Upon exposure to DEV there is a 3-7 day for domestic fowl and up to a 14 day for wildfowl incubation period for the onset of symptoms. Sudden and persistent increases in flock mortality is often the first observation of DEV. Symptoms in individual birds include loss of appetite, decreased egg production (nearing 20-40% decreases), nasal discharge, increased thirst, diarrhea, ataxia, tremors, a drooped-wing appearance, and in males a prolapsed penis. Mortality rates for DEV may reach 90 percent. Death usually occurs within 5 days after onset of symptoms. The clinical signs of DEV "vary with virulence of virus strain, species, sex, and immune system status" of the host.