Equine Influenza Virus Research Articles

A 113-amino-acid truncation at the NS1 C-terminus is a determinant for viral replication of H5N6 avian influenza virus in vitro and in vivo

Virulence of highly pathogenic avian influenza viruses (AIV) is determined by multiple genes and their encoded proteins. In particular, the nonstructural protein 1 (NS1) of viruses is a multifunctional protein that plays an important role in type I interferon (IFN) antagonism, pathogenicity, and determining viral host range. Naturally-occurring truncation or mutation of NS1 during virus evolution attenuates viral replication and pathogenicity, but the mechanisms underlying this phenomenon remain poorly understood. In the present study, we rescued an H5N6 AIV harboring a 113-amino-acid (aa) truncated NS1 at the C-terminus that had previously naturally occurred in an H3N8 equine influenza virus (designated as rHN109 NS1/112). The replication and pathogenicity of the rescued and parental viruses were then assessed in vitro in cells and in vivo in chickens and mice. Replication of rHN109 NS1/112 virus was significantly attenuated in various cells compared to its parental virus. The attenuation of rHN109 NS1/112 virus was subsequently clarified by investigating the effects on IFN and apoptosis signaling pathways via multiple experiments. The results indicated that the 113-aa truncation of NS1 impairs viral inhibition of IFN production and enhances cellular apoptosis in avian and mammalian cells. Animal studies further indicated that replication of the rHN109 NS1/112 virus is remarkably attenuated in chickens. The results of this study improve our understanding of C-terminal region function for NS1 proteins of influenza viruses.

Reemergence of H3N8 Equine Influenza A virus in Chile, 2018.

A new outbreak of equine Influenza A virus (IAV) was reported in Chile in January 2018, 6years after its last report in 2012. Equine IAV was detected by rtRT-PCR, followed by virus isolation and full genome sequencing. Genetic characterization of equine IAV classified the virus within clade 1 of the Florida sublineage. Although this is the same sublineage that caused an outbreak in Chile in 2012, the virus has a high similarity to other cocirculating viruses that were recently identified in Europe and Asia. The Chilean 2018 equine influenza (EI) outbreak was caused by an H3N8 strain circulating globally that spread through horse movements.

Evidence of equine influenza A (H3N8) activity in horses from Eastern and Central Saudi Arabia: 2013-2015.

Equine influenza virus (EIV) is one of the main causes of viral respiratory affections in horses. Little is known about the prevalence of EIV in Saudi Arabia especially the H3N8 serotype. To assess prevalence of equine influenza in horse populations in Eastern and Central Saudi Arabia. Cross-sectional study. We collected 145 sera, 323 nasal and 323 rectal swabs from horses from six major cities in Eastern and Central regions. None of the horses were vaccinated against EIV. Sera were tested in ELISA assays for influenza A type-specific antibodies and by haemagglutination inhibition (HI) tests using equine H3N8. The swabs were tested by RT-qPCR assay targeting a conserved region of the influenza A matrix gene that detects influenza A viruses of all subtypes. None of the swabs had detectable influenza A virus RNA. Of the 145 serasamples tested by ELISA, 81 (55.9%) were positive and 98 (67.6%) of 145 sera tested by HI tests were positive for equine H3. Our failure to detect and sequence any EIV prevents identification of the lineage of virus that circulates in the Kingdom of Saudi Arabia. These results confirm that EIV H3N8 is circulating in Saudi Arabia and should be considered as a possible cause when investigating horses with respiratory disease in Saudi Arabia.

Immunization by Replication-Competent Controlled Herpesvirus Vectors.

