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Topic:Virus

The study of viral infections that affect equine species assesses the relationship between viruses and horses. Infections can lead to a range of clinical symptoms and may impact the health and performance of horses. Common equine viruses include Equine Influenza Virus, Equine Herpesvirus, and West Nile Virus, among others. Understanding the mechanisms of viral transmission, pathogenesis, and host immune responses is essential for developing effective prevention and treatment strategies. This page compiles peer-reviewed research studies and scholarly articles that explore the epidemiology, molecular biology, and clinical management of viral infections in horses.
Development of African horse sickness disabled infectious single animal (DISA)-DIVA vaccine platform applied for all nine serotypes.
Vaccine    September 23, 2025   Volume 64 127772 doi: 10.1016/j.vaccine.2025.127772
van Rijn PA, Wernery U, Feddema AJ, Maris-Veldhuis MA, Joseph S, van Gennip RGP.African Horse Sickness (AHS) is a devastating vector-borne viral disease of equids with a mortality up to 95 % in naïve domestic horses. The causative African horse sickness virus (AHSV) is a distinct species of the genus Orbivirus of the family Sedoreoviridae, consisting of nine serotypes showing limited cross protection. AHSV is transmitted by Culicoides biting midges. Outbreaks cause huge economic losses in developing African countries. AHS has become a serious threat for countries outside Africa, since endemic Culicoides species in moderate climates appear competent vectors of the closel...
The VP7 protein of the African horse sickness virus core particle facilitates binding to Culicoides sonorensis cells in an RGD-independent manner.
Virology    September 15, 2025   Volume 612 110694 doi: 10.1016/j.virol.2025.110694
Buyens ARM, van Staden V, Theron J.African horse sickness, caused by African horse sickness virus (AHSV) that is transmitted by midges of the Culicoides genus, leads to rapid mortality among horses. Proteases in the saliva of Culicoides midges cleave the VP2 outer capsid protein, resulting in infectious sub-virus particles that have increased infectivity for the Culicoides vector insect and Culicoides-derived cells (KC cells). The AHSV VP7 protein has an arginine-glycine-aspartate (RGD) motif, but the functional relevance of this protein and motif in facilitating binding to insect cells is unknown. To investigate, core-like par...
The Viremic Phase and Humoral Immune Response Against African Horse Sickness Virus That Emerged in Thailand in 2020.
Veterinary sciences    September 11, 2025   Volume 12, Issue 9 878 doi: 10.3390/vetsci12090878
Pipitpornsirikul P, Thangthamniyom N, Laikul A, Songkasupa T, Pathomsakulwong W, Apichaimongkonkun T, Kasemsuwan S, E-Kobon T, Lekcharoensuk P.African horse sickness (AHS), a life-threatening disease caused by African horse sickness virus serotype 1 (AHSV-1), emerged in Thailand in February 2020 with 607 cases and a 93% fatality rate. The outbreak was mitigated by vector control and a live attenuated virus (LAV) vaccine. Information regarding viremia and immunity after infection and vaccination during outbreaks are essential for controlling disease transmission. This study evaluated these parameters in 15 infected naïve horses and 11 vaccinated horses during the 2020 outbreak. Whole blood was collected and subjected to RT real-time ...
Immunohistochemical and molecular confirmation of West Nile Virus associated polioencephalomyelitis in a mule from Southern Brazil.
Microbial pathogenesis    September 8, 2025   Volume 208 108025 doi: 10.1016/j.micpath.2025.108025
de Mello Zanim M, Rodriguez MC, Martins FDC, Camargos MF, Headley SA.West Nile fever is a zoonotic arboviral disease caused by the West Nile Virus (WNV), responsible for deaths in humans, mammals, and birds with associated neurological manifestations. All previous investigations of WNV from Brazil were based primarily on serological and molecular analyses and in humans, equids, and birds in the northern and southeastern regions of the country. This study describes the pathological and molecular findings observed in a mule, from the state of Paraná, southern Brazil, that died during an outbreak involving equids with clinical manifestations of a neurological dis...
West Nile virus in horses: surveillance, diagnosis and prevention in the UK.
The Veterinary record    September 5, 2025   Volume 197, Issue 5 e5926 doi: 10.1002/vetr.5926
Whitlock F, Newton R, King S, Ionescu AM, Higgins S.With the geographical distribution of West Nile virus expanding, there is growing concern about the potential for an incursion to the UK. Here, Fleur Whitlock, Richard Newton, Simon King, Andra-Maria Ionescu and Sara Higgins provide a timely reminder of key aspects of the virus' biology.
