ON MODERN APPROACHES TO CREATION OF A SINGLE-CYCLE VACCINE AGAINST TICK-BORNE ENCEPHALITIS.

In Russia, about 2000 people get tick-borne encephalitis (TBE) every year. Almost none of them are vaccinated. For the prevention of TBE, inactivated vaccines (IVTBE) are used. IVTBE are safe and protect from TBE not less than 95% of vaccinated. The disadvantages of IVTBE are the need for numerous intramuscular injections by medical personnel, the high cost of vaccination and the vaccination refusals. A new vaccine against TBE should not be inferior to IVTBE in its safety and efficacy, should cause long-term immunity after a single application, and, preferably, be effective after oral administration. Currently, genetic engineering methods for producing replication-defective (single-cycle) flaviviruses that can serve as the basis for creating new types of safe vaccines similar in many characteristics to classic live vaccines based on attenuated strains of viruses have been proposed. The possibility of infecting humans with TBE by the use of milk of naturally infected animals, as well as the experience of using experimental live TBE vaccines, are prerequisites for the creation of a safe oral single-dose TBE vaccine.

[History of development of the live poliomyelitis vaccine from Sabin attenuated strains in 1959 and idea of poliomyelitis eradication].

In 1958 Poliomyelitis Institute in Moscow and Institute of Experimental Medicine in St. Petersburg received from A. Sabin the attenuated strains of poliomyelitis virus. The characteristics of the strains were thoroughly studied by A. A. Smorodintsev and coworkers. They found that the virulence of the strains fluctuated slightly in 10 consecutive passages through the intestine of the non-immune children. A part of the Sabin material was used by A. A. Smorodintsev and M. P. Chumakov in the beginning of 1959 for immunizing approximately 40000 children in Estonia, Lithuania, and Latvia. Epidemic poliomyelitis rate in these republics decreased from approximately 1000 cases yearly before vaccination to less than 20 in the third quarter of 1959. This was a convincing proof of the efficacy and safety of the vaccine from the attenuated Sabin strains. In 1959, according to A. Sabin's recommendation, a technology of live vaccine production was developed at the Poliomyelitis Institute, and several experimental lots of vaccine were prepared. In the second part of 1959, 13.5 million children in USSR were immunized. The epidemic poliomyelitis rate decreased 3-5 times in different regions without paralytic cases, which could be attributed to the vaccination. These results were the final proof of high efficiency and safety of live poliomyelitis vaccine from the attenuated Sabin strains. Based on these results, A. Sabin and M. P. Chumakov suggested in 1960 the idea of poliomyelitis eradication using mass immunization of children with live vaccine. 72 million persons up to 20 years old were vaccinated in USSR in 1960 with a 5 times drop in the paralytic rate. 50-year-long use of live vaccine results in poliomyelitis eradication in almost all countries worldwide. More than 10 million children were rescued from the death and palsy. Poliomyelitis eradication in a few countries where it still exists depends not on medical services but is defined by the attitude of their leaders to fight against poliomyelitis. In some developing countries the vaccination data are falsified, thereby threatening the polio epidemics reappearance and the virus spreading to other countries. Methods must be developed for detection and dealing with extremely rare persistent virus carriers. Because of all these constraints the outcome of poliomyelitis eradication at present is uncertain and vaccination must be continued. The world has become poliovaccine dependent.

[Antiviral humanized and human monoclonal antibodies].

The paper considers the characteristics of monoclonal antibodies, methods for their experimental preparation, problems of their production, and possibilities of their use for the emergency prevention of viral infections and for the treatment of chronic diseases caused by human immunodeficiency virus, hepatitis B and C viruses, and herpes viruses. The future of experimentally produced or clinically trialed monoclonal antibodies is mainly determined by commercial considerations. It is possible that simplification of industrial production technologies and a reduction in the cost of evidence-based methods for evaluation of clinical effectiveness will allow monoclonal antibodies to be extensively used for the prevention and treatment of viral infections.

[Encephalomyelitis caused by enterovirus type 71 in children].

