Oral Complications of Chemotherapy and Head/Neck Radiation (PDQ®): Supportive care - Health Professional Information [NCI] - Infection
In most instances, herpes simplex virus (HSV), varicella-zoster virus (VZV), and Epstein-Barr virus (EBV) infections result from reactivation of latent virus, while cytomegalovirus (CMV) infections can result from either reactivation of a latent virus, or via a newly acquired virus. The viral infections can cause oral mucosal lesions. The prevalence of HSV infection was found to be higher when oral ulcers existed than when no oral ulcers were present.
A systematic review was conducted by the Mucositis Study Group (MSG) of the Multinational Association of Supportive Care in Cancer/International Society of Oral Oncology. One of the aims of this review was to evaluate studies conducted since 1989 that considered the prevalence of oral viral infections. The reported prevalence of oral HSV infection was 49.8% (95% CI, 31.3–68.2%) among neutropenic cancer patients. The prevalence was much lower in head and neck cancer (HNC) patients who were treated with radiation therapy (0%); however, it rose to 43.2% (95% CI, 0–100%) in irradiated HNC patients who were treated with radiation therapy combined with chemotherapy. This finding is not surprising because neutropenic patients—mainly patients with hematological malignancies—develop deeper immunosuppression during cancer treatment than do other groups of cancer patients. However, the addition of chemotherapy to the conventional radiation therapy increased risks for HNC patients.
With the recognition of the increased risk of HSV and VZV reactivation in seropositive patients who are expected to become profoundly immunosuppressed during cancer therapy, prophylaxis with antiviral medications has drastically reduced the incidence of disease, primarily in patients receiving high-dose chemotherapy and undergoing hematopoietic stem cell transplant (HSCT). The MSG systematic review identified a series of randomized controlled trials testing various antiviral prophylactic protocols. It concluded that there was a significant benefit to using acyclovir to prevent HSV oral infection (at 800 mg/d).[Level of evidence: I] In addition, the systematic review pointed out that HSV reactivation was reported in a similar prevalence whether acyclovir or valacyclovir was prescribed  and that the prevention of HSV reactivation was achieved in various dosing protocols of valacyclovir (500 or 1,000 mg/d).
The Centers for Disease Control and Prevention (CDC), the Infectious Diseases Society of America (IDSA), and the American Society for Blood and Marrow Transplantation (ASBMT) have published guidelines for the prevention of opportunistic infections in HSCT recipients, which have become a benchmark in this field.[28,29] This significant body of literature presents a global perspective on the prevention of viral infections. CDC, IDSA, and ASBMT concluded that acyclovir prophylaxis is recommended for all HSV seropositive allograft recipients. Valacyclovir instead of acyclovir has been ranked moderately as an effective prevention for HSV in HSCT; foscarnet was mentioned as a drug to avoid for routine HSV prophylaxis because of substantial renal toxicity.