Sample A: Cover Page of Thesis, Project, or Dissertation Proposal

The inter-epizootic survival of RVF virus is not clear (Evans et al. 2007). In wet or
irrigated areas low level virus circulation may persist all year round in permanent Culex
populations (Chevalier et al. 2004a), however, in areas with a dry season there are times
when no vectors are present and therefore no transmission occurs. The prevailing hypothesis
is that enzootic virus maintenance in these areas depends on transovarial transmission of the
virus in floodwater Aedes mosquitoes (Davies et al. 1985, 1992; Linthicum et al. 1985,
House et al. 1992). As shown in Ae. mcintoshi, RVF virus is maintained in the eggs of
female floodwater Aedes mosquitoes which breed in isolated grassland depressions called
dambos (Linthicum et al. 1985). The eggs are capable of surviving in dry soil until the next
heavy rainfall floods the dambos producing favorable conditions for the eggs to hatch.
Subsequently, very large numbers of adult mosquitoes emerge (Linthicum et al. 1984; Davies
et al. 1985, Ba et al. 2005, Anyamba et al. 2006) and, if infected, transfer the RVF virus to
livestock and other animals on which they feed. These vertebrate bloodmeal hosts may
become infected and develop a viremia (Linthicum et al. 1985, Evans et al. 2007). RVF
epizootic periods result when waters persist a month or more past the emergence of Aedes
mosquitoes. This enables secondary vector species (e.g., Culex spp.) to breed, generate large
populations, feed on animals with high levels of viremia (Linthicum et al. 1985, Davis and
Martin 2003, Chevalier et al. 2004a, Evans et al. 2007), and subsequently spread infection to
animals beyond the area of the original outbreaks (Linthicum et al. 1999, Anyamba et al.
2001, Woods 2002, CDC 2004b). Cattle and sheep are the primary amplifiers of the disease
(Meegan and Bailey 1988, Longstreth and Wiseman 1989, Kasari et al. 2008).
It has also been suggested that reservoir animals (RVF infected rodents or wild
ruminants) may be affecting domestic animals in shared grasslands, and thus, maintain the
23