Genus of parasitic tapeworm whose larvae infect mammals. They form large, spherical cysts which cause serious or fatal disease.

Common names: Echinococcus, Hydatidosis, Echinococcosis, Hydatid disease, Cystic Hydatid disease, Alveolar Hydatid disease, Polycystic Hydatid disease

Four species of Echinococcus are generally known as parasites of man:
Echinococcus granulosus - Causing Cystic Hydatid disease
Echinococcus multilocularis - Causing Alveolar Hydatid disease
Echinococcus vogeli - Causing Cystic or Polycystic Hydatid disease
Echinococcus oligarthus – Causing Cystic or Polycystic Hydatid disease
A number of subspecies exists, each with particular preferences for the mammals it parasitises.

Echinococcus is a genus of parasitic tapeworm whose larvae infect mammals. The parasites can form large, spherical cysts (or, in the 'Alveolar' forms of the disease, lesions), which cause serious or even fatal disease. Species of this tapeworm are found throughout the world, even in arctic regions. The eggs can survive freezing and drying on the ground for up to a year. The classic transmitters are dogs and other canids. The intermediate hosts, in whom cysts and lesions develop, include humans. Hydatid disease, caused by Echinococcus granulosus, is especially common in Mediterranean regions, and is severely endemic in Greece.

The adult parasites are tapeworms measuring between 3 and 9mm in length and usually consisting of only 3 proglottids: an immature, a mature, and a gravid proglottid. The scolex is globular in shape, and has a prominent rostellum, armed with a double row of between 30 and 36 hooks. The eggs measure between 30 and 40µm in diameter. In the intermediate host, cysts or lesions develop during the larval stage in the internal organs, causing functional impairment which can lead to the death of the host. The rupture of a cyst can lead to severe reactions from the highly allergenic 'Hydatid fluid' released.

The egg enters the host through the mouth, typically through the ingestion of the carrion of a previous host or grass contaminated with faeces, or in the case of humans through poor hygiene or an accident such as a dog licking the face. The eggs then hatch in the intestine, penetrate the gut wall, and travel via the lymphatic or blood system throughout the body and lodge within the body’s tissues. The cysts may develop anywhere within the body, but most commonly it is the liver. Development of the cysts to produce thousands of infective protoscolices takes approximately 1 to 2 years.

Cell-mediated immunity (CMI) may play a large role in suppression of larval growth. Sometimes the infection is asymptomatic, the only evidence being the presence of calcified cysts on autopsy after death due to an unrelated cause. Sometimes symptoms include abdominal pain in the upper right quadrant, severe itching of the skin, cough, bloody sputum, chest pain or fever. The major pathology is due to the size of the cyst (with a volume up to several litres), giving rise to pressure-related injury. A complication may arise if the cyst is ruptured due to a blow to the body, muscular strain, an operation or some other cause. In this case the contents of the hydatid are released into the body's circulatory system, and the liberated protoscolices may give rise to numerous secondary cysts throughout the body. Rupture of a hydatid cyst also commonly gives rise to anaphylactic shock.

Hydatid disease, caused by the cestode Echinococcus granulosus, is common in Mediterranean regions, being highly endemic in Greece. Depending on its size, an intact hydatid cyst may be "silent" or may cause symptoms from compression of adjacent organs. Rupture of a hydatid cyst commonly gives to allergic phenomena, which can include anaphylactic shock. (Giulekas 1986 ref.8436 4)

Allergens/Function:

A protein identical to E. granulosus cyclophilin has been isolated, and named named EA21, and has close homology with Malassezia furfur cyclophilin allergen (Mal f 6) and with human cyclophilin. Of the 58 sera from patients with cystic echinococcosis, 29 (50%) were IgE positive to EA21, whereas, despite the high sequence homology, none were IgE positive to Mal f 6 or human cyclophilin. Only 26 of the 58 patients (45%) had IgG specific to EA21, whereas all patients (100%) had IgG specific to Mal f 6 and human cyclophilin. IB analysis showed that serum IgE-binding reactivity to EA21 differed significantly in patients with and without allergic reactions (20 of 25, 80% versus nine of 33, 27%). Conversely, five of the 25 patients who had CE-related allergic manifestations (20%) and 21 of the 33 who did not (63%) had specific IgG4 (P = 10(-3)) and total IgG to EA21. Overall, these findings suggest that E. granulosus cyclophilin is a conserved, constitutive, parasite protein that does not cross-react with cyclophilins from other organisms and is involved in the allergic symptoms related to CE. (Ortona 2002 ref.8430 5)

