The ParaSight-F dipstick test as a routine diagnostic tool for malaria in Sri Lanka

Rapid Antigen Tests during the COVID-19 Era in Korea and Their Implementation as a Detection Tool for Other Infectious Diseases

Rapid antigen tests (RATs) are diagnostic tools developed to specifically detect a certain protein of infectious agents (viruses, bacteria, or parasites). RATs are easily accessible due to their rapidity and simplicity. During the COVID-19 pandemic, RATs have been widely used in detecting the presence of the specific SARS-CoV-2 antigen in respiratory samples from suspected individuals. Here, the authors review the application of RATs as detection tools for COVID-19, particularly in Korea, as well as for several other infectious diseases. To address these issues, we present general knowledge on the design of RATs that adopt the lateral flow immunoassay for the detection of the analyte (antigen). The authors then discuss the clinical utilization of the authorized RATs amidst the battle against the COVID-19 pandemic in Korea and their role in comparison with other detection methods. We also discuss the implementation of RATs for other, non-COVID-19 infectious diseases, the challenges that may arise during the application, the limitations of RATs as clinical detection tools, as well as the possible problem solving for those challenges to maximize the performance of RATs and avoiding any misinterpretation of the test result.

A diagnostic tool for malaria based on computer software

Nowadays, the gold standard method for malaria diagnosis is a staining of thick and thin blood film examined by expert laboratorists. It requires well-trained laboratorists, which is a time consuming task, and is un-automated protocol. For this study, Maladiag Software was developed to predict malaria infection in suspected malaria patients. The demographic data of patients, examination for malaria parasites, and complete blood count (CBC) profiles were analyzed. Binary logistic regression was used to create the equation for the malaria diagnosis. The diagnostic parameters of the equation were tested on 4,985 samples (703 infected and 4,282 control samples). The equation indicated 81.2% sensitivity and 80.3% specificity for predicting infection of malaria. The positive likelihood and negative likelihood ratio were 4.12 (95% CI = 4.01–4.23) and 0.23 (95% CI = 0.22–0.25), respectively. This parameter also had odds ratios (P value < 0.0001, OR = 17.6, 95% CI = 16.0–19.3). The equation can predict malaria infection after adjust for age, gender, nationality, monocyte (%), platelet count, neutrophil (%), lymphocyte (%), and the RBC count of patients. The diagnostic accuracy was 0.877 (Area under curve, AUC) (95% CI = 0.871–0.883). The system, when used in combination with other clinical and microscopy methods, might improve malaria diagnoses and enhance prompt treatment.

Rapid diagnostic tests for diagnosing uncomplicated non-falciparum or Plasmodium vivax malaria in endemic countries

BACKGROUND

In settings where both Plasmodium vivax and Plasmodium falciparum infection cause malaria, rapid diagnostic tests (RDTs) need to distinguish which species is causing the patients' symptoms, as different treatments are required. Older RDTs incorporated two test lines to distinguish malaria due to P. falciparum, from malaria due to any other Plasmodium species (non-falciparum). These RDTs can be classified according to which antibodies they use: Type 2 RDTs use HRP-2 (for P. falciparum) and aldolase (all species); Type 3 RDTs use HRP-2 (for P. falciparum) and pLDH (all species); Type 4 use pLDH (fromP. falciparum) and pLDH (all species).More recently, RDTs have been developed to distinguish P. vivax parasitaemia by utilizing a pLDH antibody specific to P. vivax.

OBJECTIVES

To assess the diagnostic accuracy of RDTs for detecting non-falciparum or P. vivax parasitaemia in people living in malaria-endemic areas who present to ambulatory healthcare facilities with symptoms suggestive of malaria, and to identify which types and brands of commercial test best detect non-falciparum and P. vivax malaria.

SEARCH METHODS

We undertook a comprehensive search of the following databases up to 31 December 2013: Cochrane Infectious Diseases Group Specialized Register; MEDLINE; EMBASE; MEDION; Science Citation Index; Web of Knowledge; African Index Medicus; LILACS; and IndMED.

