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Diagnosis

Cystic Echinococcosis

The diagnosis of E. granulosus infection (cystic hydatid disease) is suggested by identification of a cyst-like mass in a person with a history of exposure to sheepdogs in areas where the parasite is endemic. Cystic echinococcosis must be differentiated from benign cysts, cavitary tuberculosis, mycoses, abscesses, and benign or malignant neoplasms. Noninvasive imaging techniques such as CT scans, MRI, and ultrasound imaging are all used for detecting and defining the extent and condition of avascular fluid-filled cysts in most organs. These techniques have proved valuable for diagnosis and preoperative evaluation by staging the condition of the lesion, the extent of the lesion in reference to other organs and vital structures, and identifying the presence of additional occult lesions. Radiography permits the detection of hydatid cysts in the lungs; however, in other organ sites, calcification is necessary for visualization. Ultrasonography has been widely used for screening, clinical diagnosis, and monitoring of treatment of liver and intra-abdominal cysts. Cyst viability cannot be reliably determined with radiography or parasite antigen detection; calcification can be present in all stages of cysts.

Serologic tests, such as enzyme-linked immunosorbent assay (ELISA) and indirect hemagglutination test, are highly sensitive methods for detecting infection. Specific confirmation can be obtained by demonstrating echinococcal antigens by immunodiffusion (arc 5) procedures or immunoblot assays (8-, 21 –kD bands).

Alveolar Echinococcosis

Alveolar echinococcosis closely mimics hepatic carcinoma or cirrhosis and is more commonly diagnosed in people of an advanced age. Plain radiographs show hepatomegaly and characteristic scattered areas of radiolucency outlined by calcific rings 2 to 4 mm in diameter. The usual CT image of E. multilocularis infection is that of indistinct solid tumors with central necrotic areas and perinecrotic plaque-like calcifications. Serologic test results are usually positive at high titers. Comparing a patient’s titers with both purified-specific and shared antigens permits the serologic discrimination between patients infected with E. multilocularis and those infected with E. granulosus.

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Disease

Cystic Echinococcosis

The incubation period of cystic echinococcosis is often prolonged for several years and most cases of cystic echinococcosis remain asymptomatic until the cysts reach a large enough size to cause dysfunction. Most primary infections in humans consist of a single cyst. The liver is the most common site of the hydatid cysts, followed by the lungs. Cysts in the spleen, kidneys, heart, bone and central nervous system are less common. In secondary echinococcosis, larval tissue spreads from the primary site and new cysts develop after spontaneous or trauma-induced cyst rupture or after release of viable parasite material during invasive treatment procedures.

Signs and symptoms may include hepatic enlargement with or without a palpable mass in the right upper quadrant, right epigastric pain, nausea, and vomiting. Rupture or leakage usually results in acute or intermittent allergic manifestations.

Alveolar Echinococcosis

The primary infection of alveolar echinococcosis is in the liver, usually the right lobe, but direct extension to contiguous organs, as well as hematogenous metastases to the lungs and brain is not uncommon. Alveolar echinococcosis is inhibited by the host from completing its development and remains in the proliferative stage indefinitely. The larval mass resembles a malignancy in appearance and behavior. In chronic alveolar hydatid infections, the lesion consists of a central necrotic cavity filled with a white amorphous material that is covered with a thin peripheral layer of dense fibrous tissue. Host tissue is directly invaded by extension of the budding and proliferating cyst wall, causing a pressure necrosis of surrounding host tissue. A vigorous inflammatory and fibrous tissue reaction usually surrounds the larval mass. Diagnosis is often delayed until an advanced and inoperable stage; mortality rates have traditionally been high, ranging between 50% and 75%.

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Treatment

Cystic Echinococcosis

In the past, surgery was the only treatment for cystic echinococcal cysts. Chemotherapy, cyst puncture, and PAIR (percutaneous aspiration, injection of chemicals and reaspiration) have been used to replace surgery as effective treatments for cystic echinococcosis and, for some cases, no treatment but a conservative “watch and wait” approach is best. Treatment indications vary with cyst characteristics, including cyst type, location, size, and complications. Surgery may be the best treatment for liver cysts that are secondarily infected or cysts located in the brain, lungs, or kidney. Liver cysts larger than 7.5 cm are likely to have biliary communication; surgery may be the best option for these cysts. Many abdominal cysts can be treated by injection of protoscolicidal chemical solutions into the cyst, followed by evacuation, prior to further manipulations and extirpation of cysts.

For some patients, chemotherapy with benzimidazoles is the preferred treatment. Patients with small cysts or multiple cysts in several organs can be treated successfully with albendazole. Approximately one third of patients treated with chemotherapy with benzimidazole drugs have been cured of the disease and even higher proportions, between 30-50%, have responded with significant regression of the cyst size and alleviation of symptoms. Both albendazole 10 to 15 mg/kg body weight per day (max 800 mg orally in two doses) and, as a second choice for treatment, mebendazole 40-50 mg/kg body weight per day continuously for several months have been highly effective. Additionally, chemotherapy can be very effective when used in conjunction with surgery. Albendazole has been administered to patients prior to surgery for the intended purpose of facilitating the safe surgical manipulation of the cysts by inactivating protoscolices, altering the integrity of the cysts membranes, and reducing the turgidity of the cysts. A third treatment option, PAIR (percutaneous aspiration, injection of chemicals and reaspiration), has been shown to be effective. This option is indicated for patients with relapse after surgery, failure of chemotherapy alone, or who refuse surgery.

Drug*	Adult Dosage	Pediatric Dosage
Albendazole	400 mg orally twice a day for 1-6 months	10-15 mg/kg/day (max 800 mg) orally in two doses for 1-6 months

*Praziquantel may be useful preoperatively or in case of spillage of cyst contents during surgery (Bygott JM, Chiodini PL. Acta Tropica 2009; 111: 95-101).

* Oral albendazole is available for human use in the United States.

* Mebendazole is available in the United States only through compounding pharmacies.

Alveolar Echinococcosis

Alveolar echinococcosis requires chemotherapy with or without surgery; radical surgery is the preferred approach in suitable cases. Effective treatment involves benzimidazoles administered continuously for at least 2 years and patient monitoring for 10 years or more since recurrence is possible. This has inhibited progression of alveolar echinococcosis and reduced lesion size in approximately half of treated cases. Intermittent treatment with albendazole is not recommended.

More on: Echinococcosis, WHO

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This information is provided as an informational resource for licensed health care providers as guidance only. It is not intended as a substitute for professional judgment.

Albendazole

Mebendazole