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In Switzerland, a 16-year-old Holstein horse was plagued by neurological problems and was diagnosed with tick-borne encephalitis. Researchers report that he is recovering well.
The case report, published in the journal Virus, is the first to describe the recommended diagnostic criteria for horses in humans with suspected tick-borne encephalitis virus (TBEV) infection.
Tick-borne encephalitis can cause neurological symptoms in humans and animals. Research on its occurrence in horses includes reports of non-specific and neurological symptoms. However, only one horse with obvious neurological symptoms was confirmed after death in an earlier published case study.
Nathalie Fouché and her colleagues pointed out that so far, no investigation has been conducted on the seroprevalence of the virus in Swiss horse herds. In other European countries, the seroprevalence of horses (indicating previous exposure to the virus) ranges from 2.9% to 37.5%.
The horse in the case study was referred for evaluation after showing lack of coordination and lethargy. He also showed muscle tremors and slight sweating.
Before being referred to the equine hospital, the steers were treated with Analgin (a painkiller and antispasmodic) and the anti-inflammatory drug dexamethasone.
At home, this horse has been kept in a stable and can go to the ranch with other horses in rural areas every day. The steers have never traveled abroad, nor have they traveled within Switzerland.
According to the owner, this horse is often bitten by ticks, except in winter.
In the hospital, the horse's heart rate was found to increase. In the first clinical examination, the animal was smart, responsive, and mentally active. There is no cranial nerve defect except for suspected mild facial nerve palsy with drooping right upper and lower lip.
Also noticed a slight decrease in the asymmetry of the right temporal muscle. The horse's nostrils, lips and eyelids showed subtle muscle twitches and tremors.
Gelding eats, drinks, defecates and urinates normally.
During the first 24 hours of hospitalization, the horse showed severe lethargy, during which time the horse was observed to drift to the right uncoordinatedly while walking. The hind limbs are more pronounced than the forelimbs.
Perform complete blood count and serum biochemical analysis, and collect cerebrospinal fluid samples for analysis. The results of the horse’s laboratory examination showed viral infection and systemic inflammation.
Molecular testing of horse samples confirmed TBEV infection, and there is evidence of acute and recent infection.
Treatment includes the non-steroidal anti-inflammatory drug flunixin meglumine, the steroid prednisolone, and vitamin E.
The horse was hospitalized for six days and continued to exhibit muscle twitches and lethargy, during which time a lack of coordination was still observed.
The clinical symptoms gradually became less obvious and infrequent, and disappeared at the end of the 6th day of hospitalization. The horse was discharged from the hospital, but continued to take the medicine for two weeks.
Three weeks after being discharged from the hospital, the horse was re-examined. According to the owner, the important parameters were within the normal range and the horse did not show any signs of lethargy.
Nervous system examination was normal, except for slight persistent facial asymmetry and drooping right nostril.
The owner reported that the steer showed no signs of illness 12 months after being discharged from the hospital.
"All in all, this is the first report describing the pre-mortem diagnosis of TBEV in horses based on the diagnostic criteria recommended by human medicine.
"This diagnostic protocol can be used to investigate TBEV infection in horses that live in endemic areas and exhibit compatible neurological symptoms.
"We recommend that after excluding potential West Nile virus infections, combined with seasonal tick activity, diagnostic tests for neurological cases with uncertain etiology (causes), even in countries that are not considered to be West Nile virus infections."
When discussing their findings, the authors pointed out that recent serological and PCR investigations of horses showed that only a few horses were exposed to and infected with the virus and developed neurological symptoms—similar to humans.
Despite this, the increased awareness and testing of West Nile virus infection (and related testing for TBEV infection) in Europe has also raised suspicions about TBEV-related neurological diseases.
"However, to date, reports on the investigation of pre-mortem diagnosis of suspected cases are limited. Raising awareness of the disease should encourage equine veterinarians to investigate suspected clinical cases in accordance with human diagnostic guidelines."
The definition of a virus case is the presence of clinical symptoms of meningitis, meningoencephalitis, or meningoencephalomyelitis, an increase in the white blood cell count in the cerebrospinal fluid, and the presence of specific antibodies against the virus, including cerebrospinal fluid or TBEV immunoglobulin G seroconversion.
The treatment of humans and animals focuses on reducing the signs of disease because there is no antiviral treatment available.
The researchers said that the horses in the case study responded well to the combination of anti-inflammatory drugs and antioxidant therapies.
Currently, disease prevention is limited to reducing contact with potentially infected ticks in endemic areas.
The case report team consisted of Fouché, Solange Oesch and Vinzenz Gerber of the Swiss Equine Institute of the University of Bern; and Ute Ziegler, in collaboration with the newly emerging Institute of Infectious Diseases, which is owned by the Friedrich Loeffler Institute Part.
Foucher, N.; Ersch, S.; Ziegler, USA; Gerber, V. Clinical manifestations and laboratory diagnostics of a horse with tick-borne encephalitis in Switzerland. Virus 2021, 13, 1474. https://doi.org/10.3390/v13081474
The case report published under the Creative Commons license can be read here.
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