Assessment of a serological test for the detection of Echinococcus granulosus infection in dogs in Kenya

Africa-wide meta-analysis on the prevalence and distribution of human cystic echinococcosis and canine Echinococcus granulosus infections

BACKGROUND

Echinococcosis is a neglected zoonosis of increasing public health concern worldwide. According to the World Health Organization, 19,300 lives and 871,000 disability-adjusted life-years are lost globally each year because of cystic echinococcosis. Annual costs associated with cystic echinococcosis were estimated at US$ 3 billion because of treatment of cases and losses in the livestock industry.

METHODS

We performed the random-effects model of meta-analysis using 51-year (1970-2021) data available from AJOL, Google Scholar, PubMed, Science Direct, Scopus and Web of Science. We also applied the Joanna Briggs Institute critical appraisal instrument for studies reporting prevalence data, the Cochran's Q-test, Egger's regression test and the single study deletion technique to respectively examine within-study bias, heterogeneity, across-study bias and sensitivity.

RESULTS

Thirty-nine eligible studies on human cystic echinococcosis (HCE) from 13 countries across the five African sub-regions showed an overall prevalence of 1.7% (95% CI 1.1, 2.6) with a statistically significant (P < 0.001) sub-group range of 0.0% (95% CI 0.0, 14.1) to 11.0% (95% CI 7.6, 15.7). Highest prevalences were observed in Eastern Africa (2.7%; 95% CI 1.4, 5.4) by sub-region and Sudan (49.6%; 95% 41.2, 58.1) by country. Another set of 42 studies on Echinococcus granulosus infections (EGI) in dogs from 14 countries across the five African sub-regions revealed an overall prevalence of 16.9% (95% CI 12.7, 22.3) with a significant (P < 0.001) variation of 0.4 (95% CI 0.0, 5.9) to 35.8% (95% CI 25.4, 47.8) across sub-groups. Highest prevalences of E. granulosus were observed in North Africa (25.6%; 95% CI 20.4, 31.6) by sub-region and Libya (9.2%; 95% CI 5.7, 13.9) by country.

CONCLUSION

Human cystic echinococcosis and EGI are respectively prevalent among Africans and African dogs. We recommend a holistic control approach that targets humans, livestock, dogs and the environment, which all play roles in disease transmission. This approach should involve strategic use of anthelminthics in animals, standardized veterinary meat inspection in abattoirs, control of stray dogs to reduce environmental contamination and proper environmental sanitation. Mass screening of humans in hyper-endemic regions will also encourage early detection and treatment.

Advances in the treatment, diagnosis, control and scientific understanding of taeniid cestode parasite infections over the past 50 years

In the past 50 years, enormous progress has been made in the diagnosis, treatment and control of taeniid cestode infections/diseases and in the scientific understanding thereof. Most interest in this group of parasites stems from the serious diseases that they cause in humans. It is through this lens that we summarize here the most important breakthroughs that have made a difference to the treatment of human diseases caused by these parasites, reduction in transmission of the taeniid species associated with human disease, or understanding of the parasites' biology likely to impact diagnosis or treatment in the foreseeable future. Key topics discussed are the introduction of anti-cestode drugs, including benzimidazoles and praziquantel, and the development of new imaging modalities that have transformed the diagnosis and post-treatment monitoring of human echinococcoses and neurocysticercosis. The availability of new anti-cestode drugs for use in dogs and a detailed understanding of the transmission dynamics of Echinococcus granulosus sensu lato have underpinned successful programs that have eliminated cystic echinococcosis in some areas of the world and greatly reduced the incidence of infection in others. Despite these successes, cystic and alveolar echinococcosis and neurocysticercosis continue to be prevalent in many parts of the world, requiring new or renewed efforts to prevent the associated taeniid infections. Major advances made in the development of practical vaccines against E. granulosus and Taenia solium will hopefully assist in this endeavour, as might the understanding of the parasites' biology that have come from an elucidation of the nuclear genomes of each of the most important taeniid species causing human diseases.

