Seroepidemiological survey of distemper virus infection in the Caspian Sea and in Lake Baikal

Forty Caspian seals were surveyed seroepidemiologically between 1993 and 1998 around the times of mass mortality that occurred in 1997 in the Caspian Sea and seven Baikal seals were also surveyed in 1998. Virus neutralizing tests and ELISA clearly suggested that distemper virus epidemic was caused in Caspian seals before the spring of 1997 and that CDV infection continued to occur in Lake Baikal in recent years.     

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.     

Seroepidemiological survey of morbillivirus infection in Kuril harbor seals (Phoca vitulina stejnegeri) of Hokkaido, Japan

Serological analysis was performed to detect morbillivirus infection in Kuril harbor seals in Hokkaido, Japan. Serum samples were collected from the seals at Nosappu (231 sera), Akkeshi (16), and Erimo (75) between 1998 and 2005. Antibodies to phocine distemper virus (PDV) were detected by ELISA in seals from Nosappu and Erimo. Antibodies to PDV were found in 56% (5/9) of the sampled seals from Nosappu in 1998, versus only 5% (3/66) for 2003, 1% (1/79) for 2004, and 1% (1/77) for 2005. These suggest epidemic caused by the virus in or before 1998. As antibody-positive seals included juvenile seals in 2003 and 2005, sporadic infections of the virus are thought to have occurred in recent years. In Erimo, antibodies to PDV were found in 50% (14/28) of sampled seals in 2004, versus only 13% (1/8) for 1999, 7% (1/15) for 2003, and 0% (0/24) for 2005. These suggest sporadic infection by the virus before 2003 and the epizootic between after autumn in 2003, when samples of 2003 were collected, and 2004. Since antibodies to canine distemper virus (CDV) were detected in one adult seal from Nosappu in each year from 2003 to 2005, sporadic infections of the virus were suggested. There were no difference in incidence of seals with antibodies to the viruses between males and females and between juveniles and adults.     

Humoral immune responses in seals infected by phocine distemper virus

Recently the isolation and characterisation of a morbillivirus which caused high mortality in common seals (Phoca vitulina) in 1988 have been reported. Because of the clinical and pathological similarity of the disease in seals to that of distemper in dogs, the name phocine distemper virus (PDV) has been proposed. There are marked differences in the virus-induced proteins of PDV compared to other morbilliviruses and the humoral immune response of moribund and dead seals to PDV was restricted to some of the internal antigens of PDV, similar to the response described earlier for canine distemper virus infection in dogs.     

The seal death in Danish waters 1988. 2. Virological studies.

Mass abortions and high mortality were observed in harbour seals in Danish waters during 1988. Severe pneumonia and emphysema were typical clinical and post-mortem findings. Virological studies were carried out to identify the cause of the epidemic. Although seal herpesvirus (SeHV) was isolated in 23 of 114 animals this virus was subsequently found not to be the primary cause of the disease. Following the observation of seroconversion against canine distemper virus (CDV) in diseased seals (Osterhaus & Vedder 1988) a CDV-like morbillivirus (phocine distemper virus, PDV) was identified in organs of diseased animals. It is concluded that the epidemic was caused by introduction of PDV into a highly susceptible population presumably free from morbillivirus infection. The origin of PDV remains unknown but evidence of prior morbillivirus infection has been found in arctic and antarctic seal populations.     

Fatal enterocolitis in harbour seals (Phoca vitulina) caused by infection with Eimeria phocae

Coccidiosis due to Eimeria phocae infection has been described in harbour seals (Phoca vitulina) from the western Atlantic population, but not in any detail in seals from the eastern Atlantic population. This paper describes fatal enterocolitis due to E phocae infection in three juvenile harbour seals at a rehabilitation centre in the Netherlands in July 2003. The clinical signs were lethargy, bloody faeces, and intermittent convulsions and muscle tremors just before they died; the nervous signs resembled those of nervous coccidiosis in calves. The main pathological finding was severe, diffuse, haemorrhagic enterocolitis; there were diffuse inflammatory changes in the lamina propria of the jejunal, ileal, caecal and colonic mucosa that were associated with the presence of the sexual stages and oocysts of a coccidian species identified as E phocae. A retrospective microscopical examination of intestinal tissues from 113 harbour seals that had died between 1999 and 2004 revealed one seal that was positive for E phocae.     

