Equine Influenza Outbreak Research Articles

Antigenic and molecular characterisation of viruses responsible for outbreaks of equine influenza (2021–2024)

Antigenic and molecular characterisation of viruses responsible for outbreaks of equine influenza (2021–2024)

Horse populations are severely underestimated in a region at risk of Hendra virus spillover.

To identify the size and distribution of the horse population in the Northern Rivers Region of NSW, including changes from 2007 to 2021, to better understand populations at risk of Hendra virus transmission. Census data from the 2007 Equine Influenza (EI) outbreak were compared with data collected annually by New South Wales Local Land Services (LLS) (2011-2021), and with field observations via road line transects (2021). The horse populations reported to LLS in 2011 (3000 horses; 0.77 horses/km2) was 145% larger than that reported during the EI outbreak in 2007 (1225 horses; 0.32 horses/km2). This was inconsistent with the 6% increase in horses recorded from 2011 to 2020 within the longitudinal LLS dataset. Linear modelling suggested the true horse population of this region in 2007 was at least double that reported at the time. Distance sampling in 2021 estimated the region's population at 10,185 horses (3.89 per km2; 95% CI = 4854-21,372). Field sampling and modelling identified higher horse densities in rural cropland, with the percentage of conservation land, modified grazing, and rural residential land identified as the best predictors of horse densities. Data from the 2007 EI outbreak no longer correlates to the current horse population in size or distribution and was likely not a true representation at the time. Current LLS data also likely underestimates horse populations. Ongoing efforts to further quantify and map horse populations in Australia are important for estimating and managing the risk of equine zoonoses.

Equine influenza outbreak in Eastern of Algeria in 2021: The first introduction of Florida Clade 1 to Maghreb area

We have performed an equine influenza (EI) serological study of the equine population in Algeria by testing 298 serum samples collected between February and August 2021 from 5 provinces. The results were obtained performing an NP-ELISA. Our results revealed that 49.3% (147/298) samples positive for antibodies to EI (H3N8). During this study and after a gap of one decade an outbreak of EI was reported in Algeria in the first week of March 2021. The disease was confirmed by virus detection from the nasal swabs (n = 39) by qRT-PCR and by identifying 5 EI seroconversion. The virus sequences were identified as H3N8 by sequencing the haemagglutinin (HA) and neuraminidase (NA) genes. Alignment of HA1 amino acid sequence confirmed that viruses belong to Clade 1 of the Florida sublineage in the American lineage. This study indicate the first detection of FC1 strain of EIV in Maghreb area.

Evaluation of a novel real-time polymerase chain reaction assay for identifying H3 equine influenza virus in Kazakhstan.

Equine influenza (EI) is a highly contagious disease that causes fever and upper respiratory tract inflammation. It is caused by influenza virus A, belonging to the Orthomyxoviridae family, with subtypes H3N8 and H7N7. This study presents data on the development of a real-time polymerase chain reaction (RT-PCR) assay using TaqMan probes to detect the H3 subtype of EI virus (EIV). The evaluation of the developed RT-PCR assay involved five strains of EIV as positive controls and ten nasopharyngeal swab samples collected from horses. RNA was isolated using the GeneJet Viral DNA and RNA Purification Kit, and primers and probes were designed using the Integrated DNA Technology PrimerQuest Tool. The assay was optimized by investigating the annealing temperature, primer and probes concentrations, sensitivity, and specificity. Sequencing was performed using the Thermo Fisher 3130 Genetic Analyzer, and the evolutionary history was inferred using the Neighbor-Joining method. The designed primers and probes, targeting the H3 gene, were found to be specific to the EIV. The RT-PCR assay was capable of detecting as low as 50 femtogram (f) or 3 × 103 copies of genomic RNA. No cross-reactions were observed with other respiratory viral and bacterial pathogens, indicating the high specificity of the assay. To evaluate its effectiveness, ten nasopharyngeal swab samples collected from farms in North Kazakhstan regions during disease monitoring were analyzed. The accuracy of the analysis was confirmed by comparing the results with those obtained from a commercial RT-PCR assay for EI identification. The developed RT-PCR assay exhibited high sensitivity and specificity for detecting the EIV. The results demonstrate that the developed RT-PCR assay is suitable for diagnosing EI. This simple, highly sensitive, and specific assay for detecting H3 EIV can be a reliable tool for diagnosing and surveilling EI. Implementing this RT-PCR assay in veterinary practice will enhance and expedite the timely response to potential outbreaks of EI, thus positively impacting the overall epizootic well-being of EI in Kazakhstan.

