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Dispatch
Phocine Distemper in German
Seals, 2002
Gundi Müller,*
Peter Wohlsein,* Andreas Beineke,* Ludwig Haas,* Irene Greiser-Wilke,*
Ursula Siebert,† Sonja Fonfara,† Timm Harder,‡ Michael Stede,§ Achim.D.
Gruber,* and Wolfgang Baumgärtner*
*School of Veterinary Medicine Hannover, Hannover, Germany; †Christian-Albrechts-University
at Kiel, Büsum, Germany; ‡Food, Veterinary and Environmental Diagnostic
Laboratory of Schleswig-Holstein, Neumünster, Germany; and §State Veterinary
Investigation Centre for Fish, Cuxhaven, Germany
Suggested citation
for this article:
Müller G, Wohlsein P, Beineke A, Haas L, Greiser-Wilke I, et al. Phocine
distemper in German seals, 2002. Emerg Infect Dis [serial online] 2004
Apr [date cited]. Available from: URL: http://www.cdc.gov/ncidod/EID/vol10no4/03-0591.htm
Approximately 21,700
seals died during a morbillivirus epidemic in northwestern Europe in
2002. Phocine distemper virus 1 was isolated from seals in German waters.
The sequence of the P gene showed 97% identity with the Dutch virus
isolated in 1988. There was 100% identity with the Dutch isolate from
2002 and a single nucleotide mismatch with the Danish isolate.
In the past, fatal morbillivirus infections have been reported in various
cetacean and seal species. In pinnipeds, the disease has been described
in crabeater seals (Phoca carcinophagus) from the Antarctic (1),
Baikal seals (P. siberica [2]), monk seals (Monachus
monachus; [3]), Caspian seals (P. caspica
[4]), and harbor seals (P. vitulina) from the
North and Baltic Sea (5). Phocine and canine distemper
viruses (CDV) were isolated as causative agents in different epidemics
of seals. Phocine distemper virus 1 (PDV-1) and CDV represent two distinct
but antigenetically and genetically related morbilliviruses (5).
An increased number of deaths in the Danish seal population was noticed
in May 2002, starting at the Kattegat Isle of Anholt. PDV-1 was isolated
as the causative agent (6), and the disease spread to
Sweden and Norway in the following month. A second outbreak was observed
mid-June in the Netherlands. Subsequently, the disease spread to Germany
and Denmark in an eastern direction, and to Belgium, France, Great Britain,
and Ireland to the West. In Germany, approximately 7,500 harbor seals
died during the epidemic (7). We present morphologic,
virologic, and serologic findings in affected seals from German waters.
The Study
Necropsies of 95 harbor seals (P. vitulina) collected from July
to December 2002 showed a moderate-to-severe pulmonary alveolar and interstitial
emphysema and alveolar edema as the predominant findings. Additional lesions
included mediastinal emphysema, gradually variable suppurative bronchopneumonia,
and catarrhalic enteritis. Histologic lesions consisted of interstitial
pneumonia with multinucleated syncytial cells and a moderate-to-severe
lymphocytic depletion in the lymphoid tissues. Single animals had an acute,
focal, nonsuppurative encephalitis (Figure 1A).
In addition, neuronal necrosis and mild gliosis were observed. Cytoplasmic
and nuclear acidophilic inclusion bodies were detected in respiratory
epithelial cells, gastric surface mucous and chief cells, intestinal crypt
epithelial cells, and hepatic and pancreatic duct epithelial cells. In
the urogenital tract, inclusion bodies were observed in endometrial, vaginal,
and epididymal epithelial cells as well as epithelial cells of the renal
pelvis and urinary bladder. Occasionally, inclusion bodies were present
in neuronal and glial cells of the central nervous system.
Immunohistochemical analyses were performed by using a cross-reacting
murine monoclonal antibody specific for the morbillivirus nucleoprotein.
