PHNOM PENH, Dec 15 (Reuters) - Cambodia has detected the country"s first case of the Omicron variant of the coronavirus in a local woman who had travelled from Ghana, the ministry of health said. The 23-year old woman had returned from Ghana via Dubai and Bangkok, the ministry said in a statement issued on Tuesday. The woman, who was 15 weeks pregnant, had been admitted to hospital for treatment, it said. The Omicron variant first detected in South Africa and Hong Kong last month has now been reported by over 70 countries and is probably present in most worldwide, but should not be dismissed as "mild", the World Health Organization (WHO) said on Tuesday. The Southeast Asian nation reopened its borders last month to vaccinated tourists after achieving one of Asia"s highest COVID-19 vaccination rates, with more than 88% of its 16 million people now inoculated.