Diagnostic serology of tropical parasitic diseases

An ELISA kit with two detection modes for the diagnosis of lymphatic filariasis

The aim of this study was to develop a low-cost antifilarial immunoglobulin (Ig) G4 detection kit for the diagnosis of lymphatic filariasis. The kit was designed to be used by minimally trained personnel without the constraints of expensive laboratory equipment. We provide a description of the development and validation of a single-serum-dilution based enzyme-linked immunosorbent assay (ELISA) kit with ready-to-use reagents for measuring antifilarial IgG4 antibodies. The kit was tested on residents in Brugia malayi-endemic areas in southern Thailand. Detection was performed by naked-eye observation of the resultant colour of the immunological reactivity. The coefficient of variation (CV) was used to assess the reproducibility of the results. Long-term stability was measured over a 6-month period. Sensitivity of the test kit was 97% when compared with microfilariae detection in thick blood smears. Specificity was 98.7% based on the sera of 57 patients living outside the endemic areas who were infected with other parasites and 100 parasite-free subjects. All positive CVs were < 10%. The test kit was remarkably stable over 6 months. Field validation was performed by the detection of antifilarial IgG4 in 4365 serum samples collected from residents of brugian filariasis-endemic areas and compared with outcome colours of the test samples by the naked eye. Subsequent ELISA evaluation of these results using an ELISA reader indicated high agreement by the kappa statistic. These results demonstrate that the test kit is efficient and useful for public health laboratories as an alternative tool for the diagnosis of lymphatic filarial infection.

Serological screening for antenatal toxoplasma infection in India

PURPOSE

Detection of infection caused by Toxoplasma gondii during pregnancy to prevent congenital infection.

MATERIALS AND METHODS

This study was carried out from January 2005 to 2006 in 300 pregnant women. Antitoxoplasma IgG, IgM, IgA antibody and IgG avidity were assessed using ELISA. At least two samples were taken at least 3 weeks apart preferably one in each trimester.

RESULT

Of these 300 pregnant women, anti toxoplasma IgG antibodies were detected in 46 (15.33%) cases, while 9 (3%) had positive anti toxoplasma IgM with IgA and /low IgG avidity antibodies suggestive of acute infection during or just before pregnancy.

CONCLUSION

The results indicate that about 85% of female population of Chandigarh is susceptible to toxoplasma infection and thus should be specifically educated about prevention of this infection during pregnancy.

Onchocerca antigens in protection, diagnosis and pathology

Characterization of the immune response to Onchocerca volvulus is important for the diagnosis, control and understanding of the disease it causes. The antibody response to surface, secreted and somatic antigens of the worm has therefore been examined at an individual immunoglobulin (Ig) class level, by using a panel of different human sera. Onchocerca-specific antigens tend to be of low molecular mass and preferentially recognized by IgG4 and IgE. There is considerable cross-reaction between O. volvulus and O. gibsoni, so that the latter may be an alternative source of material for use in diagnosis. A surface-enriched fraction of low molecular mass appears to be a most promising diagnostic tool. Amongst somatic antigens, two were uniquely recognized by IgG3 antibodies in sera from sowda patients, thereby providing a molecular correlate for a recognized pathological condition. Improved diagnosis is needed for detecting infection in both humans and the vector. Our target for detection in humans is a continuously released, nonimmunogenic product, which is ideally stage and parasite specific. The excretions of adult worms do contain components not recognized by antibodies in infected serum, but we cannot rule out that these are of host, rather than parasite origin. Excretions of Litomosoides carinii contain both host and parasite molecules and, in addition, stage-specific and sex-specific components. Unfortunately, however, the rate of production of excretions varies during the life of L. carinii. This finding may be relevant to the detection of Onchocerca excretions if they are produced at a similarly uneven rate. Finally, for detecting infective larvae in the vectors, we are currently screening a genomic library of O. volvulus for an appropriate probe. To date, one DNA sequence has been cloned that shows promising specificity.

Onchocerciasis-associated limb swelling in a traveler returning from Cameroon

Travelers to West Central Africa are at risk for infection with Onchocerca volvulus. We describe the case of an adventurous traveler who became infected with O volvulus after a 10-day stay in rural Cameroon. Two years after his return, he was diagnosed with a 3-month history of limb swelling with pruritus and fixed edema of the right arm. He was successfully treated by a single dose of ivermectin, with an additional treatment with doxycycline. The patient was followed-up during 1 year after therapy without relapse. Such travelers experiencing unusual dermatitis syndromes should prompt evaluation for onchocerciasis.

Characterization of Leishmania infantum strains in blood samples from infected dogs and humans by PCR-RFLP

Characterization of Leishmania infantum is based on zymodeme analysis, which requires parasite isolation and therefore is not routinely employed. Moreover, the majority of strains in the Mediterranean Basin belong to zymodeme MON-1, and this is a major limitation for this technique in epidemiological studies in this region. We developed a PCR-RFLP method based on kDNA amplification, which was able to discriminate L. infantum strains directly from peripheral blood. Twenty-eight samples were tested with this technique: four obtained from promastigote cultures, and 24 collected from dogs (18) and human donors (six) from traditionally endemic and newly endemic areas of northwestern Italy. Extracted DNAs were amplified using RV1-RV2 primers and PCR products were digested using two restriction enzymes separately: BsiY I and Mlun NI. Some patterns were specific to certain areas. In particular, the identity of PCR-RFLP patterns from a human patient from a newly endemic area and three dogs allow the confirmation of the autochthonous origin of this case. This approach could be applied to epidemiological studies in order to trace the diffusion of L. infantum within dog populations, as well as its transmission to humans.

