Do thin-clients need antivirus?

I've just taken over as IT Manager in an environment where most of the end-users are using HP-based Win7 thin clients (approx 50 seats) to access a remote desktop server.

All the servers & fat clients on site are protected with ESET Endpoint Antivirus, however I notice none of the thin clients have any type of AV enabled.

A brief Google search doesn't show much interest in securing these little beasties. Should I look into a lightweigh AV system for these, or are they fine?