Yes and no.
VirusViruses/trojans are just programs, and will work on Wine... Also, your normal Linux fsfile system is exposed to Wine with the user that launches Wine credentials.
BUT, usually viruses are based on lots of hacks, and they expect a "standard" and common Windows installation. I doubt that any virus is coded thinking that it will be executed on Wine, and if it exists, it will probably not be too successful.
Why? Because Wine users are a small portion of normal users, they have "weird" and strange installations (think in all flavours of Linux+Wine), usually are avanced users, and they have a strong community aware of security.
So: yes, you are exposed to windows viruses, but not totally exposed, and most probably your linux installation will not be contaminedcontaminated. Just be carefullcareful as you are on windows.
On the other hand, you can use several techniques to increase the security: use chrooted wine (search google for chroot), virtualized environments, etc...