Influenza D Virus Circulation Among Bovines, Swine, Equines, and Wild Boars in Italy: A Sero-Epidemiological Study.
Pathogens (Basel, Switzerland)    September 5, 2025   Volume 14, Issue 9 891 doi: 10.3390/pathogens14090891
Falsini A, Coppola C, Fiori A, Buonavoglia D, Marchi S, Montomoli E, Pellegrini F, Lanave G, Martella V, Camero M, Trombetta CM.Influenza D virus (IDV), belonging to the family, was first discovered in 2011 in pigs. Surveys in humans and animals have been carried out to decipher IDV ecology. In this seroepidemiological study, we investigated the circulation of IDV lineages across Italy in livestock and wildlife animals. A total of 1038 animal serum samples (from 246 bovines, 249 swine, 98 equines, and 445 wild boars) were tested using hemagglutination inhibition and virus neutralization assays. The results confirm bovines as the primary reservoir for IDV, with high seroprevalence for both D/660 (87%) and D/OK (80%) st...
Equine Sarcoid Arising From the Medial Caruncle With Invasion of the Third Eyelid in a Quarter Horse Gelding.
Veterinary ophthalmology    September 4, 2025   Volume 29, Issue 2 e70074 doi: 10.1111/vop.70074
Plotsker NM, Taylor R, Coffin HR, Beatty A, Newbold G, Knickelbein KE.To describe the clinical and histologic features of a sarcoid arising from the medial caruncle with spread to the third eyelid of a horse. Methods: A 20-year-old Quarter Horse gelding. Methods: An incisional biopsy of the medial caruncle mass was initially performed, with histopathology suggesting a sarcoid or other spindle cell neoplasm. The mass grew rapidly following the biopsy, expanding to affect the third eyelid and adjacent superior palpebral conjunctiva. A complete third eyelid and medial caruncle excision with resection of affected palpebral conjunctiva and adjunctive cryotherapy was ...
Genetic and serological analyses of equine influenza viruses isolated in Kumamoto and Hokkaido, Japan in 2025.
Veterinary microbiology    August 30, 2025   Volume 310 110701 doi: 10.1016/j.vetmic.2025.110701
Nemoto M, Kawanishi N, Kamei R, Furusho K, Kawauchi K, Yabuuchi Y, Oue Y, Uchida Y, Nishiura H, Reedy SE, Chambers TM, Li F, Bannai H, Yamanaka T....In April and May 2025, outbreaks of equine influenza occurred for the first time in 17 years in Japan. Equine influenza virus (EIV) of the H3N8 subtype was mainly detected in heavy draft horse populations in Kumamoto Prefecture and the Tokachi area of Hokkaido. In total, 10 EIVs were isolated from infected horses and then were used for genetic and serological analyses. Phylogenetic analysis of all eight genes revealed that all Japanese isolates were clustered with the Florida sublineage clade 1 (Fc1) viruses and were closely related to North American Fc1 viruses detected in 2024-2025. The resu...
Development of an In-House ELISA for Serological Detection of Equine Herpesvirus-1/4 Antibodies in Turkish Horses.
Animals : an open access journal from MDPI    August 27, 2025   Volume 15, Issue 17 2523 doi: 10.3390/ani15172523
Şahinkesen İ, Bilge-Dağalp S.Equine herpesvirus 1 (EHV-1) and Equine herpesvirus 4 (EHV-4) are major viral pathogens of horses that contribute to respiratory disease, abortion, and neurological disorders, leading to economic losses in the equine industry. Accurate serological diagnosis is critical for disease surveillance and control. This study aimed to develop and validate an in-house enzyme-linked immunosorbent assay (ELISA) for detecting antibodies against EHV-1 and EHV-4 in horse sera. Serum samples previously confirmed by virus neutralization test (VNT) and a commercial ELISA were used to optimize the assay. Cut-off...
Development and application of a NP-cELISA for the detection of nucleoprotein antibodies of equine influenza virus.
