Equine Influenza Outbreak Research Articles

Accelerated vaccination schedule provides protective levels of antibody and complete herd immunity to equine influenza

During the 2007 Australian equine influenza (EI) outbreak, an accelerated primary course 14 day intervaccination schedule was proposed, but not widely implemented. Expert opinion was divided as to the efficacy of such a schedule given the lack of published data. This study determined the level and duration of humoral immunity following administration of a recombinant canarypox-vectored vaccine (ALVAC-EIV) with a primary intervaccination interval of 14 days and booster at 105 days. To examine whether protective levels of immunity of adequate duration were achieved following a primary course reduced from a minimum interval of 28 to 14 days. Antibody responses to 2 H3N8 American lineage virus strains (including A/equine/Sydney/6085/2007) were assessed and compared to previous challenge studies using ALVAC-EIV at conventional intervaccination intervals. Fourteen Thoroughbred horses and 2 ponies from a rural racehorse training property in Victoria, Australia, were vaccinated with ALVAC-EIV on Days 0, 14 and 105. Serial blood samples were collected over the next 32 weeks and tested with haemagglutination inhibition and single radial haemolysis (SRH) in full assays to evaluate the serological response. All horses and ponies responded to the accelerated ALVAC-EIV vaccination schedule. Mean SRH antibodies remained above those consistent with clinical protection for the duration of the study period. All vaccinates demonstrated high SRH antibodies 14 days following V2, thereby achieving 100% herd immunity to homologous viral challenge. An accelerated vaccination schedule conferred long-lasting protective antibody levels despite a >50% reduction in the recommended V1-V2 interval. High levels of rapidly acquired herd immunity are critical in containing an outbreak of such a highly contagious pathogen as EIV. In a strategic vaccination programme, it is important that horses remain protected for sufficient time to allow control programmes to succeed. An accelerated 14 day primary course intervaccination interval and booster at 105 days achieves both of these objectives.

Case-control study on cluster detection of equine influenza in China

This study investigated the distribution patterns of reported equine influenza (EI) cases in China. Geographical risk pattern analysis of a retrospective case-control study was assessed using geographical information sciences and the likelihood ratio test. The analysis showed that: (1) Equine production in China accounts for 15% of the worldwide total, among which, the highest densities were identified in Yunnan, Gansu, Hebei, Liaoning and Jiling administrative regions. Qinghai, Xizang and most southern administrative regions had relatively low densities. (2) Retrospective studies revealed three major EI epidemics across China pre-2000, which were mainly distributed in northwestern and northeastern regions. (3) EI cases were also reported in China after 2000, mainly in the Xingjiang administrative region and neighboring regions. Geographical risk pattern analysis suggested these reported EI cases were significantly spatial related in 95% confidence interval (CI), with an R -value of 0.3415, standard Z -value of 5.7588, a higher critical value compared with the theoretic random distribution. (4) Likelihood ratio testing of the Bernoulli-based case-control study for pre-2000 cases showed that cases positioned at site (6960036, 4432260) ( P R =1165880 M, RR =9.11) were most likely clustered, as were cases at site (9768346, 5338305) ( P R =1174519 M, RR =6.69). From a risk management perspective, these two regions should be the focus of active surveillance. (5) Likelihood ratio testing of the Bernoulli-based case-control study for the EI cases reported after 2000 showed that cases positioned at (6460039.00, 4277548.50) ( P R =7487976.06 M, RR =273.94) and nearby locations were most likely clustered. This indicated the existence of risk factors associated with EI infestation in these regions, and active surveillances should therefore be conducted. In this study, case-control cluster detection of EI occurrence indicated that northwestern China is currently the main region at risk of EI outbreak. Timely implementation of active surveillance programs and enhanced monitoring of equine movement should be carried out.

