectious agents including influenza, smallpox and hemorrhagic fever viruses is an area of active research as many of these agents pose dramatic health and economic challenges to the human population. Many of these infectious agents are not only endemic threats in different parts of the globe, but are also considered to have the potential of being used as bioterrorism agents.

AREAS COVERED

this review focuses on inhibitors that are currently in use in the research community against specific emerging infectious agents and those that have bioterrorism potential. The paper provides information about the availability of FDA approved drugs, whenever applicable, and insights into the specific aspect of the agent life cycle that is affected by drug treatment, when known.

EXPERT OPINION

the key message that is conveyed in this review is that a combination of pathogen and host-based inhibitors may have to be used for successful control of viral replication to limit the development of drug resistance.

Study of camelpox virus pathogenesis in athymic nude mice

Camelpox virus (CMLV) is the closest known orthopoxvirus genetically related to variola virus. So far, CMLV was restricted to camelids but, recently, three human cases of camelpox have been described in India, highlighting the need to pursue research on its pathogenesis, which has been hampered by the lack of small animal models. Here, we confirm that NMRI immunocompetent mice are resistant to intranasal (i.n.) CMLV infection. However, we demonstrate that CMLV induced a severe disease following i.n. challenge of athymic nude mice, which was accompanied with a failure in gaining weight, leading to euthanasia of the animals. On the other hand, intracutaneous (i.c.) infection resulted in disease development without impacting the body weight evolution. CMLV replication in tissues and body fluids was confirmed in the two models. We further analyzed innate immune and B cell responses induced in the spleen and draining lymph nodes after exposure to CMLV. In both models, strong increases in CD11b⁺F4/80⁺ macrophages were seen in the spleen, while neutrophils, NK and B cell responses varied between the routes of infection. In the lymph nodes, the magnitude of CD11c⁺CD8α⁺ lymphoid and CD11c⁺CD11b⁺ myeloid dendritic cell responses increased in i.n. challenged animals. Analysis of cytokine profiles revealed significant increases of interleukin (IL)-6 and IL-18 in the sera of infected animals, while those of other cytokines were similar to uninfected controls. The efficacy of two antivirals (cidofovir or HPMPC, and its 2, 6-diaminopurine analog) was evaluated in both models. HPMPC was the most effective molecule affording 100% protection from morbidity. It appeared that both treatments did not affect immune cell responses or cytokine expression. In conclusion, we demonstrated that immunodeficient mice are permissive for CMLV propagation. These results provide a basis for studying the pathogenesis of CMLV, as well as for evaluating potential antiviral therapies in an immunodeficiency context.

Topical treatment of cutaneous vaccinia virus infections in immunosuppressed hairless mice with selected antiviral substances

BACKGROUND

Certain nucleoside, nucleotide and pyrophosphate analogues may be useful for treating severe complications arising as a result of virus dissemination following smallpox (live vaccinia virus) vaccinations, especially in immunocompromised individuals. We used an immunosuppressed hairless mouse model to study the effects of 10 antiviral agents on progressive vaccinia infections.

METHODS

Hairless mice were immunosuppressed by treatment with cyclophosphamide (100 mg/kg) every 4 days starting 1 day prior to vaccinia virus (WR strain) infection of wounded skin. Topical treatments with antiviral agents were applied twice a day for 7 days starting 5 days after virus exposure.

RESULTS

Topical 1% cidofovir cream treatment was effective in significantly reducing primary lesion severity and decreasing the number of satellite lesions. Topical 1% cyclic HPMPC and 1% phosphonoacetic acid were not quite as active as cidofovir. Ribavirin (5%) treatment reduced lesion severity and diminished the numbers of satellite lesions, but the mice died significantly sooner than placebos. 2-Amino-7-[(1,3,-dihydroxy-2-propoxy)methyl]purine (compound S2242; 1%) moderately reduced primary lesion sizes. Ineffective treatments included 5% arabinosyladenine, 1% arabinosylcytosine, 1% 5-chloro-arabinosylcytosine, 5% arabinosylhypoxanthine 5-monophosphate and 5% viramidine.

CONCLUSIONS

Of the compounds tested, topically applied cidofovir was the most effective treatment of cutaneous vaccinia virus infections in immunosuppressed mice. Topical treatment with cidofovir could be considered as an adjunct to intravenous drug therapy for serious infections.

