Fever is rare. Occasionally, infected persons develop chronic diarrhea lasting several weeks or months, with significant weight loss. Many infected persons show no signs of illness. It is caused by a microscopic parasite called Giardia lamblia . The Nebraska Health and Human Services System receives an average of 350 reports of giardiasis each year.
Illness occurs more often in the warm months.
Infections may occur sporadically or in clusters or outbreaks. Giardia is passed in the stools of an infected person or animal which may contaminate food or water. The carrier stage varies from person to person, generally from a few weeks to a few months. Treatment with antibiotics may shorten this stage. Both wild and domestic animals can carry and shed giardia, contaminating lakes, rivers, and streams.