Influenza experts generally maintain that infection from birds to humans, which might lead to the emergence of a new pandemic, is made difficult primarily because of the lack of any suitable receptors (the component of the host cell that the virus binds itself to) in humans. By analogy with other viruses, it is now being proposed that it is highly probable that suitable receptors can be found in our eyes.

The research team includes Niklas Arnberg and Urban Kumlin from the Section for Virology, Umeå University, along with Sigvard Olofsson, Göteborg University, and Ken Dimock, University of Ottawa, Canada. They are now recommending, on the one hand, that authorities in exposed areas focus their monitoring for avian flu virus in humans via analysis of eye secretions and, on the other, that they use eye protection if there is any risk of being exposed to these viruses.

It was previously known that two different viruses, adenovirus type 37 [Ad37] and enterovirus type 70 [EV70], cause more or less severe eye infections. The researchers have recently shown that both types of virus attack the eye via the same receptor, alfa2,3-linked sialic acid. It was previously known that avian flu mainly uses precisely alfa2,3-linked sialic acid as a receptor. The type of sialic acid that Ad37 and EV70 use (alfa2,3-linked) occur above all on the outside of eye cells. On the outside of airway cells there is another type of sialic acid (alf2,6-linked), which is used instead by ordinary (human) influenza. The different types of sialic acid that occur in the eyes and airways (and in surrounding secretions such as tears and mucus), create a barrier that makes it difficult for a virus to infect both organs at the same time. The fact that avian flu can nevertheless make people seriously ill with pneumonia can probably be explained by the fact that some people are exposed to extremely high doses of virus and the fact that the barrier does not provide 100-percent protection.

There is a threat that avian flu, not least in cases of simultaneous infection with ordinary (human) influenza, will acquire the ability to spread directly from person to person as an infection of the airways. This does not happen very often, but the more people there are who are exposed to avian flu virus via the eye or the airways, the more people will be who develop an airway infection and thereby increase the risk of a global epidemic (pandemic) similar to the Spanish flu with millions of people running the risk of dying.

The article is titled “Avian influenza and sialic acid receptors: More than meets the eye?”
Niklas Arnberg can be reached at phone: +46 90-7588440 (office), +46 90-192949 (residence); cell phone: +46 70-4297220; e-mail niklas.arnberg@climi.umu.se.
Urban Kumlin is available at phone: +46 90-7851347, e-mail: urban.kumlin@infdis.umu.se .