Identification of African swine fever virus-like elements in the soft tick genome provides insights into the virus' evolution.

BACKGROUND: African swine fever virus (ASFV) is a most devastating pathogen affecting swine. In 2007, ASFV was introduced into Eastern Europe where it continuously circulates and recently reached Western Europe and Asia, leading to a socio-economic crisis of global proportion. In Africa, where ASFV was first described in 1921, it is transmitted between warthogs and soft ticks of the genus Ornithodoros in a so-called sylvatic cycle. However, analyses into this virus' evolution are aggravated by the absence of any closely related viruses. Even ancient endogenous viral elements, viral sequences integrated into a host's genome many thousand years ago that have proven extremely valuable to analyse virus evolution, remain to be identified. Therefore, the evolution of ASFV, the only known DNA virus transmitted by arthropods, remains a mystery. RESULTS: For the identification of ASFV-like sequences, we sequenced DNA from different recent Ornithodoros tick species, e.g. O. moubata and O. porcinus, O. moubata tick cells and also 100-year-old O. moubata and O. porcinus ticks using high-throughput sequencing. We used BLAST analyses for the identification of ASFV-like sequences and further analysed the data through phylogenetic reconstruction and molecular clock analyses. In addition, we performed tick infection experiments as well as additional small RNA sequencing of O. moubata and O. porcinus soft ticks. CONCLUSION: Here, we show that soft ticks of the Ornithodoros moubata group, the natural arthropod vector of ASFV, harbour African swine fever virus-like integrated (ASFLI) elements corresponding to up to 10% (over 20 kb) of the ASFV genome. Through orthologous dating and molecular clock analyses, we provide data suggesting that integration could have occurred over 1.47 million years ago. Furthermore, we provide data showing ASFLI-element specific siRNA and piRNA in ticks and tick cells allowing for speculations on a possible role of ASFLI-elements in RNA interference-based protection against ASFV in ticks. We suggest that these elements, shaped through many years of co-evolution, could be part of an evolutionary virus-vector 'arms race', a finding that has not only high impact on our understanding of the co-evolution of viruses with their hosts but also provides a glimpse into the evolution of ASFV.

Related strains of African swine fever virus with different virulence: genome comparison and analysis.

Two strains of African swine fever virus (ASFV), the high-virulence Lisboa60 (L60) and the low-virulence NH/P68 (NHV), which have previously been used in effective immunization/protection studies, were sequenced. Both were isolated in Portugal during the 11-year period after the introduction of ASFV to the European Continent in 1957. The predicted proteins coded by both strains were compared, and where differences were found these were also compared to other strains of known virulence. This highlighted several genes with significant alterations in low-virulence strains of ASFV that may constitute virulence factors, several of which are still uncharacterized regarding their function. Phylogenetic analysis grouped L60 and NHV closest to other P72 genotype I ASFV strains from Europe and West Africa, consistent with the assumed West African origin of all European strains. Interestingly, a relatively lower genomic identity exists between L60 and NHV, both isolated in a similar geographical location 8 years apart, than with other European and west African strains isolated subsequently and in more distant locations. This may reflect the intensive passage in tissue culture, during the early 1960s, of a Portuguese isolate to obtain an attenuated vaccine, which may have led to NHV. This study contributes to a better understanding of the evolution of ASFV, and defines additional potential virulence genes for future studies of pathogenesis towards the development of effective vaccines.

Course and transmission characteristics of oral low-dose infection of domestic pigs and European wild boar with a Caucasian African swine fever virus isolate.

In 2007, African swine fever virus (ASFV) was introduced into the Transcaucasian countries and Russia. Since then, it has spread alarmingly and reached the European Union. ASFV strains are highly virulent and lead to almost 100% mortality under experimental conditions. However, the possibility of dose-dependent disease courses has been discussed. For this reason, a study was undertaken to assess the risk of chronic disease and the establishment of carriers upon low-dose oronasal infection of domestic pigs and European wild boar. It was demonstrated that very low doses of ASFV are sufficient to infect especially weak or runted animals by the oronasal route. Some of these animals did not show clinical signs indicative of ASF, and they developed almost no fever. However, no changes were observed in individual animal regarding the onset, course and outcome of infection as assessed by diagnostic tests. After amplification of ASFV by these animals, pen- and stablemates became infected and developed acute lethal disease with similar characteristics in all animals. Thus, we found no indication of prolonged or chronic individual courses upon low-dose infection in either species. The scattered onset of clinical signs and pathogen detection within and among groups confirms moderate contagiosity that is strongly linked with blood contact. In conclusion, the prolonged course at the "herd level" together with the exceptionally low dose that proved to be sufficient to infect a runted wild boar could be important for disease dynamics in wild-boar populations and in backyard settings.

