Efficacy of a commercial vaccine for preventing disease caused by influenza virus infection in horses.

OBJECTIVE: To evaluate efficacy of a commercial vaccine for prevention of infectious upper respiratory tract disease (IURD) caused by equine influenza virus. DESIGN: Double-masked, randomized, controlled field trial. ANIMALS: 462 horses stabled at a Thoroughbred racetrack. PROCEDURE: Vaccine or saline solution placebo was administered 4 times in the population at 6-week intervals. The vaccine contained 3 strains of inactivated influenza virus, and inactivated equine herpesvirus type 4. Horses received 1 or 2 doses of vaccine or placebo prior to onset of a natural influenza epidemic, and were examined 5 d/wk to identify and monitor horses with IURD. Serum antibody concentrations were determined, and virus isolation was performed. RESULTS: Vaccination of horses prior to the influenza epidemic did not result in significant decrease in risk of developing respiratory tract disease. Severity of clinical disease was not different between affected vaccinated horses with IURD and controls with IURD, but median duration of clinical disease was 3 days shorter in vaccinated horses. Serum concentrations of antibodies to H3N8 influenza viruses were lower prior to initial vaccination in horses that were sick during the epidemic, and did not increase in these horses in response to vaccination. On arrival at the racetrack, young horses had lower antibody concentrations than older horses, and did not respond to vaccination as well. CONCLUSIONS AND CLINICAL RELEVANCE: Vaccination was of questionable benefit. A greater degree of protection must be obtained for influenza vaccines to be effective in protecting horses from IURD. Objective field evaluations of commercial vaccines are needed to adequately document their efficacy.     

Risk factors for disease associated with influenza virus infections during three epidemics in horses

OBJECTIVE: To identify risk factors associated with respiratory tract disease in horses during 3 epidemics caused by influenza virus infections. DESIGN: Cross-sectional and prospective longitudinal observational studies. ANIMALS: 1,163 horses stabled at a Thoroughbred racetrack. PROCEDURES: Investigations were conducted during a 3-year period. An epidemic of respiratory tract disease caused by influenza virus infections was identified in each year. Routine observations and physical examinations were used to classify horses' disease status. Data were analyzed to identify factors associated with development of disease. RESULTS: Results were quite similar among the epidemics. Concentrations of serum antibodies against influenza virus and age were strongly associated with risk of disease; young horses and those with low antibody concentrations had the highest risk of disease. Calculation of population attributable fractions suggested that respiratory tract disease would have been prevented in 25% of affected horses of all horses had high serum antibody concentrations prior to exposure. However, recent history of vaccination was not associated with reduction in disease risk. Exercise ponies had greater risk of disease than racehorses, which was likely attributable to frequent horse-to-horse contact. CONCLUSIONS AND CLINICAL RELEVANCE: Particular attention should be paid to young horses, those with low serum antibody concentrations, and horses that have frequent contact with other horses when designing and implementing control programs for respiratory tract disease caused by influenza virus infections. It appears that control programs should not rely on the efficacy of commercial vaccines to substantially reduce the risk of disease caused by influenza virus infections.     

Occurrence of infectious upper respiratory tract disease and response to vaccination in horses on six sentinel premises in northern Colorado

REASONS FOR PERFORMING STUDY: Horses vaccinated against common agents of infectious upper respiratory disease (IURD) may not have detectable serum antibody and may not be protected from clinical disease. OBJECTIVES: The objectives of this study were to 1) investigate the serological response of horses to vaccination against influenza virus (H3N8 and H7N7) and equine herpesviruses (EHV) in a field setting and 2) evaluate associations among vaccination status, serum antibody concentrations, and occurrences of IURD in monitored horses. METHODS: In this study, horses on 6 Colorado premises were vaccinated parenterally against influenza virus and EHV, and serological response evaluated. Horses were monitored, and biological samples collected from individuals with clinical IURD and control horses. RESULTS: Of 173 horses, 61 (35.3%), 21 (12.1%) and 4 (2.3%) seroconverted in response to vaccination against EHV, influenza virus H7N7 and influenza virus H3N8, respectively. CONCLUSIONS: Outbreaks of IURD in study horses were associated with influenza virus H3N8 and Streptococcus equi infection, and serological response to vaccination with conventional products was poor. POTENTIAL RELEVANCE: These results confirm that horses may not respond with detectable serological responses to conventional vaccination against common respiratory viruses and, therefore, suggest that alternate methods of protecting horses against common respiratory viruses should be sought.     

