Analysis of the fusion protein gene of the porcine rubulavirus LPMV: comparative analysis of paramyxovirus F proteins

Development of Novel Recombinant Antigens of Nucleoprotein and Matrix Proteins of Porcine orthorubulavirus: Antigenicity and Structural Prediction

Blue eye disease (BED) is a swine viral infection that affects the pork industry of Mexico. Porcine orthorubulavirus (PRV) is the etiological agent, and the hemagglutinin-neuraminidase protein (HN) is characterized as the best antigen for serological tests, although other structural proteins, including the nucleoprotein (NP) and the matrix (M) protein, have been investigated during the infection of members of the Paramyxoviridae family, generating promising results. Herein, for the first time, we successfully produced and characterized both the NP and M proteins of PRV by using a recombinant strategy in the E. coli heterologous system. The ORF of the NP and M genes were cloned in-frame with the pET-SUMO expression vector. Recombinant proteins proved to be a sensitive target to detect seroconversion at 7 days until 28 days in vaccinated mice (BALB/c) by indirect ELISAs. Immunoreactivity was also tested using porcine serum samples, in which antibodies were recognized from early stages to a persistence of PRV infection, which is indicative that these proteins contain properties similar to native antigens. The predicted tertiary structure showed that both proteins have a conserved structure that resembles those found in others Paramyxovirus. Our results pave the way for developing biotechnological tools based on these proteins for the control and prevention of BED.

Immunoinformatics approach for predicting epitopes in HN and F proteins of Porcine rubulavirus

Porcine rubulavirus (PRV), which belongs to the family Paramyxoviridae, causes blue eye disease in pigs, characterized by encephalitis and reproductive failure in newborn and adult pigs, respectively. There is no effective treatment against PRV and no information on the effectiveness of the available vaccines. Continuous outbreaks have occurred in Mexico since the early 1980s, which have caused serious economic losses to pig producers. Vaccination can be used to control this disease. Searching for effective antigen candidates against PRV, we first sequenced the PAC1 F protein, then we used various immunoinformatics tools to predict antigenic determinants of B-cells and T-cells against the two glycoproteins of the virus (HN and F proteins). Finally, we used AutoDock Vina to determine the binding energies. We obtained the F gene sequence of a PRV strain collected in the early 1990s in Mexico and compared its amino acid profile with previous and more recent strains, obtaining an identity similarity of 97.78 to 99.26%. For the F proteins, seven linear B-cell epitopes, six conformational B-cell epitopes and twenty-nine T-cell MHC class I epitopes were predicted. For the HN proteins, sixteen linear B-cell epitopes, seven conformational B-cell epitopes and thirty-four T-cell MHC class I epitopes were predicted. The ATRSETDYY and AAYTTTTCF epitopes of the HN protein might be important for neutralizing the viral infection. We determined the in silico binding energy between the predicted epitopes on the F and HN proteins and swine MHC-I molecules. The binding energy of these epitopes ranged from -5.8 to -7.8 kcal/mol. The present study aimed to assess the use of HN and F proteins as antigens, either as recombinant proteins or as a series of peptides that could activate different responses of the immune system. This may help identify relevant immunogens, saving time and costs in the development of new vaccines or diagnostic tools.

Molecular and epidemiological studies of Porcine rubulavirus infection - an overview

Porcine rubulavirus-La Piedad-Michoacan-Mexico virus (PorPV-LPMV) was identified as the causative agent of a viral disease that emerged spontaneously in Mexican swine in the 1980s. Since the report of the initial outbreak of the disease, only one full-length genome from a strain isolated in 1984 (PorPV-LPMV/1984) has been sequenced; sequence data are scarce from other isolates. The genetic variation of this virus that has spread throughout the main endemic region of Mexico is almost a complete mystery. The development of molecular techniques for improved diagnostics and to investigate the persistence, molecular epidemiology, and the possible reservoirs of PorPV are needed. Together, this will provide greater knowledge regarding the molecular genetic changes and useful data to establish new strategies in the control of this virus in Mexico.

