[Vaccines to prevent Ebola virus disease: current challenges and perspectives]

RELEVANCE

Ebola virus disease (EVD) is an acute infectious disease with an extremely high case fatality rate reaching up to 90%. EVD has become widely known since 2014-2016, when outbreak in West Africa occurred and led to epidemic, which caused travel-related cases on the territory of other continents. There are two vaccines against EVD, prequalified by WHO for emergency use, as well as a number of vaccines, approved by local regulators in certain countries. However, even with the availability of effective vaccines, the lack of data on immune correlates of protection and duration of protective immune response in humans and primates is limiting factor for effectively preventing the spread of EVD outbreaks.

AIMS

This review highlights experience of use of EVD vaccines during outbreaks in endemic areas, summarizes data on vaccine immunogenicity in clinical trials, and discusses perspectives for further development and use of effective EVD vaccines.

The Omicron Variant of the Sars-Cov-2 Virus As the Dominant Agent of a New Risk of Disease amid the COVID-19 Pandemic

Over the two years that have passed since the WHO announced on March 11, 2020, a pandemic of the new coronavirus disease COVID-19, more than 460 million cases of the disease have been detected in the world, of which more than five million have been fatal. During the natural evolution of the COVID-19 pathogen, dominant variants emerge that account for most new infections. The WHO constantly monitors coronavirus mutations that potentially pose an epidemiological danger. Currently, the WHO divides modified variants of the SARS-CoV-2 virus into variants of concern (VOC) and variants of interest (VOI). The WHO-designated group of variants of concern includes potentially the most dangerous lines, which are characterized by a complex of new properties. This group also includes the Omicron variant, which has become the dominant agent of the new wave of the COVID-19 pandemic. The aim of this work is to analyze the characteristics of the SARS-CoV-2 Omicron strain, the dominant agent of the new wave of the COVID-19 pandemic. The proposed mechanism of origin of the Omicron variant, its geographical distribution, the features of the disease caused by it, and the distinguishing features from diseases caused by the Delta variant and the original Wuhan strain of the SARS-CoV-2 virus, mutations of the Omicron variant compared to the parent strain of the SARS-CoV-2 virus, the genetic variability of the Omicron variant, and the epidemiological characteristics of the disease it causes are considered. Particular attention is paid to evaluation of the preventive and therapeutic effectiveness of the existing medical means of protection against COVID-19 in relation to the Omicron strain.

[The molecular evolution of Dabie bandavirus (Phenuiviridae: Bandavirus: Dabie bandavirus), the agent of severe fever with thrombocytopenia syndrome]

Since the Dabie bandavirus (DBV; former SFTS virus, SFTSV) was identified, the epidemics of severe fever with thrombocytopenic syndrome (SFTS) caused by this virus have occurred in several countries in East Asia. The rapid increase in incidence indicates that this infectious agent has a pandemic potential and poses an imminent global public health threat.The analysis of molecular evolution of SFTS agent that includes its variants isolated in China, Japan and South Korea was performed in this review. The evolution rate of DBV and the estimated dates of existence of the common ancestor were ascertained, and the possibility of reassortation was demonstrated.The evolutionary rates of DBV genome segments were estimated to be 2.28 × 10-4 nucleotides/site/year for S-segment, 2.42 × 10-4 for M-segment, and 1.19 × 10-4 for L-segment. The positions of positive selection were detected in the viral genome.Phylogenetic analyses showed that virus may be divided into two clades, containing six different genotypes. The structures of phylogenetic trees for S-, M- and L-segments showed that all genotypes originate from the common ancestor.Data of sequence analysis suggest that DBV use several mechanisms to maintain the high level of its genetic diversity. Understanding the phylogenetic factors that determine the virus transmission is important for assessing the epidemiological characteristics of the disease and predicting its possible outbreaks.

Analysis of Promising Approaches to COVID-19 Vaccine Development

The number of confirmed COVID-19 cases worldwide amounted to 50 million at the beginning of November 2020. This is clearly not enough for the formation of herd immunity, which will prevent repeated outbreaks of the disease. Quarantine measures can only curb the spread of the disease to some extent, therefore specific preventive measures are needed to create collective immunity to COVID-19.The underlying principle of collective immunity is indirect protection of the whole of the population by immunising a certain part of it. Vaccination is the most effective approach to prevention of epidemic outbreaks.

