During the past 50 years, a great deal of interest had been initiated in screening therapeutic agents from plants. Bidens pilosa L. was widely used as a traditional remedy for treating influenza, diabetes and gastroenteritis worldwide. Houttuynia cordata Thunb. was used in traditional Chinese medicine for treating infectious disease, refractory hemoptysis, malignant pleural effusion, nephrotic syndrome. Studies had shown that B. pilosa possessed antihyperglycemic, antiulcerogenic, immunosuppressive, anti-inflammatory, vasodilative, antimalarial, antibacterial, and hepatoprotective activities. However, there was no previous report of antiviral activity. Also co-carcinogenesis and photocytotoxicity were reported with different species of B. pilosa.
H. cordata was reported to possess antimicrobial, antiviral, immunostimulatory, diuretic, anticance, sedative, anti-inflammatory and antitussive effects. Although H. cordata was found to have activity against herpes simplex virus type 1 (HSV-1), no effect against herpes simplex virus type 2 (HSV-2) was reported. In searching natural crude drugs for potential anti-HSV activity, hot water extracts of whole plant of B. pilosa (HWBP) and H. cordata (HWHC) were tested.