Nasal Shedding of Equine Herpesvirus‐1 from Horses in an Outbreak of Equine Herpes Myeloencephalopathy in Western Canada

Abstract

Background: There is little information on the duration of nasal shedding of EHV-1 from horses with naturally occurring equine herpesvirus myeloencephalopathy (EHM).Objectives: To evaluate the duration of nasal shedding of EHV-1 in horses affected by EHM. Animals: One hundred and four horses naturally exposed to EHV-1, 20 of which had clinical signs of EHM. Methods: All horses on affected premises were monitored. Those horses developing EHM were sampled in a longitudinal outbreak investigation. Nasal swabs were collected daily from 16 of 20 horses affected by EHM. A qPCR was performed on 98 of 246 nasal swab samples to determine nasal shedding duration. Historical and clinical information was analyzed to evaluate potential risk factors for developing EHM and duration of shedding during this outbreak.Results: The last day shedding was detected in any horse was Disease Day 9. EHV-1 was detected in two-thirds of horses tested on Disease Days 0-3. The amount of EHV-1 DNA found in nasal swabs varied markedly and was not associated with disease severity or age. The odds of developing EHM were greater for febrile horses (OR = 20.3; 95% CI 3.4-390.3; P = .01) as well as for horses attending the riding clinic (OR = 4.1; 95% CI 0.84-21.65; P = .08).Conclusions and Clinical Importance: Biosecurity measures should be implemented for a minimum of 14 days beyond the onset of clinical signs of EHM. Animal managers cannot rely on the severity of clinical signs to predict the duration of EHV-1 shedding.

Quantitative molecular viral loads in 7 horses with naturally occurring equine herpesvirus‐1 infection

“…Interestingly, the 2 nonsurviving horses had peak viral loads in nasal secretions and blood 1000 and 100 times higher, respectively, than horses that survived, indicating that viral load and development of encephalopathy rather than recumbency alone were associated with nonsurvival. Previous studies have concluded that the severity of neurological signs is not associated with the magnitude of viral shedding, although they did not differentiate between signs of encephalopathy and myelopathy [6]. Conversely, in experimentally induced EHM, the development of neurological signs has been associated with the magnitude of cell-associated viraemia [2].…”

Emergence of equine herpes virus 1 myeloencephalopathy: A brief review

“…Europian countries viz., France (Pronost et al, 2010;van Galen et al, 2015), Germany (Fritsche & Borchers, 2011;Damiani et al, 2014), Belgium (van der Meulen et al, 2003;Gryspeerdt et al, 2011), Poland (Stasiak et al, 2015), Netherlands (Goehring et al, 2006) and Croatia (Barbic et al, 2012); North American countries viz., Canada (Burgess et al, 2012) and U.S.A (Nugent et al, 2006;Henninger et al, 2007;Perkins et al, 2009;Smith et al, 2010;Pusterla et al, 2012); South American countries viz., Brazil (Mori et al, 2011) and Argentina (Vissani et al, 2009); Asian countries viz., Turkey (Yilmaz et al, 2012); Japan (Tsujimura et al, 2011) and India (Unpublished data); Islands viz ., Australia (Cuxson et al, 2014) and Newzealand (McFadden et al, 2016); African countries viz., Ethiopia (Negussie et al, 2015) experienced…”

Nasal Shedding of Equid Herpesvirus Type 1 and Type 4 in Hospitalized, Febrile Horses

“…Over the last decade, there have been several reports on nosocomial spread of EHV-1 infection in hospitalized horses, including development of equid herpesvirusassociated myeloencephalopathy (EHM) [3][4][5]. These infections have led to fatal losses of patients and voluntary quarantine of equine hospitals, with substantial financial losses and were associated with significant loss of image for the affected institutions, as perceived by the public.…”

“…Arguably the most commonly observed clinical signs during outbreaks of EHV-1 or -4 infection are pyrexia and (mandibular) lymphadenopathy [5,6]. Fever was also the main clinical sign in EHV-1-positive horses in a surveillance study that determined infectious agents in respiratory conditions in horses [7].…”

“…A number of experimental infection studies have shown that viral replication in the nasopharynx is continuous and spans the viremic phase in most cases, which has been shown by using polymerase chain reaction (PCR) assays or viral culture techniques [8]. During a recent EHM outbreak, significant nasal shedding, detected by quantitative PCR (qPCR) methods, continued in horses beyond a secondary fever and beyond the onset of EHM [5].…”