Antiserum raised in pigs against canine distemper virus and its utility in diagnostic procedures for morbillivirus infections (canine distemper, phocine distemper, rinderpest)

Polioencephalomalacia in captive harbour seals (Phoca vitulina)

In a colony of 11 harbour seals (Phoca vitulina Linné 1758) two episodes of central nervous disorders occurred within 2 years causing fatalities in seven adult animals. Clinical signs comprised dyspnoea, anorexia, apathy, incoordination and lateral recumbency. Vitamin B complex therapy was successful once. Pathomorphological examination of seven carcasses revealed acute and subacute malacia of the cerebellar grey matter. Additional acute malacic lesions located in the cerebral cortices and basal ganglia were observed. Mesencephalic nuclei were less severely affected and displayed acute changes. Despite intense search for environmental toxins and infectious agents, the cause of the fatalities remained undetermined. However, the type and pattern of the lesions are most suggestive of a thiamine deficiency.

Rapid and sensitive detection of immunoglobulin M (IgM) and IgG antibodies against canine distemper virus by a new recombinant nucleocapsid protein-based enzyme-linked immunosorbent assay

Canine distemper morbillivirus (CDV) infection causes a frequently fatal systemic disease in a broad range of carnivore species, including domestic dogs. In CDV infection, classical serology provides data of diagnostic and prognostic values (kinetics of seroconversion) and is also used to predict the optimal vaccination age of pups. Routine CDV serology is still based on time- and cost-intensive virus neutralization assays (V-NA). Here, we describe a new capture-sandwich enzyme-linked immunosorbent assay (ELISA) that uses recombinant baculovirus-expressed nucleocapsid (N) protein of a recent CDV wild-type isolate (2544/Han95) for the detection of CDV-specific antibodies in canine sera. Recombinant antigen was produced with high efficacy in Heliothis virescens larvae. The capture-sandwich ELISA enabled a clear-cut qualitative evaluation of the CDV-specific immunoglobulin G (IgG) and IgM serostatuses of 196 and 35 dog sera, respectively. Inter-rater agreement analysis (kappa = 0.988) indicated that the ELISA can be used unrestrictedly as a substitute for the V-NA for the qualitative determination of CDV-specific IgG serostatus. In an attempt to semiquantify N-specific antibodies, a one-step-dilution (alpha method) IgG-specific ELISA was implemented. Alpha values of >/=50% showed very good inter-rater agreement (kappa = 0.968) with V-NA titers of >/=1/100 50% neutralizing dose (ND50) as measured against the central European CDV wild-type isolate 2544/Han95 in canine sera originating from northern Germany. An ND50 titer of 1/100 is considered a threshold, and titers of >/=1/100 indicate a resilient, protective immunity. CDV N-specific antibodies of the IgM class were detected by the newly developed ELISA in 9 of 15 sera obtained from dogs with symptoms of acute distemper. In leucocytes of 5 of the 15 dogs (all of which were also IgM positive) CDV RNA was detected by reverse transcription (RT)-PCR. The recombinant capture-sandwich ELISA detecting N-specific antibodies of the IgG class provided superior sensitivity and specificity and thus represents a rapid and cost-effective alternative to classical CDV V-NA. By detection of specific IgM antibodies, the ELISA will be complementary to RT-PCR and V-NA in the diagnosis of acute distemper infections.

Analysis of the haemagglutinin gene of current wild-type canine distemper virus isolates from Germany

The haemagglutinin (H) gene sequences from three wild-type canine distemper viruses (CDV) isolated during 1994-1995 were sequenced to determine whether contemporary strains had undergone significant genetic changes relative to the currently used vaccine strains. The new isolates were closely related to each other (> 99%) and displayed about 90-91% sequence homology to the Onderstepoort and Convac vaccine strains. There were one to four additional potential glycosylation sites compared to the vaccine strains which were also present in a German dog CDV isolate dating from 1990. However, only a very slight reduction in neutralizing titre against the new isolates was found when compared with the Onderstepoort and Rockborn vaccine strains. Cysteine and proline residues were well conserved indicating a conserved three dimensional structure for the protein. By phylogenetic analysis the recent isolates showed a narrow clustering close to the previous canine isolates indicating a linear pattern of evolutionary changes. A comparison with published CDV H gene sequences suggested the presence of different lineages of CDV on a global scale and possible cocirculation of more than one genotype of CDV.

