Human Adenovirus Type 52: a Type 41 in Disguise?

Abstract

Recently, Jones et al. described a new human adenovirus (HAdV) (3) and claimed it to be a “new type” and even a “new species”: “human adenovirus 52 or HAdV-52 of species G.” We dispute both claims. By virus neutralization (VN), they showed it to be different from its phylogenetically closest relative, simian adenovirus 1. Surprisingly, they failed to provide additional VN data corroborating their claim of a novel serotype. Consequently, the new adenovirus may later, on the basis of VN data, prove to be a known serotype, e.g., HAdV-40 or HAdV-41. In their attempts to show that the virus was sufficiently distinct from HAdV-40 and HAdV-41 to be considered a new type, they embarked on phylogenetic analyses. These viruses were accepted as separate serotypes by the ICTV (1) on the basis of differences in their DNAs and their antigenic distances as measured by VN (1, 2), complying with the definition of serotypes (or “types”) as follows. Adenovirus serotypes are differentiated on the basis of neutralization assays. A serotype is defined as one which either exhibits no cross-reaction with others, or shows a homologous/heterologous titer ratio greater than 16 (in both directions). For homologous/heterologous titer ratios of 8 or 16, a serotype assignment is made if either the viral haemagglutinins are unrelated (as shown by lack of cross-reaction in haemagglutination-inhibition tests), or if substantial biophysical, biochemical or phylogenetic differences exist (1). Jones et al. also claim that the new adenovirus belongs to a novel species, named “G.” They argue that the phylogenetic distance between “HAdV-52” and HAdV-40 and HAdV-41 is “at least as great as those differentiating the other HAdV species.” This species designation would also be unprecedented. The phylogenetic distance between HAdV-40 and HAdV-41 is also at least as great as those differentiating other HAdV species, and also these two adenoviruses are not considered different species (1). In summary, according to current taxonomical criteria and the data presented, the newly identified adenovirus should not be considered a novel serotype, let alone a novel species.