First evidence of Schmallenberg virus exposure in horses

The Schmallenberg virus. Photo: AJC ( CC BY-SA 2.0 via Wikimedia Commons
The Schmallenberg virus. Photo: AJC ( CC BY-SA 2.0 via Wikimedia Commons

Researchers in Iran have found evidence of an immune response among horses to the Schmallenberg virus that affects livestock in Europe.

While the presence of antibodies points to the exposure of horses to the virus, and a reaction by their immune system, it does not necessarily mean they suffered ill-health as a result.

Schmallenberg virus affects mainly ruminants – sheep, cattle and goats. It was first documented in Northern Europe in August 2011, with subsequent outbreaks across the continent. The first reported cases in Britain occurred in January 2012.

It is classified as an orthobunyavirus, some of which have been reported to cause disease in horses.

Schmallenberg appears to be spread by Culicoides biting midges. It can cause a brief fever, diarrhoea and reduced milk production in cows, and in pregnant animals it can trigger congenital malformations in newborns, often without the mother showing outward signs of illness.

Mehdi Rasekh and his colleagues from the University of Zabol in Iran set out to test the blood of horses in the north and northeast of the country for antibodies to the virus.

Blood samples were taken from 200 healthy horses from different rural areas for analysis.

The study team then employed what is known as an ELISA test – an enzyme-linked immunosorbent assay. It is a plate-based test technique designed to detect substances such as proteins, antibodies and hormones.

The study team used a multispecies ELISA test kit sourced from France designed to specifically detect antibodies to the Schmallenberg virus.

Ten of the 200 samples (5%) were positive for Schmallenberg antibodies and a further four (2%) were assessed as doubtful. In all, 186 were negative.

Rasekh and his colleagues, writing in the journal Veterinary World, said published reports to date revealed no serological evidence of Schmallenberg virus antibodies in horses.

“Thus, this is the first serological report which detected the Schmallenberg virus antibody in the equine population.”

The researchers said the high population and activity of Culicoides midges, and the good living conditions for them, especially in temperate and humid parts of Iran, are the possible causes of insect-borne diseases in the country.

They said unpublished data from another study performed by the current authors reveals
a “considerable level” of antibody against Schmallenberg virus among the ruminant population of Iran.

The authors stressed that while their testing revealed antibodies against the virus in horses, “more
solid shreds of evidence are needed to conclude the association between seropositivity and existence of
the disease.”

The ELISA testing should be repeated to express the definite existence of the disease, they said. They also proposed the use of more accurate testing techniques.

Rasekh’s fellow researchers were Ali Sarani and S. H. Hashemi, all of whom are with Zabol University’s Department of Clinical Sciences, within its Faculty of Veterinary Medicine.

Rasekh M, Sarani A, Hashemi SH (2018) Detection of
Schmallenberg virus antibody in equine population of Northern and North-East of Iran, Veterinary World, 11(1): 30-33.

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

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