An outbreak of equine influenza virus in vaccinated horses in Italy is due to an H3N8 strain closely related to recent North American representatives of the Florida sub-lineage

Adaptation potential of H3N8 canine influenza virus in human respiratory cells

In 2004, the equine-origin H3N8 canine influenza virus (CIV) first caused an outbreak with lethal cases in racing greyhounds in Florida, USA, and then spread to domestic dogs nationwide. Although transmission of this canine virus to humans has not been reported, it is important to evaluate its zoonotic potential because of the high contact opportunities between companion dogs and humans. To gain insight into the interspecies transmissibility of H3N8 CIV, we tested its adaptability to human respiratory A549 cells through successive passages. We found that CIV acquired high growth properties in these cells mainly through mutations in surface glycoproteins, such as hemagglutinin (HA) and neuraminidase (NA). Our reverse genetics approach revealed that HA2-K82E, HA2-R163K, and NA-S18L mutations were responsible for the increased growth of CIV in human cells. Molecular analyses revealed that both HA2 mutations altered the optimum pH for HA membrane fusion activity and that the NA mutation changed the HA-NA functional balance. These findings suggest that H3N8 CIV could evolve into a human pathogen with pandemic potential through a small number of mutations, thereby posing a threat to public health in the future.

First Molecular Detection and Epidemiological Analysis of Equine Influenza Virus in Two Regions of Colombia, 2020-2023

Equine influenza is a viral disease caused by the equine influenza virus (EIV), and according to the WOAH, it is mandatory to report these infections. In Latin America and Colombia, EIV risk factors have not been analyzed. The objective of this research is to perform an epidemiological and molecular analysis of the EIV in horses with respiratory symptoms from 2020 to 2023 in Colombia. Molecular EIV detection was performed using RT-qPCR and nanopore sequencing. A risk analysis was also performed via the GEE method. A total of 188 equines with EIV respiratory symptoms were recruited. The positivity rate was 33.5%. The descriptive analysis showed that only 12.8% of the horses were vaccinated, and measures such as the quarantine and isolation of symptomatic animals accounted for 91.5% and 88.8%, respectively. The variables associated with the EIV were the non-isolation of positive individuals (OR = 8.16, 95% CI (1.52-43.67), p = 0.014) and sharing space with poultry (OR = 2.16, 95% CI (1.09-4.26), p = 0.027). In conclusion, this is the first EIV investigation in symptomatic horses in Colombia, highlighting the presence of the virus in the country and the need to improve preventive and control measures.

Assessment of Equine Influenza Virus Status in the Republic of Korea from 2020 to 2022

Equine influenza virus (EIV) causes acute respiratory disease in horses and belongs to the influenza A virus family Orthomyxoviridae, genus Orthomyxovirus. This virus may have severe financial implications for the horse industry owing to its highly contagious nature and rapid transmission. In the Republic of Korea, vaccination against EIV has been practiced with the active involvement of the Korea Racing Authority since 1974. In this study, we monitored the viral RNA for EIV using PCR, as well as the antibody levels against 'A/equine/South Africa/4/03 (H3N8, clade 1)', from 2020 to 2022. EIV was not detected using RT-PCR. The seropositivity rates detected using a hemagglutination inhibition assay were 90.3% in 2020, 96.7% in 2021, and 91.8% in 2022. The geometric mean of antibody titer (GMT) was 83.4 in 2020, 135.7 in 2021, and 95.6 in 2022. Yearlings and two-year-olds in training exhibited lower positive rates (59.1% in 2020, 38.9% in 2021, and 44.1% in 2022) than the average. These younger horses may require more attention for vaccination and vaccine responses against EIV. Continuous surveillance of EIV should be performed to monitor the prevalence and spread of this disease.

A Cold Case of Equine Influenza Disentangled with Nanopore Sequencing

Massive sequencing techniques have allowed us to develop straightforward approaches for the whole genome sequencing of viruses, including influenza viruses, generating information that is useful for improving the levels and dimensions of data analysis, even for archival samples. Using the Nanopore platform, we determined the whole genome sequence of an H3N8 equine influenza virus, identified from a 2005 outbreak in Apulia, Italy, whose origin had remained epidemiologically unexplained. The virus was tightly related (>99% at the nucleotide level) in all the genome segments to viruses identified in Poland in 2005–2008 and it was seemingly introduced locally with horse trading for the meat industry. In the phylogenetic analysis based on the eight genome segments, strain ITA/2005/horse/Bari was found to cluster with sub-lineage Florida 2 in the HA and M genes, whilst in the other genes it clustered with strains of the Eurasian lineage, revealing a multi-reassortant nature.

