Influenza A(H10N7) Virus in Dead Harbor Seals, Denmark

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Jesper S. Krog

, Mette S. Hansen, Elisabeth Holm, Charlotte K. Hjulsager, Mariann Chriél, Karl Pedersen, Lars O. Andresen, Morten Abildstrøm, Trine H. Jensen, and Lars E. Larsen

Author affiliations: Technical University of Denmark, Frederiksberg, Denmark (J.S. Krog, M.S. Hansen, E. Holm, C.K. Hjulsager, M. Chriél, K. Pedersen, L.O. Andresen, L.E. Larsen); Anholt Gartneri & Naturpleje, Anholt, Denmark (M. Abildstrøm); Aalborg Zoo/Aalborg University, Aalborg, Denmark (T.H. Jensen)

Abstract

Since April 2014, an outbreak of influenza in harbor seals has been ongoing in northern Europe. In Denmark during June–August, 152 harbor seals on the island of Anholt were found dead from severe pneumonia. We detected influenza A(H10N7) virus in 2 of 4 seals examined.

Influenza A virus is widespread and affects a wide range of species, including humans (1). Waterfowl are considered the natural reservoir for most subtypes of influenza A virus, and most mammalian-adapted viruses initially originated in interspecies transmission from aquatic birds (2). Avian influenza A virus (AIV) replicates primarily in the intestinal tract of birds and is transmitted mainly through the fecal–oral route (1). Pinnipeds (e.g., seals) share the same shoreline habitats as many waterfowl species and therefore can be exposed to AIV. Several instances of interspecies transmission between birds and harbor seals (Phoca vitulina) with AIV subtypes H7N7, H4N5, H4N6, H3N8, and H3N3 have been reported in the United States, and antibodies against a wide range of subtypes have been identified in Europe, Asia, and South America (reviewed by White [3]). Human infections with seal influenza A virus have occasionally been reported (3). More recently, A(H1N1)pdm09 virus was isolated from elephant seals (Mirounga angustirostris) off the central coast of California, USA (4). To our knowledge, AIV in harbor seals off the coast of northern Europe was first reported in April 2014 (5).

The Study

Thumbnail of Deaths of harbor seals (Phoca vitulina) on the small island of Anholt, Denmark, summer 2014.

Figure 1. Deaths of harbor seals (Phoca vitulina) on the small island of Anholt, Denmark, summer 2014.

During June 16–August 13, 2014, a total of 152 harbor seals were found dead on the shore of the small island of Anholt in Denmark. A few carcasses were reported in late June, and deaths peaked in mid-July (Figure 1). Four freshly or recently dead harbor seals were submitted to the National Veterinary Institute, Technical University of Denmark, for necropsy and laboratory examination. The seals were juveniles; 3 were males; and the animals’ body conditions were normal or slightly below normal (2 seals each). All had intense reddening of the lungs, with multifocal condensation of lung tissue, moderate to massive amounts of blood in thorax, and an intensely hyperemic trachea. One seal also had blood in the mouth. No lesions were apparent in other organs, but all 4 animals had empty stomachs. In all seals, histopathologic examination of the lungs showed massive suppurative and necrotizing bronchopneumonia and many bacteria in the alveoli. In the interstitial tissues, edema, fibrin, and neutrophils were seen. Samples from relevant organs were tested for bacteria on selective and nonselective culture media. Samples from the lungs revealed massive growth of Pseudomonas aeruginosa in all animals, indicating severe bacterial pneumonia (6). In addition, variable growth of Streptococcus equi subsp. zooepidemicus was found.

We tested samples of lung and spleen for influenza A virus by a slightly modified version of a previously described real-time reverse transcription PCR (RT-PCR) that targeted the matrix gene (7) and for phocine and canine distemper virus by 1-step RT-PCR using previously described primers that targeted the P (phosphoprotein) gene (8). All 4 samples were negative for distemper virus. Samples from lungs and spleen from 2 seals were positive for influenza A virus (Table). RNA from the influenza A virus–positive samples subsequently tested negative for H5 and H7 subtypes by subtype-specific real-time RT-PCR.

Dr. Krog is a molecular biologist at the National Veterinary Institute. His primary research focus is national surveillance of avian and swine influenza A virus and other zoonotic viruses.

Acknowledgments

We thank Ivar Høst for submitting the material; Y.M Deng and P. Iannello for contributing the hemagglutinin sequence EPI339225; R. Bodewes and colleagues for contributing EPI544356 and EPI544357; and S. Zohari and colleagues for EPI545212, EPI545213, EPI547696, and EPI547697 to the Global Initiative on Sharing All Influenza Data EpiFlu database.

Surveillance of diseases in wildlife is financed by the Danish Forest and Nature Agency, project no. NST-410239.

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Figures

Table

Table. Results of PCR and sequence analysis of the 2 influenza A virus–positive harbor seals, Denmark, 2014

Suggested citation for this article: Krog JS, Hansen MS, Holm E, Hjulsager CK, Chriél M, Pedersen K, et al. Influenza A(H10N7) virus in dead harbor seals, Denmark. Emerg Infect Dis [Internet]. 2015 Apr [date cited]. http://dx.doi.org/10.3201/eid2104.141484

DOI: 10.3201/eid2104.141484