SELECTION CRITERIA

Studies comparing RDTs with a reference standard (microscopy or polymerase chain reaction) in blood samples from a random or consecutive series of patients attending ambulatory health facilities with symptoms suggestive of malaria in non-falciparum endemic areas.

DATA COLLECTION AND ANALYSIS

For each study, two review authors independently extracted a standard set of data using a tailored data extraction form. We grouped comparisons by type of RDT (defined by the combinations of antibodies used), and combined in meta-analysis where appropriate. Average sensitivities and specificities are presented alongside 95% confidence intervals (95% CI).

MAIN RESULTS

We included 47 studies enrolling 22,862 participants. Patient characteristics, sampling methods and reference standard methods were poorly reported in most studies. RDTs detecting 'non-falciparum' parasitaemiaEleven studies evaluated Type 2 tests compared with microscopy, 25 evaluated Type 3 tests, and 11 evaluated Type 4 tests. In meta-analyses, average sensitivities and specificities were 78% (95% CI 73% to 82%) and 99% (95% CI 97% to 99%) for Type 2 tests, 78% (95% CI 69% to 84%) and 99% (95% CI 98% to 99%) for Type 3 tests, and 89% (95% CI 79% to 95%) and 98% (95% CI 97% to 99%) for Type 4 tests, respectively. Type 4 tests were more sensitive than both Type 2 (P = 0.01) and Type 3 tests (P = 0.03).Five studies compared Type 3 tests with PCR; in meta-analysis, the average sensitivity and specificity were 81% (95% CI 72% to 88%) and 99% (95% CI 97% to 99%) respectively. RDTs detecting P.vivax parasitaemiaEight studies compared pLDH tests to microscopy; the average sensitivity and specificity were 95% (95% CI 86% to 99%) and 99% (95% CI 99% to 100%), respectively.

AUTHORS' CONCLUSIONS

RDTs designed to detect P. vivax specifically, whether alone or as part of a mixed infection, appear to be more accurate than older tests designed to distinguish P. falciparum malaria from non-falciparum malaria. Compared to microscopy, these tests fail to detect around 5% ofP. vivax cases. This Cochrane Review, in combination with other published information about in vitro test performance and stability in the field, can assist policy-makers to choose between the available RDTs.

Fermentation and downstream process for high yield production of Plasmodium falciparum recombinant HRP II protein and its application in diagnosis

Malaria represents the world's greatest public health problem in terms of number of people affected, levels of morbidity and mortality in tropical and subtropical countries. Malaria parasites are members of the Apicomplexa, family of Plasmodiidae. Histidine-rich protein-II secreted by Plasmodium falciparum is known to be a compelling marker in malaria diagnosis and follow-up. In our present study, we have optimized the batch fermentation and downstream process for large scale production of recombinant P. falciparum HRP-II 62 kDa protein for diagnostic application. The culture broth was effectively induced with IPTG twice at different time intervals to sustain induction for a long period. Batch fermentation resulted in a wet weight of 61.34 g/L and dry cell biomass 12.81 g/L. With the improved downstream process, purified recombinant protein had a yield of 304.60 mg/L. The authenticity of the purified recombinant protein was confirmed via western blotting using indigenously developed HRP-II specific monoclonal antibodies and known positive human clinical sera samples. Further, the reactivity of recombinant HRP-II protein was validated using commercially available immuno chromatographic strips. Indirect ELISA using recombinant purified protein recognized the P. falciparum specific antibodies in suspected human sera samples. Our results clearly suggest that the recombinant HRP-II protein produced via batch fermentation has immense potential for routine diagnostic application.

Rapid diagnostic tests for diagnosing uncomplicated P. falciparum malaria in endemic countries

BACKGROUND

Rapid diagnostic tests (RDTs) for Plasmodium falciparum malaria use antibodies to detect either HRP-2 antigen or pLDH antigen, and can improve access to diagnostics in developing countries.

