**2.2.1 Cystic echinococcosis (CE)**

The causative agent of CE is the metacestode of *Echinococcus granulosus*, becoming a cystic structure filled with a clear fluid. Most of the cysts grow slowly in size and become surrounded by host tissue (pericyst) encompassing the endocyst of metacestode origin. The endocyst consists of the outer laminated layer and the inner cellular germinal layer, which may form brood capsules and protoscoleces. The minimum time required for the development of protoscoleces in cysts in humans is not exactly known, but it is expected to be 10 months or longer after infection (Pawlowski, 1997). Fertile (with protoscoleces) and sterile (without protoscoleces) cysts may coexist in the same patient. Frequently, smaller daughter cysts are formed within a larger mother cyst. If these smaller cysts are growing in close proximity to each other forming clusters the appearance of "polycystic" needs to be distinguished from AE or PE.

The initial phase of primary infection is always asymptomatic remaining as this for many years or permanently. However, the infection may become symptomatic when cysts press adjacent tissues or induce other pathological events. When symptoms appear suddenly a spontaneous or traumatic cyst rupture has to be suspected. Spontaneous cure is possible but improbable, and is due to the collapse and resolution of cysts or due to the cyst rupture into the bile duct or the bronchial tree. The fatality rate is highly dependent on the severity of the infection and on facilities for treatment.

The age of the symptomatic infected patients can vary from below 1 year of age to over 75 years old. In a study from Madrid (Spain), over 1,473 patients admitted to a children's hospital, 2%were <1 year old, 21% between 1 and 4 years and 77% between 5 and 14 years (Utrilla et al., 1991). Many patients (about 40% up to 80%) with CE have a single organ involved and harbour a solitary cyst.

#### **2.2.1.1 Clinical presentation of CE**

Clinical symptoms of CE are variable and depend on the organ involved, the size of the cysts, the interaction between the expanding cysts and the adjacent organ structures, and the complications related to the cyst rupture and bacterial infection. CE involving the liver can remain asymptomatic for more than ten years (Frider et al., 1999). Liver and lungs are the two more frequent organ sites involved. Complications affecting the biliary tract are the most common and include the cystic rupture into bile ducts. Other complications are bacterial infection of the cyst, intraperitoneal rupture, and lung involvement.

#### **2.2.1.2 Diagnosis of CE**

Diagnosis of CE is done through different steps as follows:


Ultrasonography (US) is used for the diagnosis of the cystic structure and portable units are suitable to take into account in field situations. Immunodiagnostic tests for detecting specific antibodies are commonly used for the aetiological confirmation of the findings of imaging examinations.

Protoscoleces or hooks of *E. granulosus* are found in aspirated fluid samples. This technique is not performed frequently because the material can only be available after a surgical intervention, therapeutic puncture (PAIR) or diagnostic puncture. Direct diagnosis can also

Echinococcosis/Hydatidosis 305

 Computed tomography (CT) can detect small cysts, and it also facilitates differential diagnosis of lesions caused by *Echinococcus* metacestodes from non-parasitic lesions (figure 3) (Soriano Arandes et al., 2010). CT is only indicated when US diagnosis is uncertain, mainly in cysts CE4 or CE5. However, CT is the principal method for diagnosis of cerebral cysts showing a spherical cyst with a thin wall, not enhanced after injection of contrast medium, without perilesional oedema the adjacent structures.

The WHO classification of CE cysts (WHO, 2001) is done according to the US images:

CL CE1 CE2 CE3 CE4 CE5 **Cystic lesion (CL):** Unilocular, cystic lesion (s) (CL) with uniform anechoic content, not

Status: If CE - active.If these cystic lesions are caused by CE at an early stage of

Size: variable but usually small. CLs (< 5.0 cm), CLm (5 – 10 cm), CLl (> 10cm).

 Differential diagnosis of these cystic lesions requires further diagnostic techniques. **CE1:** Unilocular, simple cyst with uniform anechoic content. Cyst may exhibit fine echoes due to shifting of brood capsules which is often called hydatid sand ("snow flake sign") (figure 4).

Fig. 4. Hydatid sand containing a protoscolex of *Echinococcus granulosus* seen by light

clearly delimited by a hyperechoic rim (= cyst wall not visible).

development then usually these cysts are not fertile. Ultrasound does not detect any pathognomonic signs.

**2.2.1.3 WHO classification of CE** 

Normally round but may be oval.

microcopy (Soriano Arandes et al., 2010).

be made by macroscopic identification of the *E. granulosus* obtained by surgery or biopsy. Other methods include the identification of specific *E. granulosus* antigen (antigen 5) in the fluid from sterile cysts or DNA markers in the cysts fluid or parasite tissue (e.g. by PCR). Imaging techniques for diagnosis:


Fig. 3. Image from a computed tomography study of the abdomen of a patient (Soriano Arandes et al., 2010).

be made by macroscopic identification of the *E. granulosus* obtained by surgery or biopsy. Other methods include the identification of specific *E. granulosus* antigen (antigen 5) in the fluid from sterile cysts or DNA markers in the cysts fluid or parasite tissue (e.g. by PCR).