Replication-competent controlled virus vectors were derived from the virulent herpes simplex virus 1 (HSV-1) wild-type strain 17syn+ by placing one or two replication-essential genes under the stringent control of a gene switch that is coactivated by heat and an antiprogestin. Upon activation of the gene switch, the vectors replicate in infected cells with an efficacy that approaches that of the wild-type virus from which they were derived. Essentially no replication occurs in the absence of activation. When administered to mice, localized application of a transient heat treatment in the presence of systemic antiprogestin results in efficient but limited virus replication at the site of administration. The immunogenicity of these viral vectors was tested in a mouse footpad lethal challenge model. Unactivated viral vectors-which may be regarded as equivalents of inactivated vaccines-induced detectable protection against lethality caused by wild-type virus challenge. Single activation of the viral vectors at the site of administration (rear footpads) greatly enhanced protective immune responses, and a second immunization resulted in complete protection. Once activated, vectors also induced far better neutralizing antibody and HSV-1-specific cellular immune responses than unactivated vectors. To find out whether the immunogenicity of a heterologous antigen was also enhanced in the context of efficient transient vector replication, a virus vector constitutively expressing an equine influenza virus hemagglutinin was constructed. Immunization of mice with this recombinant induced detectable antibody-mediated neutralization of equine influenza virus, as well as a hemagglutinin-specific cellular immune response. Single activation of viral replication resulted in a severalfold enhancement of these immune responses.IMPORTANCE We hypothesized that vigorous replication of a pathogen may be critical for eliciting the most potent and balanced immune response against it. Hence, attenuation/inactivation (as in conventional vaccines) should be avoided. Instead, the necessary safety should be provided by placing replication of the pathogen under stringent control and by activating time-limited replication of the pathogen strictly in an administration region in which pathology cannot develop. Immunization will then occur in the context of highly efficient pathogen replication and uncompromised safety. We found that localized activation in mice of efficient but limited replication of a replication-competent controlled herpesvirus vector resulted in a greatly enhanced immune response to the virus or an expressed heterologous antigen. This finding supports the above-mentioned hypothesis and suggests that the vectors may be promising novel agents worth exploring for the prevention/mitigation of infectious diseases for which efficient vaccination is lacking, in particular in immunocompromised patients.

The Immunity Gap Challenge: Protection against a Recent Florida Clade 2 Equine Influenza Strain.

Vaccination is one of the most effective tools for limiting the impact of equine influenza (EI). The humoral immunity established following a primary vaccination course can decrease significantly between the second (V2) and third immunisations (V3), leaving some horses insufficiently protected for several weeks. This so-called “immunity gap” poses a challenge to all EI vaccines. During this period, the EI infection of vaccinated animals may be followed by marked clinical signs and virus shedding. However, several EI vaccines have been shown to stimulate equine influenza virus (EIV)-specific cell-mediated immunity, which is likely to play a role in protection against EIV infection and/or mitigate the clinical and virological signs of EI. Reducing the interval between V2 and V3 has been shown to be counterproductive to longer-term immunity. Further research is needed to define and address the “immunity gap” in horses. This study aimed to measure the level of protection induced by a whole inactivated, ISCOMatrix adjuvanted, EI and tetanus vaccine (Equilis Prequenza-Te) when challenged during the immunity gap (i.e., immediately before the recommended boost immunisation, more than 5 months after V2) using infection with a recent heterologous Florida Clade 2 (FC2) equine influenza virus (EIV) strain. This vaccine was tested in a Welsh mountain pony model. A group of seven ponies was vaccinated twice, 4 weeks apart. The protective antibody response was measured and ponies were challenged, along with 5 unvaccinated control ponies, by experimental infection with the FC2 A/eq/Northamptonshire/1/13 EIV strain, 158 days (around 5.2 months) after V2 and their clinical signs and virus shedding were monitored. EI serology was measured by single radial haemolysis (SRH) and haemagglutination inhibition (HI). Clinical signs and virus shedding (measured by qRT-PCR and hen’s egg titration) were compared with controls. All vaccinates had detectable, low SRH antibody titres and most had detectable, low HI titres. Significant clinical and virological protection was observed in vaccinates (p < 0.05), supporting the good performance of this vaccine against a recent EIV strain. In this study, the impact of the immunity gap in ponies was limited after primary vaccination with this whole inactivated, ISCOMatrix adjuvanted EI and tetanus vaccine (Equilis Prequenza-Te) when infected several months after V2 with a recent FC2 strain, which is representative of EIV circulating in the EU.

Complete Genome Sequencing of Two Equine Influenza A(H3N8) Virus Strains Isolated in Kazakhstan.

Here, we report the complete genome sequencing of strains A/equine/Kostanay/9/2012(H3N8) and A/equine/LKZ/9/2012(H3N8) of the equine influenza virus belonging to Florida sublineage, clade 2. The strains were isolated in 2012 in the northern and southern regions of Kazakhstan, respectively.

