After being infected with Giardia in humans, those without clinical symptoms are called carriers. The main symptoms of this disease include abdominal pain, diarrhea, abdominal distension and fullness, vomiting, fever, and anorexia. Typical patients exhibit malabsorption syndrome primarily characterized by diarrhea, with watery stools that are large in volume, foul-smelling, and without pus or blood. Pediatric patients may experience malnutrition such as anemia due to diarrhea, leading to growth retardation. If treatment is deficient, the condition often progresses to a chronic stage, manifesting as periodic loose stools, recurrent episodes, extremely foul-smelling stools, and a disease course that can last for several years.

bubble_chart Epidemiology

Giardia lamblia is prevalent worldwide, with the highest incidence in tropical and subtropical regions, and is also a common protozoan parasite in humans in China. Due to differences in survey timing and diagnostic methods, reported infection rates vary. Recent data show fecal examination results of 2.7% in Beijing and Gansu, while ELISA yielded 12.8%. In Yueqing County, Zhejiang, fecal examination showed 2.5%, in Chaoyang City, Liaoning, farmers had a rate of 6.1%, and in Shenyang, it was 12.5%. Global infection rates range from 1% to 30%. Most cases are sporadic, but under special circumstances, outbreaks can occur. Former Soviet Union countries had higher infection rates, with travelers from the UK, US, and other nations often infected after visiting.

Humans are the primary source of infection, particularly cyst carriers, with documented cases of one carrier infecting entire households both domestically and internationally. Cysts are the main transmission vehicle, with infection occurring through ingestion of contaminated water or food. Cysts are highly resistant in the environment. Transmission electron microscopy of freeze-fractured cysts reveals a wall composed of over a thousand layers of membranous structures, indicating strong self-protection. Cysts survive for 3 weeks in moist feces, 5 weeks in water, and 2–3 days in chlorinated water, but die quickly at 50°C or in dry conditions. Cysts remain viable for 24 hours in fly digestive tracts and Neijing 12 days in cockroach digestive tracts. The large quantity of cysts in feces, combined with their environmental resilience and simple transmission route, explains the parasite's widespread distribution. Reports from the US indicate otters can carry cysts, and cattle, horses, sheep, wolves, and dogs may also host the parasite, which could have epidemiological significance and warrants attention.

1. Trophozoite: Inverted pear-shaped, bilaterally symmetrical, measuring 9–21 μm in length, 5–15 μm in width, and 2–4 μm in thickness. The anterior end is bluntly rounded, while the posterior end is tapered. Lateral view shows a convex dorsal surface and a flattened ventral surface, with the anterior half inwardly concave. A bilobed sucking disk is located within this concave area. Electron microscopy reveals that the disk is reinforced by microtubules and microfilaments, surrounded by a striated cytoplasmic margin containing contractile proteins, making it flexible and contractile for adhering to the host's intestinal mucosa. A ventral groove between the two lobes enhances attachment. Stained specimens show one spherical vesicular nucleus on the dorsal side of each lobe. Each nucleus contains a large karyosome, surrounded by a clear peripheral zone, giving the paired nuclei a distinctive appearance. The trophozoite possesses a pair of axostyles running longitudinally through the organism, with a crescent-shaped basal body complex visible in the middle, serving as the origin for four pairs of flagella. The flagella are categorized into anterior lateral, posterior lateral, ventral, and caudal pairs based on their emergence points. The trophozoite exhibits vigorous tumbling motility driven by its flagella. The flow generated by ventral flagellar movement provides the force for suction by the disk. Nutrients are acquired via pinocytosis, while glucose and lipids are absorbed through the body surface.

2. Cyst: Oval-shaped with a thick wall, measuring 10–14 × 7.5–9 μm. Stained with iodine, it appears yellow-green and contains four nuclei clustered at one end, along with filamentous structures composed of flagella and axostyles. When stained with iron Sappan Wood dye, the cyst wall remains unstained, while nuclei contain nucleoli, the filaments appear black, and a curved parabasal body is visible.

