Low prevalence of equine coronavirus in foals in the largest thoroughbred horse breeding region of Japan, 2012-2014

Diagnostic approaches, aetiological agents and their associations with short-term survival and laminitis in horses with acute diarrhoea admitted to referral institutions

BACKGROUND

An international description of the diagnostic approaches used in different institutions to diagnose acute equine diarrhoea and the pathogens detected is lacking.

OBJECTIVES

To describe the diagnostic approach, aetiological agents, outcome, and development of laminitis for diarrhoeic horses worldwide.

STUDY DESIGN

Multicentre retrospective case series.

METHODS

Information from horses with acute diarrhoea presenting to participating institutions between 2016 and 2020, including diagnostic approaches, pathogens detected and their associations with outcomes, were compared between institutions or geographic regions.

RESULTS

One thousand four hundred and thirty-eight horses from 26 participating institutions from 4 continents were included. Overall, aetiological testing was limited (44% for Salmonella spp., 42% for Neorickettsia risticii [only North America], 40% for Clostridiodes difficile, and 29% for ECoV); however, 13% (81/633) of horses tested positive for Salmonella, 13% (35/262) for N. risticii, 9% (37/422) for ECoV, and 5% (27/578) for C. difficile. C. difficile positive cases had greater odds of non-survival than horses negative for C. difficile (OR: 2.69, 95%CI: 1.23-5.91). In addition, horses that were positive for N. risticii had greater odds of developing laminitis than negative horses (OR: 2.76, 95%CI: 1.12-6.81; p = 0.029).

MAIN LIMITATIONS

Due to the study's retrospective nature, there are missing data.

CONCLUSIONS

This study highlighted limited diagnostic investigations in cases of acute equine diarrhoea. Detection rates of pathogens are similar to previous reports. Non-survival and development of laminitis are related to certain detected pathogens.

Serosurveillance of equine coronavirus infection among Thoroughbreds in Japan

BACKGROUND

Equine coronavirus (ECoV) causes fever, lethargy, anorexia and gastrointestinal signs in horses. There has been limited information about the prevalence and seasonality of ECoV among Thoroughbreds in Japan.

OBJECTIVES

To understand the epidemiology and to evaluate the potential risk of ECoV infection to the horse industry in Japan.

STUDY DESIGN

Longitudinal.

METHODS

The virus-neutralisation (VN) test was performed using sera collected three times a year at 4 months intervals from 161 yearlings and at 6-7 months intervals from 181 active racehorses in Japan in 2017-18, 2018-19 and 2019-20. VN titre ≥1:8 was defined as seropositive, and ≥ 4-fold increase in titres between paired sera was regarded as indicative of infection.

RESULTS

The VN test showed that 44.1% (71/161) of yearlings were seropositive in August, when they first entered the yearling farm. The infection rate was significantly higher between August and December (60.9%, 98/161) than between December and the following April (5.6%, 9/161; P = 0.002). Among the racehorses, it was significantly higher between November and the following May (15.5%, 28/181) than between the preceding April/May and November (0%; P = 0.02). The morbidity rates during the estimated periods of viral exposure were 39.2% in the yearlings and 4% in the racehorses. No horses showed any severe clinical signs.

MAIN LIMITATIONS

Clinical records did not cover the period during horses' absence from the training centre.

CONCLUSIONS

ECoV was substantially prevalent in Thoroughbred yearlings and racehorses in Japan, and there was a difference in epizootic pattern between these populations in terms of predominant periods of infection. ECoV infection was considered to be responsible for some of the pyretic cases in the yearlings. However, no diseased horses were severely affected in either population, suggesting that the potential risk of ECoV infection to the horse industry in Japan is low.

Bacterial and viral enterocolitis in horses: a review

Enteritis, colitis, and enterocolitis are considered some of the most common causes of disease and death in horses. Determining the etiology of these conditions is challenging, among other reasons because different causes produce similar clinical signs and lesions, and also because some agents of colitis can be present in the intestine of normal animals. We review here the main bacterial and viral causes of enterocolitis of horses, including Salmonella spp., Clostridium perfringens type A NetF-positive, C. perfringens type C, Clostridioides difficile, Clostridium piliforme, Paeniclostridium sordellii, other clostridia, Rhodococcus equi, Neorickettsia risticii, Lawsonia intracellularis, equine rotavirus, and equine coronavirus. Diarrhea and colic are the hallmark clinical signs of colitis and enterocolitis, and the majority of these conditions are characterized by necrotizing changes in the mucosa of the small intestine, colon, cecum, or in a combination of these organs. The presumptive diagnosis is based on clinical, gross, and microscopic findings, and confirmed by detection of some of the agents and/or their toxins in the intestinal content or feces.