Respiratory disease and sero-epidemiology of respiratory pathogens in the working horses of Ethiopia.

SummaryBackgroundPathogens are frequently implicated in equine respiratory disease. In Ethiopia, respiratory disease is a frequent cause for presentation at veterinary clinics and a priority concern for users of working horses. However, there is little existing literature on possible aetiologies.ObjectivesDetermine prevalence of respiratory signs and exposure to major respiratory pathogens through a serological survey.Study designCross‐sectional.MethodsSystematically selected horses from 19 sites in central Ethiopia were examined clinically and sampled once (August‐December 2013). A face‐to‐face interview collected data on horses’ management and history. Serological testing targeted equine influenza virus (EIV), equine herpesviruses‐1 (EHV‐1) and ‐4 (EHV‐4), equine rhinitis viruses A (ERAV) and B (ERBV), equine arteritis virus (EAV) and Streptococcus equi subspecies equi (S. equi).ResultsOwners reported a recent history of coughing in 38% of horses and nasal discharge in 7%. No animals were observed coughing during examination but 6% had a nasal discharge. Antibodies towards S. equi, were most prevalent (8%, 33/350). Antibodies to EAV were confirmed in one animal (0.3%). Low antibody titres to EHV‐1/4 and ERA/BV suggested prior exposure but antibodies to EIV were not detected. Multivariable, multilevel logistic regression analysis for risk factors associated with S. equi serostatus showed higher odds of seropositivity in younger animals and those working less frequently.Main limitationsA single serological sample cannot describe dynamic changes in antibodies. Sampling horses at the place of work may result in healthy‐worker bias.Conclusions S. equi may be endemic in this population and contributing, in part, to the occurrence of respiratory disease. Low prevalence of antibodies to viruses, with the exception of EIV, indicates these pathogens are present, but unlikely a predominant cause of respiratory signs and noninfectious causes of disease should also be investigated. Working horses in this region would be vulnerable to incursion of equine influenza.

Frequency of shedding of respiratory pathogens in horses recently imported to the United States.

BackgroundImported horses that have undergone recent long distance transport might represent a serious risk for spreading infectious respiratory pathogens into populations of horses.ObjectiveTo investigate the frequency of shedding of respiratory pathogens in recently imported horses.AnimalsAll imported horses with signed owner consent (n = 167) entering a USDA quarantine for contagious equine metritis from October 2014 to June 2016 were enrolled in the study.MethodsProspective observational study. Enrolled horses had a physical examination performed and nasal secretions collected at the time of entry and subsequently if any horse developed signs of respiratory disease during quarantine. Samples were assayed for equine influenza virus (EIV), equine herpesvirus type‐1, −2, −4, and −5 (EHV‐1, −2, −4, −5), equine rhinitis virus A (ERAV), and B (ERBV) and Streptococcus equi subspecies equi (S. equi) using quantitative PCR (qPCR).ResultsEquine herpesviruses were detected by qPCR in 52% of the study horses including EHV‐2 (28.7%), EHV‐5 (40.7%), EHV‐1 (1.2%), and EHV‐4 (3.0%). Clinical signs were not correlated with being qPCR‐positive for EHV‐4, EHV‐2, or EHV‐5. None of the samples were qPCR‐positive for EIV, ERAV, ERBV, and S. equi. The qPCR assay failed quality control for RNA viruses in 25% (46/167) of samples.Conclusions and Clinical ImportanceClinical signs of respiratory disease were poorly correlated with qPCR positive status for EHV‐2, −4, and −5. The importance of γ‐herpesviruses (EHV‐2 and 5) in respiratory disease is poorly understood. Equine herpesvirus type‐1 or 4 (EHV‐1 or EHV‐4) were detected in 4.2% of horses, which could have serious consequences if shedding animals entered a population of susceptible horses. Biosecurity measures are important when introducing recently imported horses into resident US populations of horses.

Complete Genomic Sequences of H3N8 Equine Influenza Virus Strains Used as Vaccine Strains in Japan.