Three viruses of the bovine respiratory disease complex apply different strategies to initiate infection.

Bovine respiratory disease complex (BRDC) is the major cause of serious respiratory tract infections in calves. The disease is multifactorial, with either stress or reduced immunity allowing several pathogens to emerge. We investigated the susceptibility of bovine airway epithelial cells (BAEC) to infection by the three major viruses associated with the BRDC: bovine respiratory syncytial virus (BRSV), bovine herpesvirus type 1 (BHV-1) and bovine parainfluenza virus type 3 (BPIV3). For this purpose, two culture systems for well-differentiated BAEC were used: the air-liquid interface (ALI) system, where filter-grown BAEC differentiate into a pseudostratified respiratory epithelium and precision-cut lung slices (PCLS) where BAEC are maintained in the original tissue organisation. Comparative infection studies demonstrated that entry and release of BPIV3 occurred specifically via the apical membrane with ciliated cells being the major target cells. By contrast, airway epithelial cells were largely resistant to infection by BHV-1. When the epithelial barrier was abolished by opening tight junctions or by injuring the cell monolayer, BHV-1 infected mainly basal cells. Respiratory epithelial cells were also refractory to infection by BRSV. However, this virus infected neither differentiated epithelial cells nor basal cells when the integrity of the epithelial barrier was destroyed. In contrast to cells of the airway epithelium, subepithelial cells were susceptible to infection by BRSV. Altogether, these results indicate that the three viruses of the same disease complex follow different strategies to interact with the airway epithelium. Possible entry mechanisms are discussed.

A novel bromodeoxyuridine-resistant wild boar lung cell line facilitates generation of African swine fever virus recombinants.

Manipulation of African swine fever virus (ASFV) genomes, in particular those from field strains, is still a challenge. We have shown recently that generation of a green-fluorescent-protein-expressing, thymidine-kinase-negative (TK-) mutant of the low-pathogenic African swine fever virus field strain NHV was supported by a TK- Vero cell line. Since NHV, like other ASFV field strains, does not replicate well in Vero cells, a bromodeoxyuridine (BrdU)- resistant cell line derived from wild boar lung (WSL) cells, named WSL-Bu, was selected. WSL cells were used because they are suitable for productive replication of NHV and other ASFV field strains. Here, we show that WSL-Bu cells enable positive selection of both TK- and TK+ ASFV recombinants, which allows for novel strategies for construction of ASFV mutants. We further demonstrate for a low-pathogenic ASFV strain that TK expression is required for infectious replication in macrophages infected at low multiplicity and that vaccinia TK fully complements ASFV TK in this respect.

Virus species polemics: 14 senior virologists oppose a proposed change to the ICTV definition of virus species.

The Executive Committee of the International Committee on Taxonomy of Viruses (ICTV) has recently decided to modify the current definition of virus species (Code of Virus Classification and Nomenclature Rule 3.21) and will soon ask the full ICTV membership (189 voting members) to ratify the proposed controversial change. In this discussion paper, 14 senior virologists, including six Life members of the ICTV, compare the present and proposed new definition and recommend that the existing definition of virus species should be retained. Since the pros and cons of the proposal posted on the ICTV website are not widely consulted, the arguments are summarized here in order to reach a wider audience.

Deletion of the CD2v Gene from the Genome of ASFV-Kenya-IX-1033 Partially Reduces Virulence and Induces Protection in Pigs.

Infection of pigs with the African swine fever virus (ASFV) leads to a devastating hemorrhagic disease with a high mortality of up to 100%. In this study, a CD2v gene deletion was introduced to a genotype IX virus from East Africa, ASFV-Kenya-IX-1033 (ASFV-Kenya-IX-1033-∆CD2v), to investigate whether this deletion led to reduced virulence in domestic pigs and to see if inoculation with this LA-ASFV could induce protective immunity against parental virus challenge. All pigs inoculated with ASFV-Kenya-IX-1033-ΔCD2v survived inoculation but presented with fever, reduced appetite and lethargy. ASFV genomic copies were detected in only one animal at one time point. Seven out of eight animals survived subsequent challenge with the pathogenic parental strain (87.5%) but had mild to moderate clinical symptoms and had a gross pathology compatible with chronic ASFV infection. All mock-immunised animals developed acute ASF upon challenge with ASFV-Kenya-IX-1033 and were euthanised upon meeting the humane endpoint criteria. ASFV genome copy numbers after challenge were similar in the two groups. ASFV-Kenya-IX-1033-∆CD2v is therefore a useful tool to investigate the development of immunity to ASFV genotype IX, but safety concerns preclude its use as a candidate vaccine without further attenuation.

