Giardia

What is giardia?

Giardiasis is an infection of the bowels (a gastroenteritis infection). Giardia intestinalis is a protozoan parasite. A protozoa is a microscopic, single-celled organism.

Giardiasis is also quite common in dogs and cats.

How do you catch giardia?

From contaminated water

An infected individual passes out the giardia in their stools (faeces). If water or food (for example, fruit or vegetables) is contaminated by the infected faeces, giardia can be passed on to others who then eat or drink the contaminated food. Transmission is often from drinking contaminated water containing the parasite.

Giardia are not killed by standard chlorination of drinking water. If there are deficiencies in water filtration, or if there is sewage contamination of water, giardia infection can be transmitted.

Direct contact with an infected person

Giardia can also be passed on through direct contact with someone who has giardia. This is known as faecal-oral transmission of the infection. For example, the infected person may have the parasite on their hands after going to the toilet. They can pass the parasite on to the hands of someone they touch. The parasite can then enter the mouth of that person when they eat or touch their mouth, and infect their small intestines. This means of transmission of infection is particularly common in young children. Spread within families in this way is also common.

Sexual activity with an infected person

Sexual activity involving contact with another person's back passage (anus) is another way of acquiring giardia infection.

Swimming in contaminated water

It can also be caught by a person swimming in contaminated water (for example, in lakes, rivers, or swimming pools).

How common is giardia?

Giardia infection is a common cause of infective diarrhoea throughout the world. The parasite is very commonly found in countries where sanitation is relatively poor. However, it can also be found in the developed world and outbreaks have occurred in day centres and institutions.

It is the most common gut (intestinal) parasite infection in the UK. In 2017, 4,793 cases of giardia were reported in England and Wales. Those most at risk of infection include travellers to areas where giardia is common, young children, men who have sex with men, and people with weakened immune systems.

It is thought that 75% of giardia infections in the UK originated within the UK and not following travel

It is estimated that, in the developing world, up to 3 in 10 people are infected with giardia, and up to 7 in 100 people in the United States. Children with giardia can have reduced growth as a result.

What are the symptoms of giardia?

In about half the people infected with giardia, there are no symptoms of giardiasis following infection as it is cleared by their immune system.

If symptoms do occur, they usually develop one to two weeks after first contact with the giardia. Symptoms of giardia infection can be divided into sudden-onset (acute) and persistent (chronic) diarrhoea symptoms.

Acute diarrhoea symptoms

Acute diarrhoea is the most common presentation of giardia infection. There is a sudden onset of diarrhoea which is often explosive and watery.

Other very common symptoms are:

• Nausea (feeling sick).

• Cramping abdominal pains.

• Bloating.

• Farting (passing wind) a lot with very smelly farts.

The symptoms usually settle down after a few days but diarrhoea can continue for more than a week. Vomiting and fever are less common symptoms with giardia infection.

Because of the severity of the diarrhoea, some people with giardia infection, particularly children, can become dehydrated. It is common to lose some weight as well during this acute infection.

Chronic diarrhoea symptoms

In some people, symptoms may be less acute in their onset. A more chronic diarrhoea can develop which may be persistent or may come and go. Stools (faeces) tend to be smelly and fatty/greasy.

Other chronic symptoms include:

• Tiredness.

• Feeling sick (nausea).

• Reduced appetite.

• Weight loss.

• Belching (burping).

• Bloating.

• Heartburn.

• Vitamin deficiencies.

Chronic giardia infection can last for months, or even years, if it goes undiagnosed and untreated.

Symptoms of dehydration

If diarrhoea caused by giardia infection is severe, lack of fluid in the body (dehydration) can occur.

How is giardia diagnosed?

Giardia infection is usually diagnosed when giardia is found in the stool (faeces) after a stool sample is sent to the laboratory. Ideally, three stool specimens from different days should be examined because of potential variations in the excretion of the giardia in the stools.

Giardia infection should be considered in someone who develops sudden-onset (acute) or persistent (chronic) diarrhoea. A stool sample should be sent if the symptoms do not resolve after a few days.

What is the treatment for giardia?

Antibiotic medicines

It's typical to treat giardiasis with antibiotics. Metronidazole is the antibiotic that is most commonly used. An alternative that may be used is tinidazole.

Fluids and food

The advice given for other causes of traveller's diarrhoea should be followed.

Does giardia go away on its own?

Mild infections with giardia, with only minor symptoms, can go away on their own within a few weeks, without any treatment. However, more severe infections need treatment and will not go away on their own.

Complications of giardia

Most people who have giardia infection make a full recovery and do not have any complications or further problems. However, there is a risk of re-infection if preventative measures are not followed (see below). Complications are similar to those for other causes of traveller's diarrhoea.

Other complications specific to giardia infection include:

• Weight loss - can occur in persistent (chronic) giardia infection.

• Growth restriction in children - can occur in chronic giardia infection. This is especially a problem in developing countries where the condition may not be picked up and treated.

• Malabsorption and vitamin deficiencies - are possible in chronic giardia infection. This is because the gut infection can interfere with the absorption of essential nutrients from the food being eaten.

• Gallbladder infection and infection of the pancreas (pancreatitis) - can also occur.

• Lactose intolerance - some people infected with giardia develop an intolerance to dairy which can persist long after the infection has resolved.

Can giardia infection be prevented?

In general, good hygiene is essential to prevent giardiasis and the spread of many other infections.

In addition to this, when travelling to areas with poor sanitation, caution should be used when drinking untreated water or foods cleaned in the water.

Sexual activity involving contact with the back passage (anus) is particularly risky. If your fingers come into contact with another person's anus during sex, or you touch a condom used in anal sex, hands should be washed thoroughly. Contact between the mouth and the anus (sometimes called 'rimming') is risky and should be avoided.