Rate of natural transmission of Marek's disease virus (MDV) to susceptible chickens in the post-challenge period: effect of vaccination with HVT and association with MDV genome count in air

Marek's disease virus (MDV) is transmitted by inhalation of contaminated feather dander released by infected chickens. There is ongoing evolution of MDV to greater virulence. Investigation of the underlying causes requires determination of viral fitness under different conditions, in turn requiring determination of viral transmission rate between chickens. This study investigated the transmission rate of MDV to in contact chickens. MDV was quantified in blood, feather, spleen and dust of infected and HVT-vaccinated and unvaccinated in contact chickens in several treatments over a period of 28 days using real-time PCR. MDV was transmitted to 1 of 8 chickens (12.5%) prior to 12 days post infection (d.p.i.) and to 9/34 (26.5) and 2/34 (5.9%) unvaccinated and vaccinated chickens respectively between 12 and 28 d.p.i. Daily infection rate of uninfected chickens did not increase significantly after 21 d.p.i. MDV load in air increased significantly over time but was not clearly associated with infection rate.