How are animal viruses primarily classified?

Animal viruses are primarily classified by the type of nucleic acid they contain, which can be either DNA or RNA. This classification is crucial because it provides insights into the virus's replication strategy, pathogenesis, and the specific immune responses they may elicit in the host. Nucleic acid type determines how the virus interacts with the host's cellular machinery to replicate, which influences both the characteristics of the virus and the types of treatments that may be effective against them.

While other classification methods, such as host species, size and shape, and transmission method, can provide useful information about a virus, they do not encompass the fundamental biological characteristics that define the virus's behavior and categorization in virology. Focusing on the nucleic acid type offers a more scientifically relevant and universally accepted basis for classifying viruses across various species, including those affecting animals.