OBJECTIVES

To assess the diagnostic accuracy of RDTs for detecting P. falciparum parasitaemia in persons living in endemic areas who present to ambulatory healthcare facilities with symptoms suggestive of malaria by type and brand.

SEARCH STRATEGY

We undertook a comprehensive search of the following databases: Cochrane Infectious Diseases Group Specialized Register; MEDLINE; EMBASE; MEDION; Science Citation Index; Web of Knowledge; African Index Medicus; LILACS; IndMED; to January 14, 2010.

SELECTION CRITERIA

Studies comparing RDTs with a reference standard (microscopy or polymerase chain reaction) in blood samples from a random or consecutive series of patients attending ambulatory health facilities with symptoms suggestive of malaria in P. falciparum endemic areas.

DATA COLLECTION AND ANALYSIS

For each study, a standard set of data was extracted independently by two authors, using a tailored data extraction form. Comparisons were grouped hierarchically by target antigen, and type and brand of RDT, and combined in meta-analysis where appropriate.

MAIN RESULTS

We identified 74 unique studies as eligible for this review and categorized them according to the antigens they detected. Types 1 to 3 include HRP-2 (from P. falciparum) either by itself or with other antigens. Types 4 and 5 included pLDH (from P. falciparum) either by itself or with other antigens. In comparisons with microscopy, we identified 71 evaluations of Type 1 tests, eight evaluations of Type 2 tests and five evaluations of Type 3 tests. In meta-analyses, average sensitivities and specificities (95% CI) were 94.8% (93.1% to 96.1%) and 95.2% (93.2% to 96.7%) for Type 1 tests, 96.0% (94.0% to 97.3%) and 95.3% (87.3% to 98.3%) for Type 2 tests, and 99.5% (71.0% to 100.0%) and 90.6% (80.5% to 95.7%) for Type 3 tests, respectively. Overall for HRP-2, the meta-analytical average sensitivity and specificity (95% CI) were 95.0% (93.5% to 96.2%) and 95.2% (93.4% to 99.4%), respectively. For pLDH antibody-based RDTs verified with microscopy, we identified 17 evaluations of Type 4 RDTs and three evaluations of Type 5 RDTs. In meta-analyses, average sensitivity for Type 4 tests was 91.5% (84.7% to 95.3%) and average specificity was 98.7% (96.9% to 99.5%). For Type 5 tests, average sensitivity was 98.4% (95.1% to 99.5%) and average specificity was 97.5% (93.5% to 99.1%). Overall for pLDH, the meta-analytical average sensitivity and specificity (95% CI) were 93.2% (88.0% to 96.2%) and 98.5% (96.7% to 99.4%), respectively. For both categories of test, there was substantial heterogeneity in study results. Quality of the microscopy reference standard could only be assessed in 40% of studies due to inadequate reporting, but results did not seem to be influenced by the reporting quality.Overall, HRP-2 antibody-based tests (such as the Type 1 tests) tended to be more sensitive and were significantly less specific than pLDH-based tests (such as the Type 4 tests). If the point estimates for Type 1 and Type 4 tests are applied to a hypothetical cohort of 1000 patients where 30% of those presenting with symptoms have P. falciparum, Type 1 tests will miss 16 cases, and Type 4 tests will miss 26 cases. The number of people wrongly diagnosed with P. falciparum would be 34 with Type 1 tests, and nine with Type 4 tests.

AUTHORS' CONCLUSIONS

The sensitivity and specificity of all RDTs is such that they can replace or extend the access of diagnostic services for uncomplicated P. falciparum malaria. HRP-2 antibody types may be more sensitive but are less specific than pLDH antibody-based tests, but the differences are small. The HRP-2 antigen persists even after effective treatment and so is not useful for detecting treatment failures. 

