Abstract
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.