Seroprevalence of Equine Influenza and Its Associated Risk Factors in Northwest Nigeria.

Equine influenza (EI) is a fast-spreading respiratory disease of equids caused by equine influenza A virus (EIV), often resulting in high morbidity and a huge economic impact on the equine industry globally. In this cross-sectional study to determine the seroprevalence of EI and its associated risk factors, sera from 830 horses bled on a single occasion in Northwest Nigeria between October 2019 and January 2020 were screened for antibodies to A/equine/Richmond/1/2007 (H3N8) using the single radial haemolysis (SRH) assay. Antibodies were detected in 71.3% (592/830, 95% CI: 68-74%) of horses (SRH area ≥ 0.5 mm2). Although there were statistically significant univariable associations between seropositivity and age, sex, breed, purpose and coat colour, only age remained significant when included with each of the other variables in bivariable analyses. There was a clear trend for increasing odds of seropositivity with increasing age: OR 1.6, 95% CI: 1.05-2.40 (p = 0.03) for 5-14-year-olds and OR 8.13, 95% CI: 2.75-24.1 (p < 0.001) for ≥15-year-olds compared to horses <5 years old. The mean SRH value was 78.2 mm2 (median = 88 mm2, interquartile range = 0-121 mm2) with only 9% of the horses having an SRH value > 150 mm2, considered sufficient to protect against clinical disease and virus shedding. Comparative screening of a subset of the horses (n = 118) with a 2019 H3N8 virus (A/equine/Worcestershire/2019) revealed a significantly greater seropositivity (p = 0.0001) than A/equine/Richmond/1/2007 consistent with exposure of the population during a widespread outbreak of EI in the region in 2019. In conclusion, there was an insufficient level of protection against EI in the region and introduction of a vaccination programme with vaccines containing recently circulating virus is recommended to mitigate against further outbreaks of EI in Nigeria.

Serological and molecular investigation of canine influenza virus in Plateau State, Nigeria

Canine influenza is a highly contagious respiratory infection of dogs caused by the Influenza A Virus (IAV), characterized by cough, sneeze, nasal secretions, and inappetence. Infections can be mild, severe or fatal. Aquatic birds constitute a natural reservoir for IAV, which is transmitted to terrestrial birds, including poultry. IAV has also emerged in other mammalian species, including humans, swine, horses, and dogs. IAV epidemics in dogs are a recent development. Commonly detected Canine Influenza Virus (CIV) strains are A/H3N2 and A/H3N8 from avian and equine influenza, respectively. Nigeria’s agro-ecology witnessed widespread circulation of avian influenza since 2006, and recent outbreaks of equine influenza in 2018/2019 raise the possibility of inter-species transmission to dogs. To investigate canine Influenza in Plateau State, we collected 113 nasal swabs and 270 sera samples from dogs in clinics, live dog markets, and during dog vaccination campaigns. After extracting nucleic acid with the Qiagen kit, RT-PCR analysed swabs for the Influenza A matrix gene. Sera samples were screened by Enzyme-Linked Immunosorbent Assay before subtyping a cross-section for H3 antibody by Hemagglutination Inhibition. No matrix gene was amplified from extracted nucleic acid from the nasal swabs. Though few sera were reactive to influenza A nucleoprotein, none was positive for influenza A/H3. The H3N8 strain of equine influenza virus first caused an epidemic in dogs in 1999 in the United States. Subsequently, avian-origin H3N2 CIV emerged in dogs in China and South Korea in 2005. Past CIV epidemics arose from a single cross-species transmission of H3N8 subtype from a mammalian intermediate host and the H3N2 subtype from an avian reservoir. Even though this limited investigation did not detect CIV in Plateau State, the potential remains because of the persistent circulation of avian, swine, and equine Influenza in Nigeria, which requires more extensive virological and serological surveillance.

