Simian rhesus rotavirus is a unique heterologous (non-lapine) rotavirus strain capable of productive replication and horizontal transmission in rabbits

Simian rhesus rotavirus (RRV) is the only identified heterologous (non-lapi ne) rotavirus strain capable of productive replication at a high inoculum d ose of virus (> 10(8) p.f.u.) in rabbits. To evaluate whether lower doses o f RRV would productively infect rabbits and to obtain an estimate of the 50 % infectious dose, rotavirus antibody-free rabbits were inoculated orally w ith RRV at inoculum doses of 10(3), 10(5) Or 10(7) p.f.u. Based on faecal v irus antigen or infectious virus shedding, RRV replication was observed wit h inoculum doses of 10(7) and 10(5) p.f.u., but not 10(3) p.f.u. Horizontal transmission of RRV to one of three mock-inoculated rabbits occurred 4-5 d ays after onset of virus antigen shedding in RRV-infected rabbits. Rabbits infected at 10(7) and 10(5), but not 10(3), p.f.u. of RRV developed rotavir us-specific immune responses and were completely (100%) protected from lapi ne ALA rotavirus challenge. These data confirm that RRV can replicate produ ctively and spread horizontally in rabbits. In attempts to elucidate the ge netic basis of the unusual replication efficacy of RRV in rabbits, the sequ ence of the gene encoding the lapine nonstructural protein NSP1 was determi ned. Sequence analysis of the NSP1 of three lapine rotaviruses revealed a h igh degree of amino acid identity (85-88%) with RRV, Since RRV and lapine s trains also share similar VP7s (96-97 %) and VP4s (69-70%), RRV might repli cate efficiently in rabbits because of the high relatedness of these three gene products, each implicated in host range restriction.