A Natural HSV‑1 Replication Inhibitor Based on Tagetes patula Extract

The relevance of this study stems from the increasing resistance of herpes simplex virus type 1 (HSV‑1) to traditional antiviral drugs and the need to identify novel plant-derived bioactive compounds inhibiting viral replication without promoting resistance. Plants of the genus Tagetes are known for a high content of terpenes, flavonoids, and other metabolites that may exhibit antiviral activity; therefore, their investigation provides a promising basis for the development of new plant‑based therapeutics.

The aim of this study was to evaluate the effect of a Tagetes patula inflorescence ethanol extract on HSV-1 replication post-viral adsorption. Plant material was washed, dried at 25°C, ground (2 g), homogenized in a mortar, and extracted in 20 mL of 70% ethanol (72 h, cool dark place, periodic stirring). The extract was filtered and stored at 4–6°C in the dark until use. Following viral adsorption (1–1.5 h, 37°C, 5% CO₂), culture medium containing extract dilutions (1:400 to 1:50) was added to the cells. Untreated infected Vero cells served as the control. Quantitative assessment of viral DNA was performed by qPCR using a standard curve.

The infectivity titration results demonstrated that the extract exerted a pronounced antiviral effect at dilutions of 1:50–1:200, reducing the HSV‑1 titer by 4.49–2.9 log₁₀ TCID₅₀/mL. qPCR data confirmed a reduction in viral load across all tested dilutions, with the lowest level of viral DNA observed at the 1:50 dilution, consistent with a marked decrease in cytopathic effect (CPE). The highest viral DNA level was detected at 1:400 extract dilution. Parallel analysis of samples from wells with and without CPE revealed a clear correlation: wells lacking CPE showed significantly higher Ct​ values, indicating effective inhibition of viral replication.

Overall, the results demonstrate the antiviral activity of the T. patula extract and highlight its potential as a source of natural compounds for the development of new treatments against HSV‑1.