Giardia
Giardia duodenalis (Giardia for short) is a parasite. Illness caused by Giardia is called giardiasis.
Very common in USA.
Fecal transmission - including via anal sex.
Symptoms usually begin 1 to 2 weeks after becoming infected with Giardia and last for 2 to 6 weeks. Occasionally, people have long-term symptoms that can last for years.