Epidemiology of equine upper respiratory tract disease on standardbred racetracks.

The outbreaks of upper respiratory tract infections in horses at Standardbred racetracks were investigated over a three year period. The most serious epidemics of respiratory disease occurred in the winter and spring seasons. Both influenza viruses and equine herpesvirus 1 were shown to be present in the horse population. The herpesvirus was associated with respiratory disease particularly in the winter but the equine influenza viruses apparently were responsible for the major epidemics of respiratory disease at these tracks. Younger horses, two or three years of age, were particularly susceptible to upper respiratory disease and showed the greatest rate of seroconversion to influenza viruses. Major outbreaks of respiratory disease occurred when the proportion of young horses which had not previously been exposed to epidemics of respiratory disease reached 30 to 40% of the population at the track. Most horses over four years of age appeared to develop resistance to the infections.     

An outbreak of equine influenza at a harness horse racetrack

An outbreak of an influenza-like illness affected approximately 1/3 of the 1050 race horses stabled at a standardbred racetrack and resulted in a 3-day suspension of racing. A/Equi-2 influenza virus was isolated from 1 affected horse and 8 of 10 horses sampled seroconverted. Threshold protective levels of HI antibody against A/Equi-2 influenza virus were not demonstrated in unaffected horses. Resistance in unaffected horses was assumed to result from other factors following previous exposure. Few of the horses had been vaccinated against equine influenza. It was felt that an outbreak of this magnitude might have been prevented if a vaccination program had been followed.     

Surveillance programme for important equine infectious respiratory pathogens in the USA

The prevalence and epidemiology of important viral (equine influenza virus [EIV], equine herpesvirus type 1 [EHV-1] and EHV-4) and bacterial (Streptococcus equi subspecies equi) respiratory pathogens shed by horses presented to equine veterinarians with upper respiratory tract signs and/or acute febrile neurological disease were studied. Veterinarians from throughout the USA were enrolled in a surveillance programme and were asked to collect blood and nasal secretions from equine cases with acute infectious upper respiratory tract disease and/or acute onset of neurological disease. A questionnaire was used to collect information pertaining to each case and its clinical signs. Samples were tested by real-time PCR for the presence of EHV-1, EHV-4, EIV and S equi subspecies equi. A total of 761 horses, mules and donkeys were enrolled in the surveillance programme over a 24-month study period. In total, 201 (26.4 per cent) index cases tested PCR-positive for one or more of the four pathogens. The highest detection rate was for EHV-4 (82 cases), followed by EIV (60 cases), S equi subspecies equi (49 cases) and EHV-1 (23 cases). There were 15 horses with double infections and one horse with a triple infection. The detection rate by PCR for the different pathogens varied with season and with the age, breed, sex and use of the animal.     

Pulmonary ultrasonographic abnormalities associated with naturally occurring equine influenza virus infection in standardbred racehorses

