Giardia lamblia is a protozoan flagellate that lives attached to the mucosa of the duodenum and jejunum.
Epidemiology
Giardia is found worldwide with prevalence varying from abundant (5 to 50% in developing countries) to moderate (0.5 to 7% in industrialized areas).
Giardia may cause epidemics through contaminated water or food.
Transmission
Transmission takes place through stools of an infected individual by ingestion of cysts in food or water or through direct contact.
Conventional chlorination of water does not reduce infection risk; filtering, however, does.
Cysts may remain viable in cold water for 2 to 3 months.
Several species of wild animals may transmit the disease.
Transmission from person to person within family is possible.
High risk of transmission among children for example in day-care centres
Symptoms
Clinical picture varies from symptomless cases to severe acute gastroenteritis and chronic malabsorption.
Specific diagnosis cannot be based on clinical picture.
Symptoms of acute giardiasis
Symptoms usually begin 1-3 weeks from infection.
Epigastric cramps, nausea
Stools may vary from watery to more solid, and they may be profuse, foul smelling, pale and may float.
Tenesmus is present especially in the mornings and after meals.
Bloating, flatulence, anorexia, weight loss
Symptoms of chronic giardiasis
Similar to the acute form but milder
Symptoms fluctuate with symptomatic and symptomless periods.
The following complications are possible: secondary malabsorption, e.g., lactose intolerance, even subtotal villus atrophy, pancreatitis, cholangitis, rarely growth retardation in children and possibly also reactive arthritis, urticaria and uveitis.
Diagnosis
Based on detection of Giardia lamblia either by nucleic acid detection or microscopy
Nucleic acid detection is more sensitive than microscopy in the diagnostics of Giardia and more broadly in the diagnostics of diarrhoea or prolonged abdominal discomforts caused by protozoa. Since nucleic acid detection test is so sensitive, it only needs to be conducted on one or a maximum of two stool samples.
In microscopy based diagnostics, the stool sample is fixated with formaline, enriched, and then searched for the cyst forms of Giardia. At least 3 samples at intervals of 2-4 days are required for proper diagnostics.
Trophozoite forms may be searched for in a sample of duodenal or jejunal mucus collected through endoscopy, or examining an object slide that is ”stamped” with the biopsy specimen.
Giardiasis is characterized by a so-called prepatental period, which means that the protozoa may be detected in stools rather late after the transmission. Incubation period is often shorter which may lead to false negative stool samples at the onset of symptoms of the disease.
In chronic giardiasis the protozoa are few, and detection of cysts or Giardia antigens in stools is only sporadic. Therefore the sensitive nucleic acid detection is the primary examination method especially in the diagnostics of chronic abdominal discomforts.
Differential diagnosis
Other intestinal infections, particularly Dientamoeba infections Dientamoebiasis in Adults, should be considered in the differential diagnostics, as well as bile disorders, ulcus, coeliac disease, other malabsorption diseases and lactose intolerance.
It should be borne in mind that detecting one intestinal pathogen does not rule out others, and especially in water-borne infections giardiasis only becomes symptomatic after viral or bacterial diarrhoea.
Treatment and prognosis
The aim is to eradicate both symptoms and the protozoa. Treating symptomless individuals is indicated in order
to eliminate the source of transmission
to prevent development of further disorders associated with giardiasis.
The most effective drugs are metronidazole (for adults 400 mg 3 times daily for 5-7 days, for children 5 mg/kg as an oral suspension 3 times daily for 7-10 days, maximum dose 750 mg/day) and tinidazole (a single dose of 2 g, for children a single dose of 50 mg/kg but not exceeding 2 g); these drugs provide cure for over 90% of the patients. Special regulations may apply to the prescription of tinidazole.
Also albendazole and nitazoxanide are effective against Giardia (special regulations may apply to these drugs as well).
During pregnancy, a case of giardiasis with mild symptoms may be temporally left untreated. In an infection with severe symptoms non-absorbable paromomycin p.o. (500 mg 3 times daily for 7 days) is the safest treatment alternative. In such a case, a specialist in infectious diseases should be consulted.
Relapses occur in most cases 2 weeks after treatment, although they may be seen even after 2 months.
In case of relapse it is advisable to examine all persons living in the same household with the patient and to treat all diagnosed cases.
In relapses, a longer course of metronidazole with a higher dose is often efficient (up to 800 mg 3 times daily for 3 weeks). The sensitivity of giardia to metronidazole or tinidazole may be decreased. If giardia cysts are found in the faeces despite several treatment attempts and despite the treatment of close contacts, the patient is treated with quinacrine (100 mg 3 times daily for 5 days; special regulations may apply). A specialist in infectious diseases should be consulted.
Relapses can also be symptomless. Control specimens are useful at least 1 and 2 months after treatment.
The symptoms may continue for weeks or even months after successful treatment until the destroyed intestinal villi of the small bowel are restored. Lactose-free diet high in fibre often relieves the symptoms.
References
Rimhanen-Finne R, Hänninen ML, Vuento R et al. Contaminated water caused the first outbreak of giardiasis in Finland, 2007: a descriptive study. Scand J Infect Dis 2010;42(8):613-9. [PubMed]
Rimhanen-Finne R, Sakari Jokiranta T, Virtanen MJ et al. Giardia and Cryptosporidium infection in Finland: a registry-based study of their demographic determinants. APMIS 2011;119(11):735-40. [PubMed]
Heyworth MF. Diagnostic testing for Giardia infections. Trans R Soc Trop Med Hyg 2014;108(3):123-5. [PubMed]
van Lieshout L, Roestenberg M. Clinical consequences of new diagnostic tools for intestinal parasites. Clin Microbiol Infect 2015;21(6):520-8. [PubMed]