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

Abstract

Rispens et. al. (1972) showed that low passage CVI988 Rispens virus spread laterally while Witter et al. (1987) found limited transmission with a higher passage vaccinal strain. To test whether current vaccinal strains of the virus transmit effectively we measured the shedding rate, lateral transmission and changes in viral load over time. In each of three rooms, 10 SPF chickens were vaccinated at day old with one of the three commercial Rispens vaccines available in Australia and left in contact with 10 unvaccinated chickens for 56 days post vaccination. A separate room contained unvaccinated control birds. As determined by quantitative real-time PCR of room dust and peripheral blood lymphocytes, vaccine virus was shed from the vaccinated chickens in dander from day 7 and transmitted effectively to in-contact chickens, producing higher viral loads in these birds than observed in the vaccinated chickens. However, there was a lag time of 2-3 weeks in infection of in-contact birds.