Erythema infectiosum is caused by -

Ans. is 'a' i.e., Parvovirus B-19 * Parvovirus are non-enveloped DNA (ss DNA) viruses.* Only DNA virus which has single stranded DNA.* Smallest virus* Has smallest genome* Only one medically important human parvovirus - Parvovirus B19* Transmission is by respiratory route and through blood.* Infection is commonly acquired in childhood (5-10 yrs).* Most of the infections are asymptomatic.* Most common presentation is respiratory infection with an erythematous maculopapular rash and arthralgia - Erythema infectiosum or Fifth disease.* Starts with prominant erythema of cheeks ->> slapped cheek disease.* Parvovirus B-19 induces aplastic crisis in children with chronic hemolytic anemias, as in sickle cell disease.* Parvovirus B-19 infection during second or third trimester of pregnancy may result in nonimmune fetal hydrops. Transplacental transmission rate is 30% or higher.* In adults, parvovirus infection commonly causes acute arthralgia and arthritis.* Parvovirus B-19 is difficult to grow and virus isolation is not used to detect infection.