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Equine herpesvirus-1 (EHV-1) belongs to the subfamily Alphaherpesvirinae, and within that, to the genus Varicellovirus. It is an infectious disease that still causes significant economic damage, respiratory disease, abortion at the end of pregnancy, and neurological symptoms (myeloencephalopathy) in adult horses. It is efficiently transmitted by respiratory secretions and can persist in animals for long periods, a characteristic that has contributed to the outbreaks of several epidemics over the years. One of the most serious of these is the outbreak linked to the CES Valencia Spring Tour in Spain in January-February 2021, which has led to increased attention being paid to the infection and immunity of horses during the current competition season.

Although EHV-1 infection is an OIE-listed disease, it is not notifiable in Hungary, but after the outbreak in Valencia, there has been increased interest from both owners and practising veterinarians in the pre-competition screening for the virus and laboratory diagnostic testing of horses with symptoms of suspected infection. In my thesis, I summarise the results of the testing of samples received at the Virology Laboratory of the Department of Microbiology and Infectious Diseases of the University of Veterinary Medicine Budapest, as well as the detailed virological and epidemiological analysis of positive cases.

The laboratory received 457 samples during the study period (February 2021 to July 2022), of which 448 samples were tested for the presence of the virus, and 9 samples were tested for the detection of antibodies to confirm infection. Direct virus detection was performed by real-time polymerase chain reaction, 7 of the received samples were positive, and one was dubious. The positive samples were subjected to a detailed genetic analysis in collaboration with the Irish Equine Centre, which showed that none of the infections was linked to the Valencia outbreak but that the genetic pattern of the detected viruses correlated with clinical signs. In some of the samples sent for indirect virus detection, high antibody levels were measured, indicating recent infection, while other samples’ results suggest previous infection or reactivation of latent infection.

Based on the results of my study, I consider it necessary to map the EHV-1 epidemic situation in Hungary and raise awareness of herpesvirus infections among horse owners and veterinarians as well.