Development of diagnostic reagents: raising antibodies against synthetic peptides of PfHRP-2 and LDH using microsphere delivery

Malaria causes significant morbidity and mortality worldwide, including countries with mainly imported malaria. In developing nations, scarce resources lead to inadequate diagnostic procedures. Microscopy of Giemsa-stained thick and thin films remains the current gold standard for diagnosis. Although it has good sensitivity and allows species identification, it is time consuming, requires microscopical expertise and maintenance of equipment. Antigen tests are promising tools for the diagnosis of malaria. Two such antigens are Plasmodium falciparum histidine rich protein (pfHRP-2) and lactate dehydrogenase (LDH). The present study was aimed to develop indigenous, rapid and sensitive immunodiagnostic method based on detection of PfHRP-2 and LDH antigen in the blood. Unique peptide sequences of PfHRP-2 (two regions) and LDH (three regions) antigen were synthesized by solid phase technique and purified to homogeneity. The antibodies raised against these sequences were raised in mice as well as rabbit using microspheres (PLGA) to generate high titre and affinity antibodies. The peptide-specific peak titres varied from 25,000 to 50,000 and affinity of the antibodies produced was found to be in order of 0.73-5.3 nM. The antibodies generated using microspheres were able to detect the PfHRP-2 and LDH antigen in the culture supernatant and parasitized RBC lysate of P. falciparum respectively by sandwich ELISA up to 0.002% parasitaemia level. The assay allowed the detection of parasite infections of 0.08-2.68% parasitaemia with a sensitivity of 100% in the whole blood of P. falciparum positive patients. No cross-reactivity was observed with P. vivax infected patients.

NEUROLOGICAL INFECTIONS IN THE RETURNING INTERNATIONAL TRAVELER

Clinicians may encounter international travelers returning with exotic infections, emerging infectious diseases, or resurgent old-world infections. Many of these infectious diseases can affect the nervous system directly or indirectly. The contemporary neurologist should therefore be cognizant of the clinical manifestations, potential complications, and appropriate management of common travel-related infections. This chapter focuses on five important infections that affect the central nervous system and that may be encountered in returning travelers: Japanese encephalitis, malaria, rabies, dengue, and neurocysticercosis. The clinical manifestations, suggested evaluation, and treatment are discussed for each infection.

Parasitic central nervous system infections in immunocompromised hosts: malaria, microsporidiosis, leishmaniasis, and African trypanosomiasis

Immunosuppression associated with HIV infection or following transplantation increases susceptibility to central nervous system (CNS) infections. Because of increasing international travel, parasites that were previously limited to tropical regions pose an increasing infectious threat to populations at risk for acquiring opportunistic infection, especially people with HIV infection or individuals who have received a solid organ or bone marrow transplant. Although long-term immunosuppression caused by medications such as prednisone likely also increases the risk for acquiring infection and for developing CNS manifestations, little published information is available to support this hypothesis. In an earlier article published in Clinical Infectious Diseases, we described the neurologic manifestations of some of the more common parasitic CNS infections. This review will discuss the presentation, diagnosis, and treatment of the following additional parasitic CNS infections: malaria, microsporidiosis, leishmaniasis, and African trypanosomiasis.

The changing dynamics of Plasmodium vivax and P. falciparum in central India: trends over a 27-year period (1975--2002)

