Equine viral arteritis: current status and prevention

Identification of Equine Arteritis Virus Immunodominant Epitopes Using a Peptide Microarray

Using the commercially available PEPperCHIP® microarray platform, a peptide microarray was developed to identify immunodominant epitopes for the detection of antibodies against Equine arteritis virus (EAV). For this purpose, the whole EAV Bucyrus sequence was used to design a total of 1250 peptides that were synthesized and spotted onto a microarray slide. A panel of 28 serum samples representing a selection of EAV strains was tested using the microarray. Of the 1250 peptides, 97 peptides (7.76%) showed reactivity with the EAV-positive samples. No single peptide was detected by all the positive serum samples. Seven peptides repeatedly showed reactivity above the cut-off and were considered to have diagnostic potential. Five of these peptides were within the immunodominant GP5 protein and two were within the replicase polyprotein regions NSP2 and NSP10, located in ORF1. The diagnostic sensitivity of the seven peptides selected was low, ranging from 5% to 55%; however, the combined diagnostic sensitivity and specificity of the seven peptides was 90% and 100%, respectively. This data demonstrate that multiple peptide sequences would be required to design a comprehensive serological test to cover the diversity of the EAV strains and the individual immune responses of horses.

An intermolecular salt bridge linking substrate binding and P1 substrate specificity switch of arterivirus 3C-like proteases

Equine arteritis virus (EAV) and porcine reproductive and respiratory syndrome virus (PRRSV) represent two members of the family Arteriviridae and pose a major threat to the equine- and swine-breeding industries throughout the world. Previously, we and others demonstrated that PRRSV 3C-like protease (3CL^pro) had very high glutamic acid (Glu)-specificity at the P1 position (P1-Glu). Comparably, EAV 3CL^pro exhibited recognition of both Glu and glutamine (Gln) at the P1 position. However, the underlying mechanisms of the P1 substrate specificity shift of arterivirus 3CL^pro remain unclear. We systematically screened the specific amino acids in the S1 subsite of arterivirus 3CL^pro using a cyclized luciferase-based biosensor and identified Gly116, His133 and Ser136 (using PRRSV 3CL^pro numbering) are important for recognition of P1-Glu, whereas Ser136 is nonessential for recognition of P1-Gln. Molecular dynamics simulations and biochemical experiments highlighted that the PRRSV 3CL^pro and EAV 3CL^pro formed distinct S1 subsites for the P1 substrate specificity switch. Mechanistically, a specific intermolecular salt bridge between PRRSV 3CL^pro and substrate P1-Glu (Lys138/P1-Glu) are invaluable for high Glu-specificity at the P1 position, and the exchange of K138T (salt bridge interruption, from PRRSV to EAV) shifted the specificity of PRRSV 3CL^pro toward P1-Gln. In turn, the T139K exchange of EAV 3CL^pro showed a noticeable shift in substrate specificity, such that substrates containing P1-Glu are likely to be recognized more efficiently. These findings identify an evolutionarily accessible mechanism for disrupting or reorganizing salt bridge with only a single mutation of arterivirus 3CL^pro to trigger a substrate specificity switch.

Methodology of Selecting the Optimal Receptor to Create an Electrochemical Immunosensor for Equine Arteritis Virus Protein Detection

The study reports a methodology of selecting the optimal receptor to create an electrochemical immunosensor for equine arteritis virus (EAV) protein detection. The detection was based on antigen recognition by antibodies immobilized on gold electrodes. Modification steps were controlled by electrochemical impedance spectroscopy and cyclic voltammetry measurements. In order to obtain the impedance immunosensor with the best parameters, seven different receptors complementary to equine arteritis virus protein were used. In order to make the selection, a rapid screening test was carried out to check the sensor’s response to blank, extremely low and high concentrations of target EAV protein, and negative sample: M protein from Streptococcus equi and glycoprotein G from Equid alphaherpesvirus 1. F6 10G receptor showed the best performance.

Equine viral arteritis: not just a reproductive disease

Following the recent confirmation of cases of equine viral arteritis in stallions in south-west England, James Crabtree of Equine Reproductive Services (UK) discusses the disease and its potential routes of spread into and around the UK.

