Mapping of functional elements in the stem-anchor region of tick-borne encephalitis virus envelope protein E

Envelope protein E of the flavivirus tick-borne encephalitis virus mediates membrane fusion, and the structure of the N-terminal 80% of this 496-amino-acid-long protein has been shown to differ significantly from that of other viral fusion proteins. The structure of the carboxy-terminal 20%, the stem-anchor region, is not known. It contains sequences that are important for membrane anchoring, interactions with prM (the precursor of membrane protein M) during virion assembly, and low-pH-induced structural changes associated with the fusion process. To identify specific functional elements in this region, a series of C-terminal deletion mutants were constructed and the properties of the resulting truncated recombinant E proteins were examined. Full-length E proteins and proteins lacking the second of two predicted transmembrane segments were secreted in a particulate form when coexpressed with prM, whereas deletion of both segments resulted in the secretion of soluble homodimeric E proteins. Sites located within a predicted alpha-helical region of the stem (amino acids 431 to 449) and the first membrane-spanning region (amino acids 450 to 472) were found to be important for the stability of the prM-E heterodimer but not essential for prM-mediated intracellular transport and secretion of soluble E proteins. A separate site in the stem, also corresponding to a predicted alpha-helix (amino acids 401 to 413), was essential for the conversion of soluble protein E dimers to a homotrimeric form upon low-pH treatment, a process resembling the transition to the fusogenic state in whole virions. This functional mapping will aid in the understanding of the molecular mechanisms of membrane fusion and virus assembly.

Comparison of line probe assay (LIPA) and sequence analysis for detection of HIV-1 drug resistance

The identification of HIV strains that are resistant to antiretroviral drugs, which emerge during a patient's therapy or are already present in infected individuals prior to treatment, is of increasing importance for the clinical management of HIV-infected persons. Two different methods were compared for the genotypic detection of resistance development in the HIV-1 reverse transcriptase (RT) gene, the commonly used sequence analysis, and the commercially available RT-line immunoprobe assay (LIPA), which can detect mutations at six separate codons of the RT gene, which are known to confer resistance to certain nucleoside inhibitors. Eighty serum samples from HIV-1-infected persons, some of whom were receiving antiretroviral therapy, were investigated in parallel by sequencing as well as by LIPA. LIPA results agreed with sequence data in the vast majority of the cases. However, in 40% of the samples, LIPA failed to yield evaluable results for one or more of the codon positions. In particular, LIPA detection rate was low at codon 41 (75%), whereas at codons 69/70, 74, 184, and 215 results were obtained from 90%-95% of the samples. A number of mutations in the vicinity of the respective codons were detected by sequencing, and these may have been responsible for the LIPA hybridization failure. There remained a number of samples, however, where no explanation for the lack of hybridization could be derived from sequence data. Our results indicate that the use of the LIPA does not eliminate the need for sequence analysis for detection of drug-resistant HIV strains.

Sequence analysis and genetic classification of tick-borne encephalitis viruses from Europe and Asia

The epidemiology of tick-borne encephalitis virus was investigated by comparative sequence analysis of virus strains isolated in endemic areas of Europe and Asia. Phylogenetic relationships were determined from the nucleotide and amino acid sequences of the major envelope (E) protein of 16 newly sequenced strains and nine previously published sequences. Three genetic lineages could be clearly distinguished, corresponding to a European, a Far Eastern and a Siberian subtype. Amino acids characteristic for each of the subtypes ('signature' amino a cids) were identified and their location in the atomic structure of protein E was determined. The degree of variation between strains within subtypes was low and exhibited a maximum of only 2.2% at the amino acid level. A maximum difference of 5.6% was found between the three subtypes, which is in the range of variation reported for other flaviviruses.

In vitro-synthesized infectious RNA as an attenuated live vaccine in a flavivirus model

Live virus vaccines have in many cases proven to be an extremely effective tool for the prevention of viral diseases. However, the production of conventional live vaccines in eukaryotic cell cultures has many disadvantages, including the potential for contamination with adventitious agents and genetic alterations during propagation, making it necessary to do extensive testing before distribution. Based on results obtained with a flavivirus (tick-borne encephalitis virus) in an experimental animal system, we propose a novel live attenuated virus vaccination strategy consisting of the application of in vitro-synthesized infectious RNA instead of the live virus itself. When administered using the GeneGun, less than 1 ng of RNA was required to initiate replication of virus that was attenuated by a specifically engineered deletion and this induced a protective immunity in laboratory mice. Because this approach uses RNA, it does not have the potential drawbacks of DNA vaccines and thus combines the advantages of conventional live virus vaccines (for example, mimicking natural infection and inducing long-lasting immunity) with those of nucleic acid-based vaccines (for example, ease of production without a requirement for eukaryotic cell culture, stability and purity).

Possible influence of the mutant CCR5 Allele on vertical transmission of HIV-1

A possible correlation between the rate of vertical transmission of HIV-1 and the presence of the defective HIV co-receptor gene delta 32ccr5 in the chromosomes of infants born to HIV-positive mothers was assessed. The prevalence and genotypic distribution of the delta 32ccr5 gene were studied in 451 uninfected and 225 HIV-1-infected adults and 79 children born to HIV-1-positive mothers in Austria (45 uninfected and 34 infected by vertical transmission). As expected in a Caucasian population, the delta 32ccr5 allele was found in uninfected Austrians at a frequency of 10% (17.3% heterozygotes and 1.3% delta 32ccr5/ delta 32ccr5 homozygotes, consistent with the expected Hardy-Weinberg distribution). The mutant allele frequency was 11.1% in uninfected children (17.8% heterozygotes, 2.2% homozygotes) and 9.6% in HIV-positive adults (19.1% heterozygotes but no delta 32ccr5/delta 32ccr5 homozygotes). Among the group of 34 vertically infected children, however, there were only two heterozygotes and no delta 32ccr5/delta 32ccr5 homozygotes, corresponding to a significantly reduced mutant allele frequency of 2.9% (P = 0.05 compared to HIV-negative children). These results suggest that CCR5/delta 32ccr5 heterozygous children are less susceptible to vertical transmission of HIV-1. The data also support the hypothesis that delta 32ccr5 homozygous individuals are resistant to HIV-1 infection.

