Proof of concept for the inhibition of foot-and-mouth disease virus replication by the anti-viral drug 2'-C-methylcytidine in severe combined immunodeficient mice

Antiviral agents and disinfectants for foot‑and‑mouth disease (Review)

Fluorouracil, 5-azacytidine, 6-azauridine, ribavirin, favipiravir (T-705) and its derivative (T-1105) exhibit anti-foot-and-mouth disease virus (FMDV) effects. In particular, T-1105 exhibits promising results when administered to guinea pigs orally, and pigs in their feed. FMDV is excreted in the early stages of infection in aerosols and oral or nasal droplets from animals. T-1105 along with the FMDV vaccine can be used to combat foot-and-mouth disease (FMD) epidemics. Several studies have shown that sodium hypochlorous solutions are widely used to inactivate viruses, including FMDV. However, these solutions must be stored under cool and dark conditions to maintain their virucidal effects. Interestingly, a study indicated that the virucidal activity of a calcium bicarbonate solution with a mesoscopic structure (CAC-717) did not decrease after storage at room temperature for at least four years outside direct sunlight. Numerous lessons acquired from the 2010 FMD outbreak in Japan are relevant for the control of COVID-19. However, the widespread use of chlorite can cause environmental issues. Chlorite can be combined with nitrogen to produce chloramine or N-nitrosodimethylamine, which plays a role in carcinogenesis. Therefore, risk assessments should be conducted in aquatic environments. Moreover, there is a need to develop nonchlorine disinfectants that can be used during epidemics, including FMD. The approach of 'One Health' should be shared between the public health and veterinary fields to improve the management of viral outbreaks, including those due to FMD.

The prevalence of foot-and-mouth disease in Asia

Foot-and-mouth disease (FMD) is listed among the highly contagious diseases in animals and is endemic throughout the Asian continent. The disease is caused by the Foot-and-mouth disease virus (FMDV) and affects a wide variety of domesticated animals as well as wild ungulates. Clinically, the disease is described as a vesicular lesion on the tongue, muzzle, lips, gum, dental pad, interdigital cleft, coronary band, and heel of the foot. Sometimes these lesions give rise to lameness. Mastitis is also caused due to teat lesions. A biochemical test reveals that during FMD infection, there are elevated levels of interleukin-1 (IL-1), tumor necrosis factor-alpha, interferon-gamma (IFN-γ), interleukin-6, serum amyloid A protein, lactoferrin, mannose-binding lectin, and monocytes chemo-attractant protein-1 in the serum of infected animals. There is no specific treatment for FMD although some antivirals are given as prophylaxis and antibiotics are given to prevent secondary bacterial infection. This review presents comprehensive data on the prevalence of FMD and serotypes of FMDV that are attributable to the cause of FMD from a regional point of view. It also explains the worldwide dynamics of the seven serotypes of FMD and tries to identify epidemiological clusters of FMD in various geographical areas. Furthermore, the pathology associated with the foot and mouth disease virus along with the pathophysiology is discussed. The continent-wide prevalence and diversity patterns of FMD suggest that there is a need for stringent policies and legislation implementation regarding research and development aimed at manufacturing strain-specific vaccination, infection prevention, and control of the disease.

A SCID Mouse Model To Evaluate the Efficacy of Antivirals against SARS-CoV-2 Infection

Ancestral severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) lacks the intrinsic ability to bind to the mouse ACE2 receptor, and therefore establishment of SARS-CoV-2 mouse models has been limited to the use of mouse-adapted viruses or genetically modified mice. Interestingly, some of the variants of concern, such as the Beta B.1.351 variant, show an improved binding to the mouse receptor and hence better replication in different wild-type (WT) mouse species. Here, we describe the establishment of a SARS-CoV-2 Beta B.1.351 variant infection model in male SCID mice as a tool to assess the antiviral efficacy of potential SARS-CoV-2 small-molecule inhibitors. Intranasal infection of male SCID mice with 10⁵ 50% tissue culture infective doses (TCID₅₀) of the Beta B.1.351 variant resulted in high viral loads in the lungs and moderate signs of lung pathology on day 3 postinfection. Treatment of infected mice with the antiviral drugs molnupiravir (200 mg/kg, twice a day [BID]) or nirmatrelvir (300 mg/kg, BID) for 3 consecutive days significantly reduced the infectious virus titers in the lungs by 2 and 3.9 log₁₀ TCID₅₀/mg of tissue, respectively, and significantly improved lung pathology. Together, these data demonstrate the validity of this SCID mouse Beta B.1.351 variant infection model as a convenient preclinical model for assessment of potential activity of antivirals against SARS-CoV-2.