Serological Hendra Virus Diagnostics Using an Indirect ELISA-Based DIVA Approach with Recombinant Hendra G and N Proteins.

Since the identification of Hendra virus (HeV) infections in horses in Australia in 1994, more than 80 outbreaks in horses have been reported, and four out of seven spillover infections in humans had a fatal outcome. With the availability of a subunit vaccine based on the HeV-Glycoprotein (HeV-G), there is a need to serologically Differentiate the Infected from the Vaccinated Animals (DIVA). We developed an indirect ELISA using HeV-G expressed in Leishmania tarentolae and HeV-Nucleoprotein (HeV-N) expressed in recombinant baculovirus-infected insect cells as antigens. During evaluation, we tested panels of sera from naïve, vaccinated and infected horses that either originated from a Hendra-virus free region, or had been pre-tested in validated diagnostic tests. Our data confirm the reliability of this approach, as HeV-N-specific antibodies were only detected in sera from infected horses, while HeV-G-specific antibodies were detected in infected and vaccinated horses with a high level of specificity and sensitivity. Given the excellent correlation of data obtained for German and Australian HeV-negative horses, we assume that this test can be applied for the testing of horse serum samples from a variety of geographical regions.

In vitro-generated interspecific recombinants between bovine herpesviruses 1 and 5 show attenuated replication characteristics and establish latency in the natural host.

BACKGROUND: Interspecific recombinant viruses R1ΔgC and R2ΔgI were isolated after in vitro co-infection with BoHV-1 and BoHV-5, two closely related alphaherpesviruses that infect cattle. The genetic characterization of R1ΔgC and R2ΔgI showed that they are composed of different sections of the parental genomes. The aim of this study was the characterization of the in vivo behavior of these recombinants in the natural host. RESULTS: Four groups of four 3-month-old calves of both genders were intranasally inoculated with either the recombinant or parental viruses. A control group of two animals was also included. Viral excretion and clinical signs were monitored after infection. Histopathological examination of the central nervous system (CNS) was performed and the establishment of latency in trigeminal ganglia was analyzed by PCR. The humoral response was also evaluated using ELISA tests. Three out of four animals from the BoHV-5 infected group excreted virus for 4-10 days. Two calves shed R1ΔgC virus for one day. In R2ΔgI and BoHV-1.2ΔgCΔgI groups, infectious virus was isolated only after two or three blind passages. None of the infected animals developed neurological signs, although those infected with BoHV-5 showed histopathological evidence of viral infection. Latent viral DNA was detected in at least one calf from each infected group. Serum and/or mucosal antibodies were detected in all groups. CONCLUSION: Both BoHV-1/-5 recombinants and the BoHV-1 parental strain are attenuated in calves, although they are able to replicate in animals at low rates and to establish latent infections.

Efficacy of Newcastle disease virus recombinant expressing avian influenza virus H6 hemagglutinin against Newcastle disease and low pathogenic avian influenza in chickens and turkeys.

A recombinant Newcastle disease virus (NDV) expressing H6 hemagglutinin (HA) of a low pathogenic avian influenza virus (LPAIV) was generated by reverse genetics (NDVH6). The H6 open reading frame was inserted as an additional transcription unit between the fusion and hemagglutinin-neuraminidase (HN) gene of lentogenic NDV clone 30. Expression of the foreign gene was demonstrated by northern blot, western blot, and indirect immunofluorescence analyses. The protective efficacy against Newcastle disease and avian influenza of subtype H6 was evaluated in 3-wk-old chickens and turkeys. A single vaccination protected specific-pathogen-free (SPF) chickens against a subsequent lethal NDV infection and prevented shedding of AIV after homologous H6 LPAIV infection. Furthermore, vaccinated and AIV-infected animals could be differentiated by detection of AIV nucleoprotein-specific antibodies. Three-week-old commercial turkeys, exhibiting NDV-specific maternal antibodies, were partially protected against a lethal NDV challenge infection. The mortality rate of NDVH6-immunized turkeys was reduced to 40% compared to 90% in unvaccinated birds. After H6 LPAIV infection, shedding in NDVH6-immunized turkeys was only marginally reduced compared to NDV-immunized control birds. We previously described HA-expressing NDV recombinants as potent bivalent vaccines against Newcastle disease and highly pathogenic avian influenza of subtype H5 or H7. The results presented here are in contrast to the high protective efficacy in SPF chickens, as a single vaccination with NDVH6 was insufficient in turkeys in the presence of maternal antibodies against NDV. Therefore, the vector virus has to be improved to overcome these limitations.