Identification of antigens with potential for immunodiagnosis of Parelaphostrongylus tenuis and Elaphostrongylus cervi infections in red deer (Cervus elaphus elaphus)

Red deer (Cervus elaphus elaphus) were infected experimentally with Parelaphostrongylus tenuis in New Brunswick, Canada, and with Elaphostrongylus cervi in New Zealand. Excretory-secretory (E-S) antigens from adult P. tenuis were evaluated for their serodiagnostic potential in identifying P. tenuis and heterologous E. cervi infections in a Western blot. The antigen recognition profile of sera from animals infected with P. tenuis varied between individuals and with duration of infections, whereas that of pooled sera from animals infected with E. cervi showed less variation. A single molecule of 42-43 kDa was recognized consistently by sera from all animals infected with either P. tenuis or E. cervi. Sera from unexposed control deer and from those with other heterologous nematode infections did not consistently identify this antigen. Serorecognition of the 42-43-kDa antigen by deer infected with P. tenuis resulted in a sensitivity of 99% and a specificity of 85% (> or =1 mo postinfection). Although antibody to this antigen waned with time, the persistence of recognition up to 34 mo postinfection with P. tenuis exemplifies its diagnostic value. The sensitivity and specificity of diagnosis using this molecule were each 100% for identifying deer infected with E. cervi (> or =3 mo postinfection). Two other molecules from E-S of adult P. tenuis, 26-28 and 10-12 kDa, were also diagnostic, although their recognition was not persistent throughout infections. These 2 molecules may prove useful in combination with the 42-43-kDa antigen to help identify all infected animals during all phases of infections. This research represents the first conclusive identification of antigens with real potential for reliable antemortem immunodiagnosis of both P. tenuis infections and heterologous E. cervi infections.

Natural and experimental nematode infections in red deer (Cervus elaphus elaphus) and the potential for antemortem serodiagnosis of the tissue worm Elaphostrongylus cervi

Red deer (Cervus elaphus elaphus) were exposed to a variety of nematodes, either naturally on pasture (n = 12) or experimentally under controlled conditions (n = 30). Experimental exposures included a combination of one or more of Elaphostrongylus cervi, Dictyocaulus sp., and Muellerius capillaris. The prepatent period of E. cervi infections was 92–133 days post exposure (dpe) in 12 deer each given 20–42 infective larvae (L3) and maintained under controlled conditions. Adult E. cervi were recovered from all 12 animals at necropsy. The prepatent period of Dictyocaulus sp. was 23–37 dpe in 10 deer each given 100 L3 and maintained under controlled conditions. Adult Dictyocaulus sp. were recovered from seven animals at necropsy. No animal exposed to 42–54 M. capillaris L3 developed patent infections, nor were adult worms recovered at necropsy. There was no evidence of neurologic signs in any deer at any time during the experiment. An enzyme-linked immunosorbent assay (ELISA) using somatic protein extracts of adult E. cervi or those from the closely related nematode Parelaphostrongylus tenuis was evaluated. Although the ELISA was sensitive, it lacked specificity with heterologous infections. However, the close phylogenetic relationship of E. cervi to P. tenuis, and our ELISA results, suggest that molecules from P. tenuis may represent a viable alternative source for use in the future development of a reliable antemortem serodiagnostic assay for E. cervi.

Serological evaluation of thin-layer immunoassay-enzyme-linked immunosorbent assay for antibody detection in human trichinellosis

A new immunoenzymatic test, named the thin-layer immunoassay-enzyme-linked immunosorbent assay (TIA-ELISA), was evaluated for antibody detection in human trichinellosis using excretion and secretion products prepared from Trichinella spiralis muscle larvae. Serum samples from people with positive muscle biopsies or symptoms compatible with the disease (n = 8 or 26, respectively), all reactive in enzyme-linked immunoelectrotransfer blot assay (EITB), as well as 67 serum samples from healthy, EITB-negative people, were tested in an ELISA and TIA-ELISA. TIA-ELISA was performed in polystyrene plastic petri dishes by adding dots of 10 microl each of antigen (7 microg/ml) followed by adding diluted serum and the conjugate. Finally, the substrate mixed with agar was added to develop the reaction. Enzymatic by-products were easily detected by the naked eye as defined dots. Sensitivity and specificity were 76 and 94% for ELISA, and both parameters were 91% for TIA-ELISA. The kappa correlation indices for both tests in relation to EITB were 0.73 and 0.80, respectively. The TIA-ELISA can be carried out with common laboratory equipment in 3 h and uses lower quantities of antigen than EITB and ELISA. Since TIA-ELISA is easy to perform, cheap, sensitive, and specific, the test could be an acceptable alternative to use in clinical laboratories lacking specialized equipment needed for ELISA and EITB and in field studies for antibody detection in human trichinellosis.

Prevalence of antibodies to Coxiella burnetii (Q fever) in bulk tank milk in England and Wales

In the United Kingdom, the infection of people with Coxiella burnetii, the causative agent of Q fever, is of significant public health importance and is associated with contact with dairy cattle. An ELISA was developed for the detection of IgG antibodies against C burnetii in bulk tank milk, and in a survey of randomly selected samples from dairy herds in England and Wales, 21 per cent showed serological evidence of C burnetii infection.

Presence of IgM antibodies to Trypanosoma cruzi urinary antigen in sera from patients with acute Chagas' disease

An 80-kilodalton Trypanosoma cruzi antigen is eliminated in the urine of infected hosts during the acute stage of Chagas' disease. We show that affinity-purified urinary antigen is recognised by IgM antibodies in the sera from acute chagasic patients. Comparing our urinary antigen assay with that using a whole T. cruzi lysate antigen for IgM antibody detection, we demonstrated that ELISA with urinary antigen increases the diagnostic sensitivity and specificity of IgM serology in recent chagasic infection. Twenty-six of 30 patients with acute T. cruzi infection had serum IgM antibodies that reacted with urinary antigen by ELISA, while lysate antigen IgM was detected in 24 sera. When sera from patients suffering other parasitoses were tested, strong cross-reactions occurred in ELISA with T. cruzi lysate antigen, whereas ELISA with urinary antigen proved to better discriminate acute chagasic patients. Human antibodies to urinary antigen immunoprecipitated this T. cruzi urinary antigen and also inhibited the binding of monoclonal antibody to urinary antigen in an inhibition assay. These findings suggest that urinary antigen may be useful for the development of serodiagnostic procedures for acute T. cruzi infection.

