Prevalence of antibody to Trypanosoma cruzi among blood donors in Los Angeles, California

Trypanosoma cruzi seroprevalence among solid organ donors in Ceará State, Brazil

INTRODUCTION

The transmission of Chagas disease (CD) through blood transfusion, organ transplantation, and oral transmission has gained greater visibility as a result of intensified vector control activities in endemic regions and to control CD in non-endemic regions. In Brazil, Ceará is one of the states that perform the most organ transplants. Therefore, the objective of this study was to assess the prevalence of Trypanosoma cruzi infection in organ donor candidates.

METHODS

A retrospective analysis was performed on data from potential organ donors at the Center of Transplantation of the State of Ceará from 2010 - 2015.

RESULTS

Data from a total of 2,822 potential donors were obtained, of which 1,038 were effective donors and 1,784 were excluded, likely due to lack of family authorization or medical contraindication. The prevalence of T. cruzi infection among these potential donors was 1.3% (n = 29). The majority of infected donors were males aged 41 - 60 years, residing in the interior of the state. Interestingly, 72.4% (n = 21) had positive or inconclusive serology for additional infections, such as cytomegalovirus, hepatitis B and C, and toxoplasmosis. Probability analysis revealed that stroke was the most common cause of death among potential donors with CD.

CONCLUSIONS

There was a high prevalence of CD and other coinfections among potential solid organ donors in Ceará, and statistical tests have shown that these individuals are at increased risk of stroke when compared to potential non-reactive donors. This work highlights the importance of screening DC infection in potential donors.

Infectious Disease Transmission through Cell, Tissue, and Organ Transplantation: Reducing the Risk through Donor Selection

The incidence of cell transplant-transmitted infection is unknown and can only be inferred from prospective studies–that have not yet been performed and reported. The possibility of donor-to-recipient disease transmission through cell transplant therapy can be considered by reviewing the risk associated with other transplanted tissues and organs. Viral, bacterial, and fungal infections have been transmitted via transplantation of organs, tissue allografts such as bone, skin, cornea, and heart valves, and cells such as islets, hematopoietic stem cells, and semen. Several types of protozoan and worm parasites have been transferred via organ transplants. Bone allografts have transmitted hepatitis, tuberculosis, and human immunodeficiency virus (HIV-1). Corneas have transmitted rabies, Creutzfeldt-Jakob disease (CJD), hepatitis B (HBV), cytomegalovirus (CMV), herpes simplex virus (HSV), bacteria, and fungi. Heart valves have been implicated in transmitting tuberculosis and hepatitis B. HIV-1 and CMV seroconversion has been reported in patients receiving skin from seropositive donors. CJD has been transmitted by dura and pericardium transplants. Over the past several years, improvements in donor screening criteria, such as excluding potential donors with infection and those with behaviors risky for HIV-1 and hepatitis infection, and introduction of new donor blood tests have greatly reduced the risk of HIV-1 and hepatitis and may have nearly eliminated the risk of tuberculosis and CJD. Prior to use, many tissues are exposed to antibiotics, disinfectants, and sterilants, which further reduce or remove the risk of transmitted disease. Because organs, cells, and some tissue grafts cannot be subjected to sterilization steps, the risk of infectious disease transmission remains and thorough donor screening and testing is especially important.

A case of vertical transmission of Chagas disease contracted via blood transfusion in Canada

Chagas disease is caused by the protozoan parasite Trypanosoma cruzi and is endemic in many countries in Latin America, where infected bugs of the Triatominea subfamily carry the parasite in the gut and transmit it to humans through fecal contamination of a bite. However, vertical transmission and transmission through blood transfusion and organ transplantation is well documented. Increasing immigration from endemic countries to North America has prompted blood operators, including Canadian Blood Services and Hema Quebec, to initiate blood donor testing for Chagas antibody. In the present report, an unusual case of vertical transmission from a mother, most likely infected through blood transfusion, and detected as part of a concurrent seroprevalence study in blood donors is described.

Seroprevalence of Chagas infection in the donor population

We retrospectively calculated the prevalence and epidemiologic characteristics of Chagas infection in the New York blood donor population over three years utilizing the New York Blood Center's database of the New York metropolitan area donor population. Seventy Trypanosoma cruzi positive donors were identified from among 876,614 donors over a 3-year period, giving an adjusted prevalence of 0.0083%, with 0.0080% in 2007, 0.0073% in 2008, and 0.0097% in 2009. When filtered only for self-described “Hispanic/Latino” donors, there were 52 Chagas positive donors in that 3-year period (among 105,122 self-described Hispanic donors) with an adjusted prevalence of 0.052%, with 0.055% in 2007, 0.047% in 2008, and 0.053% in 2009. In conclusion, we found a persistent population of patients with Chagas infection in the New York metropolitan area donor population. There was geographic localization of cases which aligned with Latin American immigration clusters.

Chagas Disease is a common and economically devastating disease of Latin America, with millions infected and many more at risk of infection. The hallmark of Chagas Disease is a long asymptomatic latent period (after an often tiny bug bite) followed by potentially fatal cardiac or gastrointestinal sequelae. Despite the significant number of immigrants from Chagas-endemic regions, prevalence data outside of its countries of origin remains limited. Our study looks at Trypanosoma cruzi infection in one group, blood donors in the New York metropolitan area, as this was a non invasive way to sample a sometimes difficult-to-reach population. We found that Chagas infection is in fact present, particularly in the Hispanic donors, at a consistent level over the three years we studied. We then compared the blood donor locations to a map of foreign born Hispanics in eastern Long Island in New York and found overlapping concentrations. This may mean that there is an opportunity for large scale community-focused screenings of foreign-born populations that could be both lifesaving and cost effective.

Parasitic infections in solid-organ transplant recipients

PURPOSE OF REVIEW

To provide an updated perspective of the most common parasitic infections occurring in solid-organ transplant (SOT) recipients.

RECENT FINDINGS

Parasitic infections are an emerging problem in SOT programs and represent a diagnostic and therapeutic challenge. Transplantation in endemic areas - including medical tourism, international travel and migration - justify the necessity of considering parasitic infections in the differential diagnosis of posttransplant complications. Molecular techniques, such as PCR, may improve the diagnostic accuracy and help during the follow-up.

