The presence of Equine herpesvirus-3 (EHV-3) has been confirmed for the first time in the native Icelandic horse population.
The finding, reported in the journal Acta Veterinaria Scandinavia, means that four types of equine herpesvirus have been identified in horses in Iceland — EHV-2, EHV-4, EHV-5, and now EHV-3.
EHV-1 has never been detected in a horse living in the island nation.
EHV-3 is behind a contagious venereal disease known as equine coital exanthema (ECE). It is characterized by papules, vesicles, pustules and ulcers on the external genitals of mares and stallions.
Lilja Thorsteinsdóttir and her colleagues, in a brief communication, noted that symptoms resembling ECE have previously been seen in horses in Iceland, arousing suspicions of EHV-3 infection, but this has never been confirmed by testing.
Samples were collected from a three-year-old Icelandic mare with papules on her vulva, with molecular-based testing confirming the presence of EHV-3.
“On the basis of the findings, EHV-3 infection was verified for the first time in the native Icelandic horse population.” the scientists reported.
EHV-3, first isolated in 1986, has worldwide distribution.
In uncomplicated cases, healing of the lesions is usually completed within 10 to 14 days, but scars can persist.
General signs of infections, such as fever, dullness and loss of appetite, are sometimes more intense in stallions than in mares. Stallions with extensive lesions can exhibit loss of sex drive and refuse to mate with mares.
However, the virus is non-invasive and the disease relatively benign. It does not usually result in systemic illness, the authors noted.
After primary infection, the virus establishes a latent infection.
The Icelandic horse is the only breed in Iceland and has lived isolated in the country for more than 1000 years.
Due to the isolation, the horses are immunologically naïve to many pathogens known to infect horses in other countries.
However, the authors noted that Icelandic horses can now be found in more than 30 countries worldwide, and less than one-third of the population is living in Iceland.
“They are still retained as a closed population and the import of horses as well as semen and embryos is prohibited by law.”
However, the growing popularity of the breed abroad, with frequent traveling of people working with Icelandic horses, offers a threat to the unique infectious status, they said.
“Consequences of this can be seen in several introductions of new infectious equine agents in recent decades.
“Therefore it is of importance to have an updated overview and knowledge of infectious agents already present in the population.”
They said the prevalence of EHV-3 infections in Iceland is unknown and yet to be examined, but until now infections with EHV-3 have not been considered to have a severe impact on horse breeding in Iceland.
“We have previously speculated that the absence of EHV-1 infections in the Icelandic horse population might indicate that this virus was not as common in Europe in the 9th and 10th centuries as it is today.
“The existence of ECE in the Icelandic horse breed could indicate the opposite for EHV-3, i.e. that the virus was common in horses in medieval Europe.”
The brief communication was provided by Lilja Thorsteinsdóttir, Sigurbjörg Torsteinsdóttir and Vilhjálmur Svansson, all with the University of Iceland; and Gunnar Örn Guðmundsson and Höskuldur Jensson, who undertook the clinical examination of the mare and collected the sample.
The work received funding from the Icelandic Horse Conservation Fund.
Thorsteinsdóttir, L., Guðmundsson, G.Ö., Jensson, H. et al. Isolation of equid alphaherpesvirus 3 from a horse in Iceland with equine coital exanthema. Acta Vet Scand 63, 6 (2021). https://doi.org/10.1186/s13028-021-00572-4