Effect of foot-and-mouth disease virus capsid precursor protein and 3C protease expression on bovine herpesvirus 1 replication.

Several reports have previously shown that expression of the foot-and-mouth disease virus (FMDV) capsid precursor protein encoding region P1-2A together with the 3C protease (P1-2A/3C) results in correct processing of the capsid precursor into VP0, VP1 and VP3 and formation of FMDV capsid structures that are able to induce a protective immune response against FMDV challenge after immunization using naked DNA constructs or recombinant viruses. To elucidate whether bovine herpesvirus 1 (BHV-1) might also be suitable as a viral vector for empty capsid generation, we aimed to integrate a P1-2A/3C expression cassette into the BHV-1 genome, which, however, failed repeatedly. In contrast, BHV-1 recombinants that expressed an inactive 3C protease or the P1-2A polyprotein alone could be easily generated, although the recombinant that expressed P1-2A exhibited a defect in direct cell-cell spread and release of infectious particles. These results suggested that expression of the original, active FMDV 3C protease is not compatible with BHV-1 replication. This conclusion is supported by the isolation of recombinant BHV-1/3C*, which contained mutations within the 3C ORF (3C* ORF)--probably introduced spontaneously during generation of BHV-1/3C*--instead of the authentic 3C ORF contained in the transfer plasmids. Within the 3C* ORF, the codons for glycine 38 and phenylalanine 48 were both substituted by codons for serine. The resulting 3C* protease exhibits a highly reduced activity for proteolytic processing of the P1-2A polyprotein and thus might be a good candidate for the generation of live attenuated FMDV variants.

A proposal to change existing virus species names to non-Latinized binomials.

A proposal has been posted on the ICTV website (2011.001aG.N.v1.binomial_sp_names) to replace virus species names by non-Latinized binomial names consisting of the current italicized species name with the terminal word "virus" replaced by the italicized and non-capitalized genus name to which the species belongs. If implemented, the current italicized species name Measles virus, for instance, would become Measles morbillivirus while the current virus name measles virus and its abbreviation MeV would remain unchanged. The rationale for the proposed change is presented.

Pea-derived vaccines demonstrate high immunogenicity and protection in rabbits against rabbit haemorrhagic disease virus.

Vaccines against rabbit haemorrhagic disease virus (RHDV) are commercially produced in experimentally infected rabbits. A genetically engineered and manufactured version of the major structural protein of RHDV (VP60) is considered to be an alternative approach for vaccine production. Plants have the potential to become an excellent recombinant production system, but the low expression level and insufficient immunogenic potency of plant-derived VP60 still hamper its practical use. In this study, we analysed the expression of a novel multimeric VP60-based antigen in four different plant species, including Nicotiana tabacum L., Solanum tuberosum L., Brassica napus L. and Pisum sativum L. Significant differences were detected in the expression patterns of the novel fusion antigen cholera toxin B subunit (CTB)::VP60 (ctbvp60(SEKDEL)) at the mRNA and protein levels. Pentameric CTB::VP60 molecules were only detected in N. tabacum and P. sativum, and displayed equal levels of CTB, at approximately 0.01% of total soluble protein (TSP), and traces of detectable VP60. However, strong enhancement of the CTB protein content via self-fertilization was only observed in P. sativum, where it reached up to 0.7% of TSP. In rabbits, a strong decrease in the protective vaccine dose required from 48-400 microg potato-derived VP60 [Castanon, S., Marin, M.S., Martin-Alonso, J.M., Boga, J.A., Casais, R., Humara, J.M., Ordas, R.J. and Parra, F. (1999) Immunization with potato plants expressing VP60 protein protects against rabbit hemorrhagic disease virus. J. Virol. 73, 4452-4455; Castanon, S., Martin-Alonso, J.M., Marin, M.S., Boga, J.A., Alonso, P., Parra, F. and Ordas, R.J. (2002) The effect of the promoter on expression of VP60 gene from rabbit hemorrhagic disease virus in potato plants. Plant Sci. 162, 87-95] to 0.56-0.28 microg antigenic VP60 (measured with VP60 enzyme-linked immunosorbent assay) of crude CTB::VP60 pea extracts was demonstrated. Rabbits immunized with pea-derived CTB::VP60 showed anti-VP60-specific antibodies, similar to RikaVacc((R))-immunized rabbits, and survived RHDV challenge.