Microbiology spectrum    August 25, 2025   Volume 13, Issue 10 e0093925 doi: 10.1128/spectrum.00939-25
Yang Y, Guo K, Xu L, Guo W, Dong M, Liu W, Li S, Zhang Z, Chu X, Wang Y, Zhang Z, Hu Z, Wang X.Equine influenza (EI), caused by the equine influenza virus (EIV), is an acute respiratory disease that has become enzootic worldwide, resulting in frequent outbreaks and substantial economic losses within the equine industry. In this study, we developed a competitive enzyme-linked immunosorbent assay (NP-cELISA) for the detection of antibodies against the EIV nucleoprotein (NP). The assay was designed by coating plates with purified monoclonal antibodies (mAbs) against the NP protein, followed by simultaneous incubation of the test serum samples and HRP-NP antigen in a competitive binding rea...
Bovine and ovine deltapapillomavirus coinfection associated with equine sarcoid.
Brazilian journal of microbiology : [publication of the Brazilian Society for Microbiology]    August 22, 2025   Volume 56, Issue 4 2901-2908 doi: 10.1007/s42770-025-01759-x
Pereira EL, Pereira GR, Osório ML, Terra JLA, Gayger JB, Gularte JS, Demoliner M, Pereira VMAG, Filippi M, de Matos QS, Tessman A, Canal CW, Daudt C....Papillomaviruses (PV) are significant agents capable of inducing simple, multiple, and/or proliferative lesions in the dermis and epidermis of animals, known as cutaneous papillomatosis. These lesions can be benign or malignant and have been identified in various hosts, including mammals, birds, reptiles, and fish. PVs are strictly species- and tissue-specific, although some established and unusual cases of cross-infection, such as BPV in equine sarcoids, have been reported. Sarcoids are horses' most common skin tumors, which can be locally aggressive and cause significant clinical signs. It i...
Prevalence of African Horse Sickness Virus Antibodies in Horses and Selected Wildlife in Four Geographical Regions of Nigeria.
Veterinary medicine international    August 21, 2025   Volume 2025 4106678 doi: 10.1155/vmi/4106678
Chinyere CN, Ajaebili AC, Peter-Ajuzie IK, Galadima HB, Daodu OB, Fatola OI, Okolo CC, Alaba BA, Akinniyi OO, Omoniwa DO, Edeh ER, Olorunfemi AB....African horse sickness (AHS) is a severe, infectious arthropod-borne disease of equids caused by the AHS virus (AHSV). It is endemic in Sub-Saharan Africa, and several sporadic outbreaks of the disease have been reported in Nigeria in the past 5 decades. Following a recent outbreak of the disease in Lagos State, this study was conducted to investigate the prevalence of (AHSV) antibodies in apparently healthy horses and some selected wildlife sampled in four geographical regions of Nigeria. Using a competitive enzyme-linked immunosorbent assay, 575 serum samples collected from horses in five ...
Spatial Modeling of Equine Herpesviruses 1 (EHVs-1) Risks in Kazakhstan Using 2017-2024 Surveillance Data.
Transboundary and emerging diseases    August 21, 2025   Volume 2025 5536099 doi: 10.1155/tbed/5536099
Mukhanbetkaliyev Y, Yessembekova G, Mukhanbetkaliyeva A, Akmambayeva B, Kadyrov A, Uskenov R, Bostanova S, Ashirbek A, Korennoy F, Abdrakhmanov S.Equine herpesvirus 1 (EHV-1) is one of the most dangerous viral diseases affecting ungulates, and is characterized by a wide range of clinical manifestations in horses, including rhinopneumonia, abortion, neonatal death, and myeloencephalopathy. It is well known for causing mass abortions in mares and respiratory diseases in young animals. Once introduced into a horse breeding farm of any type, EHV-1 tends to establish as a persistent infection. The disease is reported on nearly all continents and causes substantial annual economic losses to horse breeding operations. In Kazakhstan, 34 EHV-1 o...
Seroprevalence of segmented flavi-like Alongshan virus in horses.
Veterinary microbiology    August 20, 2025   Volume 309 110686 doi: 10.1016/j.vetmic.2025.110686
Janshoff S, Plümers R, Ramsauer AS, Cavalleri J, Vollmer T, Todt D, Brown RJP, Steinmann E, Gömer A.The emergence of new pathogens poses a significant threat to global health, exacerbated by climate change, biodiversity loss, and increased globalization. Ticks, as vectors for various pathogens, contribute to the rising incidence of diseases. Surveillance programs are crucial for identifying and controlling emerging pathogens. This study focuses on the Alongshan virus (ALSV), a segmented flavi-like virus first identified in humans in China in 2017. Despite its ability to infect a wide range of mammals, the natural hosts and transmission pathways of ALSV remain poorly understood. Therefore, we...