Laboratory Diagnosis of Echinococcus spp. in Human Patients and Infected Animals

Among the species composing the genus Echinococcus, four species are of human clinical interest. The most prevalent species are Echinococcus granulosus and Echinococcus multilocularis, followed by Echinococcus vogeli and Echinococcus oligarthrus. The first two species cause cystic echinococcosis (CE) and alveolar echinococcosis (AE) respectively. Both diseases have a complex clinical management, in which laboratory diagnosis could be an adjunctive to the imaging techniques. To date, several approaches have been described for the laboratory diagnosis and followup of CE and AE, including antibody, antigen and cytokine detection. All of these approaches are far from being optimal as adjunctive diagnosis particularly for CE, since they do not reach enough sensitivity and/or specificity. A combination of several methods (e.g., antibody and antigen detection) or of several (recombinant) antigens could improve the performance of the adjunctive laboratory methods, although the complexity of echinococcosis and heterogeneity of clinical cases make necessary a deep understanding of the host-parasite relationships and the parasite phenotype at different developmental stages to reach the best diagnostic tool and to make it accepted in clinical practice. Standardization approaches and a deep understanding of the performance of each of the available antigens in the diagnosis of echinococcosis for the different clinical pictures are also needed. The detection of the parasite in definitive hosts is also reviewed in this chapter. Finally, the different methods for the detection of parasite DNA in different analytes and matrices are also reviewed.

Sero-diagnosis of Echinococcus granulosus infection in dogs using faecal supernatant antigen

In the present study, sero-diagnosis of Echinococcus granulosus infection in dogs was studied using 250 field serum samples, collected from stray dogs. The three serological techniques viz., latex agglutination test (LAT), Dot-ELISA and enzyme immunotransfer blot (EITB) were used to detect E. granulosus specific anti-bodies using fecal supernatant antigen. The LAT detected positivity in 53 (21.2 %) serum samples with the sensitivity and specificity of 100 and 78.80 % respectively. Whereas, the Dot-ELISA, showed positivity in 45 (18.0 %) samples and the sensitivity and specificity were 100 and 82.0 % respectively. The specific antibodies were detected in 47 (18.80 %) serum samples by EITB and the polypeptides of 45 and 34 kDa were identified in all the positive serum samples. The sensitivity and specificity of EITB were found to be 100 and 86.80 %, respectively.

Echinococcus granulosus: Epidemiology and state-of-the-art of diagnostics in animals

Diagnosis and detection of Echinococcus granulosus (sensu lato) infection in animals is a prerequisite for epidemiological studies and surveillance of echinococcosis in endemic, re-emergent or emergent transmission zones. Advances in diagnostic approaches for definitive hosts and livestock, however, have not progressed equally over the last 20 years. Development of laboratory based diagnostics for canids using coproantigen ELISA and also coproPCR, have had a huge impact on epidemiological studies and more recently on surveillance during hydatid control programmes. In contrast, diagnosis of cystic echinococcosis (CE) in livestock still relies largely on conventional post-mortem inspection, despite a relatively low diagnostic sensitivity especially in early infections, as current serodiagnostics do not provide a sufficiently specific and sensitive practical pre-mortem alternative. As a result, testing of dog faecal samples by coproantigen ELISA, often combined with mass ultrasound screening programmes for human CE, has been the preferred approach for monitoring and surveillance in resource-poor endemic areas and during control schemes. In this article we review the current options and approaches for diagnosis of E. granulosus infection in definitive and animal intermediate hosts (including applications in non-domesticated species) and make conclusions and recommendations for further improvements in diagnosis for use in epidemiological studies and surveillance schemes.