Polycyclic N-benzamido imides with potent activity against vaccinia virus

The synthesis and antiviral activity of a series of novel polycyclic analogues of the orthopoxvirus egress inhibitor tecovirimat (ST-246) is presented. Several of these compounds display sub-micromolar activity against vaccinia virus, and were more potent than cidofovir (CDV). The more active compounds were about 10-fold more active than CDV, with minimum cytotoxic concentrations above 100 μM. Chemical manipulations of the two carbon-carbon double bonds present in the compounds were carried out to further explore the structure-activity relationships of these new polycyclic imides. Hydrogenation of the two carbon-carbon double bonds decreases antiviral activity, whereas either cyclopropanation or epoxidation of the double bonds fully eliminates the antiviral activity.

Cidofovir Activity against Poxvirus Infections

Cidofovir [(S)-1-(3-hydroxy-2-phosphonylmethoxypropyl)cytosine, HPMPC] is an acyclic nucleoside analog approved since 1996 for clinical use in the treatment of cytomegalovirus (CMV) retinitis in AIDS patients. Cidofovir (CDV) has broad-spectrum activity against DNA viruses, including herpes-, adeno-, polyoma-, papilloma- and poxviruses. Among poxviruses, cidofovir has shown in vitro activity against orthopox [vaccinia, variola (smallpox), cowpox, monkeypox, camelpox, ectromelia], molluscipox [molluscum contagiosum] and parapox [orf] viruses. The anti-poxvirus activity of cidofovir in vivo has been shown in different models of infection when the compound was administered either intraperitoneal, intranasal (aerosolized) or topically. In humans, cidofovir has been successfully used for the treatment of recalcitrant molluscum contagiosum virus and orf virus in immunocompromised patients. CDV remains a reference compound against poxviruses and holds potential for the therapy and short-term prophylaxis of not only orthopox- but also parapox- and molluscipoxvirus infections.

Development of ST-246® for Treatment of Poxvirus Infections

ST-246 (Tecovirimat) is a small synthetic antiviral compound being developed to treat pathogenic orthopoxvirus infections of humans. The compound was discovered as part of a high throughput screen designed to identify inhibitors of vaccinia virus-induced cytopathic effects. The antiviral activity is specific for orthopoxviruses and the compound does not inhibit the replication of other RNA- and DNA-containing viruses or inhibit cell proliferation at concentrations of compound that are antiviral. ST-246 targets vaccinia virus p37, a viral protein required for envelopment and secretion of extracellular forms of virus. The compound is orally bioavailable and protects multiple animal species from lethal orthopoxvirus challenge. Preclinical safety pharmacology studies in mice and non-human primates indicate that ST-246 is readily absorbed by the oral route and well tolerated with the no observable adverse effect level (NOAEL) in mice measured at 2000 mg/kg and the no observable effect level (NOEL) in non-human primates measured at 300 mg/kg. Drug substance and drug product processes have been developed and commercial scale batches have been produced using Good Manufacturing Processes (GMP). Human phase I clinical trials have shown that ST-246 is safe and well tolerated in healthy human volunteers. Based on the results of the clinical evaluation, once a day dosing should provide plasma drug exposure in the range predicted to be antiviral based on data from efficacy studies in animal models of orthopoxvirus disease. These data support the use of ST-246 as a therapeutic to treat pathogenic orthopoxvirus infections of humans.

Rabbitpox: a model of airborne transmission of smallpox

Smallpox is a human disease caused by infection with variola virus, a member of the genus Orthopoxvirus. Although smallpox has been eradicated, concern that it might be reintroduced through bioterrorism has therefore led to intensive efforts to develop new vaccines and antiviral drugs against this disease. Because these vaccines and therapeutics cannot be tested in human trials, it is necessary to test such medical countermeasures in different animal models. Although several orthopoxviruses cause disease in laboratory animals, only rabbitpox virus (RPXV) infection of rabbits shows patterns of natural airborne transmission similar to smallpox. Studies have shown that a smallpox-like disease can be produced in rabbits in a controlled fashion through exposure to a small-particle RPXV aerosol, and rabbitpox spreads from animal to animal by the airborne route in a laboratory setting. This model can therefore be utilized to test drugs and vaccines against variola virus and other aerosolized orthopoxviruses.