SUMMARY

Parasitic infections are an uncommon but potentially severe complication in SOT recipients. An increase of donors emigrated from tropical areas and more posttransplant patients traveling to endemic areas have led to a rise in parasitic infections reported among SOT recipients. Transplant physicians should get familiar with parasitic infections and promote adherence to preventive measures in SOT recipients.

Trypanosoma cruzi infection in North America and Spain: evidence in support of transfusion transmission

BACKGROUND

The United States, Canada, and Spain perform selective testing of blood donors for Trypanosoma cruzi infection (Chagas disease) to prevent transfusion transmission. The donor, product, and patient characteristics associated with transfusion-transmitted infections are reviewed and the infectivity of components from donors with serologic evidence of infection is estimated.

STUDY DESIGN AND METHODS

A systematic review of transfusion-transmitted T. cruzi cases and recipient tracing undertaken in North America and Spain is described. Cases were assessed for the imputability of the evidence for transfusion transmission.

RESULTS

T. cruzi infection in 20 transfusion recipients was linked to 18 serologically confirmed donors between 1987 and 2011, including 11 identified only by recipient tracing. Cases were geographically widely distributed and were not associated with incident or autochthonous infections. Index clinical cases were described only in immunocompromised patients. All definite transmissions (n = 11) implicated apheresis or whole blood-derived platelets (PLTs), including leukoreduced and irradiated products. There is no evidence of transmission by red blood cells (RBCs) or frozen products, while transmission by whole blood transfusion remains a possibility. Recipient tracing reveals low component infectivity from serologically confirmed, infected donors of 1.7% (95% confidence interval [CI], 0.7%-3.5%) overall: 13.3% (95% CI, 5.6%-25.7%) for PLTs, 0.0% (95% CI, 0.0%-1.5%) for RBCs, and 0.0% (95% CI, 0%-3.7%) for plasma and cryoprecipitate.

CONCLUSIONS

T. cruzi is transmitted by PLT components from some donors with serologic evidence of infection. Evidence of transmission before the implementation of widespread testing in the countries studied is sparse, and selective testing of only PLT and fresh whole blood donations should be considered.

[Control of transfusional transmission]

The high prevalence of chagasic blood donors in blood centers in Brazil (6.9%) and in Latin America (6.5%) in the 60's and 70's, together with the combat to the vector since the 70's have made transfusion Chagas disease the main mechanism of the disease transmission in the 80's. However, the highly favorable results achieved to eliminate the vector and the serologic screening of blood donors, reduced the prevalence of serum positivity to 0.2% and 1.3%, respectively and the rate of annual transmission through blood transfusion from 20.000 to 13 in four decades in Brazil. Nevertheless, despite outstanding advancements in endemic countries, Chagas disease reached, via migration, non-endemic countries in North America and Europe besides Japan and Australia, placing their blood recipients at risk and turning Chagas disease into a worldwide health problem. Transfusion safety through serologic selection raised another big issue i.e. high proportion of inconclusive reactions as well as two great challenges: the meaning of such exams and what guidelines to provide the donor. However, the strategies adopted by non-endemic countries and the advancements achieved by endemics so far forecast the highly wished vector and transfusion control of Chagas disease.

Parasitic infections in solid organ transplant recipients

Parasitic infections are an uncommon but potentially severe complication in solid organ transplant (SOT) recipients. An increase in donors who have emigrated from tropical areas and more transplant recipients traveling to endemic areas have led to a rise in parasitic infections reported among SOT recipients. Clinicians should include these infections in their differential diagnosis and promote adherence to preventive measures in SOT recipients.

[Chagas disease in the Americas: an ecohealth perspective]

The historical processes involved in Chagas disease transmission relate to the patterns and conditions of human settlements, especially in rural areas, due to proximity to forest areas, where both vectors and Trypanosoma cruzi can occur, combined with precarious housing conditions and underlying poverty. However, seasonal and permanent rural-urban migration has played a major role in re-mobilizing vectors, T. cruzi, and Chagas-infected individuals. A new agricultural frontier in the Amazon has led to a new transmission pattern, especially with palm trees located close to houses. Improved blood bank surveillance has decreased transmission by blood transfusions. International migration also plays a role in Chagas disease epidemiology. The United States and Spain, where specific health services for Chagas disease diagnosis and treatment are largely absent, harbor an unknown number of individuals with Chagas, probably infected decades ago. The article discusses major strides in Chagas disease knowledge and control, besides identifying persistent gaps, such as the need for housing improvements, especially in poor rural areas in the Americas.

Epidemiology of Chagas disease in non-endemic countries: the role of international migration

Human infection with the protozoa Trypanosoma cruzi extends through North, Central, and South America, affecting 21 countries. Most human infections in the Western Hemisphere occur through contact with infected bloodsucking insects of the triatomine species. As T. cruzi can be detected in the blood of untreated infected individuals, decades after infection took place; the infection can be also transmitted through blood transfusion and organ transplant, which is considered the second most common mode of transmission for T. cruzi. The third mode of transmission is congenital infection. Economic hardship, political problems, or both, have spurred migration from Chagas endemic countries to developed countries. The main destination of this immigration is Australia, Canada, Spain, and the United States. In fact, human infection through blood or organ transplantation, as well as confirmed or potential cases of congenital infections has been described in Spain and in the United States. Estimates reported here indicates that in Australia in 2005-2006, 1067 of the 65,255 Latin American immigrants (16 per 1000) may be infected with T. cruzi, and in Canada, in 2001, 1218 of the 131,135 immigrants (9 per 1000) whose country of origin was identified may have been also infected. In Spain, a magnet for Latin American immigrants since the 2000, 6141 of 38,777 to 339,954 [corrected] legal immigrants in 2003 (25 per 1000), could be infected. In the United States, 56,028 to 357,205 of the 7,20 million, legal immigrants (8 to 50 per 1000), depending on the scenario, from the period 1981-2005 may be infected with T. cruzi. On the other hand, 33,193 to 336,097 of the estimated 5,6 million undocumented immigrants in 2000 (6 to 59 per 1000) could be infected. Non endemic countries receiving immigrants from the endemic ones should develop policies to protect organ recipients from T. cruzi infection, prevent tainting the blood supply with T. cruzi, and implement secondary prevention of congenital Chagas disease.