Canine distemper virus--an agent looking for new hosts

Canine distemper is caused by the canine distemper virus (CDV), a RNA virus belonging to the genus Morbillivirus of the family Paramyxoviridae. The genus Morbillivirus includes measles virus, Rinderpest virus and peste-des-petits-ruminants virus. The host spectrum of CDV, which includes numerous families of Carnivores, has been changed in the last years and distemper-like diseases have been observed in numerous other species. These include epidemics in large felids, marine mammals and javelinas. Different viruses have been isolated from pinnipeds including a seal-specific isolate, termed phocine distemper virus 1, PDV-1, and a CDV strain, named PDV-2. Retrospective analysis of previous epidemics among marine mammals in various regions of the world provide evidence for the occurrence of so far unrecognized morbillivirus epidemics. In some including the mass mortalities of Baikal and Caspian seals and of large felids in the Serengeti, terrestrial carnivores including dogs and wolves have been suspected as a vector for the infectious agent. However, in other epidemics among marine mammals the source of infection remains unknown including both seal epidemics in northwestern Europe in 1988 and 2002. It remains to be determined whether a morbillivirus from other marine mammals or terrestrial carnivores caused the infection in this unprotected seal populations.     

Morbillivirus infections of seals during the 1988 epidemic in the Bay of Heligoland: III. Transmission studies of cell culture-propagated phocine distemper virus in harbour seals (Phoca vitulina) and a grey seal (Halichoerus grypus): clinical, virological and serological results

Eight harbour seals (Phoca vitulina), two of them seronegative, six seropositive against PDV and a seronegative grey seal (Halichoerus grypus) were exposed to a low doses of a cell culture-propagated phocine distemper virus isolate (PDV 2558/Han 88). An intranasal route of inoculation was chosen. Clinical signs, resembling those of 1988's seal disease and seroconversion were observed in both seronegative harbour seals. One of them succumbed to the infection. The virus was not transmitted to another susceptible harbour seal which served as in-contact animal. Virus could be recovered from leucocytes of the diseased seals. Viremia was also present in a seropositive harbour seal that developed mild clinical signs; other seropositive seals were protected from clinical disease. The grey seal showed seroconversion upon inoculation, but did not develop any signs of disease. The humoral immune response of the seals plainly discriminated between homologous (PDV) and heterologous (canine distemper virus, CDV) virus as shown by virus neutralization tests and an antibody-binding assay (PLA).     

Mass mortality in seals caused by a newly discovered morbillivirus

During a recent disease outbreak among harbour seals (Phoca vitulina) in the North and Baltic seas, more than 17,000 animals have died. The clinical symptoms and pathological findings were similar to those of distemper in dogs. Based on a seroepizootiological study, using a canine distemper virus (CDV) neutralization assay, it was shown that CDV or a closely related morbillivirus (phocid distemper virus-PDV) was the primary cause of the disease. The virus was isolated in cell culture from the organs of dead seals and characterized as a morbillivirus by serology (immunofluorescence neutralization and enzyme-linked immunosorbent assays) and by negative contrast electron microscopy. Experimental infection of SPF dogs resulted in the development of mild clinical signs of distemper and CDV-neutralizing antibodies. The disease was reproduced in seals by experimental inoculation of organ material from animals that had died during the outbreak. However, seals that had been vaccinated with experimental inactivated CDV vaccines were protected against this challenge. This fulfilled the last of Koch's postulates, confirming that the morbillivirus isolated from the seal organs, was the primary cause of the disease outbreak. The recent demonstration of the presence of a similar virus in Lake Baikal seals (Phoca sibirica), which infected these Siberian seals 1 year before the northwestern European seals were infected, raises new questions about the origin of this infectious disease in pinnipeds.     

The seal death in Danish waters 1988. 1. Pathological and bacteriological studies.

During the seal epizootic in Danish waters in 1988 a total of 81 adult seals were necropsied. The cause of death was suppurative bronchopneumonia complicated by pleurisy. Histologically, an interstitial pneumonia with cytoplasmatic inclusion bodies typical of canine distemper was identified in many of the seals. The condition was in many cases complicated with a secondary infection with Bordetella bronchiseptica.     

A review of the 1988 European seal morbillivirus epizootic

An epizootic of morbillivirus infection killed thousands of common seals (Phoca vitulina) in European seas in 1988. Most of the affected seals had respiratory signs and the main post mortem finding was acute pneumonia. The histopathological changes were similar to those of canine distemper. Six common porpoises (Phocoena phocoena) found stranded on the coast of Northern Ireland in late 1988 had similar lesions. Morbillivirus infection also killed several thousand Siberian seals (Phoca siberica) in Lake Baikal in 1987 and 1988. A morbillivirus (phocine distemper virus) has been isolated from affected seals in several European countries and studies of the antigenicity of the virus indicate that it has several unique epitopes that distinguish it from the other known morbilliviruses. Biochemical studies of the viral proteins, RNA and nucleotide sequence confirm that it is a new morbillivirus. There is seroepizootiological evidence of morbillivirus infection in Greenland harp seals (Pagophilus groenlandicus), ringed seals (Phoca hispida) and Dutch common seals several years before the 1988 epizootic. Antibodies to a morbillivirus have also been found in bottlenose dolphins (Tursiops truncatus) from the eastern coast of the USA. Further studies are required to determine whether these sea mammal populations have been infected with phocine distemper virus.     

