In EHV-1 infection, what is the main prerequisite leading to abortions and equine herpes myeloencephalopathy?

• A. Transmission via mosquitoes
• B. Viremia
• C. Latent infection
• D. Infection by 2 years of age

Answer: (B)

Systemic spread through viremia is what allows EHV-1 to cause its most severe outcomes. After the virus is acquired via the respiratory tract, it must enter the bloodstream to reach distant sites. When viremia occurs, the virus can reach the uterus and infect the placenta, leading to abortion, and it can also invade vascular endothelium in the central nervous system, producing the vasculitis and neurologic signs of equine herpes myeloencephalopathy. Latent infection is a normal feature of herpesviruses and explains reactivation potential, but abortions and EHM happen during active viremia with tissue dissemination, not from latency alone. Mosquito transmission is not a known route for EHV-1, and age at infection does not determine these outcomes.