Chagas disease in Texas: Recognizing the significance and implications of evidence in the literature

Chagas disease is endemic and is recognized as a major health problem in many Latin American countries. Despite the parallels between socio-economic and environmental conditions in Texas and much of Latin America, Chagas disease is not a notifiable human disease in Texas. Based on extensive review of related literature, this paper seeks to recognize the evidence that Chagas Disease is endemic to Texas but the epidemiological, parasitological and entomological patterns of Chagas disease in Texas are both different from and parallel to other endemic regions. We find that with a growing immigrant human reservoir, the epidemiological differences may be reduced and result in increasing incidence of the disease. Chagas disease should be recognized as an emerging disease among both immigrant and indigenous populations. Without proper actions, Chagas disease will place increasing burden on the health care system. Current medical treatments consist of chemotherapies that carry the risk of serious side effects; curing the potentially fatal disease remains equivocal. Therefore, as shown in South America, prevention is paramount and can be successfully achieved through intervention and education. We conclude that biogeographical research is needed to (1) distinguish the dynamic evolution of the agent-vector-host system, (2) document locations with greater risk and identify mechanisms responsible for observed changes in risk, and (3) assist in developing a model for Triatomid vector-borne disease in states like Texas where the disease is both endemic and may be carried by a sizeable immigrant population. Tracking of Chagas disease and planning for appropriate health care services would also be aided by including Chagas disease on the list of reportable diseases for humans.

Transfusion-acquired Trypanosoma cruzi infection

BACKGROUND

A 3(1/2)-year-old girl with Stage 4 neuroblastoma received multiple blood components and was subsequently diagnosed with Chagas disease, which is caused by Trypanosoma cruzi.

STUDY DESIGN AND METHODS

All blood donors of the units that were transfused were requested to return to the collection facility for a blood sample to be tested for antibodies to T. cruzi.

RESULTS

One first-time donor was found to be positive for the presence of T. cruzi antibodies. This donor was originally from Bolivia and immigrated to the United States 17 years previously. She had not returned to her native country since her emigration.

CONCLUSIONS

This is the seventh reported case of Chagas disease transmission by blood transfusion in the United States and Canada. Although this would not be expected to occur in New England, it did, and this case demonstrates the significance of the immune status of patients as it relates to transfusion-acquired infections, the impact of geographic mobility in disease transmission, and the need for a licensed screening test for Chagas disease for the US blood supply.

Field evaluation of four novel enzyme immunoassays for Chagas' disease in Venezuela blood banks: comparison of assays using fixed-epimastigotes, fixed-trypomastigotes or trypomastigote excreted?secreted antigens from two Trypanosoma cruzi strains

Many serological tests have been developed for the diagnosis of Chagas' disease, but few have been subjected to a rigorous field evaluation. We have recently described several novel enzyme immunoassays (EIAs) based on fixed-whole organisms or trypomastigote excretory-secretory antigens (TESA) from different Trypanosoma cruzi strains (Tulahuen or Brazil). This study evaluated the most promising of these novel assays (e.g. fixed-epimastigotes, fixed-trypomastigotes, TESA Brazil and TESA Tulahuen antigens) in a field study of Venezuelan blood bank specimens. The assays were tested in an operator-blinded fashion using 2038 blood bank samples obtained from low and high T.cruzi prevalence regions of Venezuela (n= 1050 and n= 988 from Bolivar and Portuguesa states, respectively). Based on National Laboratory for Chagas Immunodiagnosis (NLCI) 'gold standard' results, all novel EIAs were superior to the commercial kit currently used in Venezuela, achieving 100% sensitivity and >99% specificity at optimal cut-off values. The novel assays identified seven false-negative samples compared with the routine screening performed by the Venezuelan blood bank although two samples were also misclassified as positive. Minor differences in the performance of the four novel assays were observed at lower arbitrary cut-off values. This study confirms the potential utility of both the fixed-organism and the TESA-based assays in the diagnosis of T.cruzi infection.

The Sero-Prevalence of Antibodies to Trypanosoma cruzi in Latin American Refugees and Immigrants to Canada

BACKGROUND

Chagas' disease is caused by infection with the protozoan agent Trypanosoma cruzi. An estimated sixteen to eighteen million people are infected in Latin America. Outside of endemic regions, Chagas' disease may be transmitted through the transfusion of infected blood components, congenital infection and organ transplantation. We sought to determine the sero-prevalence of antibodies to T. cruzi in a community sample of Latin American refugees and immigrants to Canada.

METHODS

This was a sero-prevalence study in Latin American refugees and immigrants living in Canada. Eligible subjects were born in South America, Central America or in Mexico. Participants were recruited from a variety of community settings, as well as from medical clinics. Serum was tested by enzyme-linked immunoassay for antibodies to T. cruzi.

RESULTS

A total of 102 participants were enrolled. One sample tested positive for antibodies for T. cruzi. The seroprevalence in our sample was 1.0% (95% CI: 0.2%- 5.3%).

INTERPRETATION

We found a low sero-prevalence of Chagas' disease in a community sample of Latin American immigrants and refugees. Physicians who treat Latin American immigrants should consider the risk profile and clinical status of the individual in their decision to screen for Chagas' disease.

Serological diagnosis of Trypanosoma cruzi: evaluation of three enzyme immunoassays and an indirect immunofluorescent assay

Chagas' disease is an important cause of heart failure in Latin America, but is rare in the United States. The immigration of persons from endemic countries increases the potential of encountering patients with the disease. Concerns have also been raised about the introduction of Trypanosoma cruzi, the parasite that causes the disease, into the blood supply and during organ transplantation. To compare Chagas' antibody tests that are available in the United States, we evaluated three IgG ELISAs, CeLLabs T. cruzi ELISA, Hemagen Chagas' kit and IVD Research Chagas' Serum Microwell ELISA, and MarDx indirect immunofluorescent assays. The CeLLabs and Hemagen IgG ELISAs had 100 % agreement, sensitivity and specificity. The IVD Research IgG ELISA had 94·6 % agreement, 100 % sensitivity and 93 % specificity.

Prevalence of Antibodies to Trypanosoma cruzi among Solid Organ Donors in Southern California: A Population at Risk

Trypanosoma cruzi, a parasite that causes Chagas' disease, is endemic in parts of Mexico, South America, and Central America. Transmission of T. cruzi infection by solid organ transplantation has been reported in Latin America and recently in the United States. To determine the prevalence of T. cruzi antibodies in Southern California organ donors, 404 samples from deceased organ donors between May 2002 to April 2004 were screened using a qualitative enzyme-linked immunosorbent assay (EIA) and confirmed with an immunofluorescence assay (IFA) available through the Centers for Disease Control (CDC). Six donors were initially reactive by EIA. Three donors were repeatedly reactive after repeat testing and were sent to the CDC for confirmation. One donor (0.25%) had an IFA-confirmed reactivity to anti-T. cruzi antibodies. In areas where there is a high number of immigrants from T. cruzi endemic countries, screening for anti-T. cruzi donor antibodies may be beneficial.