Dog echinococcosis in northern Spain: comparison of coproantigen and serum antibody assays with coprological exam

A large sheep-dog population from the province of Alava (northern Spain) has been investigated in order to determine the prevalence of the cestode parasite Echinococcus granulosus. Worms were detected in 14.0% of 721 dog faecal supernatants by coproantigen ELISA, and in 9.1% of 754 dog serum samples by serum antibody ELISA. A weak but statistically significant correlation (Spearman's rho=0.103, 95% CI: 0.023-0.178) between the two immunoassay results was found. In addition, eggs of the family Taeniidae were detected in 10.3% of 726 faecal samples examined by coproparasitological (flotation and sedimentation) tests. The overall E. granulosus infection rate, based on a Bayesian latent class model that accounts for the imperfect sensitivities and specificities of all diagnostic tests used, was estimated to be 8.0% (95% credible interval: 5.4-11.4%), corroborating that sheep-dog is the dog class most vulnerable to acquiring the infection. Dog sex did not influence the prevalence of E. granulosus, independently of the diagnostic test used or the dog region of origin. No significant linear correlation was found between the coproantigen ELISA OD values and the dog age (Spearman's rho=-0.049, 95% CI: -0.234 to 0.135), suggesting that there were no differences in prevalence of E. granulosus between old and young dogs. The obtained results highlight the importance of initiating a control program based on regular treatment of the sheep-dogs with praziquantel in the province of Alava.

Canid immunity to Echinococcus spp.: impact on transmission

The canid intestinal immune system recognizes the cestode parasite Echinococcus following infection, but it is still unclear the extent to which protection against reinfection occurs. An increasing number of studies have shown that there are convex age-related abundance or prevalence rates in naturally infected populations of dogs with E. granulosus and foxes infected with E. multilocularis. Data from dogs naturally infected with E. granulosus give a better fit to a model that incorporates herd immunity compared to competing models of age-related changes in infection pressure. A theoretical framework suggests that such herd immunity will act as a stabilizing force for Echinococcus populations. Hence a decrease in infection pressure to dogs or foxes will not result in a corresponding decrease in infection pressure to intermediate hosts or to humans. In addition the age structure of the canid population could affect transmission.

Antigens for the immunodiagnosis of Echinococcus granulosus infection: An update

The taeniid tapeworm Echinococcus granulosus is the causative agent of the echinococcal disease, an important zoonosis with worldwide distribution. Accurate immunodiagnosis of the infection requires highly specific and sensitive antigens to be used in immunodiagnostic assays. The choice of an appropriate source of antigenic material is a crucial point in the improvement of the diagnostic features of tests, and must be based on the developmental stage of the parasite and the host. The most common antigenic sources used for the immunodiagnosis of echinococcal disease are hydatid cyst fluid, somatic extracts and excretory-secretory products from protoscoleces or adults of E. granulosus. Hydatid cyst fluid is the antigenic source of reference for immunodiagnosis of human hydatidosis, which is mainly based on the detection of antigens B and 5. Somatic extracts have been widely used in the serodiagnosis for E. granulosus infection in dogs and ruminant intermediate hosts, although in the last few years the detection of excretory-secretory products of the worm in faeces (coproantigens) have become the most reliable method for the detection of the parasite in the definitive host. This review emphasizes recent advances in the identification and characterization of novel antigens with potential for the immunodiagnosis of echinococcal disease. Progress in recombinant technologies and synthetic peptides are also discussed. The paper highlights the need to search for new antigenic components with high diagnostic sensitivity and specificity, a fact that remains a crucial task in the improvement of the immunodiagnosis of the disease.