IMPORTANCE Unlike the ancestral SARS-CoV-2 strain, the Beta (B.1.351) variant of concern has been reported to replicate to some extent in WT mice (C57BL/6 and BALB/c). We demonstrate here that infection of SCID mice with the Beta variant resulted in high viral loads in the lungs on day 3 postinfection. Treatment of infected mice with molnupiravir or nirmatrelvir for 3 consecutive days markedly reduced the infectious virus titers in the lungs and improved lung pathology. The SARS-CoV2 SCID mouse infection model, which is ideally suited for antiviral studies, offers an advantage in comparison to other SARS-CoV2 mouse models, in that there is no need for the use of mouse-adapted virus strains or genetically modified mice. Mouse models also have advantages over hamster models because (i) lower amounts of test drugs are needed, (ii) more animals can be housed in a cage, and (iii) reagents to analyze mouse samples are more readily available than those for hamsters.

Targeting viral genome synthesis as broad-spectrum approach against RNA virus infections

Zoonotic spillover, i.e. pathogen transmission from animal to human, has repeatedly introduced RNA viruses into the human population. In some cases, where these viruses were then efficiently transmitted between humans, they caused large disease outbreaks such as the 1918 flu pandemic or, more recently, outbreaks of Ebola and Coronavirus disease. These examples demonstrate that RNA viruses pose an immense burden on individual and public health with outbreaks threatening the economy and social cohesion within and across borders. And while emerging RNA viruses are introduced more frequently as human activities increasingly disrupt wild-life eco-systems, therapeutic or preventative medicines satisfying the “one drug-multiple bugs”-aim are unavailable. As one central aspect of preparedness efforts, this review digs into the development of broadly acting antivirals via targeting viral genome synthesis with host- or virus-directed drugs centering around nucleotides, the genomes’ universal building blocks. Following the first strategy, selected examples of host de novo nucleotide synthesis inhibitors are presented that ultimately interfere with viral nucleic acid synthesis, with ribavirin being the most prominent and widely used example. For directly targeting the viral polymerase, nucleoside and nucleotide analogues (NNAs) have long been at the core of antiviral drug development and this review illustrates different molecular strategies by which NNAs inhibit viral infection. Highlighting well-known as well as recent, clinically promising compounds, structural features and mechanistic details that may confer broad-spectrum activity are discussed. The final part addresses limitations of NNAs for clinical development such as low efficacy or mitochondrial toxicity and illustrates strategies to overcome these.

In vitro antiviral efficacy of pleconaril and ribavirin on foot-and-mouth disease virus replication

Antiviral therapy is a promising strategy to control acute viral infections. FMDV causes an acute infection and the vaccination provides a protective immunity 7 days post immunization. If the infection is uncontained, then it affects the entire herd. In such circumstances, if antiviral drug is administered the infection can be checked in a herd. Ribavirin is known to cure persistently infected BHK21 cells with FMD virus. However, there have been no systematic studies on antiviral activity of ribavirin against FMDV at different time points with the application of ELISA, PCR or real-time PCR. Pleconaril is known to inhibit enteroviruses and rhinoviruses but has not been explored on FMDV. Hence, the present study evaluates the in vitro antiviral efficacy of pleconaril and ribavirin on FMDV replication. The maximum non-toxic concentrations (MNTC) of pleconaril and ribavirin for BHK21 cells respectively were 7.81 μg/50 μL and 15.62 μg/50 μL. Thus, drug concentrations below MNTC were tested for their antiviral activity against serial tenfold diluted FMDV O, A and Asia 1 serotypes. Pleconaril did not inhibit FMDV serotype O replication at 7.5 μg/50 μL based on CPE inhibition assay and this was further confirmed using sandwich ELISA, PCR/real-time PCR. On the other hand, ribavirin at 15.62 μg/50 μL inhibited the in vitro replication of FMDV O, A and Asia 1 and the inhibition was confirmed by serotype specific sandwich ELISA, PCR and real-time PCR assays. The inhibition was directly proportional to the concentration of ribavirin. Therefore, ribavirin could be explored for its in vivo efficacy as a potential therapeutic in the prevention of early spread of FMDV infection in a herd.

Viral RNA-Dependent RNA Polymerase Inhibitor 7-Deaza-2'-C-Methyladenosine Prevents Death in a Mouse Model of West Nile Virus Infection

West Nile virus (WNV) is a medically important emerging arbovirus causing serious neuroinfections in humans and against which no approved antiviral therapy is currently available. In this study, we demonstrate that 2'-C-methyl- or 4'-azido-modified nucleosides are highly effective inhibitors of WNV replication, showing nanomolar or low micromolar anti-WNV activity and negligible cytotoxicity in cell culture. One representative of C2'-methylated nucleosides, 7-deaza-2'-C-methyladenosine, significantly protected WNV-infected mice from disease progression and mortality. Twice daily treatment at 25 mg/kg starting at the time of infection resulted in 100% survival of the mice. This compound was highly effective, even if the treatment was initiated 3 days postinfection, at the time of a peak of viremia, which resulted in a 90% survival rate. However, the antiviral effect of 7-deaza-2'-C-methyladenosine was absent or negligible when the treatment was started 8 days postinfection (i.e., at the time of extensive brain infection). The 4'-azido moiety appears to be another important determinant for highly efficient inhibition of WNV replication in vitro However, the strong anti-WNV effect of 4'-azidocytidine and 4'-azido-aracytidine was cell type dependent and observed predominantly in porcine kidney stable (PS) cells. The effect was much less pronounced in Vero cells. Our results indicate that 2'-C-methylated or 4'-azidated nucleosides merit further investigation as potential therapeutic agents for treating WNV infections as well as infections caused by other medically important flaviviruses.