Comparative study of the presence of Trypanosoma cruzi kDNA, inflammation and denervation in chagasic patients with and without megaesophagus

Neuronal lesions have been considered the hallmark of chagasic megaesophagus, but the role of Trypanosoma cruzi and the participation of the inflammatory cells in this process are still debated. In the present study we counted neurons in the oesophagus from patients with and without megaesophagus and further examined these samples for the presence of parasite kDNA and cells with cytolytic potential (Natural Killer cells, cytotoxic lymphocytes and macrophages). The presence of parasite kDNA was demonstrated in 100% of cases with megaesophagus and in 60% of patients without megaesophagus. When analysed for the number of neurons, the patients without megaesophagus could be classified into 2 groups, as having normal or a decreased number of neurons. The former group did not show any inflammatory process, but interestingly, all patients without megaesophagus presenting decreased number of neurons also presented both parasite kDNA and inflammatory process in the organ. We further observed that the numbers of cytotoxic cells in the myenteric plexus region inversely correlate with the number of neurons. These data together strongly suggest that chronic lesions in chagasic megaesophagus might be a consequence of immune-mediated mechanisms, that last until the chronic phase of infection, and are dependent on the persistence of parasite in the host's tissue.

Chagas' disease in an obstetrical patient

We report a case of a parturient with documented chronic Chagas' disease with cardiac manifestations presenting for labor management and complicated by the need for emergent hysterectomy after delivery. Chagas' disease is a common human hematogenous trypanosomiasis in Central and South America which is now, because of population migration, appearing in the USA. This disease predominantly affects the heart and the gastrointestinal system. This report discusses the parasite, the acute and chronic phases of Chagas' disease and highlights its medical implications, including maternal-fetal transfer of Trypanosoma cruzi.

Concurrent Cerebral American Trypanosomiasis and Toxoplasmosis in a Patient with AIDS

We report a case of concurrent cerebral infection with Trypanosoma cruzi and Toxoplasma gondii in a patient with acquired immunodeficiency syndrome (AIDS). A 22-year-old El Salvadoran man initially improved during receipt of antitoxoplasmosis therapy, but he had rapidly progressive hemiplegia. Magnetic resonance imaging showed an abnormal finding in the left internal capsule, and cytological analysis of cerebrospinal fluid revealed T. cruzi trypomastigotes. Despite prompt therapy with nifurtimox, the patient's mental status declined, and he died of nosocomial complications. Although infrequent, T. cruzi infection should be considered in the differential diagnosis of brain lesions in patients with AIDS from regions of endemicity.

Structural characterization of a recombinant flagellar calcium-binding protein from Trypanosoma cruzi

Calflagin are flagellar calcium-binding proteins belonging to the EF-hand super family described in several protozoa, including Trypanosoma cruzi. Evidences have shown that Ca(2+) may play an important regulatory role in trypanosomatid flagellar mobility. In these parasites, the response of the cell to variations of Ca(2+) levels is determined by a variety of calcium-modulated proteins. Starting from T. cruzi cDNA lambdagt11 library trypomastigote, a clone encoding a 29-kDa flagellar protein designated recombinant calflagin (rC29) was selected. rC29 is a calcium-acyl switch protein modified by the addition of myristate and palmitate at its amino terminal segment. In this work, unmyristoylated rC29 was expressed in Escherichia coli as an intein fusion protein and purified by affinity chromatography. Circular dichroism (CD) and fluorescence measurements showed conformational changes of rC29 due to Ca(2+) binding. The Ca(2+) binding constants were obtained by tryptophan intrinsic fluorescence spectroscopy. Fluorescence titration exhibited two classes of Ca(2+)-binding sites in the unmyristoylated rC29, which bind calcium with apparent association constant of K(a) of 3.3+/-0.5 (10(6)) and 1.9+/-0.2 (10(4)) M(-1). Experiment using 8-anilinonaphthalene-1-sulfonic acid (ANS) as hydrophobic probe showed that the Ca(2+)-loaded form of rC29 contains exposed hydrophobic surfaces, thus suggesting that rC29 is probably functioning as a calcium sensor.

Trypanosoma cruzi in Los Angeles and Miami blood donors: impact of evolving donor demographics on seroprevalence and implications for transfusion transmission

BACKGROUND

Trypanosoma cruzi, the agent of Chagas' disease, continues to be a concern for blood safety, as demonstrated by recent transfusion-transmitted cases in the United States and Canada. The chronic nature of Chagas', coupled with increasing numbers of immigrants from T. cruzi-endemic countries, suggests that Chagas' is a long-term public health problem. Herein, we report on a multiyear epidemiologic study of T. cruzi in Los Angeles and Miami blood donors.

STUDY DESIGN AND METHODS

From May 1994 to September 1998, blood donors in Los Angeles and Miami were queried regarding birth or time spent in an endemic country. Donations of "yes" respondents were tested by EIA, confirmed by radioimmunoprecipitation assay, and if confirmed as seropositive, enrolled in look-back investigations.

RESULTS

A total of 1,104,030 Los Angeles and 181,139 Miami donors were queried regarding risk; 7.3 and 14.3 percent, respectively, responded yes. Seropositive rates were 1 in 7,500 Los Angeles and 1 in 9,000 Miami donors. In Los Angeles, seroprevalence rates increased significantly from 1996 to 1998 and were significantly higher for directed donors than nondirected donors. Look back identified 18 recipients, all of whom were seronegative for T. cruzi.

CONCLUSION

Significant numbers of T. cruzi-seropositive donors contribute to the U.S. blood supply. The incidence of seropositivity is enhanced by minority recruitment efforts necessitated by donor demographic shifts. Similarly, high rates among directed donations in Los Angeles are attributable to a disproportionate number of at-risk directed donors. Current look-back data likely underestimate the frequency of transfusion- transmitted T. cruzi. These results indicate that continued evaluation of transfusion as a mode of T. cruzi transmission in the United States is needed.

