Tests paint picture of exposure to common viruses in partially isolated horse herd

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Hucul horses graze in the Ukranian Mountains in the summer. Photo: AlexTodorchuk, CC BY-SA 4.0 via Wikimedia Commons

Researchers have taken a snapshot of common equine viral infections in a remote herd of a primitive horse breed native to the Carpathian Mountains of Europe.

The mainly isolated lives of the 20 Hucul horses enrolled in the study had not spared them from exposure to some of the most common equine viruses, the study team found.

Huculs, also known as Carpathian horses or Carpathian ponies, are a breed of primitive, small, mountain horses originally from the eastern part of the Carpathian Mountains.

The first written record of the animals dates back to the beginning of the 17th century. It is assumed that Huculs may be descendants of Tarpan horses mixed with Arabian horses, as well as Lipican, Hafling and Norik breeds.

Barbara Bażanów and her fellow researchers, in a study published in the journal Animals, set out to analyse the virological and immunological status of a semi-isolated herd of Hucul horses living in semi-natural conditions in a remote part of southwestern Poland, in the Kalisz District.

None of the horses had been vaccinated against any common equine viral infections. The animals had no contact with either other horses or wild equines, and they were kept on extensive pasture distant from inhabited areas throughout the year.

Blood samples and nasal swabs were taken from the animals, none of whom showed any clinical symptoms at the time of sampling.

The blood test results revealed the presence of antibodies against equine herpesvirus-1 in 12 horses (60%); equine Influenza A/H7N7 in 13 horses (65%), the H3N8 flu subtype in 12 horses (60%); Usutu virus in 5 animals (25%), and equine rhinitis A virus in 1 animal (5%).

The presence of antibodies indicates previous exposure to the viruses in question, but not necessarily a current infection.

Antibodies against equine arteritis virus, equine infectious anaemia virus, and West Nile virus were not present in the tested samples.

The nasal swab specimens were tested for equine rhinitis A virus, equine herpesvirus-1, equine arteritis virus and equine influenza virus. All were negative, indicating no ongoing infection with these viruses.

The study team noted that the H7N7 equine influenza subtype was first isolated in 1956 from horses in Eastern Europe. It has not been isolated since the last outbreak recorded in 1979 and was thought to be extinct.

“However, antibodies to this subtype are still detectable in horses, suggesting that it still circulates in equine populations.” During the last decade of the 20th century, H7N7-positive horses were reported in Belgium, Russia, the United States, India, and Nigeria.

They said the relatively high Usutu virus seropositivity detected in the horses corroborates the results of a survey recently carried out in Poland, where 27.98% of the tested horses were seropositive to this virus.

The seroprevalence of the Usutu virus is highly variable in Europe, they noted.

The authors said the serological data from this small group of horses, especially information concerning the absence of antibodies against certain viruses, cannot be extrapolated to the whole Hucul population in Poland, which number more than 1500.

“In order to understand the epidemiological status of the breed in our country in a statistically appropriate manner, a larger number of analyses need to be performed,” they said.

The study team said the findings provide useful epidemiological data regarding viral infections in Hucul horses, supplementing the sparse information available to date.

“Partial isolation of the tested herd, in addition to the fact that it was also devoid of any specific prophylaxis, allowed us to analyse the circulation within a local ecosystem of viruses causing infections in horses.

“The fact that the tested animals were apparently healthy at the moment of sampling and throughout the year prior suggests that the detected antibodies are a result of earlier exposures, but it may also be related to the natural resistance of Huculs, as indicated by other authors.

“In such a case, in order to recognise the epidemiology of viral infections concerning the breed, further serological surveys are required.”

The method of maintenance and lack of medical intervention makes the studied herd, despite its small size, a useful model of sentinel animals/surveillance, they said.

The study team comprised Bażanów, Janusz Pawęska, Aleksandra Pogorzelska, Magdalena Florek, Agnieszka Frącka, Tomasz Gębarowski, Wojciech Chwirot and Dominika Stygar, with a range of mostly Polish institutions.

Bażanów, B.; Pawęska, J.T.; Pogorzelska, A.; Florek, M.; Frącka, A.; Gębarowski, T.; Chwirot, W.; Stygar, D. Serological Evidence of Common Equine Viral Infections in a Semi-Isolated, Unvaccinated Population of Hucul Horses. Animals 2021, 11, 2261. https://doi.org/10.3390/ani11082261

The study, published under a Creative Commons License, can be read here

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