WUHAN, China—A World Health Organization-led team investigating the origins of the COVID-19 pandemic left its quarantine hotel in Wuhan on Thursday to begin field work, two weeks after arriving in the Chinese city where the virus emerged in late 2019. The mission has been plagued by delays, concern over access, and bickering between China and the United States, which has accused China of hiding the extent of the initial outbreak and criticized the terms of the visit, under which Chinese experts conducted the first phase of research. “Thanks, Chinese Health Minister Ma Xiaowei, for a frank discussion on the #COVID19 virus origins mission,” WHO Director-General Tedros Adhanom Ghebreyesus wrote on Twitter. “I asked that the international scientists get the support, access & data needed, and the chance to engage fully with their Chinese counterparts.” The WHO has not provided details of the mission’s itinerary, although team leader Peter Ben Embarek …