The aim of the study was to analyse promising approaches to the development of vaccines against novel coronavirus COVID-19 infection. The paper summarises data on development studies and clinical trials of COVID-19 vaccines conducted in different countries. It analyses the pros and cons of different platforms for vaccine development (attenuated vaccines, inactivated vaccines, subunit vaccines, DNA and RNA vaccines, recombinant vector vaccines). The paper presents a potential design of novel vaccines. It was concluded that COVID-19 vaccines might be developed both for immunising high-risk groups and for mass immunisation. An optimal solution for the second task would be to develop human or monkey adenovirus vector-based vaccines whose mass production has already been unveiled.

[Virus specific antibody - based remedies for the urgent prevention and treatment of Ebola virus disease]

The Ebola virus (member of Ebolavirus genus Filoviridae family) is the etiologic agent of extremely hazard human disease with high mortality rates (up to 90%). The most important components of spectrum of therapeutics for special prophylactic and current of disease, caused by Ebola virus, are prepares, based on virus specific antibodies (convalescent's plasma, geterologic immunoglobulins, monoclonal antibodies. The use of different class therapeutics, based on virus specific antibodies, the possible improvements of its composition and strategy of its application for special prophylactic and current of disease, caused by Ebola virus, are considered in this review.

[The use of transgenic mosquitoes for prevention of spread of arboviral diseases.]

The mosquitoes of Aedes genus are the most important vector such arboviral diseases as dengue, yellow, Chikungunya, West Nile and Zika fevers. Work is currently in progress to control the transmission of agents of these diseases by forming of transgenic mosquitoes in order to altering the capacity of wild mosquitoes to support of virus replication. There are two main strategies of genetic control of mosquitoes population. Sterile Insect Technique (SIT), that mainly uses population suppression methods for making self-sustaining genetic systems and Release of insects carrying of a Dominant Lethal (RIDL) that uses mainly gene transfer methods for making of self-limiting genetic systems. The RIDL is more expensive, but it has some significant preferences, according compares with SIT. The field trials of genetic control methods are conducted in several countries from 2009 to present time. Genetic control, transgenic technologies to induce sterility, genetic elimination and stable transformation of Aedes mosquitoes are viewed in this review.

[The use of genetic engineering constructions as control samples on evaluation of diagnostic kits for reveal of rna of hazard and extremely hazard agents of virus infections by reverse transcription - polymerase chain reaction.]

The reverse transcription - polymerase chain reaction method (RT-PCR) has leading position on diagnostic infections, caused by RNA-containing viruses. This method presents severe requirements to carrying out of everybody stages of analysis (extraction of nucleic acid, carry out reverse transcription, amplification of DNA). It is necessary to account the possibility of false positive or false negative results appearance. The use on RT-PCR only positive (PCS) and negative (NCS) control samples is insufficient for the control of stages of RNA extraction and reverse transcription. That is way there is necessity the construction of inner control sample (ICS) to control of these stages. The main goal of present is the ground of use genetic engineering constructions (GEC) as control samples (PCS and ICS) on evaluation of diagnostic kits for reveal of RNA of hazard and extremely hazard agents of virus infections by RT-PCR. The vector recombinant plasmids, containing the insertion of cDNA of agent´s genomic RNA are used as PCS, RNA was packed in membrane protein of MS2 bacteriophage, is used as ICS. It is demonstrated that ICS does no influence on sensitivity of RT-PCR both for use of native agents and for use of synthetic nucleic acids of Ebola, Marburg, Lassa, Machupo, Venezuelan encephalitis equine (VEE), Rift Valley fever and rabies viruses. The possibility of use of PCS and ICS for standardization of diagnostic kits is discussed.

[The use of monoclonal antibodies for the treatment of Ebola virus disease.]

Some drugs candidates for treatment of Ebola virus disease (EVD), have been studied, monoclonal antibody (mAb) cocktails have shown great potential as EVD therapeutics. The advantages of mAb therapy include low toxicity, high specifcity and versatility, with the range of biological effects being dependent upon the Fc region. Functions of mAbs include pathogen opsonisation, complement activation, antibody-dependent cell cytotoxicity and virus neutralization characteristics. The most known mAb cocktail, used as therapeutic, is ZMapр, manufactured by «Leaf Biopharmaceutical» from 2004. The elaborated mAb cocktails, structures and properties s of mAbs, the protective characteristics of mAbs and development of new pan-ebolavirus mAbs are reviewed in this article.

[Plasmids of archaea as possible ancestors of DNA-containing viruses]

Тhе kingdom Archaea, as well as Bacteria, belongs to the overkingdom Prokaryota. Halophilic archaea (Halorubrum lacusprofundi) isolated from Antarctic saline lakes contain plasmids (pR1SE) that code proteins taking part in the formation of membranes of archaea vesicles. The molecular and biological properties of pR1SE and the peculiarity of its interaction with sensitive cells are considered in this article. The role of structural proteins coded by pR1S in the process of formation of vesicle membrane complex is paid special attention. Plasmid-containing archaea vesicles model some properties of viruses. Archaea plasmids can be viewed as possible ancestors of DNA-containing viruses.

