Giardiasis
Giardia is a single-celled parasite that settles in the small bowel and stops it absorbing fats and sugars properly.
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Medicines commonly prescribed for Giardiasis
For informational purposes only. Always consult a doctor before using any medicine.
Dosage form: INJECTABLE PERFUSION, 5 mg/mlActive substance: metronidazoleManufacturer: Noridem Enterprises LimitedPrescription requiredDosage form: INJECTABLE PERFUSION, 5 mg/mlActive substance: metronidazoleManufacturer: Laboratorios Serra Pamies S.A.Prescription requiredDosage form: INJECTABLE PERFUSION, 5 mg/mlActive substance: metronidazoleManufacturer: Laboratorios Normon S.A.Prescription required
Giardia is a single-celled parasite that settles in the small bowel and stops it absorbing fats and sugars properly. The illness it causes is rarely dramatic, but it is stubborn: loose stools with a sharp smell, bloating that makes the waistband uncomfortable, burps that have you turning your head away mid-sentence, and weight that slips off unnoticed. The course of treatment is short. What tends to drag on is the puzzlement afterwards, and the commonest question is why the gut takes so long to settle. There is a whole section on that further down.
How giardia reaches the gut
The parasite leaves the body in the faeces of an infected person or animal as cysts, tough capsules that survive for weeks in cold water. Ordinary chlorination barely dents them, which is why tap water in countries with an unreliable supply, and swimming pool water, are genuine sources rather than theoretical ones. People pick it up by:
- drinking from a stream, a well or a spring, and while travelling from the tap or with ice in a glass;
- swimming in a lake, river or pool and swallowing a few mouthfuls;
- eating salad leaves, herbs or berries washed in that water, or food prepared by someone who did not wash their hands after the toilet;
- living alongside someone who is ill: a shared towel, a potty, door handles, nursery and school;
- sex involving oral or anal contact.
The infectious dose is tiny, a dozen or so cysts, which is why it travels so easily around a household or a classroom. A dog, a calf or a beaver can be a source in theory, but people usually catch it from other people and from water, so hunting for the culprit among the pets rarely leads anywhere.
What it feels like
One to two weeks pass between picking up the parasite and the first complaints. After that come:
- frequent diarrhoea with a strong sour smell, often greasy and hard to flush away;
- bloating and gurgling, with cramping pain across the upper abdomen;
- burps that smell of rotten eggs, a detail patients describe in almost identical words;
- nausea, a distaste for fatty food, loss of appetite;
- weight loss and flatness once it has run on for more than a few days.
What giardiasis does not do matters just as much. Blood and mucus in the stool, a high fever and constant painful urging are not its handwriting, and with those symptoms a doctor will be looking for something else. There is also an awkward feature of this infection: someone can feel entirely well and still pass cysts for months. That is exactly how it keeps circulating in families and nurseries.
In children it tends to run longer. The worrying sign is not the diarrhoea itself but a weight and height chart that flattens out: a gut occupied by the parasite does not hand over what the child eats.
When to be seen without waiting
Ask for an appointment the same day if:
- the diarrhoea has gone past a week, or has come back just as you thought it was over;
- there are signs of dehydration: little and dark urine, a dry mouth, dizziness on standing; in a child, crying without tears, a sunken fontanelle, unusual drowsiness;
- there is blood in the stool, the stool turns black, a fever develops, or the abdominal pain is severe and unrelenting;
- weight is dropping noticeably, or a child has stopped growing;
- you are pregnant, taking medicines that suppress the immune system, or having cancer treatment.
An ambulance, reached in Europe on the single number 112, is for something else: when the person cannot be roused or is confused, when repeated vomiting means not even a sip of water stays down, or when the abdomen goes board-hard and the pain is unbearable. Everything else belongs in a normal appointment, and calling emergency services for it is worse than useless, because the treatment that is actually needed gets delayed.
How the diagnosis is confirmed
The stool is what gets examined. Cysts are shed in bursts rather than steadily, so a single negative result rules nothing out: the usual approach is two or three samples on different days. Tests that look for the parasite's antigen or its genetic material in stool are more reliable than classical microscopy, and where they are available they are the place to start.