ABSTRACTWe sequenced the eight segments of influenza A virus strains A/equine/Ibaraki/1/2007 and A/equine/Yokohama/aq13/2010, which are strains of the Florida sublineage clades 1 and 2 of the H3N8 subtype equine influenza virus. These strains have been used as vaccine strains in Japan since 2016 in accordance with World Organization for Animal Health (OIE) recommendations.

Trial for Preparation of Combined Equine Influenza virus, Equine Herpesvirus-1 and Tetanus Toxoid Vaccine

Vaccination remains an important strategy to fight Equine influenza (EI), Equine herpesvirus-1 (EHV- 1) and tetanus infection, in combination with management measures. A combined inactivated EIV, EHV-1 and Tetanus toxoid (TT) vaccine adjuvanted with saponin and Alhydrogel was prepared and tested in four groups of guinea pigs in comparison with each vaccine separately beside another group as control. The humoral immune response in vaccinated guinea pigs against EI, EHV-1 and tetanus was evaluated by Haemagglutination Inhibition (HI) antibody titers, Enzyme linked immunosorbent assay (ELISA) titers, and toxin neutralizing (TN) antibody titers respectively. All vaccines proved to be safe and potent in guinea pigs. Also, the obtained antibodies titers with combined vaccine was nearly similar to titer obtained with separated vaccine of each target agent in vaccinated guinea pigs. The evaluation of keeping quality of the prepared combined inactivated vaccine showed that it is was stable at 4C up to 12 months and for 3 months at room temperature.

Mammalian Adaptation of an Avian Influenza A Virus Involves Stepwise Changes in NS1.

ABSTRACTInfluenza A viruses (IAVs) are common pathogens of birds that occasionally establish endemic infections in mammals. The processes and mechanisms that result in IAV mammalian adaptation are poorly understood. The viral nonstructural 1 (NS1) protein counteracts the interferon (IFN) response, a central component of the host species barrier. We characterized the NS1 proteins of equine influenza virus (EIV), a mammalian IAV lineage of avian origin. We showed that evolutionarily distinct NS1 proteins counteract the IFN response using different and mutually exclusive mechanisms: while the NS1 proteins of early EIVs block general gene expression by binding to cellular polyadenylation-specific factor 30 (CPSF30), NS1 proteins from more evolved EIVs specifically block the induction of IFN-stimulated genes by interfering with the JAK/STAT pathway. These contrasting anti-IFN strategies are associated with two mutations that appeared sequentially and were rapidly selected for during EIV evolution, highlighting the importance of evolutionary processes in immune evasion mechanisms during IAV adaptation.IMPORTANCE Influenza A viruses (IAVs) infect certain avian reservoir species and occasionally transfer to and cause epidemics of infections in some mammalian hosts. However, the processes by which IAVs gain the ability to efficiently infect and transmit in mammals remain unclear. H3N8 equine influenza virus (EIV) is an avian-origin virus that successfully established a new lineage in horses in the early 1960s and is currently circulating worldwide in the equine population. Here, we analyzed the molecular evolution of the virulence factor nonstructural protein 1 (NS1) and show that NS1 proteins from different time periods after EIV emergence counteract the host innate immune response using contrasting strategies, which are associated with two mutations that appeared sequentially during EIV evolution. The results shown here indicate that the interplay between virus evolution and immune evasion plays a key role in IAV mammalian adaptation.

Whole-genome sequencing and antigenic analysis of the first equine influenza virus identified in Turkey.