Disease progression, pathologic, and virologic findings of an equine influenza outbreak in rescue donkeys.

Equine influenza virus is a common cause of respiratory disease in equids. Few reports describe clinical presentation and disease progression in donkeys. Describe the clinical and diagnostic findings, outcome, and pathologic lesions associated with influenza pneumonia in donkeys. Thirteen unvaccinated donkeys ranging from 1week to 12 years of age and sharing clinical signs and exposure history. Retrospective case series. Medical records from June to July 2020 at the Colorado State Veterinary Teaching Hospital and collaborating referring veterinary practices were reviewed. The diagnosis was confirmed by molecular testing, virus isolation, and partial genetic and phylogenetic analysis of the virus. Survival in donkeys <1 year old was 16.6% (1/6) whereas survival in animals >1 year of age was 85.7% (6/7). Hemagglutinin gene sequencing and phylogenetic analysis confirmed a contemporary clade 1 Florida sublineage H3 virus as the causative agent. Clinical signs of equine influenza virus infection in donkeys are similar to those observed in horses. Prognosis for survival generally is good, but deaths have been observed especially in foals born to seronegative dams. This finding emphasizes the importance of prenatal vaccination protocols in all equids, including donkeys.

Assessment of Humoral and Long-Term Cell-Mediated Immune Responses to Recombinant Canarypox-Vectored Equine Influenza Virus Vaccination in Horses Using Conventional and Accelerated Regimens Respectively.

During Australia’s first and only outbreak of equine influenza (EI), which was restricted to two northeastern states, horses were strategically vaccinated with a recombinant canarypox-vectored vaccine (rCP-EIV; ProteqFlu™, Merial P/L). The vaccine encoded for haemagglutinin (HA) belonging to two equine influenza viruses (EIVs), including an American and Eurasian lineage subtype that predated the EIV responsible for the outbreak (A/equine/Sydney/07). Racehorses in Victoria (a southern state that remained free of EI) were vaccinated prophylactically. Although the vaccine encoded for (HA) belonged to two EIVs of distinct strains of the field virus, clinical protection was reported in vaccinated horses. Our aim is to assess the extent of humoral immunity in one group of vaccinated horses and interferon-gamma ((EIV)-IFN-γ)) production in the peripheral blood mononuclear cells (PBMCs) of a second population of vaccinated horses. Twelve racehorses at work were monitored for haemagglutination inhibition antibodies to three antigenically distinct equine influenza viruses (EIVs) The EIV antigens included two H3N8 subtypes: A/equine/Sydney/07) A/equine/Newmarket/95 (a European lineage strain) and an H7N7 subtype (A/equine/Prague1956). Cell-mediated immune responses of: seven racehorses following an accelerated vaccination schedule, two horses vaccinated using a conventional regimen, and six unvaccinated horses were evaluated by determining (EIV)-IFN-γ levels. Antibody responses following vaccination with ProteqFlu™ were cross-reactive in nature, with responses to both H3N8 EIV strains. Although (EIV)IFN-γ was clearly detected following the in vitro re-stimulation of PBMC, there was no significant difference between the different groups of horses. Results of this study support reports of clinical protection of Australian horses following vaccination with Proteq-Flu™ with objective evidence of humoral cross-reactivity to the outbreak viral strain A/equine/Sydney/07.

