Newcastle Disease (ND) is caused by avian paramyxovirus-1 (APMV-1) and is one of the most important viral diseases of poultry, with strongly varying symptoms of disease. The APMV-1 of pigeon (pigeontype paramyxovirus, PPMV-1) mainly infects racing pigeons, purebred pigeons, city pigeons and wild pigeons, but poultry is also susceptible to this pathogen. The disease is widespread worldwide and especially the severe forms, caused by the mesogenic and the velogenic pathotype, lead to high economic losses. Using the reverse genetic system for NDV, it is possible to exchange different regions of the viral genome of NDV isolates with different pathogenicity and to generate recombinant viruses to identify possible virulence determinants. For a long time, the amino acid sequence at the proteolytic cleavage site of the fusion protein was regarded as the virulence determinant of NDV. However, studies in recent years have increasingly shown that there are further regions in the genome that influence pathogenicity. Especially pigeon isolates showed that despite presence of a polybasic amino acid sequence at the proteolytic cleavage site of the F protein, which is typical for meso- and velogenic APMV-1, they are classified as lentogenic (low virulent) with a determined intracerebral pathogenicity index (ICPI) < 0.7. The determination of the complete sequence of the PPMV-1 isolate R75/98 and the development of the corresponding recombinant virus rR75/98 were the aim of this work. After ...