Immunoblotting analysis showed that serum IgE-binding reactivity to Echinococcus granulosus elongation factor-1 beta/delta (EgEF-1 beta/delta) differed significantly in patients with and without allergic reactions (38 of 42, 90% vs. 31 of 56, 56%). EgEF-1 beta/delta induced a proliferative response in 14 of 19 (74%) patients' peripheral blood mononuclear cells (PBMC) irrespective of the allergic manifestations and skewed Th1/Th2 cytokine activation towards a preferentially Th2 polarization. Epitope mapping identified an immunodominant epitope of 18 residues with 78% identity and 89% similarity with an IgE-immunoreactive Strongyloides stercoralis antigen. These findings suggest that EgEF-1 beta/delta is an allergenic molecule that may be a general marker of the intensity of CE immune response and that could lead to a deeper understanding of the specific antigen-induced mechanisms underlying allergic reactions in the human host. (Ortona 2001 ref.8431 1)

The EgEF-1 beta/delta is located predominantly in the endoplasmic reticulum and is probably released into the hydatic fluid only after degeneration of the protoscoleces due to ageing, calcification or drug treatment. (Margutti 1992 ref.8445 3)

Adverse Reactions:

IGE AND IMMUNE:
Among the many common features that the host’s immune response to parasitic helminths and the response of atopic individuals to extrinsic allergens share is the prominent is probably the production of high levels of specific IgE antibodies. (Weiss 2000 ref.8444 4) In allergic individuals, these antibodies are largely responsible for initiating the hypersensitivity reactions such as asthma whereas in helminth infections the IgE production may also be responsible for a protective immune response to the parasite or immune-mediated pathology or for both events. (Ortona 2001 ref.8431 1)

Cystic echinococcosis shares with other helminthiases three responses typical of immediate hypersensitive reactions: elevated IgE/IgG4 antibody production, eosinophilia and mastocystos. The clinically observed immunological consequences of CE, both related and unrelated to cyst rupture, arise from acute hypersensitivity reactions, immunosuppressive action and complications associated with circulating immunological complexes. Hypersensitivity reactions vary widely, from benign urticaria and short episodes of shaking chills or fever, to both events, to potentially fatal asthma, angioneurotic oedema and anaphylaxis. Anaphylaxis occurs most frequently after the accidental rupture of the hydatid cysts or during surgery. (Ortona 2001 ref.8431 1)

Allergic reactions, such as urticaria, itching and anaphylactic shock, often complicate the course of cystic echinococcosis (CE). (Ortona 2001 ref.8431 1)

A woman suffering from cystic echinococcosis of the liver, who consequently developed urticaria and acute generalized exanthematous pustolosis. Serum immunoglobulin (Ig)E and IgG4 specific to Echinococcus granulosus antigens were detected by immunoblotting. (Cannistraci 2003 ref.8426 3)

A 25-year-old was admitted to hospital with acute right upper quadrant abdominal pain, vertigo, dyspnea, generalized urticaria and shock several minutes after eating an instant soup. Abdominal ultrasound scan revealed a multivesicular septated cystic space-occupying lesion of the right liver lobe. The study concluded that in patients from echinococcosis-endemic regions who develop an anaphylactic reaction, a ruptured Echinococcus granulosus cyst should be considered in the differential diagnosis. (Koppen 2003 ref.8428 3)

A 66-year-old woman developed anaphylactic shock due to traumatic rupture of a hydatid liver cyst. This study emphasizes that Echinococcus liver cysts should be suspected in cases of anaphylaxis of uncertain etiology in individuals living in Echinococcus endemic areas. (Ruiz-Castro 1997 ref.8432 4)

During the excision of a cystic tumor of the left proximal thigh under general anesthesia a severe anaphylactic shock was observed in a patient. (Heinze 1987 ref.8435 6)

A case is presented in which there was a two-year history of recurrent anaphylactic shock due to small, incomplete ruptures of hydatid cyst. The case emphasizes the potentially life-saving importance of early diagnosis of hydatid cyst. (Giulekas 1986 ref.8436 4)

A boy with inoperable mediastinal echinococcosis is reported, who developed anaphylactic reactions during chemotherapy with mebendazole. IgE-mediated hypersensitivity was demonstrated by elevated echinococcus-specific serum IgE-antibody concentrations, by allergen-induced histamine release from washed leukocytes, and by passive sensitization of nonsensitized leukocytes with the patient's serum. (Appell 1983 ref.8438 3)

NON IMMUNE:
A patient with echinococcosis, acquired deficiency of the inhibitor of the activated first component of complement and angioedema symptoms has been studied. These symptoms started 7 months after the surgical removal of an echinococcus liver cyst. Eight years later, when the complement was investigated, a marked deficiency of the C1 inhibitor, C1, C4 and CH50 was present. (Cicardi 1985 ref.8437 2)