Influenza A and B Virus Attachment to Respiratory Tract in Marine Mammals - Vol. 18 No. 5 - May 2012 - Emerging Infectious Disease journal - CDC
Volume 18, Number 5—May 2012
Dispatch
Influenza A and B Virus Attachment to Respiratory Tract in Marine Mammals
Article Contents
Abstract
Patterns of virus attachment to the respiratory tract of 4 marine mammal species were determined for avian and human influenza viruses. Attachment of avian influenza A viruses (H4N5) and (H7N7) and human influenza B viruses to trachea and bronchi of harbor seals is consistent with reported influenza outbreaks in this species.Attachment of influenza virus to tissues in the respiratory tract is a major determinant of host susceptibility to infection, efficiency of transmission, and pathogenicity and has been studied only to a limited degree (8,9). Attachment is determined largely by the specificity with which influenza virus attaches to sialosaccharide receptors on the host cell surface. In general, human influenza viruses prefer sialosaccharides in which sialic acid is linked to galactose by an α-2,3 linkage (SA-α-2,3-Gal), and avian influenza viruses prefer those with an α-2,6 linkage (SA-α-2,6-Gal) (10).
To understand differences in these properties between harbor seals and other marine mammals, we determined patterns of attachment for influenza virus strains known to have infected the respiratory tract of harbor seals, gray seals (Halichoerus grypus), harbor porpoises (Phocoena phocoena), and bottlenose dolphins (Tursiops truncatus). We chose gray seals, porpoises, and dolphins because their ranges overlap those of harbor seals and they are commonly kept in captivity.
The Study
For each of these 3 viruses, we also included a closely related strain from the putative donor host species (H7N7 A/Mallard/Sweden/100/02, H4N5 A/Mallard/Netherlands/13/2008, and B/Harbin/7/94, respectively) to determine whether adaptation to the new host species was associated with a change in attachment. Influenza virus A(H1N1)pdm09 (A/Netherlands/164/09) and seasonal subtype (H3N2) virus (A/Netherlands/213/03) were chosen because they circulate endemically in humans and might have contact with captive marine mammals through their caretakers. All viruses were isolated as described (11–13).
We obtained respiratory tract specimens from marine mammals from archives of paraffin-embedded tissues. Trachea and lung (including bronchus, bronchiole, and pulmonary alveoli) from 3 animals per species were examined.
Attachment of influenza virus to tissues was visualized by histochemical analysis as described (13). A positive result by light microscopy was granular to diffuse red staining on the apical surface of epithelial cells in trachea, bronchi, and bronchioles and on alveolar cells. Staining was scored as the percentage of cells in a section showing virus attachment. We also evaluated virus attachment to submucosal glands.
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