Shared and non-shared antigens from three different extracts of the metacestode of Echinococcus granulosus

Hydatid cyst fluid (HCF), somatic antigens (S-Ag) and excretory-secretory products (ES-Ag) of Echinococcus granulosus protoscoleces are used as the main antigenic sources for immunodiagnosis of human and dog echinococcosis. In order to determine their non-shared as well as their shared antigenic components, these extracts were studied by ELISA-inhibition and immunoblot-inhibition. Assays were carried out using homologous rabbit polyclonal antisera, human sera from individuals with surgically confirmed hydatidosis, and sera from dogs naturally infected with E. granulosus. High levels of cross-reactivity were observed for all antigenic extracts, but especially for ES-Ag and S-Ag. Canine antibodies evidenced lesser avidity for their specific antigens than antibodies from human origin. The major antigenic components shared by HCF, S-Ag, and ES-Ag have apparent molecular masses of 4-6, 20-24, 52, 80, and 100-104 kDa, including doublets of 41/45, 54/57, and 65/68 kDa. Non-shared polypeptides of each antigenic extract of E. granulosus were identified, having apparent masses of 108 and 78 kDa for HCF, of 124, 94, 83, and 75 kDa for S-Ag, and of 89, 66, 42, 39, 37, and 35 kDa for ES-Ag.

Detection of Echinococcus granulosus coproantigens in faeces from naturally infected rural domestic dogs in south eastern Australia

OBJECTIVE

To investigate the occurrence of Echinococcus granulosus in rural domestic dogs in farming areas around Yass, New South Wales, and Mansfield and Whitfield, Victoria.

DESIGN

Faeces were collected per-rectally from farm dogs voluntarily presented by their owners in four farming districts in New South Wales and two in Victoria.

PROCEDURE

Faeces were collected in the field, an extract prepared from each sample and E granulosus coproantigens detected in an ELISA. Farmers were also questioned about their dog feeding and worming practices.

RESULTS

Echinococcus granulosus coproantigens were detected in 99 of 344 dogs (29%) from 95 farms in south eastern New South Wales and 38 of 217 dogs (17.5%) from 43 farms in Victoria. Cross-reactions between E granulosus coproantigen trapping antibody and coproantigens in faeces from dogs monospecifically infected with other species of intestinal helminthes (Taenia ovis, T hydatigena, T pisiformis, Spirometra ericacei, Dipylidium caninum, hookworm, Toxocara canis, Trichuris vulpis) were not evident. Dietary and worming data revealed many owners fed raw meat and occasionally offal from domestic livestock and wildlife to their dogs and few owners wormed their dogs frequently enough to preclude the chance of patent E granulosus being present in their dogs.

CONCLUSION

Echinococcus granulosus occurs commonly in rural dogs in south eastern Australia and an education program promoting the public health importance of responsible management of rural dogs is urgently needed.

Double-antibody sandwich ELISA using biotinylated antibodies for the detection of Echinococcus granulosus coproantigens in dogs

Here we present the diagnostic evaluation of an improved double-antibody sandwich ELISA for detecting Echinococcus granulosus antigens in dog faecal samples (coproantigens). A purified rabbit IgG fraction against protoscolex excretory-secretory products was used as primary antibody, and the same fraction conjugated with biotin as secondary antibody. In order to validate the sandwich ELISA, intra- and inter-assay precision, linearity, and recovery percentages were calculated. The diagnostic evaluation of the method was carried out by investigating faecal samples from 37 dogs naturally infected with E. granulosus, 15 Echinococcus-free dogs infected with Taenia spp., 82 dogs with non-taeniid helminths and 66 dogs free of helminth infections. An overall sensitivity of 78.4% and specificity of 93.3% were determined. Positive and negative predictive values were 72 and 95%, respectively, and the diagnostic efficiency was 90.5%. In addition, the sandwich ELISA detection limit was estimated in 5.12 ng ml(-1). These results are highly satisfactory, allowing the use of this methodology in surveillance and control programs for intestinal echinococcosis in dogs.

