Introduction 

Giardiasis is a diarrheal illness caused by Giardia intestinalis (also known as Giardia lamblia) a microscopic single celled parasite that affects humans and animals. Giardia parasites can be found in contaminated food and water. Giardiasis is characterised by diarrhoea, nausea, flatulence and abdominal discomfort. The primary route of transmission for Giardiasis is faecal-oral (when faecal particles from one individual are introduced into the mouth of another). This can occur when an individual accidentally ingests water that has come in contact with faeces, food that has been handled with faeces present, or by poor cleaning after handling faeces. Once a human or animal is infected with Giardia, the parasite lives in the intestine and produces cysts, which are resting stages of the parasite that are covered in a protective layer. Large numbers of cysts are passed in the faeces, and survive outside the body for a long time. Only a few cysts need to be ingested for infection to occur.

 

The symptoms of Giardiasis include diarrhoea, loose or watery stool, stomach cramps and nausea. Symptoms generally begin 1-2 weeks after being infected, and in healthy people, resolve spontaneously.

 

Everyone is at risk of developing Giardiasis. Those most at risk include:-

 

§  Child care workers

§  Children who attend child care centres

§  Travellers, hikers and campers

§  Swimmers and people who may ingest untreated water

 

Giardiasis often occurs as community wide outbreaks from contaminated drinking or recreational water. Within the last 20 years, Giardiasis has become the most common cause of waterborne disease outbreak in the United States. In Australia, the main route of infection is hand-to-mouth, and the illness is becoming increasingly diagnosed due to changes in socio-economic factors (for example, growing number of toddlers in child care centres and increases in overseas travel to places such as South East Asia and India, where Giardiasis in prevalent).

 

Life cycle

 

Giardia parasites begin life as cysts, which are excreted into the environment by infected individuals through their faeces. The cysts are tough, resting stages of the parasites, and are able to survive in the environment for long periods of time, particularly in cool, moist conditions. Once several cysts are ingested by another (or the same) individual, Giardia emerge as active parasites that are able to colonise the small intestine by attaching to the epithelium (wall of the intestine). The Giardia parasites remain confined to this area where they can readily absorb nutrients, but do not spread through the body in the blood stream. As the parasites grow and multiply, they are excreted in the faeces as cysts, and are able to start their life-cycle again. If the same individual re-ingests more cysts, then the infective process starts over again.