Yale is based in the densely populated downtown New Haven, Connecticut area. Like Manhattan, parking is impossible so lots of students and non-students use public and university transportation. That can make the possibility of contagion of anything higher. Also university communities tend to be very open.
Right now, reports The New York Times, 3 Yale students and 6 others in the New Haven area are being monitored for Ebola. Some of those had been in West Africa.
If cases develop, Yale Law School might no longer be able to be so selective. Recently, Businss Insider noted it was the most selective law school in the nation. Applications for the 2015-2016 academic year could dry up if the virus takes hold.