La Piedad Michoacán Mexico Virus V protein antagonizes type I interferon response by binding STAT2 protein and preventing STATs nuclear translocation

La Piedad Michoacán Mexico Virus (LPMV) is a member of the Rubulavirus genus within the Paramyxoviridae family. LPMV is the etiologic agent of "blue eye disease", causing a significant disease burden in swine in Mexico with long-term implications for the agricultural industry. This virus mainly affects piglets and is characterized by meningoencephalitis and respiratory distress. It also affects adult pigs, causing reduced fertility and abortions in females, and orchitis and epididymitis in males. Viruses of the Paramyxoviridae family evade the innate immune response by targeting components of the interferon (IFN) signaling pathway. The V protein, expressed by most paramyxoviruses, is a well-characterized IFN signaling antagonist. Until now, there were no reports on the role of the LPMV-V protein in inhibiting the IFN response. In this study we demonstrate that LPMV-V protein antagonizes type I but not type II IFN signaling by binding STAT2, a component of the type I IFN cascade. Our results indicate that the last 18 amino acids of LPMV-V protein are required for binding to STAT2 in human and swine cells. While LPMV-V protein does not affect the protein levels of STAT1 or STAT2, it does prevent the IFN-induced phosphorylation and nuclear translocation of STAT1 and STAT2 thereby inhibiting cellular responses to IFN α/β.

Development of a real-time RT-PCR method for detection of porcine rubulavirus (PoRV-LPMV)

In order to provide a rapid and sensitive method for detection of the Porcine rubulavirus La Piedad-Michoacan-Mexico Virus (PoRV-LPMV), we have developed a specific real-time reverse transcriptase polymerase chain reaction assay. The detection of PoRV-LPMV, represents a diagnostic challenge due to the viral RNA being present in very small amounts in tissue samples. In this study, a TaqMan(®) real-time PCR assay was designed based on the phosphoprotein gene of PoRV-LPMV, to allow specific amplification and detection of viral RNA in clinical samples. Assay conditions for the primers and probe were optimized using infected PK15 cells and ten-fold serial dilutions of a plasmid containing the whole P-gene. The sensitivity of the developed TaqMan(®) assay was approximately 10 plasmid copies per reaction, and was shown to be 1000 fold better than a conventional nested RT-PCR. The performance of this real-time RT-PCR method enables studies of various aspects of PoRV-LPMV infection. Finally, the assay detects all current known variants of the virus.

Transcription of interferon stimulated genes in response to Porcine rubulavirus infection in vitro

Porcine rubulavirus (PoRV) is an emerging virus causing meningo-encephalitis and reproductive failures in pigs. Little is known about the pathogenesis and immune evasion of this virus; therefore research on the mechanisms underlying tissue damage during infection is essential. To explore these mechanisms, the effect of PoRV on the transcription of interferon (IFN) pathway members was analyzed in vitro by semi-quantitative RT-PCR. Ten TCID₅₀ of PoRV stimulated transcription of IFNα, IFNβ, STAT1, STAT2, p48 and OAS genes in neuroblastoma cells, whereas infection with 100 TCID₅₀ did not stimulate transcription levels more than non-infected cells. When the cells were primed with IFNα, infection with 1 TCDI₅₀ of PoRV sufficed to stimulate the transcription of the same genes, but 10 and 100 TCID₅₀ did not modify the transcription level of those genes as compared with non-infected and primed controls. MxA gene transcription was observed only when the cells were primed with IFNα and stimulated with 10 TCID50, whereas 100 TCID50 of PoRV did not modify the MxA transcription level as compared to non-infected and primed cells. Our results show that PoRV replication at low titers stimulates the expression of IFN-responsive genes in neuroblastoma cells, and suggest that replication of PoRV at higher titers inhibits the transcription of several members of the IFN pathway. These findings may contribute to the understanding of the pathogenesis of PoRV.

