Ebola Virus Transmission in Guinea Pigs

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Abstract
Ebola virus (EBOV) transmission is currently poorly characterized and thought to occur primarily by direct contact with infectious material; however transmission from swine to nonhuman primates via the respiratory tract has been documented. To establish an EBOV transmission model for performing studies with statistical significance, groups of six guinea pigs (gps) were challenged intranasally (IN) or intraperitoneally (IP) with 10,000 x LD50 of gp-adapted EBOV, and naïve gps were then introduced as cage-mates for contact exposure at 1 day post-infection (dpi). Animals were monitored for survival and clinical signs of disease, and quantitated for virus shedding post-exposure. Changes in contact duration of naïve gps with infected animals were evaluated for impact on transmission efficiency. Transmission was more efficient from IN compared to IP-challenged gps, with 17% versus 83% of naïve gps surviving exposure, respectively. Virus shedding was detected beginning at 3 dpi from both IN- and IP-challenged animals. Contact duration positively correlated with transmission efficiency, and the abrogation of direct contact between infected and naïve animals through the erection of a steel mesh is effective at stopping virus spread, provided that infectious animal bedding was absent in the cages. Histopathological and immunohistochemical findings show that IN-infected gps display enhanced lung pathology and EBOV antigen in the trachea, which support increased virus transmission from these animals. The results suggest that IN-challenged gps are more infectious to naïve animals than their systemically-infected counterparts, and that transmission occurs through direct contact with infectious materials, including those transported through air movement over short distances.