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

Monkeypox virus (MPXV) infection in humans results in clinical symptoms very similar to ordinary smallpox. Aerosol is a route of secondary transmission for monkeypox, and a primary route of smallpox transmission in humans. Therefore, an animal model for aerosol exposure to MPXV is needed to test medical countermeasures. To characterize the pathogenesis in cynomolgus macaques (Macaca fascicularis), groups of macaques were exposed to four different doses of aerosolized MPXV. Blood was collected the day before, and every other day after exposure and assessed for complete blood count (CBC), clinical chemistry analysis, and quantitative PCR. Macaques showed mild anorexia, depression, and fever on day 6 post-exposure. Lymphadenopathy, which differentiates monkeypox from smallpox, was observed in exposed macaques around day 6 post-exposure. CBC and clinical chemistries showed abnormalities similar to human monkeypox cases. Whole blood and throat swab viral loads peaked around day 10, and in survivors, gradually decreased until day 28 post-exposure. Survival was not dose dependent. As such, doses of 4 × 10(4) PFU, 1 × 10(5) PFU, or 1 × 10(6) PFU resulted in lethality for 70% of the animals, whereas a dose of 4 × 10(5) PFU resulted in 85% lethality. Overall, cynomolgus macaques exposed to aerosolized MPXV develop a clinical disease that resembles that of human monkeypox. These findings provide a strong foundation for the use of aerosolized MPXV exposure of cynomolgus macaques as an animal model to test medical countermeasures against orthopoxviruses.

Lack of efficacy of aurintricarboxylic acid and ethacrynic acid against vaccinia virus respiratory infections in mice

BACKGROUND

Aurintricarboxylic acid (ATA) and ethacrynic acid (ECA) have been reported to exhibit antiviral activity against vaccinia virus infections in cell culture by inhibiting early and late gene transcription, respectively. The purpose of this work was to determine if these inhibitors would effectively treat vaccinia virus infections in mice, which has not previously been studied.

METHODS

ECA was investigated by cell culture plaque reduction assay for the inhibition of cowpox and vaccinia virus infections to clarify issues regarding its potency and selectivity. Mice infected intranasally with vaccinia virus were treated by intraperitoneal route twice daily for 5 days with ATA (10 and 30 mg/kg/day) and ECA (15 and 30 mg/kg/day) or once daily for 2 days with cidofovir (100 mg/kg/day).

RESULTS

ECA caused 50% inhibition of virus plaque formation at 20-79 muM in four cultured cell lines, with 50% cytotoxicity at 84-173 muM, giving low (1.3-4.2) selectivity index values. Preliminary toxicity tests in uninfected mice indicated that ATA and ECA were both overtly toxic at 100 mg/kg/day. No protection from mortality was afforded by treatment of vaccinia virus infections with ATA or ECA, but 100% survival was achieved in the cidofovir group. ATA- and ECA-treated mice died significantly sooner than placebo-treated animals, indicating that these compounds exacerbated the infection.

CONCLUSIONS

Both ATA and ECA lack antiviral potency and selectivity in cell culture. The compounds were ineffective in treating mice at intraperitoneal doses of <or=30 mg/kg/day. These compounds do not appear to have potential for the treatment of poxvirus infections in vivo.

Effective post-exposure protection against lethal orthopoxviruses infection by vaccinia immune globulin involves induction of adaptive immune response

The therapeutic potential of human vaccinia immunoglobulin (VIG) in orthopoxvirus infection was examined using two mouse models for human poxvirus, based on Ectromelia virus and Vaccinia Western Reserve (WR) respiratory infections. Despite the relatively fast clearance of human VIG from mice circulation, a single VIG injection protected immune-competent mice against both infections. Full protection against lethal Ectromelia virus infection was achieved by VIG injection up to one day post-exposure, and even injection of VIG two or three days post-infection conferred solid protection (60-80%). Nevertheless, VIG failed to protect VACV-WR challenged immune-deficient mice, even though repeated injections prolonged SCID mice survival. These results suggest the involvement of host immunity in protection. VIG provides the initial protective time-window allowing induction of the adaptive response required to achieve complete protection. Additionally, VIG can be administered in conjunction with active Vaccinia-Lister vaccination. Vaccine efficiency is not impaired, providing a non-prohibitive VIG dose is used. Thus, VIG can be used as a prophylactic measure against post-vaccinal complications but could also serve for post-exposure treatment against smallpox.