Tularemia is a severe zoonotic disease in humans with fatality rates exceeding 30% in untreated
subjects. Francisella tularensis, the causative organism, is a gram-negative coccobacillus and a
facultative intracellular pathogen. Infection can occur by direct contact with infected animals or tissues
as well as by inhalation; inhalation causes the most severe form of the disease. There is concern that F.
tularensis could be used as a biological weapon. A vaccine is needed to protect against the threat posed
by the intentional release of this organism, particularly against infection by inhalation. An attenuated
strain dubbect the Live Vaccine Strain (LVS) was developed in the 1950s and gives good protection,
however this protection breaks down at higher challenge doses and there are concerns about reversion.
We have previously shown that aerosol prime-boost vacination with a live attenuated vaccine, S4aroD,
provides good protection in an outbred rabbit model against aerosol challenge with virulent F. tularensis
SCHU S4. Antibody in plasma corresponded with the level of protection, which was determined by the
route of vaccination, the vaccine used, and the number of doses. In this proposal we will evaluate
whether restricting deposition of S4aroD to the upper or lower respiratory tract impacts the subsequent
immune response and protection against challenge with SCHU S4. Our hypothesis is that deposition of
LVS in the lower respiratory tract will provide good immunity against aerosol challenge with SCHU S4
while deposition of S4aroD in the upper respiratory tract may not generate effective immunity. The first
aim will develop the technical procedures necessary to generate large particle aerosols and to evaluate
deposition of S4aroD in these particles in the respiratory tract of rabbits. In the second aim, rabbits will
be vaccinated with S4arpD by large- or small-particle aerosol; we will then compare the immunological
response and subsequent protection against aerosol challenge with SCHU S4. The information gained
under this proposal will explore whether regional deposition in the respiratory tract impacts subsequent
protection, information important for generation of immunity in the respiratory tract and protection
against pathogens entering the respiratory tract.