Antigenic comparison of H3N8 equine influenza viruses belonging to Florida sublineage clade 1 between vaccine strains and North American strains isolated in 2021-2022

Equine influenza virus strains of Florida sublineage clade 1 (Fc1) have been circulating in North America. In this study, virus neutralization assays were performed to evaluate antigenic differences between Fc1 vaccine strains and North American Fc1 strains isolated in 2021-2022, using equine antisera against A/equine/South Africa/4/2003 (a vaccine strain recommended by the World Organisation for Animal Health) and A/equine/Ibaraki/1/2007 (a Japanese vaccine strain). Antibody titers against four North American Fc1 strains isolated in 2021-2022 were comparable to those against the homologous vaccine strains. These results suggest that current Fc1 vaccine strains are effective against North American strains from 2021-2022.

Frequency of Detection and Prevalence Factors Associated with Common Respiratory Pathogens in Equids with Acute Onset of Fever and/or Respiratory Signs (2008–2021)

A voluntary biosurveillance program was established in 2008 in order to determine the shedding frequency and prevalence factors for common respiratory pathogens associated with acute onset of fever and/or respiratory signs in equids from the USA. Over a period of 13 years, a total of 10,296 equids were enrolled in the program and nasal secretions were analyzed for the qPCR detection of equine influenza virus (EIV), equine herpesvirus-1 (EHV-1), EHV-4, equine rhinitis A and B virus (ERVs), and Streptococcus equi subspecies equi (S. equi). Single infections with respiratory pathogens were detected in 21.1% of the submissions with EIV (6.8%) and EHV-4 (6.6%) as the two most prevalent viruses, followed by S. equi (4.7%), ERVs (2.3%), and EHV-1 (0.7%). Multiple pathogens were detected in 274 horses (2.7%) and no respiratory pathogens in 7836 horses (76.2%). Specific prevalence factors were determined for each of the six respiratory pathogen groups; most differences were associated with age, breed, and use of the horses, while the clinical signs were fairly consistent between viral and bacterial respiratory infections. Monitoring the frequency of detection of common respiratory pathogens is important in order to gain a better understanding of their epidemiology and to implement management practices aimed at controlling disease spread.

Equine influenza: a comprehensive review from etiology to treatment

Influenza is an extremely contagious respiratory disease, which predominantly affects the upper respiratory tract. There are four types of influenza virus, and pigs and chickens are considered two key reservoirs of this virus. Equine influenza (EI) virus was first identified in horses in 1956, in Prague. The influenza A viruses responsible for EI are H7N7 and H3N8. Outbreaks of EI are characterized by their visible and rapid spread, and it has been possible to isolate and characterize H3N8 outbreaks in several countries. The clinical diagnosis of this disease is based on the clinical signs presented by the infected animals, which can be confirmed by performing complementary diagnostic tests. In the diagnosis of EI, in the field, rapid antigen detection tests can be used for a first approach. Treatment is based on the management of the disease and rest for the animal. Regarding the prognosis, it will depend on several factors, such as the animal's vaccination status. One of the important points in this disease is its prevention, which can be done through vaccination. In addition to decreasing the severity of clinical signs and morbidity during outbreaks, vaccination ensures immunity for the animals, reducing the economic impact of this disease.

Antigenic differences between equine influenza virus vaccine strains and Florida sublineage clade 1 strains isolated in Europe in 2019

From late 2018 to 2019, equine influenza virus (EIV) strains of Florida sublineage clade 1 (Fc1), which had until then been circulating mainly in the United States, suddenly spread across Europe causing many outbreaks, and Florida sublineage clade 2 (Fc2) strains, which had been circulating mainly in Europe, have not been detected in Europe since 2018. Since 2010, the World Organisation for Animal Health (OIE) has recommended that EIV vaccines contain an Fc1 strain that is like A/equine/South Africa/4/2003 or A/equine/Ohio/2003. Accordingly, Japanese vaccines contain A/equine/Ibaraki/1/2007 as the Fc1 strain. To evaluate the effectiveness of these vaccines against the Fc1 strains detected in Europe in 2019, we performed virus neutralization tests using horse antisera. Challenge viruses used were Irish strain A/equine/Tipperary/1/2019 and two recombinant viruses generated by reverse genetics. Recombinant viruses possessing hemagglutinin (HA) and neuraminidase (NA) derived from A/equine/Tipperary/1/2019 (rA/equine/Tipperary/1/2019) or British strain A/equine/Essex/1/2019 (rA/equine/Essex/1/2019) were generated. Equine antisera against A/equine/South Africa/2003 and A/equine/Ibaraki/2007 were produced by experimental infection. Antibody titers against A/equine/Tipperary/1/2019, rA/equine/Tipperary/1/2019, and rA/equine/Essex/1/2019 were 2.5- to 6.3-fold lower than those against the homologous vaccine strains A/equine/South Africa/4/2003 or A/equine/Ibaraki/2007. These results suggest that the ongoing evolution of the Fc1 viruses may impact on antigenicity and although antibodies against current vaccine strains neutralize the 2019 strains, ongoing surveillance is essential for optimum choice of candidate vaccine strains.

