Mutagenesis in Norovirus in Response to Favipiravir Treatment

Abstract

Chronic norovirus infection in immunocompromised patients can lead to malabsorption and other complications1; currently, no treatment has proved to be effective. Favipiravir is an antiviral medication that has been approved for the treatment of influenza in Japan2 and has been used by some as treatment for Ebola virus infection, with mixed results.3 Preclinical data have shown that favipiravir can induce mutagenesis and impair norovirus infectivity in mice.4 We used favipiravir to treat chronic norovirus infection in a 48-year-old man with common variable immunodeficiency. The patient had a long history of common variable immunodeficiency enteropathy, a condition characterized by diarrhea, malabsorption, and duodenal villous atrophy with intraepithelial lymphocytosis; it had previously been treated with immunosuppressive agents, including infliximab. Administration of parenteral nutrition caused unacceptable side effects in this patient. Serial polymerase-chain-reaction–positive stool samples obtained in July 2014 led to a diagnosis of chronic norovirus infection. Six months later, Mycobacterium avium–associated bronchiolitis also developed and was treated with antimicrobial therapy and with oral glucocorticoids for airflow obstruction. Treatment with high-dose intravenous immune globulin, nitazoxanide, and ribavirin was ineffective against the norovirus infection. We administered 6000 mg of favipiravir on day 1 in three divided doses, followed by 1200 mg twice daily. We used doses that had been evaluated in a trial of treatment for Ebola virus infection (higher doses than have been used for influenza), on the basis of the predicted 50% inhibitory concentration, the impaired enteral absorption in the patient, and the absence of serious adverse events attributed to the drug when given at these doses during the trial for Ebola.3 Administration of favipiravir was approved by the Royal Free London NHS Trust Drug and Therapeutics Committee, and collection of records and samples for research was approved by the NHS Research Ethics Committee. Written informed consent from the patient was obtained for both the administration of the drug and the use of the data for this research. Figure 1. Clinical Course and Laboratory and Molecular Results. With treatment, the patient’s diarrhea and the use of adjunctive loperamide decreased, his body weight increased, and the norovirus viral load decreased (Figure 1A, 1B, and 1C). An increase in serum levels of aspartate aminotransferase, alanine aminotransferase, and alkaline phosphatase on liver-function testing prompted a treatment interruption on day 19, and the patient’s gastrointestinal symptoms promptly relapsed. Reintroduction of favipiravir was associated with rapid deterioration in liver-function test results and treatment interruption on day 6; on both occasions, he was also receiving intravenous levofloxacin. A third treatment course was attempted without a loading dose and after stopping treatment with levofloxacin. The symptomatic response was slower but notable (Figure 1A), albeit without sustained weight gain, and the results of liver-function tests remained stable. Again, the patient had a relapse after discontinuation of favipiravir treatment due to a lack of available medication. Unfortunately, his pulmonary disease progressed, and he eventually died from respiratory failure. Viral deep sequencing5 and phylogenetic analysis of norovirus isolates obtained from the patient revealed a monophyletic clade containing substantial diversity (Figure 1D). The divergence point from other GII.4 sequences suggested acquisition of the infection before 2002. During the first course of favipiravir treatment, there was apparent selection for a distinct viral variant (Figure 1E); this variant also increased in frequency during the third course of treatment. At the consensus level, it differed from the dominant variant observed before or after treatment by 118 nonsynonymous substitutions throughout the genome. We also found increasing A→G and T→C minority single-nucleotide variants during favipiravir treatment (Figure 1F), as has been described for murine norovirus.4 In summary, despite the presence of complex coexisting conditions, the patient in this case had some symptomatic response to favipiravir treatment, along with evidence for selective pressure on the infecting norovirus population. Further study of favipiravir for chronic norovirus infection should be considered.