BACKGROUND: The genus Flavivirus currently consists of approximately 80 
single-strand positive-sense RNA viruses. These replicate in a range of hosts 
including myriad vertebrate, insect, and tick species. As a consequence of this 
broad host range, the majority of flaviviruses can be propagated in most 
vertebrate and insect cell cultures. This ability to infect arthropods and 
vertebrates usually is essential for maintenance of these viruses in nature. But 
recently, there has been the discovery of a number of flaviviruses that infect 
mosquitoes but not vertebrates. It remains largely unknown why certain 
flaviviruses infect vertebrates and mosquitoes while others infect mosquitoes or 
vertebrates exclusively.
METHODS: Here, we initiated in vitro host range studies of Rabensburg virus 
(RABV), an intermediate between the mosquito-specific and horizontally 
transmitted flaviviruses, to provide information on the factor(s) that underlie 
the varying host range of flaviviruses. RABV is an intermediate between the 
mosquito-specific and horizontally transmitted flaviviruses because it does not 
infect mammalian or avian cell cultures, house sparrows, or chickens, but it 
does share genetic characteristics with the Japanese Encephalitis serogroup of 
flaviviruses.
RESULTS: In vitro growth kinetic assays revealed the complete abrogation of RABV 
growth on Vero and E6 cells incubated at temperatures 35°C and higher, but 
surprisingly RABV infected, replicated efficiently, and displayed overt 
cytopathic effects (CPE) on Vero and E6 cell cultures incubated below 35°C. In 
contrast, RABV was fully viable, replicated efficiently, and displayed overt CPE 
on C6/36 cells incubated at 28°C or 37°C, thus implicating temperature as an 
important factor limiting the host range of RABV.
CONCLUSIONS: These data are critical for further study to more fully identify 
the determinants that mediate the evolution of biological transmission among 
flaviviruses. It also will be useful for studies that look to provide a 
comprehensive molecular definition of flavivirus-host cell interactions. And it 
will provide a cadre of information to design wet lab experiments to investigate 
the genetic changes that facilitate host switching, which may lead to new 
vertebrate pathogens or transmission pathways.