7 - Pathological responses to infection

Abstract

This chapter discusses the pathology and pathogenesis of Marek's disease (MD). The pathology of MD is complex and varies in different hosts. The changing pathology is mainly a result of changes in the virulence and tropism of the virus, although the mutations responsible are yet to be defined. Under natural conditions, MD infection is usually acquired by the inhalation of infective feather debris in the poultry house. Infection by Marek's disease virus (MDV) is followed by an early and persistent cell-associated viremia. The knowledge of the types of virus–cell interactions that occur in MD is crucial for understanding the pathogenesis and pathology of the disease. These interactions are common to a number of members of the family Herpesviridae, and they include (1) fully productive infection, (2) semiproductive infection, (3) nonproductive latent infection, and (4) nonproductive neoplastic infection. During an acute infection of a lymphoid tissue, other tissues may show evidence of a usually low-grade restrictively productive infection, characterized by cytolysis and often the presence of intranuclear inclusion bodies or lesions. The types of lesions are affected by factors such as virus strain and host. The ability to track the sites of virus replication and to characterize the nature of the cellular responses in MD has resulted in significant progress in the understanding of the molecular pathogenesis of the MD lesions.