Spontaneous and engineered deletions in the 3' noncoding region of tick-borne encephalitis virus: construction of highly attenuated mutants of a flavivirus

The flavivirus genome is a positive-strand RNA molecule containing a single long open reading frame flanked by noncoding regions (NCR) that mediate crucial processes of the viral life cycle. The 3' NCR of tick-borne encephalitis (TBE) virus can be divided into a variable region that is highly heterogeneous in length among strains of TBE virus and in certain cases includes an internal poly(A) tract and a 3'-terminal conserved core element that is believed to fold as a whole into a well-defined secondary structure. We have now investigated the genetic stability of the TBE virus 3' NCR and its influence on viral growth properties and virulence. We observed spontaneous deletions in the variable region during growth of TBE virus in cell culture and in mice. These deletions varied in size and location but always included the internal poly(A) element of the TBE virus 3' NCR and never extended into the conserved 3'-terminal core element. Subsequently, we constructed specific deletion mutants by using infectious cDNA clones with the entire variable region and increasing segments of the core element removed. A virus mutant lacking the entire variable region was indistinguishable from wild-type virus with respect to cell culture growth properties and virulence in the mouse model. In contrast, even small extensions of the deletion into the core element led to significant biological effects. Deletions extending to nucleotides 10826, 10847, and 10870 caused distinct attenuation in mice without measurable reduction of cell culture growth properties, which, however, were significantly restricted when the deletion was extended to nucleotide 10919. An even larger deletion (to nucleotide 10994) abolished viral viability. In spite of their high degree of attenuation, these mutants efficiently induced protective immune responses even at low inoculation doses. Thus, 3'-NCR deletions represent a useful technique for achieving stable attenuation of flaviviruses that can be included in the rational design of novel flavivirus live vaccines.

Introduction of HIV-1 subtypes C, E and A into Austria

BACKGROUND

Different subtypes of HIV-1 are prevalent in various geographical regions. Knowledge of their distribution is of importance with respect to possible differences in biological properties (such as reported for subtype E) as well as to diagnostic problems that may arise when specific subtypes are not recognized by standard serological assays.

OBJECTIVES

The objectives of this study were to investigate the presence of the five major subtypes of HIV-1 (A-E) in the Austrian population and to estimate the prevalence of the individual subtypes in different risk groups.

STUDY DESIGN

Serum samples from 88 HIV-1 positive patients were tested for the presence of subtype-specific antibodies using a peptide ELISA.

RESULTS

The majority of the patients were shown to be infected with HIV-1 subtype B, but infections with subtypes A, C, and E were also detected in the Austrian population, primarily in the heterosexual transmission group. While subtypes A and C were probably imported from different African countries, subtype E appears to have been introduced by sex tourists returning from Thailand.

CONCLUSION

Introduction of HIV subtypes other than B from Africa and Asia into Austria has already occurred and will certainly increase within the next few years.

Proteolytic activation of tick-borne encephalitis virus by furin

Flaviviruses are assembled intracellularly in an immature form containing heterodimers of two envelope proteins, E and prM. Shortly before the virion exits the cell, prM is cleaved by a cellular enzyme, and this processing step can be blocked by treatment with agents that raise the pH of exocytic compartments. We carried out in vivo and in vitro studies with tick-borne encephalitis (TBE) virus to investigate the possible role of furin in this process as well as the functional consequences of prM cleavage. We found that prM in immature virions can be correctly cleaved in vitro by recombinant bovine furin but that efficient cleavage occurs only after exposure of the virion to mildly acidic pH. The data suggest that exposure to an acidic environment induces an irreversible structural change that renders the cleavage site accessible to the enzyme. Cleavage by furin in vitro resulted in biological activation, as shown by a 100-fold increase in specific infectivity, the acquisition of membrane fusion and hemagglutination activity, and the ability of the envelope proteins to undergo low-pH-induced structural rearrangements characteristic of mature virions. In vivo, prM cleavage was blocked by a furin inhibitor, and infection of the furin-deficient cell line LoVo yielded only immature virions, suggesting that furin is essential for cleavage activation of flaviviruses.

Secondary structure of the 3'-noncoding region of flavivirus genomes: comparative analysis of base pairing probabilities

The prediction of the complete matrix of base pairing probabilities was applied to the 3' noncoding region (NCR) of flavivirus genomes. This approach identifies not only well-defined secondary structure elements, but also regions of high structural flexibility. Flaviviruses, many of which are important human pathogens, have a common genomic organization, but exhibit a significant degree of RNA sequence diversity in the functionally important 3'-NCR. We demonstrate the presence of secondary structures shared by all flaviviruses, as well as structural features that are characteristic for groups of viruses within the genus reflecting the established classification scheme. The significance of most of the predicted structures is corroborated by compensatory mutations. The availability of infectious clones for several flaviviruses will allow the assessment of these structural elements in processes of the viral life cycle, such as replication and assembly.

Infectious cDNA clones of tick-borne encephalitis virus European subtype prototypic strain Neudoerfl and high virulence strain Hypr

Infectious cDNA clones of two strains of tick-borne encephalitis (TBE) virus, i.e. European subtype prototypic strain Neudoerfl and the closely related but more virulent strain Hypr, were constructed. The recombinant constructs consisted of cDNAs stably inserted into the bacterial plasmid pBR322 under the control of T7 promoter elements. The genome of TBE virus strain Neudoerfl was successfully cloned, both as a full-length cDNA and as two partial cDNAs. In the case of strain Hypr, the genome is represented by two cDNA clones corresponding to the 5'- and 3'-terminal halves of the genome. Highly infectious RNAs can be produced from the full-length cDNA clone or from the partial clones ligated in vitro to form full-length cDNA templates prior to T7 transcription. The biological properties of the recombinant progeny viruses, including virulence characteristics, were indistinguishable from the corresponding parent virus strains. Thus, the described infectious cDNA clones represent a useful and reliable experimental system for the specific mutagenesis of TBE virus.

Characterization of monoclonal antibody-escape mutants of tick-borne encephalitis virus with reduced neuroinvasiveness in mice

Escape mutants of tick-borne encephalitis (TBE) virus were selected using neutralizing monoclonal antibodies (MAbs) that react with three different and previously unrecognized epitopes in the envelope protein E of TBE virus. Two of these variants (V-IC3 and V-IE3) exhibited a significantly reduced reactivity with their selecting MAbs, as determined by ELISA, whereas with one variant (V-IO3), reactivity was completely unchanged. Comparative sequence analyses demonstrated that each of the variants differed from the wild-type virus by a single amino acid substitution located at exposed positions within domains I, II and III of protein E. In the mouse model, all three mutants were still neuro-virulent but exhibited a significantly reduced neuro-invasiveness after subcutaneous inoculation. Virus replication, however, was sufficient to induce a specific antibody response. The observed alterations in virulence properties were not associated with reduced growth rates in vertebrate cell cultures, but one variant (V-IE3) exhibited a small plaque phenotype. The mutation of variant V-IO3 resulted in a temperature-sensitive phenotype and a significant elevation of the pH-threshold of the conformational change necessary for fusion activity.

