OAHN Projects

Investigation of a respiratory disease outbreak in the Ontario harness racing industry and the economic impact on industry participants

Project Lead: Alison Moore

Collaborators: OAHN Equine Network, Drs. Liz Shiland and Chris Grossenbacher

In July 2020, a respiratory outbreak occurred in Ontario’s southwestern harness horse racing industry. Veterinarians reported horses with high fevers, nasal discharge and cough. A viral cause was suspected given the rapid progression through a given barn and the clinical signs and the Ontario Animal Health Network (OAHN)– Equine Network was contacted to help determine the cause. As well, since upper respiratory viral infections are one of the leading causes of training loss, the cost of illness was important to capture in the hopes of changing behavior with respect to vaccination and biosecurity practices. To characterize the etiologic agent and to determine the “cost” associated with respiratory disease in this cohort of horses, the OAHN network designed the following study.

METHODS

Animals

Between July 18 and August 8, 2020, 11 Standardbreds based on clinical signs and convenience sampling were included in the project. They were located at 6 training facilities in southwestern Ontario.

Sampling

One nasal swab and two serum samples were obtained from each horse. The nasal swab was sent to IDEXX Canada for RT-PCR testing for the following pathogens: influenza A (EIV), Streptococcus equi, Streptococcus zooepidemicus, Streptococcus dysgalactiae subsp equisimilis, equine herpesvirus 1 (EHV-1) and 4 (EHV-4). Influenza A positive samples were sent to Cornell University for virus isolation and serotyping. Serum samples were tested at the Animal Health Laboratory, Guelph, Ontario for antibody titres for EHV-1/4, EIV, equine rhinitis A (ERAV), B (ERBV) and equine arteritis virus.

Determining the potential effect or respiratory infection on racing performance

The change in racing performance following evaluation for respiratory disease, was assessed by the change, in seconds, from the previous start. Speed ratings for each track (kylekazak.com) were used to adjust for racing at different tracks. Track variance was also added or subtracted to the final mile time.

RESULTS AND DISCUSSION

The 11 horses were stabled at 6 different facilities in southwestern Ontario. Ages of affected horses ranged from 2 to 6 years old (9/11 were between 2 and 3 years of age); the majority were geldings (6/11), and there was an even number of pacers and trotters. Nine horses were actively racing at the time. The average fever reported was 103.4 F (range 102 – 105); most horses (9/11) had some nasal discharge but only three had a cough. Nasal swabs and blood samples were submitted for each horse.

The following were the most significant results of molecular and serologic testing; 5 horses were positive for EIV RT-PCR, and 8 horses were positive for ERAV serologically (titre range 1:128 – 1:6144). Three horses had co-infections; 2 with EIV and ERAV and 1 with S. zooepidemicus and ERAV. Ten horses were positive for ERBV. Five horses had negative influenza titres (<1:8) suggesting that had not been appropriately vaccinated or exposed to influenza previously. Of these 5, 4 horses were positive on EIV RT-PCR. Five horses had positive influenza titres indicating previous exposure or vaccination and none of these horses were positive for EIV RTPCR.

No EIV PCR positive samples were positive on virus isolation which is not uncommon and may be related to the way in which the samples were preserved.

Eight of the horses received antibiotics (2 received trimethoprim sulpha (TMS), 2 received TMS followed by ceftiofur, 4 received only ceftiofur or ceftiofur crystalline free acid). The frequent use of antibiotics to treat respiratory disease is not unusual in the racing industry but more emphasis should be on appropriate and judicious use of antimicrobials.

The average cost of veterinary treatment per horse was $213.90 (range $0-$412). The average number of days until resolution of clinical signs was 8.6 (range 1-21).

The average number of days until horses were back jogging was 8.4 (range 0-12); average days until back training was 13.3 ( range 0-20) and average days until the horse was back racing was 14 (range 2-27). At an average daily training fee per horse of $100 and an average of 7 days between race starts, the delay in racing for an average of 14 days could cost $1400 in extra training days due to recovery from illness.

For a table of results see Table 1.

Complete race lines were only available for 6 of the nine racehorses. Three horses raced within 14 days of being diagnosed and all three horses showed potential impairment in performance. Horse B (ERVA positive) raced three days after diagnosis. Although the horse raced well it did not race again for 34 days at which time he was 4 seconds (20 horse lengths) slower than his previous time. Lameness may have been a confounding factor. Interestingly, in cattle with bovine respiratory disease complex (BRD), lameness is a risk factor for developing BRD thought due to changes in the immune system from the stress of lameness. Horse D (Influenza A and ERAV positive) raced 2 days after diagnosis and then again 7 days later. Although he raced comparatively well the first time, he was 1.4 seconds (7 horse lengths) slower than his previous start for the second race. Horse E (ERAV positive) raced just once after being scratched from a race when diagnosed. She was 1.6 seconds (8 horse lengths) slower in her start back after illness. Three other horses had slower race times from 20 days post diagnosis to 45 days post diagnosis. Horse A (ERAV positive) had a 2 second (10 horse length) increase at day 31 , Horse C (Influenza A and ERAV positive) had a 4.8 second (24 horse lengths) increase at day 45 and Horse F (ERAV positive) had an 0.8 second (3 horse length) increase between days 26 and 33. (Figure 1). For comparison, Figure 2 shows a healthy group of aged conditioned horses that raced against Horse A and were from other stables not involved in the study to show that consistency in performance is possible.

