Which of the following diseases is least likely to be viral?

The bubonic plague is caused by the bacterium Yersinia pestis, making it a bacterial disease rather than a viral one. This distinguishes it from the other options listed, which are all viral diseases. Influenza is caused by influenza viruses, COVID-19 by the SARS-CoV-2 virus, and measles by the measles virus. Bacterial and viral pathogens differ considerably in their structure, replication processes, and treatments, which is essential knowledge in the context of microbiology in mortuary science. By recognizing that bubonic plague is a bacterial infection, it can be understood that the other diseases stem from viral origins, confirming that the correct answer to the question is indeed the bubonic plague.