Which virus is known to cause mild rash and fever?

The virus known to cause a mild rash and fever is associated with measles. Measles is a highly contagious viral disease that typically presents with a high fever, cough, runny nose, and sore throat, followed by a characteristic red, blotchy rash. The rash usually starts at the head and spreads downward to the rest of the body. This clinical presentation distinguishes measles from other viral infections listed.

In contrast, rabies primarily affects the nervous system and presents with symptoms like confusion, agitation, and paralysis but does not typically involve a rash. HIV, while it can cause a range of symptoms, including fever and rash, is more often associated with immunocompromised states and chronic infections rather than just mild febrile illness. Hepatitis primarily affects the liver and can cause fever, but it does not typically present with a rash. Therefore, measles is the most appropriate choice for a virus known to cause both mild rash and fever.