The Influence of Meteorology on the Spread of Influenza: Survival Analysis of an Equine Influenza (A/H3N8) Outbreak

The influences of relative humidity and ambient temperature on the transmission of influenza A viruses have recently been established under controlled laboratory conditions. The interplay of meteorological factors during an actual influenza epidemic is less clear, and research into the contribution of wind to epidemic spread is scarce. By applying geostatistics and survival analysis to data from a large outbreak of equine influenza (A/H3N8), we quantified the association between hazard of infection and air temperature, relative humidity, rainfall, and wind velocity, whilst controlling for premises-level covariates. The pattern of disease spread in space and time was described using extraction mapping and instantaneous hazard curves. Meteorological conditions at each premises location were estimated by kriging daily meteorological data and analysed as time-lagged time-varying predictors using generalised Cox regression. Meteorological covariates time-lagged by three days were strongly associated with hazard of influenza infection, corresponding closely with the incubation period of equine influenza. Hazard of equine influenza infection was higher when relative humidity was <60% and lowest on days when daily maximum air temperature was 20–25°C. Wind speeds >30 km hour−1 from the direction of nearby infected premises were associated with increased hazard of infection. Through combining detailed influenza outbreak and meteorological data, we provide empirical evidence for the underlying environmental mechanisms that influenced the local spread of an outbreak of influenza A. Our analysis supports, and extends, the findings of studies into influenza A transmission conducted under laboratory conditions. The relationships described are of direct importance for managing disease risk during influenza outbreaks in horses, and more generally, advance our understanding of the transmission of influenza A viruses under field conditions.

Equine Influenza: Prevention and Control

Equine influenza (EI) is a highly contagious selflimiting respiratory disease in horses that is caused by equine influenza virus (EIV) infection. EIV is presented by horses worldwide and has a huge financial impact on the horse industry in many countries. Although an outbreak of EI can be controlled by prior immunization by using vaccination, the efficacy of the vaccine is influenced by antigenic differences between epidemic strains and vaccine strains. Thus, to keep the vaccine effective, the vaccine strains should be reviewed periodically on the basis of global surveillance, such as the epidemiological report issued annually in the bulletin of the World Organization for Animal Health. Once an outbreak occurs, sanitary management, including the restriction of horse movement, should be conducted to eliminate the source of the causative virus and protect susceptible horses. The rapid identification of EIV in respiratory tract secretions enables the prompt administration of sanitary management. Although commercially available rapid antigen detection tests should be improved in terms of sensitivity, one of the tests (ESPLINE Flu A+B) worked as a convenient method for the rapid diagnosis and screening of a number of horses for EI during the 2007 outbreak in Japan, in addition to laboratory tests such as virus isolation. A more sensitive test must be developed that can be performed easily without special equipment or technical expertise.

Adding the spatial dimension to the social network analysis of an epidemic: Investigation of the 2007 outbreak of equine influenza in Australia

Equine influenza is a highly contagious and widespread viral respiratory disease of horses and other equid species, characterised by fever and a harsh dry cough. In 2007, in the first reported outbreak in Australia, the virus spread through the horse populations of two states within 4 months. Most of the geographic spread occurred within the first 10 days and was associated with the movement of infected horses prior to the implementation of movement controls. This study applies social network analysis to describe spread of equine influenza between horse premises infected in the early outbreak period, identifying spread occurring through a contact network and secondary local spatial spread.Social networks were constructed by combining contact-tracing data on horse movements with a distance matrix between all premises holding horses infected within the first 10 days of the outbreak. These networks were analysed to provide a description of the epidemic, identify premises that were central to disease spread and to estimate the relative proportion of premises infected through infected horse movements and through local spatial spread. We then explored the effect of distance on disease spread by estimating the range of local spread (through direct contact, transmission on fomites and windborne transmission) based on the level of fragmentation in the network and also by directly estimating the shape of the outbreak's spatial transmission kernel.During the first 10 days of this epidemic, 197 horse premises were infected; 70 of these were included in the contact-traced network. Most local spread occurred within 5km. Local spread was estimated to have occurred up to a distance of 15.3km – based on the contact-and-proximity network – and at a very low incidence beyond this distance based on the transmission kernel estimate. Of the 70 premises in the contact network, spread to 14 premises (95% CI: 9, 20 premises) was likely to have occurred through local spatial spread from nearby infected premises, suggesting that 28.3% of spread in the early epidemic period was ‘network-associated’ (95% CI: 25.6, 31.0%). By constructing a ‘maximal network’ of contact and proximity (based on a distance cut-off of 15.3km), 44 spatial clusters were described, and the horse movements that initiated infection in these locations were identified.Characteristics of the combined network, incorporating both spatial and underlying contact relationships between infected premises, explained the high rate of spread, the sequence of cluster formation and the widespread dispersal experienced in the early phase of this epidemic. These results can inform outbreak control planning by guiding the imposition of appropriate control zone diameters around infected premises and the targeting of surveillance and interventions.

