The potential impact of a single amino-acid substitution on the efficacy of equine influenza vaccines.

REASONS FOR PERFORMING STUDY: The protection induced by an equine influenza (EI) vaccine strain depends on its antigenic relatedness to the challenge virus. Although the World Organisation for Animal Health (OIE) recommend that both Florida sublineage clade 1 (Fc1) and clade 2 (Fc2) viruses should be included in EI vaccines, Japanese EI vaccines have not, thus far, been updated to include a Fc2 virus. OBJECTIVES: To evaluate the efficacy of antibodies raised against Japanese EI vaccine strains in the neutralisation of recent Fc2 viruses. STUDY DESIGN: Antigenic analysis. METHODS: Virus neutralisation tests were performed using antisera from experimentally infected horses and from horses that had received a primary course of the currently available vaccines. RESULTS: Antiserum raised against the Japanese EI vaccine strain, A/equine/La Plata/1993, exhibited poor cross-neutralising activity against the Fc2 viruses isolated recently in Ireland and the UK, which have the substitution of alanine to valine at position 144 in antigenic site A of the haemagglutinin gene. In contrast, the antiserum exhibited good cross-neutralising activity against the Fc2 viruses without the substitution. This finding was supported in experiments with antisera collected from vaccinated horses. CONCLUSIONS: This suggests that the efficacy of the Japanese EI vaccine for some of the recent Fc2 viruses is suboptimal and that vaccines should be updated in accordance with the OIE recommendations.

The impact of different equine influenza vaccine products and other factors on equine influenza antibody levels in Thoroughbred racehorses.

REASONS FOR PERFORMING STUDY: More knowledge of equine influenza (EI) vaccine usage in training yards and the factors that influence serological response to vaccination are required to determine evidence-based vaccination strategies. OBJECTIVES: The aim of this study was to ascertain the vaccination history of a population of Thoroughbred racehorses and identify factors that impacted on their antibody titres against EI. STUDY DESIGN: Observational field study. METHODS: The study population consisted of 102 vaccinated Thoroughbred horses in training on a single premises. The vaccination histories recorded in their official passports were analysed. Blood samples for serological testing were collected by the veterinary surgeon one month after booster vaccination with ProteqFlu-Te. Antibodies against EI were measured by single radial haemolysis (SRH). Multivariate statistical analysis was undertaken to determine the predictors of SRH antibody titres. RESULTS: There was a strong correlation between age and number of vaccine doses received. Over 70% of horses received their first vaccine dose between ages 6 and 12 months. On average, horses had received 6 vaccine doses and the mean interval between booster vaccinations was 7.7 months. The majority of horses (95%) received more than one influenza vaccine product while 32% had received 3 vaccine products. Significantly higher antibody levels were observed in females than males and there was a significant association between the number of vaccine products administered and antibody levels. In contrast, a negative association between number of vaccine doses and SRH antibody level was demonstrated. CONCLUSIONS: Important predictors of EI antibody titres in racehorses were sex, number of vaccine doses received and number of different vaccine products administered.

Comparison of primary vaccination regimes for equine influenza: working towards an evidence-based regime.

REASONS FOR PERFORMING STUDY: Vaccination is crucial to the control of equine influenza (EI). The study was conducted in an effort to lay the groundwork for achieving international harmonisation of regulatory requirements based on scientific evidence of performance of different vaccination regimes. OBJECTIVES: To evaluate the effectiveness of 3 different primary vaccination regimes: vaccination with the minimal intervals permitted by the racing authorities; vaccination in accordance with the manufacturer's instructions and vaccination with the longest intervals permitted by the racing authorities. STUDY DESIGN: Randomised, prospective clinical trial. METHODS: The 55 seronegative unvaccinated horses in this study were subdivided by age and randomly allocated one of the 3 vaccination regimes. All groups were sampled each time a group was vaccinated and 3-5 weeks post vaccination. Horses were vaccinated with a subunit immune stimulating complex-based vaccine (Equip FT). Antibodies against EI were measured by single radial haemolysis. RESULTS: Lengthening the vaccination intervals increased the immunity gaps between first (V1) and second (V2) doses, and V2 and third dose (V3) but did not inhibit the response to V2 and V3. The response to V2 and V3 was similar irrespective of the regime. Poor responders to V1 were identified in all age groups included in this study but the greatest number of poor responders was among the yearlings. The 2- and 3-year-old horses responded better to vaccination than the weanlings or yearlings. CONCLUSIONS: Longer vaccination intervals permitted by racing authorities increase the periods of susceptibility to EI but they may facilitate strategic vaccination prior to times of increased risk of exposure to virus. The study provides the type of evidence-based data necessary to commence meaningful discussion of international harmonisation of EI vaccination requirements.