Preliminary study of the presence of antibodies against excretory-secretory antigens from protoscoleces of Echinococcus granulosus in dogs with intestinal echinococcosis

The aim of the present study was to analyze the antibody response against excretory-secretory antigens (ES-Ag) from Echinococcus granulosus protoscoleces, using sera from dogs infected with E. granulosus and other helminths. ES-Ag were obtained from the first 50 h maintenance of protoscoleces in vitro. Immunochemical characterization was performed by immunoblotting with sera from dogs naturally infected with E. granulosus (n = 12), sera from dogs infected with helminths other than E. granulosus (n = 30), and helminth-free dog sera (n = 20). These findings were compared to those obtained from a somatic extract of protoscoleces (S-Ag). ES-Ag only showed four cross-reacting proteins of 65, 61, 54, and 45-46 kDa. Antigens with apparent masses of 89 and 50 kDa in ES-Ag and of 130 and 67 kDa in S-Ag were identified by sera of dogs infected with E. granulosus only, whereas a protein of 41-43 kDa was recognised by the majority of the sera from dogs with non-echinococcal infection. Employing ELISA to study the same sera, S-Ag revealed higher immunoreactivity than ES-Ag, but also showed higher cross-reactivity levels when sera from dogs with non-echinococcal infection were assayed in immunoblotting.

Hydatid control in Australia: where it began, what we have achieved and where to from here

Echinococcus granulosus was imported into Australia with domestic livestock about 200 years ago. It spread rapidly through domestic animals and quickly became a public health problem in the new colony. Control was hampered by ignorance of the transmission pattern. The association between metacestodes and tapeworms was not elucidated until 63 years after the arrival of the First Fleet. Australian wildlife were highly susceptible to infection with E. granulosus and wildlife/domestic animal interaction facilated rapid infiltration of wildlife by E. granulosus. The wildlife reservoir has hampered hydatid control campaigns on mainland Australia but successful eradication has been achieved in the island state of Tasmania where there was no wildlife reservoir. The application of a new recombinant vaccine for sheep in control campaigns and the use of praziquantel baits for controlling infection in dingoes around bush campsites and picnic areas is discussed.

Detection of Echinococcus multilocularis in the definitive host: coprodiagnosis by PCR as an alternative to necropsy

Recently, extensions of the range of Echinococcus multilocularis in Europe and North America and drastic increases in fox populations in Europe put an increasing proportion of the human population at risk of alveolar echinococcosis. To obtain data on the local infection pressure, studies of the prevalence of the parasite in the animals that transmit the parasite, foxes, dogs, and cats, are urgently required. Such investigations, however, have been hampered by the need for necropsy of the host animal to specifically diagnose infection with the parasite. In this study, a nested PCR and an improved method for DNA extraction were developed to allow the sensitive and specific diagnosis of E. multilocularis infections directly from diluted fecal samples from foxes. The target sequence for amplification is part of the E. multilocularis mitochondrial 12S rRNA gene. The specificity of the method was 100% when it was tested against 18 isolates (metacestodes and adult worms) of 11 cestode species, including E. granulosus. The sensitivity of the method was evaluated by adding egg suspensions and individual eggs to samples of diluted feces from uninfected foxes. The presence of one egg was sufficient to give a specific signal. To confirm the PCR results, an internal probe which hybridized only with E. multilocularis amplification products but not with the DNA of other cestodes was constructed. In order to investigate the applicability of this method for epidemiological studies, 250 wild foxes from a area in southern Germany where echinococcosis is highly endemic were examined by both necropsy and PCR of rectal contents. The sensitivity correlated with the parasites' number and stage of maturity. It ranged from 100% (>1,000 gravid worms) to 70% (<10 nongravid worms). On the basis of positive PCR results for 165 foxes, the sensitivity of the traditional and widely used necropsy method was found to be not higher than 76%. We therefore present this PCR system as an alternative method for the routine diagnosis of E. multilocularis in carnivores.