Structural requirements for low-pH-induced rearrangements in the envelope glycoprotein of tick-borne encephalitis virus

The exposure of the flavivirus tick-borne encephalitis (TBE) virus to an acidic pH is necessary for virus-induced membrane fusion and leads to a quantitative and irreversible conversion of the envelope protein E dimers to trimers. To study the structural requirements for this oligomeric rearrangement, the effect of low-pH treatment on the oligomeric state of different isolated forms of protein E was investigated. Full-length E dimers obtained by solubilization of virus with the detergent Triton X-100 formed trimers at low pH, whereas truncated E dimers lacking the stem-anchor region underwent a reversible dissociation into monomers without forming trimers. These data suggest that the low-pH-induced rearrangement in virions is a two-step process involving a reversible dissociation of the E dimers followed by an irreversible formation of trimers, a process which requires the stem-anchor portion of the protein. This region contains potential amphipathic alpha-helical and conserved structural elements whose interactions may contribute to the rearrangements which initiate the fusion process.

Recombinant subviral particles from tick-borne encephalitis virus are fusogenic and provide a model system for studying flavivirus envelope glycoprotein functions

Recombinant subviral particles (RSPs) obtained by coexpression of the envelope (E) and premembrane (prM) proteins of tick-borne encephalitis virus in COS cells (S. L. Allison, K. Stadler, C. W. Mandl, C. Kunz, and F. X. Heinz, J. Virol. 69:5816-5820, 1995) were extensively characterized and shown to be ordered structures containing envelope glycoproteins with structural and functional properties very similar to those in the virion envelope. The particles were spherical, with a diameter of about 30 nm and a buoyant density of 1.14 g/cm3 in sucrose gradients. They contained mature E proteins with endoglycosidase H-resistant glycans as well as fully cleaved mature M proteins. Cleavage of prM, which requires an acidic pH in exocytic compartments, could be inhibited by treatment of transfected cells with ammonium chloride, implying a common maturation pathway for RSPs and virions. RSPs incorporated [14C]choline but not [3H]uridine, demonstrating that they contain lipid but probably lack nucleic acid. The envelope proteins of RSPs exhibited a native antigenic and oligomeric structure compared with virions, and incubation at an acidic pH (pH <6.5) induced identical conformational changes and structural rearrangements, including an irreversible quantitative conversion of dimers to trimers. The RSPs were also shown to be functionally active, inducing membrane fusion in a low-pH-dependent manner and demonstrating the same specific hemagglutination activity as whole virions. Tick-borne encephalitis virus RSPs thus represent an excellent model system for investigating the structural basis of viral envelope glycoprotein functions.

Characterization and complete genome sequences of high- and low- virulence variants of tick-borne encephalitis virus

The entire genomic sequences of two strains (Hypr and 263) of the flavivirus tick-borne encephalitis (TBE) virus differing in virulence from the prototypic strain Neudoerfl were determined. Strain Hypr is a human isolate of TBE virus with a high laboratory passage history which exhibits a significantly higher neuro-invasiveness in mice compared to the prototype strain. Strain 263 is a low-passage tick-isolate with a temperature-sensitive and attenuated phenotype. Except for the heterogeneous 3' non-coding regions strains Hypr and 263 share, respectively, 97.2% and 97.6% nucleotide sequence identity with strain Neudoerfl, and differ by a total of 42 and 36 amino acids from the prototypic strain. Of these, only 12 amino acids for each of the two strains represent non-conservative differences unique to an individual strain and some of these are located at positions highly conserved among flaviviruses. Based on these observations, the potential biological significance of particular sequence differences is discussed in the context of the current knowledge about molecular determinants of flavivirus virulence.

Correlation between ELISA, hemagglutination inhibition, and neutralization tests after vaccination against tick-borne encephalitis

The significance of IgG antibody levels determined by a binding assay (ELISA) was investigated as a surrogate marker for the presence of neutralizing and hemagglutination inhibiting antibodies in sera from individuals vaccinated against tick-borne encephalitis (TBE). To assess the extent of interference by flavivirus cross-reactive antibodies, sera from persons with a proven or suspected history of other flavivirus infections and/or vaccinations were also examined. An excellent and highly significant correlation was found between ELISA IgG units and the antibody titers obtained by the hemagglutination inhibition (HI) as well as by the neutralization test (NT), provided that there was no other exposure to flavivirus antigens except TBE vaccination. Yellow fever vaccination and/or dengue virus infections induced significant levels of antibodies reactive in the TBE ELISA and HI test, which did not exhibit, however, neutralizing activity against TBE virus. The phenomenon and problem of "original antigenic sin" was demonstrated in a TBE vaccinee with a history of previous flavivirus infections. TBE vaccination first induced a booster reaction resulting in a rise in the level of cross-reactive antibodies only, whereas TBE virus-neutralizing antibodies became detectable only after the third vaccination. It is concluded that the level of IgG antibodies determined by ELISA is a good marker for predicting the presence of neutralizing antibodies after TBE vaccination, but only in the absence of flavivirus cross-reactive antibodies. Otherwise, a neutralization assay is necessary for assessing immunity.

Recombinant and virion-derived soluble and particulate immunogens for vaccination against tick-borne encephalitis

Using different forms of the envelope glycoprotein E from tick-borne encephalitis virus we investigated the influence of physical and antigenic structure on the efficacy of vaccination. Different protein E-containing preparations were either derived from purified virions or were produced as recombinant proteins in COS cells. These included soluble dimeric forms (virion-derived protein E dimers with and without membrane anchor; recombinant protein E dimers without membrane anchor), micellar aggregates of protein E (rosettes), and recombinant subviral particles (RSPs). The structural differences between these immunogens were verified by sedimentation analysis, immunoblotting and epitope mapping with a panel of monoclonal antibodies. Specific immunogenicities were determined in mice in comparison to formalin-inactivated whole virus. Rosettes and RSPs were excellent immunogens and exhibited similar efficacies as inactivated virus in terms of antibody induction and protection against challenge, whereas all of the soluble forms were much less immunogenic. These data emphasize the importance of the immunogen's antigenic and physical structure for an effective stimulation of the immune system and indicate that RSPs represent an excellent candidate for a recombinant vaccine against tick-borne encephalitis.

Identification of tick-borne encephalitis virus ribonucleic acid in tick suspensions and in clinical specimens by a reverse transcription-nested polymerase chain reaction assay

BACKGROUND

Tick-borne encephalitis virus (TBEV) is a major human pathogenic flavivirus. Sensitive assays for the detection of viral RNA may be valuable both for the identification of virus in ticks as well as for diagnostic purposes.