Pathological findings indicative of distemper in European seals

The first recorded cases of the recent epizootic were harbour seals observed at the Danish island of Anholt, 12 April 1988. The disease then spread throughout the sea waters of north-western Europe. The total mortality in Europe up to November 1988, was estimated to be at least 17,000 seals. The mortality rate in Danish-Swedish waters was about 60%. Autopsies including sampling for histology of most organs were performed on 37 harbour seals and 12 grey seals, collected mainly at the Swedish west coast and in the southern Baltic. In most of the harbour seals and in three of the grey seals we found histological changes in the upper and lower respiratory tracts, in the lower urinary tract and in the lymphatic system consistent with those diagnostic of distemper viral infection in the canine. These diagnostic criteria were: presence of intracytoplasmic eosinophilic inclusion bodies of epithelial cells of the trachea and the urinary bladder, interstitial pneumonia, and atrophy of lymphatic organs due to depletion of lymphocytes. Our findings in pathology of a canine distemper-like disease in the seals were presented in late August 1988, together with the Dutch findings in virology by Dr. Osterhaus and collaborators.     

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.     

Morbillivirus infection of seals (Phoca vitulina) during the 1988 epidemic in the Bay of Heligoland. I. Mode, frequency and significance of cultural virus isolation and neutralizing antibody detection

From 16 (14%) out of 112 dead or euthanized seals originating from wildlife and seal orphanages phocine morbillivirus was isolated. The majority of viral isolates in cell cultures was obtained from lung homogenates of 15 out of 71 free-ranging seals (21%). The virus was isolated by longterm cultivation in roller cultures of seal kidney cells. The phocine morbillivirus was detected by typical cytopathogenic alteration and by peroxidase-linked antibody (PLA) assay, respectively. A neutralization test based on PLA was used for antibody detection in seals using a canine distemper virus (CDV) strain and in parallel one of the phocine morbillivirus isolates. All sera tested were proven to contain neutralizing antibodies of higher titres against the latter virus than against the CDV strain. Several seals furnished morbillivirus isolates and at the same time exhibited neutralizing antibodies of low to medium titres. No viral isolates were obtained from the majority of sick animals with moderate to high neutralizing titres (greater than 1/1,000). The significance of these findings is discussed in relation to the cause of the mass mortality amongst seals observed in 1988 in the Bay of Heligoland.     

Serosurvey for canine distemper virus exposure in dogs in communal lands in Zimbabwe

Sera from 173 apparently healthy, unvaccinated dogs from 4 widely separated communal lands in Zimbabwe were tested by ELISA for antibodies against canine distemper virus. Overall, 82% were positive with high prevalences found in each communal land. The highest seroprevalence was in dogs between 1 and 2 years of age (91%; 49/54). These results show dogs in the communal lands of Zimbabwe are commonly exposed to canine distemper virus and that a substantial number survive infection. The role that the virus might play in the high mortality rate of the dog population on communal land warrants further investigation.     

Streptococcus phocae isolated from a spotted seal (Phoca largha) with pyometra in Alaska

A spotted seal harvested by subsistence hunters in Kotzebue Sound, Alaska (USA), showed a grossly enlarged uterus and associated lymph nodes. Streptococcus phocae was isolated from the purulent uterine discharge. Histopathologic examination revealed inflammation that was limited to the uterine mucosa. Lymph nodes draining the affected organ were reactive but no evidence of active infection was found in the lymph nodes. This report is the first Streptococcus phocae isolated from spotted seals as well as the first report of pyometra as the main pathologic finding associated with this pathogen. Isolation of this pathogen from Alaska expands the reported range to arctic pinnipeds. Zoonotic potential remains unknown.     

郑州市犬瘟热病毒感染血清学调查

为了解郑州市犬瘟热流行情况,为犬瘟热的预防提供参考依据。采用间接ELISA法对来自郑州市480份血清进行抗体水平的检测,结果显示480份犬血清中犬瘟热抗体平均阳性率为16.04%,其中3岁以下犬犬瘟热阳性率为13.13%,3岁以上犬犬瘟热阳性率为 2.91%。犬瘟热的发病率仍然很高,尤其是3岁以下的犬犬瘟热阳性率较为高,应引起高度重视,防止犬瘟热的传播。     

Evaluation of the efficacy and duration of immunity of a canine combination vaccine against virulent parvovirus, infectious canine hepatitis virus, and distemper virus experimental challenges

The results of this study confirmed that dogs vaccinated subcutaneously with a commercially available multivalent vaccine containing modified-live canine distemper virus, canine adenovirus type 2, canine parvovirus type 2b, and canine parainfluenza virus antigens were protected against sequential experimental challenge 55 to 57 months after initial vaccination given at 7 to 8 weeks of age. All 10 vaccinates were protected against clinical diseases and mortality following parvovirus and infectious canine hepatitis experimental infections. All vaccinates were protected against mortality and 90% against clinical disease following distemper challenge. These data support at least a 4-year duration of immunity for these three "core" fractions in the combination vaccine.