The changing epidemiology of malaria since 1975 was studied in a tribal forested belt of central India, Chhattisgarh state, which is the second most highly malarious state in India. Chhattisgarh, which accounts for 2% of the total population of the country, contributed >16% of the total malaria cases, 23% of Plasmodium falciparum, and 7% of deaths due to malaria in the country. Retrospective analysis further revealed that, in 1975--76, P. vivax was the predominant species (58%); however, since 1979, P. falciparum showed a steady upward trend (50%), and in 2002. P. vivax reduced to 28%. Between 1986 and 2000, P. falciparum cases reported by the National Anti Malaria Programme have increased 500%, and the number of deaths also showed a similar alarming increase. From 2000 to 2002, though the number of malaria infections and number of deaths declined sharply as a result of intensive intervention measures (30% and 95%, respectively), which included new drugs like Sulfadoxine Pyrimethamine and Arteether under Enhanced Malaria Control Programme, the proportion of P. falciparum has held steady without any decline. Moreover, along with Anopheles fluviatilis, the traditional vector in the forest, An. culicifacies has also established itself in the forest. The comeback of malaria and establishment of new vectors was largely due to the deterioration of health services along with emergence of resistance in P. falciparum to Chloroquine and in An. culicifacies to DDT. Therefore, a more diversified malaria control program might be needed for sustainable malaria control.

Neurologic aspects of infections in international travelers

BACKGROUND

As international travel for business and pleasure becomes part of contemporary lifestyle, the clinician today is confronted with an increasing number of travelers returning ill with unfamiliar syndromes. The physician will encounter a myriad of patients with exotic infections, emerging infectious diseases, or resurgent Old-World infections.

REVIEW SUMMARY

This review article will discuss salient points of important infectious diseases associated with overseas travel, provide a syndromic approach to the traveler who returns with neurologic manifestations, and list resources for additional diagnostic, therapeutic, and preventive information.

CONCLUSIONS

As many of infections acquired in other countries can directly or indirectly affect the nervous system, the care of the ill traveler often falls into the hands of neurologists. The contemporary neurologist should therefore be knowledgeable of the clinical manifestations, potential complications, and appropriate management of region-specific infections.

How useful is PCR in the diagnosis of malaria?

Polymerase chain reaction (PCR) assays are the most sensitive and specific method to detect malaria parasites, and have acknowledged value in research settings. However, the time lag between sample collection, transportation and processing, and dissemination of results back to the physician limits the usefulness of PCR in routine clinical practice. Furthermore, in most areas with malaria transmission, factors such as limited financial resources, persistent subclinical parasitaemia, inadequate laboratory infrastructures in the poorer, remote rural areas preclude PCR as a diagnostic method. Even in affluent, non-endemic countries, PCR is not a suitable method for routine use. Nonetheless, PCR could be clinically useful in selected situations.

Malaria: a rising incidence in the United States

Malaria is frequently a deadly disease, particularly in tropical countries of the world where this protozoan infection is endemic. While physicians in tropical countries are familiar with the presentation, those who do not practice in endemic regions of the world may neglect to add tropical diseases to their differential diagnosis of fever. Epidemiologic data from the CDC show the number of cases of malaria being diagnosed in the United States in the last decade has risen sharply. With international travel continuing to rise, there is strong reason to consider malaria as a source of fever.

Field and laboratory comparative evaluation of ten rapid malaria diagnostic tests

The paper reports on a comparative evaluation of 10 rapid malaria tests available in South Africa in 1998: AccuCheck (AC, developmental), Cape Biotech (CB), ICT Malaria Pf (ICT1) and Pf/Pv (ICT2), Kat Medical (KAT), MakroMal (MM), OptiMAL (OP), ParaSight-F (PS), Quorum (Q), Determine-Malaria (DM). In a laboratory study, designed to test absolute detection limits, Plasmodium falciparum-infected blood was diluted with uninfected blood to known parasite concentrations ranging from 500 to 0.1 parasites per microlitre (P/microL). The 50% detection limits were: ICT1, 3.28; ICT2, 4.86; KAT, 6.36; MM, 9.37; CB, 11.42; DM, 12.40; Q, 16.98; PS, 20; AC, 31.15 and OP, 91.16 P/microL. A field study was carried out to test post-treatment specificity. Blood samples from malaria patients were tested with all products (except AC and DM) on the day of treatment and 3 and 7 days thereafter, against a gold standard of microscopy and polymerase chain reaction (PCR). OP and PS produced fewer false-positive results on day 7 (18 and 19%, respectively) than the other rapid tests (38-56%). However, microscopy, PCR, OP and PS disagreed largely as to which individuals remained positive. The tests were further compared with regard to general specificity, particularly cross-reactivity with rheumatoid factor, speed, simplicity, their ability to detect other species, storage requirements and general presentation.

