13 : Countermeasures to the Reemergence of Smallpox Virus as an Agent of Bioterrorism

Fever curve and clinical highlights for cynomolgus monkeys exposed to aerosolized variola virus. (Redrawn from reference S.)

Schematic illustrating the procedure for exposing primates to aerosolized MPOX. All steps are conducted in a gas-tight, class III cabinet system. The monkey's head is placed in an exposure chamber, and a Collison nebulizer generates an aerosol from a concentrated virus suspension. The concentration of the aerosol is determined by sampling the air and collecting virus on an all-glass impinger. Monkeys receive a calculated inhaled dose of 1 x 104 to 3 x 104 PFU based on an average inhaled volume of 300 ml/min.

Composite summary of clinical signs in lethally infected cynomolgus monkeys exposed to aerosolized MPOX. Temperatures are unremarkable until plummeting immediately prior to death, corresponding to a precipitous fall in blood pressure and heart rate. Oxygen saturation (Sp02) falls from a normal level of 88% to <50% by the time animals become sick. Virus is isolated from buffy coat cells corresponding with detection of viral genomes by Taqman PCR in these cells beginning at 4 days after exposure. Virus titers of > 106 PFU / g are isolated from lungs and spleens collected at necropsy.

(A) Facial exanthema, ulcerative cheilitis, and gingivitis in a monkey infected with a lethal dose of MPOX at 13 days after exposure, (B) Necrotizing bronchopneumonia and fibrinous pleuritis from a monkey dying on day 13. (Hematoxylin- eosin stain; magnification, ×10.3.) (C) Severe necrosis of bronchial epithelium with expansion of the peribronchovascular interstitium by edema, inflammatory cells, and proliferating fibroblasts. Adjacent alveoli contain various amounts of fibrin admixed with inflammatory cells, necrotic cellular debris, and edema. (IHC, SAAP; magnification, x7.9.) (D) Lung with typ II pneumocyte. Note naked viroplasm, semicircular shells, formative shells containing viroplasm, intracellular mature virion, and lamellar structures. (Transmission electron microscopy; magnification, X7,900.) (E) Lymph node. MPOX antigen is concentrated in macrophages or dendritic cells of follicular germinal centers, coupled with extensive necrosis. (IHC, SAAP; magnification, ×52.1.) (F) Colon. Note extensive necrosis and MPOX antigen immunoreactivity of the gut-associated lymphoid tissue, with relatively mild involvement of overlying mucosa (IHC, IPO; magnification, X7.9.)