The present invention provides recombinant viral vectors carrying a vector construct which directs the expression of a gene product (eg. HSVTK) that activates a compound with little or no cytotoxicity into a toxic product. Also provided are methods of destroying or inhibiting pathogenic agents in a warm blooded animal, comprising the step of administering to the animal a viral vector such as that described above, in order to inhibit or destroy the pathogenic agent.