Giardiasis was initially regarded as non-pathogenic and often found in asymptomatic patients. However, there is now copious evidence for the pathogenic nature of Giardia lamblia.
The major symptom of acute giardiasis, mainly seen in travelers, is protracted diarrhea. The incubation period for infection is generally 9-15 days. The acute stage usually begins with a feeling of intestinal uneasiness followed by nausea and anorexia.1 Low grade fever and chills may occur. These symptoms are followed by watery, foul-smelling, explosive diarrhea, abdominal pain, passage of foul gas and belching. This stage lasts for 3-4 days, often resembling other causes of travelers' diarrhea, so giardiasis may go undiagnosed. If left untreated, symptoms may persist for months. Malabsorption due to chronic Giardia infection has also been reported.
Other common symptoms of giardiasis include abdominal pain, flatulence, bloating, vomiting and weight loss.2 Symptoms vary from person to person, often depending on the inoculum size, duration of infection, and individual host and parasite factors.1 The diarrhea can be mild and produce semi-solid stools, or it can be intense and debilitating.3 Children generally become less ill than adults and frequently develop asymptomatic infection.2 It has been suggested that as many as 50% of infections are asymptomatic.
Differential Diagnosis
The primary symptoms of giardiasis such as diarrhea, abdominal pain, and bloating overlap with many other gastrointestinal disorders. The following is a differential diagnosis chart for giardiasis:
- Cryptosporidium parvum
- Cyclospora coyetanesis
- E. histolytica infection (amebiasis)
- Dientameoba fragilis
- Irritable bowel syndrome
- Inflammatory bowel disease (Crohn's, microscopic colitis)
- Gallbladder or pancreatic disease
Giardiasis generally has a longer incubation period than most other intestinal infections. Patients with high fever and blood or mucus in the stool are more likely to have an invasive bacterial infection like Shigella, Campylobacter, or Clostrodium difficile.4 Giardiasis may imitate duodenal ulcer, hiatal hernia, gallbladder disease, or pancreatic disease. If peripheral blood eosinophilia is detected, the infection is unlikely to be giardiasis but perhaps other parasites.1 The physician should obtain a recent history regarding travel, wilderness activities, sexual practices, and exposure to unsanitary conditions.4 In patients with strong clinical and epidemiological evidence of giardiasis, marked improvement and cure may follow empiric treatment with specific anti-Giardia drugs.1
- Wolfe MS. Giardiasis. Clin Microbiol Rev. 1992 Jan;5(1):93-100.
- Flanagan PA. Giardia--diagnosis, clinical course and epidemiology. A review. Epidemiol Infect. 1992 Aug;109(1):1-22.
- Mank TG, Diagnostic advantages and therapeutic options for giardiasis. Expert Opin Investig Drugs. 2001 Aug;10(8):1513-9.
- Adrabbo K, Peura D. Giardiasis: A Review. Practical Gastroenterology. 2002 June; 15-29.
