The Batai virus has been isolated from mosquitoes, cattle, pigs, and febrile patients, and has been identified as a naturally occurring genetic reassortant. It is transmitted to humans and livestock by mosquitoes, biting midges (Culicoides spp.), and ticks, from frigid to tropical zones of Africa, Asia, and Europe. Despite the potential health risks posed by bunyavirus reassortment (for example, the recent emergence of Schmallenberg virus)  a lack of complete sequencing data for many of these viruses complicates surveillance and virus identification efforts. Full-length genome sequence data are available for very few orthobunyaviruses .
The genomic sequences of the BATV strains of Japan, Malaysia, India, and other Asian countries share more homologies compared with the strains of Asia and European countries. Yet, they do have genetic differences and a propensity for genetic reassortment. Reassortment between the BATV M segment and the BUNV S and L segments is associated with increased virulence [13, 14]. In 1997 and 1998, M segment reassortment between the Batai and Ngari viruses was associated with severe febrile disease outbreaks in East Africa, and hundreds of thousands of people died from the disease . Genomic reassortments between different viruses within the genus Orthobunyavirus, such as reassortment between the Tinaroo and Jatobal viruses of the Simbu serogroup , have also been previously observed. These findings emphasize the need for full-length characterization of all three genomic segments of the bunyaviruses to better identify newly emerging viruses with potential significance for human or animal health.
In China, the Batai virus was first isolated from an Anopheles philippines mosquito in Yunnan Province in 1998. Phylogenetic analyses based on the genomic sequences of the S, M, and L segments revealed that the YN92-4 strain isolated in China belongs to the same group as the MM 2222 strain isolated in Malaysia, but the complete genomic sequence has not been published.
In the present study, we first isolated a novel Batai virus NM/12 strain from bovine serum in the Inner Mongolian region of China and performed the complete genome sequencing of the emerging BATV NM/12 strain. This is the first report of a BATV strain isolated from cattle in China. To elucidate the phylogenic relationship of the NM/12 strain, we carried out multi-segment phylogenetic analyses of the NM/12 strain and all other strains in GenBank. We found that the NM/12 strain is closely related to strains in different regions of Asia and distantly related to European BATV strains. Based on partial sequencing, NM/12, ON-1/E/94, and ON-7/B/01 appeared in the same phylogenetic lineage but diverged at different times despite that both were isolated separately from bovine blood in China and Japan.
Our full-length genomic analysis indicated that the virus may not have undergone any reassortment. Homologies of the nucleotide (amino acid) sequences between the S, M, and L segments of NM/12 and the original MM 2222 strain were 92.1% (97.3%), 97.2% (95.4%), and 93.8% (95.8%). The sequence comparison showed that the NM/12 strains had a number of nucleotide substitutions that were scattered throughout the genome containing 5′-NCR. In addition, the 5′ NCR nucleotide substitution rate was significantly higher than that of the 3′ NCR. The open reading frames and untranslated region genomic segment were conserved among BATV . Nucleotide substitution rates were 2.56%, 4.49%, and 4.21% in the parts of the genome that code for the nucleocapsid, envelope glycoprotein, and polymerase protein, respectively (Table 2).
Pair-wise alignment of the complete S, M, and L segments of the BATV NM/12 strain with those of the strains in GenBank revealed the phylogenetic relatedness among these BATV strains (Figure 3a-c). Unlike the Ngari virus, the NM/12 strain had no genetic reassortment among all the compared viruses but was close to the Batai virus strains isolated in Asian countries, except Japan. The S and M segments of the NM/12 strain were close to ON-7/B/01 isolated from cattle serum in Japan, but they were in different phylogenetic lineages. Only the L segment was closely related to Chittoor/IG-20217 (isolated in India). This finding indicates that all the BATV strains have few variations, and no reassortment among the compared BATV strains was found. This was confirmed by the amino acid divergence shown through complete sequence analysis in this study. However, there are genomic reassortments between different viruses within the genus Orthobunyavirus, such as the reassortment between the Tinaroo and Jatobal viruses.
Batai virus isolated from mosquitoes, cattle, pigs, and febrile patients were identified as naturally occurring reassortants between the BATV M segment and the BUNV S and L segments. This reassortment is associated with increased virulence. BATV antibody was found in fever patients in Yunnan province, China after the BATV was isolated from Anopheles philippines in Yunnan Province in 1998 [13, 14, 16]. We found that suckling mice infected with the NM/12 strain had high morbidity, indicating that the NM/12 strain of BATV may also have strong infectivity in other vertebrate hosts. The findings in this study provide further insight into the genetic diversity of Orthobunyavirus and draw attention to the need for prevention of BATV infection in cattle and humans in China.