A federal air marshal is in "quarantine" in a Houston, Texas hospital after being attacked with a syringe at Lagos airport in Nigeria, the FBI said.
The contents of the syringe are not known but officials fear it could contain some form of the Ebola virus.
The assailant managed to evade capture but the syringe was recovered and is being tested in the US.
The unprovoked attack took place in a public area of the airport terminal where the air marshal had been traveling with a team of other marshals.
"The victim did not exhibit any signs of illness during the flight back to the US and was transported to a hospital upon landing for further testing," an FBI spokesperson said.
"None of the testing conducted has indicated a danger to other passengers."
The Federal Law Enforcement Officers Association said there was no immediate signs that this was a targeted attack.
