A federal air marshal was stabbed with a syringe at the airport in Lagos, Nigeria, on Sunday, an incident that is raising concerns about whether the deadly Ebola virus could be harvested from the widespread outbreak in West Africa and used as a bioweapon.

Initial tests on the substance in the syringe, conducted at a special biodefense forensics laboratory at Fort Detrick, Md., did not detect the virus or any other threatening agent, a spokesman for the Federal Bureau of Investigation, Christos Sinos, said Wednesday. The marshal, who arrived in Houston on Monday, was examined there and has been released from the hospital with no sign of illness, according to a spokesman for the Transportation Security Administration.

Experts say it would be extremely hard for a group to grow large amounts of the virus and turn it into a weapon that could be dispersed over a wide area, infecting and killing many people.

“The bad guys are more likely to kill themselves trying to develop it,” said Dr. Philip K. Russell, a retired major general who was the commander of the Army Medical Research and Development Command.