Abstract:
Orthobunyaviruses, tri-segmented, negative-sense RNA viruses, have long been associated with
mild to severe human disease in Africa, but not haemorrhagic fever. However, during a Rift
Valley fever outbreak in East Africa in 1997–1998, Ngari virus was isolated from two patients
and antibody detected in several others with haemorrhagic fever. The isolates were used to
identify Ngari virus as a natural Orthobunyavirus reassortant. Despite their potential to reassort
and cause severe human disease, characterization of orthobunyaviruses is hampered by paucity
of genetic sequences. Our objective was to obtain complete gene sequences of two Bunyamwera
virus and three Ngari virus isolates from recent surveys in Kenya and to determine their
phylogenetic positioning within the Bunyamwera serogroup. Newly sequenced Kenyan
Bunyamwera virus isolates clustered closest to a Bunyamwera virus isolate from the same
locality and a Central African Republic isolate indicating that similar strains may be circulating
regionally. Recent Kenyan Ngari isolates were closest to the Ngari isolates associated with the
1997–1998 haemorrhagic fever outbreak. We observed a temporal/geographical relationship
among Ngari isolates in all three gene segments suggesting a geographical/temporal association
with genetic diversity. These sequences in addition to earlier sequences can be used for future
analyses of this neglected but potentially deadly group of viruses.