Glutathione-s-transferase is an important antigen in the eel nematodeAnguillicola crassus

Different organs and secretions/excretions of the swimbladder parasite, Anguillicola crassus (Nematoda), were tested for the presence of antigens to the humoral immune response previously detected in the European eel, Anguilla anguilla. Proteins from different fractions of Anguillicola crassus were separated using SDS-PAGE (sodium-dodecyl-sulphate polyacrylamide-gel electrophoresis) under reducing conditions and electroblotted onto nitrocellulose membranes. Infected eels showed a specific antibody response to a 43 kDa antigen in the cuticle and towards two gonad antigens around 34 and 43 kDa. In protein released from the worms, two secretory/excretory antigens of approximately 28 kDa were found. The secretion/excretion rate of protein from the parasite to the surroundings was determined. Subsequently, an ELISA system was established applying these antigens as the first layer of coating. Furthermore, antigens from Anguillicola crassus were examined for the presence of glutathione-s-transferase (GST) using a specific antibody against GST. The antigens were found to be subunits of GST.

Onchocerciasis in an expatriate living in Cameroon

Travelers to West, central and eastern Africa as well as to selected areas of Latin America are at risk for infection with Onchocerca volvulus. Infection with this tissue nematode may cause chorioretinitis and keratitis, and it is responsible in endemic areas for blindness in millions.1 In addition to ocular manifestations, it can produce a distressing pruriginous dermatitis or subcutaneous nodules. Clinical manifestations vary according to the parasitic load, previous immunity, and duration of infection.1 Infection is initiated by inoculation with larvae during the bite of the Simulium black fly. Once in the connective tissue, larvae mature to filiform adults and may remain in tissues for years, with the clinical manifestations being produced by the inflammatory reaction to dying parasites. Female adults produce large amounts of microfilaria that migrate through skin and connective tissue; once an infected host is bitten, the infectious larvae develop again in the female Simulium black fly and the life cycle is completed. Transmission is from person to person, and may occur even after a relatively short exposure.2 Although infection of travelers with O. volvulus is rare, according to the Centers for Disease Control and Prevention, 46 new cases of onchocerciasis were diagnosed in the United States in 1994 (Dr. David Addis, personal communication, June 1996). We describe the case of an expatriate who became infected with O. volvulus and we review the treatment and recommendations for prevention of this parasitic infection.

Evaluation of IgG4 response in ascariasis by ELISA for serodiagnosis

The excretory/secretory (ES) antigen(s) of Ascaris lumbricoides was fractionated into 10 fractions by gel chromatography on a Suparose 12 column in FPLC. Of these, the third fraction (Al III), showing binding activity with both IgE and IgG antibodies of A. lumbricoides infected patients' sera, was further resolved into 2 fractions (Al IIIa and Al IIIb) on passage through a Mono Q column. Al IIIb was found to be the most potent antigen due to its high binding affinity with IgE and IgG antibodies of Ascaris infected patients as evidenced by ELISA inhibition. Although a two to five-fold increase of serum IgE level was observed in all helminthic parasite infected patients studied compared to control subjects, Al IIIb specific IgE was detected in sera of all Ascaris infected and only 40% of hookworm infected patients. When Al IIIb was tested by ELISA with sera of control subjects, Ascaris, hookworm, Strongyloides and Trichuris infected patients, strong binding was observed with the IgE and also IgG of all the Ascaris infected patients; however, it cross-reacted with IgG in 50% of hookworm, 28.6% of Trichuris trichura and 22.2% of Strongyloides infected patients' sera; but with IgE only in 40% of hookworm infected patients' sera. Further study showed specific detection of IgG4 in all the serum samples of 65 Ascaris infected patients when Al IIIb antigen was allowed to react with different subclasses of IgG by ELISA, giving a sensitivity of 100%. Reactivities of Al IIIb with IgG1 and IgG3 were only 47.6 and 11.8% respectively and there was no reactivity with IgG2 subclass. No IgG4 reactivity against Al IIIb was observed in the sera of hookworm, Trichuris or Strongyloides infected patients and was similar to that observed with control subjects showing the 100% specificity of the test system. This study may therefore be regarded as a novel technique for serodiagnosis of ascariasis by measuring Ascaris specific IgG4.

Enzyme-linked immunosorbent assay (ELISA) for the detection of antibodies to Anoplocephala perfoliata in horse sera

A scolex antigen of the horse tapeworm Anoplocephala perfoliata containing at least 14 different proteins was employed in an enzyme-linked immunosorbent assay (ELISA) for detection of antibodies to A. perfoliata in equine sera. The assay was applied to sera from 426 slaughtered horses with different numbers of worms and with varying degrees of intestinal lesions. As measured by the ELISA, there was a very strong effect on the antibody levels both from the number of tapeworms present and from the intestinal lesion score. However, considerable individual variation was observed between horses with similar worm counts. The ELISA values of horses that were either negative for strongyles and tapeworms or positive only for strongyles were similar, whereas both of these groups differed significantly from animals that harboured only A. perfoliata. Thus it seemed that cross-reactivity with concurrent nematode infections did not occur. Furthermore, a significant seasonal pattern in antibody levels was observed which reflected the establishment of newly acquired infections. No observations were made of confounding effects owing to age and previous anthelmintic treatment of the horses. It is concluded that the ELISA presented here has a potential for monitoring A. perfoliata infection on a herd level and can be used as a complementary diagnostic tool in epidemiological studies. The present study indicates that transmission of A. perfoliata in Central Sweden occurred during a short period in spring and more consistently in late autumn.

Detection of parasites of the Leishmania donovani-complex by a polymerase chain reaction-solution hybridization enzyme-linked immunoassay (PCR-SHELA)

A polymerase chain reaction (PCR) based on the detection of the Lmet2 repeat sequence specific to members of the Leishmania donovani-complex is described. To improve PCR specificity, a post-PCR hybridization step is often performed but this usually involves an entirely new procedure with additional manipulations, expense and time. We have simplified this post-PCR hybridization by developing a strategy which includes the probe in the PCR and enables the hybridization to be performed automatically as part of the PCR programme. The hybrids are afterwards detected by capture in microtitre wells and colorimetric visualization. This method, which we have termed PCR-solution hybridization enzyme-linked immunoassay (PCR-SHELA), is rapid, able to detect less than 5 cultured parasites and is specific for parasites of the Leishmania donovani-complex. We also describe the application of PCR-SHELA to the detection of amastigotes in various tissues of infected laboratory animals.

