Echinococcosis: a review

Human cystic echinococcosis (hydatid disease) continues to be a substantial cause of morbidity and mortality in many parts of the world. Elimination is difficult to obtain and it is estimated that, using current control options, achieving such a goal will take around 20 years of sustained efforts. Since the introduction of current (and past) hydatid control campaigns, there have been clear technological improvements made in the diagnosis and treatment of human and animal cystic echinococcosis, the diagnosis of canine echinococcosis, and the genetic characterisation of strains and vaccination against Echinococcus granulosus in animals. Incorporation of these new measures could increase the efficiency of hydatid control programmes, potentially reducing the time required to achieve effective prevention of disease transmission to as little as 5-10 years.

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Prevention and control of cystic echinococcosis

Echinococcosis is a cosmopolitan zoonosis caused by adult or larval stages of cestodes belonging to the genus Echinococcus (family Taeniidae). The two major species of medical and public health importance are Echinococcus granulosus and E. multilocularis, which cause cystic echinococcosis (CE) and alveolar echinococcosis (AE), respectively. Both CE and AE are both serious diseases, the latter especially so, with a high fatality rate and poor prognosis if managed inappropriately. This review discusses new concepts and approaches in the immunology and diagnosis of CE, but comparative reference has also been made to AE infection and to earlier pivotal studies of both diseases. The review considers immunity to infection in the intermediate and definitive hosts, innate resistance, evasion of the immune system, and vaccination of intermediate and definitive hosts, and it particularly emphasizes procedures for diagnosis of CE and AE, including the value of immunodiagnostic approaches. There is also discussion of the new advances in recombinant and related DNA technologies, especially application of PCR, that are providing powerful tools in the fields of vaccinology and molecular diagnosis of echinococcosis.

Concepts in Immunology and Diagnosis of Hydatid Disease

Antigens for the immunodiagnosis of Echinococcus granulosus infection: An update.

We screened 3,199 people from Shiqu County, Sichuan Province, China, for abdominal echinococcosis (hydatid disease) by portable ultrasound combined with specific serodiagnostic tests. Both cystic echinococcosis (CE) (Echinococcus granulosus infection) and alveolar echinococcosis (AE) (E. multilocularis) were co-endemic in this area at the highest village prevalence values recorded anywhere in the world: 12.9% were infected with one or the other form (6.8% CE and 6.2% AE). Prevalences of both CE and AE were significantly higher in female than male patients and increased with the age of the person screened. Pastoral herdsmen were at highest risk for infection (prevalence 19.0%). Prevalence of CE varied in 5 townships from 0% to 12.1%, whereas AE prevalence ranged from 0% to 14.3%. Risk factors associated with both infections included the number of owned dogs, frequency of contact with dogs, and sources of drinking water.

Echinococcosis in Tibetan populations, western Sichuan Province, China.

Echinococcus granulosus cyst fluid and E. multilocularis protoscolex extract were fractionated by a single step of preparative isoelectric focusing, resulting in an antigen B-rich fraction (8-kD) and an Em18-rich fraction, respectively. The usefulness of both fractions for differential serodiagnosis of cystic (CE) and alveolar (AE) echinococcosis was evaluated by a large-scale immunoblot analysis on a battery of 354 serum samples. These included 66 from AE patients originating from four different endemic areas, 173 from CE patients originating from seven different endemic areas, 71 from patients with other parasitic diseases, 15 from patients with hepatomas, and 29 from healthy individuals. In an immunoblot with the antigen B-rich fraction, 92% (158 of 173) of the CE sera as well as 79% (52 of 66) of the AE sera reacted with the 8-kD subunit. No cross-reactivity occurred with any sera from patients with cysticercosis, other parasitic diseases, or with hepatomas, or from healthy controls. In an immunoblot with the Em18-rich fraction, all but two sera from AE patients (64 of 66, 97%) recognized Em18, and only nine of 34 CE sera from China reacted with it. All other (139) CE sera from six other countries were negative as were all (115) other non-echinococcosis sera. These findings indicate that antigen B (8-kD) is not species-specific for E. granulosus but is genus-specific for Echinococcus, and that the Em18 antigen is a reliable serologic marker for species-specific differentiation of AE from CE.

Differential serodiagnosis for cystic and alveolar echinococcosis using fractions of Echinococcus granulosus cyst fluid (antigen B) and E. multilocularis protoscolex (EM18).

D D Joshi

Papers

Differential serodiagnosis for cystic and alveolar echinococcosis using fractions of Echinococcus granulosus cyst fluid (antigen B) and E. multilocularis protoscolex (EM18).