LLOVIU VIRUS - A NOVEL FILOVIRUS, ENDEMIC IN EUROPE

The data on a recently revealed novel filovirus (Lloviu virus, family Filoviridae, genera Cuevavirus) in Europe are viewed in this issue. The molecular-biological properties of genome fragments of Lloviu virus were isolated from perished bats (Miniopterus sсhreibersii). Because infectious Lloviu virus has not been isolated yet, the capacity of virus to infect cells of different species and its potential to cause disease in humans is unclear. The recombinant vectors (vesicular stomatitis virus and plasmids) expressing structural proteins of Lloviu virus were used to study different elements of the virus. The question of interaction of structural proteins of Lloviu virus expressed by recombinant vectors with receptors of bat and human cells is considered. The possibility of pathogenicity of the novel agent for humans is considered. The conclusion is made about the necessity of continuous epidemical and epizootical monitoring of the new filovirus infection.

GIANT VIRUSES: ORIGIN, SPREADING, TAXONOMICAL, STRUCTURAL-MORPHOLOGICAL AND MOLECULAR-BIOLOGICAL CHARACTERISTICS

The brief review is devoted to description of the discovery of giant viruses belonging to the families of Mimiviridae and Marseilleviridae, as well as unassigned genera Pithoviruses, Pandoravirus, and Molliviruses. The review presents issues of their origin, evolution, and molecular-biological characteristics.

Severe fever with thrombocytopenia syndrome: the disease, caused by the novel phlebovirus

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease caused by a new virus (SFTS virus) reported to be endemic to central and northeastern parts of China. SFTS virus, which is classified into the genus Phlebovirus (the Bunyaviridae family), is suspected to be a tick-borne virus owing to evidence in two species of ticks: Haemaphysalis longicornis and Rhipicephalus microplus. SFTS virus is detected among many species of domestic animals in China. The clinical symptoms of SFTS include fever, thrombocytopenia, leucocytopenia, gastrointestinal symptoms, neural symptoms, bleeding tendency. The fatality rate of SFTS is 6-30%. Person-to-person transmission of SFTS virus is possible through blood contact. Clinical and epidemiological studies of SFTS, the cases of SFTS outside China, person-to-person transmission of SFTS virus, evolutionary and molecular analysis of the emergent SFTS virus, and risk assessment of human infection with a novel phlebovirus are considered in this review.

[Lujo hemorrhagic fever]

Lujo hemorrhagic fever (LHF) is a viral disease accompanied with fever, headache, vomiting, diarrhea, arthralgia, myalgia and numerous signs of hemorrhagic syndrome. LHF causes a clinical syndrome remarkably similar to Lassa hemorrhagic fever. The first case of LHF occurred in Johannesburg, South Africa, in 2008. There was a secondary transmission from the index patient to four healthcare workers. Four of the five patients died. The etiologic agent of LHF is Lujo virus (LUJV) belonging to Arenavirus genus of the Arenaviridae Family. Virus Lujo is the second pathogenic arenavirus, after Lassa virus, to be recognized in Africa during the last 40 years. Data about epidemiology, clinical characteristics and diagnostics of LHF, properties of Lujo virus (according to phylogenetic analysis), and recommended precautions for preventing secondary transmission are considered in this paper.

[EXPERIENCE OF STUDY AND POSSIBLE WAYS OF ELIMINATION OF FALSE POSITIVE AND FALSE NEGATIVE RESULTS DURING EXECUTION OF POLYMERASE CHAIN REACTION ON AN EXAMPLE OF JUNIN VIRUS RNA DETECTION]

AIM

Experience of study and possible ways of elimination of false positive and false negative results during execution of polymerase chain reaction on an example of Junin virus RNA detection. MATERIALSS AND METHODS: Junin virus--causative agent of Argentine hemorrhagic fever (AHF) strain XJpR37/5787 was obtained from the State collection of pathogenicity group I causative agents of the 48th Central Research Institute. Reagent kit for detection of Junin virus RNA by RT-PCR was developed in the Institute and consists of 4 sets: for isolation of RNA, execution of reverse-transcription reaction, execution of PCR and electrophoretic detection of PCR products. RT-PCR was carried out by a standard technique. Continuous cell cultures of African green monkey Vero B, GMK-AH-1(D) were obtained from the museum of cell culture department of the Centre.