The purpose of this investigation was to determine if naturally occurring acute infectious upper respiratory disease (IRD) caused by equine influenza virus is associated with ultrasonographically detectable pleural and pulmonary abnormalities in horses. Standardbred racehorses were evaluated for signs of IRD, defined as acute coughing or mucopurulent nasal discharge. For every horse with IRD (n = 16), 1 or 2 horses with no signs of IRD and the same owner or trainer (n = 30) were included. Thoracic ultrasonography was performed within 5-10 days of the onset of clinical disease in horses with IRD. Horses without IRD were examined at the same time as the horses with IRD with which they were enrolled. The rank of the ultrasound scores of horses with IRD was compared to that of horses without IRD. Equine influenza virus was identified as the primary etiologic agent associated with IRD in this study. Mild lung consolidation and peripheral pulmonary irregularities were found in 11 (69%) of 16 of the horses with IRD and 11 (37%) of 30 of control horses. Lung consolidation (median score = 1) and peripheral irregularities scores (median score = 1) were greater in horses with IRD compared to horses without IRD (median score = 0; P < .05). Pleural effusion was not observed. Equine influenza virus infection can result in abnormalities of the equine lower respiratory tract. Despite the mild nature of IRD observed in this study, lung consolidation and peripheral pulmonary irregularities were more commonly observed in horses with clinical signs of IRD. Further work is needed to determine the clinical significance of these ultrasonographic abnormalities.     

Epizootiological investigation if strangles in the equine stables in tehran

Strangles is an acute disease of horses caused by infec- tion with Streptococcus equi. It is characterized by inflamma- tion of the upper respiratory tract and abscessation in the adjacent lymph nodes. The distribution of strangles is world- wide. When an outbreak does occur in a large group of horses, it is usually restricted to the younger age groups, under adverse climatic conditions, and when shelter is inadequate. When the group is made up of predominantly young horses, up to 100% may be affected. Such a high incidence is encountered soon after large numbers of susceptible horses, which may have come from many localities, are stabled to get her. The source of infection is the nasal discharge from infected animals, which contaminates the pasture and feed and water troughs. Infection occurs by ingestion or by inhalation o f droplets. During April (1990), two cases of strangles were diag- nosed at Veterinary Faculty Teaching Hospital in Tehran. An epizootiological survey commenced immediately and showed 89-100% of horses were affected. The clinical symp- toms were severe in young horses and the mortality rate was zero. All of the infected horses responded to treatment with intramuscular injection of penicillin/streptomycin.     

A survey of respiratory viruses in New Zealand horses

AIMS: To determine which viruses circulate among selected populations of New Zealand horses and whether or not viral infections were associated with development of respiratory disease.

METHODS: Nasal swabs were collected from 33 healthy horses and 52 horses with respiratory disease and tested by virus isolation and/or PCR for the presence of equine herpesviruses (EHV) and equine rhinitis viruses.

RESULTS: Herpesviruses were the only viruses detected in nasal swab samples. When both the results of nasal swab PCR and virus isolation were considered together, a total of 41/52 (79%) horses with respiratory disease and 2/32 (6%) healthy horses were positive for at least one virus. As such, rates of virus detection were significantly higher (p<0.001) in samples from horses with respiratory disease than from healthy horses. More than half of the virus-positive horses were infected with multiple viruses. Infection with EHV-5 was most common (28 horses), followed by EHV-2 (27 horses), EHV-4 (21 horses) and EHV-1 (3 horses).

CONCLUSIONS: Herpesviruses were more commonly detected in nasal swabs from horses with respiratory disease than from healthy horses suggesting their aetiological involvement in the development of clinical signs among sampled horses. Further investigation to elucidate the exact relationships between these viruses and respiratory disease in horses is warranted.

CLINICAL RELEVANCE: Equine respiratory disease has been recognised as an important cause of wastage for the equine industry worldwide. It is likely multifactorial, involving complex interactions between different microorganisms, the environment and the host. Ability to control, or minimise, the adverse effects of equine respiratory disease is critically dependent on our understanding of microbial agents involved in these interactions. The results of the present study update our knowledge on the equine respiratory viruses currently circulating among selected populations of horses in New Zealand.     