OBJECTIVES

(1) The development of a sensitive polymerase chain reaction (PCR) test system for the detection of TBEV-RNA and its application to the identification of infected ticks; and (2) evaluation of the PCR assay for diagnostic purposes, i.e., detection of TBE virus RNA in blood and in cerebrospinal fluid (CSF) of TBE patients.

STUDY DESIGN

(1) Establishment of a TBEV-specific reverse transcription (RT)-nested PCR assay and evaluation of its sensitivity; (2) comparison of the PCR assay with that of virus isolation from tick suspensions; and (3) investigation of 105; serum and CSF samples from patients with serologically confirmed TBE by RT-nested PCR.

RESULTS

An RT-nested PCR assay was established with a detection limit of 100-1000 copies of TBEV RNA. All tick suspensions from which the virus could be isolated by inoculation of suckling mice also screened positive in the PCR assay. Of the 105 clinical samples investigated, only one serum and one CSF sample were positive by PCR assay, and these were both obtained very early in the course of the disease.

CONCLUSIONS

The PCR assay described is valuable for the detection of TBEV in tick suspensions and can substitute for the usual virus isolation procedure in which suckling mice are inoculated. Its application for diagnostic purposes, however, does not seem to provide a significant improvement over serological diagnosis. Only in very rare cases, when a sample is drawn extremely early in the course of disease, may TBEV RNA be detected in serum or CSF before the appearance of specific IgM antibodies and thus allow an earlier diagnosis.

Antibodies to the nonstructural protein of parvovirus B19 in persistently infected patients: implications for pathogenesis

Three patients with persistent parvovirus B19 infection, as documented by the prolonged presence of IgM directed to the viral capsid proteins and detection of viral DNA in serum by dot-blot hybridization or polymerase chain reaction (PCR), were investigated for the presence of antibodies to the nonstructural protein NS-1 of parvovirus B19. This was done by using an ELISA based on recombinant NS-1 protein. Whereas control sera displayed no reactivity, sera from persistently infected patients showed a strong specific antibody response to NS-1. Patients were followed for 3-18 months, during which IgM titers declined but IgG directed to the nonstructural protein remained detectable. The appearance of NS-1-specific antibodies might indicate an altered course of viral infection leading to the establishment of persistently active infection and subsequent destruction of cells of nonerythroid lineage.

The flavivirus 3'-noncoding region: extensive size heterogeneity independent of evolutionary relationships among strains of tick-borne encephalitis virus

The sequences of the 3'-noncoding regions (NCR) of 12 strains of tick-borne encephalitis (TBE) virus were analyzed and found to vary in length from 350 to approximately 750 nucleotides. The size heterogeneity is restricted to a variable region following the stop codon, whereas the most 3'-terminal 350 nucleotides form a highly conserved core element containing several potentially important sequence motifs and secondary structure elements. A homoadenosine tract previously thought to form the 3'-terminus of some TBE virus strains was now shown to be an internal part of the variable region of certain strains. The strains included in this study were isolated from both humans and ticks over a time period of more than 40 years at various locations throughout the entire endemic area of TBE virus, but there was no correlation between these parameters and the observed lengths of the 3'-NCRs. Identity data calculated from common 3'-NCR sequences and also from short sections of the open reading frame indicated that coding and noncoding sequences were linked during evolution, but the lengths of the 3'-NCRs were independent of these relationships. These observations together with detailed analyses and alignments of the sequences suggest that the variable region was originally acquired through duplication and recombination events, but--much more recently during evolution--various portions of this region were lost again, resulting in the now observed heterogeneous 3'-NCRs.

Synthesis and secretion of recombinant tick-borne encephalitis virus protein E in soluble and particulate form

A quantitative study was performed to investigate the requirements for secretion of recombinant soluble and particulate forms of the envelope glycoprotein E of tick-borne encephalitis (TBE) virus. Full-length E and a carboxy terminally truncated anchor-free form were expressed in COS cells in the presence and absence of prM, the precursor of the viral membrane protein M. Formation of a heteromeric complex with prM was found to be necessary for efficient secretion of both forms of E, whereas only low levels of anchor-free E were secreted in the absence of prM. The prM-mediated transport function could also be provided by coexpression of prM and E from separate constructs, but a prM-to-E ratio of greater than 1:1 did not further enhance secretion. Full-length E formed stable intracellular heterodimers with prM and was secreted as a subviral particle, whereas anchor-free E was not associated with particles and formed a less stable complex with prM, suggesting that prM interacts with both the ectodomain and anchor region of E.

Laboratory acquired tick-borne meningoencephalitis: characterisation of virus strains

BACKGROUND

The handling of tick-borne encephalitis (TBE) virus is potentially hazardous, as indicated by a number of laboratory-acquired infections in the prevaccination era.

OBJECTIVES

(1) To reemphasize the hazard of handling TBE virus without being vaccinated by describing the case of a laboratory-acquired full-blown TBE in a microbiologist who isolated the virus from a blood sample. (2) To molecularly characterize the causative virus strain isolated in Slovenia in comparison with the European prototype strain Neudoerfl.

STUDY DESIGN

The virological diagnosis of the laboratory infection was established by serology and virus isolation. The virus was characterized by restriction fragment analysis of PCR products of amplified genomic sequences and a panel of monoclonal antibodies reacting with the major envelope protein.

RESULTS

The laboratory infection, most probably acquired by aerosol, resulted in a biphasic course of the disease with a severe meningoencephalitis in the second phase. Both by restriction fragment and monoclonal antibody analysis the Slovenian virus strains involved were indistinguishable from the European prototype strain.

CONCLUSIONS

This report confirms the potential hazard of handling TBE virus in the laboratory without being vaccinated. The similarity of the virus isolates from Slovenia with the European prototype strain confirms the previously observed homogeneity of TBE virus strains from different European countries.

The envelope glycoprotein from tick-borne encephalitis virus at 2 A resolution

The crystallographically determined structure of a soluble fragment from the major envelope protein of a flavivirus reveals an unusual architecture. The flat, elongated dimer extends in a direction that would be parallel to the viral membrane. Residues that influence binding of monoclonal antibodies lie on the outward-facing surface of the protein. The clustering of mutations that affect virulence in various flaviviruses indicates a possible receptor binding site and, together with other mutational and biochemical data, suggests a picture for the fusion-activating, conformational change triggered by low pH.

Tick-borne encephalitis virus envelope protein E-specific monoclonal antibodies for the study of low pH-induced conformational changes and immature virions

A set of ten monoconal antibodies (mabs) specific for the tick-borne encephalitis (TBE) virus envelope protein E were prepared and characterized with respect to their functional activities, the location of their binding sites on protein E and the involvement of their epitopes in acid pH-induced conformational changes and interactions with the precursor to the membrane protein (prM) in immature virions. The majority of these mabs mapped to the previously defined antigenic domain A. All of the mabs recognize parts of the E protein which undergo low pH-induced structural rearrangements believed to be necessary for the fusion activity of the virus, and six of the mabs define epitopes which are affected by the prM-E interaction in immature virions. They are therefore of potential value as specific reagents for studying the structure and function of protein E, as well as the function of the prM-E association. Five of the mabs exhibited neutralizing activity, and can therefore be used for the selection of escape mutants.