Trypanosoma cruzi: a considerable phylogenetic divergence indicates that the agent of Chagas disease is indigenous to the native fauna of the United States

Thirty U.S. Trypanosoma cruzi stocks isolated mainly from wild mammals were characterized by multilocus enzyme electrophoresis at 22 genetic loci and random amplification of polymorphic DNA for 10 primers. Two main phylogenetic clusters, separated by large genetic distances, were discriminated by both methods, corresponding, respectively, to the formerly described zymodemes I and III. Two stocks isolated from indigenous human cases were identified as zymodeme I. Genetic diversity of the U.S. T. cruzi isolates was considerable, comparable to that scored in similarly sized samples from South America. These results favor the hypothesis that T. cruzi U.S. stocks were not imported at a historical time and are indigenous to the native fauna of the United States. The population structure of these stocks appeared to be basically clonal, as previously reported in South America, and no evidence of hybrid genotypes was found in the United States.

Antibodies to Trypanosoma cruzi among blood donors in Buenos Aires, Argentina

OBJECTIVES

The aim of this work was to study the prevalence of anti-Trypanosoma cruzi in the blood donor population in Buenos Aires, to compare the relative sensitivity and specificity of the two screening tests used and to confirm the results with a third assay.

MATERIAL AND METHODS

Between May 1995 and July 1999, 64,887 blood donor consecutive samples were screened with the following commercial tests: indirect hemagglutination (IHA) (Polychaco, Buenos Aires, Argentina) and enzyme-linked immunosorbent assay (ELISA) (40,222 with Chagatek, Organon Teknika, Buenos Aires, Argentina, and 24,665 with Chagas EIA, Abbott, São Paulo, Brazil). Repeatedly reactive samples in one or both tests were analyzed with a third method: dot blot (Bio Chagas, Gador, Buenos Aires, Argentina) or particle agglutination (Serodia, Fujirebio, Tokyo, Japan). Sera that reacted in at least two tests were considered positive.

RESULTS

The seroprevalence was 2.66% (1744 samples were reactive for one or both screening tests), and 1.46% (949 samples) were confirmed positive. The ELISAs proved to be more sensitive (relative sensitivity: 99.67-99.71%) whereas 192 samples (0.47%) were IHA false-negatives (relative sensitivity: 79.77%). Relative specificity for EIA was 98.47--99.23% and for IHA 99.85%.

CONCLUSIONS

Results suggest the need of performing two screening tests for Chagas disease in blood banks from endemic areas and the importance of a third confirmatory assay to avoid unnecessary medical counseling.

Serologic testing for Trypanosoma cruzi: comparison of radioimmunoprecipitation assay with commercially available indirect immunofluorescence assay, indirect hemagglutination assay, and enzyme-linked immunosorbent assay kits

The radioimmunoprecipitation assay (RIPA) has been used as a confirmatory test in several ongoing and published studies of Trypanosoma cruzi in blood donors in the United States. Despite its use as a confirmatory test, few studies are available comparing RIPA to commercially available serologic test methods. Thus, we compared RIPA with two indirect hemagglutination assays (Biolab Diagnostica SA, São Paulo, Brazil; Hemagen Diagnostics, Inc., Waltham, Mass.) and four different enzyme-linked immunosorbent assays (Abbott Laboratories, Abbott Park, Ill.; Embrabio, São Paulo, Brazil; Organon Teknika, São Paulo, Brazil; and Gull Laboratories, Salt Lake City, Utah) using a panel of 220 serum specimens from Brazilian blood donors with a range of T. cruzi antibody titers as determined by indirect immunofluorescence assay (IFA). A titer of 1:20 was used as the baseline for seropositivity. All IFA-negative serum specimens (n = 19) were nonreactive on all tests. At a titer of 1:20 (n = 9), reactivity rates varied considerably among the tests, with only the RIPA and the Organon and Gull assays identifying reactive specimens. For specimens at a 1:40 titer (n = 35), most assays identified at least 32 of 35 (91%) specimens as reactive, but the Biolab assay only identified 24 (69%). At higher titers (1:80, n = 56; 1:160, n = 101) the assays were comparable, with the exception of the Biolab assay, demonstrating rates of agreement with IFA of >/=98%. Overall, when compared with several other test formats, RIPA demonstrated equivalent or superior rates of agreement with IFA-positive specimens across all titers examined. In particular, at titers of >1:40, the RIPA compared favorably with other test methods currently in use, supporting its application as a confirmatory test, particularly in a research setting.

Trypanosoma cruzi: suppression of tuzin gene expression by its 5'-UTR and spliced leader addition site

Teixeira, S. M. R., Kirchhoff, L. V., and Donelson, J. E. 1999. Trypanosoma cruzi: Suppression of tuzin gene expression by its 5'-UTR and spliced leader addition site. Experimental Parasitology 93, 143-151. The genome of the protozoan parasite Trypanosoma cruzi contains a tandemly repeated array of two alternating genes, one encoding amastin and the other encoding tuzin. Amastin is an abundant amastigote surface protein, whereas tuzin is thought to be a rare protein whose location and function are unknown. The 137-nucleotide 5' untranslated region (5'-UTR) of the tuzin mRNA has a 22-codon open translation reading frame containing 3 methionine codons followed by a stop codon that overlaps the methionine start codon of the tuzin coding region. A fragment containing the tuzin 5'-UTR and upstream intergenic region was placed in front of a luciferase reporter gene in a plasmid for transient transfection assays of luciferase activity. By mutating the three upstream ATGs in the tuzin 5'-UTR and replacing the tuzin spliced leader (SL) acceptor site with that of the amastin gene, we found that the 22-codon reading frame and the tuzin SL acceptor site combine to substantially reduce expression of the luciferase gene. These results indicate that expression of the multicopy tuzin gene is posttranscriptionally suppressed by both inefficient RNA processing and poor translation initiation, resulting in a low level of tuzin.

American trypanosomiasis (Chagas' disease) and blood banking in Mexico City: seroprevalence and its potential transfusional transmission risk

BACKGROUND

American trypanosomiasis (Chagas' disease), an anthropozoonosis fairly common in rural Latin America, has become an urban disease due to continuous migration, intra- and internationally. Blood transfusion, the second important pathway for transmission, increases its impact. Recognition of seropositive subjects among blood donors is now recommended, and clinical and serological screening enforced. Maneuvers to inactivate or remove Trypanosoma cruzi present in collected blood are recommended.