Mechanisms of infection in the respiratory tract

Related to its potential vulnerability the respiratory tract has a very complex and effective defence apparatus. The interaction between these defence mechanisms and certain characteristics of aetiological agents results in a pattern in which initial infections by these agents tend to occur at specific sites in the tract. Infections in which the primary portal of entry is in the upper respiratory tract include Bordetella bronchiseptica and Haemophilus spp in pigs; Pasteurella spp in cattle, sheep, pigs; Mycoplasma spp in cattle, sheep, pigs and poultry; equine herpesvirus 1 in horses; infectious bovine rhinotracheitis in cattle; parainfluenza 3 in cattle and sheep; infectious laryngo-tracheitis and infectious bronchitis in poultry; feline viral rhinotracheitis and calicivirus in cats; Aujeszky's disease virus and swine influenza in pigs; and equine influenza in horses. Infections in which the primary portal of entry is in the lower respiratory tract include Aspergillus fumigatus in poultry and mammals, respiratory syncytial virus in cattle, distemper virus in dogs and adenovirus in cattle and dogs. A fuller understanding of the interactions between an agent and the host at the point of entry would make it much easier to develop effective vaccines and therapeutic agents.     

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 na?ve population and to assist in determining an endpoint to infection spread to allow resumption of racing events.     

Comparison of Serum Amyloid A in Horses With Infectious and Noninfectious Respiratory Diseases

The acute phase protein serum amyloid A (SAA) has been shown to be a useful inflammatory parameter in the horse, but studies showing SAA responses to specific respiratory disease etiologies are limited. The goal of this study was to evaluate SAA responses in horses with infectious and noninfectious respiratory diseases as well as healthy, control horses. Two hundred seven horses were grouped into the following categories: equine influenza virus (EIV), equine herpesvirus-4 (EHV-4), Streptococcus equi subspecies equi (S. equi ss equi), inflammatory airway disease (IAD), and healthy controls. Serum amyloid A concentrations were determined for all horses on serum using a stall-side lateral flow immunoassay test. Serum amyloid A levels were found to be significantly greater for infectious respiratory diseases (EIV, EHV-4, S. equi ss equi) and horses with IAD when compared to control horses. There was a significant difference between viral and bacterial infections and IAD. Although SAA values from horses with S. equi ss equi were significantly greater when compared to horses with viral infections (EIV/EHV-4), the wide range of SAA values precluded accurate classification of the infectious cases. In conclusion, SAA is more reliably elevated with infections of the respiratory tract rather than noninfectious airway conditions. This can facilitate early detection of respiratory infections, help track disease progression, and aid practitioners in making recommendations about proper biosecurity and isolation of potentially contagious horses.     

Clinical outcomes and virology of equine influenza in a naïve population and in horses infected soon after receiving one dose of vaccine

As part of the control measures of the equine influenza (EI) outbreak, in addition to the strategic use of vaccination to provide buffer zones around infected populations, approval was obtained to vaccinate Thoroughbred racing horses. We review the clinical expression of the disease and virus excretion in a population of racehorses that were exposed to EI approximately 7 days after administration of a single dose of the canarypox-vectored recombinant compared with a similar unvaccinated population of horses at a nearby racetrack. Although this study was undertaken opportunistically and under the difficult field conditions that prevailed during the outbreak, our observations demonstrate that an appropriate vaccine can be effectively used as a disease control measure, even in the face of an outbreak, and therefore should be rapidly implemented as soon as there is evidence of infection in a na?ve population.     

Description of the outbreak of equine influenza (H3N8) in the United Kingdom in 2003, during which recently vaccinated horses in Newmarket developed respiratory disease

