Giardia: Causes, Symptoms, and Treatments You Need to Know

When you have persistent diarrhea, bloating, and fatigue that won’t go away, it might not be food poisoning—it could be Giardia, a microscopic parasite that infects the small intestine and causes giardiasis. Also known as Giardia lamblia, it’s one of the most common causes of waterborne illness worldwide, especially in areas with poor sanitation or after hiking, camping, or traveling abroad. This isn’t just a tourist problem—it shows up in daycare centers, households with pets, and even in treated municipal water supplies when filters fail.

Giardia spreads through feces, often via contaminated water, food, or surfaces. You don’t need to drink dirty water to catch it—washing your hands after changing a diaper or touching a pet that’s been outside is enough to prevent it. The parasite forms tough cysts that survive chlorine in pools and even brief boiling. Once inside your gut, it attaches to the lining and messes with digestion, leading to greasy stools, gas, cramps, and sometimes weight loss. Symptoms can show up as early as three days after exposure, or take weeks. Some people carry it without symptoms but still spread it.

What makes Giardia tricky is that it’s often mistaken for a stomach bug. Antibiotics don’t always work, and over-the-counter anti-diarrhea meds just mask the problem. Effective treatment usually means a short course of prescription drugs like metronidazole or tinidazole—meds that target the parasite directly. But prevention matters more than cure. Boiling water for at least one minute, using certified filters, and washing hands thoroughly after using the bathroom or handling pets can cut your risk dramatically. Pets like dogs and cats can carry Giardia too, so if your dog has loose stools, get it checked.

Below, you’ll find real comparisons between treatments, tips for managing symptoms at home, and how to avoid spreading it to others. Whether you’re dealing with recurring diarrhea, worried about your kids in daycare, or planning a camping trip, these guides give you the facts without the fluff.