Which of the following is an example of a virus?

Measles is an example of a virus, specifically a member of the Paramyxoviridae family. It is a contagious viral infection that primarily affects the respiratory system and can lead to serious complications. Viruses are distinct from bacteria in that they cannot grow or reproduce independently; they require a host cell to replicate.

In contrast, Streptococcus and Escherichia coli are both types of bacteria. Streptococcus refers to a group of bacteria that can cause a variety of infections, some of which can be serious, while Escherichia coli (commonly known as E. coli) is a type of bacteria that is often found in the intestines of healthy individuals but can also cause foodborne illnesses.

The term "Influenza bacterium" contains a mistake. Influenza is a viral infection, not caused by bacteria. The confusion may stem from the common practice of categorizing illnesses based on their symptoms, but it is essential to note that influenza is caused by influenza viruses, not bacteria.

Understanding these distinctions is important in the context of microbiology and human health, specifically in identifying the correct treatment approaches since antibiotics are effective against bacterial infections but not viral infections like measles or influenza.