Enterovirus type 71 (EV71) is a causative agent of large outbreaks of hand, foot, and mouth disease (HFMD) in Europe (Bulgaria, 1975; Hungary, 1978) and South-East Asia (Malaysia, 1977; Taiwan, 1998; Singapore, 2000-2007; People's Republic of China, 2007-2009). HFMD afflicted children less than 10 years of age and resulted in recovery within 3-7 days. In a small percentage of infants (aged 6 months to 3 years), HFMD was accompanied by acute neurological complications, such as serous meningitis, poliomyelitis-like syndrome (extremity pareses and muscle paralyses); brain stem encephalitis (myoclonic jerks, tremor, lethargy, swallowing and speech disorders, cardiopulmonary failure, pulmonary edema, shock, coma, death). X-ray study revealed pulmonary hemorrhages and edema. Mortality rates were as high as 82-94% in severe cases. Incapacitating motor, respiratory, and psychoemotional disorders persisted in some surviving children. Pathomorphologically, patients with central nervous system disease and cardiopulmonary failure were found to have acute inflammation of the grey matter of the brain stem (medulla oblongata, pons) and spinal cord. Inflammatory changes in the lung and myocardial tissues were negligible or absent. Fatal pulmonary edema was neurogenic in origin and resulted from damage to the respiratory and vasomotor centers of the brain stem.

[Enterovirus 71: epidemiology and diagnostics].

In 1970s enterovirus type 71 (EV71) caused several epidemics of poliomyelitis-like disease with severe neurologic sequelae. In the last 20 years EV71 was the cause of series of outbreaks and epidemics of foot-and-mouth disease-like conditions with neurologic sequelae in countries of South-East Asia. During the last epidemic of EV71 infection, which occurred in China in 2008, more than 60,000 cases was registered, 38 of which were lethal. Some aspects of epidemiology and laboratory diagnostics of disease caused by EV71 are considered in this review.

[100 years of studying poliomyelitis virus and nonpoliomyelitis enteroviruses].

M. P. Chumakov Institute of Poliomyelitis and Viral Encephalitis, Russian Academy of Medical Sciences, Moscow The paper deals with the history of discovery of poliomyelitis virus by K. Landsteiner and E. Popper in 1908, the identification of three immunological types of the virus in 1949, the discovery of viral multiplication in the cultures of non-nerve cells with a cytopathogenic effect by A. Anders in 1949, the development of new diagnostic techniques, the design of inactivated poliovirus vaccine by D. Salk in 1953 and its live vaccine by A. Sabin in 1957. The advantages and disadvantages of these vaccines and the prospects for further poliomyelitis control are discussed. The characteristics and role of nonpoliomyelitis enteroviruses are considered. The most important scientific discoveries made in the study of enteroviruses are noted.

[Molecular epidemiology of ECHO 6 virus, the causative agent of the 2006 outbreak of serous meningitis in Khabarovsk].

A total of 3194 cases of enterovirus meningitis were notified in the Russian Federation in 2005, of them there were 1434 cases in the Khabarovsk Territory. Enteroviruses were isolated from 1020 out of the virologically studied 1362 patients from the Khabarovsk Territory. Viruses E6 and E30 were isolated in 80 and 14.7% of cases, respectively. E1, E3, E7, E33, Coxsackie virus B1, B4, B5, and A10 were sporadically detected. The E6 strains isolated in Komsomolsk-on-Amur were identical while E6 strains isolated in Khabarovsk belonged to two different genotypes and greatly differed from those isolated in Konsomolsk-on-Amur. The virus E30 strains isolated in Khabarovsk and Komsomolsk-on-Amur had a 1% difference in VP1 genome nucleotide sequence and belonged to E30 subtype that circulated in Russia and Kazakhstan in 2004-2005.

[Prevention of tick-borne encephalitis: current aspects].

The authors consider the present tick-borne encephalitis situation in our country and prospects for this infection control.

[Change in the antigenic structure of surface glycoprotein E of tick-borne encephalitis virus during its adaptation to ticks and mammals].

Enzyme immunoassay and immunoprecipitation test of viral proteins, by applying a tick-borne encephalitis (TBE) viral protein E monoclonal antibody kit, have shown that TBE adaptation to ticks and mammals may cause a considerable change in the antigenic structure of surface glycoprotein E, by involving different antigenic domains, including a neutralizing epitope that seems to participate at the early stages of interaction of virions with the cell membrane.

[Acute enterovirus uveitis in infants].