Life Cycle

Trophozoites primarily inhabit the duodenum and upper jejunum of humans (Chinese Taxillus Herb), though they may also be found in the gallbladder. They adhere to the intestinal wall via their sucking disks and reproduce by longitudinal binary fission. Under unfavorable conditions, cysts begin to form in the lower ileum and large intestine. Within the cyst wall, the organism divides into two, though multiple fission may also occur. Typically, only cysts are detected in formed stools, while trophozoites may be observed during diarrhea. Infection occurs mainly through ingestion of mature quadrinucleate cysts. After exposure to gastric acid, the cysts excyst in the duodenum (scrotal swelling) to become trophozoites. Cysts are highly resistant. Statistics indicate that a single diarrheal stool may contain over 14 billion trophozoites, while a normal stool may contain 300 million cysts. Another study reports a daily cyst excretion of up to 900 million.

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When the parasite Chinese Taxillus Herb is in the biliary system, it may cause cholecystitis or cholangitis. Symptoms such as upper abdominal pain, loss of appetite, hepatomegaly, and fat metabolism disorders may occur. The pathogenic mechanism of Giardia is not yet fully understood, but it is generally believed that the patient's condition is related to multiple factors, including the virulence of the parasite strain, the host's immune response, and the symbiotic internal environment. Mechanical obstruction by the parasites, competition for nutrients, stimulation and injury caused by trophozoites attaching to the intestinal mucosa via their suckers, and the synergistic effects of intestinal bacteria can all contribute to varying degrees of intestinal dysfunction. The host's immune status is particularly important in determining the severity of clinical symptoms. For example, patients with hypogammaglobulinemia, immunodeficiency, or Acquired Immune Deficiency Syndrome are more prone to severe infections.

bubble_chart Clinical Manifestations

Most patients infected with Giardia lamblia are asymptomatic carriers. The incubation period is typically around two weeks but can extend to several months. Clinical symptoms vary depending on the affected site, presenting in diverse forms and varying severity. These symptoms can generally be categorized into three types: systemic symptoms, biliary system symptoms, and gastrointestinal symptoms.

(I) Systemic Symptoms:

1. Neurological symptoms: Such as insomnia, headache, lack of strength, vertigo, darkening of vision, sweating, increased nervous excitability, and hyperactive tendon reflexes are relatively common.

2. Thyroid dysfunction: Some studies have found that a portion (15.5%) of Giardia lamblia patients exhibit changes in thyroid function, with hyperthyroidism being the most common. Basal metabolic rates may increase by 16–20%, and in some cases by up to 30%, leading to symptoms of hyperthyroidism.

(II) Biliary System Symptoms: Giardia lamblia in the biliary system (Chinese Taxillus Herb) can cause cholecystitis and cholangitis. Main symptoms include upper abdominal pain, loss of appetite, indigestion, nausea, belching, a burning sensation in the stomach, hepatosplenomegaly, tenderness, and exacerbation after consuming fatty foods. Jaundice may sometimes occur.

1. Duodenitis type: Symptoms resemble duodenal ulcer-like pain, accompanied by poor appetite and hypotension. X-ray examinations often show deformation of the bulb or even ulcer signs. Antiparasitic treatment can alleviate these symptoms.

2. Acute or chronic appendicitis type: Symptoms are similar to typical appendicitis. The removed appendix shows inflammatory changes, with ulcers sometimes visible on the mucous membrane, and a large number of trophozoites can be found between the villi.

3. Colitis type: Main symptoms include dull abdominal pain that worsens intermittently, accompanied by nausea, vomiting, and diarrhea, often misdiagnosed as dysentery.

4. Rectosigmoiditis type: Similar to general rectosigmoiditis. Sigmoidoscopy reveals diffuse congestion, edema, and in severe cases, round ulcers covered with exudative pseudomembranes. Swab tests show numerous trophozoites, with no specific pathological changes.