Morbillivirus antigen was demonstrated in 39 (45%) of the 86 cases. Morbillivirus
antigen was detected in lung, trachea, stomach, intestine, liver, pancreas,
kidneys, urinary bladder, female genital mucosa, and epididymal tubules
(Figure 1B). In the lymphoid tissues, variable
numbers of lymphocytes and macrophages of the follicular and parafollicular
areas were positive. In affected areas of the brain, neurons and glial
cells contained morbillivirus antigen in the nuclei and cytoplasm.
Screening for morbillivirus-specific nucleic acid in tissue samples from
lung, spleen, and lymph nodes as well as in blood samples from 85 seals
was performed by reverse transcription–polymerase chain reaction (RT-PCR).
For this procedure, universal morbillivirus primers based on the conserved
sequence of a 457-bp fragment of the phosphoprotein gene (6,8)
were used. PDV-specific RNA was detected in 46 (54%) of the 85 seals from
German waters affected from July onward. Both PDV-specific RNA and morbillivirus
antigen were detected in 33 (43%) of 77 animals. Seals with no detectable
morbillivirus antigen or nucleic acid had pneumonia and endoparasitosis
of varying degrees of severity or died of undetermined causes.
Sequence analysis of the RT-PCR product showed an identity of 97% compared
to the Dutch isolate of 1988. The German isolate was 100% identical with
the PDV isolate from the Netherlands and differed in 1 nt from the Danish
isolate (6) (not shown). Phylogenetic analysis showed
that the phocine isolates from the two epidemics in European waters formed
a discrete cluster, separated from the CDV isolates, including those from
lion and Siberan seal (Figure 2).
Neutralization assays using the CDV strain Onderstepoort were performed
to determine the titers of serum samples from 187 harbor seals from German
waters, collected from 1996 until the outbreak of the epidemic in 2002
(9,10). Because of the cytotoxicity of some serum samples,
only titers of >10 were considered positive. No neutralizing
antibodies were found in 164 (88%) of 187 serum samples. Titers from 22
(12%) of the 187 animals ranged from 14 to 240 (mean 50.5, ± 52.6 standard
deviation). One animal had a titer of 480.
Conclusions
The morphologic and immunohistochemical findings in harbor seals from
German waters during the recent morbillivirus epidemic in northwestern
Europe closely resembled those observed in 1988 (5,11–13)
and confirmed the epithelio-, lympho- and neurotropism of the PDV. The
distribution of the viral antigen indicates that the respiratory tract
was the primary route of morbillivirus infection. The virus-induced marked
lymphoid depletion may have allowed secondary bacterial infections. In
contrast to reports about European harbor seals from 1988, no demyelination
was detected in seals from German waters in 2002 (5).
Whether this finding represents a distinct feature of the 2002 epidemic
or is a result of the small number of investigated animals remains unclear.
Seals that died during the morbillivirus epidemic with no detectable viral
antigen or nucleic acid may have cleared the virus but still have virus-induced
immunosuppression, which could result in fatal secondary bacterial or
parasitic infections. Furthermore, poor preservation of some carcasses
may have caused false-negative results. The RNA sequences of the recent
virus isolates showed a virus population along the German coast during
this epidemic that was almost identical to the isolates from the Netherlands
and Denmark in 2002 and that had a high identity to the isolate from 1988
(6). Protective morbillivirus-specific antibody titers
were detectable in only a few seals from German waters before the outbreak
in 2002, suggesting a high susceptibility for morbillivirus infection
in this naive population.
During the morbillivirus epidemic in 1988, approximately 65% of the Dutch,
Danish, and German Wadden Sea seal population died (7).
The death rate in 2002 is estimated at approximately 51% on the basis
of the number of dead seals and the count of the Wadden Sea seal population
in 2003 (14). The lower death rate in 2002 may have
been influenced by different factors, such as decreased social contacts
at the beginning of the epidemic during the late breeding season. In addition,
genetic selection of a less susceptible population originating from the
survivors of the 1988 outbreak might have resulted in a lower number of
deaths during the second epidemic. It remains unclear why both outbreaks
started at the Danish Kattegat isle of Anholt. In the past, migrating
Arctic seal species, such as harp seals from Greenland, have been suspected
as carriers that introduced a morbillivirus into an immunologically naive
population (15). This species may have served as a reservoir
that maintains the circulation of PDV.