Risk factors for infection with equine influenza virus in donkeys (Equus asinus) in Senegal

In recent years, outbreaks of equine influenza are reported in several countries in the world particulary in Africa. This study is designed to assess the potential risk factors associated with equine influenza virus infection in donkeys in Senegal. The study consists in comparing, depending on the exposure to risk factors, a batch of donkeys infected with the equine influenza virus to another batch of donkeys not infected with the virus during the epizootic of March 2019 which affected the department of Foundiougne. The study reveals that the spread of the equine influenza virus in Foundiougne is associated with the lack of access to veterinary care and infected donkeys were exposed in a ratio of 2 times (95% CI: 1.38; 4.71) more than donkeys unharmed. The wandering of donkeys is also linked with the disease. The indicator reflecting the strength of the relationship, the Odds Ratio is 2.06 (95% CI: 1.10; 3.87). However, the results indicate that attendance at rural markets (Odds Ratio = 0.90; 95% CI: 0.44; 1.82), young age (Odds Ratio = 0.90; 95% CI: 0.52, 1.55) and female sex (Odds Ratio = 0.97; 95% CI: 0.57; 1, 66) do not appear to be related to the spread of the disease. At present, in Senegal, control focused on sensitizing and informing donkey owners on the sanitary management and rational use of donkeys is essential for their well-being.

Association of Equine Herpesvirus 5 with Mild Respiratory Disease in a Survey of EHV1, -2, -4 and -5 in 407 Australian Horses.

Equine herpesviruses (EHVs) are common respiratory pathogens in horses; whilst the alphaherpesviruses are better understood, the clinical importance of the gammaherpesviruses remains undetermined. This study aimed to determine the prevalence of, and any association between, equine respiratory herpesviruses EHV1, -2, -4 and -5 infection in horses with and without clinical signs of respiratory disease. Nasal swabs were collected from 407 horses in Victoria and included clinically normal horses that had been screened for regulatory purposes. Samples were collected from horses during Australia's equine influenza outbreak in 2007; however, horses in Victoria required testing for proof of freedom from EIV. All horses tested in Victoria were negative for EIV, hence archived swabs were available to screen for other pathogens such as EHVs. Quantitative PCR techniques were used to detect EHVs. Of the 407 horses sampled, 249 (61%) were clinically normal, 120 (29%) presented with clinical signs consistent with mild respiratory disease and 38 (9%) horses had an unknown clinical history. Of the three horses detected shedding EHV1, and the five shedding EHV4, only one was noted to have clinical signs referable to respiratory disease. The proportion of EHV5-infected horses in the diseased group (85/120, 70.8%) was significantly greater than those not showing signs of disease (137/249, 55%). The odds of EHV5-positive horses demonstrating clinical signs of respiratory disease were twice that of EHV5-negative horses (OR 1.98, 95% CI 1.25 to 3.16). No quantitative difference between mean loads of EHV shedding between diseased and non-diseased horses was detected. The clinical significance of respiratory gammaherpesvirus infections in horses remains to be determined; however, this survey adds to the mounting body of evidence associating EHV5 with equine respiratory disease.

Outbreaks of Equine Influenza in Italy during 2019

Outbreaks of Equine Influenza in Italy during 2019

Equine influenza outbreaks in Kazakhstan in 2020

Equine influenza outbreaks in Kazakhstan in 2020

Molecular characterisation of viruses responsible for outbreaks of equine influenza (2019‐2020)

Molecular characterisation of viruses responsible for outbreaks of equine influenza (2019‐2020)

Equine Influenza Virus and Vaccines.

