Symptoms of giardiasis usually appear 7 to 10 days after infection, though it may take 25 days or longer. Symptoms can last 7 weeks or more.

• In children or adults who are otherwise healthy, the symptoms of giardiasis may eventually go away, even without treatment.
• Long-term diarrhea may result in weight loss, dehydration, or nutritional problems, because food is not being properly absorbed by the body. These conditions usually can be corrected with treatment.

Many people who are infected with Giardia lamblia do not have symptoms. But it is possible to infect others even if no symptoms are present, because the parasite still exists in the stool (feces).

About 20 to 40 people out of 100 people with giardiasis develop temporary difficulty digesting milk and milk products (lactase deficiency, or lactose intolerance).¹ This problem can last for up to 1 month after treatment for giardiasis. This does not mean that the treatment did not work or that the person has been infected again.

Babies or toddlers who have giardiasis may stop eating or growing normally until the condition is cured. Normal growth may not start right away but should begin again within a few weeks or months.