Several epizootics of infectious diseases in marine mammals with increases
in air temperature were observed, indicating that environmental influences
may have also resulted in the emergence of new epidemics (16).
Further studies are needed to determine whether alterations in migration
patterns of Arctic seal species caused by changes in climatic conditions
are responsible for the two PDV epidemics in northwestern Europe.
Dr. Müller is a
research assistant in the Department of Pathology of the School of Veterinary
Medicine in Hannover, Germany. Her research activities include a health
status monitoring program in seals and cetaceans from the German North
and Baltic Sea and cetaceans from the Black Sea with special emphasis
on morbillivirus infections.
References
- Bengtson JL, Boveng P, Franzen U, Have P, Heide-Jorgensen
MP, Harkonen TL. Antibodies to canine distemper virus in Antarctic seals.
Marine Mammal Science 1991;7:85–7.
- Grachev MA, Kumarev VP, Mamaev LV, Zorin VL, Baranova LV, Denikina
NN, et al. Distemper
in Baikal seals. Nature 1989;338:209–10.
- Van de Bilt MWG, Vedder EJ, Martina BEE, Sidi BA, Jiddou AB, Barham
MEO, et al. Morbilliviruses
in Mediterranean monk seals. Vet Microbiol 1999;69:19–21.
- Kennedy S, Kuiken T, Jepson PD, Deaville R, Forsyth M, Barrett T,
et al. Mass
die-off of Caspian seals caused by canine distemper virus. Emerg
Infect Dis 2000;6:637–9.
- Kennedy, S. A
review of the 1988 European seal epizootic. Vet Rec 1990;563–7.
- Jensen T, van de Bildt M, Dietz HH, Andersen TH, Hammer AS, Kuiken
T, et al. Another
phocine distemper outbreak in Europe. Science 2002;297:209.
- Bericht des Ministers für Umwelt, Natur und Forsten an den Umweltausschuss
des Landtages. Verlauf der Seehundstaupeepidemie im schleswig-holsteinischen
Wattenmeer im Jahr 2002. Stand: Jan 2003. Available from: http://www.wattenmeer-nationalpark.de/seehundstaupe.pdf
(in German).
- Barrett T, Visser IKG, Mamaev L, Goatley L, van Bressem MF, Osterhaus
ADME. Dolphin
and porpoise morbilliviruses are genetically distinct from phocine distemper
virus. Virology 1993;193:1010–2.
- Frisk AL, König M, Moritz A, Baumgärtner W. Detection
of canine distemper virus nucleoprotein RNA by reverse transcription-PCR
using serum, whole blood, and cerebrospinal fluid from dogs with distemper.
J Clin Microbiol 1999;37:3634–43.
- Müller G, Siebert U, Wünschmann A, Baumgärtner W. Immunohistological
and serological investigation of morbillivirus infection in harbour
porpoises (Phocoena phocoena) from the Baltic and North Sea.
Vet Microbiol 2000;75:17–25.
- Bergman A, Järplid B, Svensson BM. Pathological
findings indicative of distemper in European seals. Vet Microbiol
1990;23:331–41.
- Heide-Jorgensen MP, Harkonen T, Dietz R, Thompson PM. Retrospective
of the 1988 European seal epizootic. Dis Aquat Organ 1992;13:37–62.
- Heje NI, Henriksen P, Aalbaek B. The
seal death in Danish waters 1988. I. Pathological studies. Acta
Vet Scand 1991;32:205–10.
- Reijnders PJH, Brasseur S, Abt KF, Siebert U, Stede M, Tougaard S.
The harbour seal population in the Wadden Sea as revealed by the aerial
surveys in 2003. Wadden Sea Newsletter 2003;2:11–2.
- Dietz R, Hansen CT, Have P, Heide-Jorgensen MP. Clue
to seal epizootic. Nature 1989;338:627.
- Lavigne DM, Schmitz OJ. Global warming and increasing population densities:
a prescription for seal plagues. Mar Pollut Bull 1990;21:280–4.
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