Characterization and Pathogenesis of Aerosolized Eastern Equine Encephalitis in the Common Marmoset (Callithrix jacchus)
USAMRIID Frederick United States
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Licensed antiviral therapeutics and vaccines to protect against eastern equine encephalitis virus EEEV in humans currently do not exist. Animal models which faithfully recapitulate the epidemiology of the human EEEV disease are needed to satisfy requirements of the Food and Drug Administration FDA for clinical product licensing under the Animal Rule. In an effort to meet this requirement, we estimated the median lethal dose and described the pathogenesis of aerosolized EEEV in the common marmoset Callithrix jacchus. Five marmosets were exposed to aerosolized EEEV FL93-939 in doses ranging from 2.4 x 10expn 1 PFU to 7.95 x 10expn 5 PFU, with a median lethal dose of 2.05 x 10expn 2 PFU. Euthanasia criteria was met by day 4 post exposure in the highest dose marmoset but animals at lower inhaled doses had a protracted disease course where euthanasia criteria was not met until as late as day 19 post exposure. Clinical signs were observed as early as 3 to 4 days post-exposure, including fever, ruffled fur, decreased grooming, and lymphopenia. Clinical signs of disease increased in severity as disease progressed to include decreased body weight, subdued behavior, tremors, and lack of balance. Fever was evident as early as day 2-3 post exposure in the highest dose groups and hypothermia was observed in several cases as animals became moribund. Infectious virus was found in several key tissues, including brain, liver, kidney, and lymph nodes. Clinical hematology results included early neutrophilia, lymphopenia, and thrombocytopenia. Key pathological changes included meningoencephalitis and retinitis. Immunohistochemical staining for viral antigen was positive in the brain, retina, and lymph nodes. More intense and widespread IHC labeling occurred with increased aerosol dose. In summary, we have estimated the medial lethal dose of aerosolized EEEV and described the pathology of clinical disease in the marmoset model.