Effect on humoral tolerance (IgG and IgE) in dogs by oral administration of ovalbumin and Der pI

The effect of oral administration of ovalbumin (OVA) or recombinant house dust mite allergen (Der p I) to dogs upon specific IgG and IgE reactions to subcutaneous immunization with these antigens was studied. Daily feeding of 10 x 10 g of OVA resulted in a non-responsiveness to subsequent parenteral immunization with OVA in two young dogs. The same two dogs were also immunized parenterally with Der p I and showed a pronounced IgG response against native Der p I, confirming that the non-responsiveness to OVA was antigen-specific. Thus, it has been demonstrated that it is possible to induce oral tolerance in dogs. Two other dogs of the same litter that received 2 x 10 mg of recombinant Der p I in a crude yeast lysate per os reacted to immunization with OVA with pronounced IgG and IgE production against OVA, further confirming the antigen-specificity of the OVA tolerance. However, tolerance to Der p I was not induced, as evidenced by a strong IgG response to immunization after per os application of the antigen, possibly because the oral dose was too small.

Diagnosis of canine echinococcosis: comparison of coproantigen and serum antibody tests with arecoline purgation in Uruguay

Echinococcus granulosus is one of the most important and widespread of the helminth zoonoses. Diagnosis of E. granulosus infection in dogs currently relies on arecoline dosing and detailed examination of the purge for adult worms. Two immunodiagnostic tests (ELISA) based on genus specific coproantigen detection or serum antibody (IgG, IgA and IgE) detection were compared against arecoline purgation for the detection of Echinococcus in naturally infected dogs in Uruguay. The coproantigen ELISA had a sensitivity of 76.9% compared with 34.6% for the serum IgG ELISA when assessed against 26 purge positive dogs (purge worm count range 1-4331). Coproantigen reactivity was positively correlated (r = 0.65) to purge worm count, with a threshold at over 20 worms. There was no positive correlation of antibody levels with worm counts. In 26 matched Echinococcus positive dog samples, the overall sensitivity of serological detection increased to 69.2% when seroreactivity for IgA and IgE antibodies were included and to 96.2% for both coproantigen and antibody assays combined. The detection of current infection of individual dogs with E. granulosus by coproantigen ELISA has the potential to replace arecoline purgation, while specific serum antibody detection should be useful in assessing Echinococcus exposure in dog populations.

Primary infection of dogs with Echinococcus granulosus: systemic and local (Peyer's patches) immune responses

Local and systemic lymphocyte proliferation and antibody production were tested in five dogs 35 days after primary experimental infection with Echinococcus granulosus. A significant cell proliferation was demonstrated by [3H] thymidine incorporation in mesenteric, popliteal and/or Peyer's patches (PPs) cells in response to E. granulosus protoscolex or adult worm antigen in three of five infected dogs, but not in five control animals. In contrast, blood mononuclear cells responded very weakly in only two of the infected dogs to parasite antigens. Elevated levels (compared with preinfection status) of protoscolex- and adult worm antigen-specific serum IgG were detected (ELISA) in four of the five dogs 35 days after infection. Furthermore, slightly elevated levels of parasite-specific IgE and IgA were observed in the sera of three and four in four infected dogs, respectively. Specific serum IgM was not significantly higher 35 days after infection than before infection. Local antibody production was studied in vitro using PPs, mesenteric and popliteal cells isolated from three infected and three uninfected dogs by ELISA using adult worm antigen. In two of three cultures of unstimulated PPs cells of infected dogs, parasite-specific IgG was detectable. Parasite-specific IgA and IgM were detected in one of the unstimulated PPs cell culture derived from an infected dog. Following in vitro stimulation with parasite antigen, PPs cells from two infected dogs showed increased parasite-specific IgG and PPs cells of all three infected dogs produced parasite-specific IgA. PPs cells from uninfected dogs did not produce significant quantities of parasite-specific antibodies and cells from mesenteric and popliteal lymph nodes of infected or uninfected dogs neither produced antibodies whilst in in vitro cultures.