Molecular characterization of the hemagglutinin-neuraminidase gene of porcine rubulavirus isolates associated with neurological disorders in fattening and adult pigs

"Blue eye disease" is a viral infection of swine endemic in Mexico, which produces fatal encephalitis accompanied by respiratory signs and corneal opacity in suckling piglets. An atypical blue eye disease outbreak presented high rates of neurological signs in fattening and adult pigs from 2000 to 2003. In order to identify the basis of increased neurovirulence, the hemagglutinin-neuraminidase (HN) gene of several porcine rubulavirus isolates were sequenced and compared with that of La Piedad Michoacan virus and other isolates that did not produce neurological disorders in weaned pigs. Nine amino acid mutations distinguished the high neurovirulent PAC6-PAC9 viruses, whereas five mutations characterized the low neurovirulent PAC2 and PAC3 viruses. HN protein three-dimensional models showed that the main conformation and functional domains were preserved, although substitutions A223T and A291D occurred in PAC2 and PAC3 viruses, as well as A511K and E514K presented in PAC6-PAC9 viruses considerably modified the properties of the HN protein surface. The increased positive charge of the HN protein of PAC6-PAC9 viruses seems to be associated with their increased neurovirulence.

Fibrotic lesions in the testis of bulls and relationship to semen quality

Ultrasonography of the testes was done in bulls at three locations in western Canada (n=325) and one in Argentina (n=387) to determine the prevalence of fibrotic lesions and to examine the relationship between fibrotic lesions and location, age, breed, right compared with left testes, testis size and semen quality. Fibrotic lesions were common in the testes of bulls raised under intensive rearing conditions in western Canada as well as in the more extensive rearing conditions of Argentina. Fibrotic lesions appeared as early as 5-6 months of age and the number of cases continued to increase until at least 12-14 months of age. The severity of lesions increased in some cases during this period; however, it appears that the development of lesions occurred during a finite period of pubertal development. It is unlikely that the prevalence of lesions is influenced by breed, right compared with left testes or testis size. The cause of the lesions is unknown, but there was an association between the development of fibrotic lesions and an outbreak of BRSV disease in Argentina in one group of bulls. There was some indication that during the active process that leads to fibrosis spermatogenesis is adversely affected; however, the presence of a large number of fibrotic lesions that may occupy as much as 50% of the testis parenchyma did not preclude the production of a greater percentage of sperm with normal morphology.

Full-length genome sequence and genetic relationship of two paramyxoviruses isolated from bat and pigs in the Americas

Mapuera virus (MPRV) was isolated from a fruit bat in Brazil in 1979, but its host range and disease-causing potential are unknown. Porcine rubulavirus (PoRV) was identified as the aetiological agent of disease outbreaks in pigs in Mexico during early 1980s, but the origin of PoRV remains elusive. In this study, the completed genome sequence of MPRV was determined, and the complete genome sequence of PoRV was assembled from previously published protein-coding genes and the non-coding genome regions determined from this study. Comparison of sequence and genome organization indicated that PoRV is more closely related to MPRV than to any other members of the genus Rubulavirus. In the P gene coding region of both viruses, there is an ORF located at the 5' end of the P gene overlapping with the P protein coding region, similar to the C protein ORF present in most viruses of the subfamily Paramyxovirinae, but absent in other known rubulaviruses. Based on these findings, we hypothesise that PoRV may also originate from bats, and spillover events from bats to pigs, either directly or via an intermediate host, were responsible for the sporadic disease outbreaks observed in Mexico.

