Virus transmissibility following i.o. inoculation was assessed by inoculating ferrets by the ocular route with indicated viruses and, 24 hrs p.i., placing a naïve ferret in the same cage as an inoculated ferret [to assess transmission in the presence of direct contact (DC)] or in an adjacent cage with modified side-walls to allow air exchange between inoculated and contact animals via perforations but inhibiting direct or indirect contact between animals [to assess transmission by respiratory droplets (RD)] as previously described [30] . For each i.o. transmission experiment, an aliquot of each virus stock used to characterize transmissibility in previous publications by the i.n. route was tested. NW, CW, and RS samples were collected on alternate days p.i./post-contact (p.c.) to assess kinetics of virus shedding. Serum was collected days 17-21 p.i./p.c. to measure seroconverison. Animal research was conducted under the guidance of the Centers for Disease Control and Prevention's Institutional Animal Care and Use Committee in an Association for Assessment and Accreditation of Laboratory Animal Care International-accredited animal facility.