Spread of equine arteritis virus among Hucul horses with different EqCXCL16 genotypes and analysis of viral quasispecies from semen of selected stallions

Equine arteritis virus (EAV) is maintained in the horse populations through persistently infected stallions. The aims of the study were to monitor the spread of EAV among Polish Hucul horses, to analyse the variability of circulating EAVs both between- and within-horses, and to identify allelic variants of the serving stallions EqCXCL16 gene that had been previously shown to strongly correlate with long-term EAV persistence in stallions. Serum samples (n = 221) from 62 horses including 46 mares and 16 stallions were collected on routine basis between December 2010 and May 2013 and tested for EAV antibodies. In addition, semen from 11 stallions was tested for EAV RNA. A full genomic sequence of EAV from selected breeding stallions was determined using next generation sequencing. The proportion of seropositive mares among the tested population increased from 7% to 92% during the study period, while the proportion of seropositive stallions remained similar (64 to 71%). The EAV genomes from different stallions were 94.7% to 99.6% identical to each other. A number (41 to 310) of single nucleotide variants were identified within EAV sequences from infected stallions. Four stallions possessed EqCXCL16S genotype correlated with development of long-term carrier status, three of which were persistent shedders and the shedder status of the remaining one was undetermined. None of the remaining 12 stallions with EqCXCL16R genotype was identified as a persistent shedder.

Serological investigation of equine viral arteritis in donkeys in eastern and south-eastern Anatolia regions of Turkey

Equine arteritis virus is classified in the Arteriviridae family and causes reproductive and respiratory disorders. The host spectrum includes many species of the Equidae family. Horses, donkeys and mules are the most sensitive species. The infection was serologically investigated in adult donkeys on small private family type enterprises in eastern and south-eastern Anatolia in this study. A total of 1,532 samples were collected from 28 different locations in 6 different provinces in these two regions. The number of donkeys sampled from each farm was between 1 and 3. Serum samples were tested by indirect enzyme-linked immunosorbent assay (ELISA). As a result of sero-controls, 53 animals were positive (3.45%). The presence of infection was determined in all the provinces; Elazığ (7%, 17/241), Tunceli (2.4%, 3/122), Van (2.9%, 10/342), Bitlis (4.6%, 5/107), Şırnak (2.7%, 12/440) and Siirt (2.1%, 6/280). Seropositivity was detected in 22 of the 28 locations. In this study, data were obtained from a significant number of animals for the first time in these regions. Although the values were not high, the findings revealed the presence of infection in the majority of the investigated sites. Despite the fact that the incidence was not high in donkeys probably due to restricted management conditions, the incidence may increase over time and may pose a risk for thoroughbred horses unless necessary measures are taken.

Equine viral arteritis in breeding and sport horses in central Spain

Equine viral arteritis (EVA) may have a high economic impact on breeding stud farms due to the occurrence of EVA-associated abortion outbreaks and the ability of the virus to persist in carrier stallions. While the consequences of EVA in premises with sport horses are usually less severe, the first confirmed outbreak of EVA in Spain occurred in a riding club in Barcelona, but no data on the seroprevalence of EVA in sport horses have been reported in Spain. Given the importance of both Spanish Purebred (SP) breeding horses and sport horses for Spain's equine industry, the aim of this study was to determine and compare the seroprevalence of EVA in these two horse populations in central Spain. Serum samples from 155 SP breeding horses residing in 16 stud farms and 105 sport horses of different breeds housed in 12 riding clubs, collected between September 2011 and November 2013, were tested using a commercial EVA antibody ELISA test with a 100% sensitivity, and confirmed by seroneutralisation (SN) test. EVA seroprevalence in SP breeding horses was higher 21.1% (95% CI 15.3-26.8%) than that in sport horses (6.7%, 95% CI 1.89-11.45%). However, the primary use (breeding vs. sport) was not significantly associated with seropositivity to Equine Arteritis Virus (EAV), suggesting that different management factors do not affect EVA circulation in these two horse populations.

Detection of equine arteritis virus by two chromogenic RNA in situ hybridization assays (conventional and RNAscope(®)) and assessment of their performance in tissues from aborted equine fetuses

