Which condition is Flagyl (metronidazole) used to treat?

Flagyl, or metronidazole, is an antibiotic and antiprotozoal medication that is particularly effective against certain bacterial and parasitic infections. The correct choice of bacterial vaginosis is significant because this condition is characterized by an imbalance of normal bacterial flora in the vagina, often leading to symptoms such as discharge, odor, and discomfort. Metronidazole targets the anaerobic bacteria that are typically responsible for this condition, thereby restoring normalcy in the vaginal environment.

In this context, the other options highlight infections that are either not treatable by metronidazole or are not its primary use. Viral infections are typically treated with antiviral medications, while fungal infections are usually addressed with antifungal agents. Parasitic infections are indeed treatable with metronidazole, such as giardiasis or trichomoniasis, but the specific focus on bacterial vaginosis in this context makes it the most relevant choice for the question asked.