Comparison of 12 turkey hemorrhagic enteritis virus isolates allows prediction of genetic factors affecting virulence

Abstract

Turkey hemorrhagic enteritis virus (THEV) is a member of the genus Siadenovirus and causes disease in turkey poults characterized by splenomegaly, bloody diarrhoea and death. The mechanism responsible for intestinal lesion formation and mortality is not known, although there is strong evidence that it is immune-mediated. All strains of THEV are serologically indistinguishable, although there are naturally occurring avirulent strains of THEV that replicate efficiently in turkeys without the intestinal haemorrhage or mortality associated with more virulent strains. The purpose of this study was to determine which viral genes are involved in virulence. The full-length genome of an avirulent vaccine strain was sequenced and compared with the genome of a virulent field isolate from Israel that was sequenced in 1998. Comparison of the two 26.3 kb genomes revealed 49 nucleotide differences resulting in 14 putative amino acid changes within viral proteins. Sequencing of the regions surrounding the 14 missense mutations revealed variations in ORF1, E3 and the fiber (fib) knob domain in five additional strains with varying degrees of virulence. Complete sequences of these genes were determined in a total of 11 different strains of THEV. All strains had at least one missense mutation in ORF1, and all but two of the strains had one missense mutation in E3. At least one missense mutation was found in the fiber knob domain in six out of seven virulent strains. Sequence variation of ORF1, E3 and fib in strains of THEV with different phenotypes strongly indicates that these genes are the key factors affecting virulence.

Full genome analysis of a novel adenovirus from the South Polar skua (Catharacta maccormicki) in Antarctica

“…Atadenovirus has been found in snake, marsupial and ruminants (Dan et al, 1998;Farkas et al, 2008;Thomson et al, 2002). Siadenovirus has been detected in frog, raptor and turkey (Beach et al, 2009;Davison and Harrach, 2002;Davison et al, 2000;Kovács and Benkö, 2009). A new genus, Ichtadenovirus, has been identified recently in fish (Benkö et al, 2005).…”

“…Typically, adenovirus infection in most species is characterized by enteritis and respiratory disease (Beach et al, 2009;Russell, 2009;Rux and Burnett, 2004;Schrenzel et al, 2005). However, other clinical manifestations have been observed.…”

“…However, other clinical manifestations have been observed. For example, turkey hemorrhagic enteritis virus (THEV) causes inclusion body hepatitis, depression, splenomegaly, immunosuppression and death (Beach et al, 2009;Jucker et al, 1996;Pitcovski et al, 1998); falcon adenovirus also causes hepatitis ; and agamid adenovirus infection can be subclinical or lethal (Wellehan et al, 2004).…”

Crystallization of the C-terminal head domain of the fibre protein from a siadenovirus, turkey adenovirus 3

“…In the PCR, 1 ml of this dilution was used as template without any further treatment or exact determination of the viral DNA concentration. The primer sequences to amplify the carboxy-terminus of the fibre gene encoding amino acids 304-454 were taken from the genome sequence of the Virginia strain of TAdV-3 recently deposited in GenBank (entry AY849321; Beach et al, 2009b). To facilitate the molecular cloning, the oligonucleotides (forward primer 5 0 -GCGAATTCATGGCTAC-TCCTGG-3 0 ; reverse primer 5 0 -CGAAGCTTTCAGCCTATCA-AAC-3 0 ) were synthesized with an eight-nucleotide-long 5 0 extension to allow cleavage by the restriction enzymes EcoRI and HindIII, respectively (restriction sites are shown in bold).…”

“…Some of the less virulent strains are being used for vaccination against turkey haemorrhagic enteritis (Beach et al, 2009a). A study comparing the genome sequence of several virulent and avirulent TAdV-3 strains has shown differences in terms of mutations in the fibre sequence (Beach et al, 2009b).…”