Evaluation of Onchocerca volvulus-specific IgG4 subclass serology as an index of onchocerciasis transmission potential of three Gabonese villages

The major objective of this study was to evaluate the usefulness of IgG4 ELISA and Western blot analysis, using a crude extract of Onchocerca volvulus adult worms as antigens, for diagnosing onchocerciasis in a Gabonese paediatric population with mixed filarial infections. The subjects had loaisis, streptocercosis or mansonellosis in addition to onchocerciasis. Control sera from loaisis or mansonellosis subjects residing outside the endemic zone were used to provide the cut-off point for positive results. The IgG4 ELISA had a specificity of 96% but a lower sensitivity of 78.7%. It detected 25 onchocerciasis cases out of 65 individuals who were negative on parasitological examination. Furthermore, the ELISA provided a more accurate picture of onchocerciasis transmission in a village with very low skin microfilarial load. A 27.5-kD antigen was identified on Western blots as a marker of onchocerciasis. The paediatric population provided a reliable window for assessing the parasitologic and serologic parameters in the three villages with disparate levels of onchocerciasis transmission.

Heterogeneity of IgG antibody responses to cloned Onchocerca volvulus antigens in microfiladermia positive individuals from Esmeraldas Province, Ecuador

The prevalence of IgG antibodies to three recombinant O. volvulus antigens, OvMBP/10, OvMBP/11 and OvMBP/29 was determined in a group of 94 microfilaria positive (mf+) individuals resident in the hyperendemic onchocercal area of Esmeraldas Province, Ecuador. Clone OvMBP/11 was the antigen most frequently recognized by patients sera followed by OvMBP/10 and OvMBP/29. When a cocktail of the three recombinant antigens was used the proportion of positive sera increased to 100%. Antibody responses to the fusion partner maltose binding protein (MBP) were low in comparison with those to the cloned antigens and no correlation of responses between individual antigens was observed. The relative level of antibody response to each of the clones in the cocktail varied between individuals. The distribution of IgG responses to OvMBP/11 was bimodal and those to OvMBP/29 and OvMBP/10 were positively and negatively skewed, respectively. When the three recombinant antigens were used in combination this variation was minimized and the pattern of responses showed a normal distribution as was also seen to crude O. volvulus antigen. The cocktail of recombinants thus offers excellent diagnostic sensitivity in combination with the parasite specificity demonstrated previously.

The effects of vector control on the antibody response to antigens of Onchocerca volvulus

The effects of exposure to infective larvae on the antibody response to a cocktail of specific recombinant antigens of Onchocerca volvulus and to a worm extract were evaluated by comparing the responses of individuals from a vector controlled area with those from an area of continuing transmission by ELISA. Individuals from the vector controlled areas were found to have reduced responses to both antigen preparations. A microfilerdermic (mf-) individuals from the area of vector control exhibited significantly lower total and subclass IgG responses to the worm extract. In contrast, the responses to the cocktail of specific recombinants were significantly reduced in individuals from the area of vector control who were still microfilerdermia positive (mf+). The distribution of IgG subclass specific responses was similar to both antigen preparations, both dominated by the IgG4 and IgG1 subclasses. IgG1 responses to the worm extract remained elevated in the vector controlled individuals but IgG4 was significantly reduced in the mf- individuals. Both subclasses reflected the total IgG response to the cocktail of recombinants and were significantly reduced in individuals from the vector controlled area, when compared to individuals from the hyperendemic area. IgG1 responses to the cocktail of recombinants are significantly lower than IgG4 in all individuals and virtually absent in individuals from the vector-controlled area. Measuring total IgG and IgG4 is more sensitive than IgG1 in detecting infection, 100 or 97% respectively, but they remain elevated in the individuals from the vector controlled areas even after 8-10 years interruption of transmission. These results have important implications for the serological monitoring of control programmes in individuals who have previously been infected.

Comparison of antibody- and antigen-detection enzyme immunoassays for the diagnosis of Trypanosoma evansi infections in camels

A total of 183 camels from Kenya were examined for circulating trypanosomal antigens by four methods: (1) a monoclonal antigen-detection enzyme-linked immunosorbent assay (Ag-ELISA) and circulating anti-trypanosomal antibodies; (2) antibody-detection enzyme-linked immunosorbent assay (Ab-ELISA); (3) buffy-coat examination (BCE); (4) mouse subinoculation (MI). Thirty-seven camels (20%) were parasite-positive by BCE and 60 camels (33%) were parasite-positive by MI. Sixty-three camels (34%) tested positive on Ag-ELISA. Of the 24 camels which could not be detected by BCE, Ag-ELISA detected 18 (75%). Ab-ELISA detected 90 (49%) positive camels. Of all the parasite-positive camels (61), Ag-ELISA detected 93% and Ab-ELISA 95%. Based on the results of 55 camels, there was a significant statistical difference (P < 0.0001) in Ag-ELISA optical density (OD) values (of either serum or plasma antigen analysis) between parasite-positive and parasite-negative camels. No significant difference was observed in Ab-ELISA OD values between parasite-positive and parasite-negative camels. Diagnosis of T. evansi infection in camels by the use of Ag-ELISA alone or in combination with BCE could therefore be a more preferred approach in assessing patient infection than the use of Ab-ELISA.

Magnetic bead antigen capture enzyme-linked immunoassay in microtitre trays for rapid detection of schistosomal circulating anodic antigen

We have developed a new magnetic bead antigen capture enzyme-linked immunoassay for the detection of schistosomal circulating anodic antigen. The assay utilizes IgG1 monoclonal antibody coated monodisperse magnetic beads in microtitre trays fitted to a special magnet. The total test time was found to be 1-2 h, using 0.05 mg beads per well. The lower detection level was 0.7 ng AWA-TCA per ml (approximately 0.07 ng CAA per ml). Validation by sera from uninfected and Schistosoma mansoni infected Africans and Norwegians resulted in an assay specificity of 100% and sensitivity was close to 90% for cases excreting more than 100 eggs per gram faeces. At such clinically relevant levels the inter-assay CV was below 10% and photometric absorbance correlated to antigen levels was nearly linear. There was a significant correlation between the magnetic bead EIA absorbance values and the titres obtained using the previously established ELISA. The new bead assay, however, was easier and less laborious because TCA pretreatment and the titration of positive results were unnecessary.

