Equine herpesvirus 4 DNA in trigeminal ganglia of naturally infected horses detected by direct in situ PCR.

This research investigated the presence and location of equine herpesvirus 4 (EHV-4) DNA in the bodies of 15 horses, finding that the virus establishes latency in the trigeminal ganglia in a similar manner to other Alpha-herpesvirinae members.

Methodology and Findings

• In the study, 15 horses were selected randomly and their neuronal and lymphoid tissues were analysed after death using liquid nested-PCR, a method used for detecting and amplifying the DNA of EHV-4.
• Through this method, it was found that in 4 horses, the trigeminal ganglia were infected with EHV-4, and in one case the virus was detected in the lung.
• Using direct in situ PCR, a technique which allows for the precise localization of specific DNA sequences within a cell, the researchers found EHV-4 genome in the nuclei of neurons and in the bronchiolar and alveolar epithelium of the lung.
• Despite these findings, neither the virus nor viral antigens could be detected in the infected tissues. This might suggest that the virus was not actively replicating or causing disease at the time of examination.

Further Investigation and Discovery

• Further analysis using the more sensitive liquid RT-PCR technique, which is used for the detection of viral RNA, revealed active EHV-4 infection in one of the trigeminal ganglia by detecting viral transcripts coding for glycoprotein B.
• Glycoprotein B plays a crucial role in viral entry into the host cell and initiation of infection, and its detection is indicative of active viral infection.
• However, these transcripts were not detected in the other trigeminal ganglia and the lung, signifying a latent or inactive infection in these areas.
• This research thus formally proves that EHV-4, like other members of the Alpha-herpesvirinae family, establishes latency in the trigeminal ganglia in horses.