Oligomeric rearrangement of tick-borne encephalitis virus envelope proteins induced by an acidic pH

The flavivirus envelope protein E undergoes irreversible conformational changes at a mildly acidic pH which are believed to be necessary for membrane fusion in endosomes. In this study we used a combination of chemical cross-linking and sedimentation analysis to show that the envelope proteins of the flavivirus tick-borne encephalitis virus also change their oligomeric structure when exposed to a mildly acidic environment. Under neutral or slightly alkaline conditions, protein E on the surface of native virions exists as a homodimer which can be isolated by solubilization with the nonionic detergent Triton X-100. Solubilization with the same detergent after pretreatment at an acidic pH, however, yielded homotrimers rather than homodimers, suggesting that exposure to an acidic pH had induced a simultaneous weakening of dimeric contacts and a strengthening of trimeric ones. The pH threshold for the dimer-to-trimer transition was found to be 6.5. Because the pH dependence of this transition parallels that of previously observed changes in the conformation and hydrophobicity of protein E and that of virus-induced membrane fusion, it appears likely that the mechanism of fusion with endosomal membranes involves a specific rearrangement of the proteins in the viral envelope. Immature virions in which protein E is associated with the uncleaved precursor (prM) of the membrane protein M did not undergo a low-pH-induced rearrangement. This is consistent with a protective role of protein prM for protein E during intracellular transport of immature virions through acidic compartments of the trans-Golgi network.

Expression of cloned envelope protein genes from the flavivirus tick-borne encephalitis virus in mammalian cells and random mutagenesis by PCR

The structural membrane proteins prM and E of the flavivirus tick-borne encephalitis (TBE) virus were expressed in mammalian cells for the purpose of probing the structure and molecular interactions of these proteins. Advantage was taken of the natural error frequency of the Taq polymerase used in the PCR amplification to generate a randomly mutated population of genes that were then cloned directly into plasmid expression vectors under the control of an SV40 promoter. Analysis of the mutation frequency by direct sequencing of 22 separate clones showed that the PCR produced mutations at a rate yielding an average of one to two amino acid changes per clone in the 496 amino acid long protein E. This is an ideal rate for assessing the importance of individual amino acid residues within protein domains, thus demonstrating the potential value of the PCR as a random mutagenesis method. Clones encoding wild-type prM and E proteins, and a truncated form of E, were also constructed by recombining portions of selected PCR clones. Transfection of COS-1 cells with these constructs resulted in expression of the prM and E proteins, which was demonstrated by indirect immunofluorescence using monoclonal antibodies (Mabs). The intracellular level of TBE virus antigen, measured in lysates of transfected cells by ELISA, reached approximately 25% of that found in virus-infected COS cells. Furthermore, it was shown by immunofluorescence using a panel of 19 anti-E Mabs that the antigenic structure of the expressed E proteins was nearly identical to that of E protein in infected cells, thus confirming the suitability of this model system as a tool for studying flavivirus protein structure.

Prevalence of hepatitis-C virus RNA in serum and throat washings of children with chronic hepatitis

Serum samples from 46 children with chronic and probably transfusion acquired hepatitis were tested for the presence of hepatitis C virus (HCV) RNA by a "nested" polymerase chain reaction (PCR) assay, to judge a possible risk of HCV transmission from these patients. In 73% of the samples, viral RNA was detected, indicating a high virus prevalence in this patient group. High titers of HCV-RNA were observed in some sera as shown by the detection of virus in some samples even at dilutions of 10(-3). Comparison of simultaneously obtained PCR results and ALT values revealed no significant correlation between virus presence in serum and higher ALT levels. It was, however, shown that unusually high ALT values may reflect a high titer of viral RNA in serum. To investigate the prevalence of viral RNA in saliva, which could be a vehicle of virus transmission, 35 throat washing samples from the HCV-infected children were screened by PCR. Using three different sample preparation procedures, 20% of the throat washings were found to be positive for HCV-RNA. This indicates a prevalence of virus in this fluid lower than that reported previously.

Structural changes and functional control of the tick-borne encephalitis virus glycoprotein E by the heterodimeric association with protein prM

We have used tick-borne encephalitis virus to study the involvement of acidic compartments during the entry and release phases of flavivirus infection and to elucidate the role of protein prM in immature virions. Elevation of the pH in acidic intracellular compartments by either bafilyomycin A1, a specific inhibitor of the vacuolar type H(+)-ATPase or by NH4Cl had a strong inhibitory effect during virus penetration and also prevented the cleavage of prM when added in the late phase of the viral life cycle. In the latter case the release of virus particles was not impaired. These immature (prM-containing) virions exhibited a 20- to 50-fold lower specific infectivity and HA activity than mature virions and in contrast to these did not undergo low pH-triggered aggregation. The presence of prM also affected the binding of monoclonal antibodies to protein E, especially at sites which have been shown to undergo acid pH-induced conformational changes in mature virions. Crosslinking, solubilization, and sedimentation analyses revealed the existence of prM-E heterooligomeric complexes, suggesting that the function of prM is to protect protein E from undergoing the irreversible conformational changes in acidic compartments of the secretory pathway that are necessary for triggering fusion activity in the endosome during virus entry.

The interactions of the flavivirus envelope proteins: implications for virus entry and release

Viral membrane proteins play an important role in the assembly and disassembly of enveloped viruses. Oligomerization and proteolytic cleavage events are involved in controlling the functions of these proteins during virus entry and release. Using tick-borne encephalitis virus as a model we have studied the role of the flavivirus envelope proteins E and prM/M in these processes. Experiments with acidotropic agents provide evidence that the virus is taken up by receptor-mediated endocytosis and that the acidic pH in endosomes plays an important role for virus entry. The envelope glycoprotein E undergoes irreversible conformational changes at acidic pH, as indicated by the loss of several monoclonal antibody-defined epitopes, which coincide with the viral fusion activity in vitro. Sedimentation analysis reveals that these conformational changes lead to aggregation of virus particles, apparently by the exposure of hydrophobic sequence elements. None of these features are exhibited by immature virions containing E and prM rather than E and M. Detergent solubilization, sedimentation, and crosslinking experiments provide evidence that prM forms a complex with protein E which prevents the conformational changes necessary for fusion activity. The functional role of prM before its endoproteolytic cleavage by a cellular protease thus seems to be the protection of protein E from acid-inactivation during its passage through acidic trans Golgi vesicles in the course of virus release.

