The case is a 66-year-old man from a European country who had arrived in Thailand last week from an unspecified African country where the disease was spreading.
"The test results confirm that he is infected with the Clade 1b strain of monkeypox, which is the first case diagnosed in Thailand, but this man is likely infected from an endemic country," Thongchai Keeratihattayakorn, director-general of the Department of Disease Control, told Reuters.
He said no other local infections had been detected through contact tracing.
Clade 1b has triggered global concern due to the ease with which it spreads though routine close contact.
A case of the variant was confirmed last week in Sweden and linked to a growing outbreak in Africa, the first sign of its spread outside the continent.
The World Health Organisation declared the recent outbreak of the disease a public health emergency of international concern after the new variant was identified.
LIVE: Q&A on — World Health Organization (WHO) (@WHO) #mpox. Join us and #AskWHO your questions! https://t.co/wGe3LQUiBsAugust 22, 2024
Thai authorities on Wednesday said the man confirmed as having mpox had transited in a Middle Eastern country, which they also did not name, before flying on to Thailand.
Thailand has detected 800 cases of mpox Clade 2 since 2022 but so far not detected a case of the Clade 1 or Clade 1b variants.
Singapore's health ministry said it had detected 13 cases of mpox Clade 2 infections this year.
To date, all mpox infections in the city state have been the "less severe" Clade 2 infections, the ministry said in a bulletin on Thursday.
The government said it was monitoring the global situation closely.
The health ministry said that as a precaution, it will from Friday screen the temperatures of travellers arriving at Changi and Seletar airports from places exposed to the risk of mpox outbreaks.
5°C