Marburg has caused small, episodic outbreaks since first being identified, most recently last year in Tanzania and Ghana. It is one of the deadliest known viruses, with no approved vaccines or specific treatments.

An outbreak of Marburg, a contagious virus similar to Ebola, has impacted Rwanda and is causing concern of international spread.

The U.S. government is also working closely with international partners and Rwanda's ministry of health on the start of clinical trials to evaluate investigational countermeasures, he said.