The First Detection of Equine Coronavirus in Adult Horses and Foals in Ireland

The objective of this study was to investigate the presence of equine coronavirus (ECoV) in clinical samples submitted to a diagnostic laboratory in Ireland. A total of 424 clinical samples were examined from equids with enteric disease in 24 Irish counties between 2011 and 2015. A real-time reverse transcription polymerase chain reaction was used to detect ECoV RNA. Nucleocapsid, spike and the region from the p4.7 to p12.7 genes of positive samples were sequenced, and sequence and phylogenetic analyses were conducted. Five samples (1.2%) collected in 2011 and 2013 tested positive for ECoV. Positive samples were collected from adult horses, Thoroughbred foals and a donkey foal. Sequence and/or phylogenetic analysis showed that nucleocapsid, spike and p12.7 genes were highly conserved and were closely related to ECoVs identified in other countries. In contrast, the region from p4.7 and the non-coding region following the p4.7 gene had deletions or insertions. The differences in the p4.7 region between the Irish ECoVs and other ECoVs indicated that the Irish viruses were distinguishable from those circulating in other countries. This is the first report of ECoV detected in both foals and adult horses in Ireland.

Frequency of molecular detection of equine coronavirus in faeces and nasal secretions in 277 horses with acute onset of fever

CONTEXT

Due to the inconsistent development of enteric signs associated with ECoV infection in adult horses, many practitioners collect nasal secretions rather than feces for the molecular diagnostic work-up of such horses.

MAIN CONCLUSION

ECoV infection should be considered in horses presenting with acute onset of fever, especially when nasal discharge is absent as one of the cardinal clinical sign.

APPROACH

A total of 277 adult horses with acute onset of fever were enrolled in this study. Feces were tested for ECoV and nasal secretions for common respiratory pathogens (equine herpesvirus (EHV)-1, EHV-4, equine influenza virus (EIV), equine rhinitis viruses (ERVs) and Streptococcus equi ss. equi) and ECoV by qPCR. Each submission was accompanied by a questionnaire requesting information pertaining to signalment, use, recent transportation, number of affected horses on the premise and presence of clinical signs at the time of sample collection.

RESULTS

The total number of horses testing qPCR-positive for ECoV in feces was 20 (7.2%), 4 of which also tested qPCR-positive for ECoV in nasal secretions. In the same population 9.0% of horses tested qPCR-positive for EHV-4, 6.1% for EIV, 4.3% for Streptococcus equi ss. equi, 3.2% for ERVs and 0.7% for EHV-1. Draft horses, pleasure use, multiple horses affected on a premise and lack of nasal discharge were significantly associated with ECoV qPCR-positive horses.

INTERPRETATION

The present study results showed that 7.2% of horses with acute onset of fever tested qPCR-positive for ECoV in feces, highlighting the importance of testing such horses for ECoV in feces. The various prevalence factors associated with ECoV qPCR-positive status likely relate to the high infectious nature of ECoV and breed-specific differences in management and husbandry practices.

SIGNIFICANCE OF FINDINGS

ECoV infection should be suspected and tested for in horses presenting with acute onset of fever, lethargy and anorexia with no respiratory signs. A two-step approach should be consider in which respiratory secretions and feces should be collected from such horses and submitted to a diagnostic laboratory. If the respiratory secretions test negative by qPCR for a panel of respiratory pathogens, feces already submitted to the laboratory should be tested for ECoV.

Enteric coronavirus infection in adult horses

A new enteric virus of adult horses, equine coronavirus (ECoV), has recently been recognized. It is associated with fever, lethargy, anorexia, and less frequently, colic and diarrhea. This enteric virus is transmitted via the feco-oral route and horses become infected by ingesting fecally contaminated feed and water. Various outbreaks have been reported since 2010 from Japan, Europe and the USA. While the clinical signs are fairly non-specific, lymphopenia and neutropenia are often seen. Specific diagnosis is made by the detection of ECoV in feces by either quantitative real-time PCR, electron microscopy or antigen-capture ELISA. Supportive treatment is usually required, as most infections are self-limiting. However, rare complications, such as endotoxemia, septicemia and hyperammonemia-associated encephalopathy, have been reported, and have been related to the loss of barrier function at the intestinal mucosa. This review article will focus on the latest information pertaining to the virus, epidemiology, clinical signs, diagnosis, pathology, treatment and prevention of ECoV infection in adult horses.