Influenza A viruses occur worldwide in wild birds and are occasionally associated with outbreaks in commercial chickens and turkeys. However, avian influenza viruses have not been isolated from wild birds or poultry in South America. A recent outbreak in chickens of H7N3 low pathogenic avian influenza (LPAI) occurred in Chile. One month later, after a sudden increase in deaths, H7N3 highly pathogenic avian influenza (HPAI) virus was isolated. Sequence analysis of all eight genes of the LPAI virus and the HPAI viruses showed minor differences between the viruses except at the hemagglutinin (HA) cleavage site. The LPAI virus had a cleavage site similar to other low pathogenic H7 viruses, but the HPAI isolates had a 30 nucleotide insert. The insertion likely occurred by recombination between the HA and nucleoprotein genes of the LPAI virus, resulting in a virulence shift. Sequence comparison of all eight gene segments showed the Chilean viruses were also distinct from all other avian influenza viruses and represent a distinct South American clade.
Avipoxvirus infections have been observed in an extensive range of wild, captive and domesticated avian hosts, yet little is known about the genome diversity and host-range specificity of the causative agent(s). Genome-sequence data are largely restricted to Fowlpox virus (FWPV) and Canarypox virus (CNPV), which have been sequenced completely, showing considerable divergence between them. It is therefore proving difficult, by empirical approaches, to identify pan-genus, avipoxvirus-specific oligonucleotide probes for PCR and sequencing to support phylogenetic studies. A previous preliminary study used the fpv167 locus, which encodes orthologues of vaccinia virus core protein P4b (A3). PCR per se did not discriminate between viruses, but restriction-enzyme or sequence analysis indicated that the avipoxviruses clustered either with FWPV or with CNPV. Here, further study of the P4b locus demonstrated a third cluster, from psittacine birds. A newly identified locus, flanking fpv140 (orthologue of vaccinia virus H3L), confirms the taxonomic structure. This locus is particularly useful in that viruses from the fowlpox-like and canarypox-like clusters can be discriminated by PCR on the basis of fragment size, whilst sequence comparison allows discrimination for the first time between Pigeonpox virus and Turkeypox virus. Except within the psittacines, virus and avian host taxonomies do not show tight correlation, with viruses from the same species located in very different clades. Nor are all the existing recognized avipoxvirus species, defined primarily by avian host species (such as CNPV and Sparrowpox virus), resolved within the present structure.
Background The World Health Organisation (WHO) recommended the development of simple, safe, sensitive and specific neutralization assays for avian influenza antibodies. We have used retroviral pseudotypes bearing influenza H5 hemagglutinin (HA) as safe, surrogate viruses for influenza neutralization assays which can be carried out at Biosafety Level 2.
Results Using our assay, sera from patients who had recovered from infection with influenza H5N1, and sera from animals experimentally immunized or infected with H5 tested positive for the presence of neutralizing antibodies to H5N1. Pseudotype neutralizing antibody titers were compared with titers obtained by hemagglutinin inhibition (HI) assays and microneutralization (MN) assays using live virus, and showed a high degree of correlation, sensitivity and specificity.
Conclusions The pseudotype neutralization assay is as sensitive as horse erythrocyte HI and MN for the detection of antibodies to H5N1. It is safer, and can be applied in a high‐throughput format for human and animal surveillance and for the evaluation of vaccines.
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