METHODS

We surveyed voluntary donors at the National Institute of Cardiology in Mexico City in search of anti-T. cruzi by indirect immunofluorescence, ELISA, and Western blot analysis. Seropositive donors were identified and tested for immunoglobulin. We used types and fractions of donated blood to extract DNA and perform the PCR technique using kinetoplast primers seeking parasite DNA in blood.

RESULTS

After 3,300 donors were screened, we identified 10 seropositive subjects (0.3%). These subjects were considered as indeterminate chagasic patients, came mainly from rural areas, and had IgG (100%) and IgA (30%) antibodies against a crude extract as well as a recombinant T. cruzi antigen. Identification of parasite DNA in red cell and platelet fraction was achieved from eight blood units.

CONCLUSIONS

The present data provide evidence that blood donors at an urban hospital are seropositive for T. cruzi and at least 50% of donors carry the parasite potentially able to transmit T. cruzi in their cellular blood products. Serological screening should be included in routine blood-making. It is also necessary to adopt measures to inactivate or eliminate organisms in donated blood.

Trypanosoma cruzi in a low- to moderate-risk blood donor population: seroprevalence and possible congenital transmission

BACKGROUND

Several recent studies documented the seroprevalence of Trypanosoma cruzi in blood donors at high risk for infection, but little information is available regarding donors with lower levels of risk. Thus, the present study was designed to measure the seroprevalence of T. cruzi in a donor population with a low to moderate risk for infection.

STUDY DESIGN AND METHODS

During a 10-month period, donations from all allogeneic blood donors in the American Red Cross Southwest Region were tested for T. cruzi antibodies by enzyme immunoassay, and results were confirmed by radioimmunoprecipitation. Confirmed-seropositive donors were counseled and lookback investigations were initiated for those who were repeat donors.

RESULTS

A total of 100,089 donations were tested: 150 were repeatably reactive, and 3 (0.003%) were confirmed as positive for T. cruziantibodies. All three seropositive donors were from the Waco, TX, area, where the estimated seroprevalence rate was 1 in 7700. Two of these three donors reported no risk factors; both were born in the United States and had not traveled to an endemic area. Both had extensive familial histories of cardiac disease and complications.

CONCLUSION

Blood donors seropositive for T. cruzi are present in populations with low to moderate risk, albeit at lower rates. The presence of seropositive blood donors without the usual identifiable risk factors argues against the use of a geographic screening question and also suggests that other routes of transmission, including the congenital route, should be considered in efforts to increase blood safety.

Decreased CD4(+) circulating T lymphocytes in patients with gastrointestinal chagas disease

The gastrointestinal form of Chagas disease is characterized by lumenal enlargement and wall thickening of the esophagus and/or colon. Very little is known about the involvement of the immune system in the development of the gastrointestinal form of the disease. In this paper we describe our initial observations on the phenotypic analysis of peripheral blood mononuclear cells from patients with the gastrointestinal form of Chagas disease. A significant decrease in the absolute number of CD3(+) T cells as well as in CD19(+) B lymphocytes was observed. However, the most striking observation was an inversion of the CD4/CD8 ratio, contrasting with results from cardiac chagasic patients in whom the ratio is normal. A decrease of the percentage of CD4(+)CD28(+) cells and an increase in the expression of HLA-DR both on CD4(+) and on CD8(+) cells suggest that although these T cells express activation markers their function may be altered by the lack of CD28 expression.

Prevalence and epidemiological significance of Trypanosoma cruzi infection among Latin American immigrants in Berlin, Germany

A survey was conducted among Latin American immigrants living in Berlin to investigate the presence of Trypanosoma cruzi infection and to evaluate possible risk factors. One hundred persons were interviewed about risk factors (rural origin, contact with the reduviid bug) and evaluated serologically. The sera were tested with indirect immunofluorescence (IIF). All samples seroreactive with IIF were additionally evaluated with an ELISA for T. cruzi antibodies. To rule out cross-reactivity all seroreactive sera were tested with IIF for Leishmania infantum antibodies. Two persons were seroreactive in IIF and ELISA and three were seroreactive in the IIF only. The overall seroprevalence according to WHO criteria was therefore 2% (2/100). All samples were negative for Leishmania antibodies. Only one of the seropositive persons showed a risk factor for T. cruzi infection in their medical history. These findings suggest that routine serologic testing of Latin Americans is indicated to reduce the risk of transmission by blood transfusion and congenital transmission.

A highly sensitive and specific chemiluminescent enzyme-linked immunosorbent assay for diagnosis of active Trypanosoma cruzi infection

BACKGROUND

Chagas' disease is transmitted to man either by the bite of insects harboring Trypanosoma cruzi or by the transfusion of blood from infected donors. The conventional serologic testing as presently used in blood banks in South America is unsatisfactory, because of a high number of inconclusive and false-positive results. Other methods such as polymerase chain reaction and enzyme-linked immunosorbent assay (ELISA) with recombinant antigens have been proposed, but inherent difficulties have so far precluded their adoption in the large-scale screening required by blood banks.

STUDY DESIGN AND METHODS

A highly sensitive and specific chemiluminescent ELISA using a purified trypomastigote glycoconjugate antigen and a complex epimastigote antigen was devised for the diagnosis of active T. cruzi infection.

RESULTS

Chemiluminescent ELISA was 100-percent sensitive in the diagnosis of 100 cases of confirmed Chagas' disease. Inconclusive results and false-positive reactions were eliminated in a panel of 115 sera. The specificity of the chemiluminescent ELISA was 100 percent with a purified trypomastigote glycoconjugate antigen and 99.7 percent with a complex epimastigote antigen when applied to 1000 normal human sera and 288 heterologous sera from patients with other infections, including leishmaniasis, and vaccinated individuals.

CONCLUSION

The chemiluminescent ELISAs provide a test that is highly sensitive (purified trypomastigote glycoconjugate and complex epimastigote antigens) and specific (purified trypomastigote glycoconjugate antigen) for Chagas' disease diagnosis. It can be used in blood bank screening and to monitor the treatment of patients undergoing chemotherapy.

