Viral load, shedding rate and lateral transmission of Marek's disease vaccinal virus (Rispens/CV1988) in SPF chickens

Abstract

The Rispens (CVI988) attenuated Serotype 1 Marek's Disease virus vaccine is highly effective and used worldwide. It has been shown that this virus is present in feather tips of vaccinated chickens but the extent to which current commercial Rispens vaccines transmit effectively between chickens is unknown. To determine this, we measured the shedding rate, lateral transmission and changes in viral load over time, of the three commercial Rispens vaccines available in Australia. In each of three climate-controlled rooms, 10 SPF (specific pathogen free) chickens were vaccinated with a commercial Rispens vaccine at day old and left in contact with 10 unvaccinated chickens. A separate room contained unvaccinated control birds. As determined by quantitative real-time polymerase chain reaction (PCR) of room dust and peripheral blood lymphocytes (PBL), vaccine virus was shed from the vaccinated chickens in dander from day 7 and transmitted effectively from vaccinated to in-contact chickens with a lag period of 2-3 weeks.