In order to evaluate prophylaxis and therapy for individuals
infected with pathogens by the airborne route, we have designed and
built a simple apparatus in which small laboratory animals may be
exposed to aerosols of infectious microorganisms. Animals are kept in
a chamber closed by a HEPA filter and exposed to the pathogen
aerosolized using a Collison nebulizer. Air in the exposure chamber
may be sampled to show that the infectious agent is present but the
dose of agent must be expressed as 50% effective doses determined by
titration. An effective dose may be defined by whatever criteria are
chosen to judge disease. Using this apparatus we have shown that St
Louis encephalitis (SLE) virus is infectious for mice by the airborne
route. These data support the idea that there may be significant
hazard to personnel exposed to aerosols of infectious SLE after a
laboratory accident.