Determining Equine Influenza Virus Vaccine Efficacy-The Specific Contribution of Strain Versus Other Vaccine Attributes

Vaccination is an effective tool to limit equine influenza virus (EIV H3N8) infection, a contagious respiratory disease with potentially huge economic impact. The study assessed the effects of antigenic change on vaccine efficacy and the need for strain update. Horses were vaccinated (V1 and V2) with an ISCOMatrix-adjuvanted, whole inactivated virus vaccine (Equilis Prequenza, group 2, FC1 and European strains) or a carbomer-adjuvanted, modified vector vaccine (ProteqFlu, group 3, FC1 and FC2 HA genes). Serology (SRH, HI, VN), clinical signs and viral shedding were assessed in comparison to unvaccinated control horses. The hypothesis was that group 2 (no FC2 vaccine strain) would be less well protected than group 3 following experimental infection with a recent FC2 field strain (A/equi-2/Wexford/14) 4.5 months after vaccination. All vaccinated horses had antibody titres to FC1 and FC2. After challenge, serology increased more markedly in group 3 than in group 2. Vaccinated horses had significantly lower total clinical scores and viral shedding. Unexpectedly, viral RNA shedding was significantly lower in group 2 than in group 3. Vaccination induced protective antibody titres to FC1 and FC2 and reduced clinical signs and viral shedding. The two tested vaccines provided equivalent protection against a recent FC2 EIV field strain.

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

BACKGROUND

In 2013, there was an outbreak of acute respiratory disease in racehorses in Turkey. The clinical signs were consistent with equine influenza (EI).

OBJECTIVE

The aim was to confirm the cause of the outbreak and characterise the causal virus.

METHODS

A 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.

RESULTS

A 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.

CONCLUSIONS

The 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.

Multifocal Equine Influenza Outbreak with Vaccination Breakdown in Thoroughbred Racehorses

Equine influenza (EI) outbreaks occurred on 19 premises in Ireland during 2014. Disease affected thoroughbred (TB) and non-TB horses/ponies on a variety of premises including four racing yards. Initial clinical signs presented on 16 premises within a two-month period. Extensive field investigations were undertaken, and the diagnostic effectiveness of a TaqMan RT-PCR assay was demonstrated in regularly-vaccinated and sub-clinically-affected horses. Epidemiological data and repeat clinical samples were collected from 305 horses, of which 40% were reported as clinically affected, 39% were identified as confirmed cases and 11% were sub-clinically affected. Multivariable analysis demonstrated a significant association between clinical signs and age, vaccination status and number of vaccine doses received. Vaccine breakdown was identified in 31% of horses with up to date vaccination records. This included 27 horses in four different racing yards. Genetic and antigenic analysis identified causal viruses as belonging to Clade 2 of the Florida sublineage (FCL2). At the time of this study, no commercially available EI vaccine in Ireland had been updated in line with World Organisation for Animal Health (OIE) recommendations to include a FCL2 virus. The findings of this study highlight the potential ease with which EI can spread among partially immune equine populations.

Molecular Epidemiology of a novel re-assorted epidemic strain of equine influenza virus in Pakistan in 2015-16

BACKGROUND

A widespread epidemic of equine influenza (EI) occurred in nonvaccinated equine population across multiple districts in Khyber Pakhtunkhwa Province of Pakistan during 2015-2016.

OBJECTIVES AND METHODS

An epidemiological surveillance study was conducted from Oct 2015 to April 2016 to investigate the outbreak. EI virus strains were isolated in embryonated eggs from suspected equines swab samples and were subjected to genome sequencing using M13 tagged segment specific primers. Phylogenetic analyses of the nucleotide sequences were concluded using Geneious. Haemagglutinin (HA), Neuraminidase (NA), Matrix (M) and nucleoprotein (NP) genes nucleotide and amino acid sequences of the isolated viruses were aligned with those of OIE recommended, FC-1, FC-2, and contemporary isolates of influenza A viruses from other species.

