Immunohistological and serological investigation of morbillivirus infection in harbour porpoises (Phocoena phocoena) from the German Baltic and NorthSea

The role of morbillivirus infection as a cause of disease or death in harbo ur porpoises (Phocoena phocoena) from the German North and Baltic Sea was i nvestigated by serology, histology and immunohistochemistry. Blood and tiss ue samples of lung, brain and lymph nodes from 74 stranded or by-caught har bour porpoises from German waters were collected between 1991 and 1997. Acc ording to dentinal growth layers and body length, animals were grouped into four age classes (neonates, 0-1, 1-4, 3-16 years of age). Formalin-fixed, paraffin-embedded sections were stained by hematoxylin and eosin (HE). Immu nohistology was done in all lung tissues using the avidin-biotin-peroxidase technique and a polyclonal canine distemper virus (CDV) nucleoprotein-spec ific antibody, which cross-reacts with porpoise morbillivirus (PMV) antigen . A virus neutralization assay for detection of (Onderstepoort-strain) CDV- and PMV-specific antibodies was performed. Due to the cytotoxicity of some sera, only titres of 1:20 or greater were considered positive. PMV or CDV- specific neutralizing antibody titres were found in 88 and 50% of the anima ls, respectively. Titres were always highest against PMV indicating infecti on with a homologous porpoise virus strain. There were no significant diffe rences in neutralizing antibody titres between animals of the different age groups. No histological lesions specific for morbillivirus infection were detected and by immunohistology all cases were negative for morbillivirus a ntigen. The absence of morbillivirus antigen and the lack of characteristic morbillivirus-specific lesions showed that morbillivirus infection was not a cause of death or illness in the investigated population. However, the h igh incidence of PMV-specific antibodies in all age groups indicated a cont inuous spread of infection with a morbillivirus among harbour porpoises fro m the German Baltic and North Sea. (C) 2000 Elsevier Science B.V. All right s reserved.