Equine encephalomyelitis outbreak caused by a genetic lineage 2 West Nile virus in Hungary.

The study outlines an outbreak of Equine encephalomyelitis caused by a lineage 2 West Nile virus (WNV) amongst horses in Hungary. Interestingly, the lineage 2 WNV strain, usually considered nonpathogenic, exhibited similar neurological symptoms and survival rates as the pathogenic lineage 1 virus infections in previous outbreaks.

Objective and Methodology

The objective of the research was to understand the clinical and virological aspects of the first outbreak of lineage 2 West Nile virus encephalomyelitis in horses. The study involved analysis on 17 horses showing neurological signs of the disease.

• Data on each animal’s signalment, clinical signs, and outcome was collected.
• Serology, the study of blood serum, was carried out on 15 horses.
• A clinicopathological examination was conducted on 7 horses.
• Cerebrospinal fluid was collected from 2 horses for analysis.
• 4 horses underwent a histopathology examination, with 2 of these horses studied for presence of WNV in their nervous system.

Results

The findings showed that WNV neutralizing antibody titers in horses ranged between 10 and 270, with a median of 90. The symptoms most observed included ataxia, weakness, asymmetric gait, muscle tremors, hypersensitivity, cranial nerve deficits, and recumbency. Of the 17 horses affected, 12 survived.

Additionally, the viral strain was molecularly characterized through amplicons derived from the infection-positive specimens. This allowed the researchers to confirm that the virus, lineage 2 WNV, was indeed involved in the outbreak.

Conclusions

The findings concluded that the outbreak was caused by a lineage 2 WNV strain. This is noteworthy as such strains are typically considered nonpathogenic, yet the neurological signs and survival rates observed were on par with those reported for lineage 1 infection.

The research also noted that this outbreak indicated a geographic spread of the pathogen which was not typical in European outbreaks. This observed shift could be significant for future tracking and prevention strategies against such pathogens.