| Oropouche (ORO) virus is a member of the Simbu serogroup, genus Bunyavirus, family Bunyavifidae, and is the causative agent of ORO fever, an emerging disease in tropical South America. The studies described in this dissertation investigated the molecular biology of Oropouche and related Simbu serogroup viruses. The small (S) genomic segment of the prototype ORO virus strain was sequenced and found to be 754 nucleotides in length. In the virion complementary orientation, it contained two overlapping open reading frames (ORFs), corresponding to the nucleocapsid (N) and small non-structural (NSs) protein-coding regions of other bunyaviruses. Genetically ORO virus was related to, but distinct from, other members of the Simbu serogroup. Phylogenetic analyses of the N gene nucleotide sequences of 28 ORO virus strains revealed that ORO virus has evolved into three distinct lineages. Lineage I consisted of the prototype and most of the Brazilian strains, lineage II comprised six Peruvian and two Brazilian strains, while lineage III contained four Panamanian strains. Geographically, the distribution of these lineages was restricted to the eastern, western, and northern regions of tropical America, respectively.;The ORO virus N gene was expressed in E. coli. Purified recombinant N (rN) protein was investigated as a diagnostic reagent and compared with hamster serum antigen (HSA) and Vero cell lysate antigen (VCLA), the two antigens currently used for the diagnosis of ORO virus infection in Brazil and Peru, respectively. The results indicated that in enzyme immunoassays, sensitivity and specificity of the rN protein were very high (>90%) for the detection of ORO virus-specific IgM and IgG antibodies and its efficiency was comparable to those of HSA and VCLA.;Relationships among Simbu serogroup viruses were studied by phylogenetic analyses of the N ORF nucleotide sequences and found to correlate well with the relationships deduced by previous serological studies. However, phylogenetic analyses resolved relationships among viruses that were not previously resolved by serological data. The N gene sequence of Jatobal (JAT) and ORO virus were nearly identical (>95% nucleotide sequence identity), while the partial nucleotide sequence of the G2 protein-coding region (encoded by the medium RNA segment) exhibited significant variation (<70% nucleotide sequence identity). These data suggested that JAT virus is a reassortant of ORO virus. |