The molecular biology of tick-borne encephalitis virus. Review article

Tick-borne encephalitis (TBE) virus is a member of the flavivirus genus and the family Flaviviridae. Like other flaviviruses such as yellow fever, Japanese encephalitis or the dengue viruses, it is an important human pathogen, endemic in many European countries, Russia and China. The disease can be effectively prevented by vaccination with a formalin-inactivated whole virus vaccine. In recent years major advances have been made in the understanding of the molecular biology of TBE virus, including the complete sequence analysis of the genomic RNA of the European and Far Eastern strains. As shown in these studies, the virion RNA contains a single long open reading frame that codes for the structural proteins at the 5' end and the nonstructural proteins at the 3' end. Co- and posttranslational cleavages by a viral and cellular proteases lead to the formation of individual viral proteins. The mature virion is composed of an isometric capsid surrounded by a lipid envelope with two membrane-associated proteins. One of these, protein E, is of paramount importance for several important viral functions, especially during the entry phase of the viral life cycle. Protein E is also responsible for the induction of a protective immune response. A detailed map of antigenic sites has been established and the structure of an anchor-free form of E is currently being investigated by X-ray diffraction analysis. Understanding the molecular basis of the functions of this protein together with the knowledge of its three-dimensional structure may provide clues for developing specific antiviral agents. Protein E has also been shown to be an important determinant of virulence, with single amino acid substitutions at selected sites leading to attenuation. Engineering of such mutations into cDNA clones to produce new recombinant viruses may open up new avenues for the development of live vaccines.

Assessment of the antigenic structure of tick-borne encephalitis virus by the use of synthetic peptides

The feasibility of using synthetic peptides for the identification of individual monoclonal antibody (MAb)-defined epitopes was assessed on the basis of a structural model of the tick-borne encephalitis (TBE) virus envelope glycoprotein E. For this purpose a series of 19 synthetic peptides was prepared, covering most of the E protein sequence. Each of the peptides was tested by ELISA for reactivity with 19 protein E-specific MAbs raised against TBE virus strain Neudoerfl. Specific reactivity was observed with three MAbs and two peptides (representing amino acids 1 to 22 and 221 to 240, respectively), thus providing new information on the location of the corresponding epitopes. Specificity was confirmed in a competition ELISA by the ability of the peptides to block MAb binding to TBE virus antigen. However, in contrast to the other MAbs, these peptide-reactive MAbs were not blocked by native virus particles in the competition ELISA, indicating that they do not recognize the native conformation of the E protein. These three MAbs also showed increased reactivity with denatured forms of the virus in a dot blot assay. Additionally, they reacted only in ELISA systems in which the virus was directly coated to the solid phase and thereby presumably partially denatured, but not when a capture antibody was used, which preserves the native antigen conformation. We have thus identified two classes of MAbs, those which recognize the native form and those which recognize the denatured form of protein E. The latter may be useful for the analysis of sites probably involved in protein folding and oligomerization.

Evaluation of 3 nonradioactive DNA detection systems for identification of herpes simplex DNA amplified from cerebrospinal fluid

The efficiencies of 4 different hybridization assays, using probes labeled with 32P, digoxigenin (DIG) and biotin, were compared for the detection of herpes simplex virus (HSV) DNA amplified from cerebrospinal fluid during herpes simplex encephalitis (HSE). The biotinylated probe was shown to provide a clearly lower sensitivity than the radioactive hybridization system, regardless of whether the biotin-labeled probe was detected by a colorimetric or by a photobiotin assay. In contrast, the DIG system, which includes a luminescent detection step was shown to be equivalent to the 32P system, at least at lower template concentrations. Although generally higher background signals were observed with the DIG assay the analysis of 73 CSF samples yielded identical results with the 32P and the DIG test systems in all cases, identifying concordantly an HSE in 6 patients. Since the time necessary for the performance of both assays is similar the DIG system seems to be a powerful alternative to the radioactive detection of amplified HSV DNA.

Complete genomic sequence of Powassan virus: evaluation of genetic elements in tick-borne versus mosquito-borne flaviviruses

The complete nucleotide sequence of the positive-stranded RNA genome of the tick-borne flavivirus Powassan (10,839 nucleotides) was elucidated and the amino acid sequence of all viral proteins was derived. Based on this sequence as well as serological data, Powassan virus represents the most divergent member of the tick-borne serocomplex within the genus flaviviruses, family Flaviviridae. The primary nucleotide sequence and potential RNA secondary structures of the Powassan virus genome as well as the protein sequences and the reactivities of the virion with a panel of monoclonal antibodies were compared to other tick-borne and mosquito-borne flaviviruses. These analyses corroborated significant differences between tick-borne and mosquito-borne flaviviruses, but also emphasized structural elements that are conserved among both vector groups. The comparisons among tick-borne flaviviruses revealed conserved sequence elements that might represent important determinants of the tick-borne flavivirus phenotype.

Evaluation of the polymerase chain reaction for diagnosis of herpes simplex virus encephalitis

Cerebrospinal fluid samples from 257 patients with suspected herpes simplex virus encephalitis were prospectively analyzed by herpes simplex virus polymerase chain reaction. The polymerase chain reaction indicated herpes simplex virus encephalitis in 9 serologically proven cases and in 14 additional patients. Increased polymerase chain reaction signals were observed together with more severe neurological symptoms (P < 0.01) and within the first days of acyclovir treatment (P < 0.05).

Prevalence of hepatitis-C virus infection in children with chronic post-transfusion hepatitis

The prevalence of hepatitis-C virus (HCV) infection was investigated in a group of children with chronic post-transfusion hepatitis using a first- and second-generation HCV-antibody ELISA, 2 confirmatory tests (a second-generation recombinant immunoblot assay and a line immunoassay) as well as an HCV-polymerase chain reaction (PCR). In 33% of the children, clear discrepancies were observed between the 4 different HCV-antibody detection assays, indicating that the serological diagnosis of HCV infection is still problematic. HCV RNA was detectable by PCR in only 69% of the antibody positive patients, which may be due to a fluctuation of viraemia during the course of infection. Such a fluctuation was demonstrated in 6 patients from whom serum samples drawn at different times were investigated. In contrast, in 8 of the 15 seronegative patients, HCV infection was identified only by PCR, although the hepatitis had already persisted for more than 2 years. Antibody assays and PCR together detected HCV infection in about 90% of the patients with chronic hepatitis. When markers of hepatitis B infection were also investigated, only 6% of the cases remained undiagnosed.