Between March and May 2003, equine influenza virus infection was confirmed as the cause of clinical respiratory disease among both vaccinated and unvaccinated horses of different breeds and types in at least 12 locations in the UK. In the largest outbreak, 21 thoroughbred training yards in Newmarket, with more than 1300 racehorses, were affected, with the horses showing signs of coughing and nasal discharge during a period of nine weeks. Many of the infected horses had been vaccinated during the previous three months with a vaccine that contained representatives from both the European (A/eq/Newmarket/2/93) and American (A/eq/Newmarket/1/93) H3NN8 influenza virus lineages. Antigenic and genetic characterisation of the viruses from Newmarket and elsewhere indicated that they were all closely related to representatives of a sublineage of American viruses, for example, Kentucky/5/02, the first time that this sublineage had been isolated in the uk. In the recently vaccinated racehorses in Newmarket the single radial haemolysis antibody levels in acute sera appeared to be adequate, and there did not appear to be significant antigenic differences between the infecting virus and A/eq/Newmarket/1/93, the representative of the American lineage virus present in the most widely used vaccine, to explain the vaccine failure. However, there was evidence for significantly fewer infections among two-year-old horses than older animals, despite their having similar high levels of antibody, consistent with a qualitative rather than a quantitative difference in the immunity conveyed by the vaccination.     

2007年华北地区H3N8亚型马流感病毒的分离与鉴定

2007年10月,华北地区某赛马场的马同时发生了以发烧、流水样鼻汁或脓性分泌物、咳嗽等临床症状为主的疾病,疑似马流行性感冒。采集患病赛马的鼻腔分泌物,发病期和发病后14d血清,经鸡胚接种法分离病毒,并用鸡红细胞血凝抑制试验(HI)、神经氨酸酶抑制试验(NI)、病毒回归试验、血清学检测和基因序列分析对分离的病毒进行了系统鉴定。结果表明分离的毒株(A/equine/Huabei/1/2007(H3N8)为马源H3N8亚型马流感病毒,基因型属于美洲分支。我们通过动物回归感染试验建立起分离毒株的实验感染模型。     

Canine pedal dermatitis due to percutaneous Uncinaria stenocephala infection

Related to its potential vulnerability the respiratory tract has a very complex and effective defence apparatus. The interaction between these defence mechanisms and certain characteristics of aetiological agents results in a pattern in which initial infections by these agents tend to occur at specific sites in the tract.

Infections in which the primary portal of entry is in the upper respiratory tract include Bordetella bronchiseptica and Haemophilus spp in pigs; Pasteurella spp in cattle, sheep, pigs; Mycoplasma spp in cattle, sheep, pigs and poultry; equine herpesvirus 1 in horses; infectious bovine rhinotracheitis in cattle; parainfluenza 3 in cattle and sheep; infectious laryngo-tracheitis and infectious bronchitis in poultry; feline viral rhinotracheitis and calicivirus in cats; Aujeszky' disease virus and swine influenza in pigs; and equine influenza in horses. Infections in which the primary portal of entry is in the lower respiratory tract include Aspergillrrs fumigatus in poultry and mammals, respiratory syncytial virus in cattle, distemper virus in dogs and adenovirus in cattle and dogs. A fuller understanding of the interactions between an agent and the host at the point of entry would make it much easier to develop effective vaccines and therapeutic agents.     

2. Persistence of Equine Herpesviruses in Experimentally Infected Horses and the Experimental Induction of Abortion

An 8-month-old filly (No. 2) developed an acute vulvo-vaginitis and respiratory disease following inoculation of equine herpesvirus (EH virus) type 1 (EH 39 virus; equine rhinopneumonitis virus) into the vestibule of the vagina. The same virus produced acute respiratory disease but not balanoposthitis following intranasal, intravenous and intrapreputial inoculation of a 12-month-old colt (No. 3). A second 8-month-old filly (No. 1) developed a mild respiratory disease but not vulvo-vaginitis following intravestibular inoculation of EH 39 virus. EH viruses that were slowly cytopathic for equine foetal kidney cell cultures and serologically unrelated to the inoculated EH 39 virus were isolated from the buffy coat cells at 3 days and from the nasal cavity at 6 days after inoculation of horse No. 1. EH virus that was slowly cytopathic and serologically unrelated to EH 39 virus was isolated at 16 days from the vagina of the filly (No. 2) that developed acute vulvovaginitis and was frequently isolated from the nasal cavities of 2 of the 3 horses for 83 days and from the nasal cavity of the third horse for 57 days under conditions that precluded reinfection from other equidae except from each other. EH viruses were recovered from the 3 horses for a further 58 days under conditions where contact with other equidae may, although was not known to, have occurred between 83 and 141 days postinoculation. It was concluded that these viruses represented a single virus type that was present in the nasal cavity (designated EH 1–6 virus) perhaps also the blood stream of filly No. 1 at the time the 3 horses were purchased and that this virus was subsequently transmitted to the vagina of 1 and the nasal cavities of the other 2 horses. Accordingly a carrier state for EH 39 virus was not shown to occur. These findings are discussed in relation to the natural history of EH virus infections. Attempts to reactivate the EH viruses to cause clinical respiratory disease, by a series of injections of adrenalin and cortisone, were inconclusive. The 3 horses showed no clinical evidence of respiratory disease when they were reinfected intranasally with EH 39 virus 360 days (1 horse) and 412 days (2 horses) after the initial infection with this virus. Abortion was produced when EH 39 virus was inoculated directly into the allantoic or amniotic cavity of a pregnant mare although naturally occurring EH virus abortion remains unrecognised in Australia.     