Serum antibodies in canine echinococcosis

Specific IgG, IgA and IgE antibodies against E. granulosus protoscolex antigen were detected by enzyme-linked immunosorbent assay (ELISA) in sera from dogs experimentally or naturally infected with E. granulosus. The specificities of the IgG, IgA and IgE ELISAs were 100, 100 and 97.3%, respectively. Sera from 626 dogs of different categories and geographic regions in Australia, Uruguay and Kenya were tested. There were distinct differences in antibody responses in experimentally infected canids and in the number of naturally infected dogs found seropositive, depending on geographic region. The overall sensitivities of the ELISA (IgG, IgA and IgE) ranged between 73 and 84%, except for one geographic region where it was 54%. Genetic differences of the dogs and/or antigenic variations of the parasite appear to be responsible for the variations in specific antibody levels in infected dogs. In average, approximately one third of dogs from hyperendemic hydatid regions, without E. granulosus worms at autopsy or negative for E. granulosus infection by arecoline testing, were seropositive for anti-E. granulosus antibodies, suggesting previous infection with or exposure to the parasite. The results of this study demonstrate that, although the diagnosis of current intestinal E. granulosus infection on an individual dog basis is not always reliable by serology, serum antibody ELISA is useful as an epidemiological/educational tool for seroprevalence studies on canine echinococcosis.

Use of Echinococcus granulosus worm antigens for immunodiagnosis of E. granulosus infection in dogs

Echinococcus granulosus worm excretory/secretory antigens (WES) were used in ELISA for diagnosis of E. granulosus infection in dogs and compared with protoscolex somatic antigens (PSM). Sera from 224 dogs were tested. There was no correlation between ELISA absorbance values and E. granulosus worm burdens using either antigen. There was a significant linear relationship between absorbance values of sera tested in the ELISA using WES (W-ELISA) and the ELISA using PSM (P-ELISA). However, there was a small but significant difference between the absorbance values of the sera tested against the two antigens. Western blot analysis of WES using sera from E. granulosus-infected and uninfected dogs revealed antigenic components of relative molecular mass (Mr) larger than 94,000, Mr 94,000-68,000 and Mr 43,000-39,000 in worms, and these were specific for E. granulosus and not identified in PSM; these antigenic differences may be responsible for differences in reactivity in ELISA. The sensitivities of W-ELISA and P-ELISA were 80.8% and 75.6%, respectively. The specificities of W-ELISA and P-ELISA were 93.7% and 97.9%, respectively. The reduced specificity in W-ELISA was mainly attributable to increased background reactivity of sera from Taenia hydatigena-infected dogs. Despite the reduction in specificity, both ELISAs are valuable epidemiological tools to determine the prevalence of antibody to E. granulosus in dog populations and to monitor the success of hydatid control campaigns.

Molecular and immunological diagnosis of echinococcosis

Echinococcosis is an infectious disease of humans caused by the larval (metacestode) stage of the cestode species Echinococcus granulosus (cystic echinococcosis or hydatid disease) or Echinococcus multilocularis (alveolar echinococcosis or alveolar hydatid disease). Clinical manifestations depend primarily on localization and size of hepatic lesions and may include hepatomegaly, obstructive jaundice, or cholangitis. Prognostically, alveolar echinococcosis is considered similar to liver malignancies, including a lethality rate of 90% for untreated cases. Diagnosis is based on imaging techniques coupled with immunodiagnostic procedures. Antibody detection tests for E. multilocularis have markedly improved with the use of affinity-purified Em2 antigen and recombinant antigen II/3-10 in enzyme immunoassays. Antigens of corresponding quality for E. granulosus are still unavailable. The detection of circulating antigens and immune complexes in the sera of patients with cystic echinococcosis, the demonstration of in vitro lymphocyte proliferation in response to stimulation with Echinococcus antigens, and the discrimination of serum immunoglobulin isotype activity to various Echinococcus antigens in both cystic and alveolar echinococcosis have been suggested for diagnostic purposes as well as for monitoring patients after treatment. New diagnostic molecular tools include DNA probes for Southern hybridization tests and polymerase chain reaction for the amplification of E. multilocularis and E. granulosus species-specific DNA fragments.