Equine arteritis virus (EAV) is the causative agent of equine viral arteritis, a respiratory and reproductive disease of equids. EAV infection can induce abortion in pregnant mares, fulminant bronchointerstitial pneumonia in foals, and persistent infection in stallions. Here, we developed two RNA in situ hybridization (ISH) assays (conventional and RNAscope(®) ISH) for the detection of viral RNA in formalin-fixed paraffin-embedded (FFPE) tissues and evaluated and compared their performance with nucleocapsid-specific immunohistochemistry (IHC) and virus isolation (VI; gold standard) techniques. The distribution and cellular localization of EAV RNA and antigen were similar in tissues from aborted equine fetuses. Evaluation of 80 FFPE tissues collected from 16 aborted fetuses showed that the conventional RNA ISH assay had a significantly lower sensitivity than the RNAscope(®) and IHC assays, whereas there was no difference between the latter two assays. The use of oligonucleotide probes along with a signal amplification system (RNAscope(®)) can enhance detection of EAV RNA in FFPE tissues, with sensitivity comparable to that of IHC. Most importantly, these assays provide important tools with which to investigate the mechanisms of EAV pathogenesis.

Prevalência de anticorpos contra o vírus da arterite equina nas mesorregiões Noroeste, Centro Ocidental e Norte Central do Paraná

RESUMO: O objetivo deste estudo foi investigar a prevalência de anticorpos contra o vírus da arterite viral equina (EVAV) em equinos sadios criados nas mesorregiões Noroeste, Centro Ocidental e Norte Central do estado do Paraná. Após o cálculo do tamanho amostral, foram analisadas, utilizando a técnica de soroneutralização, amostras de soro sanguíneo de 653 equinos. Nenhum animal sororreagente foi encontrado nas mesorregiões Noroeste (0/236) e Centro Ocidental (0/99). Na mesorregião Norte Central a prevalência foi de 0,62% (2/318), totalizando 0,30%. Pode-se concluir que a arterite viral equina (AVE) ainda não representa um problema de importância epidemiológica nos equinos criados nas mesorregiões paranaenses estudadas.

Variability of non-structural proteins of equine arteritis virus during persistent infection of the stallion

The genetic stability of ORF1a encoding non-structural proteins nsp1, nsp2, nsp3 and nsp4 of equine arteritis virus (EAV) has been analysed for nearly seven years in a persistently infected stallion of the Malopolska breed. Between November 2004 and June 2011, 11 semen samples were collected. Viral RNA extracted from semen of this carrier stallion was amplified, sequenced and compared with the sequences of the other known strains of EAV. Sequence analysis of ORF1a showed 84 synonymous and 16 non-synonymous mutations. The most variable part of ORF1a was the region encoding nsp2 protein with 13 non-synonymous substitutions. The degree of amino acid identity between isolates ranged from 98.91 to 100%. Only single non-synonymous mutations were detected in nsp1 (one substitution) and nsp4 (two substitutions). The most stable was nsp3 in which no amino acid substitutions were observed during the whole period of observation.

Arterivirus molecular biology and pathogenesis

Arteriviruses are positive-stranded RNA viruses that infect mammals. They can cause persistent or asymptomatic infections, but also acute disease associated with a respiratory syndrome, abortion or lethal haemorrhagic fever. During the past two decades, porcine reproductive and respiratory syndrome virus (PRRSV) and, to a lesser extent, equine arteritis virus (EAV) have attracted attention as veterinary pathogens with significant economic impact. Particularly noteworthy were the 'porcine high fever disease' outbreaks in South-East Asia and the emergence of new virulent PRRSV strains in the USA. Recently, the family was expanded with several previously unknown arteriviruses isolated from different African monkey species. At the molecular level, arteriviruses share an intriguing but distant evolutionary relationship with coronaviruses and other members of the order Nidovirales. Nevertheless, several of their characteristics are unique, including virion composition and structure, and the conservation of only a subset of the replicase domains encountered in nidoviruses with larger genomes. During the past 15 years, the advent of reverse genetics systems for EAV and PRRSV has changed and accelerated the structure-function analysis of arterivirus RNA and protein sequences. These systems now also facilitate studies into host immune responses and arterivirus immune evasion and pathogenesis. In this review, we have summarized recent advances in the areas of arterivirus genome expression, RNA and protein functions, virion architecture, virus-host interactions, immunity, and pathogenesis. We have also briefly reviewed the impact of these advances on disease management, the engineering of novel candidate live vaccines and the diagnosis of arterivirus infection.