Serological diagnosis of Chagas' disease: a potential confirmatory assay using preserved protein antigens of Trypanosoma cruzi

The diagnosis of Chagas' disease relies mostly on data provided by immunologic tests, but inconclusive results often require elucidation, especially in blood banks. When six different types of Trypanosoma cruzi epimastigote antigens were studied by an immunoblotting assay (IBA), a preserved protein antigen (Ag PP) was found to present the most interesting immunochemical features because of its high reactivity with anti-T. cruzi antibodies. Thus, the IBA with Ag PP (PP IBA) was assessed with panels of coded and noncoded serum samples prepared in different laboratories, including the Brazilian Reference Laboratory for Chagas' Disease. It was found that serum samples from patients proved (clinically, eletrocardiographically, serologically, and epidemiologically) to have Chagas' disease consistently recognized 12 bands (140, 100, 85, 78, 59, 57, 46, 35, 27, 23, 20, and 18 kDa) of Ag PP. In contrast, sera from nonchagasic patients, including patients with mucocutaneous leishmaniasis, were negative or reacted weakly, and one serum sample did not have more than five different bands. These bands were 78, 57, 46, 35, 27, 23, 20, or 18 kDa. A criterion was adopted to interpret the results obtained in the PP IBA. The criterion considered positive a serum sample recognizing all 12 bands and considered negative a serum sample that did not recognize any of the bands except the eight nonspecific bands mentioned above. The PP IBA indicated maximum sensitivity and specificity as well as high positive and negative predictive values. The data demonstrate that the PP IBA discriminates chagasic from nonchagasic infections and seems to be applicable as a confirmatory assay for elucidating inconclusive results obtained by standard serology.

A simple Trypanosoma cruzi enzyme-linked immunoassay for control of human infection in nonendemic areas

An enzyme linked immunosorbent assay (ELISA) was developed for detecting IgM and IgG antibodies against Trypanosoma cruzi in blood bank donors from endemic or nonendemic areas. A crude extract of trypomastigotes from cultures was used as antigen. A total of 494 serum samples from patients with acute, congenital, or chronic form of Chagas' disease, and from healthy French individuals were studied. The sensitivity of the ELISA was determined with 89 serum samples from chagasic patients and was evaluated to 98.8%. The specificity was determined with 405 serum samples from French blood transfusion centers donors and evaluated to 98.3%. Two hundred and eighty-five serum samples from blood donors from Argentina and Brazil were also tested. Furthermore, in order to assess the absence of cross-reactivity with other protozoan infections, we studied 86 serum samples including (i) 32 individuals with cutaneous leishmaniasis living in a T. cruzi endemic region of Bolivia, and (ii) 54 patients from nonendemic area for Chagas' disease, 19 of them with kala-azar and 35 others with malaria.

Photosensitized inactivation of Plasmodium falciparum- and Babesia divergens-infected erythrocytes in whole blood by lipophilic pheophorbide derivatives

BACKGROUND AND OBJECTIVES

Blood transfusions can transmit parasitic infections, such as those caused by Plasmodium (malaria), Trypanosoma cruzi (Chagas' disease), and Babesia (babesiosis). A higher degree of blood transfusion safety would be reached if methods were available for inactivating such parasites.

MATERIALS AND METHODS

We evaluated the effectiveness of photosensitization using lipophilic pheophorbide and red light illumination to eradicate red blood cells infected with Plasmodium falciparum, and with Babesia divergens, in whole blood. Fluorescence microscopy and conventional fluorometry showed the specific accumulation of pheophorbide derivatives in the RBC infected with either parasite, compared with uninfected RBC. The effectiveness of different derivatives in eradicating infected RBC was first estimated in parasite cultures.

RESULTS

The best photosensitizer was the N-(4-butanol) pheophorbide derivative (Ph4-OH) at 0.2 microM concentration and 5-min illumination. In whole blood, the eradication of RBC infected with B. divergens and P. falciparum was obtained with 2 microM Ph4-OH and 10 and 20 min illumination, respectively. Under these conditions of photosensitization, low levels of RBC hemolysis were noted even after 2 weeks of storage at 4 degrees C and a subsequent 48-hour incubation at 37 degrees C. No reduction of negative charges on treated RBC was noted and no increase in methemoglobin content.

CONCLUSIONS

In plasma, Ph4-OH is mainly transported by high-density lipoproteins (HDL). This high affinity for HDL may explain the selective accumulation of lipophilic pheophorbide derivatives in the intracellular parasites. Photosensitization with pheophorbide derivatives may be a promising approach to inactivation of transfusion-transmissible parasites and viruses in blood bank units.

American trypanosomiasis (Chagas' disease)

Gastrointestinal dysfunction is a major problem for many patients with chronic Chagas' disease, as are cardiac dysrhythmias and cardiomyopathy. The underlying anatomic abnormality in these patients is a denervation of the gastrointestinal tract. This process of nerve destruction usually develops insidiously over many years, and it is highly variable in terms of its extent in individual patients as well as in the segments of the gastrointestinal tract that are most affected. Megaesophagus is the most common manifestation of gastrointestinal Chagas disease, and mechanical dilation of the esophageal sphincter or surgery in advanced cases usually give satisfactory relief of symptoms. Megacolon, particularly of the sigmoid segment, is also common in patients with chronic T. cruzi infections, and its presence can be complicated by fecal impaction or sigmoid volvulus. Patients with advanced megacolon who have resections of the sigmoid colon and most of the rectum generally do well postoperatively.

Strategies for prevention of transfusion-associated Chagas' disease

Available epidemiological data indicate that Chagas' disease, a zoonosis caused by the flagellate protozoan parasite T cruzi, is a very important medical and social problem in Latin America. More than 60% of T cruzi-infected individuals have migrated to urban areas, in both endemic and nonendemic countries. Thus, with the implementation and maintenance of regular vector control programs in some countries, allogeneic blood transfusions have been the main mechanism for the continuation of this endemy. The risk of infection after transfusion of a unit of T cruzi-infected blood product depends mainly on the amount of blood transfused, parasite concentration in the infected transfused blood unit, and the recipient's immunological status. Current strategies to prevent transfusion-associated Chagas' disease include the identification of T cruzi-infected blood donors by predonation questionnaire, serological tests for T cruzi antibodies, and the treatment of the blood collected with gentian violet. Because T cruzi infection is lifelong, and most infected persons are asymptomatic, the identification of high-risk blood donors by a predonation questionnaire is relevant in nonendemic countries but this strategy seems to be of limited usefulness for donor deferral in endemic areas. Because T cruzi antigens are shared by other parasites, the serological diagnosis of T cruzi infection is complex yielding both false-positive and false-negative results. Although sensitive, the tests currently available for the serodiagnosis of T cruzi infection lack specificity and a more specific, confirmatory test is still needed for the routine confirmation of T cruzi chronic infection. In areas of high endemicity or where serological screening is not available, the risk of T cruzi transmission by blood transfusion may be reduced by the addition of gentian violet to the collected blood. The use of gentian violet, alone or combined with ascorbic acid and light, effectively inactivate T cruzi present in donor blood; however, the long-term toxicity of this agent for blood recipients is still an open issue. In conclusion, the prevention of TA-CD is based on various strategies that are not mutually exclusive. Blood donor education, identification of putatively infectious blood donors by questionnaire or serological screening tests, and methods of parasite inactivation may significantly reduce the transmission of T cruzi by allogeneic blood transfusions.