Horse owners’/managers’ perceptions about effectiveness of biosecurity measures based on their experiences during the 2007 equine influenza outbreak in Australia

Following the first ever equine influenza outbreak in Australia in 2007, a study was conducted involving 200 horse owners and managers to determine their perceptions about effectiveness of biosecurity measures and the factors associated with these perceptions. Face-to-face interviews were conducted with horse owners/managers to obtain information about their perceptions of the effectiveness of biosecurity practices, their sources of information about infection control during the outbreak and their horse industry involvement. Two outcome variables were created from horse owners’ responses to a 17-item question on the perceived effectiveness of various recommended equine influenza biosecurity measures: (a) a binary outcome variable (Low/High biosecurity effectiveness) and (b) a continuous outcome variable (the proportion of the 17 measures considered ‘very effective’). These outcomes were used in binomial logistic and linear regression analyses, respectively, to determine factors associated with perceptions of biosecurity effectiveness. Variables with a p-value <0.05 in multivariable models were retained in the final models.The majority (83%) of the 200 horse owners and managers interviewed believed that more than half of the recommended equine influenza biosecurity measures were very effective for protecting their horses from equine influenza infection in the event of a future outbreak. Interviewees that were more likely to judge on-farm biosecurity measures as effective were those who received infection control information from a veterinarian during the outbreak, did not experience equine influenza infection in their horses, and those on small acreage premises (homes with horses on site). Greater levels of preparedness for a future equine influenza outbreak and greater interest in information about infection control were associated with a better perception about effectiveness of biosecurity measures.This study identified factors associated with horse owners’ and managers’ perception of effectiveness of biosecurity measures. These findings should be considered in the design of infection control programs.

From the Horse’s Mouth: Perceptions of the Management of the 2007 Equine Influenza Outbreak in Australia

In August 2007, Australia experienced its first-ever outbreak of equine influenza, a highly infectious respiratory disease of horses. Although the outbreak spread over a large geographic area, it was eradicated within 5 months following a substantial disease control effort led by federal and state animal health authorities. Despite its timely control, this large-scale outbreak caused severe impacts on horse owners and industry participants. This study aimed to describe the perceptions of horse owners and managers, impacted by outbreak control measures, regarding the state government's animal health authority outbreak management. Participants were interviewed face-to-face. Factors associated with ordinal ratings of perception ('well managed', 'adequately managed' and 'poorly managed') were identified using ordinal logistic regression. Factors significantly associated with a reduced likelihood of 'well-managed' outbreak response ratings, adjusted for age and gender, were being involved in horse competitions/sporting events (OR = 0.48; 95% CI: 0.25-0.91), managing a horse stud (OR = 0.09; 95% CI: 0.03-0.28) and believing that another outbreak of equine influenza was highly likely in the next 5 years (OR = 0.29; 95% CI: 0.12-0.68). Possible reasons for these ratings were further investigated using content analyses. Outbreak communications and government efficiency/support were mentioned most frequently as both strengths (30% and 28%, respectively) and weaknesses (40% and 30%, respectively) of the outbreak management. To promote manager-government rapport and future compliance with disease control regulations, we recommend that outbreak communications and outbreak information systems be reviewed.

Equine disease surveillance: quarterly summary

Equine influenza outbreaks lower than expected in the UK during summerDourine reported in ItalyMarked increase in Hendra virus cases in Australia in 2011Summary of surveillance testing, April to June 2011These...

A prospective longitudinal study of naturally infected horses to evaluate the performance characteristics of rapid diagnostic tests for equine influenza virus

An outbreak of equine influenza (EI) occurred in Australia in 2007. During the laboratory support for this outbreak, real-time reverse transcriptase polymerase chain reaction (qRT-PCR) assays and a blocking enzyme linked immunosorbent assay (bELISA) were used as testing methods to detect infection with the virus. The qRT-PCR and bELISA tests had not been used for EI diagnosis before, so it was not known how soon after infection these tests would yield positive results, or for how long these results would remain positive. To answer these questions, nasal swabs and blood samples were collected daily from a group of 36 naturally infected horses. EI viral RNA was detected in all horses by qRT-PCR from the first to tenth day after clinical signs were evident, and was detected in some horses for up to 34 days. Antibody was detected in the bELISA in some horses by day 3, with a median time to seroconversion of 5 days. The results from this study indicate that viral RNA can be detected from nasal swabs for much longer than infectious virus is thought to be shed from horses. The bELISA detected antibodies against EI virus in all horses for 139 days following infection, but only detected approximately 50% of horses 12 months following infection. Haemagglutination inhibition testing detected antibodies against H3 antigens in all horses for 28 days following infection, but 2 were negative by 35 days following infection.