V4020 Venezuelan Equine Encephalitis Vaccine: Mitigating Neuroinvasion and Reversion Through Rational Design.
Viruses    August 19, 2025   Volume 17, Issue 8 1136 doi: 10.3390/v17081136
Centers A, Barnaby K, Goedeker S, Pignataro A, Tretyakova I, Lukashevich I, Pushko P, Chung D.There is a need for safe and effective vaccines against the Venezuelan equine encephalitis virus that infects both humans and equines. However, development of a live-attenuated vaccine using the TC-83 strain has been hampered by substantial reactogenicity and the potential for neuroinvasion. In this study, we demonstrate that V4020, a new TC-83-based investigational VEEV vaccine with redundant safety features preventing neuroinvasion and reversion, exhibited no neuroinvasion potential in a murine model. Following subcutaneous or intramuscular administration, a subset of mice that received the ...
A novel G-quadruplex aptamer with high affinity for the specific detection of equine herpesvirus type 1: Comprehensive biophysical and analytical characterization.
Talanta    August 16, 2025   Volume 297, Issue Pt B 128713 doi: 10.1016/j.talanta.2025.128713
Davoudi N, Behbahani M, Mohabatkar H, Dini G, Bakhshesh M.Equine herpesvirus type 1 (EHV-1) is a globally prevalent equine pathogen responsible for severe respiratory, neurological, and reproductive disorders. Accurate and ultrasensitive detection of EHV-1 is critical for timely disease management. In this study, we report the development of the first G-quadruplex-forming aptamer specifically designed for EHV-1 detection. The aptamer was generated using an in silico approach, and its G-quadruplex conformation was confirmed using circular dichroism (CD) spectroscopy and crystal violet fluorescence assays. Binding affinity and specificity were assessed...
Suspected tickborne virus infection in a horse from Dartmoor.
The Veterinary record    August 15, 2025   Volume 197, Issue 4 151-152 doi: 10.1002/vetr.5905
Ionescu AM, Folly AJ, Johnson N, Cornelisse K.No abstract available
Development of an African horse sickness VP6 DIVA diagnostic ELISA.
Virology journal    August 12, 2025   Volume 22, Issue 1 276 doi: 10.1186/s12985-025-02898-1
Tinarwo M, Dennis SJ, Hitzeroth II, Meyers AE, Rybicki EP, Mbewana S.African horse sickness (AHS) is a severe, noncontagious disease of equines caused by the African horse sickness virus (AHSV). The virus has nine serotypes and is transmitted by the midge. AHS is endemic in South Africa and other sub-Saharan African countries. Currently, the disease is managed using a live attenuated vaccine manufactured by Onderstepoort Biological Products (OBP). Although this vaccine has been in use for decades, it has several drawbacks, including the possibility of reversion to virulence, and it does not allow for the differentiation of infected horses from vaccinated horse...
Tracing the 2021 equine influenza Outbreak: First characterization and phylogeographic analysis of H3N8 Florida clade 1 virus in Tunisia.
Virology    August 12, 2025   Volume 611 110655 doi: 10.1016/j.virol.2025.110655
Badr C, Arbi M, Souiai O, Larbi I, Nsiri J, Elbehi I, Bouslama Z, Bennour MA, Essaied MS, Ines Khosrof , Chabchoub A, Ben Aoun B, Ghram A, Lachheb J.Equine influenza (EI) is a highly contagious viral respiratory disease affecting equids, with the potential of causing widespread outbreaks across Europe, the Americas, Asia, and other regions of the world. In Tunisia, in the spring of 2021, an EI virus outbreak occurred in a farm housing purebred Arabian horses that exhibited respiratory signs. This outbreak led to a national lockdown on horse movements and the cancellation of equestrian events. A total of 432 serum samples, collected from 2018 to 2021, were tested using ELISA competition assay. In addition, 100 Nasal swabs were collected dur...
Correction: Modelling African horse sickness emergence and transmission in the South African control area using a deterministic metapopulation approach.
PLoS computational biology    August 12, 2025   Volume 21, Issue 8 e1013377 doi: 10.1371/journal.pcbi.1013377
de Klerk JN, Gorsich EE, Grewar JD, Atkins BD, Tennant WSD, Labuschagne K, Tildesley MJ.[This corrects the article DOI: 10.1371/journal.pcbi.1011448.].
