Leading companies offering medical evacuation services are balking at flying Ebola patients out of West Africa for treatment abroad as the cost and the complexities of the deadly epidemic grow.

Several airlines have cut flights to the region and there are reports of countries not allowing air ambulances to make refueling stops, further complicating the so-called medevac option many companies provide for staffers in risky regions.

The world's worst Ebola epidemic since the disease was identified in 1976 has killed more than 4,000 people, mainly in West Africa. The virus, spread by contact with bodily fluids, causes fevers and potentially fatal bleeding.