BackgroundIn 2013, there was an outbreak of acute respiratory disease in racehorses in Turkey. The clinical signs were consistent with equine influenza (EI).ObjectiveThe aim was to confirm the cause of the outbreak and characterise the causal virus.MethodsA pan‐reactive influenza type A real‐time RT‐PCR and a rapid antigen detection kit were used for confirmatory diagnosis of equine influenza virus (EIV). Immunological susceptibility to EIV was examined using single radial haemolysis and ELISA. Antigenic characterisation was completed by haemagglutinin inhibition using a panel of specific ferret antisera. Genetic characterisation was achieved by whole‐genome sequencing using segment‐specific primers with M13 tags.ResultsA H3N8 EIV of the Florida clade 2 sublineage (FC2) was confirmed as the causal agent. The index cases were unvaccinated and immunologically susceptible. Phylogenetic analysis of the HA1 and NA genes demonstrated that A/equine/Ankara/1/2013 clustered with the FC2 strains circulating in Europe. Antigenic characterisation confirmed the FC2 classification and demonstrated the absence of significant drift. Whole‐genome sequencing indicated that A/equine/Ankara/1/2013 is most closely related to the viruses described as the 179 group based on the substitution I179V in HA1, for example A/equine/East Renfrewshire/2/2011, A/equine/Cambremer/1/2012 and A/equine/Saone et Loire/1/2015. The greatest diversity was observed in the NS1 segment and the polymerase complex.ConclusionsThe first recorded outbreak of EI in Turkey was caused by an FC2 virus closely related to viruses circulating in Europe. Antigenic and genetic characterisation gave no indication that the current OIE recommendations for EI vaccine composition require modification.

Development of a novel equine influenza virus live-attenuated vaccine

H3N8 equine influenza virus (EIV) is an important and significant respiratory pathogen of horses. EIV is enzootic in Europe and North America, mainly due to the suboptimal efficacy of current vaccines. We describe, for the first time, the generation of a temperature sensitive (ts) H3N8 EIV live-attenuated influenza vaccine (LAIV) using reverse-genetics approaches. Our EIV LAIV was attenuated (att) in vivo and able to induce, upon a single intranasal administration, protection against H3N8 EIV wild-type (WT) challenge in both a mouse model and the natural host, the horse. Notably, since our EIV LAIV was generated using reverse genetics, the vaccine can be easily updated against drifting or emerging strains of EIV using the safety backbone of our EIV LAIV as master donor virus (MDV). These results demonstrate the feasibility of implementing a novel EIV LAIV approach for the prevention and control of currently circulating H3N8 EIVs in horse populations.

Филогенетический анализ поверхностного НА-гена штамма A/equine/LKZ/09/2012 (H3N8) вируса гриппа лошадей

This paper presents the results of epizootological monitoring of equine influenza in the Republic ofKazakhstan, which were organized the expeditions to South Kazakhstan, Zhambyl, Almaty, East Kazakhstan, Kostanai, Aktobe and West Kazakhstan regions. For laboratory investigations in different regions ofthe Republic of Kazakhstan, 2404 samples were collected and delivered to RIBSP. The outbreak of equineinfluenza virus (EIV) in Kazakhstan was confirmed by isolating the virus in chick embryos, sequencing thesurface hemagglutinin HA gene, and then analyzing the resulting nucleotide sequence at the BLAST base.All investigated samples were taken from un-vaccinated horses with expressed clinical signs of respiratorydisease in 2007 and 2012 in southern and northern Kazakhstan. EIV H3N8 was isolated in chicken eggsfrom 30 nasal swabs from horses with acute respiratory disease, which were tested positive by DirectigenFlu A. Isolation was confirmed by haemagglutination assay and RT-PCR assay of the M, HA and NA gene.HA sequences of the Kazakhstan isolates appeared to be more closely related to viruses isolated in early2000 in Asia. These results suggested that viruses with fewer changes than those on the main evolutionarylineage may continue to circulate. On the other hand, analysis of deduced NA amino acid sequences weremore closely related to viruses isolated in outbreaks in Europe and Asia during 2003-2007. Phylogeneticanalysis characterized the Kazakhstan EIV isolates as a member of the Eurasian lineage by the haemagglutinin (HA) protein alignment, but appeared to be a member of the Florida sublineage clade 2 by theneuraminidase (NA) protein sequence suggesting that reassortment might be a possible explanation. Thetopology of the maximum-likehood tree for both HA and NA sequences showed four clades correspondingto the Pre-diverge, American, Eurasian and Florida lineage viruses. The Kazakhstan isolates were well supported within the Eurasian clade, as seen for the HA protein with bootstrap value 90% and 99% within theFlorida sublineage clade II for the HA protein. Our findings suggest that the Kazakhstan strains representan example of “evolution” and probably reassortment between genetically distinct co-circulated strains.Key words: virus, equine influenza, PCR, sequencing, phylogenetic analysis.