Intestinal lesions in experimental phocine distemper: light microscopy, immunohistochemistry and electron microscopy

The involvement of the intestinal mucosa and of the gut-associated lymphoid tissue in phocine distemper was studied in six severely diseased harbour seals 11 to 16 days after experimental infection. Five seals exhibited a mild or moderate enteritis in the small or large intestine. In all the seals, a moderate to severe depletion of submucosal lymphoid follicles was found. Likewise, antigen of phocine distemper virus (PDV) was demonstrated immunohistochemically in the intestinal wall of all the seals. Most antigen was found in the submucosal lymphoid follicles, followed by the crypt epithelium and follicle-associated epithelium (FAE). Ultrastructurally, intracytoplasmic tubular structures were detected in the FAE and interpreted as morbilliviral nucleocapsids. The results indicate a direct cytopathogenic effect of PDV on intestinal lymphoid and epithelial cells and suggest an important role of the intestinal tract in phocine distemper and, by analogy, in other morbillivirus infections as a regular site of virus replication, virus shedding and immunosuppression.

Intertypic differentiation and detection of intratypic variants among canine and phocid morbillivirus isolates by kinetic neutralization using a novel immunoplaque assay

Intertypic antigenic differences and the intratypic variability of the closely related canine (CVD) and phocid distemper viruses (PDV) were examined using a molecular (monoclonal antibodies specific for the H- and F-glycoproteins) and a functional (kinetic neutralization, KN) approach. KN studies were carried out using a novel immunoplaque technique which combined conventional plaque assay and antigen-specific enzyme-immunostaining techniques. Morbillivirus isolates of canine and phocid origin clearly formed two separate groups. Minor antigenic differences were also evident within each cluster. A distemper isolate of mustelid origin was distinguishable from both CDV- and PDV-like prototype viruses by kinetic neutralization.

Round table on morbilliviruses in marine mammals

Since 1988 morbilliviruses have been increasingly recognized and held responsible for mass mortality amongst harbour seals (Phoca vitulina) and other seal species. Virus isolations and characterization proved that morbilliviruses from seals in Northwest Europe were genetically distinct from other known members of this group including canine distemper virus (CDV), rinderpest virus, peste des petits ruminants virus and measles virus. An epidemic in Baikal seals in 1987 was apparently caused by a morbillivirus closely related to CDV so that two morbilliviruses have now been identified in two geographically distant seal populations, with only the group of isolates from Northwest Europe forming a new member of the genus morbillivirus: phocid distemper virus (PDV). Because of distemper-like disease, the Baikal seal morbillivirus was tentatively named PDV-2 in spite of its possible identity with CDV. The appearance of morbilliviruses in the Mediterranean Sea causing high mortality amongst dolphins should further increase the research activities on protection strategies for endangered species of marine mammals.

Investigations on course and outcome of phocine distemper virus infection in harbour seals (Phoca vitulina) exposed to polychlorinated biphenyls. Virological and serological investigations

The influence of polychlorinated biphenyls (PCBs) on phocine distemper virus (PDV) infections in harbour seals (Phoca vitulina) was studied. Six out of ten seals had been conditioned with a defined mixture of PCB-congeners for several weeks. Following exposure to the cell culture-propagated PDV isolate 2558/Han 88 the complete clinical picture of "1988 seal plague" was provoked in all ten seals inoculated. Four out of six PCB-conditioned seals and two out of four seals not loaded with PCBs succumbed to the infection within three weeks post inoculation. With regard to the clinical course, duration of cell-associated viremia, PDV-antigen distribution in tissues of fatally infected seals and the humoral immune response to PDV no differences between PCB-loaded and unloaded seals were recognized. Evidence was obtained that the pathogenesis of experimental PDV-infection in harbour seals shares some features with those of canine distemper in terrestrial carnivores. In contrast, however, to experimental distemper infection of gnotobiotic dogs prompt development of high titres of PDV-specific IgG did not correlate with recovery from infection.