Cellular Immune Response in Horses After West Nile Neuroinvasive Disease.
Animals : an open access journal from MDPI    August 11, 2025   Volume 15, Issue 16 2352 doi: 10.3390/ani15162352
Tolnai C, O'Sullivan C, Lőrincz M, Karvouni M, Tenk M, Marosi A, Forgách P, Paszerbovics B, Wagenhoffer Z, Kutasi O.West Nile virus (WNV) is a mosquito-borne neurotropic virus that causes neurologic disease in both humans and horses. Yet the long-term cellular immune response following natural infection in horses remains poorly understood. This study aims to evaluate the WNV-specific T-cell response in horses recovered from West Nile neuroinvasive disease (WNND). Twelve client-owned horses (4 Hungarian sport horses, 2 Lippizaners, 1 KWPN, 1 Shagya Arabian, 1 Friesian, 1 Gidran, 1 Andalusian, and 1 draft cross horse) with confirmed clinical WNV infection were enrolled, and peripheral blood mononuclear cells ...
Correction: Horse handlers’ knowledge, attitudes, and perceptions of African horse sickness in South-West, Nigeria.
Scientific reports    August 7, 2025   Volume 15, Issue 1 28899 doi: 10.1038/s41598-025-14926-9
Akinniyi OO, Lawal TR, Rufai N, Jolayemi KO, Amaje J.No abstract available
Serological differentiation of West Nile, Usutu, and tick-borne encephalitis virus antibodies in birds and horses using mutant E protein ELISAs.
Scientific reports    August 6, 2025   Volume 15, Issue 1 28752 doi: 10.1038/s41598-025-14448-4
Schwarzer A, Ziegler U, Fertey J, Kreuz M, Vahlenkamp TW, Groschup MH, Ulbert S.West Nile virus (WNV), Usutu virus (USUV) and tick-borne encephalitis virus (TBEV) are worldwide endemic zoonotic orthoflaviviruses, often co-circulating in the same areas. Serological studies in animals, mostly birds and horses, are important means to monitor the spread of these viruses and the infection risks for humans. However, cross-reactive antibodies to these structurally similar flaviviruses frequently impact serological differentiation in enzyme-linked immunosorbent assays (ELISAs), hence time-consuming virus neutralization tests (VNTs) have to be employed in laboratories with high bi...
Mapping Bornavirus encephalitis-A comparative study of viral spread and immune response in human and animal dead-end hosts.
PLoS pathogens    August 4, 2025   Volume 21, Issue 8 e1013400 doi: 10.1371/journal.ppat.1013400
Vollmuth Y, Jungbäck N, Grochowski P, Mögele T, Stark L, Zarrabi NS, Schlegel J, Schaller T, Märkl B, Matiasek K, Liesche-Starnecker F.Borna disease virus 1 (BoDV-1) has long been recognized as a cause of fatal encephalitis in animals and was only recently identified as a zoonotic pathogen causing a similar disease in humans. This study provides the first comprehensive comparative analysis of BoDV-1-induced neuropathology in human and animal end hosts, including horses, sheep, and alpacas. Using immunohistochemical analyses, we investigated the topographical distribution of BoDV-1 and inflammatory responses in the central nervous system across 19 cases. Key findings reveal distinct differences and overlaps between humans and ...
Screening for Borna disease virus 1 (BoDV-1) in Austria: Absence of human cases in a retrospective case-finding study. Bauswein M, Arnold L, Springer DN, Redlberger-Fritz M.Borna disease virus 1 (BoDV-1) is a zoonotic virus with a recently confirmed potential to cause rare but severe cases of encephalitis in humans. While the bicolored white-toothed shrew (Crocidura leucodon), which represents the reservoir, is widely distributed over eastern, central, and southern Europe as well as south-west Asia, human infections have so far only been reported from Germany. As infections in sentinels such as horses indicate the endemic circulation of the virus also in circumscribed regions of neighboring countries (Austria, Liechtenstein, Switzerland), we initiated a retrospec...
Equine influenza antigen-based particle vaccine protects mice against homologous and heterosubtypic viral challenges.
