Topic:H3N8
H3N8 is an influenza virus subtype that affects horses, resulting in equine influenza, a highly contagious respiratory disease. This virus is characterized by its ability to spread rapidly among equine populations, leading to symptoms such as fever, coughing, nasal discharge, and reduced performance. H3N8 is part of the Orthomyxoviridae family and is known for its potential to mutate, which can complicate control and prevention efforts. Vaccination is a common preventive measure, and biosecurity practices are employed to limit transmission. This page compiles peer-reviewed research studies and scholarly articles that explore the virology, epidemiology, and impact of H3N8 on equine health, including vaccine development and outbreak management strategies.
[Epizootic equine influenza in Tunisia]. The authors describe an equine influenza epizootic that occurred in Tunisia during February and March 1998 in the regions of Tozeur, Sousse and Tunis. They relate the symptoms, the different stages of diagnosis and the serological results.
Comparison of hamster and pony challenge models for evaluation of effect of antigenic drift on cross protection afforded by equine influenza vaccines. Vaccination and challenge studies in ponies are the most relevant experimental system for predicting whether strains included in equine influenza vaccines are relevant, but they are difficult to perform. Objective: In order to investigate the feasibility of using a small animal model, results of a cross-protection study in hamsters were compared with those from a previous pony challenge experiment. Methods: Animals were immunised with inactivated vaccines containing one of 4 strains of equine influenza A H3N8 subtype virus isolated over a 26 year period (1963 to 1989), then challenged with a 1...
Experimental infection of ponies with equine influenza A2 (H3N8) virus strains of different pathogenicity elicits varying interferon and interleukin-6 responses. The production of interferon (IFN), interleukin-6 (IL-6), and tumor necrosis factor (TNF) was monitored in horses during the course of influenza A2 virus infections. The effects of two virus strains, Newmarket/2/93 and Sussex/89, were compared, of which the latter is considered the more pathogenic in terms of clinical signs. Ten naive ponies were infected with influenza A/equine/Sussex/89 and 10 with influenza A/equine/Newmarket/2/93, respectively. As expected ponies infected with Sussex/89 showed the most pronounced clinical signs but there was no notable difference in viral excretion compare...
Diagnostic methods applied to analysis of an outbreak of equine influenza in a riding school in which vaccine failure occurred. An outbreak of equine influenza H3N8 in a riding school is described retrospectively with emphasis on diagnosis and putative vaccine failure. In March 1995 an outbreak of equine influenza occurred among 11 horses in a riding school, where most horses had received basic primary immunizations and several booster vaccinations against influenza. Six of the 11 diseased horses had received their last booster vaccination within 5 months of the outbreak. Nevertheless, the influenza infection spread rapidly and clinical manifestations were prominent with frequent, harsh, dry coughing often accompanied ...
Area under the curve calculations as a tool to compare the efficacy of equine influenza vaccines–a retrospective analysis of three independent field trials. Using the area under the curve (AUC) concept as is commonly used in pharmaceutical bioequivalence studies, the bioequivalence of three equine influenza vaccines was demonstrated. A retrospective analysis was performed using this technique on data generated in three trials in which each of the three vaccines had been used. In total, data from 63 pony and horse foals were used. The AUC of the single radial hemolysis (SRH) titres against Influenza A/equi-1/Prague/56 (Pr/56), A/equi-2/Newmarket-1/93, and A/equi-2/Suffolk/89 (Suf/89) were calculated for each horse. It was concluded that calculation...
Cultures of equine respiratory epithelial cells and organ explants as tools for the study of equine influenza virus infection. Equine nasal turbinate epithelial cells and tracheal rafts were maintained with sustained viability in culture. Both types of culture supported productive replication of equine influenza virus (equine-2, subtype H3N8) and cell death occurred through apoptosis following viral infection. Thus, primary respiratory epithelial cell and organ cultures of equine origin may be valuable as alternatives to the intact animal for studying the virus-host interaction of equine respiratory viruses including influenza.
Derivation and characterization of a live attenuated equine influenza vaccine virus. To develop and characterize a cold-adapted live attenuated equine-2 influenza virus effective as an intranasal vaccine. Methods: 8 ponies approximately 18 months of age. Methods: A wild-type equine-2 virus, A/Equine/Kentucky/1/91 (H3N8), was serially passaged in embryonated chicken eggs at temperatures gradually reduced in a stepwise manner from 34 C to 30 C to 28 C to 26 C. At different passages, infected allantoic fluids were tested for the ability of progeny virus to replicate in Madin-Darby canine kidney (MDCK) cells at 34 C and 39.5 C. Virus clones that replicated at 26 C in eggs and at 3...