Quantitative detection of schistosomal circulating anodic antigen by a magnetic bead antigen capture enzyme-linked immunosorbent assay (MBAC-EIA) before and after mass chemotherapy

The magnetic bead antigen capture enzyme-linked immunosorbent assay (MBAC-EIA) has been applied to detect schistosomal circulating anodic antigen (CAA) in pre- and post-treatment sera from 55 individuals in a Schistosoma mansoni control project in the Blue Nile valley of western Ethiopia. The amounts of CAA detected by this assay were positively correlated with the numbers of eggs per gram of faeces (epg). A significant reduction in CAA levels as measured by the MBAC-EIA was observed after mass chemotherapy. The sensitivity was 88-89% in clinically significant cases excreting more than 100 epg. In light infections, however, the sensitivity was lower. None of 32 uninfected Norwegian blood donors or 12 Ethiopian immigrants to Norway were positive. The specificity was thus estimated to be 100%. The test is rapid (1-2 h) and simple to perform without sophisticated equipment and could therefore, with slight modification, be used as a reliable method of diagnosis at field level in endemic areas undergoing mass chemotherapy campaigns or population surveys.

Early detection of circulating anodic antigen (CAA) in a case of acute schistosomiasis mansoni with Katayama fever

A 34-year-old male developed acute Katayama fever with fever, diarrhoea, joint pains, headache, urticarial rash and eosinophilia 18 days after falling into and spending 15 min in the water during water-skiing in the outlet of the Volta river. Low anti-schistosomal antibody titres were found by the immunofluorescence assay after 4 weeks, and the first Schistosoma mansoni eggs were found in faeces after 6 weeks. Both symptoms and eosinophilia increased the first days after treatment with oxamniquine, after which he improved gradually. Examination of frozen sera by the newly developed Magnetic Beads Antigen Capture-EIA (MBAC-EIA) later demonstrated a peak in schistosomal circulating anodic antigen (CAA) levels of diagnostic significance already 4 weeks after he was infected.

cDNA clones of Onchocerca volvulus low molecular weight antigens provide immunologically specific diagnostic probes

We report here a panel of cDNA clones from Onchocerca volvulus which were isolated on the basis of being uniquely recognised by onchocerciasis sera and not by sera from patients infected with the major lymphatic filarial nematode parasite Wuchereria bancrofti. Over 90% of O. volvulus recombinants from a primary screen were found to cross-react with lymphatic filariasis sera and were discarded. The subset of specific clones, selected with pooled sera, was then screened with panels of individual patient sera. Individual onchocerciasis cases showed a highly heterogeneous pattern of recognition of recombinant peptides, but several clones were identified which could be combined in a cocktail of antigenic epitopes to successfully detect all infected cases in the study. All these clones encode low molecular weight proteins of the parasite, confirming earlier reports that antigens of this size class show greater species specificity. Several clones encode proteins of 20-23 kDa, the same molecular weight range as the major surface protein of adult worms. The two most commonly recognised clones, Ov22/31M and Ov20/36M were subcloned into the vector pNGS 8 which produces fusion proteins attached to a polyasparagine leader. The fusion peptides of both Ov22/31M and Ov20/36M were soluble and easily purified by gel filtration. Purified fusion protein was used in ELISA to assess reactivity of infected patients giving 90% sensitivity with 100% specificity.

Nucleic acid techniques and the detection of parasitic diseases

The detection of infectious disease-causing organisms is important for the initiation of effective treatment, in monitoring response to therapy and in epidemiological studies of disease of human or animal hosts. In this article Stuart Wilson primarily considers parasitic diseases, but much can be applied to infectious diseases in general.

Diagnosing multiple parasitic infections: trypanosomiasis, loiasis and schistosomiasis in a single case

A case is reported of a 32-year-old traveller with loiasis, schistosomiasis and African trypanosomiasis. The patient had been working in oil exploration in Nigeria and Gabon and presented with Calabar swellings and carpal tunnel syndrome. Serology for all 3 diseases was positive but microfilariae of Loa loa and ova of schistosomiasis were not found. Treatment with diethylcarbamazine and praziquantel was given for loiasis and schistosomiasis respectively. Trypanosomes were isolated from a lymph node aspirate only after repetition of the procedure 2 months later and the patient was treated with suramin. He developed a drug induced nephritis and was then treated successfully with alpha-difluoromethylornithine. There is a discussion of the difficulties encountered making these diagnoses in Europeans particularly where there are atypical clinical features. The risks of rural work in West Africa are noted and the importance of considering all parasitic diseases relevant to the travel/occupational history is emphasised.

[Positive serology of syphilis, toxoplasmosis and Chagas' disease in pregnant women in their first visit to health centers in a metropolitan area, Brazil]

The diagnosis of some infectious diseases contracted during pregnancy is very important, as these diseases can be transmitted to the fetus. Four hundred and eighty-one pregnant women were studied, of an average 24.5 years of age (from 14 to 46), during their first prenatal visit to the State of S. Paulo's Health Care Centres in the subdistrict of Paz (Butantan), City of S. Paulo, Brazil, between April and October, 1988. Classified by trimester of pregnancy, 230 patients (47.8%) fell into the first, 203 (42.2%) into the second and 48 (10%) into the third trimester. Of the 474 patients that declared their income, 309 (65.2%) earned 1 MSPC (minimum salary per capita) per month, which gives some indication of the low socioeconomic status of our patients is. The serologic tests for syphilis, toxoplasmosis and Chagas' disease were analysed for each patient, more than one technique being used for each. The results were as follows: 25 patients (5.2%) had a positive test for syphilis; in 67 patients (13.9%) active toxoplasmosis was diagnosed (Presence of IgM antibodies in 6); 14 patients (2.9%) were positive for Chagas' disease, among which 10 (71.4%) came from the States of Bahia and Minas Gerais, where this disease has a high prevalence.

