Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 6/1/2005
Publication Date: 11/2/2005
Citation: O'Toole, D., Taus, N.S., Oaks, J.L., Li, H. Defining the minimum intranasal infectious dose of OvHV-2 that is required to induce infection and malignant catarrhal fever in bison. October, 2005, 48th Annual Meeting of American Association of Laboratory Diagnosticians, Hershey, PA. P. 114.
Technical Abstract: Sheep-associated malignant catarrhal fever (MCF) is caused by ovine herpesvirus-2 (OvHV-2), which has not yet been propagated in vitro. Nasal mucus containing infectious virus obtained from sheep during intense shedding events can be collected and used for challenge studies. In current study, 12 bison were used to define the minimum infectious dose of OvHV-2 that is capable of establishing infection and/or disease. Bison (2 animals per group) were challenged by intranasal nebulization of 2 ml of inoculum containing ~1 x 10 (7) to 10 (3) OvHV-2 DNA copies. The six bison inoculated with the three higher doses seroconverted at 15 - 47 days post-inoculation (PI) and had detectable OvHV-2 DNA in PBLs by nested PCR at 21 - 32 days PI. Clinical signs of acute MCF developed as follows: 46 and 49 days PI (1 x 10 (5)); 52 and 54 days PI (1 x 10 (6)); 39 and 44 days PI (1x10 (7)). The two bison given 1 x 10 (4 ) were positive for OvHV-2 DNA in PBLs after 25 and 36 days PI, respectively; one bison seroconverted at 41 days PI and died of MCF at 50 days PI. The other animal did not seroconvert and remained clinically healthy throughout the three month study period. Neither bison in the 1 x 10 (3) group seroconverted nor had detectable OvHV-2 DNA in PBLs. All bison that developed clinical MCF had significant levels of OvHV-2 DNA in PBLs about 11 days prior to onset of clinical signs. Based on gross lesions and clinical signs, there is apparently no indication that higher inocula result in consistently more rapid induction of disease, or a different pattern of lesions. The infectious dose from the currently established pool of sheep nasal inoculum required to induce MCF following intranasal challenge in young seronegative bison is about 1 x 10 (5) OvHV-2 DNA copies. Establishment of a bison model of OvHV-2 infection using a defined minimum dose to induce clinical MCF is a critical step toward the development of a vaccine and in understanding the pathogenesis of the disease.