Detection of antibodies to the nonstructural protein (NS1) of influenza A virus allows distinction between vaccinated and infected horses. Antibodies to the nonstructural protein (NS1) of A/equine/Miami/1/63 (H3N8) influenza virus were detected exclusively in the sera of mice experimentally infected with A/Aichi/2/68 (H3N2) and horses infected with A/equine/Kentucky/1/81 (H3N8) or A/equine/La Plata/1/93 (H3N8), but not in those of the animals immunized with the inactivated viruses, by enzyme-linked immunosorbent assay (ELISA) using a recombinant NS1 as antigen. The results indicate that the present method is useful for serological diagnosis to distinguish horses infected with equine H3 influenza viruses from those immunized with ...
Antigenic variation among equine H 3 N 8 influenza virus hemagglutinins. To provide information on the antigenic variation of the hemagglutinins (HA) among equine H 3 influenza viruses, 26 strains isolated from horses in different areas in the world during the 1963-1996 period were analyzed using a panel of monoclonal antibodies recognizing at least 7 distinct epitopes on the H 3 HA molecule of the prototype strain A/equine/Miami/1/63 (H 3 N 8). The reactivity patterns of the virus strains with the panel indicate that antigenic drift of the HA has occurred with the year of isolation, but less extensively than that of human H 3 N 2 influenza virus isolates, and diff...
The acute phase protein serum amyloid A (SAA) as an inflammatory marker in equine influenza virus infection. The acute phase protein serum amyloid A (SAA) has proven potentially useful as an inflammatory marker in the horse, but the knowledge of SAA responses in viral diseases is limited. The aim of this study was to evaluate SAA as a marker for acute equine influenza A2 (H3N8) virus infection. This is a highly contagious, serious condition that inflicts suffering on affected horses and predisposes them to secondary bacterial infections and impaired performance. Seventy horses, suffering from equine influenza, as verified by clinical signs and seroconversion, were sampled in the acute (the first 48 h...
Equine influenza vaccine efficacy: the significance of antigenic variation. To investigate the level of cross-protection induced by equine influenza H3N8 vaccines derived from different lineages, two studies have been carried out with ponies vaccinated with 'American-like' and 'European-like' vaccines and experimentally challenged with a European-like strain. The results demonstrated that equine influenza vaccines clearly protect against challenge with homologous virus if serum antibody titres are sufficiently high. On the other hand, protection is incomplete even when animals vaccinated with heterologous strains have comparative antibody levels. Nevertheless, the pro...
Immunity to equine influenza: relationship of vaccine-induced antibody in young Thoroughbred racehorses to protection against field infection with influenza A/equine-2 viruses (H3N8). Field outbreaks of influenza that occurred in vaccinated Thoroughbred racehorses in Newmarket in 1995 and 1996 were investigated by nucleoprotein ELISA and serology. Investigations showed that serum levels of vaccine-induced single radial haemolysis (SRH) antibody correlated closely with protective immunity against equine influenza and were consistent with observations made in previous experimental studies using nebulised aerosol challenge. In the second part of this study, antibody levels stimulated by vaccination were investigated to examine probable protection in high risk groups, such as y...
Plasma glutamine status in the equine at rest, during exercise and following viral challenge. The variation over 24 h of plasma glutamine concentration in nonexercising horses was studied in 3 Thoroughbreds (TB) fed at 1600 h and 0700 h. This indicated a small but regular change associated with feeding. Starting at a mean of 482 mumol/l at 1600 h the concentration increased to 522 mumol/l at 2000 h, falling to 476 mumol/l at 1600 h and increasing again to 525 mumol/l at 2000 h. 'Normal' values were established in 19 part-bred TB horses, lacking clinical signs or remarkable pathology and in light training, by sampling weekly at 1000 h over a 10 week period. The mean concentration was 49...
A PCR based method for the identification of equine influenza virus from clinical samples. In this paper we describe the development of a nested RT-PCR assay for the rapid diagnosis and characterisation of influenza virus directly from clinical specimens. Viral RNA is extracted from nasal swabs by the guanidine thiocyanate extraction method, and subsequently reverse transcribed. The complementary DNA is then used as template in a nested PCR reaction. Primers designed for use in this assay are specific for three templates; (1) the nucleoprotein (NP) gene, (2) the haemagglutinin gene of the H7N7 equine influenza virus (A1), and (3) the haemagglutinin gene of the H3N8 equine influenza ...