Acta biomaterialia    July 22, 2025   Volume 203 578-590 doi: 10.1016/j.actbio.2025.07.042
Siddoway AC, Van Zanten A, Verhoeven D, Wannemuehler MJ, Mallapragada SK, Narasimhan B.Influenza virus is a common source of respiratory illness and poses a major public health burden globally. Significant efforts have been dedicated towards developing and deploying effective vaccines. However, since being licensed in 1945, influenza vaccines have made limited progress and still suffer from several limitations, including suboptimal efficacy against variants. In this work, we report on two influenza A polyanhydride particle- and pentablock copolymer-based vaccine formulations intended for intranasal or subcutaneous administration. These nanovaccines are based on a newly discovere...
West Nile virus transmission in the Metropolitan Area of Barcelona (Spain): A One-Health surveillance approach.
One health (Amsterdam, Netherlands)    July 21, 2025   Volume 21 101150 doi: 10.1016/j.onehlt.2025.101150
Busquets N, Gardela J, José-Cunilleras E, Solé A, Salvador MJ, Obón E, Molina-López R, Aranda C, Montalvo T, Corbella I, Bou-Monclús MA....West Nile virus (WNV), mainly transmitted by mosquitoes, poses significant health risks to humans and horses, particularly in endemic regions. The first detection of WNV lineage 2 in Spain was in 2017 in Catalonia (northeastern Spain). In 2023, WNV was confirmed in a young yellow-legged gull and a probable human case was notified within the urban settings. We aimed to define the zone of WNV circulation in the Barcelona Metropolitan Area where these infections occurred and the effectiveness of the One Health approach for early WNV detection. The Catalan WNV surveillance and control programs in...
First detection of equine hepacivirus RNA in Stomoxys calcitrans (Diptera, Muscidae) in eastern Austria.
BMC veterinary research    July 17, 2025   Volume 21, Issue 1 474 doi: 10.1186/s12917-025-04890-x
Frisch V, Ramsauer AS, Preining I, Unterköfler MS, Fuehrer HP, Hofer M, Lyrakis M, Bouhsira E, Liénard E, Cavalleri JV.Equine hepacivirus (EqHV) from the family, has been detected in horses worldwide with a global RNA prevalence of up to 7.9%. While vertical transmission and iatrogenic transmission with infected blood products have been demonstrated for this virus, field infection rates suggest an additional horizontal transmission route. The aim of this study was to investigate the potential role of (Diptera, Muscidae) – a hematophagous fly that is found in stables with ruminants and horses as preferred hosts– in the transmission of EqHV RNA. From 2021 to 2022, were collected from three horse barns in ...
Streptococcus equi subsp. zooepidemicus Supernatant Containing Streptolysin S Alters the Equine Nasal and Vaginal Mucosa, Modulating Equine Herpesvirus 1, 3 and 4 Infections.
Viruses    July 14, 2025   Volume 17, Issue 7 980 doi: 10.3390/v17070980
Mohamed E, Van Cleemput J, Şahin B, Van den Broeck W, Boyen F, Nauwynck H.The equine respiratory and reproductive tract microbiomes are complex and subject to constant fluctuations. Among the microbial inhabitants, subsp. (SEZ) is recognized as the dominant bacterium. It is an opportunistic pathogen that may occasionally lead to various types of infections. A key virulence factor of SEZ is the streptolysin S (SLS) toxin, which is responsible for the characteristic β-hemolysis on blood agar and tissue damage. Viruses and bacteria may interact and aggravate lesions and disease. This study aimed to evaluate the impact of an SLS-containing supernatant from SEZ on the...
Growth properties of recombinant equine influenza viruses with different backbones generated by reverse genetics in embryonated chicken eggs.
Archives of virology    July 12, 2025   Volume 170, Issue 8 181 doi: 10.1007/s00705-025-06368-5
Nemoto M, Kawanishi N, Kambayashi Y, Bannai H, Yamanaka T, Garvey M, Cullinane A, Yamayoshi S, Kawaoka Y, Tsujimura K.Reverse genetics (RG) technology is useful for quickly updating influenza vaccine strains. A high-yield backbone (i.e., six segments other than hemagglutinin and neuraminidase) derived from A/Puerto Rico/8/1934 (PR8) has been developed to improve the growth of avian and human influenza viruses. However, for equine influenza virus (EIV), an EIV-derived backbone may have better growth properties due to more-natural segment combinations. We compared the growth properties in eggs between the PR8 backbone and an EIV backbone from A/equine/Ibaraki/1/2007, a vaccine strain in Japan. The results showe...