Monitoring Drug Resistance for Herpesviruses

Herpes simplex type 1 (HSV-1) and type 2 (HSV-2), varicella-zoster virus (VZV) and human cytomegalovirus (CMV) cause diseases that are usually self-limiting in the immunocompetent host. However, HSV-1, HSV-2, VZV, and CMV are major causes of morbidity and mortality in the immunocompromised patient. Prolonged antiviral treatment is often required for the clinical management of herpesvirus infections in the immunocompromised patient, and this favors the emergence of drug-resistant strains. The isolation of acyclovir-resistant (ACV^r ) HSV-1, HSV-2, and VZV strains as well as ganciclovir-resistant (GCV^r ) CMV strains has been reported with increasing frequency and is a major concern (1 –3 ). Resistance to foscarnet (phosphonoformic acid [PFA]), the drug of choice when ACV or GCV fails, has also been described in the clinic (4 ,5 ). Furthermore, double resistance to both GCV and PFA (for CMV) and to both ACV and PFA (for HSV) has been observed in immuno-compromised patients after sequential and concomitant treatment with either or both drugs.