Researchers describe fatal equine herpesvirus-4 outbreak at donkey farm in Romania

Nine deaths were reported, as well as abortions. The authors want more extensive seroprevalence studies on EHV-4 in the country.
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A fatal outbreak of equine herpesvirus-4 (EHV-4) at an ecological donkey milk farm in Romania has been described by researchers, who say there is a need for more extensive seroprevalence studies to assess the status of the virus in the country.

Early in April last year, 37 donkeys at the farm in southwest Romania started showing signs of severe respiratory disease after the previous introduction – 12 days before the first symptoms – of a newly acquired and unquarantined jenny.

The farm was home to 290 jennies and 10 uncastrated males, as well as two horses. The animals had full access to the outdoors, with no rigorous separation between paddocks. One stable was designated for temporary housing.

Alexandra Mureşan and her fellow researchers, writing in the journal Vaccines, noted that none had been vaccinated in the preceding two years for any infectious disease. Some had baseline immunization against tetanus and influenza, but none had immunity against equine herpesvirus.

None had been dewormed in the preceding three years, and they had not received professional medical care such as teeth or hoof evaluation and treatment.

The affected animals initially showed a clear nasal discharge, which progressed to containing mucus and pus. In some cases, the animals were affected by shortness of breath and severe apathy, as well as coughing and a fever.

During the course of two weeks, there were 10 fetal losses – eight were stillborn and in two cases the foals died several hours after birth.

Three donkeys developed neurological problems accompanying their respiratory symptoms.

There were eight deaths on the farm in the first ten days of the outbreak, and one was euthanized in a referral clinic due to the severity of the disease.

The owner agreed to impose biosecurity measures on the farm, including complete quarantine of sick animals, with different caretakers and a different pasture. Regular temperature-taking was introduced for all remaining clinically healthy animals, and they were isolated if it was elevated. The stable where the outbreak started was also disinfected.

They said the rapid containment of the outbreak after the initial cases suggests that the biosecurity measures were effective.

Testing of samples from the sick donkeys revealed the presence of EHV-4.

Discussing the outbreak, the authors said the lack of a clear protocol at the state level, as well as not having a thorough national animal disease reporting system, rendered these types of outbreaks even more dangerous.

To date, there have been no World Animal Health Information System reports on herpesvirus infections in Romania lodged in the World Organisation for Animal Health (OIE) database, they noted.

“Romania still relies on working equids and donkeys in agriculture and cohabitation with horses is frequent; thus, exposure to viruses can become a stringent problem,” they said.

It is possible that the seroprevalence of EHV-4 is high but yet remains unknown, they said. “Several seroprevalence studies in donkeys have shown that this is the case in many countries where donkeys are common.

“The risk of transmission of disease lies not only in the rest of the country but also across the border as Hungary is very close to the location of the outbreak premises.”

The herd at the centre of the outbreak had several weak management strategies, they said, including a non-existent pasture management protocol (no organization when moving from pasture to pasture and no cleaning of pastures between lots of donkeys), lack of organized feeding (competitive feeding) and poor housing (rudimentary stalls, porous walls, irregular cleaning of bedding, low ceilings and reduced ventilation). These had possibly led to increased transmission of disease, and preventative care was lacking.

The entire herd had never been vaccinated against the virus.

“The situation in Romania regarding EHV-4 is quite similar to other countries where owner education is lacking and infectious upper respiratory tract infections are not regarded as a dangerous potential threat to animal health and production.

“Regular immunization remains questionable for EHV-4 infection prevention, as even in vaccinated individuals, the virus circulates especially between mares and foals,” they said. However, repeated vaccination might lessen economic losses within farms by preventing abortion storms, and result in milder clinical symptoms.

The authors said their work represents the first reported outbreak of EHV-4 in Romania.

“The large increase in donkey population in the country renders the investigation and report of such outbreaks vital,” they said.

The high level of illness caused by the infection on this farm suggests that specific management conditions might contribute to the expression of more severe clinical disease, with high impacts on the medical and economic status of the herd.

“There is a need for more extensive seroprevalence studies as, currently, the status of EHV-4 infections in donkeys in Romania is unknown,” they concluded.

The study team comprised Alexandra Mureşan, Cosmin Mureşan, Madalina Siteavu, Electra Avram, Diana Bochynska and Marian Taulescu, variously affiliated with the University of Agricultural Sciences and Veterinary Medicine of Cluj-Napoca, Synevovet Laboratory, and the University of Agronomic Sciences and Veterinary Medicine, all in Romania.

Mureşan, A.; Mureşan, C.; Siteavu, M.; Avram, E.; Bochynska, D.; Taulescu, M. An Outbreak of Equine Herpesvirus-4 in an Ecological Donkey Milk Farm in Romania. Vaccines 2022, 10, 468.

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

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