The circumstances surrounding the outbreak and spread of equine influenza in South Africa. Equine-2 influenza A virus (H3N8) infection first occurred among naïve horses in South Africa in December 1986. The virus was introduced following the importation of six horses from the United States of America. While the release of in-contact horses from quarantine three days after the arrival of these six horses played a role in the rapid spread of the disease in South Africa, other outbreaks of disease were associated with viral introduction by personnel or contaminated instruments. The control measures and implications of the introduction of equine influenza to South Africa are also discu...
Effect of moderate exercise on the severity of clinical signs associated with influenza virus infection in horses. The purpose of this experiment was to determine if exercising horses, infected with influenza virus, exacerbates the severity of clinical disease. Eight horses were trained on a treadmill for 42 days and then challenged with aerosolised influenza A/equine/Kentucky/91 (H3N8). Following challenge, 4 horses (exercise group) continued training for 28 days, while the other 4 horses (nonexercise group) were confined to their stalls. All horses developed clinical signs within 36 h of challenge (fever, coughing, and mucopurulent nasal discharge) and clinical scores were greater in the exercise group. ...
Direct sequencing of the HA gene of clinical equine H3N8 influenza virus and comparison with laboratory derived viruses. Equine influenza viruses propagated in the laboratory in alternate hosts such as embryonated hens' eggs or mammalian cell culture have been analysed by HA sequencing and antigenically and their sequence compared to the original virus present in clinical material. In contrast to clinically derived human influenza virus which generally grows in MDCK cells without change, the data for equine influenza virus were less clear in that variants of equine virus were derived in both eggs and cells. The study indicated that the current use of eggs for equine influenza virus surveillance and vaccine produ...
Immunogenicity and efficacy of baculovirus-expressed and DNA-based equine influenza virus hemagglutinin vaccines in mice. Two fundamentally different approaches to vaccination of BALB/c mice with the hemagglutinin (HA) of A/Equine/Kentucky/1/81 (H3N8) (Eq/KY) were evaluated, that is, administration of HA protein vs administration of HA-encoding DNA. Each vaccine was tested for its immunogenicity and ability to provide protection from homologous virus challenge. HA protein was synthesized in vitro by infection of Sf21 insect cells with a recombinant baculovirus. Intranasal administration of this vaccine induced virus-specific antibodies, as measured by enzyme-linked immunosorbent assay (ELISA), but did not induce ...
Study of the duration and distribution of equine influenza virus subtype 2 (H3N8) antigens in experimentally infected ponies in vivo. The purpose of this experiment was to study the duration and distribution of equine influenza virus in actively infected ponies over a 3 wk period. Pony foals (6-8 mo old) were infected experimentally by nebulizing equine influenza subtype-2 virus ultrasonically through a face mask. Successful infection was clinically apparent as each of the foals (n = 6) had a febrile response, a deep hacking cough and mucopurulent nasal discharge for 7 to 10 d. The virus was isolated from nasopharyngeal swabs of all the ponies 3 and 5 d after infection and all the ponies seroconverted to the virus. Samples w...
Antigenic and genetic evolution of equine H3N8 influenza A viruses. Evolution of equine influenza a H3N8 viruses was examined by antigenic and genetic analysis of a collection isolates from around the world. It was noted that antigenic and genetic variants of equine H3N8 viruses cocirculate, and in particular that variants currently circulating in Europe and the USA are distinguishable from one another both in terms of antigenic reactivity and genetic structure of the HA1 portion of the haemagglutinin (HA) molecule. Whilst the divergent evolution of American and European isolates may be due to geographical isolation of the two gene pools, some mixing is believ...
Seroepidemiological and molecular evidence for the presence of two H3N8 equine influenza viruses in China in 1993-94. In May 1993, a severe epidemic of respiratory disease began in horses in Inner Mongolia and spread throughout horses in China. The disease affected mules and donkeys as well as horses but did not spread to other species, including humans. The severity of the disease raised the question of whether the outbreak might have been caused by the new avian-like influenza viruses detected in horses in China in 1989 or by current variants ofA/equine/Miami/1/63 (H3N8) (equine-2) or by a reassortant between these viruses. Antigenic and sequence analysis established that all gene segments of the influenza ...
The relationship between single radial hemolysis, hemagglutination inhibition, and virus neutralization assays used to detect antibodies specific for equine influenza viruses. Antibodies specific for equine influenza viruses are usually quantified using single radial hemolysis (SRH), hemagglutination inhibition (HI) or virus neutralization (VN). Neutralizing antibodies are thought to provide optimum protection to challenged animals. The purpose of this study was to determine the extent to which SRH and HI assays detect antibodies which neutralize equine influenza viruses. Acute and convalescent sera from 41 horses were analyzed using VN, SRH, and HI assays. These horses were present in a population of Thoroughbred racehorses during an epidemic of upper respiratory t...