RESULTS

HA and NA genes amino acid sequences were very similar to Tennessee/14 and Malaysia/15 of FC-1 and clustered with the contemporary isolates recently reported in the USA. Phylogenetic analysis showed that these viruses were mostly identical (with 99.6% and 97.4% nucleotide homology) to, and were reassortants containing chicken/Pakistan/14 (H7N3) and Canine/Beijing/10 (H3N2) like M and NP genes. Genetic analysis indicated that A/equine/Pakistan/16 viruses were most probably the result of several re-assortments between the co-circulating avian and equine viruses, and were genetically unlike the other equine viruses due to the presence of H7N3 or H3N2 like M and NP genes.

CONCLUSION

Epidemiological data analysis indicated the potential chance of mixed, and management such as mixed farming system by keeping equine, canine and backyard poultry together in confined premises as the greater risk factors responsible for the re-assortments. Other factors might have contributed to the spread of the epidemic, including low awareness level, poor control of equine movements, and absence of border control disease strategies.

Multiple alignment comparison of the non-structural genes of three strains of equine influenza viruses (H3N8) isolated in Morocco

BACKGROUND

Three equine influenza viruses, A/equine/Nador/1/1997(H3N8), A/equine/Essaouira/2/2004(H3N8), and A/equine/Essaouira/3/2004(H3N8), were isolated from different Equidae during local respiratory disease outbreaks in Morocco in 1997 and 2004. Their non-structural (NS) genes were amplified and sequenced.

RESULTS

The results show high homology of NS nucleotide sequences of A/equine/Nador/1/1997 with European strains (i.e., A/equine/newmarket/2/93 and A/equine/Grobois/1/1998) and clustered into the European lineage. However, NS gene of A/equine/Essaouira/2/2004(H3N8) and A/equine/Essaouira/3/2004(H3N8) strains indicated high homology with equine influenza strains that had circulated before 1990 (A/equine/Fontainbleu/1/1979(H3N8), which belonged to a pre-divergent phase Amino acid sequence comparison of the NS1 protein with reference strain A/equine/Miami/1963(H3N8) shows that the A/equine/Nador/1/1997(H3N8) strain has 12 substitutions at the residues D/24/N, R/44/K, S/48/I, R/67/Q, A/86/V, E/139/K, A/112/T, E/186/K, L/185/F, A/223/E, S/213/T and S/228/P. In both A/equine/Essaouira/2/2004(H3N8) and A/equine/Essaouira/3/2004(H3N8) strains, the NS1 sequences present one common mutation at the residue: S/228/P.

CONCLUSION

It seems that all of these substitutions are not produced at the key residues of the RNA-binding domain (RBD) and the effector domain (ED). Consequently, we can suppose that they will not affect the potency of inhibition of cellular defences, and the virulence of the Moroccan equine strains will be maintained.

A Systematic Review of Recent Advances in Equine Influenza Vaccination

Equine influenza (EI) is a major respiratory disease of horses, which is still causing substantial outbreaks worldwide despite several decades of surveillance and prevention. Alongside quarantine procedures, vaccination is widely used to prevent or limit spread of the disease. The panel of EI vaccines commercially available is probably one of the most varied, including whole inactivated virus vaccines, Immuno-Stimulating Complex adjuvanted vaccines (ISCOM and ISCOM-Matrix), a live attenuated equine influenza virus (EIV) vaccine and a recombinant poxvirus-vectored vaccine. Several other strategies of vaccination are also evaluated. This systematic review reports the advances of EI vaccines during the last few years as well as some of the mechanisms behind the inefficient or sub-optimal response of horses to vaccination.

Using Bayes' rule to define the value of evidence from syndromic surveillance

In this work we propose the adoption of a statistical framework used in the evaluation of forensic evidence as a tool for evaluating and presenting circumstantial “evidence” of a disease outbreak from syndromic surveillance. The basic idea is to exploit the predicted distributions of reported cases to calculate the ratio of the likelihood of observing n cases given an ongoing outbreak over the likelihood of observing n cases given no outbreak. The likelihood ratio defines the Value of Evidence (V). Using Bayes' rule, the prior odds for an ongoing outbreak are multiplied by V to obtain the posterior odds. This approach was applied to time series on the number of horses showing clinical respiratory symptoms or neurological symptoms. The separation between prior beliefs about the probability of an outbreak and the strength of evidence from syndromic surveillance offers a transparent reasoning process suitable for supporting decision makers. The value of evidence can be translated into a verbal statement, as often done in forensics or used for the production of risk maps. Furthermore, a Bayesian approach offers seamless integration of data from syndromic surveillance with results from predictive modeling and with information from other sources such as disease introduction risk assessments.

