Early studies carried out in Glasgow demonstrated that a significant proportion of babies excreting virus particles, 12%, did not exhibit gastrointestinal symptoms; seroprevalence studies carried out in the US have shown that 90% of children have antibody to HastV-1 by age 9, suggesting that (largely asymptomatic) infection is common.
Migratory waterfowl are a major factor in the spread of this disease as they are often asymptomatic carriers of disease.
Trophozoites of Acanthamoeba hosting these strains were isolated from asymptomatic women in Germany and also in an outbreak of humidifier fever (‘Hall’s coccus’) in Vermont USA.