Molecular epidemiology of tick-borne encephalitis virus: cross-protection between European and Far Eastern subtypes

Tick-borne encephalitis virus isolates from widely separated geographic regions of the USSR, six isolates from Hungary and one from France were compared with the European and Far Eastern prototype viruses. Peptide mapping by limited proteolysis yielded similar patterns for five selected isolates from the USSR. All isolates from Hungary and France exhibited the same reactivity pattern with a panel of 16 protein E-specific monoclonal antibodies, whereas 10 out of 12 isolates from the Soviet Union showed minor differences at certain epitopes. However, no correlation between geographic origin of the isolates and their antigenic structure was observed. No statistically significant difference in the degree of protection was detected when mice were immunized with the European prototype vaccine and challenged with three selected Asian isolates and one from the European part of the USSR.

Comparative molecular biology of flaviviruses and hepatitis C virus

Currently available sequence information suggests that the genome organization of hepatitis C virus is similar to that of flaviviruses. A positive-stranded genomic RNA contains a single long open reading frame (ORF) which is flanked by 5' and 3' noncoding sequences. This RNA codes for structural proteins at the 5' end (starting with the capsid protein) and a set of nonstructural proteins in the remainder of the genome. The latter provide essential virus-specific functions for the viral life cycle, such as protease, helicase, and RNA replicase activities. The sequence motifs characteristic of the corresponding functional protein domains are separated by similar spacings in the nonstructural regions of hepatitis C virus and flaviviruses. The structural region of the hepatitis C virus appears to consist of a capsid protein which is larger than that of flaviviruses and two putative envelope proteins which are presumably different in molecular weight and much more heavily glycosylated than their counterparts in flaviviruses. A study group of the International Committee on the Taxonomy of viruses proposes to include hepatitis C virus as a genus into the family 'flaviviridae'.

Sequence of the genes encoding the structural proteins of the low-virulence tick-borne flaviviruses Langat TP21 and Yelantsev

The structural protein coding regions of the genomes of Langat virus (strain TP21) and Yelantsev virus, which was originally described to be a low virulence natural isolate of tick-borne encephalitis virus, were cloned and sequenced. These viruses had both been used as experimental live vaccines against tick-borne encephalitis in Czechoslovakia and Russia, respectively. Peptide mapping and monoclonal antibody binding experiments yielded identical reaction patterns for Langat virus and Yelantsev virus which were distinct, however, from the pattern obtained with tick-borne encephalitis virus. Sequence analysis confirmed this distinctiveness and proved that the vaccine strain Yelantsev was also Langat virus. The envelope protein E of both viruses exhibits an 88% amino acid sequence homology with that of tick-borne encephalitis virus. Assessment of the antigenic reactivity and sequence comparison with the E protein of tick-borne encephalitis virus revealed several differences affecting epitopes involved in virus neutralization. These observations suggest that Langat-like virus-based vaccines may not represent the most effective means to achieve protection against tick-borne encephalitis virus.

The flavivirus envelope protein E: isolation of a soluble form from tick-borne encephalitis virus and its crystallization

By the use of limited trypsin digestion of purified virions, we generated a membrane anchor-free and crystallizable form of the tick-borne encephalitis virus envelope glycoprotein E. It retained its reactivity with a panel of monoclonal antibodies, and only subtle structural differences from the native protein E were recognized. Treatment with the bifunctional cross-linker dimethylsuberimidate resulted in the formation of a dimer. Crystallization experiments yielded hexagonal rod-shaped crystals suitable for X-ray diffraction analysis.

Presence of poly(A) in a flavivirus: significant differences between the 3' noncoding regions of the genomic RNAs of tick-borne encephalitis virus strains

A poly(A) tail was identified on the 3' end of the prototype tick-borne encephalitis (TBE) virus strain Neudoerfl. This is in contrast to the general lack of poly(A) in the genomic RNAs of mosquito-borne flaviviruses analyzed so far. Analysis of several closely related strains of TBE virus, however, revealed the existence of two different types of 3' noncoding (NC) regions. One type (represented by strain Neudoerfl) is only 114 nucleotides long and carries a 3'-terminal poly(A) structure. This was also found in several TBE virus strains isolated from different geographic regions over a period of almost 30 years. The other type (represented by strain Hypr) is 461 nucleotides long and not polyadenylated. The sequence homology between the two types of TBE virus 3' NC regions terminates at a specific position 81 nucleotides after the stop codon. The second type of 3' NC region more closely resembles the common flavivirus pattern, including the potential for the formation of a 3'-terminal hairpin structure. However, it lacks primary sequence elements that are conserved among other flavivirus genomes.

Detection of varicella-zoster virus DNA by polymerase chain reaction in the cerebrospinal fluid of patients suffering from neurological complications associated with chicken pox or herpes zoster

The polymerase chain reaction (PCR) was used to detect varicella-zoster virus (VZV) DNA in the cerebrospinal fluid of patients with VZV infection associated with neurological symptoms. Positive results were obtained in three of five children with post-chicken pox cerebellitis and in seven of seven herpes zoster patients with neurological symptoms. The PCR thus provides a useful tool for the early diagnosis of VZV-associated neurological disease.

Fusion activity of flaviviruses: comparison of mature and immature (prM-containing) tick-borne encephalitis virions

The fusion activity of flaviviruses [tick-borne encephalitis (TBE) virus and Japanese encephalitis virus] was assessed by inducing fusion from without of C6/36 mosquito cells with purified virus preparations. Membrane fusion and polykaryocyte formation was observed only after incubating the viruses at acidic pH. Two groups of monoclonal antibodies reacting with distinct non-overlapping antigenic domains on the TBE virus protein E inhibited fusion from without. One of these domains contains the most highly conserved and putative fusion-active sequence of the flavivirus protein E. Of five TBE virus monoclonal antibody escape mutants, each defined by a single amino acid substitution in the envelope protein E, one revealed a reduced fusion activity and another one a lower pH threshold. TBE virus grown in the presence of ammonium chloride as well as Langat virus purified from the supernatant of infected chick embryo cells contained the precursor of protein M (prM) rather than M itself. These 'immature' virions did not cause fusion from without, suggesting that the proteolytic processing of prM may be necessary for the generation of fusion-competent virions.

The relationship between the flaviviruses Skalica and Langat as revealed by monoclonal antibodies, peptide mapping and RNA sequence analysis

The flavivirus Skalica was isolated from a bank vole in Czechoslovakia in 1976. It can be serologically distinguished from prototype strains of tick-borne encephalitis (TBE) virus and has a decreased virulence for adult mice. We have further defined the relationship of Skalica virus to other members of the TBE serocomplex (TBE European and Far Eastern subtypes, Langat and louping ill virus) by using a panel of 22 monoclonal antibodies, peptide mapping and RNA sequence analyses. By these criteria Skalica virus proved to be distinct from TBE virus and to be very closely related to Langat virus, differing by only two bases among a total of 416 nucleotides compared. The sequence of 22% of the Langat genome was determined and the encoded amino acid sequences were derived. Comparison of these with the corresponding amino acid sequences of TBE virus revealed a similarity of 85%, as opposed to 93% similarity between the European and Far Eastern subtypes of TBE virus.