Rapid diagnostic tests for malaria parasites

Malaria presents a diagnostic challenge to laboratories in most countries. Endemic malaria, population movements, and travelers all contribute to presenting the laboratory with diagnostic problems for which it may have little expertise available. Drug resistance and genetic variation has altered many accepted morphological appearances of malaria species, and new technology has given an opportunity to review available procedures. Concurrently the World Health Organization has opened a dialogue with scientists, clinicians, and manufacturers on the realistic possibilities for developing accurate, sensitive, and cost-effective rapid diagnostic tests for malaria, capable of detecting 100 parasites/microl from all species and with a semiquantitative measurement for monitoring successful drug treatment. New technology has to be compared with an accepted "gold standard" that makes comparisons of sensitivity and specificity between different methods. The majority of malaria is found in countries where cost-effectiveness is an important factor and ease of performance and training is a major consideration. Most new technology for malaria diagnosis incorporates immunochromatographic capture procedures, with conjugated monoclonal antibodies providing the indicator of infection. Preferred targeted antigens are those which are abundant in all asexual and sexual stages of the parasite and are currently centered on detection of HRP-2 from Plasmodium falciparum and parasite-specific lactate dehydrogenase or Plasmodium aldolase from the parasite glycolytic pathway found in all species. Clinical studies allow effective comparisons between different formats, and the reality of nonmicroscopic diagnoses of malaria is considered.

Persistent ICT malaria P.f/P.v panmalarial and HRP2 antigen reactivity after treatment of Plasmodium falciparum malaria is associated with gametocytemia and results in false-positive diagnoses of Plasmodium vivax in convalescence

A problem with rapid Plasmodium falciparum-specific antigen histidine-rich protein 2 (HRP2) detection tests for malaria is the persistence of antigen in blood after the disappearance of asexual-stage parasitemia and clinical symptoms, resulting in false-positive (FP) test results following treatment. The ICT P.f/P.v immunochromatographic test detects both HRP2 and a panmalarial antigen (PMA) found in both P. falciparum and Plasmodium vivax. To examine posttreatment antigen persistence with this test and whether persistent sexual-stage forms (gametocytes) are a cause of FP tests after treatment, we compared serial antigen test results with microscopy results from patients symptomatic with P. falciparum malaria in Indonesia for 28 days following treatment with chloroquine (CQ; n = 66), sulfadoxine-pyrimethamine (SP; n = 36), and artesunate plus sulfadoxine-pyrimethamine (ART + SP; n = 15). Persistent FP antigenemia following SP treatment occurred in 29% (HRP2) and 42% (PMA) of the patients on day 7 and in 10% (HRP2) and 23% (PMA) on day 14. The high rates of persistent HRP2 and PMA antigenemia following CQ and SP treatment were strongly associated with the presence of gametocytemia, with the proportion with gametocytes on day 7 posttreatment being significantly greater in those with FP results than in those with true-negative PMA and HRP2 results. Gametocyte frequency on day 14 post-SP treatment was also greater in those with FP PMA results. Following SP treatment, PMA persisted longer than HRP2, giving an FP diagnosis of P. vivax in up to 16% of patients on day 14, with all FP P. vivax diagnoses having gametocytemia. In contrast, PMA was rapidly cleared following ART + SP treatment in association with rapid clearance of gametocytemia. Gametocytes appear to be an important cause of persistent posttreatment panmalarial antigenemia in areas of endemicity and may also contribute in part to persistent HRP2 antigenemia following treatment.