One thing deserves its own paragraph because it is a waste of money. A blood test for antibodies to giardia, which private laboratories offer readily, cannot make the diagnosis: antibodies linger long after an infection has cleared and are absent in plenty of people who have it right now. Treatment prescribed on the strength of that single result is the most frequently repeated pointless therapy in this illness.
If symptoms persist while stool tests stay obstinately negative, a doctor may suggest an endoscopy with a sample of duodenal fluid, or a trial of treatment. That decision belongs in a consultation, not to guesswork at home.
What treats it
Giardia is not a bacterium and ordinary antibiotics do nothing to it. Treatment is with prescription antiparasitic medicines, usually from the nitroimidazole group, and alternatives exist for anyone who does not improve on the first one or tolerates it badly. The course is short, a few days as a rule.
Worth knowing in advance:
- a metallic taste, nausea and headache are common companions of the treatment and go when the course ends;
- alcohol is not mixed with nitroimidazoles: the reaction can be severe, and the gap should extend a few days beyond the last tablet;
- in pregnancy the choice of medicine and the timing are decided by a doctor, and a mild illness is sometimes better waited out;
- household members are tested and treated if they have symptoms, and when the infection keeps circling the house, those with no symptoms are treated too.
Some people are not cured by the first course. Then it is repeated, swapped for another drug or combined with a second. This is an expected turn of events rather than a sign of anything sinister.
Why the gut does not settle straight away
Diarrhoea can carry on once the parasite has gone, and there is nearly always an explanation.
- Milk intolerance. Giardia damages the lining of the small bowel, and the enzyme that breaks down milk sugar takes weeks, sometimes months, to recover. During that time milk on its own causes bloating and loose stools. Take it out temporarily and bring it back gradually; hard cheeses and fermented dairy are usually tolerated.
- Post-infectious irritable bowel. Stools stay unpredictable and the abdomen grumbles even though the tests are clean. It fades with time.
- Reinfection. If the source is the water at home or an untreated household member, the whole thing returns within weeks.
- Resistance to the first medicine. Solved by changing the regimen.
And one cause deserves saying plainly, uncommon though it is. Giardiasis that comes back again and again, or refuses to clear after two courses, can be the first visible sign of an antibody deficiency: selective IgA deficiency or common variable immunodeficiency. In a child who is also failing to gain weight, other causes of poor absorption are looked for, coeliac disease and cystic fibrosis among them. So obstinate giardiasis is a reason to widen the investigation rather than to hunt for a stronger tablet.
What to do at home, and how not to pass it on
The main home treatment is fluid. Small amounts, often; pharmacies sell sachets for rehydration solution, and with frequent loose stools they do more than plain water. The rule of thumb is simple: urine should look pale. Food can be ordinary, guided by appetite, low in fat and taken slowly. A baby carries on with breast or bottle feeds as usual.
To stop the infection going round the house:
- wash hands with soap and water after the toilet and before eating; alcohol gel does not destroy the cysts and is no substitute here;
- keep a towel to yourself and wash bedding on a hot cycle;
- wipe the flush button, taps, door handles and the toilet seat;
- do not cook for other people while the diarrhoea lasts;
- stay off work, and keep a child away from nursery, until two days have passed since the last loose stool;
- stay out of swimming pools for two weeks after recovery, because cysts are still being shed when you feel perfectly well;
- when travelling, drink bottled or boiled water, refuse ice and peel fruit yourself.
Online consultation
Two things are handled well at a distance. The first is whether it is worth looking for giardia at all: the doctor will go through what the stools look like, what you have eaten and drunk over recent weeks, where you have travelled and who else at home is unwell, then say which stool tests make sense and which ones would simply cost you money. The second is what to do about a gut that has not settled after treatment, which is precisely where unnecessary medicines pile up instead of the cause being worked out. It is also a good moment to go through test results you already have. Signs of dehydration in a child and severe, sustained abdominal pain cannot be judged through a screen: those need examining in person.
This material is for information only and does not replace medical advice.
Consult with a doctor about Giardiasis
Discuss your symptoms and possible next steps with a doctor online.
Online doctors for Giardiasis
Discuss your symptoms and possible next steps for Giardiasis with a doctor online.
