Pneumonic Tularemia in Rabbits Resembles the Human Disease as Illustrated by Radiographic and Hematological Changes after Infection

Abstract

BackgroundPneumonic tularemia is caused by inhalation of the gram negative bacterium, Francisella tularensis. Because of concerns that tularemia could be used as a bioterrorism agent, vaccines and therapeutics are urgently needed. Animal models of pneumonic tularemia with a pathophysiology similar to the human disease are needed to evaluate the efficacy of these potential medical countermeasures.Principal FindingsRabbits exposed to aerosols containing Francisella tularensis strain SCHU S4 developed a rapidly progressive fatal pneumonic disease. Clinical signs became evident on the third day after exposure with development of a fever (>40.5°C) and a sharp decline in both food and water intake. Blood samples collected on day 4 found lymphopenia and a decrease in platelet counts coupled with elevations in erythrocyte sedimentation rate, alanine aminotransferase, cholesterol, granulocytes and monocytes. Radiographs demonstrated the development of pneumonia and abnormalities of intestinal gas consistent with ileus. On average, rabbits were moribund 5.1 days after exposure; no rabbits survived exposure at any dose (190–54,000 cfu). Gross evaluation of tissues taken at necropsy showed evidence of pathology in the lungs, spleen, liver, kidney and intestines. Bacterial counts confirmed bacterial dissemination from the lungs to the liver and spleen.Conclusions/SignificanceThe pathophysiology of pneumonic tularemia in rabbits resembles what has been reported for humans. Rabbits therefore are a relevant model of the human disease caused by type A strains of F. tularensis.

Live Attenuated Mutants of Francisella tularensis Protect Rabbits against Aerosol Challenge with a Virulent Type A Strain

“…For aerosol exposures, virulent F. tularensis strain SCHU S4 was grown as previously described using brain heart infusion (BHI) broth (28,29). After the exposures were completed, nebulizer and all-glass impinger (AGI) contents were quantified on cysteine heart agar (CHA).…”

“…Aerosols were conducted inside a class III biological safety cabinet (Baker Co., Sanford, ME) located inside the RBL as previously described (28). Briefly, rabbits were exposed two at a time for 10 min in a nose-only exposure chamber (CH Technologies, Westwood, NJ) using a 3-jet Collison nebulizer controlled by the AeroMP exposure system (Biaera Technologies, Hagerstown, MD) while plethysmography data were collected in real time using Buxco XA software (Buxco Research Systems, Wilmington, NC) during the exposure.…”

“…Briefly, rabbits were exposed two at a time for 10 min in a nose-only exposure chamber (CH Technologies, Westwood, NJ) using a 3-jet Collison nebulizer controlled by the AeroMP exposure system (Biaera Technologies, Hagerstown, MD) while plethysmography data were collected in real time using Buxco XA software (Buxco Research Systems, Wilmington, NC) during the exposure. The aerosol concentration and inhaled (presented) dose were determined as described previously (28,32).…”

“…In general, these mutants have been successful in protecting mice against parenteral challenge and lowdose respiratory challenge. We report here the first efforts to advance these potential vaccines into use with the rabbit model, which we have previously shown is a relevant model of human pneumonic tularemia (28).…”

In vivoimaging in an ABSL-3 regional biocontainment laboratory

“…Our digital radiography system has been used extensively for tularemia studies in rabbits (Reed et al ., ). During radiography, rabbits were maintained on isoflurane anesthesia using a Matrx VIP 3000 anesthesia machine (Midmark, Corp, Versailles, OH).…”