Giardia

What is Giardia?

Giardia is a single-celled parasite that causes the diarrheal disease giardiasis. They can be found in soil, food, water, and on surfaces that have been contaminated with fecal matter from infected humans or animals. The parasites require a human or animal (e.g. deer, cattle, birds, rodents) host in order to reproduce. During reproduction, Giardia form a protective cyst to facilitate survival in water and other environments. This also allows it to survive for weeks or even months outside of a human or animal host.

What are the Symptoms of Giardia Infection?

The most common symptom of giardiasis (infection from Giardia) is watery diarrhea. Other symptoms include abdominal cramps, nausea, vomiting, dehydration and weight loss. Onset of symptoms of giardiasis usually begins 7 to 10 days after ingesting cysts. Illness can last anywhere from 2 to 6 weeks, although in severe cases it may last longer.

Healthy individuals who become infected may not show symptoms, or may experience varying degrees of gastrointestinal illness. Symptoms are usually self-limiting in healthy individuals. For individuals with weakened immune systems, diarrhea and dehydration may be more severe and possibly life-threatening. Individuals may continue to excrete cysts weeks after symptoms have subsided.

How does Giardia get on Fresh Fruit and Vegetables?

Giardia is widespread in the environment. The parasite is commonly found in surface waters (e.g. ponds, streams, rivers, lakes) as well as mammals, birds, reptiles and amphibians. The detection of Giardia on fresh produce indicates that at some point, the produce has come into contact with fecal matter.

Transmission onto fresh produce may occur via:

  • contaminated water used for irrigation or application of agricultural chemicals
  • flood water contaminating produce
  • contaminated dump tank or flume water used for postharvest washing of produce
  • infected workers
  • run-off from improperly composted manure
  • wild animals passing through or grazing in production fields
  • flies that spread cysts

How can I Reduce the Risk of contaminating Fresh Produce?

A food safety management system consisting of Good Agricultural Practices (GAPs) can help minimize the risk of contamination. This risk can be minimized through implementation of preventative practices involving:

  • water quality (production and postharvest)
  • worker hygiene practices and hand-washing (train employees on proper protocols)
  • management of biological soil amendments (e.g. manure, compost)
  • separation of livestock and manure from produce production
  • field sanitation of equipment and containers
  • on-farm pest control

Giardia cysts are not killed by sanitizer (i.e. chlorine bleach) levels typically used for post-harvest rinsing of produce. The physical action of washing may remove some cysts but will not completely eliminate them from produce surfaces.


For more information:
Toll Free: 1-877-424-1300
E-mail: ag.info.omafra@ontario.ca
Author: OMAFRA staff - FPO
Creation Date: July 2017
Last Reviewed: July 2017