Negative-ELISA using native and filtrated cystic fluid antigens to rule out cystic echinococcosis.

An increasing number of cases of echinococcosis in Thailand have been imported, probably native infections and medical transfers. Serodiagnosis is one diagnostic choice for interpreting infections before a further step is done. Due to limited antigen, indirect ELISA has been used as a negative screening test for IgG-detection to rule out echinococcosis. Native hydatid cystic fluid (HCF) antigen from Belgium was used for such testing, in which the ODs-ELISA of samples were compared with those of two positive controls. Subsequently, hydatid cyst fluid from a Thai patient was obtained and the filtrated cyst fluid antigen [(<30)-(>10) kDa, HCF30.10] was prepared to develop negative screening results for the serum samples. By using HCF, three of twenty-four samples resulted in higher ODs-ELISA than the controls. In an attempt to observe the cross-reactivity of this native antigen, IgG-antibodies from many helminthiases cross-reacted and showed high ODs-ELISA. The HCF30.10 Ag was used to develop the test and analyze IgG-antibodies from 5 positive controls (2 parasite-confirmed and 3 positive-serodiagnosed), 183 heterologous cases of 29 diseases and 50 healthy control sera. At a cut-off value of 0.484, the test had 100% sensitivity and 42% specificity. Only Malayan filariasis, onchocercosis, fascioliasis, amebiasis, giardiasis and blastocystosis gave true negatives. Antibodies from nematodiases strongly cross-reacted with HCF30.10 Ag. Nine of fifty (18%) healthy serum controls produced higher OD-values than the cut-off. The routine ELISA uses the HCF30.10 Ag to produce a negative result to echinococcosis, because limited cystic fluid antigen (Thai patient) for test improvement, a lot of cross-reactions and only two protoscolex-positive controls are available.

Cestode vaccines.

Studies over the past 20 years have clearly shown the potential for developing vaccines against larval cestode infections of man and animals. The important larval cestode infections of man (Echinococcus granulosus--hydatidosis: Taenia solium--cysticercosis) involve domesticated animals as intermediate hosts in their natural life-cycles. These animals develop strong immunity against reinfection, and immunity can be artificially induced by vaccination with oncosphere antigens. A major stumbling block in developing commercial vaccines against cestodes has been the difficulty in obtaining adequate supplies of these antigens. Recent studies with Taenia ovis, a larval cestode causing cysticercosis in sheep, have demonstrated the feasibility of developing commercial vaccines against cestodes using recombinant DNA technology. A cDNA library prepared using mRNA obtained from T. ovis oncospheres was used to isolate a clone which expressed T. ovis polypeptide antigen 45W as a fusion protein with Schistosoma japonicum glutathione S-transferase (GST-45W). GST-45W gave up to 94% protection against challenge infection when used to vaccinate sheep with saponin as adjuvant. The vaccine antigen was shown by SDS PAGE to be unstable, a major disadvantage in subsequent attempts to obtain high yields of antigen for commercial production. The fusion protein has now been stabilized by reducing the size of GST-45W cDNA through deleting 19 carboxyl terminal hydropathic acids, and the resultant fusion protein GST-45W (B/X) was highly host-protective. Another experiment showed that the 45W T. ovis polypeptide cleaved enzymatically from GST-45W was still host-protective, suggesting that GST had no influence on the immunogenicity of GST-45W fusion protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Application of biotechnology methods to the study of cestodes.

The advent of biotechnology has invigorated research on the control of cestode diseases, especially cysticercosis infections in man and animals. The utilization of hybridoma technology to produce antigen-specific monoclonal antibodies has resulted in great strides towards obtaining pure antigens relevant for immunodiagnostic purposes and for research on vaccines. However, the isolation and identification of antigens is only the initial step in the development of such reagents. Production of antigens in quantities sufficient for research/development and commercialization is hampered by the scarcity of viable parasite material for extraction. Expectations are that this problem can be surmounted by application of recombinant DNA methods to produce cloned genes for antigen expression in cultured microorganisms or cells. Remarkable progress has been made recently in isolating and cloning genes from several important cestode species and antigens have been expressed in vitro with genes cloned from Taenia taeniaformis and T. hydatigena. Although these early efforts have not as yet resulted in practical antigen production, the prospects for doing so appear good. The complex epidemiology of cestode diseases is another research subject that has benefited from the successful application of the tools of biotechnology. For example, the greater precision in typing biological variants afforded by DNA analysis has led to important revisions of the understanding of hydatid disease. DNA probes are now available for Echinococcus spp, which are effective for typing isolates. These probes may also find use as reagents for distinguishing eggs of Echinococcus from other taeniid eggs, a serious difficulty for field investigations.(ABSTRACT TRUNCATED AT 250 WORDS)

Biotechnology research on cestodes in the Philippines, Malaysia, and Indonesia.

There are essentially no reports on the use of modern biotechnological methods on the study of cestode parasites in the Philippines, Indonesia or Malaysia. The only recent reports of cestode studies in these countries have been on reports of new species in animals and on prevalence rates of cestode parasites in humans; Taenia solium and cysticercosis, Taenia saginata and Hymenolepis nana, etc. Reports on the use of biotechnology has emanated from outside the area on cestodes of humans and animals, and some of these methods could be used to study cestodes in this part of the world.