Establishment of PCR for the early diagnosis of herpes simplex encephalitis

The early detection of herpes simplex encephalitis (HSE) represents a major problem in viral diagnostics. We have now established a test system based on PCR for the specific amplification of HSV-DNA in cerebrospinal fluid (CSF) samples followed by oligonucleotide hybridization. The test proved to be very sensitive. Five molecules of HSV 1 DNA still yielded positive signals after hybridization. The assay was applied to CSF samples from 6 patients with confirmed HSE. All except one CSF sample obtained from the 2nd to the 8th day after onset of neurological symptoms yielded positive results. The primers used also exhibit a certain degree of crossreactivity with HSV 2, as revealed by testing of a CSF sample from an HSV 2-infected child. No positive signals were obtained with human DNA and with DNA from CMV- and VZV-infected fibroblasts. Also 42 CSF samples of patients suffering from other diseases of the CNS yielded negative results. The present results indicate that the detection of HSV DNA in CSF by PCR represents a valuable tool for the early diagnosis of HSE.

Antibody response to gp E of tick-borne encephalitis virus: comparison between natural infection and vaccination breakdown

Human sera obtained after tick-borne encephalitis (TBE) without prior vaccination were compared with sera from patients after a vaccination breakdown. Most sera previously shown to have high titers of IgG and IgM against TBE virus as detected in the ELISA and hemagglutination inhibition (HI) tests also reacted in Western blot with TBE virus E protein which is involved in virus neutralization. The serum of a patient with a vaccination breakdown, however, reacted only very weakly with the E protein in the Western blot in spite of a high amount of antibodies detectable in ELISA. Using SDS-denaturated virus as an antigen in ELISA (imitating the blotting condition), this serum revealed a significant reduction in its reactivity with denatured virus compared to the control sera. This indicates that the patient had an insufficient immune response against certain denaturation resistant epitopes which might contribute to development of disease despite vaccination. The analysis of the immune response of human sera at the epitope level revealed a characteristic "fingerprint" for each serum reflecting the genetic control of the production of antibody populations against different antigenic determinants.

Relevance of hepatitis B DNA detection in patient's serum

Detection of HBV-DNA showed a satisfactory sensitivity (6 pg/ml) and high specificity: 15 patients with hepatitis A, 6 with CMV, 7 with EBV infection, 81 with hepatitis NANB as well as 174 persons with isolated HBc antibodies and 9 hepatitis B vaccinees gave negative results. However, out of 118 persons with a history of hepatitis B (HBs and HBc antibodies positive), one repeatedly had a positive result. We followed 58 patients with chronic hepatitis B, 25 healthy antigen carries, and 16 HBV-infected dialysis patients over an extended period with multiple blood sampling. Most of those patients showed changes of detectability of HBV-DNA. Typically, periods with positive DNA tests were followed by intervals with negative tests which could last for up to a few years. 75% of dialysis patients were positive in all sera available, while 48% of healthy antigen carriers were consistently negative. Additionally, 9 patients with a history of recent hepatitis B and a positive HBs antibody test as well as 4 patients with simultaneous infection by A and B were tested for HBV-DNA. In none of these two groups, a variation from the pattern usually found in hepatitis B was established. A case of intrauterine infection with hepatitis B virus is reported. Because the blood of the mother was free from HBV-DNA and HBe antigen at delivery and because the hepatitis B immunoglobulin prophylaxis failed in the child who developed HBs antigen very soon after delivery, it has been concluded that the child was infected in utero. The highest values of HBV-DNA determined quantitatively were found in dialysis patients which explains the high risk of acquiring hepatitis B in the dialysis unit. The results from earlier studies on the prognostic relevance of HBV-DNA and the risk of medical personnel as a source of infection with hepatitis B are discussed briefly.

Discrimination between antibodies to HIV-1 and HIV-2 in sera from northern Zaire

136 selected sera from Northern Zaire were screened for antibodies against HIV-1 and HIV-2 using the ELISA method. Reactive sera were confirmed with commercially available Western Blots and additional tests. A data base was used for evaluation of the results. The sera were collected in the town Isiro and in remote rural areas. 36 sera were reactive in the HIV-1 ELISA (ELAVIA-1), 19 of them were confirmed in the HIV-1 Western Blot (Biorad). 21 sera were reactive in the HIV-2 ELISA, but they were not confirmed as HIV-2-specific in three HIV-2 Western Blots (Diagnostics Pasteur, Biorad, Paul-Ehrlich-Institut).

[HIV infection and AIDS in Austria]

AIDS is a notifiable disease in Austria. Until August 31, 1989, a total of 324 cases were recorded, with 145 deaths. Since 1988, the annual doubling of cases that was initially found is no longer observed. Centralization of confirmatory testing of samples that are positive in the ELISA permits us to follow up the incidence and prevalence of HIV infections. By September 15, 1989, a total of 3,071 persons were found to be infected. The highest rates of AIDS patients and seropositive individuals were recorded in Vienna (151/1,712), followed by Upper Austria (63/606) and the Tyrol (29/367). Among those found to be positive since October 1987, 28% are homo- or bisexual and 42% are i.v. drug addicts. About 4% of men and women report heterosexual contacts as the likely mode of infection. Since 1986 the yearly incidence of HIV infection appears to be decreasing. This development corresponds with a decline in other sexually transmitted diseases (gonorrhoea, hepatitis B) and indicates a change in the sexual behaviour of the population.

Efficiency of the polymerase chain reaction for the detection of human immunodeficiency virus type (HIV-1) DNA in the lymphocytes of infected persons: comparison to antigen-enzyme-linked immunosorbent assay and virus isolation

Seventy-one human immunodeficiency virus type (HIV-1)-positive patients were investigated by polymerase chain reaction (PCR), virus isolation, and antigen detection for the existence of HIV in blood. The identification of HIV DNA by PCR, using three different pairs of primers, yielded a clearly higher detection rate (86%) than with two primer pairs (75%) and was far more sensitive than virus isolation (45%) and antigen ELISA (14%). The PCR-negative results were clearly correlated to asymptomatic clinical stages. However, there was a limited correlation between the clinical stage of disease and the amount of HIV DNA that could be detected in equal numbers of CD4+ cells from different patients, which might be due to their treatment with azido-thymidine (AZT).