Морфометрия и некоторые физические характеристики вируса гриппа лошадей, выделенных на территории Республики Казахстан

The paper presents the results of electron microscopy of strains of equine influenza virus, isolatedfrom 2010 to 2012. when conducting monitoring activities. Expeditions to the South Kazakhstan, Zhambyl, Almaty, East Kazakhstan, Kostanay, Aktyubinsk and West Kazakhstan oblasts were conducted tocarry out epizootological monitoring of equine influenza in the Republic of Kazakhstan. In total, for theyears 2010-2012. For laboratory investigations in different regions of the Republic of Kazakhstan, 2404samples were collected and delivered to NIIIBB&nbsp;. Based on the results of the studies, the main morphometric properties were determined. Electronmicroscopic analysis showed no contamination by foreign microorganisms in purified preparations ofthe horse flu virus. During the purification process, the virions retain their structure. Strains A / equine /Baizak / 09/2012, A / equine / Kostanai / 09/2012, A / equine / Matybulak / 10/2012 and A / equine / LKZ/ 09/2012 equine influenza virus in the populations of the studied isolates have mainly round and ovalshapes. The size of round virions is 70 – 200 nm in diameter, and the length of oval ones is of the orderof 100 -300 nm. About 72% of the population of equine influenza isolates are virions with a diameterof 110 – 180 nm. The surface of the viral particles is covered with spines of 6-8 nm in height, and thethickness of the outer shell is 8.5-9 nm.In all studied isolates of the equine influenza virus, the majority of the virions are round (95%) andoval (5%) virions. For all isolates polymorphism is not typical. The conducted studies showed that theinvestigated isolates practically do not differ both in morphology and in such physical parameters as thefloating density and the sedimentation constant of the virion. All indices lie in the range of values characteristic for the family of orthomixoviruses.However, in view of the development of genetically mutation among the population of the equineinfluenza virus, A / equine / LKZ / 09/2012, rounded viruses with a size of about 450 nm were foundand filamentary lengths over 750 nm. These virions are characterized by the preservation of the surfacestructure of glycoproteins, but an initial degree of disintegration of the virus for the subsequent releaseof ribonucleoprotein (RNP) is observed.Key words: virus, equine influenza, ultracentrifugation, electron microscopy, physical constants.

Virological examination of conjunctival swabs in clinically healthy horses

The aim of the study was to determine the presence of the equine influenza virus (EIV), the equine arteritis virus (EAV), and the equine herpesvirus (EHV) in the conjunctival sac of clinically healthy horses. Fifty horses of both sexes and various breeds and ages were included in the study. Virus isolation was carried out in cell cultures (the Madin-Darby canine kidney, green monkey kidney and rabbit kidney cells) from conjunctival swabs. The hemagglutination assay was carried out in order to identify EI viral amplification. The study revealed no presence of the above listed viruses in the conjunctival sac of clinically healthy horses. .

Prevalencia de anticuerpos contra virus de influenza equina en equinos deportivos de la República Argentina durante 2015 y 2016

Mediante un muestreo en dos etapas se analizó la población de equinos de deporte o recreación de toda la República Argentina que presenta una frecuencia regular (o alta) de movimien­tos y para los cuales la vacunación contra influenza equina es obligatoria. Mediante la técnica de inhibición de la hemaglutinación se evaluó la presencia de anticuerpos contra dos cepas del virus de la influenza equina: A/eq/2 La Plata 93 y A/eq/Argentina/E2345-1/2012. Los títulos obtenidos permi­tieron clasificar a los equinos en protegidos, parcialmente protegidos y no protegidos. El 57 % y el 59 % de los equinos fueron considerados como no protegidos contra la cepa La Plata 93 y Argentina 2012, respectivamente. El 34 % fue considerado como parcialmente protegido contra la cepa La Plata 93 y el 33 % contra la cepa Argentina 2012. Finalmente, el 9 % y el 8 % de los animales fueron considerados protegidos contra la cepa La Plata 93 y Argentina 2012, respectivamente. Se constató que los animales de mayor edad, con mayor cantidad de dosis de vacunas aplicadas y con la fecha de última vacunación más cercana a la fecha del muestreo, presentaron concentraciones mayores de anticuerpos. Menos del 10 % de los equinos tuvo títulos protectores y un alto porcentaje títulos inferiores a lo requerido para evitar la enfermedad, lo cual implica que existe en Argentina una gran cantidad de equinos que pueden diseminar la enfermedad sin presentar sintomatología.

