Health officials are monitoring the condition of 12 people who were in close contact with a traveller diagnosed with monkeypox who transited through Thailand for two hours while en route to Australia.
Chakkarat Pitayawonganon, director of epidemiology at the Department of Disease Control, said on Monday that the 12 people were passengers and flight attendants on the same flight as the confirmed case.
They had remained asymptomatic over the past seven days and would be monitored until day 21, the disease incubation period.
Dr Chakkarat said the confirmed case had travelled from Europe and spent two hours in transit.
Those who were in close contact with the case were not at high risk because the infected passenger was asymptomatic during the transit period.
The confirmed case developed symptoms in Australia, where the diagnosis was made.
"So far there has not been a confirmed case in Thailand," Dr Chakkarat said.
Elsewhere there were 494 monkeypox patients in 32 countries as of Sunday comprising 406 confirmed cases and 88 suspected cases, according to Dr Chakkarat.
There included 139 cases in Spain, 101 in England, 74 in Portugal, 63 in Canada, 22 in Germany and 13 in the United States.
"There are more patients in many countries," Dr Chakkarat said.
He said that monkeypox was not a dangerous communicable disease and was rates as a communicable disease justifying surveillance, like malaria and dengue haemorrhagic fever.
Symptoms included fever, sore throat, headache, body ache, backache, swollen lymph nodes, a rash, blisters and scabs.
Health officials were looking for arrivals with such symptoms and those who came from countries where there were cases - including African countries, Spain, Canada, Germany, Portugal, England and the United States.
Officials were also looking for those in close contact with wild animals and monkeys imported from Africa. Feeding monkeys in the country and seeing animals at zoos could continue, Dr Chakkarat said.
The World Health Organisation said in its latest update, issued on Sunday, that it had received reports of 257 confirmed monkeypox cases and about 120 suspected cases in 23 nations where the virus is not endemic, as of Thursday.
"Epidemiological investigations are ongoing. The vast majority of reported cases so far have no established travel links to an endemic area and have presented through primary care or sexual health services. The identification of confirmed and suspected cases of monkeypox with no direct travel links to an endemic area is atypical.
"Early epidemiology of initial cases notified to WHO by countries shows that cases have been mainly reported amongst men who have sex with men. One case of monkeypox in a non-endemic country is considered an outbreak. The sudden appearance of monkeypox simultaneously in several non-endemic countries suggests that there may have been undetected transmission for some time as well as recent amplifying events."
According to previous reports, the disease is endemic to Central Africa.