The Pathology of Experimental Poxvirus Infection in Common Marmosets (Callithrix jacchus): Further Characterization of a New Primate Model for Orthopoxvirus Infections

SummaryZoonotic orthopoxvirus (OPV) can induce severe disease in man and the virus has potential for use in bioterrorism. New vaccines and therapeutics against OPV infections must be tested in animal models. The aim of this study was to characterize the clinical course and pathology of a new OPV isolate, calpox virus, which is infectious in marmosets. Infection experiments were performed with 28 common marmosets (Callithrix jacchus) exposed to different challenge doses of calpox virus by the intravenous, oropharyngeal and intranasal (IN) routes. The median marmoset IN infectious dose corresponded to 8.3 × 102 plaque forming units of calpox virus. Infected animals developed reproducible clinical signs and died within 4–15 days post infection. Characteristic pox-like lesions developed in affected organs, particularly in the skin, mucous membranes, lymph nodes, liver and spleen. Calpox virus disease progression and pathological findings in the common marmoset appear to be consistent with lethal OPV infections in man and in other non-human primate (NHP) models. IN inoculation with low virus doses mimics the natural route of the human variola virus infection. Thus, the marmoset model of calpox virus infection can be considered to be relevant to investigation of the mechanisms of OPV pathogenesis and pathology and for the evaluation of new vaccines and antiviral therapies.