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

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. To summarise the genetic analysis of EI viruses detected in Ireland from June 2007 to January 2010. The HA1 gene of 18 viruses was sequenced and phylogenetic analysis undertaken. 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. 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. These data also serve as a scientific basis for investigating the source of epizootics and outbreaks both nationally and internationally.

Horse owners’ biosecurity practices following the first equine influenza outbreak in Australia

A cross-sectional study was conducted involving 759 Australian horse owners to determine their biosecurity practices and perceptions one year after the 2007 equine influenza outbreak and to investigate the factors influencing these perceptions and practices. A web link to an online questionnaire was sent to 1224 horse owners as a follow-up to a previous study to obtain information about biosecurity perceptions and practices, impacts of the 2007 EI outbreak, demographic information and information about horse industry involvement. Ordinal logistic regression analyses were conducted to determine factors associated with poor biosecurity practices. Biosecurity compliance (low, medium, high), as determined by horse owners’ responses to a 16-item question on the frequency of various biosecurity measures, was used as the outcome variable in ordinal logistic regression analyses. Variables with a univariable p-value ≤0.2 were eligible for inclusion in multivariable models built using a manual stepwise approach. Variables with a p-value <0.05 in multivariable models were retained in the final model. Two potential confounders – age and gender of participants – were included in the final model irrespective of their p-values. Thirty percent of the respondents had low biosecurity compliance and were performing biosecurity practices ‘not very often’ or ‘never’. Younger people, people with two or more children, those who were not involved with horses commercially and those who had no long-term business impacts resulting from the 2007 EI outbreak were more likely to have lower biosecurity compliance. People who were not fearful of a future outbreak of equine influenza in Australia and those who thought their current hygiene and access control practices were not very effective in protecting their horses also had poor biosecurity practices. In this observational study we identified factors associated with a group of horse owners with low levels of biosecurity compliance. As this cross-sectional study only assesses associations, the identified factors should be further investigated in order to be considered in the design of extension activities to increase horse owners’ biosecurity compliance.

The importance of location in contact networks: Describing early epidemic spread using spatial social network analysis

This paper explores methods for describing the dynamics of early epidemic spread and the clustering of infected cases in space and time when an underlying contact network structure is influencing disease spread. A novel method of describing an epidemic is presented that applies social network analysis to characterise the importance of both spatial location and contact network position. This method enables the development of a model of how these clusters formed, incorporating spatial clustering and contact network topology. Based on data from the first 30 days of the 2007 equine influenza outbreak in Australia, clusters of infected premises (IPs) were identified and delineated using social network analysis to integrate contact-tracing and spatial relationships. Clusters identified by this approach were compared to those detected using the space-time scan statistic to analyse the same data. To further investigate the importance of network and spatial location in epidemic spread, kriging by date of onset of clinical signs was used to model the spatio-temporal spread without reference to underlying contact network structure. Leave-one-out cross-validation was used to derive a summary estimate of the accuracy of the kriged surface. Observations poorly explained by the kriged surface were identified, and their position within the contact network was explored to determine if they could be better explained through analysis of the underlying contact network. The contact network was found to lie at the core of a combined network model of spread, with infected horse movements connecting spatial clusters of infected premises. Kriging was imprecise in describing the pattern of spread during this early phase of the outbreak (explaining only 13% of the variation in date of onset of IPs), because early dissemination was dominated by network-based spread. Combined analysis of spatial and contact network data demonstrated that over the first 30 days of this outbreak local spread emanated outwards from the small number of infected premises in the contact network, up to a distance of around 15 km. Consequently, when a contact network structure underlies epidemic spread, we recommend applying a method of spatial analysis that incorporates the network component of disease spread. Linking the spatial and network analysis of epidemics facilitates inference of the methods of disease transmission, providing a description of the sequence of spatial cluster formation.

