Giardiasis natural history, complications and prognosis

Following transmission of Giardia, patients may remain asymptomatic for 1-3 weeks. Early symptoms typically include acute, watery diarrhea, bloating, and abdominal cramping, which are usually self-limited. If left untreated, giardiasis may persist in a small proportion of patients and subsequently results in chronic giardiasis. Complications may be related to either severe dehydration (e.g. acute kidney injury), malabsorption (e.g. vitamin B12 deficiency), post-infectious diseases (e.g. reactive arthritis, chronic fatigue syndrome), or spread of Giardia to extraluminal sites (e.g. involvement of the gallbladder, pancreas, or eyes). The prognosis is generally excellent. Recurrence of disease is common among children even with optimal treatment.

• Following transmission of Giardia, patients may remain asymptomatic for 1-3 weeks.
• The development of clinical manifestations is dependent on the parasite load, presence of virulence factors, and the host immune response (immunocompetent vs. immunocompromised).
• Early symptoms typically include watery diarrhea, bloating, and abdominal cramping.
• The majority of patients with giardiasis experience a self-limited acute infection.
• If left untreated, giardiasis may persist in a small proportion of patients and subsequently results in chronic giardiasis.
• Patients with chronic giardiasis typically report chronic watery diarrhea, steatorrhea, malaise, anorexia, malabsorption, weight loss, and failure to thrive.
• Giardiasis is generally a luminal infection (i.e. does not usually spread outside the lumen of the intestine). However, extraluminal manifestations have been reported (see Complications).

Complications of giardiasis have mostly been described in case-series. Reported complications included the following:

• Chronic fatigue syndrome
• Severe dehydration
• Acute kidney injury
• Lactase deficiency
• Vitamin B12 deficiency
• Allergic reaction (urticaria, elevated IgE)^[1]
• Erythema multiforme
• Reactive arthritis^[2]
• Ocular disease (usually in children)^[1]

• “Salt and pepper” retinal changes^[3]
• Retinal hemorrhage
• Iridocyclitis
• Choroiditis

• Hypokalemic myopathy^[4]
• Cognitive impairment
• Post-infectious irritable bowel syndrome^[1]
• Malignancy (unconfirmed association)

• Pancreatic cancer^[5]
• Gallbladder cancer^[6]

• The majority of patients with giardiasis experience a self-limited acute infection.
• Development of chronic infection generally depends on viral infectivity and host factors.
• With adequate treatment, the prognosis of giardiasis is excellent.
• Recurrence of disease is common among children even with optimal treatment.

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