Deubiquitinase function of arterivirus papain-like protease 2 suppresses the innate immune response in infected host cells

Protein ubiquitination regulates important innate immune responses. The discovery of viruses encoding deubiquitinating enzymes (DUBs) suggests they remove ubiquitin to evade ubiquitin-dependent antiviral responses; however, this has never been conclusively demonstrated in virus-infected cells. Arteriviruses are economically important positive-stranded RNA viruses that encode an ovarian tumor (OTU) domain DUB known as papain-like protease 2 (PLP2). This enzyme is essential for arterivirus replication by cleaving a site within the viral replicase polyproteins and also removes ubiquitin from cellular proteins. To dissect this dual specificity, which relies on a single catalytic site, we determined the crystal structure of equine arteritis virus PLP2 in complex with ubiquitin (1.45 Å). PLP2 binds ubiquitin using a zinc finger that is uniquely integrated into an exceptionally compact OTU-domain fold that represents a new subclass of zinc-dependent OTU DUBs. Notably, the ubiquitin-binding surface is distant from the catalytic site, which allowed us to mutate this surface to significantly reduce DUB activity without affecting polyprotein cleavage. Viruses harboring such mutations exhibited WT replication kinetics, confirming that PLP2-mediated polyprotein cleavage was intact, but the loss of DUB activity strikingly enhanced innate immune signaling. Compared with WT virus infection, IFN-β mRNA levels in equine cells infected with PLP2 mutants were increased by nearly an order of magnitude. Our findings not only establish PLP2 DUB activity as a critical factor in arteriviral innate immune evasion, but the selective inactivation of DUB activity also opens unique possibilities for developing improved live attenuated vaccines against arteriviruses and other viruses encoding similar dual-specificity proteases.

Evidence that in vitro susceptibility of CD3+ T lymphocytes to equine arteritis virus infection reflects genetic predisposition of naturally infected stallions to become carriers of the virus

We investigated the correlation between in vitro susceptibility of CD3(+) T lymphocytes to equine arteritis virus (EAV) infection and establishment of persistent infection among 14 stallions following natural infections. The data showed that carrier stallions with a CD3(+) T lymphocyte susceptibility phenotype to in vitro EAV infection may be at higher risk of becoming carriers than those that lack this phenotype (P = 0.0002).

Serological survey of equine viral diseases in Mongolia

Three hundred sera were collected from horses in various parts of Mongolia in 2007 and seroepidemiological surveys for several equine viruses performed on them. Equid herpesvirus 1 and equine rhinitis A virus were prevalent, and equine arteritis virus and equid herpesvirus 3 were detected over a wide area though their rates of antibody‐positivity were not high. Equine infectious anemia was distributed locally. The rates of horses antibody‐positive for Japanese encephalitis virus and equine influenza virus were low, but these were detected. Bovine coronavirus antibodies were detected at a high rate, but it was not clear whether they were due to horse coronavirus.

PREVALÊNCIA DE ANTICORPOS CONTRA AGENTES VIRAIS EM EQUÍDEOS NO SUL DO ESTADO DE SÃO PAULO

RESUMO Foram analisados soros de 163 equídeos (143 equinos e 20 muares) provenientes de 16 municípios do sul do Estado de São Paulo, parte no Vale do Ribeira e parte no litoral. Utilizouse uma amostra probabilística estratificada em dois estágios, sendo a unidade amostral de primeiro estágio constituída pela unidade de produção agropecuária (UPA) e a de segundo estágio pelo animal dentro da UPA sorteada. Os soros foram coletados no período de outubro de 2004 a junho de 2005. Foram estimadas as prevalências de anticorpos contra os vírus das encefalites equinas do tipo leste (EEE), oeste (WEE) e venezuelana (VEE), herpesvírus equino (HVE), arterite viral dos equinos (AVE), influenza equina 1 e 2 (IE-1 e 2) e estomatite vesicular Indiana 2 – Cocal (COCV) e Indiana 3 – Alagoas (VSAV). Foram utilizadas as técnicas de inibição da hemoaglutinação para a detecção de anticorpos contra os vírus IE-1 e 2 e de soroneutralização para os demais vírus estudados. Dos animais testados, 26% apresentaram anticorpos contra o HVE, 21% para COCV, 5% para VSAV, 16% para EEE, 2,26% para VEE, 11% para influenza Equi/2 e 2,7% para influenza Equi/1. Não se encontraram animais reagentes para WEE e AVE. A soroprevalência obtida sugere a circulação do HVE, dos vírus da IE Equi-1(H7N7) e Equi-2 (H3N8), dos vírus EEE e VEE e dos vírus da estomatite vesicular Indiana 2 – Cocal (COCV) e Indiana 3 – Alagoas (VSAV) no rebanho de equídeos do sul do Estado de São Paulo.