Giardia intestinalis - Clinical manifestations, Laboratory Diagnosis, Treatment, Prevention, Control

Clinical manifestations of Giardia intestinalis

The incubation period of Giardia intestinalis ranges from 1 to 3 weeks and the infection may remain asymptomatic in the majority of the cases. Symptoms are mostly seen in children and vary depending on whether it is acute or chronic. In adults malabsorption syndromes and weight loss occurs while in children growth retardation is seen.

Since giardiasis is self-limiting and only 5% of cases become chronic, the prognosis is good- although death may occur in severely malnourished children.

Acute giardiasis

• Symptoms to describe acute giardiasis includes watery diarrhea, abdominal cramps, bloating, flatulence, and in rare cases, nausea, vomiting, fever, rash, or constipation is presented.

• acute diarrhea, caused by Giardia intestinalis_, is the most common symptom (90% of symptomatic cases) which starts with profuse watery stool which later changes to voluminous, foul-smelling, and greasy and lasts for 5 to 7 days

• abdominal cramps, bloating, and flatulence occurs in 70%-75% of symptomatic cases

Chronic giardiasis

• symptoms include chronic diarrhea with steatorrhoea (malabsorption of fat), weight loss, nausea, anorexia, malaise

• malabsorption of other essential nutrients such as vitamin A, protein, and D-xylose is also seen

• in children, external abnormalities such as protuberance of the abdomen, spindly extremities, and stunted growth are seen

• in rare chronic cases, the infection may become extra-intestinal with manifestations such as urticaria and reactive arthritis

• if left untreated, chronic giardiasis caused by Giardia intestinalis may last from a week to several months

Laboratory Diagnosis of Giardia intestinalis

The laboratory diagnosis of Giardia intestinalis begins with the collection of specimens.

Specimen

The lab diagnosis of Giardia intestinalis includes a collection of specimens includes:

• stool

• bile-stained mucus

• duodenal/jejunal biopsy

Microscopy

• microscopy of stool samples is done to demonstrate the presence of Giardia intestinalis cysts or trophozoites.

  * Cysts are usually present in the soft and formed stool while trophozoites are mostly present in the fresh watery stool.

• after one stool examination, 50%-70% of stool with the parasitic cysts is detected and after three stool examinations, the sensitivity increases to 90%

• stool microscopic examination includes

  * Direct wet mount examination

  * Stained stool smear examination

  * examination of a stool after concentration

Direct wet mount microscopy

• the wet mount for Giardia intestinalis is prepared by mixing stool sample with saline, iodine, or lactophenol cotton blue (LPCB)

• giardiasis is confirmed by the demonstration of trophozoites which is identified by “falling leaf” motility

• useful mostly in the detection of freshly passed diarrhoeic stool

Stained stool smear examination

• permanent stains such as iron-hematoxylin, or trichrome, are used to stain the stool sample before the microscopic observation of trophozoites

• visible stained structures of Giardia intestinalis trophozoites include nuclei, adhesive discs, axostyles, and flagella

examination of a stool after concentration

• formalin-ethyl acetate and zinc sulfate concentration methods are used to concentrate the stool so that the parasites have increased yield

Stool Antigen (coproantigen) Detection:

• based on the detection of a certain protein present on the wall of the parasite

• monoclonal antibody-based capture Enzyme-Linked Immunosorbent assay (ELISA) and immunofluorescence assay (IFA) can be used to detect specific antigens in the stool

• sensitivity of 88% - 98% and specificity of 87%- 100%

Culture

Stool cultures are not routinely performed for lab diagnosis of Giardia intestinalis.

Duodenal contents examination

it includes duodenal fluids and duodenal sampling

Duodenal fluid

• in cases where giardiasis is suspected, direct examination of duodenal contents for trophozoites is done

• the duodenal content such as mucus collected by entero-test or a string test

Entero-test

• also known as string test

• a gelatin capsule is tied to the end of a nylon string with a weight attached to it

• the patient swallows the capsule while the other free end is taped to the cheek

• the capsule is dissolved in the patient’s stomach, releasing the nylon string

• since the string is attached to a weight, it travels down to the duodenum and jejunum

• after 3-4 hours or overnight, while the patient maintains fasting, the string is pulled out

• the bile stained mucus is then collected on a glass slide and immediately observed under a microscope of G. lamblia trophozoites

Duodenal sampling

• done when repeated stool examination gave negative results but the parasitic infection is strongly suspected

• by oesophagogastric-endoscopy, duodenal biopsy, or aspirates are obtained

• the duodenal samples can also be retrieved by using a Cavey’s tube or Rubin’s tube

• the samples are transferred to a glass slide by gently rubbing into it followed by standing by Giemsa and Trichrome stain

• although this method has a high sensitivity, it is not frequently done as it is invasive and expensive

Serodiagnosis

• IIF, ELISA can be used to detect serum antibodies specific to Giardia intestinalis

• however, the tests cannot differentiate between recent and past infections so acute giardiasis can't be properly diagnosed

• axenically cultured Giardia intestinalis trophozoites can be used as antigens in test assays

Molecular

• DNA probes

• PCR

Treatment of Giardia intestinalis

Durg of choice for giardiasis caused by Giardia intestinalis includes:

- Nitroimidazole derivates (metronidazole, tinidazole)

- acridine dyes (quinacrine)

- nitrofurans (furazolidone)

Prevention, Control of Giardia intestinalis

Prevention, Control of Giardia intestinalis are done by:

Individual prophylaxis

Individual prophylaxis of Giardia intestinalis is done by

• improved personal hygiene such as proper washing of hands with soap after defecation and before eating food

• treatment of water before drinking such as boiling, filtering the water used in a 0.22-micrometer membrane, iodination with tetracycline hydro per iodide

• drinking bottled water while traveling to areas endemic to amoebiasis as chlorine treatment cannot kill the cysts

• if salad is to be consumed, treat the vegetables with acetic acid or vinegar for 15 minutes

• not performing sexual acts that involve fecal-oral contact

Community prophylaxis

Community prophylaxis of Giardia intestinalis is done by

• improvement of the water management system to avoid fecal contamination

• improvement of sanitation by installing latrines for proper disposal of human feces