Giardiasis

Giardiasis is a diarrhoeal disease caused by the parasite Giardia duodenalis.

Giardia is a tiny, single-celled organism with multiple whip-like tails, called flagella. The parasite lives in the small intestine of mammals – including humans – where it interferes with the absorption of nutrients from food. As the parasite travels down the digestive tract, it develops into cysts that are shed in faeces. The cysts can survive in the environment for weeks or months.

The Giardia parasite is transmitted when people swallow cysts via hand-to-mouth contact. For example, outbreaks are common in childcare centres due to poor hand hygiene after changing nappies.

Transmission can also occur through contaminated water supplies: the parasite is spread when people drink the water, use it to wash their food or ingest it during recreational activities such as swimming. This is a common route of infection for travellers and people hiking or camping in the wilderness.

There are up to 600,000 cases of giardiasis in Australia each year, and more than 280 million cases worldwide. The disease has a disproportionately high impact on children in impoverished communities, including in remote Indigenous communities in Australia.

Symptoms of giardiasis usually develop one to three weeks following infection and can include:

• Diarrhoea and greasy stools that float
• Nausea/vomiting
• Gas
• Abdominal cramps
• Dehydration
• Post-infectious irritable bowel syndrome
• Chronic giardiasis can lead to significant long-term effects including malnutrition, weight loss, delayed physical and mental growth and predisposition to other diseases.

Some people with giardiasis show no symptoms but can still transmit the disease.

People at risk of giardiasis include:

• Children and staff at childcare centres
• Family members of people with giardiasis
• Travellers to areas where giardiasis is common
• Hikers or campers who drink untreated water from lakes and rivers
• People who swim in contaminated water, such as lakes, rivers and swimming pools
• Practising good hygiene and avoiding contaminated food and water when travelling reduces the risk of giardiasis

Many cases of giardiasis are self-limiting and resolve on their own. Other cases are more persistent and require treatment to clear the infection.

The drugs currently available to treat giardiasis have significant side effects and are not always effective; drug resistance is emerging, leading to treatment failure. Chronic giardiasis remains a major health and economic burden, particularly in resource-poor communities. These limitations highlight the need for new drugs to treat giardiasis.

Our researchers are using advanced genome technologies to study the Giardia parasite. The parasite has a compact genome and can be readily grown in the lab, making it possible to investigate genes that regulate fundamental aspects of parasite biology, including:

• Invasion of and development within the host
• Development, transmission and detection of drug resistance
• Identification of novel targets for new drug development

These genomic tools can also be used to explore how the parasites develop resistance to common drugs.

Ultimately, understanding the genes that control key aspects of parasite biology will underpin approaches to detect, treat and control giardiasis.