Efficacy of a non-updated, Matrix-C-based equine influenza subunit-tetanus vaccine following Florida sublineage clade 2 challenge

Assessing the ability of current equine influenza vaccines to provide cross-protection against emerging strains is important. Horses not vaccinated previously and seronegative for equine influenza based on haemagglutination inhibition (HI) assay were assigned at random to vaccinated (n=7) or non-vaccinated (control, n=5) groups. Vaccination was performed twice four weeks apart with a 1 ml influenza subunit (A/eq/Prague/1/56, A/eq/Newmarket/1/93, A/eq/Newmarket/2/93), tetanus toxoid vaccine with Matrix-C adjuvant (EquilisPrequenza Te). All the horses were challenged individually by aerosol with A/eq/Richmond/1/07 three weeks after the second vaccination. Rectal temperature, clinical signs, serology and virus excretion were monitored for 14 days after challenge. There was no pain at the injection site or increases in rectal temperature following vaccination. Increases in rectal temperature and characteristic clinical signs were recorded in the control horses. Clinical signs were minimal in vaccinated horses. Clinical (P=0.0345) and total clinical scores (P=0.0180) were significantly lower in the vaccinated than in the control horses. Vaccination had a significant effect on indicators of viraemia – the extent (P=0.0006) and duration (P=<0.0001) of virus excretion and the total amount of virus excreted (AUC, P=0.0006). Vaccination also had a significant effect (P=0.0017) on whether a horse was positive or negative for virus excretion during the study. Further research is needed to fully understand the specific properties of this vaccine that may contribute to its cross-protective capacity.

Controlling equine influenza: policy networks and decision-making during the 2007 Australian equine influenza outbreak

Rapid, evidence-based decision-making is critical during a disease outbreak response; however, compliance by stakeholders is necessary to ensure that such decisions are effective - especially if the response depends on voluntary action. This mixed method study evaluated technical policy decision-making processes during the 2007 outbreak of equine influenza in Australia by identifying and analysing the stakeholder network involved and the factors driving policy decision-making. The study started with a review of the outbreak literature and published policy documents. This identified six policy issues regarding policy modifications or differing interpretations by different state agencies. Data on factors influencing the decision-making process for these six issues and on stakeholder interaction were collected using a pre-tested, semi-structured questionnaire. Face-to-face interviews were conducted with 24 individuals representing 12 industry and government organizations. Quantitative data were analysed using social network analysis. Qualitative data were coded and patterns matched to test a pre-determined general theory using a method called theory-oriented process-tracing. Results revealed that technical policy decisions were framed by social, political, financial, strategic and operational considerations. Industry stakeholders had influence through formal pre-existing channels, yet specific gaps in stakeholder interaction were overcome by reactive alliances formed during the outbreak response but outside the established system. Overall, the crisis management system and response were seen as positive, and 75-100% of individuals interviewed were supportive of, had interest in and considered the outcome as good for the majority of policy decisions, yet only 46-75% of those interviewed considered that they had influence on these decisions. Training to increase awareness and knowledge of emergency animal diseases (EADs) and response systems will improve stakeholder participation in emergency disease management and preparedness for future EAD incursions.

Development and evaluation of a reverse transcription loop-mediated isothermal amplification assay for H3N8 equine influenza virus

Reverse transcription loop-mediated isothermal amplification (RT-LAMP) was applied to the detection of equine influenza virus (EIV). Because equine influenza is caused currently by EIV of the H3H8 subtype, the RT-LAMP primer set was designed to target the hemagglutinin gene of this subtype. The detection limit of the RT-LAMP assay was a virus dilution of 10(-5); which was 10(3) times more sensitive than the Espline Influenza A&B-N test and 10 times more sensitive than a reverse transcription polymerase chain reaction (RT-PCR) assay. The specificity of the RT-LAMP assay was examined by using several equine pathogens and nasal swabs collected from horses with fever in 2010 after EIV was eradicated in Japan. No cross-reactions were observed. Using 100 nasal swabs collected from horses with fever during an EIV outbreak in 2007, the RT-LAMP assay detected EIV in 52 samples, whereas the Espline test and the RT-PCR assay detected EIV in only 17 and 41 samples, respectively. These results indicate that the RT-LAMP assay is specific for EIV and more sensitive than the Espline test and the RT-PCR assay. Because it provides high sensitivity and ease of manipulation without the need for a thermal cycler or gel electrophoresis, the RT-LAMP assay should be applicable for laboratory diagnosis of EIV.

