The mumps virus belongs to the family of paramyxoviruses. It has a single-strand, nonsegmented, negative-sense RNA genome and is spread by the respiratory route. Following a 12–25-day incubation period, infection frequently causes the classic symptom of mumps: painfully swollen parotid salivary glands (parotitis). Some complications of infection include hearing loss, orchitis, oophoritis, mastitis, and pancreatitis. Mumps may also result in aseptic meningitis and, infrequently, encephalitis (5%–10% and <0.5% of unvaccinated cases, respectively). Importantly it has been estimated that as many as 30% of infections in unvaccinated individuals may be asymptomatic.