RESULTS

An experimental study of the effect of various factors of impact on the sample under investigation ("thawing-freezing", presence of formaldehyde, heparin) on the obtaining of false negative results during Junin virus RNA detection by using RT-PCR was studied. Addition of 0.01% heparin to the samples was shown to completely inhibit PCR. Addition of 0.05% formaldehyde significantly reduces sensitivity of the method. A possibility of reduction of analysis timeframe from 15 to 5 days was shown during detection of the causative agent in samples with low concentration of the latter by growing the samples and subsequent analysis of the material obtained by using RT-PCR.

CONCLUSION

During detection of causative agent by using RT-PCR false negative results could appear in the presence of formaldehyde and heparin in the sample. A possibility of elimination of false negative PCR results due to concentration of the causative agent in the sample under investigation at a level below sensitivity threshold was shown on the example of Junin virus RNA detection by using growing of the pathogen in appropriate accumulation system with subsequent analysis of the material obtained using PCR.

[Study of sensitivity of laboratory animals to a causative agent of argentine hemorrhagic fever]

AIM

Study sensitivity of laboratory animals to a causative agent ofArgentine hemorrhagic fever.

MATERIALS AND METHODS

Junin virus strain XJ P37 was obtained from the State Collection of Causative Agents of Viral Hemorrhagic Fevers of the Pathogenicity Group I of Scientific Research Center of the 33rd Central Scientific Research Test Institute (SRC of the 33rd CSRTI). Junin virus strain XJ P37 culture with biological activity of 5.2 1g PFU x ml was used in the experiments. Mice (2 - 4 and 7 - 14 days old), guinea pigs (250 - 300 g), 1.8 - 2.5 kg shinshilla breed rabbits, 2.0 - 3.0 kg javanese macaque monkeys were obtained from vivarium of the SRC of the 33rd CSRTI. Vero (B) and GMK-AH-1 (D) cell cultures were obtained from cell culture collection of the SRC of the 33rd CSRTI. Biological activity calculation of Junin virus was carried out by Kerber in I.P. Amsharin modification.

RESULTS

Lethality in animals was from 12.5 to 50% after intranasal and intraperitoneal infection of guinea pigs, intramuscular, intraperitoneal and subcutaneous infection of rabbits, intracerebral and intranasal infection of mice at the doses from 0.4 to 1.0 x 10(5) PFU. Death of infected monkeys after intramuscular administration of the virus at 1.0 x 10(4) PFU dose was not observed. In 100% of surviving animals formation of virus-neutralizing antibodies was registered.

CONCLUSION

Evaluation of sensitivity of laboratory animals to Junin virus has shown that intracerebrally infected mice may be used to maintain causative agent culture, infected guinea pigs - to prepare virus-containing cultures and modelling infection exacerbation in humans. Intramuscularly infected rabbits may be used to obtain hyper-immune sera.

[The application of external and internal control objects in case of using of polymerase chain reaction and reverse transcription of polymerase chain reaction]

The external and internal control samples are used in case of polymerase chain reaction application to ensure validity of results. The external control samples are used to establish operability of reagents included into diagnostic kit. The internal control samples make it possible to check not only all the stages of reaction but also the process of amplification in each individual test tube with reaction mixture.

[Optimization of conditions of quantitative evaluation of argentine hemorrhagic fever causative agent]

AIM

Optimization of conditions of quantitative evaluation of Argentine hemorrhagic fever causative agent.

MATERIALS AND METHODS

Junin virus (XJ P37 strain) was obtained from National collection of viral hemorrhagic fever causative agents of the 1st pathogenicity group of the 33rd Central Research Testing Institute. Junin virus (XJ P37 strain) culture with biological activity of 5.2 lg PFUxm(-1) was used in the experiments. Vero B, 6619-1(D) and GMK-AH-1(D) were obtained from collection of cell culture of the Research Scientific Centre of the 33rd Central Research Testing Institute. Calculation of biological activity of Junin virus during titration in cell cultures was carried out by Kerber method with modification by I.P. Ashmarin.

RESULTS

During incubation for 4 - 7 days after the infection of cell monolayer the determined biological activity was 4.4 - 6.4 lg PFUxml(-1); the size of the formed negative colonies--(1.5 +/- 0.5) mm.

CONCLUSION

The conditions of quantitative evaluation of Argentine hemorrhagic fever were optimized by negative colonies method (using 5 - 7 day Vero B cell culture monolayer with staining of monolayer on day 5 of secondary incubation, recording of results at day 7 after the infection).