Chapter 8.1, Problem 1QC

Summary Introduction

To explain: The way by which antigenic changes in the viral pathogens promote diseases.

Concept introduction: Antigenic variation is the mechanism in which an infectious agent like protozoa, bacterium and virus change the surface proteins to avoid the immune response from host. Antigenic variation enables immune invasion by pathogens. It will also allow the microorganisms to cause re-infection.

Explanation of Solution

The antigen variations that takes place in the viral pathogens can promote diseases. The antigenic variation that takes place in the viruses consists of six categories called the antigenic drift, shift, and rift, sift, lift, and gift. Usually, antigenic variations are minor and results from mutations.

Influenza A undergoes major antigenic changes. The virus can infect birds and mammals, and shifts occur in the animals coinfected by a human and an avian strain of influenza. The viral genome is segmented and undergoes recombination during which the human virus get new HA or NA antigen. When the shift is not occurred, clinical influenza will be considered as epidemic. When the major antigenic variation occurs, earlier protection may not exist. This results in a major pandemic and much more severe diseases.