Distribution and relevance of equine herpesvirus type 2 (EHV-2) infections.

This research investigates the prevalence and pathogenicity of Equine herpesvirus type 2 (EHV-2), a virus commonly found in horses, within the German equine population. Despite its ubiquity, the virus’s cell and tissue specificity and harmful effects are not fully understood, prompting an extensive study involving serum samples from 172 horses.

Methodology

• The study utilized both a nested polymerase chain reaction (PCR), a highly specific DNA detection technique, and classical cocultivation, a method of growing cells in culture, to analyze peripheral blood leucocytes (PBL) – a type of white blood cell – from 172 horses for the presence of EHV-2 DNA.
• The PCR-based method targeted the EcoRI-N genomic fragment of the EHV-2 virus, a specific portion of its DNA.

Results

• The PCR tests indicated that about 51% of the horses’ PBL samples were positive for EHV-2. Meanwhile, through cocultivation, the virus was isolated from 31% of the horses.
• Surprisingly, nearly all the horses tested were found to have antibodies for EHV-2, suggesting that PBL may not indefinitely harbor the virus after infection.
• No direct correlation was established between clinical signs of illness and EHV-2 presence. However, the study noted a high prevalence of the virus among horses with symptoms of upper respiratory tract disease, abortion, and severe ataxia (a neurological disorder affecting balance, coordination, and speech).

PCR results and implications

• Products from the second round of PCR testing showed size differences, attributed to repeat sequences of a specific motif in the viral DNA. These repeats occurred between 9 to 16 times, varying by isolate.
• The variations in repeated motifs suggest the nested PCR method’s potential as an effective tool in the differentiation of EHV-2 isolates.

The research presents insights into the prevalence of EHV-2 within an equine population, its lack of lasting presence in PBL, and its highly varied presentation among horses showing symptoms of disease. The study also highlights the importance of exploring tools for effectively differentiating EHV-2 isolates for future research.