Giardia is a single-celled parasite that causes a diarrheal disease called giardiasis.

The parasite can be found in:

  • soil
  • food
  • water
  • surfaces that have been contaminated with fecal matter from infected humans or animals

The parasites require a human or animal (such as 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.

Symptoms of Giardia infection

The most common symptom of giardiasis is watery diarrhea.

Other symptoms can include:

  • abdominal cramps
  • nausea
  • vomiting
  • dehydration
  • weight loss

The onset of giardiasis symptoms usually begins seven to 10 days after ingesting cysts. Illness can last anywhere from two to six weeks. It may last longer in severe cases.

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.

Giardia contamination on fresh fruit and vegetables

Giardia is widespread in the environment. The parasite is commonly found in surface waters such as:

  • ponds
  • streams
  • rivers
  • lakes

It is also found in:

  • mammals
  • birds
  • reptiles
  • 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 through:

  • contaminated water that is used for irrigation or application of agricultural chemicals
  • flood water that contaminates the 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

Reducing the risk of Giardia contamination

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:

  • checking water quality (production and postharvest)
  • employee training on proper worker hygiene practices and handwashing
  • management of biological soil amendments (such as manure and 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 (such as chlorine bleach) at 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.

Contact us

Please contact the Inspection Programs Unit by email at fpo.omafra@ontario.ca or call 1-877-424-1300 for more information.