Enterovirus uveitis (EU) is a new infant eye disease that was first detected and identified in Russia in 1980-1981. Three subtypes of human echoviruses (EV19K, EV11A, and EV11/B) caused 5 nosocomial outbreaks of EU in different Siberian cities and towns in 1980-1989, by affecting more than 750 children mainly below one year of age. Sporadic and focal EU cases (more than 200) were also retrospectively diagnosed in other regions of Russia and in different countries of the former Soviet Union. There were following clinical manifestations: common symptoms of the infection; acute uveitis (rapid focal iridic destruction, pupillary deformities, formation of membranes in the anterior chamber of the eye); and in 15-30% of cases severe complications, cataract, glaucoma, vision impairments. Uveitis strains EV19 and EV11 caused significant uveitis in primates after inoculation into the anterior chamber of the eye, as well as sepsis-like fatal disease with liver necrosis after venous infection. The uveitis strains are phylogenetically and pathogenetically close for primates to strains EV19 and EV11 isolated from young children with sepsis-like disease. The contents of this review have been published in the Reviews in Medical Virology, 2004, vol. 14, p. 241-254.

[Residual neurovirulence of the chimera of Langat and Denge-4 flaviviruses in intracerebral infection of monkeys].

The residual neurovirulence of the previously obtained chimeric virus Tp21/DEN4, containing the RNA region encoding the pre M and E structural enzymes, strain Tp21, virus Langat, and the remaining part of the genome from the Denge 4 virus, was studied in experiments with monkeys Cercopithecus aethiops involving the intracerebral administration of the virus. The tick-borne encephalitis virus, strain Absettarov, was used as positive control. A comparative analysis of the experimental and published data showed the chimeric virus to be less virulent by its degree of morphological affection in the CNS zones, its spread into the CNS and by a percentage share of animals with viremia versus the Tp21 parent strain and Elantsev strain of the Langat virus.

Tick-borne virus diseases of human interest in Europe.

Several human diseases in Europe are caused by viruses transmitted by tick bite. These viruses belong to the genus Flavivirus, and include tick-borne encephalitis virus, Omsk haemorrhagic fever virus, louping ill virus, Powassan virus, Nairovirus (Crimean-Congo haemorrhagic fever virus) and Coltivirus (Eyach virus). All of these viruses cause more or less severe neurological diseases, and some are also responsible for haemorrhagic fever. The epidemiology, clinical picture and methods for diagnosis are detailed in this review. Most of these viral pathogens are classified as Biosafety Level 3 or 4 agents, and therefore some of them have been classified in Categories A-C of potential bioterrorism agents by the Centers for Disease Control and Prevention. Their ability to cause severe disease in man means that these viruses, as well as any clinical samples suspected of containing them, must be handled with specific and stringent precautions.

[Molecular epidemiology of the ECHO 30 virus in Russia and CIS countries]. / Molekuliarnaia épidemiologiia virusa ECHO 30 na territorii Rossii i stran SNG.

Nucleotide sequences of the VP1 genome of 28 ECHO 30 strains isolated in 1998-2002 in Russia and several CIS countries were determined. The EV30 studies strain were divided into 4 groups according to isolation place and time. Group 1 is presented by 2 strains isolated in 1998 in Russia and Byelorussia. Group 2 comprises 17 strains isolated in 1999-2000 in Russia (its southern regions and Stavropol Territory), Ukraine, Georgia, and Azerbaijan. Five strains isolated in 2002 in Russia (Kalmykia) belong to Group 3; and Group 4 has 4 strains isolated in 2002 in Moldova and Russia (Magadan). A frequently changing EV30 subtype was simultaneously detected in extensive territories.

Recombination in uveitis-causing enterovirus strains.

The complete nucleotide sequences of three human echovirus (EV) 11 strains and one EV19 strain, all of which caused outbreaks of enterovirus uveitis (EU), a new infant disease first identified in 1980 in Siberia, were determined. One EV11 strain which caused an outbreak of sepsis-like disease in Hungary was also sequenced. All four EV11 strains were mosaic recombinants of the prototype EV11 strain Gregory, with their non-structural coding regions and 5' NTRs being more similar to other prototype enteroviruses (EV1, EV9). However, this finding is probably a feature of all circulating enterovirus strains and may not be related to their altered virulence. A full genome sequence comparison of the three subtypes of EU-causing strains excludes the role of recent recombination in their emergence, and points to their independent emergence.

Molecular epidemiology of enteroviruses causing uveitis and multisystem hemorrhagic disease of infants.

