Aged (10-13 months) BALB/c strain mice were challenged with 50,000 TCID 50 of HeV via the intranasal route. Mice were euthanased and samples collected every second day from days 2-14 pi, every 3 days from days 17-23 pi and, lastly, on day 28 pi; at least one replicate was used for each time point in case mice were lost from the study for reasons not associated with HeV, with three mice being sampled on day 28. If mice reached a pre-determined humane endpoint prior to the scheduled sampling day they were euthanased and samples collected and processed as for animals euthanased according to the schedule.