 Standard radiology: chest radiography detects uncomplicated cyst structures displaying a homogeneous shadow that indicates a fluid-filled space. Calcification in lung imaging is rare and cysts may be located anywhere as solitary or multiple. For differential diagnosis, cysts filled with clear fluid, with an air shadow or with water-lily sign are pathognomonic. If a rounded parenchymatous opacity is seen, it is necessary to consider tuberculoma, a tumour or pulmonary sequestration. A fluid and air shadow

 Ultrasonography (US): an expert committee of the WHO Working Group on echinococcosis presented an internationally agreed classification of US images in hepatic CE in 2001 (WHO, 2001), according to the use of PAIR (Puncture, Aspiration, Injection, Re-aspiration). This technique was proposed in 1986 by the Tunisian team that first used it in a prospective study. PAIR is a minimally invasive therapeutic option for percutaneous drainage of echinococcal cysts located in the abdomen, complementing or replacing surgery in most of the settings. PAIR also helps the use of benzimidazoles (albendazole and mebendazole) for the treatment of CE. The drainage is performed with a fine needle or a catheter, followed by the killing of the protoscolices remaining in the cyst cavity by a protoscolicide agent. If numerous and large daughter cysts are present, an alternative percutaneous technique "Percutaneous Puncture with

Fig. 3. Image from a computed tomography study of the abdomen of a patient (Soriano

will lead to consideration of a bacterial, fungal or amoebic abscess.

Drainage and Curettage" (PPDC) may be used.

Imaging techniques for diagnosis:

Arandes et al., 2010).

 Computed tomography (CT) can detect small cysts, and it also facilitates differential diagnosis of lesions caused by *Echinococcus* metacestodes from non-parasitic lesions (figure 3) (Soriano Arandes et al., 2010). CT is only indicated when US diagnosis is uncertain, mainly in cysts CE4 or CE5. However, CT is the principal method for diagnosis of cerebral cysts showing a spherical cyst with a thin wall, not enhanced after injection of contrast medium, without perilesional oedema the adjacent structures.

#### **2.2.1.3 WHO classification of CE**

The WHO classification of CE cysts (WHO, 2001) is done according to the US images:

**Cystic lesion (CL):** Unilocular, cystic lesion (s) (CL) with uniform anechoic content, not clearly delimited by a hyperechoic rim (= cyst wall not visible).


**CE1:** Unilocular, simple cyst with uniform anechoic content. Cyst may exhibit fine echoes due to shifting of brood capsules which is often called hydatid sand ("snow flake sign") (figure 4).

Fig. 4. Hydatid sand containing a protoscolex of *Echinococcus granulosus* seen by light microcopy (Soriano Arandes et al., 2010).

Echinococcosis/Hydatidosis 307

Immunodiagnosis procedures for serum antibody detection are used for the aetiological confirmation of imaging structures suggestive for CE. Certain proportion of patients with echinococcosis is unable to be diagnosed with highly sensitive diagnostic tests such as IgG-ELISA and false-negative results are obtained. Cysts in the brain or eye and calcified cysts often induce low or no antibody titres. Antibody response may also be low in certain human population groups and in young children. False positive results may also occur, especially in patients with other helminthic diseases. Approaches to the diagnosis of CE using immune

**Fisrt step: Primary antibody test**  Test for serum antibody detection: IgG-ELISA or IgE-ELISA with E. Granulosus antigen A combination of two or more primary tests may increase sensitivity **Subsequent steps** 

> **Seropositive samples + With or without suggestive images for CE**

**Asymptomatic and symptomatic cases**  Secondary antibody test: Arc 5 test IgG4-ELISA Immunoblot for antibodies reactive with subunits of *E*. *granulosus* antigens Serological differential diagnosis for AE (ELISA-Em2plus, immunoblot)

**Seronegative samples + Suggestive images for CE** 

**Asymptomatic cases**  Extended and/or advanced imaging and repeated serological examinations, including differential diagnosis for AE\* 'Wait and observe' approach with repeated serological examinations

**Symptomatic cases**  Consideration of cyst puncture Consideration of surgical intervention and/or chemotherapy without further serological examinations

IgG-ELISA is the preferable test used as a primary test for detecting anti-*Echinococcus* serum antibodies. Most of the routine laboratory test systems or commercialized test kits are based on crude or semi-purified preparations of *E. granulosus* antigens. The use of the two major hydatid cyst fluid antigens, antigen 5 (thermolabile) and antigen B (thermostable), is predominantly restricted to scientific applications, and these antigens are not generally

**2.2.1.5 Immunodiagnosis of CE** 

methods are specified in table 2.

**Seronegative samples + No suggestive images for CE** 

No further serological follow-up or further steps for differential diagnosis

Table 2. Approaches for immunodiagnosis of CE


**CE2:** Multivesicular, multiseptated cysts; cysts septations produce "wheel-like" structures, and presence of daughter cysts is indicated by "rosette-like" or "honeycomb-like" structures. Daughter cysts may partly or completely fill the unilocular mother cyst.


**CE3:** Unilocular cyst which may contain daughter cysts. Anechoic content with detachment of laminated membrane from the cyst wall is visible as floating membrane or as "water-lily sign" which is indicative of wavy membranes floating on top of remaining cyst fluid.


**CE4:** Heterogenous hypoechoic or hyperechoic degenerative contents. No daughter cysts.


**CE5:** Cysts characterized by thick calcified wall that is arch shaped, producing a cone shaped shadow.