Positive results in a real‐time PCR for type A influenza associated with the use of an inactivated vaccine

A real-time reverse transcription polymerase chain reaction (qRT-PCR) test for the matrix gene of type A influenza viruses was used during the 2007 Australian equine influenza (EI) outbreak in order to confirm diagnosis and, later, eradication of the virus. During the EI outbreak, horses being exported required vaccination and individual proof of freedom from EI. At the end of the outbreak, positive results were obtained from four horses destined for export, because of contamination of the samples with the vaccine. This report highlights the need for EI testing and vaccination to occur on separate days and with the collection of swabs for testing to precede vaccination.

Analysis of horse movements and events during the 2007 outbreak of equine influenza in New South Wales, Australia

To analyse horse event and horse movement registration data collected between September 2007 and December 2008 during the outbreak of equine influenza in New South Wales, Australia. A total of 9356 events were registered, involving 504,382 horses and 242,952 riders. Registered horse movements totalled 224,084, involving 349,327 horses (excluding mobs) travelling 34.4 million km with an average of 154 km per journey. The number of recorded events and movements were low while movement controls were most stringent, then increased from December 2007 as restrictions were eased, to peak in April 2008 with up to 290 events and 15,730 movements weekly, after which registrations declined as the disease was eradicated. The main types of events registered were pony clubs (38%), race meetings and trials (17%), competition (13%), and clinics and lessons (11%). Registration of horse events and movements allowed movement controls to be progressively eased while retaining the ability to trace the movements of large numbers of horses if needed. The number of recorded events, movements and distances travelled confirms the highly mobile nature of the recreational horse industries, helps to explain the rapid and widespread dispersal of the disease before movement restrictions were imposed, and also demonstrates the value of those restrictions as a control measure. The data provide a quantitative snap-shot of horse events and movements, albeit distorted by the prevailing movement restrictions as well as by limitations in the data recording that should be addressed when developing traceability systems for horses in future.

Impact of the Australian equine influenza outbreak on a small business that was not infected

At the outbreak of equine influenza (EI) we chose to close our horse-based business, as we did not want to risk our horses contracting the disease and the demand for our services ceased. We report our experiences of the outbreak.

Longitudinal study describing the clinical signs observed in horses naturally infected with equine influenza

We describe the clinical signs and disease course during an outbreak of equine influenza (EI) in naïve horses in a police stables in Sydney, New South Wales, Australia.

Determining the endpoint of an outbreak of equine influenza in a large population of racing Thoroughbreds

Outbreaks of equine influenza (EI) cause major disruption to the racing industry, resulting in cessation of racing until affected horses have recovered from the disease. The introduction of EI to a large population of Thoroughbred horses stabled at a Sydney racecourse provided the opportunity to observe clinical signs and monitor the spread of EI in this predominantly naïve population and to assist in determining an endpoint to infection spread to allow resumption of racing events.

Overview of the industry and social impacts of the 2007 Australian equine influenza outbreak

The equine influenza (EI) outbreak occurred at the worst time of the year as far as the horse industry was concerned. All horse sports and horse breeds had events planned in the spring, including those relating to qualification for the 2008 Beijing Olympic Games. These were all disrupted and many were cancelled. The social and industry impacts were extensive, and included difficulties related to communication, animal welfare, vaccination, movement restrictions, economics, as well as the psychological stresses experienced by those involved, especially those for whom their primary source of income was horse related.

Insights into the economic consequences of the 2007 equine influenza outbreak in Australia

We estimate and describe the financial costs of the equine influenza (EI) outbreak in Australia, including the costs of emergency response measures and lost income/assets to businesses, associations and private horse owners. Costs to associations, governments and industry are discussed. We identify a lack of reliable data about the financial costs of the EI outbreak to the non-racing sectors of the horse industry.

Evaluating the effectiveness of the response to equine influenza in the Australian outbreak and the potential role of early vaccination

To use modelling and epidemiological analyses to assess the effectiveness of control strategies employed during the equine influenza outbreak and determine if early vaccination might have had a beneficial effect. Transmission of infection was modelled using stochastic, spatial simulation, based on data from 16 regions in New South Wales and Queensland over the first month of the outbreak. The model accurately represented the spread of infection in both space and time and showed that vaccination strategies would have reduced new infections by ∼60% and reduced the size of the infected area by 8-9%, compared to the non-vaccination baseline. When used in conjunction with biosecurity measures and movement controls, early vaccination could play an important role in the containment and eradication of equine influenza.