Mutations in the putative HR-C region of the measles virus F2 glycoprotein modulate syncytium formation

The fusion (F) glycoproteins of measles virus strains Edmonston (MV-Edm) and wtF (MV-wtF) confer distinct cytopathic effects and strengths of hemagglutinin (H) interaction on a recombinant MV-Edm virus. They differ in just two amino acids, V94 and V101 in F-Edm versus M94 and F101 in F-wtF, both of which lie in the relatively uncharacterized F(2) domain. By comparing the sequence of MV F with those of the parainfluenza virus SV5 and Newcastle disease virus (NDV) F proteins, the structures of which are known, we show that MV F(2) also possesses a potential heptad repeat (HR) C domain. In NDV, the N-terminal half of HR-C interacts with HR-A in F(1) while the C-terminal half is induced to kink outward by a central proline residue. We found that this proline is part of an LXP motif conserved in all three viruses. Folding and transport of MV F require this motif to be intact and also require covalent interaction of cysteine residues that probably support the potential HR-A-HR-C interaction. Amino acids 94 and 101, both located in "d" positions of the HR-C helical wheel, lie in the potentially outwardly kinked region. We demonstrate that their effect on MV fusogenicity and glycoprotein interaction is mediated solely by amino acid 94. Substitutions at position 94 with polar or charged amino acids are tolerated poorly or not at all, while changes to smaller and more hydrophilic amino acids are tolerated in both transiently expressed F protein and recombinant virus. MV F V94A and MV F V94G viruses induce extensive syncytium formation and are relatively, or almost completely, resistant to a known inhibitor of MV glycoprotein-induced fusion. We propose that the conformational changes in MV F protein required to expose the fusion peptide involve the C-terminal half of the HR-C helix, specifically amino acid 94.

Both the P and V proteins of the porcine rubulavirus LPMV interact with the NP protein via their respective C-terminal unique parts

In this paper we show that the porcine rubulavirus LPMV phosphoprotein (P) and V protein (V) both interact with the nucleoprotein (NP). There are also indications for an interaction between P and V with L protein. Further analysis of the domains of the P and V which are necessary for interaction with the NP protein demonstrates that the interaction is not mediated from their common part but instead from their unique C-terminal parts, respectively. The common N-terminus of P and V appear to mediate the interaction with L. We also map the regions of NP that are necessary for interaction with P and V, respectively. Both P and V interact with regions of NP, which reside in the N-terminal part but appear not to overlap.

Molecular evolution of viral fusion and matrix protein genes and phylogenetic relationships among the Paramyxoviridae

Phylogenetic relationships among the Paramyxoviridae, a broad family of viruses whose members cause devastating diseases of wildlife, livestock, and humans, were examined with both fusion (F) and matrix (M) protein-coding sequences. Neighbor-joining trees of F and M protein sequences showed that the Paramyxoviridae was divided into the two traditionally recognized subfamilies, the Paramyxovirinae and the Pneumovirinae. Within the Paramyxovirinae, the results also showed groups corresponding to three currently recognized genera: Respirovirus, Morbillivirus, and Rubulavirus. The relationships among the three genera of the Paramyxovirinae were resolved with M protein sequences and there was significant bootstrap support (100%) showing that members of the genus Respirovirus and the genus Morbillivirus were more closely related to each other than to members of the genus Rubulavirus. Both F and M phylogenies showed that Newcastle disease virus (NDV) was more closely related to the genus Rubulavirus than to the other two genera but were consistent with the proposal (B. S. Seal et al., 2000, Virus Res. 66, 1-11) that NDV be classified as a separate genus within the Paramyxovirinae. Both F and M phylogenies were also consistent with the proposal (L. Wang et al., 2000, J. Virol 74, 9972-9979) that Hendra virus be classified as a new genus closely related and basal to the genus Morbillivirus. Rinderpest was most closely related to measles and a more derived virus than to canine distemper virus, phocine distemper virus, or dolphin morbillivirus.

Uptake of porcine rubulavirus (LPMV) by PK-15 cells

BACKGROUND

The porcine virus denominated La Piedad Michoacan Virus (LPMV) is a member of the family Paramyxoviridae and is the cause of a disease in pigs present only in Mexico. The disease is characterized by meningoencephalitis and respiratory distress in young pigs, epididymitis and orchitis in boars, and reproductive failure and abortion in sows.

