Antigenic diversity of psittacine herpesviruses: Cluster analysis of antigenic differences obtained from cross‐neutralization tests

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Abstract
A total number of 28 viruses were isolated from different diseased or dead psittacine birds on various occasions. All of them were end-point purified and identified as herpesviruses (HV) on the basis of chloroform sensitivity, inhibition of multiplication in cell cultures by 5 iodo 2'-deoxyuridine (IUDR), lack of haemagglutination and morphology by electron microscopy. Antisera were produced in rabbits with each of the viruses. Herpesviruses from other birds (duck plague HV, stork HV, crane HV) were used for comparison. All virus/antiserum combinations were tested for homologous and heterologous neutralization in chick embryo fibroblast (CEF) cultures. The r1 and r2, as well as R-values were calculated according to the formula of Archetti & Horsfall (1950). These values formed the basis of the production of minimal trees and dendrograms. None of the non-psittacine viruses were neutralized with antisera produced against any of the psittacine herpesviruses and vice versa. Within the psittacine viruses three distinguishable subtypes were established. It is proposed to use as representative HV for subtype 1, 2 and 3 the strains KS 144/79, 6840/87 and 3115/88, respectively. Isolates 1483/92 and 8326/87 were distinguishable from each other and all other isolates; they are candidates for possible subtypes 4 and 5.