Equine respiratory viruses, airway inflammation and performance

An important study that looks at the relation of equine respiratory viruses and equine asthma, also known as recurrent airway disease or when advanced chronic obstructive airway disease. Though several of the surveyed viruses were common, the findings did not support a strong relationship to clinical signs or decreased performance.
DrO

Equine respiratory viruses, airway inflammation and performance in thoroughbred racehorses
Vet Microbiol. 2021 Apr 10;257:109070. doi: 10.1016/j.vetmic.2021.109070. Online ahead of print.
Authors
Laurent Couetil 1 , Kathleen Ivester 2 , Samantha Barnum 3 , Nicola Pusterla 3
Affiliations

1 Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Purdue University, West Lafayette, IN, 47907, USA. Electronic address: couetill@purdue.edu.
2 Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Purdue University, West Lafayette, IN, 47907, USA.
3 Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, CA, 95616, USA.

PMID: 33865081
DOI: 10.1016/j.vetmic.2021.109070

Abstract

Equine asthma is a common cause of poor performance in racehorses but it is unclear if respiratory viruses contribute to its etiology. The objective of the study was to determine if respiratory viruses were associated with clinical signs and bronchoalveolar lavage fluid (BALF) cytology in Thoroughbred racehorses. Equine herpesviruses (EHV-1, 2, 4, 5) and equine rhinitis A and B viruses (ERBV, ERAV) genomes were quantified by qPCR in nasopharyngeal, tracheal, and BALF samples collected after racing. The relationships between virus detection and load and clinical signs, performance, BALF cytology, and environmental exposures were examined with generalized linear mixed models. Ninety-two samples were collected from 31 horses. EHV-1 and ERAV were not found; EHV-4 was detected in only one sample. EHV-2, EHV-5 and ERBV were more likely to be detected in upper airway samples than in BALF (P < 0.0001). Neither respiratory virus detection nor load was associated with clinical signs or performance. Nasopharyngeal detection and load of ERBV and tracheal detection and load of EHV-5 were associated with increased proportions of neutrophils in BALF (P < 0.003). However, nasopharyngeal detection and load of EHV-5 was not (P = 0.11). Nasopharyngeal detection and load of EHV-2 were associated with decreased BALF mast cell proportions. Respirable dust exposures were significantly higher in horses with detection of ERBV when compared to horses with no detectable ERBV (P < 0.001). Our results suggest that ERBV, EHV-2 and EHV-5 are commonly present in upper airways of healthy racehorses; however, the role they play in the etiology of equine asthma remains unclear. Keywords: Bronchoalveolar lavage; Equine asthma; Herpesvirus; Nasopharynx; Rhinovirus; Trachea.