STOP PRESS: EHV-1 Myeloencephalopathy

STOP PRESS

Mare showing dysmetria and somnolence during first outbreak of EHM in NZ in 2014. [McFadden et al. (2016).

EQUINE HERPESVIRUS MYELOENCEPHALOPATHY

A case of suspected equine herpesvirus-related Equine Herpesvirus Myeloencephalopathy [EHM] has been identified at a property in the North Island. As we look ahead towards a busy breeding, racing and performance season this serves as a timely reminder to equine veterinarians and the wider equine community to remain vigilant. Recent and continuing outbreaks of EHM in North America and Europe have illustrated the potentially devastating implications of this condition. These outbreaks can be associated with high mortality rates, widespread geographical transmission and significant economic damage to the respective equine industries. While only one confirmed outbreak of EHM has been documented in New Zealand (McFadden et al, 2014) this remains an ever-present threat given the difficulty of identifying carriers of latent disease (Bueno et al. 2019) and importation of horses into NZ from countries with a higher disease prevalence. Equine Herpesvirus is a ubiquitous and highly contagious pathogen affecting equine populations worldwide. EHV-1 infection results in multiple syndromes, most commonly respiratory disease but occasionally abortion, neonatal death and neurological syndromes. Different strains vary in their abortogenic and neuropathogenic potential, with the G

2254/D752 Pol variant predominantly associated with EHM outbreaks. Clinical effects are attributable to the effects of damage to the microvasculature of the uterus, the CNS and other organs. Although vaccination with a whole inactivated vaccine during pregnancy helps to reduce rates of transmission and abortion within a group, abortion storms in naïve populations can be devastating. There is currently no vaccine available which claims to protect against the clinical signs of EHM; hence early identification of disease and prompt implementation of stringent biosecurity strategies are essential to prevent transmission and reduce morbidity and mortality within a population. Recently updated International Codes of Practice from the Horserace Betting Levy Board (https://codes.hblb. org.uk/index.php/page/76) and ECEIM Guidelines for dealing with returning horses from EHV-1 outbreaks (https://www.eceim.info/news/outbreak-of-ehv-1-invalencia-update-16th-march-2021) provide invaluable guidance if faced with a potential outbreak situation in a breeding and performance operation respectively. FURTHER READING

Bueno, I. M. C., Pearce, P., & Dunowska, M. (2019). Frequency of latent equine herpesvirus type-1 infection among a sample of horses in the central North Island of New Zealand. NZ Vet J DOI: 10.1080/00480169.2019.1653238 Ivens, P. et al. (2019). Equine herpesviruses: a roundtable discussion. UK-Vet Equine, 3(Sup4), 1-12. 10.12968/ukve.2019.3.S2.1 Khusro, A., Aarti, C., Rivas-Caceres, R. R., & Barbabosa -Pliego, A. (2020). Equine Herpesvirus-I Infection in Horses: Recent Updates on its Pathogenicity, Vaccination, and Preventive Management Strategies. J Eq Vet Sci, 87, 102923. https://doi.org/10.1016/j. jevs.2020.102923 Maxwell, L. K. et al. (2017). Efficacy of the early administration of valacyclovir hydrochloride for the treatment of neuropathogenic equine herpesvirus type-1 infection in horses. Am J Vet Res, 78(10), 1126-1139. 10.2460/ajvr.78.10.1126 McFadden, A. M. et al. (2016). The first reported outbreak of equine herpesvirus myeloencephalopathy in New Zealand. N Z Vet J, 64(2), 125-134. 10.1080/00480169.2015.1096853 http://www.sciquest. org.nz/node/111147] Oladunni, F. S., Horohov, D. W., & Chambers, T. M. (2019). EHV-1: A Constant Threat to the Horse Industry. Front Microbiol, 10 10.3389/fmicb.2019.02668 Soboll Hussey, G. et al. (2019). Histopathologic Findings Following Experimental Equine Herpesvirus 1 Infection of Horses. Front Vet Sci, 6, 59. 10.3389/fvets.2019.00059

This Stop Press was prepared by colleagues handling the current case, who are doing a sterling job of enacting current recommended biosecurity control measures.