Giardiasis, caused by Giardia lamblia, is a disease characterized by diarrhea, weight loss, and malabsorption. It is prevalent worldwide, especially in warm and humid regions, with a global infection rate of 1-30%. The infection rate is even higher in children, reaching 50-70%. In China, the disease is widely distributed, mostly occurring sporadically. However, under special circumstances, outbreaks often occur due to travel-related infections, earning it the nickname "traveler's diarrhea."

bubble_chart Pathogen

Pear-shaped flagellates are unicellular protozoa with a simple developmental cycle, consisting of two life stages: the trophozoite and the cyst. ① **Trophozoite**: Measures approximately 9.5–21 μm × 5–15 μm, resembling half of a longitudinally split pear. The anterior end is bluntly rounded, while the posterior tapers to a fine point. The dorsal surface is convex, and the ventral surface is flattened, forming a suction disc that tightly adheres to the intestinal mucosa. It contains two nuclei and possesses four pairs of flagella, enabling agile movement. ② **Cyst**: Oval in shape, measuring about 8–12 μm × 7–10 μm. Mature cysts contain four nuclei clustered at one end and are surrounded by a thick wall, providing strong protection in external environments. Common disinfection methods are often ineffective against them. Cyst carriers serve as the primary source of infection, with a single carrier capable of excreting up to 900 million cysts per day. Transmission occurs through fecal contamination of food and water. Individuals of all age groups are susceptible, but children with hypoproteinemia and those with compromised immune function are at higher risk of infection.

bubble_chart Clinical Manifestations

The incubation period after infection is approximately 12 to 15 days. Some individuals may not exhibit symptoms, while those who do primarily present with diarrhea and malabsorption. The typical symptoms during the acute phase include explosive watery diarrhea, foul-smelling and voluminous stools, abdominal distension and fullness, abdominal pain, belching, and vomiting. Although no pus or blood is visible in the stool to the naked eye, microscopic examination may reveal pus cells, red blood cells, and trophozoites or cysts. Generally, the acute phase lasts 3 to 4 days, but in some cases, the condition may persist unresolved for months or recur repeatedly, leading to malabsorption and significant weight loss.

(1) Stool Examination

In the acute phase, direct smear examination can easily find trophozoites or cysts. If no pathogens are found, it is best to submit samples every other day, for a total of 3 times. This method has a higher positive rate than submitting samples daily for 3 consecutive days. (2) Immunodiagnosis

① Enzyme-Linked Immunosorbent Assay (ELISA): This method is highly sensitive and specific for diagnosing giardiasis, with a positive IgG antibody rate of 71.1%–98.9%. It offers advantages such as speed, objectivity, and simplicity of operation.

② Indirect Hemagglutination (IHA) Test: A widely used serological diagnostic method with high sensitivity, simplicity, and speed. It does not require complex equipment or special reagents, making it a good method for diagnosing giardiasis, with a positive rate of 73.4%. However, its specificity and reproducibility are not yet ideal.

③ Indirect Fluorescent Antibody Test (IFAT): The positive rate is higher than IHA, reaching 66%–97%. Symptomatic patients show a higher IFAT positive rate than asymptomatic ones. This test has strong specificity for diagnosing giardiasis, with no false-positive reactions.

④ Counterimmunoelectrophoresis (CIE) Test: An effective method for detecting antigens in the stool of giardiasis patients. It is fast, accurate, simple, and does not require large instruments or special reagents. Its specificity is strong, but its sensitivity is lower than ELISA and IFAT.

bubble_chart Treatment Measures

1. Metronidazole (metronidazole) pediatric dose: 15mg/kg per day, divided into 3 oral doses, 10 days as one course of treatment, can be repeated after a 7-day rest.

2. Tinidazole (tinidazole, fasigyn) dose: adults 2g, administered as a single draught, with a cure rate of 88.8%. For those treated twice, the cure rate is close to 100%, with few side effects.

3. Nimorazole adult dose: 250mg each time, twice daily, 5 days as one course of treatment. Pediatric dose should be adjusted accordingly.