Animals 2021, 11, 2851. https://doi.org/10.3390/ani11102851 www.mdpi.com/journal/animals Article Seroprevalence of Equine Herpesvirus 1 (EHV‐1) and Equine Herpesvirus 4 (EHV‐4) in the Northern Moroccan Horse Populations Zineb EL brini 1, *, Ouafaa Fassi Fihri 2 , Romain Paillot 3 , Chafiqa Lotfi 4 , Farid Amraoui 4 , Hanane El ouadi 4 , Mohamed Dehhaoui 5 , Barbara Colitti 6 , Hassan Alyakine 1 and Mohammed Piro 1 1 Department of Medicine, Surgery, and Reproduction, Agronomy and Veterinary Institute Hassan II, Rabat 10000, Morocco; hassanalyakine@gmail.com (H.A.); vetpiro@yahoo.fr (M.P.) 2 Department of Microbiology, Immunology and Contagious Diseases, Agronomy and Veterinary Institute Hassan II, Rabat 10000, Morocco; fassifihri.ouafaa@gmail.com 3 School of Equine and Veterinary Physiotherapy, Writtle University College, Lordship Road, Writtle, Chelmsford CM1 3RR, UK; romain.paillot@writtle.ac.uk 4 Society of Veterinary Pharmaceutical and Biological Productions (Biopharma), Rabat 10000, Morocco; c.loutfi@biopharma.ma (C.L.); amraoui.farid@gmail.com (F.A.); hananelouadi@gmail.com (H.E.) 5 Department of Statistics and Applied Informatics, Agronomy and Veterinary Institute Hassan II, Rabat 10000, Morocco; dehhaoui@yahoo.fr 6 Department of Veterinary Sciences, University of Turin, largo Braccini 2, 10095 Grugliasco, Italy; barbara.colitti@unito.it * Correspondence: zinebelbrini@gmail.com; Tel: +212‐6‐70‐52‐95‐32 Simple Summary: This work aims to evaluate the seroprevalence of equine EHV‐1/4 in horse pop‐ ulations in the north of Morocco and to measure the antibody titers in vaccinated horses, under field conditions, with monovalent EHV‐1 vaccines. Overall, 12.8% unvaccinated, and 21.8% vaccinated horses were positive for EHV‐1. All samples were positive for EHV‐4 when tested with the type‐ specific ELISA. The virus neutralization test showed low antibody titers in samples from vaccinated horses. Our study demonstrated that EHV‐1 and EHV‐4 are endemic in the horse populations in the north of Morocco and highlighted the necessity of reevaluating the vaccines and the vaccination protocol used. Abstract: This study reports the first equine herpesvirus‐1 (EHV‐1) and equine herpesvirus‐4 (EHV‐ 4) seroprevalence investigation in horse populations of Morocco in 24 years. It also aims to deter‐ mine antibody titers in horses vaccinated under field conditions with a monovalent EHV‐1 vaccine. Blood samples were collected from 405 horses, including 163 unvaccinated and 242 vaccinated ani‐ mals. They were tested using a commercial type‐specific enzyme‐linked immunosorbent assay (ELISA) and a virus neutralization test (VNT). Overall, 12.8% unvaccinated, and 21.8% vaccinated horses were positive for EHV‐1. All samples were positive for EHV‐4 when tested with the type‐ specific ELISA. In the vaccinated group, the VNT revealed a mean antibody titer of 1:49 for EHV‐1 and 1:45 for EHV‐4. The present study demonstrates that EHV‐1 and EHV‐4 are endemic in the horse populations in the north of Morocco, with prevalence differences between regions. Further‐ more, horses vaccinated with a monovalent EHV‐1 vaccine had low antibodies titers. This study highlights the necessity to establish and/or support efficient biosecurity strategies based on sound management of horses and characterize further and potentially improve the efficiency of the EHV vaccines and vaccination protocol used in the field. Keywords: EHV‐1; EHV‐4; seroprevalence; ELISA; VNT; Morocco Citation: EL brini, Z.; Fassi Fihri O.; Paillot, R.; Loutfi, C.; Amraoui, F.; EL ouadi, H.; Dehaoui, M.; Colitti, B.; Alyakine, H.; Piro, M. Seroprevalence of Equine Herpesvirus 1 (EHV‐1) and Equine Herpesvirus 4 (EHV‐4) in the Northern Moroccan Horse Populations. Animals 2021, 11, 2851. https://doi.org/10.3390/ani11102851 Academic Editors: Amir Steinman and Oran Erster Received: 5 July 2021 Accepted: 23 September 2021 Published: 29 September 2021 Publisher’s Note: MDPI stays neu‐ tral with regard to jurisdictional claims in published maps and institu‐ tional affiliations. Copyright: © 2021 by the authors. Li‐ censee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and con‐ ditions of the Creative Commons At‐ tribution (CC BY) license (http://crea‐ tivecommons.org/licenses/by/4.0/).