METHODS

The cytopathology, morphology, and distribution of the hemagglutination neuraminidase (HN) and nucleoprotein (NP) proteins of LPMV were investigated following inoculation into PK-15 cells. The cytopathic effect was characterized by cytoplasmic vacuolation and the formation of syncytia and cytoplasmic inclusion bodies.

RESULTS

In immunofluorescence assays using a monoclonal antibody (MAb) against the HN protein at 5-60 min post-infection (early infection), a diffuse immunofluorescence was observed near the cell membrane and adjacent to the nuclear membrane. At 24 h post-infection (late infection), a dust-like immunofluorescence was observed throughout the cytoplasm. LPMV-infected cells incubated with the MAb against the NP protein showed punctate cytoplasmic fluorescence during the early stages of infection. At the late infection stage, these fluorescent particles became larger and were seen predominantly in the cytoplasm of syncytia. This pattern was also apparent by immunohistochemical labeling and immunogold electron microscopy. The latter technique revealed that HN protein was diffusely distributed throughout the cytoplasm. When using the MAb against the NP protein, nucleocapsid organization was the most prominent feature and resulted in the formation of cytoplasmic inclusion bodies visible by light and electron microscopy. Immunogold labeling of purified nucleocapsids was shown by electron microscopy. Virus particles and nucleocapsids were morphologically similar to members of the Paramyxoviridae family.

CONCLUSIONS

The morphologic characteristics of the virions and the distribution patterns of the HN and NP proteins in PK-15 infected cells indicate that the mechanisms of LPMV replication are generally similar to those of the members of the Paramyxoviridae family.

Epidemiology and control of Menangle virus in pigs

OBJECTIVE

To describe the epidemiology and eradication of Menangle virus infection in pigs.

DESIGN

Field observations and interventions, structured and unstructured serological surveys, prospective and cross-sectional serological studies and laboratory investigations.

PROCEDURE

Serum samples were collected from pigs at a 2600-sow intensive piggery in New South Wales that experienced an outbreak of reproductive disease in 1997. Serum samples were also collected from piggeries that received pigs from or supplied pigs to the affected piggery and from other piggeries in Australia. Serum and tissue samples were collected from pigs at piggeries experiencing reproductive disease in New South Wales. Sera and faeces were collected from grey-headed flying foxes (Pteropus poliocephalus) in the region of the affected piggery. Serum samples were tested for neutralising antibodies against Menangle virus. Virus isolation was attempted from faeces.

RESULTS

Following the outbreak of reproductive disease, sera from 96% of adult pigs at the affected piggery, including sows that produced affected litters, contained neutralising antibodies against Menangle virus. Neutralising antibodies were also detected in sera from 88% of finisher pigs at two piggeries receiving weaned pigs from the affected piggery. No evidence of Menangle virus infection was found in other piggeries in Australia. In cross-sectional studies at the affected piggery, colostral antibodies were undetectable in most pigs by 14 to 15 weeks of age. By slaughter age or entry to the breeding herd, 95% of pigs developed high antibody titres (> or = 128) against Menangle virus in the virus neutralisation test. Menangle virus was eradicated from the affected piggery following a program of serological testing and segregation. Neutralising antibodies against Menangle virus were also detected in P poliocephalus from two colonies in the vicinity of the affected piggery. Two piggery workers were infected with Menangle virus. There was no evidence of infection in cattle, sheep, birds, rodents, feral cats and a dog at the affected piggery.

CONCLUSIONS

Serological evidence of infection with Menangle virus was detected in pigs at a piggery that had experienced reproductive disease, in pigs at two associated piggeries and in fruit bats in the region of the piggery. Two humans were infected. The mode of transmission between pigs is unknown, but spread by faecal or urinary excretion is postulated. This virus can be eradicated by the segregation of pigs into discrete age groups.