The fusion protein of respiratory syncytial virus triggers p53-dependent apoptosis.

Infection with respiratory syncytial virus (RSV) frequently causes inflammation and obstruction of the small airways, leading to severe pulmonary disease in infants. We show here that the RSV fusion (F) protein, an integral membrane protein of the viral envelope, is a strong elicitor of apoptosis. Inducible expression of F protein in polarized epithelial cells triggered caspase-dependent cell death, resulting in rigorous extrusion of apoptotic cells from the cell monolayer and transient loss of epithelial integrity. A monoclonal antibody directed against F protein inhibited apoptosis and was also effective if administered to A549 lung epithelial cells postinfection. F protein expression in epithelial cells caused phosphorylation of tumor suppressor p53 at serine 15, activation of p53 transcriptional activity, and conformational activation of proapoptotic Bax. Stable expression of dominant-negative p53 or p53 knockdown by RNA interference inhibited the apoptosis of RSV-infected A549 cells. HEp-2 tumor cells with low levels of p53 were not sensitive to RSV-triggered apoptosis. We propose a new model of RSV disease with the F protein as an initiator of epithelial cell shedding, airway obstruction, secondary necrosis, and consequent inflammation. This makes the RSV F protein a key target for the development of effective postinfection therapies.

Immunohistochemistry for detection of avian infectious bronchitis virus strain M41 in the proventriculus and nervous system of experimentally infected chicken embryos.

BACKGROUND: Infectious bronchitis virus primarily induces a disease of the respiratory system, different IBV strains may show variable tissue tropisms and also affect the oviduct and the kidneys. Proventriculitis was also associated with some new IBV strains. Aim of this study was to investigate by immunohistochemistry (IHC) the tissue tropism of avian infectious bronchitis virus (IBV) strain M41 in experimentally infected chicken embryos. RESULTS: To this end chicken embryos were inoculated in the allantoic sac with 10(3) EID(50) of IBV M41 at 10 days of age. At 48, 72, and 120 h postinoculation (PI), embryos and chorioallantoic membranes (CAM) were sampled, fixed, and paraffin-wax embedded. Allantoic fluid was also collected and titrated in chicken embryo kidney cells (CEK). The sensitivity of IHC in detecting IBV antigens in the CAM of inoculated eggs matched the virus reisolation and detection in CEK. Using IHC, antigens of IBV were detected in nasal epithelium, trachea, lung, spleen, myocardial vasculature, liver, gastrointestinal tract, kidney, skin, sclera of the eye, spinal cord, as well as in brain neurons of the inoculated embryos. These results were consistent with virus isolation and denote the wide tissue tropism of IBV M41 in the chicken embryo. Most importantly, we found infection of vasculature and smooth muscle of the proventriculus which has not seen before with IBV strain M41. CONCLUSION: IHC can be an additional useful tool for diagnosis of IBV infection in chickens and allows further studies to foster a deeper understanding of the pathogenesis of infections with IBV strains of different virulence. Moreover, these results underline that embryonic tissues in addition to CAM could be also used as possible source to generate IBV antigens for diagnostic purposes.

Modified bovine herpesvirus 1 for protein secretion.

The traditional way to utilize bovine herpesvirus 1 (BHV-1) and many other herpesviruses as vectors for synthesis of heterologous proteins like reporter proteins, antigens, or immunomodulatory active molecules was (and still is) the expression of the protein of interest from an entire gene consisting of promoter, 5'- and 3'-noncoding regions, the open reading frame (ORF), and a signal sequence for polyadenylation. This approach is doubtlessly appropriate especially in cases when expression of large proteins or of proteins that do not enter the secretory pathway is envisaged. My laboratory has developed an alternative expression strategy for secreted proteins and peptides that uses the essential BHV-1 glycoprotein B (gB) as transporter for a cargo protein that is embedded in gB as a furin-excisable polypeptide that is released from the gB precursor molecule in the trans-Golgi network by the ubiquitously present endoprotease furin. The general applicability of this novel expression strategy is demonstrated by using GFP as reporter protein to monitor secretion. We hypothesize that also other secreted or membrane-bound (glyco)proteins can be engineered to function as transporters for oligopeptides and also more complex larger proteins.

