A U.S. air marshal is currently being tested for Ebola and other infectious diseases at a Houston area hospital following an unprovoked attack by a man wielding a syringe filled with an unknown substance this past Sunday. Although federal officials are unsure what caused the attack at an airport in Lagos, Nigeria, they are currently investigating whether the unknown assailant targeted the air marshal due to his American heritage. Officials said they will know more about the motive of the attack once the substance in the syringe has been identified.

"Out of an abundance of caution, the Centers for Disease Control and Prevention (CDC) conducted an on-scene screening of the victim when United Flight 143 landed in Houston early Monday morning," read an FBI statement issued to CNN. "The victim did not exhibit any signs of illness during the flight and was transported to a hospital upon landing for further testing. None of the testing conducted has indicated a danger to other passengers."

A group of U.S. air marshals in plain clothes were getting ready to board United Flight 143 when they were approached by a second group of men. After the air marshal was stabbed with the syringe in the back of his arm, he pulled the syringe out and boarded the flight bound for Texas, while accompanying air marshals recovered the syringe and placed it in a container. Upon arriving at Houston’s Bush International Airport, the air marshal was met by CDC officials to undergo an on-site disease screening.

While the air marshal’s current condition has not been released to the public, health experts say symptoms related to most infectious diseases would be hard to identify so early on. Any infection would also not be considered immediately contagious. As of Monday, the air marshal was still under quarantine at a hospital in Houston while FBI officials investigate what substance the syringe contained.