Antiviral activity of ribavirin on influenza infection in ferrets

Influenza antivirals and animal models

Influenza A and B viruses are among the most prominent human respiratory pathogens. About 3-5 million severe cases of influenza are associated with 300 000-650 000 deaths per year globally. Antivirals effective at reducing morbidity and mortality are part of the first line of defense against influenza. FDA-approved antiviral drugs currently include adamantanes (rimantadine and amantadine), neuraminidase inhibitors (NAI; peramivir, zanamivir, and oseltamivir), and the PA endonuclease inhibitor (baloxavir). Mutations associated with antiviral resistance are common and highlight the need for further improvement and development of novel anti-influenza drugs. A summary is provided for the current knowledge of the approved influenza antivirals and antivirals strategies under evaluation in clinical trials. Preclinical evaluations of novel compounds effective against influenza in different animal models are also discussed.

Community-Acquired Respiratory Viruses in Transplant Patients: Diversity, Impact, Unmet Clinical Needs

Patients undergoing solid-organ transplantation (SOT) or allogeneic hematopoietic cell transplantation (HCT) are at increased risk for infectious complications. Community-acquired respiratory viruses (CARVs) pose a particular challenge due to the frequent exposure pre-, peri-, and posttransplantation. Although influenza A and B viruses have a top priority regarding prevention and treatment, recent molecular diagnostic tests detecting an array of other CARVs in real time have dramatically expanded our knowledge about the epidemiology, diversity, and impact of CARV infections in the general population and in allogeneic HCT and SOT patients. These data have demonstrated that non-influenza CARVs independently contribute to morbidity and mortality of transplant patients. However, effective vaccination and antiviral treatment is only emerging for non-influenza CARVs, placing emphasis on infection control and supportive measures. Here, we review the current knowledge about CARVs in SOT and allogeneic HCT patients to better define the magnitude of this unmet clinical need and to discuss some of the lessons learned from human influenza virus, respiratory syncytial virus, parainfluenzavirus, rhinovirus, coronavirus, adenovirus, and bocavirus regarding diagnosis, prevention, and treatment.

In vitro and in vivo assay systems for study of influenza virus inhibitors

Evaluation of potential influenza virus inhibitors may utilize multiple steps. First would be to determine if the viral target (e.g. influenza virus neuraminidase) being focused upon will be inhibited in the appropriate assay. Standard in vitro antiviral assays, used next in antiviral evaluations, may utilize inhibition of viral plaques, viral cytopathic effect (CPE), and viral hemagglutinin or other protein, with inhibition of viral yield used in follow-up evaluations. The CPE can be determined visually and by dye uptake. Animal models used for study of potential influenza virus inhibitors include the ferret, the laboratory mouse, and the chicken, with a variety of parameters used to indicate the severity of the infection and its inhibition by therapy. Multiple parameters are recommended in any in vivo antiviral evaluation. The ferret and the mouse infection models have been useful in studying the development of drug resistance and the relative virulence of drug-resistant viruses. The influenza mouse model has also been of value for the evaluation of immunomodulating effects of test compounds and for the study of the utility of antiviral drugs for use against influenza virus infections in the immunocompromised host. In considering the use of any animal model, species differences in drug pharmacology and metabolism must be taken into account. This review has described the systems which have been used most frequently by antiviral investigators, using, as examples, recent studies with the clinically approved influenza virus neuraminidase inhibitors oseltamivir and zanamivir.

Ribavirin: a clinical overview

Ribavirin, a broad spectrum, non-interferon-inducing virustatic chemotherapeutic agent, demonstrates activity against a wide range of RNA and DNA viruses, including the retrovirus known to cause the acquired immune deficiency syndrome. The drug's proposed mechanism of action, as well as pharmacokinetics are discussed, and preclinical toxicity, safety and clinical efficacy studies are presented. To date, the best success has occurred in the use of ribavirin to treat respiratory syncytial virus infection in infants and young children and to treat influenza A and B virus infections in young adults. Viral infections, particularly viral pneumonia, are often life-threatening in infants with severe combined immunodeficiency disease (SCID), and ribavirin aerosol has been used successfully to treat respiratory syncytial virus and parainfluenza virus infection of immunodeficient children. Special note is taken of ribavirin's clinical benefit in treating severe and life-threatening infections caused by the Lassa fever virus and the significant improvement over either the use of immune plasma or supportive therapy alone. Indeed, ribavirin thus emerges as the first antiviral drug that is able to reduce mortality in a highly lethal systemic disease by more than 90%. Additional studies demonstrate the drug's efficacy in acute viral hepatitis, herpesvirus infections, and measles. Controlled clinical trials are underway to test the drug in patients infected with the AIDS virus.

Ribavirin: efficacy in the treatment of murine autoimmune disease

Ribavirin, a drug with known antiviral activity, was given to mice with established lupus nephritis. Ribavirin was effective in prolonging survival, reducing the titer of antibodies to DNA, and reversing proteinuria. Other antiviral agents were not effective in the dosages used.