Phylogenetic and molecular characterization of equine H3N8 influenza viruses from Greece (2003 and 2007): evidence for reassortment between evolutionary lineages

BACKGROUND

For first time in Greece equine influenza virus infection was confirmed, by isolation and molecular analysis, as the cause of clinical respiratory disease among unvaccinated horses during 2003 and 2007 outbreaks.

METHODS

Equine influenza virus (EIV) H3N8 was isolated in MDCK cells from 30 nasal swabs from horses with acute respiratory disease, which were tested positive by Directigen Flu A. Isolation was confirmed by haemagglutination assay and RT-PCR assay of the M, HA and NA gene.

RESULTS

HA sequences of the Greek isolates appeared to be more closely related to viruses isolated in early 1990s in Europe. These results suggested that viruses with fewer changes than those on the main evolutionary lineage may continue to circulate. On the other hand, analysis of deduced NA amino acid sequences were more closely related to viruses isolated in outbreaks in Europe and Asia during 2003-2007. Phylogenetic analysis characterized the Greek 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 the neuraminidase (NA) protein sequence suggesting that reassortment might be a possible explanation.

CONCLUSION

Our findings suggest that the Greek strains represent an example of "frozen evolution" and probably reassortment between genetically distinct co-circulated strains. Therefore expanding current equine influenza surveillance efforts is a necessity.

Infectivity and pathogenicity of canine H3N8 influenza A virus in horses

Please cite this paper as: Yamanaka et al. (2010) Infectivity and pathogenicity of canine H3N8 influenza A virus in horses. Influenza and Other Respiratory Viruses 4(6), 345–351.

Background  Equine H3N8 influenza A viruses (EIVs) cause respiratory disease in horses and circulate among horses worldwide. In 2004, an outbreak of canine H3N8 influenza A virus (CIV) occurred among dogs in Florida and has spread among dogs in the United States (US). Genetic analyses revealed that this CIV is closely related to the recent EIVs. Although CIV‐infected dogs could be the source of H3N8 influenza A virus for horses, it remains unclear whether the CIV circulating in the United States still maintains its infectivity and/or pathogenicity in horses. To address this, we investigated the infectivity and pathogenicity of CIV in horses and the receptor binding specificity of CIV.

Materials and methods  Three horses were inoculated with A/canine/Colorado/30604/2006 (CO06, H3N8). Clinical signs and nasal swabs were recorded or collected every day. We also evaluated the virus binding to α2‐3‐linked 5‐N‐acetylneuraminic acid (NeuAcα2‐3Gal) and 5‐N‐glycolylneuraminic acid (NeuGcα2‐3Gal) receptor analogues.

Results  Although all the three horses inoculated with CO06 seroconverted, they showed only mild clinical signs and two of them showed no virus shedding. CO06 had reduced binding to NeuGcα2‐3Gal.

Discussion  Our results demonstrated that CO06 had reduced proliferation ability and pathogenicity in horses. As the recognition of NeuGcα2‐3Gal by EIV is known to be essential for binding to the equine respiratory system, the decreased binding of CO06 to NeuGcα2‐3Gal may be one of the important factors that reduces the proliferation ability and pathogenicity of CO06 in horses.

A Diagnostic Algorithm for Detection of Antibodies to Influenza A Viruses in Dogs in Italy (2006–2008)

Since 2004, there have been several reports of Influenza A virus (FLUAV) infection in dogs. Dogs have been infected with equine influenza H3N8, avian influenza H3N2 and H5N1, and the pandemic H1N1 virus. Because ofrecent avian and equine influenza outbreaksin Italy, the objectives of the present study were to estimate the level of exposure of Italian dogs to influenza A viruses and to assess a diagnostic algorithm for detection of FLUAV exposure in dogs. Sera collected from 6,858 dogs from 2006 to 2008 were screened in a competitive enzyme-linked immunosorbent assay (cELISA) for antibodies to the highly conserved influenza A nucleoprotein. Samples positive in the cELISA were confirmed by testing in hemagglutination inhibition (HI) and fluorescent antibody test (FAT). Two seropositive dogs had antibodies to H3 hemagglutinin proteins, consistent with exposure torecent canine and equine subtype H3N8 viruses. Using a Bayesian model, the sensitivity and specificity of the cELISA were estimated as 93.98% (probability intervals [PI]: 81.67–99.08%) and 98.71% (PI: 98.43–98.96%), respectively. After accounting for the imperfect sensitivity and specificity ofthe cELISA, the Bayesian posterior prevalence of FLUAV exposure among tested Italian dogs was 0.5% (PI: 0.1–1.4%). The study results indicate that screening with a cELISA for influenza A nucleoprotein antibody, followed by confirmatory testing with HI and/or FAT, is a highly sensitive and highly specific approach for diagnosing FLUAV exposure in dogs.

