The U.S. Army declined to say who may have exposed Cavoli to the virus inadvertently or whether Farina was at the conference.
The Pentagon said seven cases were under investigation and that three active-duty service members so far had tested positive for the virus. Beyond the Marine, they include previously reported cases of a soldier in South Korea and a sailor in Italy.
U.S. officials told Reuters that the Marine worked at the Defense Security Cooperation Agency (DSCA), which helps oversee foreign military sales and international military educational partnerships. The Marine had returned last month from Ethiopia.