Equine influenza virus (EIV) is a constantly evolving viral pathogen that is responsible for yearly outbreaks of respiratory disease in horses termed equine influenza (EI). There is currently no evidence of circulation of the original H7N7 strain of EIV worldwide; however, the EIV H3N8 strain, which was first isolated in the early 1960s, remains a major threat to most of the world’s horse populations. It can also infect dogs. The ability of EIV to constantly accumulate mutations in its antibody-binding sites enables it to evade host protective immunity, making it a successful viral pathogen. Clinical and virological protection against EIV is achieved by stimulation of strong cellular and humoral immunity in vaccinated horses. However, despite EI vaccine updates over the years, EIV remains relevant, because the protective effects of vaccines decay and permit subclinical infections that facilitate transmission into susceptible populations. In this review, we describe how the evolution of EIV drives repeated EI outbreaks even in horse populations with supposedly high vaccination coverage. Next, we discuss the approaches employed to develop efficacious EI vaccines for commercial use and the existing system for recommendations on updating vaccines based on available clinical and virological data to improve protective immunity in vaccinated horse populations. Understanding how EIV biology can be better harnessed to improve EI vaccines is central to controlling EI.

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.

Equine influenza vaccination in the UK: Current practices may leave horses with suboptimal immunity.

BackgroundVaccination is integral to preventive healthcare. Despite numerous guidelines on equine vaccination, evidence of current vaccination practices is lacking.ObjectivesTo describe current vaccination practices advised by vets treating horses in the United Kingdom (UK) and compare practices with manufacturer datasheets and current guidelines.Study designCross‐sectional survey.MethodsAn online questionnaire was distributed using email addresses acquired through professional registration listings and social media, targeting vets who treat horses in the UK. The questionnaire collected demographic data and information regarding vaccination practices and vaccine hesitancy. Descriptive statistical analysis was performed.ResultsQuestionnaires were completed by 304 UK vets working with horses used for leisure (97.4%, n = 296/304), competition (86.2%, n = 262/304), stud‐work (47.7%, n = 145/304) and racing (40.5%, n = 123/304). Variation was identified in vaccine protocols for competition and noncompetition horses. Fifty‐seven per cent (n = 170/298) of respondents reported variation in advised ‘booster’ frequency; most commonly (n = 118) advising a 6‐monthly vaccination in competition horses and annual vaccination in noncompetition horses. Most common vaccination guidelines volunteered were British Horseracing Authority (68.8%, n = 172/250) and Federation Equestre Internationale (66.4%, n = 166/250). Most vaccination practices were not consistent with datasheet guidance. Only 7.7% (n = 23/300) of respondents complied with datasheet timeframes between the second and third vaccination. Adverse events following vaccination in the previous year were encountered by 66% (n = 199/304) of respondents, representing 2760 adverse events; but only 526 (19.1%) cases were reported to the Veterinary Medicines Directorate. Most common reactions were transient, including stiffness (931), localised swelling (835), lethargy (559) and pyrexia (355). 86.4% respondents reported vaccine hesitancy from horse owners, most commonly due to perception of over‐vaccination, cost and concern regarding adverse events.Main limitationsPotential selection, respondent and recall bias. The recent Equine Influenza (EI) and Equine Herpes Virus (EHV) outbreaks in the UK may have altered responses.ConclusionsCurrent equine vaccination practices, although complying with competition rules, are mostly noncompliant with datasheet guidelines, potentially risking suboptimal immunity.

Fatal multiple outbreaks of equine influenza H3N8 in Nigeria, 2019: The first introduction of Florida clade 1 to West Africa

In December 2018, suspected outbreaks of equine influenza (EI) were observed in donkeys in Sokoto State, in the extreme northwest of Nigeria bordering the Republic of the Niger. Equine influenza virus (EIV) subtype H3N8 was the etiologic agent identified in the outbreaks using real-time RT-qPCR and sequencing of both the partial haemagglutinin (HA) gene and the complete genome. Since then the H3N8 virus spread to 7 of the 19 northern states of Nigeria, where it affected both donkeys and horses. Phylogenetic analysis of the partial and complete HA gene revealed the closest nucleotide similarity (99.7%) with EIVs belonging to the Florida clade 1 (Fc-1) of the American lineage isolated in 2018 from Argentina and Chile. In total, 80 amino acid substitutions were observed in the viral proteins when compared to the OIE-recommended Fc-1 vaccine strains. The HA and neuraminidase proteins respectively had 13 and 16 amino acid substitutions. This study represents the first reported outbreak of EI caused by an Fc-1 virus in Nigeria and in the West Africa sub-region. Based on this report, extensive disease surveillance in equids is required to establish the circulating lineages and design an effective control strategy to protect the considerable population of horses and donkeys in the country.