Increased Survivorship and Altered Cytokine Profile from Treatment of Influenza A H1N1-Infected Mice with Ekybion: A Drug Complex of Natural Extracts and Inorganic Compounds

Ekybion is a drug complex of 16 natural extracts and inorganic compounds designed to treat a variety of respiratory pathogens of bacterial and viral origin. It is licensed throughout Europe for the treatment of respiratory tract infections from equine parainfluenza type 3 and equine herpes virus type 1 in equine stables. The purpose of this paper was to test the efficacy of Ekybion on a well-developed animal model of influenza A infection and determine a mode of action. Experiments were performed with Balb/c mice infected with a lethal dose of influenza A/PR/8/34 H1N1 virus and treated with nebulized Ekybion every 8 h in a time-dependant or dose-dependant fashion. These experiments showed that mice treated prior to infection with Ekybion had a higher survival rates (~46%) compared with untreated animals (~0%). Paradoxically, these mice showed no significant difference in lung virus titer or weight loss. There was, however, a decrease in the level of GM-CSF, IL-6, and G-CSF cytokines in the lungs of Ekybion-treated, infected mice. It is possible that decreases in proinflammatory cytokines may have contributed to increased survivorship in Ekybion-treated influenza-infected mice.

Microevolution of canine influenza virus in shelters and its molecular epidemiology in the United States

Canine influenza virus (CIV) emerged around 2000 when an equine influenza virus (EIV) was transmitted to dogs in Florida. After 2003, the canine virus was carried by infected greyhounds to various parts of the United States and then became established in several large animal shelters, where it has continued to circulate. To better understand the evolution of CIV since its emergence, and particularly its microevolution in spatially restricted populations, we examined multiple gene segments of CIV from dogs resident in two large animal shelters in New York City during the period 2006 to 2009. In particular, we focused on viruses circulating in the two shelters in 2008 and 2009, which we found shared a common ancestor. While viruses in each shelter were generally monophyletic, we observed some gene flow between them. These shelter sequences were compared to earlier CIV isolates. The shelter viruses differed in 1 to 6 amino acids in each gene segment compared to viruses isolated in Florida between 2003 and 2005 and in Colorado in 2006 and 2008. A comparison of the sequences of equine and canine viruses revealed amino acid replacements that distinguished the viruses from the two hosts, but no clear evidence of positive selection indicative of host adaptation was detected, suggesting that any host range adaptation in CIV occurred early in the emergence of this virus or even before it transferred to dogs.

Equine and canine influenza: a review of current events

In the past decade, the pandemics of highly pathogenic avian influenza H5N1 and the novel H1N1 influenza have both illustrated the potential of influenza viruses to rapidly emerge and spread widely in animals and people. Since both of these viruses are zoonotic, these pandemics have been the driving force behind a renewed commitment by the medical and veterinary professions to practice One World, One Health for the control of infectious diseases. The discovery in 2004 that an equine origin H3N8 influenza virus was the cause of an extensive epidemic of respiratory disease in dogs in the USA came as a surprise; at that time dogs were thought to be refractory to infection with influenza viruses. In 2007, a second emerging canine influenza was confirmed in Korea, but this time the causal virus was an H3N2 avian influenza virus. This review focuses on recent events associated with equine and canine influenza viruses. While these viruses do not appear to be zoonotic, the close association between humans and dogs, and to a lesser extent horses, demands that we develop better surveillance and control strategies for emerging diseases in companion animals within the context of One World, One Health.

Comparison of two modern vaccines and previous influenza infection against challenge with an equine influenza virus from the Australian 2007 outbreak

