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Background and objectives: Different environmental factors, such as infection, can cause Alzheimer's disease (AD). Herpes simplex virus types 1 (HSV1) and 2 (HSV2) and cytomegalovirus (CMV) are related to AD. This study explores the potential role of HSV1, HSV2 and CMV in AD progression.
Methods: Plasma samples were taken from 100 AD patients (47 women and 53 men). After isolating viral DNA, PCR was performed using specific primers for the detection of the viruses.  
Results: The prevalence of CMV, HSV1 and HSV2 was 27%, 8% and 4%, respectively. Although CMV was most prevalent in AD patients, HSV1 and HSV2 were found in patients with advanced AD. The prevalence of HSV1 and HSV2 was significantly associated with dysphoria, hallucination, insomnia and depression (P˂0.05), while CMV was significantly associated with hallucination and dysphoria (P=0.001). AD symptoms were higher in patients with HSV1 and HSV2.
Conclusion: It seems that HSV and CMV infections may be related to the severity of AD.