A Focus on Mental Health While Social Distancing

Amid the evolving situation of COVID-19, we must take the time to address our mental health. No N95 face mask or hand sanitizer can prevent the constant worry and loneliness that is resulting from this pandemic. Data from Australia's first equine influenza outbreak showed that “34% [of quarantined respondents] report[ed] high psychological distress (K10 &gt; 22), compared to levels of around 12% in the Australian general population” (Taylor et al., 2008). Since isolation has correlated with psychological distress in past outbreak studies, many psychologists worry that long term social distancing due to coronavirus can lead to psychological problems in society like depression, aggression, or even higher suicide rates. At a time like this, mental health should be of major importance.

Annual booster vaccination and the risk of equine influenza to Thoroughbred racehorses

Equine influenza (EI) outbreaks occurred among horses on four racing yards (two National Hunt, one Flat, one mixed National Hunt racing/breeding yard) in Ireland within a 4-week period. To carry out a detailed analysis of racing yards affected in order to identify the source of infection and monitor virus spread among a vaccinated population. Observational field study. Epidemiological and vaccination data along with repeat clinical samples were collected from 118 horses on four premises. Failure to implement appropriate biosecurity measures following the introduction of new arrivals and the return of horses from equestrian events contributed to disease spread as did the movement of horses within premises. Mixing of racing and non-racing populations with inadequate vaccination histories also facilitated virus transmission. The index case(s) on all premises was vaccinated in accordance with the Turf Club rules. Vaccine breakdown was observed across all products in 27/80 horses (33.8%) with an up-to-date vaccination record. Eighteen of the 27 (66.7%) horses had not received a booster vaccination within the previous 6months and 10 (37%) horses were due annual booster vaccination at the time of developing clinical signs. The interpretation of laboratory results followed a delay in veterinary intervention. Annual booster vaccination should not be relied on as the sole preventative measure against EI. The findings of this study suggest that increasing the frequency of booster vaccinations may be beneficial particularly in young horses and that synchronised scheduling of vaccination regimes across racing yards may contribute to high-risk periods for EI virus (EIV) transmission.

Epidemiological and virological findings during an outbreak of equine influenza in Uruguay in 2018.

Equine influenza is one of the major respiratory infectious diseases in horses. In 2018, equine influenza virus (EIV) was confirmed as the cause of outbreaks of respiratory disease in horses in Chile and Argentina. In the same year, for the first time in Uruguay, EIV infection was confirmed by isolation and molecular analysis to be the cause of respiratory disease among hundreds of clinically affected thoroughbred horses in training and racing facilities. The virus was detected in nasopharyngeal swabs by a pan-reactive influenza type A realtime reverse transcription polymerase chain reaction (rRT-PCR). The partial nucleotide sequence of the haemagglutinin 1 (HA1 ) gene (994 base pairs) was determined and analysed phylogenetically using MEGA X software. Amino acid sequence alignments were constructed, and serum samples were tested by haemagglutination inhibition and single radial haemolysis. The diagnosis of EIV was confirmed by rRT-PCR, virus isolation and serological testing. The phylogenetic analysis of the partial HA1 gene sequence of the isolated virus indicated that it belongs to clade 1 of the Florida sub-lineage of the American lineage and is closely related to viruses isolated in the recent past. Study of the HA1 region (331 amino acids) of the virus identified in horses in racing facilities in Uruguay displayed the highest amino acid sequence identity with viruses detected in Argentina, Chile and the United Kingdom in 2018. The surveillance data reported illustrate the international spread of EIVs and support the recommendation of the World Organisation for Animal Health (OIE) Expert Surveillance Panel to include viruses of the Florida sub-lineage in vaccines.