Giardiasis

Key Features

Essentials of Diagnosis

• Acute diarrhea; may be profuse and watery

• Chronic diarrhea with greasy, malodorous stools

• Abdominal cramps, distention, and flatulence

• Cysts or trophozoites in stools

General Considerations

• This upper small intestine infection is caused by the flagellate Giardia lamblia (also called G intestinalis and G duodenalis)

• The organism occurs in feces as a flagellated trophozoite and as a cyst

  • Only the cyst form is infectious by the oral route

  • Trophozoites are destroyed by gastric acidity

• Reservoirs for infection

  • Humans

  • Dogs, cats, beavers, and other mammals are implicated but not confirmed

• Under moist, cool conditions, cysts can survive in the environment for weeks to months

• Transmission occurs as a result of

  • Fecal contamination of water or food

  • Person-to-person contact

  • Anal-oral sexual content

• Infectious dose is low, requiring as few as 10 cysts

• Hypogammaglobulinemia, low secretory IgA levels in the gut, achlorhydria, and malnutrition favor development of infection

Demographics

• The parasite occurs worldwide, especially in areas with poor sanitation

• In the United States and Europe, the infection is the most common intestinal protozoal pathogen

• US estimate is 100,000 to 2.5 million new infections leading to 5000 hospital admissions yearly

• Groups at special risk include

  • Travelers to endemic areas

  • Persons who swallow contaminated water during recreation or wilderness travel

  • Men who have sex with men

  • Persons with impaired immunity

• Multiple cases are common in households, children's day care centers, and residential facilities

• Outbreaks occur from contamination of water supplies

Clinical Findings

Symptoms and Signs

• About 50% of infected persons have no discernable infection and about 10% become asymptomatic cyst passers

• Acute diarrheal syndrome develops in 25–50% of persons

• Incubation period is usually 1–3 weeks but may be longer

Acute infection

• May resolve spontaneously but is commonly followed by chronic diarrhea

• May begin gradually or suddenly

• May last days or weeks and is usually self-limited

• The initial illness may include profuse watery diarrhea

• Hospitalization may be required due to dehydration, particularly in young children

Chronic infection

• Abdominal cramps, bloating, flatulence, nausea, malaise, and anorexia are typical

• Malabsorption may also be present

• Fever and vomiting are uncommon

• Diarrhea

  • Usually not severe

  • May be daily or recurrent

  • Intervening periods may include constipation

• Stools are greasy or frothy and foul smelling, without blood, pus, or mucus

• Weight loss is frequent

Differential Diagnosis

• Viral or bacterial gastroenteritis

• Amebiasis

• Lactase deficiency

• Irritable bowel syndrome

• Malabsorption due to other causes, eg, celiac sprue

• Laxative abuse

• Crohn disease

• Cryptosporidiosis

Diagnosis

Laboratory Tests

• Stool is generally without blood or leukocytes

• Diagnosis is made by the identification of trophozoites or ...