Rapid determination of Trypanosoma cruzi urinary antigens in human chronic Chagas disease by agglutination test

Detection of Trypanosoma cruzi in man becomes particularly difficult during the chronic stage of Chagas disease because of the low parasitemia. We were able to develop a simple and straightforward method for determining the concentration of T. cruzi antigens in urine using nitrocellulose micellar suspension (Nitrocell-Mr, Polychaco Argentina) and for their subsequent detection through a "latex" type agglutination test. The latex used was an esferocell nitrocellulose suspension (Esferocell-Mr, Polychaco). Specific antigens for T. cruzi were detected in 54 of 58 urine samples from chronic chagasic patients. The antigens characterized by affinity chromatography and SDS-PAGE were glycoproteins with apparent molecular weights (and pIs) of 100 kDa (pI 5 to 5.5), 80 kDa (pI 6.0), and 50 kDa (pI 6.5 to 7.0). This method is practical and fulfills the requirement of large-scale epidemiological studies. It is also helpful in cases of conflictive serology.

Molecular approaches to DNA diagnosis

The DNA of a parasite is the ultimate blueprint of that parasite, the one characteristic which normally remains unchanged during every stage of the life-cycle. All the DNA sequence in the egg of a species of parasite are also in the larvae and adults of the same species. The same DNA is present in the parasite whether it is in a free-living stage, in an invertebrate vector or in a vertebrate host such as man. The molecular basis for DNA diagnosis is to allow labelled single-stranded species or strain-specific DNA sequences, selected from well-characterized reference species, to find and hybridize with homologous DNA from, or in, the unknown isolates of parasites. DNA probes are now available for most vector borne parasitic diseases. Parasitological identification problems are mostly concerned with distinguishing closely related strains or subspecies, for example detecting Taenia solium eggs as opposed to T. saginata eggs, or finding which of the 15 man-infecting subspecies of Leishmania is present in a single cutaneous lesion, the commonest clinical sign of the disease, or in a sandfly. For efficient hybridization by the present methods there has to be enough of a particular sequence present in a parasite's genome to make a feasible target. Therefore, DNA probes for parasites have been selected from repetitive, reiterated or multicopy DNA with intrinsic extensive sequence variation. DNA, which is free of coding restraint, can evolve rapidly to give differences between species, so that introns, ribosome gene spacers, variant genes, pseudo-genes and non-conserved DNA have all been used for DNA diagnosis. The major problems of sequence selection have been greatly aided by the use of recombinant DNA methods, which have the added advantage of economical production of DNA probes. The unique characteristics of kinetoplast mini-circle DNA in Leishmania has allowed the selection of a complex species, subspecies, strain and even isolate-specific DNA probes. These have been used successfully for Southern filter endonuclease fragment DNA identification, for dot-blot recognition of less than 200 parasites and non-radioactive detection of DNA sequence homology by 'in situ' hybridization and light microscopy in a single Leishmania cell.(ABSTRACT TRUNCATED AT 400 WORDS)

A comparative assessment of four serological methods used in the detection and measurement of anti-parasite antibodies in the serum of the amphibian, bufo viridis

Antibodies against Crithidia fasciculata choanomastigotes were detected in green toad (Bufo viridis) sera by direct agglutination, indirect haemagglutination (IHA), complement-fixation test (CFT) and enzyme-linked immunosorbent assay (ELISA), Correlation coefficients (r) were calculated for comparisons between each of the techniques and regression formulae derived in order to convert antibody levels as determined by one immunological method to that of another. The highest mean titre obtained by ELISA was approximately 1.5–3.5 times greater than those obtained by the other techniques whilst CFT gave the lowest values. IHA and ELISA titres were affected by different preparations of the crithidial antigen extracts. Highly significant r values were determined for control sera when IHA was compared to ELISA (r > 0.79), and to both CFT and ELISA with immune animals (r > 0.96). ELISA would seem most applicable for screening other lower vertebrates for anti-parasite antibodies especially in areas of human disease prevalence.

Nematode antigens in protection, diagnosis and pathology

A thorough study of parasite antigens is a prerequisite for control programmes based on protection by vaccination, accurate serodiagnosis and perhaps immune modulation to diminish pathological sequelae. Stage specific surface secreted and somatic antigens may be of particular value in proceeding towards these goals. The design of vaccines is most appropriately focused on surface antigens. With respect to pathology, certain antigens must stimulate humoral and, or cellular immune responses which are responsible for the undesirable immunopathologic consequences of the disease. The ultimate objective, therefore, is identification of those particular antigens followed by appropriate down regulation of the immune system in order to delete such potentially harmful immunological reactions. The relevant illustration presented in this context is an interesting correlation between one particular clinical condition of onchocerciasis ("sowda") and the serological response, defined both in terms of the parasite antigen and an immunoglobulin class restricted antibody response. Current parasitological methods of diagnosis consistently underestimate parasite prevalence. Failure to detect low level patent infections incurs the risk of having a reservoir capable of perpetuating infections. There is, then, an urgent requirement for accurate serodiagnosis, to be used in association with, and for the evaluation of, drug treatment and vector elimination in parasite control programmes. Given the high sensitivity of current immunoassay technology, the only bar to establishing the necessary immunological tests is the choice of suitably specific antibody-antigen systems. Once these are identified, a combination of recombinant nucleic acid biochemistry and hybridoma technology should provide the necessary reagents for inexpensive, robust and specific diagnostic tests. In addition, it may not be many years before the ubiquitous RIA and ELISA technology gives way to the newly developing biosensor systems. Finally, given the sensitivity and specificity of today's nucleic acid hybridization techniques, we may soon expect to see specific identification of infective larvae in their vectors of this, a cloned DNA probe specific for Onchocerca volvulus, and with potential for the detection of infective larvae in blackflies is described.