Sequence diversity of the haemagglutinin open reading frame of recent highly pathogenic avian influenza H5N1 isolates from Egypt.

The sequences encoding the haemagglutinin (HA) of twelve H5N1 isolates obtained in 2006 and 2007 from different avian species in backyard holdings and poultry farms in Egypt revealed amino acid variations across the polypeptide and also in the polybasic cleavage motif of three of the isolates from backyard poultry with one, so far, unique mutation in an isolate from a chicken. The HAs of two isolates (A/goose/Egypt/R4/2007, A/chicken/Egypt/R3/2007) collected on the same day in the same village from two neighbouring houses were found to differ from each other. Five out of the seven nucleotide exchanges in these two isolates were translationally silent, and two resulted in amino acid substitutions: one in the polybasic cleavage motif and the other in the signal peptide. Circulation of different H5N1 strains possessing considerable variations in backyard poultry, particularly domestic waterfowl, draws attention to the evolution of H5N1 subtypes in Egypt.

Vaccination with Newcastle disease virus vectored vaccine protects chickens against highly pathogenic H7 avian influenza virus.

A recombinant Newcastle disease virus (NDV) was engineered to express the hemagglutinin (HA) gene of avian influenza virus (AIV) subtype H7. The HA gene was inserted between the genes encoding NDV fusion and hemagglutinin-neuraminidase proteins. Within the H7 open reading frame, an NDV gene end-like sequence was eliminated by silent mutation. The expression of H7 protein was detected by western blot analysis and indirect immunofluorescence. The existence of H7 protein in the envelope of recombinant Newcastle disease virions was shown by immunoelectron microscopy. The protective efficacy of recombinant NDVH7m against virulent NDV, as well as against highly pathogenic avian influenza virus (HPAIV), was evaluated in specific-pathogen-free chickens. After a single immunization, all chickens developed NDV-specific, as well as AIV H7-specific, antibodies and were completely protected from clinical disease after infection with a lethal dose of virulent NDV or the homologous H7N1 HPAIV, while all control animals died within four days. Shedding of AIV challenge virus was strongly reduced compared to nonvaccinated control birds. Furthermore, the immunized birds developed antibodies against the AIV nucleoprotein after challenge infection. Thus, NDVH7m could be used as a marker vaccine against subtype H7 avian influenza.

Productive replication of peste des petits ruminants virus Nigeria 75/1 vaccine strain in vero cells correlates with inefficiency of maturation of the viral fusion protein.

Peste des petits ruminants virus (PPRV), a member of the genus Morbillivirus, in the family Paramyxoviridae expresses two membrane glycoproteins, the fusion (F) and haemagglutinin (H) glycoproteins which mediate virus-to-cell fusion and cell-to-cell fusion leading to the induction of syncytia in PPRV infected cells. In the context of the characterization of the virulent lineage IV strain PPRV Kurdistan 2011, isolated from wild goats from the Kurdistan region in Iraq, we observed that both PPRV Kurdistan 2011 and the PPRV Nigeria 75/1 vaccine strain led to induction of large syncytia in Vero-dogSLAM cells within 48 h whereas both failed to induce detectable cell-cell fusion events in two Vero cell lines of differing passage histories. We were unable to detect syncytium formation in transiently transfected cells expressing PPRV F or H alone whereas co-expression of F and H induced large syncytia - in Vero-dogSLAM cells only. In VeroMontpellier cells expressing PPRV F and H, fused cells were rarely detectable indicating that PPRV mediated cell fusion activity is impaired in this cell line. Surprisingly, on Vero-dogSLAM cells the vaccine strain grew to titers of 105.25 TCID50/ml, whereas infectious virus yield was about 200-fold higher on VeroMontpellier and Vero-76 cells. In contrast, the virulent Kurdistan 2011 strain grew to a maximum titer of 107.0 TCID50/ml on Vero-dogSLAM cells and only 104.5 TCID50/ml on normal Vero cells. This was as expected since Vero cells lacking the SLAM receptor for PPRV are regarded as not so permissive for infection. To elucidate the divergent productive replication behaviour of PPRV Nigeria 75/1 vaccine strain on Vero vs Vero-dogSLAM cells, we examined whether intracellular transport and/or maturation of the viral envelope glycoproteins F and H might be implicated with this phenomenon. The results indicate that F in contrast to the H glycoprotein matures inefficiently during intracellular transport in VeroMontpellier cells, thus leading to an absence of detectable syncytia formation. However, in the case of the PPRV Nigeria 75/1 vaccine strain this did not impair efficient virus assembly and release.