Humans

The history of patients presenting with conditions suggestive of echinococcosis should be considered in supporting such a diagnosis, particularly with patients from endemic regions. For example, with CE, a history of exposure to sheep dogs in rural areas, or with MAE, fox trappers are clearly at risk.

Differential diagnosis for CE includes benign cystic lesions, cavitary tuberculosis, mycoses, abscesses and benign or malignant neoplasms; in the case of MAE, it is important to eliminate hepatic carcinoma and cirrhosis, which have similar clinical presentations (Schantz, 1997).

With CE, diagnosis is usually based on a combination of imaging techniques and immuno-diagnostic tests. Imaging techniques include radiography, computed tomography (CT) ultrasound imaging and, occasionally, magnetic resonance imaging (MRI). Radiography is most useful for the detection of pulmonary cysts, since in other sites some calcification of the cysts is necessary for visualisation (Schantz, 1997). CT, ultrasound and MRI are of value for detecting lesions in the liver and most other organs, especially with deep-seated lesions. Ultrasound imaging is proving to be a useful surveillance and epidemiological screening technique amongst some at-risk populations, particularly in Africa and China (Craig et al., 1996). Ultrasound is relatively easy to perform, and portable units can be employed for the examination of patients in remote areas and for mass screening of populations (Ammann and Eckert, 1995).

Serology offers a useful adjunct to imaging and may provide confirmatory diagnostic information. It may also be an important element to control, particularly where surveillance for the disease in humans may add to early diagnosis and treatment. Enzyme immunoassays and the indirect haemagglutination test are highly sensitive procedures for initial screening, but specific confirmation of reactivity can be obtained by demonstrating specific Echinococcus antigens by arc 5 immunodiffusion or immunoblot assays (Schantz, 1997). However, overall the results of serology have been disappointing because of a lack of species specificity and poor diagnostic sensitivity (Lightowlers and Gottstein, 1995). This may be improved with the availability of purified, species-specific antigens that enable serological discrimination between patients infected with E. multilocularis and E. granulosus. However, some infected individuals with CE do not develop a detectable immune response (Gottstein, 1992), and in those that do there is variability in serological sensitivity, due to differences in the host-parasite relationship and strain variation of the parasite (Lightowlers and Gottstein, 1995). Thus, antigenic differences between strains/species, such as those demonstrated between isolates of E. multilocularis (Gottstein, 1991), could affect the reliability of immunological screening strategies. To have diagnostic value, immunological studies need to be undertaken separately for different strains/ species that have been identified, because significant antigen homology would only be expected within such strains or species.

Craig (1993) raised the possibility of strain-specific antibody responses to E. granulosus several years ago, with reference to a human patient with CE in The Netherlands who was found to be seronegative against routine sheep and horse hydatid cyst fluid antigens, but seropositive when tested against local bovine hydatid cyst fluid (Van Knapen, personal communication to Craig, 1993). DNA analysis of surgical samples from the Dutch patient identified the parasite as the cattle strain (Bowles et al., 1992), and it was difficult to interpret this observation as anything other than strain/isolate-specific immunoreactivity (Craig, 1993).

In suspected CE patients who are serologically negative, diagnostic confirmation can be made by the recovery of laminated membrane and/or protoscoleces from biopsy material aspirated percutaneously from accessible and viable cysts, whereas with MAE, needle biopsy of the liver is required (Schantz, 1997). This procedure can nowadays be reliably effected with ultrasound guidance of the needle aspiration, and anticipatory precautions set in place in case of internal leakage of cyst contents.

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