Although highly pathogenic avian influenza H5N1 viruses have yet to acquire the ability to transmit efficiently among humans, the increasing genetic diversity among these viruses, and continued outbreaks in avian species underscore the need for more effective measures for the control and prevention of human H5N1 virus infection. Additional small animal models with which therapeutic approaches against virulent influenza viruses can be evaluated are needed. Here, we used the guinea pig model to evaluate the relative virulence of selected avian and human influenza A viruses. We demonstrate that guinea pigs can be infected with avian and human influenza viruses, resulting in high titers of virus shedding from nasal washes for up to five days post-inoculation and from lung tissue of inoculated animals. However, other physiologic indicators typically associated with virulent influenza strains were absent in this species. We evaluated the ability of intranasal treatment with human alpha interferon (alphaIFN) to reduce lung and nasal wash titers in guinea pigs challenged with the reconstructed 1918 pandemic H1N1 virus or a contemporary H5N1 virus. IFN treatment initiated one day prior to challenge significantly reduced or prevented infection of guinea pigs by both viruses, as measured by virus titer determination and seroconversion. The expression of the antiviral Mx protein in lung tissue correlated with the reduction of virus titers. We propose that the guinea pig may serve as a useful small-animal model for testing the efficacy of antiviral compounds and that alphaIFN treatment may be a useful antiviral strategy against highly virulent strains with pandemic potential.
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