Potential use of WR6026 as prophylaxis against transfusion-transmitted American trypanosomiasis

Since transmission of Chagas' disease by the insect vector is under control in Brazil, transmission by blood transfusion is acquiring special relevance in areas where the disease is endemic and also in countries whose populations are free of infection but that are receiving immigrants from areas where the disease is endemic. Gentian violet, a phenylmethane dye, was the first agent used for the chemical prophylaxis of blood destined for transfusion. A concentration of 0.6 mmol of this dye per liter is effective at eliminating trypomastigotes from blood after 24 h of incubation at 4 degrees C. It is the only effective trypanosomicidal agent available. In the search of alternate compounds, we examined a number of synthetic compounds. They were screened for their activities against blood trypomastigotes of the Y, CL, and B229 strains of Trypanosoma cruzi by using two or more dilutions of each compound. We found that compound Q45, a 6-methoxy-8(diethylaminohexylamino)lepidine dihydrochloride, was highly effective at clearing parasites from infected blood. Doses of 65 and 130 micrograms of this compound eliminated trypomastigotes from blood experimentally contaminated with T. cruzi parasites. These results indicate that Q45 is remarkably active against circulating trypomastigotes. Further studies evaluating Q45 as a prophylactic agent for preventing the transmission of T. cruzi by blood transfusion are of interest.

Prevalence of anti-R-13 antibodies in human Trypanosoma cruzi infection

Infection with Trypanosoma cruzi develops in three phases: acute, indeterminate or asymptomatic, and chronic phase (with cardiac or digestive manifestations). Moreover, transmission may occur from infected mothers to newborn, the so-called congenital form. In the present study, humoral responses against T. cruzi total extract and against the 13 amino acid peptide named R-13 derived from the parasite ribosomal P protein, previously described as a possible marker of chronic Chagas heart disease, were determined in chagasic patients and in blood bank donors from endemic areas. While in sera from acute phase, only IgM anti-T.cruzi response was observed, both IgM and IgG anti-T. cruzi antibodies were detected in sera from congenitally infected newborns. The percentage of positive response in sera from blood bank donors was relatively high in endemic regions. Antibodies against the R-13 peptide were present in a large proportion of cardiac chagasic patients but were totally lacking in patients with digestive form of Chagas' disease. Furthermore, anti-R-13 positive responses were detected in congenitally infected newborns.

Current concepts on the transmission of bacteria and parasites by blood components

Several bacterial and parasite transfusion-transmitted diseases have been described in the medical literature. This review deals with the main bacterial (Syphilis, Lyme disease, Gram positive and Gram negative agents), parasite (Chagas disease, malaria, leishmaniasis, toxoplasmosis and babesiosis) and rickettsial diseases that are carried by blood products. Preventional aspects (e.g. storage, screening tests, use of leukocyte-depleted components), diagnosis, geographical distribution and the incidence of these transfusional hazards are also discussed.

Utility of recombinant flagellar calcium-binding protein for serodiagnosis of Trypanosoma cruzi infection

The protozoan Trypanosoma cruzi is the causative agent of Chagas' disease, a major public health problem in Latin America and of growing concern in the United States as the number of infected immigrants increases. There is currently no testing of U.S. blood products for T. cruzi infection, and the best tests available, although highly sensitive, are not of high enough specificity to be useful for widespread screening of the blood supply in this country. Among the parasite antigens detected by sera of infected humans and mice, those in the range of 24 to 26 kDa are particularly reactive. With an aim of developing a sensitive, specific, recombinant antigen-based serologic test for T. cruzi infection, we used two antibody reagents specific for these 24- to 26-kDa antigens to isolate cDNA clones from a T. cruzi expression library. One clone was found to encode a previously characterized T. cruzi antigen, a 24-kDa flagellar calcium-binding protein (FCaBP). Recombinant FCaBP was found to be a sensitive, specific reagent for distinguishing T. cruzi-infected individuals from uninfected persons, and it therefore could potentially be used for screening purposes, especially if combined with other recombinant T. cruzi antigens that have similarly high degrees of diagnostic sensitivity and specificity.

Absence of serological surrogate markers for Trypanosoma-cruzi-infected blood donors

Specific serological screening tests for Trypanosoma-cruzi-infected donors are not yet available and thus not routinely performed in North America. With the recent increase of Latin-American immigration to North America and Europe, there is a risk of transmission by blood products. In this study, we evaluated the possibility whether any of the serological screening tests currently recommended by the AABB could be used as a surrogate marker for this protozoarium. A group of 26,365 blood donors (male = 21,053 and female = 5,312) was analysed for the correlation of T. cruzi antibodies (TcAb) with other serological markers (HIV, HBsAg, ALT, HTLV-I/II, HCV, Anti-HBc, syphilis and unexpected hemoglobins other than A1, A2 and F). Association could be demonstrated only between syphilis and TcAb in the female group (p = 0.005), but the low number of donors found with this association (n = 4) renders the effect of this correlation very small. A higher prevalence of TcAb was found in older age groups, with even gender distribution (p < 0.05), however, donors aged more than 54 years also represent a minority of the donor pool (4.83%) and the detection of positive donors in this age group also has a minor preventive effect on transfusion-transmitted Chagas disease. We conclude that when infected blood donors must be detected, specific serological screening for TcAb is essential and that currently no surrogate marker can be considered for detecting T. cruzi-infected blood donors.

Diagnosis of American trypanosomiasis (Chagas' disease) by the new complement fixation test

A new immunodiagnostic method of complement fixation was used for serodiagnosis of American trypanosomiasis; 92% sensitivity and 99% specificity were obtained, for an overall accuracy of 97%. This test can be used in field studies, obviating the use of most laboratory equipment and imported reagents; places where economic limitations hinder the use of other immunodiagnostic procedures; and in association with other tests for confirmation of the diagnosis.