Comparison of a rapid field immunochromatographic test to expert microscopy for the detection of Plasmodium falciparum asexual parasitemia in Thailand

We assessed a rapid, Plasmodium falciparum histidine rich protein 2 (PfHRP2)-based immunochromatographic test (ICT Malaria Pf Test), for detection of asexual P. falciparum parasitemia in 551 subjects in three groups: (1) symptomatic patients self-referring for diagnosis, (2) villagers in a screening survey, and (3) patients recently treated for P. falciparum malaria. Expert light microscopy was the reference standard. ICT test performance was similar for diagnostic and screening modes. Four findings emerged: (1) test sensitivity correlated directly with parasite density, (2) test band intensity correlated directly with parasite density, (3) persistent test positivity after parasite clearance precludes its use for monitoring early therapeutic responses, and (4) a false negative test at 18,000 parasites/microl is unexplained. We conclude that a strong positive ICT test is highly predictive of falciparum asexual parasitemia for the diagnosis of new cases of falciparum malaria in Thailand, but a negative test result is inadequate to exclude parasitemia < 300/microl, and in some instances, even a higher parasitemia.

Diagnosis of malaria: a review of alternatives to conventional microscopy

Malaria causes significant morbidity and mortality worldwide, including countries with mainly imported malaria. In developing nations, scarce resources lead to inadequate diagnostic procedures. In affluent countries, poor familiarity with malaria may cause clinical and laboratory misdiagnosis. Microscopy of Giemsa-stained thick and thin films remains the current standard for diagnosis. Although it has good sensitivity and allows species identification and parasite counts, it is time consuming, requires microscopical expertise and maintenance of equipment. Microscopy with fluorescent stains (QBC), dipstick antigen detection of HRP2 and pLDH (Parasight-F, ICT Malaria Pf, OptiMAL), polymerase chain reaction assays and some automated blood cell analysers offer new approaches and are reviewed here, with emphasis on clinical relevance and their potential to complement conventional microscopy, especially in countries with imported malaria.

Field evaluation of the ICT malaria P.f/P.v immunochromatographic test for detection of Plasmodium falciparum and Plasmodium vivax in patients with a presumptive clinical diagnosis of malaria in eastern Indonesia

In areas such as eastern Indonesia where both Plasmodium falciparum and Plasmodium vivax occur, rapid antigen detection tests for malaria need to be able to detect both species. We evaluated the new combined P. falciparum-P. vivax immunochromatographic test (ICT Malaria P.f/P.v.) in Radamata Primary Health Centre, Sumba, Indonesia, from February to May 1998 with 560 symptomatic adults and children with a presumptive clinical diagnosis of malaria. Blinded microscopy was used as the "gold standard," with all discordant and 20% of concordant results cross-checked blindly. Only 50% of those with a presumptive clinical diagnosis of malaria were parasitemic. The ICT Malaria P.f/P.v immunochromatographic test was sensitive (95. 5%) and specific (89.8%) for the diagnosis of falciparum malaria, with a positive predictive value (PPV) and a negative predictive value (NPV) of 88.1 and 96.2%, respectively. HRP2 and panmalarial antigen line intensities were associated with parasitemia density for both species. Although the specificity and NPV for the diagnosis of vivax malaria were 94.8 and 98.2%, respectively, the overall sensitivity (75%) and PPV (50%) for the diagnosis of vivax malaria were less than the desirable levels. The sensitivity for the diagnosis of P. vivax malaria was 96% with parasitemias of >500/microl but only 29% with parasitemias of <500/microl. Nevertheless, compared with the test with HRP2 alone, use of the combined antigen detection test would reduce the rate of undertreatment from 14.7 to 3.6% for microscopy-positive patients, and this would be at the expense of only a modest increase in the rate of overtreatment of microscopy-negative patients from 7.1 to 15. 4%. Cost remains a major obstacle to widespread use in areas of endemicity.