During 2007, large outbreaks of equine influenza (EI) caused by Florida sublineage Clade 1 viruses affected horse populations in Japan and Australia. The likely protection that would be provided by two modern vaccines commercially available in the European Union (an ISCOM-based and a canarypox-based vaccine) at the time of the outbreaks was determined. Vaccinated ponies were challenged with a representative outbreak isolate (A/eq/Sydney/2888-8/07) and levels of protection were compared.A group of ponies infected 18 months previously with a phylogenetically-related isolate from 2003 (A/eq/South Africa/4/03) was also challenged with the 2007 outbreak virus. After experimental infection with A/eq/Sydney/2888-8/07, unvaccinated control ponies all showed clinical signs of infection together with virus shedding. Protection achieved by both vaccination or long-term immunity induced by previous exposure to equine influenza virus (EIV) was characterised by minor signs of disease and reduced virus shedding when compared with unvaccinated control ponies. The three different methods of virus titration in embryonated hens' eggs, EIV NP-ELISA and quantitative RT-PCR were used to monitor EIV shedding and results were compared. Though the majority of previously infected ponies had low antibody levels at the time of challenge, they demonstrated good clinical protection and limited virus shedding. In summary, we demonstrate that vaccination with current EIV vaccines would partially protect against infection with A/eq/Sydney/2888-8/07-like strains and would help to limit the spread of disease in our vaccinated horse population.

Genetic Analyses of an H3N8 Influenza Virus Isolate, Causative Strain of the Outbreak of Equine Influenza at the Kanazawa Racecourse in Japan in 2007

In August 2007, an outbreak of equine influenza occurred among vaccinated racehorses with Japanese commercial equine influenza vaccine at Kanazawa Racecourse in Ishikawa prefecture in Japan. Apparent symptoms were pyrexia (38.2-41.0 degrees C) and nasal discharge with or without coughing, although approximately half of the infected horses were subclinical. All horses had been shot with a vaccine that contained two inactivated H3N8 influenza virus strains [A/equine/La Plata/93 (La Plata/93) of American lineage and A/equine/Avesta/93 (Avesta/93) of European lineage] and an H7N7 strain (A/equine/Newmarket/1/77). Influenza virus, A/equine/Kanazawa/1/2007 (H3N8) (Kanazawa/07), was isolated from one of the nasal swab samples of diseased horses. Phylogenetic analysis indicated that Kanazawa/07 was classified into the American sublineage Florida. In addition, four amino acid substitutions were found in the antigenic sites B and E in the HA1 subunit protein of Kanazawa/07 in comparison with that of La Plata/93. Hemagglutination-inhibition (HI) test using 16 serum samples from recovering horses revealed that 1.4- to 8-fold difference in titers between Kanazawa/07 and either of the vaccine strains. The present findings suggest that Japanese commercial inactivated vaccine contributed to reducing the morbidity rate and manifestation of the clinical signs of horses infected with Kanazawa/07 that may be antigenically different from the vaccine strains.

Inhibition of influenza A H3N8 virus infections in mice by morpholino oligomers

New methods to combat influenza A virus (FLUAV) in humans and animals are needed. The H3N8 subtype virus was the cause of the pandemic of 1890 and has recently undergone cross-species transmission from horses to dogs in the USA. In 2007 H3N8 spread to Australia, a continent previously devoid of equine influenza. Here, we show that antisense-peptide-conjugated phosphorodiamidate morpholino oligomers (PPMOs), delivered by intranasal administration, are able to inhibit the replication of FLUAV A/Eq/Miami/1/63 (H3N8) in mice by over 95% compared to controls. Monitoring of body weight and immune cell infiltrates in the lungs of noninfected mice indicated that PPMO treatment was not toxic at a concentration shown to be effectively antiviral in vivo. In addition, we detected a naturally occurring mutation within the PPMO target site of a viral gene that may be the cause of resistance to one of the two antisense PPMO sequences tested. These data indicate that PPMOs targeting highly conserved regions of FLUAV are promising novel therapeutic candidates.

Genetic characterization of equine influenza viruses isolated in Italy between 1999 and 2005

During local respiratory disease outbreaks, occurring in 2003 and 2004 in horse training stables within race-tracks in Rome, and on a stud horse farm in Bari in 2005, four strains of equine influenza (EI) virus were isolated. All outbreaks occurred in flu-vaccinated horses. Here, we are reporting the results of the genetic characterization of these isolates, together with that of another EI virus strain isolated in 1999 from a dead foal presenting pulmonary lesions. Alignment and phylogenetic analyses were carried out using the haemagglutinin amino acid sequences. The Rome and Bari isolates were identified as members of the American lineage, closely related to other recent strains isolated in America as well as in Europe, including the latest recommended American lineage vaccine prototype A/eq/SouthAfrica/4/2003. In contrast, the Italian 1999 isolate was clustered within the European lineage. In Italy, the most recent outbreaks of EI have been caused by the currently circulating American-like strains, even in vaccinated populations, confirming that vaccines should contain an updated representative strain of this lineage. Presently, companies are still in the process of registering updated vaccines but no product is yet available on the market.