We studied molecular epidemiology of highly virulent echovirus 11 and 19 strains that were isolated during five outbreaks of enterovirus uveitis (EU) in Siberia in 1980-1989, and three outbreaks of multisystem hemorrhagic disease of infants (MHD) in 1988-1991. Three genome regions, 5'NTR, VP1-2A junction, and a fragment of 3D polymerase, were analyzed. Phylogenetic grouping in the VP1-2A region correlated with serotyping results. All studied EV11 and EV19 strains, including the prototype EV11 and EV19, formed a major phylogenetic group in VP1-2A region. Within that group, several EV11 isolates from EU and MHD outbreaks formed a distinct cluster in VP1-2A and 5' NTR genome regions, designated EV11/B. All strains of this cluster possessed high virulence for monkeys compared with the prototype echoviruses. Subgrouping within this cluster correlated with year of virus isolation, not with the disease the viruses caused in infants (EU or MHD).

Tick-borne encephalitis.

Tick-borne encephalitis (TBE) is one of the most dangerous human infections occurring in Europe and many parts of Asia. The etiological agent Tick-borne encephalitis virus (TBEV), is a member of the virus genus Flavivirus, of the family Flaviviridae. TBEV is believed to cause at least 11,000 human cases of encephalitis in Russia and about 3000 cases in the rest of Europe annually. Related viruses within the same group, Louping ill virus (LIV), Langat virus (LGTV) and Powassan virus (POWV), also cause human encephalitis but rarely on an epidemic scale. Three other viruses within the same group, Omsk hemorrhagic fever virus (OHFV), Kyasanur Forest disease virus (KFDV) and Alkhurma virus (ALKV), are closely related to the TBEV complex viruses and tend to cause fatal hemorrhagic fevers rather than encephalitis. This review describes the clinical manifestations associated with TBEV infections, the main molecular-biological properties of these viruses, and the different factors that define the incidence and severity of disease. The role of ticks and their local hosts in the emergence of new virus variants with different pathogenic characteristics is also discussed. This review also contains a brief history of vaccination against TBE including trials with live attenuated vaccine and modern tendencies in developing of vaccine virus strains.

Characterization of a siberian virus isolated from a patient with progressive chronic tick-borne encephalitis.

A strain of Tick-borne encephalitis virus designated Zausaev (Za) was isolated in Siberia from a patient who died of a progressive (2-year) form of tick-borne encephalitis 10 years after being bitten by a tick. The complete genomic sequence of this virus was determined, and an attempt was made to correlate the sequence with the biological characteristics of the virus. Phylogenetic analysis demonstrated that this virus belongs to the Siberian subtype of Tick-borne encephalitis virus. Comparison of Za virus with two related viruses, a Far Eastern isolate, Sofjin, and a Siberian isolate, Vasilchenko, revealed differences among the three viruses in pathogenicity for Syrian hamsters, cytopathogenicity for PS cells, plaque morphology, and the electrophoretic profiles of virus-specific nonstructural proteins. Comparative amino acid alignments revealed 10 individual amino acid substitutions in the Za virus polyprotein sequence that were different from those of other tick-borne flaviviruses. Notably, the dimeric form of the Za virus NS1 protein migrated in polyacrylamide gels as a heterogeneous group of molecules with a significantly higher electrophoretic mobility than those of the Sofjin and Vasilchenko viruses. Two amino acid substitutions, T(277)-->V and E(279)-->G, within the NS1 dimerization domain are probably responsible for the altered oligomerization of Za virus NS1. These studies suggest that the patient from whom Za virus was isolated died due to increased pathogenicity of the latent virus following spontaneous mutagenesis.

Phylogenetic and serological characterization of echovirus 11 and echovirus 19 strains causing uveitis.

The strains of echovirus 19 (EV 19) and echovirus 11 (EV11), isolated from infants with similar clinical symptoms of acute enterovirus uveitis (EU) in Russia (Siberia) in 1980-1989, were investigated phylogenetically (nucleotide sequence of a 300 nt fragment in 5' NTR and VP4 junction) and serologically. The result confirmed that viruses belong to the Enterovirus genus, with 58-80% nt sequence homology with previously sequenced enteroviruses, and showed the genetical identity between the strains isolated during each of five outbreaks of the EU. The results also demonstrated that isolates from the last three outbreaks of EU belong to the same phylogenetic group despite the remarkable spatial and temporal distance between the outbreaks. The results confirm the role of these echoviruses in the etiology of the EU. Based on phylogenetic and serological comparisons the studied strains were divided into three distinct groups: group I, EV19/K (Krasnoyarsk, 1980-1981), group II, EV11/A (Krasnoyarsk, 1982), group III, EV11/B (Krasnoyarsk, 1986; Omsk, 1987-1988; Irkutsk, 1989). Minor details of the epidemiology of the outbreaks were also revealed.