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Giardia lamblia (syn. Giardia intestinalis, Giardia duodenalis) is a flagellated unicellular eukaryotic micro-organism. It is a common aetiological agent of enteric disease throughout the world and it is the most common cause of waterborne outbreaks of diarrhoea in the United States (Barwick et al., 2000) or, more rarely, a cause of food-borne diarrhoea (Center for Disease Control, 1989; Mintz et al., 1993).

The most dramatic impact of Giardia lamblia on public health is seen in developing countries, where there is a very high prevalence and incidence of infection, and it has been suggested that long-term growth retardation of the individual can result from a chronic form of giardiasis (Fraser et al., 2000). Widespread water contamination with G. lamblia cysts in these areas also represents a significant travel-related risk for tourists (Brodsky, Spencer and Schultz, 1974).

The life cycle of the parasite, recently reviewed by Adam (2001), is articulated in two main stages, cyst and trophozoites. Infection of a host is initiated when the cyst is ingested with contaminated water or, less commonly, food or through direct faecal-oral contact. The cyst is relatively resistant and it is able to survive in a variety of environments. In acid conditions such as in the stomach, cysts excyst into trophozoites. The trophozoite is the vegetative form and replicates in the small intestine, where it causes symptoms of diarrhoea and malabsorption. After exposure to biliary fluid, some of the trophozoites form further cysts in the jejunum and are passed in the faeces, allowing completion of the transmission cycle by infecting a new host.

The classification of Giardia spp. is still under major debate due to a recent revision of the knowledge related to:

A molecular approach to the study of Giardia spp. has been of great value in the effort to find a more precise classification. At present Giardia lamblia is considered to comprise of three genotypes, A-1, A-2, and B, even if it seems that a number of additional genotypes have been isolated recently from a variety of mammals (Adam, 2001). All of these three genotypes are scattered among mammals although little is known about their epidemiological patterns.


Giardia can infect a broad spectrum of animal species. Studies have shown prevalence rates of 4-25 percent in dogs (Hahn et al., 1988; Sykes and Fox, 1989), 1-11 percent in cats (Kirkpatrick, 1986), 10-27 percent in cattle and 18-36 percent in sheep (Buret et al., 1990). Young animals are the most susceptible category and when infected, shed a large number of cysts with faeces and often have a higher incidence of symptomatic infection.

Giardia is also a common parasite in humans. Even if infection is more often asymptomatic, two categories of people are particularly susceptible to infection: young children and especially, HIV infected adults where the parasite is one of the most common causes of diarrhoea (Glaser, Angulo and Rooney, 1994).

Persons at increased risk of giardiasis include those directly connected to animals; such as veterinarians, farmers and animal care workers. Other categories at risk include childcare workers, children who attend day care centres, including children in nappies, international travellers and hikers.


The infection is mainly asymptomatic but may induce a watery and recurrent diarrhoea. In infected organisms the parasite induces diarrhoea, loose or watery stools, stomach cramps and upset stomach. These symptoms may lead to weight loss and dehydration and can last for weeks.


In order to reduce the risks of infection the following rules should be followed:

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