Clinical features suggesting encephalitis are convulsions, focal neurological signs, movement disorder and changes in sensory perception. Sometimes polio-like paralysis ensues and fatalities have been reported. In most cases, the hearing loss is transient but permanent dysfunction may occur. Hearing problems did not correlate with meningitis and appears to be due to direct damage tothe cochlea. The incidence of hearing loss is estimated to be in the region of 1 per 15,000 cases.
Men are much more likely to be affected than women.
They are more frequent in young male adults. Rarely, congestive heart failure and deaths have been reported. Cases of symptomatic nephritis following mumps are unusual. It is thought that immunological mechanisms may be involved and certain HLA-D haplotypes are particularly susceptible. This is thought to be due to hormonal imbalances caused by virus infection.