The patient is being treated at the hospital's specialist High Consequence Infectious Diseases Unit at Royal Liverpool Hospital.
Two cases of monkeypox were identified in North Wales yesterday, health bosses said.
A spokesman for Public Health Wales said the index case was acquired overseas and the two patients are members of the same household.
“We have worked with multi agency colleagues, following tried and tested protocols and procedures, and identified all close contacts.
“Actions have been put in place to minimise the likelihood of further infection.
“Monkeypox is a rare disease caused by the monkeypox virus and has been reported mainly in central and West African countries.
“Monkeypox, in most cases, is a mild condition which will resolve on its own and have no long-term effects on a person’s health. Most people recover within a few weeks.”
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