Parvovirus B19 infection is caused by a small virus that primarily affects humans. It is known for causing a mild illness called fifth disease, which is characterized by a distinctive rash, fever, and joint pain. The virus spreads through respiratory droplets and can also be transmitted through blood. Most people recover without complications, but Parvovirus B19 can be more serious for individuals with weakened immune systems or certain blood disorders, such as sickle cell disease. Pregnant women should be cautious, as the infection can lead to complications for the fetus.