Figure 1 -change in seconds from the previous race start for study horses

Figure 2 – change in seconds from the previous race start for conditioned horses not from affected stables and who raced against Horse A

Equine upper respiratory tract viral infections are common in the harness racing industry, however, vaccination against the more common viruses is low (personal communication). It is also not commonplace for trainers to request diagnostic testing on ill horses believed to have “the virus” as many feel it does not change the treatment plan. As well, there is an impression that the influenza vaccine “does not work”. The cost of respiratory disease to the industry is also thought to be one of those inherent “costs of doing business” but the impact in lost training days and racing opportunities beyond the immediate treatment for illness is often not recognized.

This study reinforces the understanding that influenza and Equine rhinitis virus A are separately and combined, important causes of respiratory disease capable of potentially affecting performance well beyond the days the horse is clinically ill.

Equine rhinitis virus A infection is more common in winter and early spring but can happen any time of the year. In humans, rhinoviruses are associated with severe airway inflammation and exacerbate signs of asthma (1). In horses, ERAV causes persistent neutrophilic inflammation, epithelial damage and mucus secretion for up to 21 days and will also exacerbate signs of equine asthma (2). Infection may also impact cilia function affecting airway clearance and predisposing to secondary bacterial infections. High titres post infection persists for at least 21 days and will usually protect horses from reinfection for at least a year. As well, horses that develop a protective immune response will limit shedding of the virus when reinfected (3). ERAV is difficult to detect by PCR testing of nasal swabs because it is not present in the nasal cavity for long. Serological testing is the method of choice to determine infection. In this study, all affected horses with race lines were infected with ERAV and all showed impairment in performance, either within 14 days of diagnosis or after 20 days. Equine rhinitis B virus is a ubiquitous virus in the Ontario racing industry (4). Its effect on performance is believed to be less severe than ERAV. Its role in coinfection is unclear however and it may make other infections more clinically severe. Ten horses were positive for ERBV demonstrating previous/recent exposure.

Equine influenza virus (EIV) infection can occur at any time of the year but occurs more commonly in the racing industry in spring and summer when comingling is frequent. EIV can spread through the air for 1-2 km and is spread more rapidly amongst horses than other respiratory viruses (5). The virus can be shed for up to 10 days. EIV infection typically causes fever, a harsh dry cough, limb edema, muscle soreness and a serous nasal discharge which turns mucopurulent with a secondary bacterial infection. EIV damages the ciliated epithelial cells of the upper and lower respiratory tract thereby affecting the clearance of foreign substances (6). These cells will die and a protein exudate is released into the airway. Bronchiolitis and secondary bacterial infection may ensue. Horses rarely die from uncomplicated EIV infection but may succumb to secondary bacterial pneumonia (7). The respiratory epithelium takes 3 weeks to recover regardless of treatment (8). This latter fact should be emphasized to trainers so they do not resume racing their horses too quickly after infection is diagnosed.

The sample size for this study was small. More horses with performance lines would give a better indication of the true impact of disease. Additionally, a more detailed history on the general health of each horse (e.g. lameness) would provide more useful information on potential performance impacts. The number of horses affected with clinical signs of viral respiratory disease in the barn would also better identify the total economic impact on the stable. Performing paired serum testing for EHV 1/4, ERVA and B and influenza would have also supported infection (particularly for ERVA and B) however sampling challenges arose with horses leaving the province to race. Knowing the absence of disease in certain barns would also allow better selection of control horses.

CONCLUSIONS

This study was useful in identifying the pathogens involved in a recent respiratory outbreak in the harness racing industry, showing the potential negative affect of ERAV and EIV on performance and the anticipated costs of treatment. These results could be used by veterinarians to support regular vaccination against EIV, continued surveillance of circulating EIV strains and ERAV exposure and support for future development and availability of ERAV vaccination.

References:

1. The Interplay between Host Immunity and Respiratory Viral Infection in Asthma Exacerbation. Hossain FMA, Choi JY, Uyangaa E, Park SO, Eo SK.Immune Netw. 2019 Sep 9;19(5):e31

2. Association between inflammatory airway disease of horses and exposure to respiratory viruses: a case control study. Houtsma A, Bedenice D, Pusterla N, Pugliese B, Mapes S, Hoffman AM, Paxson J, Rozanski E, Mukherjee J, Wigley M, Mazan MR.Multidiscip Respir Med. 2015 Nov 3;10:33.

3. Characteristics of respiratory tract disease in horses inoculated with equine rhinitis A virus. Diaz-Méndez A, Hewson J, Shewen P, Nagy E, Viel L.Am J Vet Res. 2014 Feb;75(2):169-78.

4. Surveillance of equine respiratory viruses in Ontario. Diaz-Mendez A, Viel L, Hewson J, Doig P, Carman S, Chambers T, Tiwari A, Dewey C.Can J Vet Res. 2010 Oct;74(4):271-8.

5. A brief introduction to equine influenza and equine influenza viruses. Chambers TM.Methods Mol Biol. 2014;1161:365-70.

6. A Comprehensive Review on Equine Influenza Virus: Etiology, Epidemiology, Pathobiology, Advances in Developing Diagnostics, Vaccines, and Control Strategies. Singh RK, Dhama K, Karthik K, Khandia R, Munjal A, Khurana SK, Chakraborty S, Malik YS, Virmani N, Singh R, Tripathi BN, Munir M, van der Kolk JH.Front Microbiol. 2018 Sep 6;9:1941.

7. Current perspectives on control of equine influenza. Daly JM, Newton JR, Mumford JA.Vet Res. 2004 Jul-Aug;35(4):411-23

8. Equine influenza virus. Landolt GA.Vet Clin North Am Equine Pract. 2014 Dec;30(3):507-22.