MalaQuick versus ParaSight F as a diagnostic aid in travellers' malaria

In this study we assessed whether travellers can perform malaria rapid tests, following the provided information leaflet, and correctly interpret performed and pre-prepared test strips. Two Plasmodium falciparum testing systems, namely MalaQuick (ICT) and ParaSight F were used. Test performance and test interpretation of pre-prepared tests were compared. There was no significant difference in test performance between the 2 tests. Interpretation of prepared test strips in both test systems was very reliable in blood parasite densities between 0.1% and 2%, but major problems were encountered at low parasitaemia (< 0.1% blood parasites) and also in ParaSight F test strips showing high parasitaemia (> 2% blood parasites). Low parasitaemia ParaSight F test strips were correctly interpreted by 52.1% compared with 10.8% correct interpretations with MalaQuick (P < 0.0001). Correct interpretation of highly positive (> 2% blood parasites) pre-prepared test strips was higher with MalaQuick (96.8%) than with ParaSight F (33.8%), P < 0.0001. Both tests were associated with high levels of false-negative interpretations which render them unsuitable as self-diagnostic kits. Efforts must be made to assist lay individuals in test performance by technical test improvement, by equiping the test strips with an additional reading aid for interpretation, and by providing instruction by a skilled person.

Detection and species determination of malaria parasites by PCR: comparison with microscopy and with ParaSight-F and ICT malaria Pf tests in a clinical environment

A rapid procedure for the diagnosis of malaria infections directly from dried blood spots by PCR amplification was evaluated with samples from 52 patients. Plasmodium infections were identified with a genus-specific primer set, and species differentiation between Plasmodium falciparum and Plasmodium vivax was analyzed by multiplex PCR. The PCR test with any of the three primer sets was able to detect as few as four parasites per microliter by gel electrophoresis or by nonisotopic paper hybridization chromatography. The diagnoses obtained by PCR correlated closely with those obtained by Giemsa staining except for two samples observed to have mixed P. falciparum-P. vivax infections. These were initially missed by microscopic analysis. In comparison with antigen-capture assays for P. falciparum, the PCR assays were able to detect three infections that were missed by the ParaSight-F test. The PCR test was negative for nine ParaSight-F-positive samples and one ICT Malaria Pf-positive sample, and these were confirmed to be false-positive results. The PCR thus gave no false-negative or false-positive results. Patients undergoing antimalarial therapy were also monitored by the PCR assay. Four of seven patients who were PCR positive for P. vivax at the time of discharge were later readmitted to the hospital with a recurrence of P. vivax infection. We would like to propose that PCR is a sensitive and easy method that can serve as a useful addition to microscopy for the diagnosis and the clinical monitoring of treatment of malaria.

Application of the ParaSight-F dipstick test for malaria diagnosis in a district control program

A rapid test for the diagnosis of Plasmodium falciparum infections based on the detection of histidine-rich-protein II, the ParaSight-F test, was evaluated after introduction in a district malaria control program in Uganda. Suspected treatment failures, pregnant women and infants with clinical malaria and general fever cases were tested at health facilities in malaria hypo-, meso- and holoendemic areas. A total of 1326 tests were carried out by health unit staff, cross read by experienced laboratory staff and results compared with thick film microscopy as the standard. Rater agreement in reading the dipstick result between health unit staff and laboratory staff was high, kappa index 0.94 (0.88-0.99). Sensitivity was 99.6% (99.0-100) for parasite densities above 500/microl, 98.6% (97.7-99.6) for densities above 50/microl and 22.2% (8.6-42.3) for densities below 10/microl. With the applied testing strategies no differences were found between endemicity levels or patient categories. Specificity was 86.2% (83.3-88.8) overall, but significantly higher in general fever cases (92.7%) compared to the other patient groups (84.3%, P=0.009). At the given prevalences positive predictive values (ppv) were above 80% and negative predictive values (npv) above 90% in all cases except in pregnant women (ppv: 77.8%). We conclude that in certain situations this test is an alternative to microscopy to improve diagnostic facilities for case management in malaria control programs in endemic African countries.