1. Isolation and Characterisation of Equine Rhinopneumontis Virus and Other Equine Herpesviruses from Horses

Equine herpesviruses (EH viruses) were isolated from 9 horses in three separate outbreaks of respiratory disease. The pattern of disease in the three stables is described and evidence is presented that some of the horses were ill, possibly as a result of recurrent infection, and that reactivation of a persistent, latent infection may have occurred. An ulcerative condition of the pharyngeal region was seen in some of the horses with EH virus infection.
The cytopathogenicity for equine foetal kidney cells of the 9 EH viruses varied considerably. One isolate, EH 39 virus, which was recovered from an acute, upper respiratory tract infection, was rapidly cytopathic for equine foetal kidney cell cultures and was shown in neutralisation tests to be identical with, or closely related to equine rhinopneumonitis virus (EH virus type 1) that is associated with acute respiratory disease and abortion in other countries. More slowly cytopathic isolates were recovered from mild to subclinical upper respiratory tract infections. Evidence is presented that the property of slow cytopathogenicity is probably related to the tendency of these viruses to remain cell associated. Slowly cytopathic isolates were recovered from the nasal cavity of horse 89 on two occasions 79 days apart. One of the eight slowly cytopathic isolates, EH 86 virus, was shown to be antigenically distinct from equine rhinopneumonitis virus (EH 39 virus).     

Susceptibility to and transmission of H5N1 and H7N1 highly pathogenic avian influenza viruses in bank voles (Myodes glareolus)

The study of influenza type A (IA) infections in wild mammals populations is a critical gap in our knowledge of how IA viruses evolve in novel hosts that could be in close contact with avian reservoir species and other wild animals. The aim of this study was to evaluate the susceptibility to infection, the nasal shedding and the transmissibility of the H7N1 and H5N1 highly pathogenic avian influenza (HPAI) viruses in the bank vole (Myodes glareolus), a wild rodent common throughout Europe and Asia. Two out of 24 H5N1-infected voles displayed evident respiratory distress, while H7N1-infected voles remained asymptomatic. Viable virus was isolated from nasal washes collected from animals infected with both HPAI viruses, and extra-pulmonary infection was confirmed in both experimental groups. Histopathological lesions were evident in the respiratory tract of infected animals, although immunohistochemistry positivity was only detected in lungs and trachea of two H7N1-infected voles. Both HPAI viruses were transmitted by direct contact, and seroconversion was confirmed in 50% and 12.5% of the asymptomatic sentinels in the H7N1 and H5N1 groups, respectively. Interestingly, viable virus was isolated from lungs and nasal washes collected from contact sentinels of both groups. The present study demonstrated that two non-rodent adapted HPAI viruses caused asymptomatic infection in bank voles, which shed high amounts of the viruses and were able to infect contact voles. Further investigations are needed to determine whether bank voles could be involved as silent hosts in the transmission of HPAI viruses to other mammals and domestic poultry.