Detection of Echinococcus coproantigens by enzyme-linked immunosorbent assay in dogs, dingoes and foxes

An enzyme-linked immunosorbent assay (ELISA) was developed for the detection of Echinococcus coproantigens in fecal samples from dogs, dingoes or foxes infected with either E. granulosus or E. multilocularis. The ELISA was based on protein-A-purified polyclonal antibodies [anti-E. granulosus excretory/secretory (E/S) antigens]. The specificity of the assay as determined in 155 samples derived from carnivores that were free of helminth infection (n = 37) or infected with non-Echinococcus cestodes (n = 76) or with various nematodes (n = 42) was found to be 98% overall. The diagnostic sensitivity was strongly dependent on the homologous worm burden. All 13 samples from foxes harboring greater than 1,000 E. multilocularis worms and 13 of 15 (87%) samples from dogs or dingoes containing greater than 200 E. granulosus worms were ELISA-positive, whereas 34 of 46 samples from foxes harboring less than 1,000 E. multilocularis and 9 of 10 samples from dogs or dingoes bearing less than 200 E. granulosus tested negative. Experimental prepatent infections of dogs with E. granulosus revealed positive ELISA reactions within the prepatent period (10-20 days post-infection) for six animals bearing greater than 1,000 E. granulosus each; a low worm burden (less than 1,000 tapeworms/animal) resulted in ELISA positivity in only 2 of 3 animals at 30 days post-infection at the earliest. All five dogs that had been experimentally infected with E. multilocularis tested positive in the coproantigen ELISA as early as on day 5 post-infection.

An enzyme-linked immunosorbent assay for diagnostic detection of Taenia saginata copro-antigens in humans

An immunodiagnostic sandwich enzyme-linked immunosorbent assay (ELISA) was developed for the detection of soluble Taenia saginata antigens in stool samples (copro-antigens) of infected humans, using affinity-purified polyclonal antibodies obtained from rabbits hyperimmunized with excretory/secretory antigens derived from T. saginata maintained in vitro. Investigation of operating characteristics showed very low cross-reactivity with crude antigens from helminths other than Taenia, including Dipylidium caninum and Diphyllobothrium latum. The specificity of the assay was 95% when testing stool samples from 100 persons who were either infected with Ascaris lumbricoides, Trichuris trichiura, hookworms, Enterobius vermicularis or Hymenolepis nana, or who had no intestinal helminthosis detected. Analysis of diagnostic sensitivity demonstrated that in 85% of 34 samples from 23 untreated persons with intestinal T. saginata infection (selected by previous proglottid and/or egg detection) copro-antigens were detected by the T. saginata ELISA. In the same samples, Taenia eggs were detected in 62%. Only 41% of the samples reacted positively in a heterologous T. hydatigena ELISA. Post-treatment control revealed a high concentration of T. saginata copro-antigens for 1-4 d after administration of niclosamide or praziquantel, and negative values 9-17 d after treatment. The Taenia copro-antigens remained detectable by ELISA even after storage of untreated faeces at 25 degrees C for at least 5 d.

Antibody responses against natural Taenia hydatigena infection in dogs in Kenya

Antibody responses (IgG) against Taenia hydatigena infection in dogs in Kenya were analysed in ELISA using excretory/secretory products of T. hydatigena scoleces derived from goat cysticercus cysts. Helminth infections of individual dogs were confirmed at autopsy. T. hydatigena worms were found in 89.5% of 143 dogs, and positive anti-T. hydatigena antibody levels were detected in 58.7% of infected dogs. Positive antiscolex antibody levels were detected in 40.0% of Turkana dogs uninfected with T. hydatigena, suggesting previous infection. Antibody was not detected in 34.4% of infected dogs. There was no relationship between individual T. hydatigena worm burdens and absorbance values for sera in ELISA. It was not possible to distinguish between sera from T. hydatigena-infected and uninfected dogs.