The clinical and virological aspects of human influenza virus A (H5N1) infection in South Vietnam 2004-2005

Abstract

Since the re-emergence of avian influenza A H5N1 virus in 2003 among poultry, the virus has reached endemic levels in Vietnam and continues to cause human infections. At present (9 February 2011), 119 infections have been reported, 59 of which were fatal. The cases in 2004 and 2005 accounted for 76% (90/119) of the total number of reported cases from Vietnam. This thesis retrospectively studied the clinical course of 16 cases (14%). The clinical features in most cases were typical for the human disease caused by the H5N1 virus. The prominent clinical signs and symptoms were those of a severe influenza syndrome with fever, cough, and shortness of breath. However, this thesis also shows that human H5N1 influenza may be associated with extrapulmonary disease, including gastrointestinal and eNS symptoms and multi-organ failure. The abnormalities on chest radiographs included extensive bilateral infiltration, lobar collapse, focal consolidation, and air bronchograms. The prominent laboratory factors were thrombocytopenia, neutropenia, lymphopenia, and increased levels of serum transaminases. Most patients (15/16) were treated with standard doses of the neuraminidase inhibitor oseltamivir. This drug has antiviral efficacy against H5N1 viruses and observational studies suggest that treatment with oseltamivir reduces mortality. Drug resistance may emerge during treatment and seems associated with antiviral and clinical failure. When testing for genotypic and phenotypic resistance, we detected 2 oseltamivir resistant H5N1 variants in two patients who failed to clear the virus and died from the infection. In contrast, four other patients who showed effective suppression of viral replication during treatment all survived. Molecular analysis of 13 H5N1 virus strains isolated from 13/16 patients showed that all viruses belonged to clade 1, genotype Z H5N1 viruses. The viruses retained the molecular characteristics of avian viruses. Some virus strains had mutations in the HA 1 gene that potentially affect receptor specificity, i.e. reduce recognition of 'avian-type' receptors, increase recognition of 'human-type' receptors, or both. A Glu-627-Lys substitution in the viral polymerase PB2, associated with adaptation and virulence of H5N 1 viruses in mammals, was observed in 5 of 8 isolates from fatal cases and in 3 of 4 isolates from patients who survived. However, no association between the presence of Lys-627 and clinical outcome was observed. However, in all except one of the isolates without the Glu-627-Lys substitution, an alternative change at position 701 (Asp to Asn) was observed which has also been associated with adaptation of avian viruses to replication in mammals. Data from this study also provided evidence for the selection of mutations in HA gene during infection, supporting the notion that continuing transmission of H5N1 virus from poultry to humans may provide a greater opportunity for the virus to adapt to humans. In addition, to support the diagnostic programme, I developed a molecular diagnostic assay that can detect both clade 1 (South-Vietnam, Cambodia, Thailand) and clade 2 (North Vietnam, Indonesia, Egypt) H5N1 virus variants. This molecular assay may be useful for diagnosis of H5 virus infections in regions where different genetic clades co-circulate