According to Schulz's clinical observations of 324 cases, diarrhea occurred in 96% of patients, fatigue in 72%, weight loss in 60%, abdominal pain in 61%, nausea in 60%, loose stools in 57%, abdominal distension and fullness in 42%, and fever in 17%. Wolfe reported that acute infections present with sudden onset, explosive diarrhea, foul-smelling watery stools, and abdominal pain. Thus, acute symptoms closely resemble acute amebic dysentery, bacterial dysentery, or Salmonella infection, necessitating careful differentiation. Some patients exhibit subacute infection symptoms, mainly intermittent loose stools, abdominal pain, and loss of appetite. Chronic cases are the most common, characterized by periodic loose stools, recurrent episodes, and foul-smelling stools. Due to patients' lack of attention, the course of the disease can last for years. Children with chronic infections often experience weight loss and developmental delays, along with malabsorption of lactose, xylose, vitamins A and B₁₂, and fats.

bubble_chart Diagnosis

(1) Clinical Diagnosis: Due to the absence of specific clinical symptoms, there is no definitive diagnostic method. Inquiries can be made about travel-related diarrhea symptoms, and stool characteristics can be observed for the presence of pus, blood, or mucus, followed by further examination.

(2) Etiological Examination: The detection of trophozoites and cysts of the parasite is the most reliable diagnostic method.

1. Stool Examination:

(1) Direct Saline Smear Method: In porridge-like or watery stools, actively moving, pear-shaped trophozoites can be observed tumbling. Note that the stool sample must be fresh.

(2) Direct Iodine Smear Method: A small amount of semi-formed or formed stool is mixed with a small volume of Lugol's iodine solution to prepare a smear for microscopic examination of cysts.

(3) Zinc Sulfate (33%) Flotation Method for Cyst Concentration: A loop is commonly used to transfer the floating material onto a slide for microscopic examination. This method has a high detection rate.

(4) Merthiolate-Iodine-Formaldehyde (MIF) Sedimentation Method for Cyst Concentration: The sediment is centrifuged and examined microscopically.

Since cysts may not always be present in stool samples, examinations should be repeated every other day, at least three times consecutively.

2. Duodenal Drainage: Duodenal contents are collected and examined microscopically for trophozoites and cysts.

(3) Immunological Diagnosis:

1. Enzyme-Linked Immunosorbent Assay (ELISA): This is a highly sensitive and specific method for diagnosing giardiasis. The positive diagnosis rate for symptomatic individuals is 73.5%. It is rapid, easy to perform, and has few cross-reactions. It can detect antibodies not only in current patients but also in individuals who were previously infected but no longer excrete the parasite, as antibodies may persist in the blood for some time.

2. Indirect Hemagglutination (IHA): Due to its simplicity and lack of need for expensive equipment, IHA is a good method for diagnosing giardiasis, with a positive rate of 73.4%.

3. Indirect Fluorescent Antibody (IFA): Superior to IHA, with a serum positive rate of 83.3%.

4. Counterimmunoelectrophoresis (CIE) Test: Simple and effective, suitable for large-scale epidemiological surveys in the field. Using fresh stool samples (containing the parasite's antigens) or those stored at low temperatures for a short period yields higher detection rates. {|113|}

bubble_chart Treatment Measures

This disease is quite stubborn and ineffective against antibiotic treatment.

(1) Metronidazole: Green (1974) reported that high-dose application, 2g daily for a 3-day course, achieved a 100% cure rate, generally exceeding 90%.

(2) Tinidazole: For adults, 2g; for children, 50–70mg, both administered in a single dose. The single-dose cure rate for adults is 97.4%, while for children it is 88.8%; the two-dose cure rate approaches 100%. Side effects are minimal, and the drug's active ingredient has a serum half-life of 130 hours.

(3) Nimorazole: Administered twice daily at 250mg per dose for a 5-day course, achieving a cure rate of 94%. Children tolerate this drug well.

(4) Chloromethylimidazole: 1.5g administered in a single dose, with efficacy similar to tinidazole, and no side effects or only mild reactions.

(5) Atebrine: For adults, 100mg three times daily; for children, 8mg per kilogram of body weight three times daily, with a 5–7-day course, and the dose adjusted by age. The drawback of this drug is its potential for severe side effects. Its efficacy is superior to furazolidone.

(6) Furazolidone: 8mg per kilogram of body weight daily, administered orally three times daily for a 7-day course, achieving a cure rate of 72%.

bubble_chart Prognosis

The prognosis is good, with no sequelae.