Serodiagnostic assay for visceral leishmaniasis employing monoclonal antibodies

A highly specific and sensitive competitive serodiagnostic assay for visceral leishmaniasis (VL) was developed using species specific Leishmania donovani monoclonal antibodies. This assay, either RIA or ELISA, is based on the specific inhibition of monoclonal antibody binding to a crude parasite homogenate by serum from patients with VL. 15 monoclonal antibodies were examined. The binding of 13 antibodies was significantly inhibited by VL serum and unaffected by normal serum. 3 species-specific monoclonal antibodies, D-2, D-13 and D-14, which recognize different parasite antigens, were chosen for use in the competitive serodiagnostic assay. In 90% of the positive cases, regardless of geographic origin, VL sera inhibited monoclonal antibody binding to the parasite antigen by more than 30%. No false positive was obtained with sera from Chagas disease, lepromatous leprosy, schistosomiasis, malaria, systemic lupus erythematosus, cutaneous or mucocutaneous leishmaniasis, even at serum dilutions (1:100) which cross-react strongly with Leishmania antigen in direct binding assays. Inhibition by negative control sera from areas endemic for VL and from non-endemic areas was negligible. The assay takes less than 24 h, requires minimum amounts of sera or antigen, and is easily standardized allowing interlaboratory comparison of test data. The competitive serodiagnostic assay will be especially useful in areas where Chagas disease is coendemic and the rapid diagnosis of VL by direct binding serodiagnostic assays presents a problem.

Cloning of a gene encoding the immunodominant surface antigen of Leishmania donovani promastigotes

This study describes the characterisation of externally oriented surface peptides of both morphological forms of Leishmania donovani, the causative agent of visceral leishmaniasis (kala-azar). Using 125I surface labelling techniques and peptide extraction in the detergents Triton X-100 and Triton X-114, a major iodinable promastigote peptide at 63 kDa or 65 kDa (depending on detergent used) was identified. This peptide was demonstrated to be the immunodominant membrane peptide of L. donovani and was strongly recognised by human sera from parasitologically confirmed cases of kala-azar. This peptide was not demonstrated on the surface of tissue amastigotes, although in vitro translations of poly(A+) RNA from both promastigotes and amastigotes demonstrated that both forms possessed mRNA that directs the synthesis of a 63 kDa peptide. It is suggested therefore that in amastigotes this peptide may be a processed antigen. We also report the isolation of a recombinant cDNA clone in the bacteriophage vector lambda gt10 which encodes a 63 kDa polypeptide that is recognised by human kala-azar sera. It is proposed that this surface peptide could be used in a specific immunodiagnostic test for leishmaniasis.

Antigenuria in infants with acute and congenital Chagas' disease

Detection and partial characterization of Trypanosoma cruzi soluble antigens (SAg) in urine, as well as demonstration of parasite circulating antigens (CAg) in serum from pediatric patients with acute (10 patients) and congenital (10 patients) Chagas' disease, are reported. Classical techniques for parasite detection and antibody serology were also conducted in both groups. Samples collected before the onset of parasiticidal drug treatment were tested by an enzyme-linked immunosorbent assay for SAg and CAg demonstration. The control population consisted of 6 children with acute toxoplasmosis, 6 with cutaneous leishmaniasis, and 20 healthy individuals. Patients with acute cases were 100% positive for both SAg and CAg, whereas patients with congenital disease were 80% CAg positive and 100% SAg positive. Controls yielded negative results in all cases. Partial characterization of SAg from two patients with acute disease was performed by iodination, affinity chromatography, immunoprecipitation, and two-dimensional gel electrophoresis. Two different antigenic glycoproteins (80 kilodaltons, pI 6 to 6.5 and 55 kilodaltons, pI 6.5 to 7) were identified by these methods. Traditional serology and classical parasitologic tests failed, each in a different way, to provide an accurate diagnosis in the total of our patients. The enzyme-linked immunosorbent assay for SAg detection proved to be the most effective procedure for achieving early and precise proof of infection in acute and congenital cases of Chagas' disease.

Isolation of an antigenic fraction for diagnosis of onchocerciasis

A surface enriched fraction was prepared from adults of Onchocerca volvulus by brief extraction of entire worms with detergent. This was then gel filtered to yield a low molecular weight fraction which functioned specifically in ELISA analysis. An identical result was also obtained when the related cattle parasite, O. gibsoni, was similarly fractionated and tested. The low molecular weight fraction contained at least four antigenic components when examined by coprecipitation and immunoblotting studies. One ml of packed worms yielded sufficient low molecular weight antigen to examine about 2,000 human sera by the ELISA procedure, and the test was sensitive at human serum dilutions down to 1/400. A preliminary study with individual sera from Onchocerciasis endemic and non-endemic areas of Southern Mexico yielded 0/24 false positives, 3/24 false negatives and a significant ELISA value in 21/24 sera from proven cases of Onchocerciasis.

Identification of non-cross-reacting antigens of Onchocerca volvulus with lymphatic filariasis serum pools

Onchocerca volvulus proteins labelled with 125I were immunoprecipitated with onchocerciasis and lymphatic filariasis human serum pools in order to differentiate between cross-reacting and non-cross-reacting antigens. Analysis of the immunoprecipitates by two-dimensional gel electrophoresis revealed that all high molecular weight (Mr) O. volvulus antigens cross-reacted with the lymphatic filariasis serum pools. We observed, however, that at least 8 O. volvulus antigens were specifically immunoprecipitated only by the onchocerciasis serum pools, with Mr ranging from 20,000 up to 43,000 Daltons. These results suggest that the lower Mr O. volvulus antigens are more species specific than the other antigens. The significance of these findings for the immunodiagnosis of onchocerciasis is discussed.

Comparative evaluation of enzyme-linked immunosorbent assay for the diagnosis of pulmonary echinococcosis

An enzyme-linked immunosorbent assay was done for the detection of immunoglobulin G and M (IgG and IgM) antibodies to Echinococcus granulosus in surgically proved cases of hydatidosis, especially pulmonary hydatidosis, by use of human hydatid cyst fluid antigen and soluble scolex antigen. This assay was compared with the following standardized techniques: the indirect hemagglutination test, the indirect immunofluorescent antibody test, and Casoni's intradermal test. The enzyme-linked immunosorbent assay, with either of the antigens (human hydatid cyst fluid or soluble scolex antigen), was more sensitive and specific than the other techniques in diagnosing cases of hydatidosis, especially hydatid disease of the lung.

Immunoserology of malaria

This literature review discusses the most frequently used serodiagnostic methods for the determination of the humoral immune response to malarial parasites. The importance of malaria as a global public health problem is stressed in the light of the new discoveries leading to the future development of an anti-malarial vaccine suitable for use in humans. Serological techniques are expected to play an important role in the assessment of the relative efficacy of these candidate vaccines. A discussion of the different antigen preparation techniques is also presented.

