Identification of a novel porcine adenovirus
Halvorsen, Vibeke Sjoblom
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In this research, we identified a probably novel porcine adenovirus (PAdV). Porcine adenoviruses belong to the genus Mastadenovirus in the family Adenoviridae. So far 5 serotypes have been accepted, PAdV types 1 to 5, and two more have been proposed. While the first four serotypes were discovered in the 1960s, the fifth serotype has only been found in Japan, the first time in 1990. Adenoviruses have generally low pathogenicity and are thought to be excellent vaccine vectors. However, the regions of the genome thought to be the best for gene insertion are generally not the desired size. Thus researchers have focused on finding the maximum size of the inserted gene as well as the best region for the insertion. PAdV-3, PAdV-4, and PAdV-5 are thought to be the most suitable serotypes for foreign DNA insertion, but studies revealed PAdV-4 in a few cases leading to neurological disorders thus, not fit to be a vector. PAdV-3 does not cause any serious disease, but is however widespread throughout the world and most swine populations have pre-exisiting PAdV-3 specific virus neutralizing antibodies. Therefore it would not trigger an immune response to produce antibodies against the recombinant virus. PAdV-5 was found so far only in Japan, and shows no or little resemblance to the other serotypes, and actually is more similar to some of the bovine adenoviruses. Several regions of the PAdV-5 genome have been tried to be delete and used as an insertion site, for example E1, E3, and the fiber gene. The E3 region was especially promising and a region as large as 2.9 kb most likely could be deleted and used as an insertion site. This shows that it is worthwhile to look for further PAdV types both to see their diversity and possibly finding even better vector candidates. In our experiments, by applying a general adenovirus PCR, we found what might well be a new porcine adenovirus type identified in a wild boar sample from Hungary. The result of the PCR amplification, DNA sequencing and phylogenetic comparison of two partial viral gene sequences (DNA polymerase and IVa2) showed that our sample contained a virus different from all adenoviruses (sequenced so far in the same region). But to conclude that this in fact is a new type, we need to compare our virus with PAdV-4 and the proposed serotypes 6 and 7 from Japan. In the future, we therefore hope to compare our virus to these unsequenced or not fully sequenced serotypes, and find the pathological characteristics and economical importance of this possibly novel PAdV type. Our results confirm the possibility of using PCR screening to find novel adenovirus types.