Nucleoside analogs as a rich source of antiviral agents active against arthropod-borne flaviviruses

Nucleoside analogs represent the largest class of small molecule-based antivirals, which currently form the backbone of chemotherapy of chronic infections caused by HIV, hepatitis B or C viruses, and herpes viruses. High antiviral potency and favorable pharmacokinetics parameters make some nucleoside analogs suitable also for the treatment of acute infections caused by other medically important RNA and DNA viruses. This review summarizes available information on antiviral research of nucleoside analogs against arthropod-borne members of the genus Flavivirus within the family Flaviviridae, being primarily focused on description of nucleoside inhibitors of flaviviral RNA-dependent RNA polymerase, methyltransferase, and helicase/NTPase. Inhibitors of intracellular nucleoside synthesis and newly discovered nucleoside derivatives with high antiflavivirus potency, whose modes of action are currently not completely understood, have drawn attention. Moreover, this review highlights important challenges and complications in nucleoside analog development and suggests possible strategies to overcome these limitations.

Synthesis and in-vitro evaluation of 2-amino-4-arylthiazole as inhibitor of 3D polymerase against foot-and-mouth disease (FMD)

Foot-and-mouth disease (FMD) is a highly contagious vesicular disease of livestock caused by a highly variable RNA virus, foot-and-mouth disease virus (FMDV). One of the targets to suppress expansion of and to control FMD is 3D polymerase (FMDV 3Dpol). In this study, 2-amino-4-arylthiazole derivatives were synthesized and evaluated for their inhibitory activity against FMDV 3Dpol. Among them, compound 20i exhibited the most potent functional inhibition (IC50 = 0.39 μM) of FMDV 3D polymerase and compound 24a (EC50 = 13.09 μM) showed more potent antiviral activity than ribavirin (EC50 = 1367 μM) and T1105 (EC50 = 347 μM) with IBRS-2 cells infected by the FMDV O/SKR/2010 strain.

Inhibition of viral RNA polymerases by nucleoside and nucleotide analogs: therapeutic applications against positive-strand RNA viruses beyond hepatitis C virus

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New therapies for infections caused by positive-strand RNA viruses are needed.

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Novel nucleoside and nucleotide analogs that inhibit HCV have been developed.

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Some of these molecules also inhibit other positive-strand RNA viruses.

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Optimization of antiviral potency and/or target delivery is necessary.

A number of important human infections are caused by positive-strand RNA viruses, yet almost none can be treated with small molecule antiviral therapeutics. One exception is the chronic infection caused by hepatitis C virus (HCV), against which new generations of potent inhibitors are being developed. One of the main molecular targets for anti-HCV drugs is the viral RNA-dependent RNA polymerase, NS5B. This review summarizes the search for nucleoside and nucleotide analogs that inhibit HCV NS5B, which led to the FDA approval of sofosbuvir in 2013. Advances in anti-HCV therapeutics have also stimulated efforts to develop nucleoside analogs against other positive-strand RNA viruses. Although it remains to be validated in the clinic, the prospect of using nucleoside analogs to treat acute infections caused by RNA viruses represents an important paradigm shift and a new frontier for future antiviral therapies.

Next-generation sequencing in veterinary medicine: how can the massive amount of information arising from high-throughput technologies improve diagnosis, control, and management of infectious diseases?

The development of high-throughput molecular technologies and associated bioinformatics has dramatically changed the capacities of scientists to produce, handle, and analyze large amounts of genomic, transcriptomic, and proteomic data. A clear example of this step-change is represented by the amount of DNA sequence data that can be now produced using next-generation sequencing (NGS) platforms. Similarly, recent improvements in protein and peptide separation efficiencies and highly accurate mass spectrometry have promoted the identification and quantification of proteins in a given sample. These advancements in biotechnology have increasingly been applied to the study of animal infectious diseases and are beginning to revolutionize the way that biological and evolutionary processes can be studied at the molecular level. Studies have demonstrated the value of NGS technologies for molecular characterization, ranging from metagenomic characterization of unknown pathogens or microbial communities to molecular epidemiology and evolution of viral quasispecies. Moreover, high-throughput technologies now allow detailed studies of host-pathogen interactions at the level of their genomes (genomics), transcriptomes (transcriptomics), or proteomes (proteomics). Ultimately, the interaction between pathogen and host biological networks can be questioned by analytically integrating these levels (integrative OMICS and systems biology). The application of high-throughput biotechnology platforms in these fields and their typical low-cost per information content has revolutionized the resolution with which these processes can now be studied. The aim of this chapter is to provide a current and prospective view on the opportunities and challenges associated with the application of massive parallel sequencing technologies to veterinary medicine, with particular focus on applications that have a potential impact on disease control and management.