A Mr 90 000 surface polypeptide of Trypanosoma cruzi as a candidate for a Chagas' disease diagnostic antigen

Trypanosoma cruzi (Peru strain) trypomastigotes and epimastigotes were biosynthetically labeled with [35S]methionine, and the proteins were analyzed by two dimensional polyacrylamide gel electrophoresis (2D-PAGE). 2D-PAGE analysis of the trypomastigotes showed a complex array of polypeptides with distinct clusters at Mr 88 000-92 000, isoelectric point (pI) 5.6-6.0, and Mr 72 000-76 000, pI 5.6-5.8. 2D-PAGE analysis of the epimastigotes did not show the cluster of polypeptides at Mr 90 000. When the trypomastigote lysate was reacted with sera from either mice or humans chronically infected with T. cruzi, 10-50 polypeptides were immunoprecipitated. Five of these polypeptides were recognized by all sera tested. However, of these polypeptides, only three, two of Mr 90 000 and one of Mr 150 000, can be identified by immunoreaction of [35S]methionine-labeled live parasites as surface proteins of T. cruzi trypomastigotes. 125I-iminobiotinylated surface proteins isolated from T. cruzi trypomastigotes were immunoprecipitated with the same series of sera as described above. Chagasic sera immunoprecipitated an antigen of Mr 90 000. The [35S]methionine and 125I-labeled Mr 90 000 polypeptides were not immunoprecipitated with sera from individuals infected with Leishmania donovani, Leishmania braziliensis, Leishmania tropica or Leishmania mexicana. These data indicate that a surface polypeptide of Mr 90000, pI 5.8-5.9 is a viable candidate for a Chagas' disease diagnostic antigen.

Eosinophilia due to multiple parasitic infection

Eosinophilia is a common feature of many allergic and parasitic diseases. In the tropics multiple parasitic infection is often responsible for eosinophilia. The following illustrates this problem arising in the U.K. in a patient in whom tests for amoebiasis, filariasis, schistosomiasis and fascioliasis were all positive. Despite being treated for these conditions, the patient's symptoms did not resolve until he was treated for strongyloides infection which was found only after the 19th stool examination.

Loa loa: a simple method for isolation of microfilariae from blood with production of antigen in extraction medium

A simple method for isolating Loa loa microfilariae from the blood of patients is described. This involves sedimentation on Ficoll followed by migration of the microfilariae into an extraction medium. During migration the microfilariae release antigen-rich excretory or secretory products. The procedure thus yields two products: pure microfilariae and large amounts of antigen in the extraction medium.

A comparison of selected immunological techniques used to detect anti-leishmanial antibodies in the sera of two reptile species

European green lizards (Lacerta viridis) and spiny-tailed agamids (Agama caudospinosum) were obtained from areas endemic for human leishmaniasis. Serum antibody titres against Leishmania agamae, a reptilian leishmanial species, in normal lizards and lizards injected with Leishmania agamae promastigotes were measured by 5 immunological methods commonly used in the serodiagnosis of the human and mammalian leishmaniasis viz. immobilisation test (IMM), direct agglutination (DA), complement-fixation test (CFT), indirect haemagglutination (IHA) and enzyme-linked immunosorbent assay (ELISA). Correlation coefficients (r) were determined for comparisons between each method and linear regression equations calculated to convert antibody titres by one method to those by another. In each lizard species, the IMM test gave the lowest values while the highest were obtained with ELISA. The highest mean titre obtained by ELISA was between 2 and 10 times that obtained by the other methods for both control and immune sera. The methods of preparing the leishmanial antigen extracts affected the IHA and ELISA titres, while the source of complement was critical in obtaining good CFT values. Correlations ranging from 3% to 77% were found for the control animals but higher values ranging from 65% to 96% were obtained with the immunised lizards. Overall, the best correlation was with IHA and ELISA (r greater than 0.82) and with ELISA values for different antigen preparations compared with each other for both control (r greater than 0.67) and immune (r greater than 0.90) sera. ELISA thus appears the most sensitive method for detection and quantitation of anti-flagellate antibodies in normal lizard serum and for the determination of titres in immune serum. ELISA is the most applicable technique for screening reptiles and other lower vertebrates for anti-parasite immunoglobulins, and for screening potential carriers or reservoirs of infective flagellates in epidemiological studies aimed at disease control, especially in areas where human infections are prevalent.

Identification of an antigen of Onchocerca volvulus of possible diagnostic use

Adult Onchocerca volvulus worms obtained by enzyme digestion from nodules of infected Mexicans were radio-isotope labelled by the chloramine-T or Bolton-Hunter methods. No antigenic determinants were detected in extracts of worms labelled by the chloramine-T method but 3 antigens were detected in extracts of the Bolton-Hunter labelled worms. Two were present in such small amounts that it was impractical to investigate them further, but a major component of mol. wt 20 kDa was purified by gel filtration and used in a serological survey of inhabitants of villages in Southern Mexico. Using the 20 kDa antigen, which is superficially located on both sexes of O. volvulus, sera from both non-endemic and endemic regions were analysed by radio-immunoprecipitation of this antigen. In Southern Mexico, the average sensitivity of the test was 92%, and the specificity 98%. Whilst the 20 kDa antigen did not detect antibodies in the sera of Trinidadians infected with Wuncheria bancrofti or Mansonella ozzardi, this antigen detected high levels of antibodies in Indians exposed to W. bancrofti.

Application of hybridoma technology to the diagnosis of parasitic disease

Recent applications of hybridoma-derived monoclonal antibodies to the diagnosis of parasitic disease are reviewed. Diagnostic tests, utilizing monoclonal antibodies, have included radioimmunoassay (RIA) and enzyme-linked immunosorbent assay (ELISA) techniques to detect parasite antigen in host tissues and body fluids and circulating host antiparasite antibody. In general, the use of monoclonal-derived reagents has greatly increased the specificity of diagnosis by eliminating cross-reactions between closely related parasite species, without suffering a significant loss of sensitivity.