Modelling Marek's Disease Virus (MDV) infection: parameter estimates for mortality rate and infectiousness
1 Centre for Infectious Diseases, University Of Edinburgh, West Mains Road, EH9 3JT, UK
2 Center for Infectious Disease Dynamics, Departments of Biology and Entomology, 208 Mueller Laboratory, The Pennsylvania State University, University Park, PA 16802, USA
3 Centre for Animal Health and Welfare, School of Environmental and Rural Science, The University of New England, Armidale NSW 2351, Australia
4 Department of Epidemiology and Public Health, Yale School of Medicine, New Haven, CT 06510
BMC Veterinary Research 2011, 7:70 doi:10.1186/1746-6148-7-70Published: 11 November 2011
Marek's disease virus (MDV) is an economically important oncogenic herpesvirus of poultry. Since the 1960s, increasingly virulent strains have caused continued poultry industry production losses worldwide. To understand the mechanisms of this virulence evolution and to evaluate the epidemiological consequences of putative control strategies, it is imperative to understand how virulence is defined and how this correlates with host mortality and infectiousness during MDV infection. We present a mathematical approach to quantify key epidemiological parameters. Host lifespan, virus latent periods and host viral shedding rates were estimated for unvaccinated and vaccinated birds, infected with one of three MDV strains. The strains had previously been pathotyped to assign virulence scores according to pathogenicity of strains in hosts.
Our analyses show that strains of higher virulence have a higher viral shedding rate, and more rapidly kill hosts. Vaccination enhances host life expectancy but does not significantly reduce the shedding rate of the virus. While the primary latent period of the virus does not vary with challenge strain nor vaccine treatment of host, the time until the maximum viral shedding rate is increased with vaccination.
Our approach provides the tools necessary for a formal analysis of the evolution of virulence in MDV, and potentially simpler and cheaper approaches to comparing the virulence of MDV strains.