Neutralization antibody response to booster/priming immunization with new equine influenza vaccine in Japan.

Equine influenza (EI) vaccine has been widely used. However, the causative EI virus (H3N8) undergoes continuous antigenic drift, and the vaccine strains must be periodically reviewed and if necessary, updated to maintain vaccine efficacy against circulating viruses. In 2016, the Japanese vaccine was updated by replacing the old viruses with the Florida sub-lineage Clade (Fc) 2 virus, A/equine/Yokohama/aq13/2010 (Y10). We investigated the virus neutralization (VN) antibody response to Fc2 viruses currently circulating in Europe, after booster or primary immunization with the new vaccine. These European viruses have the amino acid substitution A144V or I179V of the hemagglutinin. In horses that had previously received a primary course and bi-annual boosters with the old vaccine booster, immunization with the updated vaccine increased the VN antibody levels against the European Fc2 viruses as well as Y10. There were no significant differences in the VN titers against Y10 and the Fc2 viruses with A144V or I179V substitution in horses that had received a primary course of the updated vaccine. However, a mixed primary course where the first dose was the old vaccine and the second dose was the updated vaccine, reduced VN titers against the European viruses compared to that against Y10. In summary, the new vaccine affords horses protective level of VN titers against the Fc2 viruses carrying A144V or I179V substitution, but our results suggest that the combination of the old and new vaccines for primary immunization would not be optimum.

Equine Vaccines: How, When and Why? Report of the Vaccinology Session, French Equine Veterinarians Association, 2016, Reims

To date, vaccination is one of the most efficient methods of prevention against equine infectious diseases. The vaccinology session, which was organised during the annual meeting of the French Equine Veterinarians Association (AVEF) at Reims (France) in 2016, aimed to approach three subjects of importance for the equine industry. Vaccination against three major equine diseases were used as examples: equine influenza (equine influenza virus), rhinopneumonitis (equine herpes virus 1/4), and tetanus (Clostridium tetani neuro-toxin). (1) Emergency vaccination: while it has been very successful to reduce the impact of equine influenza epizooties and it is also recommended for tetanus in case of surgery and accident, the benefit of emergency vaccination against equine herpes virus 1/4 remains arguable; (2) Compatibility of equine vaccines from different brands: despite being a frequent concerns for equine veterinarians, little information is available about the compatibility of equine vaccines from different commercial origins. The consequence of mixing different equine vaccines targeting the same disease is believed to be limited but scientific evidences are sparse; and, (3) Laps vaccination and vaccine shortage: they could have serious consequences in terms of protection and their impact should be evaluated on a case by case basis, taking into account the risk of contact with the pathogen and the effect on herd immunity.

Comparison among three different serological methods for the detection of equine influenza virus infection.

The equine influenza virus (EIV) H3N8 subtype is responsible for all EIV outbreaks worldwide while the H7N7 subtype is less pathogenic and is considered extinct as it has not been confirmed in outbreaks since 1980. Although EIV is enzootic in Brazil, few reports describe the actual EIV antibody status in the country. The aims of this study were: - to evaluate the efficiency of different serum treatments described by the World Organisation for Animal Health (OIE) and the World Health Organization (WHO) to remove non-specific haemagglutination inhibitors for the haemagglutination inhibition (HI) assay for EIV - to evaluate the presence of EIV antibodies by HI, enzyme-linked immunosorbent assay and agar gel immunodiffusion in 83 non-vaccinated equines from São Paulo State - to evaluate a strategy to better analyse equine sera for EIV antibodies. Although there was no statistical difference among treatments, receptor-destroying enzyme treatment followed by chicken erythrocyte adsorption showed more consistent results, which corroborate the OIE and WHO recommendation to use this treatment preferentially. The HI results suggest equine H3N8 virus circulation among the animals tested from São Paulo State. The algorithm suggested here could be used to guide antibody detection against equine influenza virus in equines, improving the test specificity by aiming to avoid false positive results.