5 - Marek's disease: A worldwide problem

Abstract

This chapter discusses the epidemiology of Marek's disease (MD). The major causes of MD outbreaks are improper handling of the vaccines, unhygienic conditions, influence of other pathogens that cause immunosuppressive effects, stressful situations, and the evolution of new Marek's disease virus (MDV) variants. After introduction of the first group of MD vaccines—such as the serotype 3 herpesvirus of turkeys (HVT) vaccine—field problems from MD appeared to be controlled. The CVI988 (Rispens) vaccine was certainly the savior of poultry industries worldwide during the 1990s. Although the infection decreased in the vaccinated birds, the vaccine was not capable of inducing immune responses that protected against infection and shedding. Consequently, there was a presence of a continuous virus reservoir in these flocks. The other approach for preventing MD problems is the introduction of best practice at all stages of the production process. Such practices include (1) auditing of the storage, (2) reconstitution and administration of the vaccines, (3) implementation of standard operating procedures for various methods, (4) checking the compatibility of additives to the MD vaccines, and (5) the use of coloring dyes while administering vaccines to confirm vaccine uptake. Currently, no major MD problems appear to be uncontrolled with existing technologies around the world.