Outbreak of equine influenza among horses in Hong Kong during 1992. Equine-2 influenza virus A (H3N8) infection occurred among vaccinated thoroughbred horses in Hong Kong during November and December 1992. The outbreak was unique in that it occurred among a large population stabled under intensive conditions. It resulted in the postponement of seven race meetings over a period of 32 days. The outbreak originated after the importation of horses 25 to 32 days before any clinical signs were reported. Vaccination did not prevent 75 per cent of the population from becoming infected, and half the infected horses developed clinical signs. Vaccination did, however, co...
Genetic and antigenic analysis of the influenza virus responsible for the 1992 Hong Kong equine influenza epizootic. An outbreak of influenza occurred among thoroughbred racehorses in Hong Kong in November-December 1992, with morbidity of 37%. All horses involved had been vaccinated against equine-1 and equine-2 influenza viruses but not against the virus responsible for the 1989 equine influenza outbreak in northern China (influenza A/equine/Jilin/89, subtype H3N8). Therefore the source and nature of the virus causing the Hong Kong outbreak was investigated. Virus isolated from a horse infected during the outbreak was used for genetic analysis. All the viral gene segments were similar to those of equine-2 (...
Antigenicity and immunogenicity of equine influenza vaccines containing a Carbomer adjuvant. Equine influenza vaccines containing inactivated whole virus and Carbomer adjuvant stimulated higher levels and longer lasting antibody to haemagglutinin in ponies than vaccines of equivalent antigenic content containing aluminium phosphate adjuvants. Five months after the third dose of vaccine containing Carbomer adjuvant, ponies were protected against clinical disease induced by an aerosol of virulent influenza virus (A/equine/Newmarket/79, H3N8). In contrast ponies which received vaccine containing aluminium phosphate adjuvant were susceptible to infection and disease. There was an inverse ...
Duration of protective efficacy of equine influenza immunostimulating complex/tetanus vaccines. Seven previously untreated five-month-old New Forest ponies received two doses of equine influenza immunostimulating complex vaccines, one with and one without an immunopurified tetanus toxoid component, given by deep intramuscular injection six weeks apart, followed by a booster dose without tetanus toxoid five months later. Fifteen months after the third dose of vaccine, the ponies were challenged by exposure to an aerosol of influenza A/Equine 2/Sussex/89 (H3N8), a virus isolated from a recent outbreak of influenza A/equine 2 in Britain. The challenge produced severe clinical signs of influ...
The outbreak of equine influenza (H3N8) in the United Kingdom in 1989: diagnostic use of an antigen capture ELISA. In July 1989 influenza A/equine-2 (H3N8) was isolated from a nasopharyngeal swab taken from a non-thoroughbred horse exhibiting acute clinical respiratory disease. This was the first isolation of equine influenza virus in the United Kingdom since 1981. Subsequent investigations of acute respiratory disease in horses indicated that the infection was dispersed throughout the UK. However, unlike the previous epidemic of 1979, the first horses from which the virus was isolated had been vaccinated. This outbreak of influenza provided an opportunity to evaluate an antigen capture ELISA, directed aga...
Equine influenza virus from the 1991 Swedish epizootic shows major genetic and antigenic divergence from the prototype virus. The antigenic properties of H3N8 equine influenza virus from the Swedish epizootic of 1991 differ from those of A/eq 2/Fontainebleau/79 (representative of the Swedish vaccine strain) in hemagglutination inhibition tests. The amino acid sequence of the hemagglutinin (HA) of an isolate from the 1991 outbreak was deduced from the nucleotide sequence and comparison was made to the A/eq 2/Fontainebleau/79 strain. Twenty-three amino acid substitutions were found, 10 mapping onto areas of the HA known to bind antibodies in human H3 influenza viruses. The amino acid changes together with the serologic...
Effect of influenza A/equine/H3N8 virus isolate variation on the measurement of equine antibody responses. This study has tested the effect of using homologous or heterologous equine influenza A virus isolates to evaluate serum antibody levels to influenza A virus in vaccinated and naturally-infected horses. In addition, the potential effect of antigenic selection of virus variants in egg versus tissue culture propagation systems was studied. Serum antibody levels in samples from horses recently infected with a local influenza A virus isolate (A/equine 2/Saskatoon/1/90) or recently vaccinated with a prototype isolate (A/equine 2/Miami/1/63) were assessed by hemagglutination inhibition and by single...