The molecular epidemiology of equine influenza in Ireland from 2007-2010 and its international significance.

REASONS FOR PERFORMING THE STUDY: Antigenic and genetic drift of equine influenza (EI) virus is monitored annually by the Expert Surveillance Panel (ESP), which make recommendations on the need to update vaccines. Surveillance programmes are essential for this process to operate effectively and to decrease the risk of disease spread through the international movement of subclinically infected vaccinated horses. Not only is surveillance necessary to inform vaccine companies which strains are in circulation, but it serves as an early warning system for horse owners, trainers and veterinary clinicians, facilitating the implementation of appropriate prophylactic and control measures. OBJECTIVE: To summarise the genetic analysis of EI viruses detected in Ireland from June 2007 to January 2010. METHODS: The HA1 gene of 18 viruses was sequenced and phylogenetic analysis undertaken. RESULTS: All viruses belonged to the Florida sublineage of the American lineage. Clade 2 viruses predominated up to 2009. The viruses identified on 4 premises in 2007 displayed 100% nucleotide identity to A/eq/Richmond/1/07, the current clade 2 prototype. The first clade 1 virus was identified in November 2009 and, thereafter, clade 1 viruses were responsible for all the outbreaks identified. The Irish clade 1 viruses differ from the clade 1 virus responsible for the EI outbreaks in Japan and Australia in 2007. No virus of the Eurasian lineage was isolated during this surveillance period. CONCLUSIONS: In 2010 the ESP recommended that the vaccines should not include a H7N7 virus or a H3N8 virus of the Eurasian lineage but that they should contain both a clade 1 and clade 2 virus of the Florida sublineage. The surveillance data presented here support these recommendations and indicate that they are epidemiologically relevant. POTENTIAL RELEVANCE: These data also serve as a scientific basis for investigating the source of epizootics and outbreaks both nationally and internationally.

Management and environmental factors involved in equine influenza outbreaks in Ireland 2007-2010.

REASONS FOR PERFORMING STUDY: Outbreaks of equine influenza (EI) in endemic populations continue to cause economic loss despite widespread vaccination. HYPOTHESIS: To identify the key management and environmental factors that determine the risk of horses contracting EI in an endemic country and to identify control strategies. METHODS: Real time-polymerase chain reaction (RT-PCR), virus isolation and haemagglutination inhibition were carried out on nasopharyngeal swabs and clotted blood samples collected from horses and ponies showing signs of respiratory disease. On premises where a diagnosis of EI was confirmed, the attending veterinary surgeon was asked to participate in an epidemiological investigation. RESULTS: Between June 2007 and January 2010, EI outbreaks were diagnosed on 28 premises located in 13 of the 32 counties of Ireland. Veterinary advice was sought on average more than 5 days after the first clinical signs were observed. The majority of diagnoses were made by RT-PCR. Data from 404 horses on 16 premises were used in the epidemiological analysis. In 15 premises, EI was identified following movement of horses. Housing type, teaser stallions or fomites/personnel contributed to virus spread. Vaccination status, number of years vaccination, time since last vaccination and age influenced disease expression. Isolation and vaccination were effective control measures on the premises where they were implemented. CONCLUSIONS: Preventative measures include: isolation, clinical monitoring, serological testing and vaccination of new arrivals, booster vaccination of horses at 6 monthly intervals, maintenance of effective boundaries between equine premises and avoidance of stabling in single air spaces. Control measures include: prompt isolation of suspected cases, rapid diagnosis by RT-PCR, booster vaccination of cohorts and implementation of biosecurity measures to avoid transmission by fomites and personnel. POTENTIAL RELEVANCE: Implementation of these preventative and control measures should reduce the economic losses associated with outbreaks of EI.

Diagnosis of equine infectious anaemia during the 2006 outbreak in Ireland.

In 2006 there was an outbreak of equine infectious anaemia (EIA) in Ireland. This paper describes the use of the diagnosis of clinical and subclinical cases of the disease. In acute cases the ELISAs and the immunoblot were more sensitive than the AGID. In one mare, fluctuating antibody levels were observed in all the serological assays before it seroconverted by AGID. Viral RNA and DNA were detected by RT-PCR and PCR in all the tissues from the infected animals examined postmortem. The PCR detected viral DNA in plasma regardless of the stage of the disease. In contrast, the RT-PCR detected RNA in only 52 per cent of the seropositive animals tested and appeared to be most sensitive for the detection of virus early in infection. Both PCR and RT-PCR demonstrated potential to detect acutely infected horses earlier than some of the official tests. The serological data suggest that the usual incubation/seroconversion period for this strain of the virus was approximately 37 days but may be more than 60 days in a few cases.