Definition, Etiology, PathogenesisTop
1. Etiologic agent: Cestode Echinococcus granulosus (E multilocularis infection: see Alveolar Echinococcosis). The adult form of the parasite (3-6 mm long) colonizes the small intestine of the definitive host (predominantly dogs), while herbivores (most frequently sheep) and omnivores (pigs) are intermediate hosts. Humans become infected upon consuming food contaminated with invasive E granulosus eggs, thus becoming an accidental intermediate host. The oncosphere hatches in the small intestine, penetrates the intestinal wall, enters the portal circulation, and colonizes internal organs (most frequently the liver), where it forms a well-demarcated and slowly growing (0.5-1 cm/year) cyst.
2. Reservoir and transmission: Dogs, occasionally wolves, foxes, raccoons, and cats (definitive hosts). In humans the infection spreads via the oral route (contaminated hands or food).
3. Risk factors: Contact with dogs (fed with butchers’ scraps), raising pigs or sheep, contact with soil, consumption of unwashed fruit and vegetables.
4. Incubation and contagious period: Infection may remain asymptomatic for a long time (from >10 months to a few years). The patient is not contagious.
The parasite is found worldwide.
Clinical Features And Natural HistoryTop
In up to 60% of patients, the disease is asymptomatic (particularly in the case of liver involvement), and diagnosis is usually incidental. Clinical manifestations depend on the location of the cyst, its size, and degree of organ damage. Some cysts regress spontaneously.
1. Echinococcosis of the liver (60% of cases): Discomfort in the right upper abdominal quadrant, feeling of upper abdominal distention (worsening when lying on the right side). Hepatomegaly is observed in patients with large cysts.
2. Other locations: Lungs (20% of cases), brain, lesser pelvis, genitals, eye, bones.
1. Identification of the etiologic agent:
1) Serologic studies: Detection of specific serum IgG using enzyme-linked immunosorbent assay (ELISA; sensitivity and specificity >80%), confirmation of the results with Western blot assay.
2) Histologic and cytologic studies (always performed during oral albendazole treatment [biopsy is performed in the case of doubtful diagnosis, only in reference centers], specimen: fine-needle aspirate from the cyst; surgical tissue sample): The presence of hooks and/or protoscolices of E granulosus and/or a specific antigen (Ag5) is a definite confirmation of the diagnosis.
2. Other studies: Imaging studies (ultrasonography of the liver, computed tomography [CT], magnetic resonance imaging [MRI]) show a well-demarcated cyst with a thick, often calcified wall and internal echoes indicating septation (daughter cysts).
Differential diagnosis should include simple cysts (these are clinically reminiscent of an early echinococcal cyst), focal malignant or benign lesions (particularly in the case of degenerating echinococcal cysts), liver abscess (fever, poor general condition, leukocytosis), angioma, polycystic liver disease (usually involves other organs, eg, the kidneys), alveolar echinococcosis.
In patients with degenerating cysts (small, thick-walled, hyperechogenic, partially or completely calcified), follow-up is sufficient. Treatment should be performed in experienced centers. The key treatment methods include oral albendazole, 400 mg every 12 hours for 4 weeks to 6 months (depending on the development stage and activity of the echinococcal cyst; according to the World Health Organization [WHO], there is no prespecified optimum treatment duration), surgical resection of the cyst, and the puncture, aspiration, injection, and reaspiration (PAIR) procedure (puncture of the cyst wall, aspiration of the cyst contents, and injection of 20% NaCl solution or 95% ethanol, followed by reaspiration after 10-15 min; PAIR is always used with pharmacologic treatment, in patients who are ineligible for surgery or experienced recurrence after surgical treatment).
Abdominal ultrasonography should be performed every 3 to 6 months to assess the cyst wall size, thickness of the septa, extent of calcification, and content density to confirm the possible degeneration of the cyst. Periodic serologic testing should be repeated every 6 months to assess the clinical response to treatment.
1. Bacterial infection of the cyst: In the liver the infection spreads mainly via the bile ducts (~25% of the cysts communicate with the biliary tree). The dominant clinical manifestations are right upper abdominal pain, fever, chills, poor general condition. In patients with echinococcosis complicated by cholangitis, jaundice is sporadically observed.
2. Anaphylactic shock and/or peritoneal dissemination and development of secondary cysts may occur in patients with a ruptured cyst (injury, surgical procedure).
3. Compression of the adjacent structures by the cyst (particularly in the case of cysts located outside the liver).
Regular deworming of dogs (particularly shepherd dogs or dogs fed with butchers’ scraps), avoiding feeding dogs with livestock offal, good hand hygiene, using protective gloves while working with soil, thorough washing of fruit and vegetables.