Equine Herpesvirus Type 4 (EHV-4) Outbreak in Germany: Virological, Serological, and Molecular Investigations

Abstract

Equine herpesvirus type 4 (EHV-4) is enzootic in equine populations throughout the world. A large outbreak of EHV-4 respiratory infection occurred at a Standardbred horse-breeding farm in northern Germany in 2017. Respiratory illness was observed in a group of in-housed foals and mares, which subsequently resulted in disease outbreak. Out of 84 horses in the stud, 76 were tested and 41 horses were affected, including 20 foals, 10 stallions, and 11 mares. Virological investigations revealed the involvement of EHV-4 in all cases of respiratory illness, as confirmed by virus isolation, qPCR, and/or serological follow-up using virus neutralization test and peptide-specific ELISA. Among infected mares, 73% (8 out of 11) and their corresponding foals shed the virus at the same time. EHV-4 was successfully isolated from four animals (including one stallion and three foals), and molecular studies revealed a different restriction fragment length polymorphism (RFLP) profile in all four isolates. We determined the complete 144 kbp genome sequence of EHV-4 isolated from infected horses by next-generation sequencing and de novo assembly. Hence, EHV-4 is genetically stable in nature, different RFLP profiles, and genome sequences of the isolates, suggesting the involvement of more than one animal as a source of infection due to either true infection or reactivation from a latent state. In addition, epidemiological investigation revealed that stress caused by seasonal changes, management practices, routine equestrian activities, and exercises contributed as a multifactorial causation for disease outbreak. This study shows the importance of implementing stress alleviating measures and management practices in breeding farms in order to avoid immunosuppression and occurrence of disease.

An Outbreak of Equine Herpesvirus-4 in an Ecological Donkey Milk Farm in Romania

“…Pusterla et al 2011 [ 11 ], as well as Badenhorst et al [ 8 ], note that the months with a higher incidence are usually during fall–winter; Matsumura et al [ 39 ] concluded that infections can become clinically overt year-round. Our outbreak took place during the seasonal change to spring, similarly to a very recent paper on EHV4 outbreak in German horses [ 40 ]. While most reports [ 1 , 2 , 8 ] note that EHV-4 infections are usually inapparent and proceed unnoticed, the outbreak in the Romanian farm had a higher morbidity than expected and led to significant economic losses.…”

“…Abortions have rarely appeared in mares infected with EHV-4 [ 50 , 51 , 52 ]; however, in our case, 24.32% of the jennies with clinical symptoms aborted—either due to the virus itself or due to poor conditions. In the most recent paper on an EHV-4 outbreak [ 40 ], the authors have not noted any abortions nor mortality; thus, our outbreak might have involved a different strain or had other external factors that influenced the outcome and might warrant a more in-depth look into genotyping the viral strain.…”

Respiratory and Reproductive Tract Disorders Causing Herpesviruses in Animals

“…Clinical signs are fever, serous nasal discharge, malaise, pharyngitis, cough, indigestion, and enlargement of regional lymphnodes. Secondary bacterial infections are not uncommon which worsen the respiratory symptoms leading to pulmonary disease (Pavulraj et al 2021). Horses which already have encountered the virus previously develop antibodies which give some protection and only mild infection occurs in subsequent attacks.…”

“…Serologic testing of mares after abortion has little diagnostic value. Recently, peptidebased ELISA has been developed that not only confirms the increasing levels of EHV-1 antibodies in mares but also allow differentiation of EHV-1 and EHV-4 specific antibodies (Pavulraj et al 2021).…”

“…A third dose is also recommended in virus prevalent areas at the age of 10-12 months. In pregnant mares, vaccination should be performed more frequently at 3rd, 5th, 7th, and 9th month of pregnancy with inactivated EHV-1/EHV-4 ( (Bryant et al 2018;Pavulraj et al 2021).…”