Less invasive muzzle swabs effective at identifying EHV-1 cases in horses – study

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Study team explored sampling options to identify a reliable and logistically more feasible protocol during a large equine herpesvirus-1 outbreak.
Image by Krzysztof Niewolny

The use of less invasive swabs around the muzzle/nostril area of horses was effective in identifying equine herpesvirus-1 infections when compared to less comfortable swabs further up the nose, researchers report.

The swabs taken in the United States study, reported in the journal Pathogens, were each subjected to a molecular-based quantitative polymerase chain reaction (qPCR) test.

Researchers with Steinbeck Peninsula Equine Clinics and the School of Veterinary Medicine at the University of California, Davis, wanted to explore sampling options for a reliable and logistically more feasible protocol during a large EHV-1 outbreak.

Danielle Price and her fellow researchers said EHV-1 outbreaks typically involve mild respiratory disease associated with fever, primarily in horses under 2 years of age, although it can also cause abortion or neurologic disease.

Several recent EHV-1 outbreaks resulting in neurological disease support the observation that morbidity and mortality during outbreaks are higher than in the past.

Recent outbreaks at national and international horse shows have shown the complexity of managing such outbreaks and preventing the often inevitable outcome of neurological disease, known as equine herpesvirus-1 myeloencephalopathy (EHM).

The collection of whole blood and respiratory secretions from horses with clinical disease for molecular testing for the virus is considered the diagnostic gold standard, but the testing of in-contact horses, or the repeated sample collection from infected horses, is sometimes difficult to justify, mostly because of the owners’ perception that nasal swabs are invasive and cause momentary discomfort.

Also, animal health professionals involved in responding to these recent outbreaks have underscored the need to improve knowledge around the disease through the systematic collection of data for analysis.

“With the increased concerns about EHV-1 neurological disease, many equine showgrounds are struggling to institute compliant protocols that reduce the risk of transmission,” the authors noted.

Updated EHV-1 vaccine protocols, increased awareness about biosecurity, daily physical monitoring, and pre-show testing are all measures that have been proposed or used during active outbreaks involving neurological disease.

The animals enrolled in their study comprised show and pleasure horses from a large boarding facility who experienced an outbreak of EHV-1 involving neurological problems early in 2022.

In all, there were 32 adult horses of various breeds, aged 4 to 27. Initially, 19 horses formed the healthy group, but four horses ended up moving to the EHV-1 clinical group as they developed clinical signs.

A total of 17 horses were diagnosed with EHV-1 infection based on the presence of fever, respiratory signs, and distal limb swelling, or fever and acute onset of neurological deficits – the latter affecting five horses.

Each horse was sampled two to four times at intervals of two to six days during the outbreak using rayon-tipped swabs. Nasal secretions were used as the diagnostic sample of choice.

Additional swab samples were taken for testing, from the muzzle/nostril area, the front limbs, rectum, feed bin and water troughs.

All swabs were tested for the presence of EHV-1 by qPCR.

The study team reported that the muzzle swabs showed, in comparison to the nasal swabs, good overall agreement in the detection of EHV-1 in horses with clinical disease.

Non-invasive swabs from the muzzle/nostril area enable identification of EHV-1 shedders during an outbreak, they concluded, allowing for prompt isolation and implementation of biosecurity measures.

The study team comprised Price and Jenny Mize, with Steinbeck Peninsula Equine Clinics in Menlo Park, California; and Samantha Barnum and Nicola Pusterla, with the Department of Medicine and Epidemiology at the University of California, Davis, School of Veterinary Medicine.

Price, D.; Barnum, S.; Mize, J.; Pusterla, N. Investigation of the Use of Non-Invasive Samples for the Molecular Detection of EHV-1 in Horses with and without Clinical Infection. Pathogens 2022, 11, 574. https://doi.org/10.3390/pathogens11050574

The study, published under a Creative Commons License, can be read here

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