Equine arteritis virus derived from an infectious cDNA clone is attenuated and genetically stable in infected stallions.

The research is about a form of equine arteritis virus (EAV) that has been genetically modified and is both attenuated and stable. When tested on stallions, the modified virus did not cause any visible signs of illness and remained genetically identical to the original virus.

Study Design and Implementation

• The study began with the creation of an equine arteritis virus (EAV030H) using a procedure designed to produce an infectious, but weakened (attenuated) virus based on a stable cDNA clone.
• Two stallions were intranasally inoculated with the genetically engineered virus. The health of the stallions was closely monitored after inoculation.
• Virus samples were taken from the stallions from their nasal swabs, semen, and mononuclear cells (a type of white blood cell).

Observations and Findings

• The researchers observed that the horses did not exhibit the symptoms associated with equine viral arteritis (EVA), indicating that the modified virus was indeed attenuated as intended.
• Isolation and analysis of the virus from different sources (nasal swabs, mononuclear cells, and semen) revealed the virus remained genetically stable.
• Both horses developed immunity (seroconverted) against EAV and maintained high neutralizing antibody levels. The constant presence of these put the body in a state of readiness to neutralize any active virus entering the body.

Analysis and Interpretation

• Next, viral RNA was detected using Reverse Transcriptase (RT) nested-PCR, helping to confirm the continued presence of the modified virus without causing disease symptoms.
• The sequence and restriction digestion analysis established the genetic stability of the virus. The virus found in the nasal swabs, mononuclear cells, and semen was identical to the original virus used for inoculation.
• The researchers concluded the modified virus stable during replication, a critical finding for potential future applications.

Implications of the research

• This study reports the first instance where a recombinant virus, derived from an order Nidovirales infectious cDNA, displayed competence to replicate in animals without causing illness.
• The researchers believed that these findings are significant for the development of new methods to study EAV, particularly the genetic factors which determine virulence (severity) and persistence.