Accuracy of routine laboratory diagnosis of malaria in the United Kingdom

AIMS

To study the accuracy of routine laboratory diagnosis of malaria with the aim of improving accuracy in diagnosis in the future.

METHODS

A comparative study was made of all blood films submitted to two laboratories in London providing a slide-diagnostic service for malaria.

RESULTS

There were 17 Plasmodium ovale infections, and of these only five (29.4%) were correctly diagnosed by the submitting laboratory; whereas of 210 other single species infections, 162 (77.1%) were correctly diagnosed (chi 2 = 18.4, p < 0.0001). There were six patients with mixed infections; only one (16.7%) was correctly diagnosed, whereas of 227 single species infections, 167 (73.6%) were correctly diagnosed (p = 0.007, using Fisher's exact test). There was no significant association between the presence of technical faults or numerous platelets and incorrect diagnosis.

CONCLUSIONS

Plasmodium ovale and mixed infections were diagnosed incorrectly significantly more often than other species. The presence of technical faults or numerous platelets had no significant effect on whether or not submitting laboratories correctly diagnosed malaria.

Plasmodium falciparum and P. vivax: factors affecting sensitivity and specificity of PCR-based diagnosis of malaria

We have previously reported on development of a simple PCR-based method to detect Plasmodium falciparum in which patient blood samples are lysed and then filtered onto paper. The present studies, conducted in Thailand, were designed to identify factors contributing to differences between results from microscopy and PCR. To analyze microscope-positive, PCR-negative results, we demonstrated that using the lysis/filtration sample preparation method, target DNA degradation is not a significant factor. Similarly, we showed that sensitivity of PCR among patient samples did not differ using the lysis centrifugation method or organically extracted DNA. We further demonstrated that 7/13 samples which were negative by PCR for P. falciparum were positive by PCR when P. vivax-specific primers were used. Microscope-negative, P. falciparum PCR-positive samples were analyzed in two ways: the true rate of false-positivity for PCR (2%) was established by analyzing 498 samples from patients living in areas without transmission. We further showed that when microscope-negative, PCR-positive samples were amplified using an independent P. falciparum-specific PCR target sequence, 42/47 were PCR-positive. We conclude that the accuracy and reduced limit of detection of microscopy are major confounders when comparing this method to PCR.

[Evaluation of the QBC system for the diagnosis of malaria]

There are currently two methods for the direct diagnosis of malaria: the thin blood smear and the thick blood smear. A third cytological method, called the QBC malaria test (QBC), has been developed. The first studies comparing the three methods report conflicting results. Thus, there is a need for a study of the three methods in parallel and to evaluate the logistic factors which have not been previously assessed. In an analysis of imported malaria, one worker performed the three tests, blind, in parallel with each of 813 samples. The following values were determined: intrinsic validity; predictive values, species diagnostic power; and logistic factors. QBC had the following characteristics: sensitivity = 93.8%; specificity = 99.8%; positive predictive value = 99.3%; negative predictive value = 98.3%; correct species diagnosis = 91.3%; time required for test = 3.7 +/- 0.1 min; storage of tubes at +4 degrees C in the dark = 50 days; cost per test = 27.3 FF (as compared to 24 FF for thin smear and 17.3 FF for thick smear). Although unsuitable for use in countries where malaria is endemic, other than for some specialised situations, QBC is valuable for the diagnosis of imported malaria. In view of our findings, we suggest the following approach to diagnosis: use of the QBC and thin smear tests in parallel first reading the QBC result, as positivity contributes to reading the thin smear result for confirmation of species diagnosis and assessment of parasitaemia.

Evaluation of different methods for Plasmodia detection, in well defined population groups in an endemic area of Brazil (1)

In Brazil, more than 500,000 new cases of malaria were notified in 1992. Plasmodium falciparum and P. vivax are the responsible species for 99.3% of the cases. For adequate treatment, precoce diagnosis is necessary. In this work, we present the results of the traditional Plasmodia detection method, thick blood film (TBF), and the results of alternative methods: Immunofluorescence assay (IFA) with polyclonal antibody and Quantitative Buffy Coat method (QBC) in a well defined population groups. The analysis were done in relation to the presence or absence of malaria clinical symptoms. Also different classes of immunoglobulins anti-P.falciparum were quantified for the global analysis of the results, mainly in the discrepant results. We concluded that alternative methods are more sensitive than TBF and that the association of epidemiological, clinical and laboratory findings is necessary to define the presence of malaria.

Imported malaria in the 1990s. A report of 59 cases from Houston, Tex

OBJECTIVE

To determine the frequency, the clinical features, and the response to therapy of imported malaria that was diagnosed in the 1990s in a major North American city.

METHOD

A retrospective case series from Houston, Tex, of 59 cases of imported malaria presenting between January 1990 and April 1993.

RESULTS

Malaria was diagnosed in 59 patients, consisting of 12 cases among patients who had acquired the infection while they were living in endemic areas prior to immigration to the United States, 32 cases among US residents who were originally from endemic areas, and 15 cases among patients originally from North America or Europe. Only 12 patients had received malarial prophylaxis: eight with chloroquine, one with chloroquine and chloroguanide (proguanil), two with chloroquine and primaquine, and one with mefloquine taken intermittently. Eight presented with Plasmodium falciparum infection after receiving chloroquine, and one, after receiving chloroquine and chloroguanide. Two presented with malaria caused by Plasmodium vivax despite receiving chloroquine and primaquine as prophylaxis. In 25 cases, malaria was not considered as an initial diagnosis. Five patients presented with severe disease (three with severe hemolysis, two each with cerebral malaria and renal failure, and one with adult respiratory distress syndrome). Four of the five had initially received a misdiagnosis. Two patients died despite treatment with intravenous quinidine and exchange transfusions. Two patients with P vivax infection had multiple relapses despite courses of chloroquine and primaquine. Six patients were pregnant (including one with a fatal case), one congenital infection was identified. Six patients had not traveled outside of the United States in over 1 year.

CONCLUSION

Imported malaria occurs frequently and usually results from the failure to use appropriate prophylaxis. Delayed diagnosis and misdiagnosis are common. Severe disease and fatal cases continue to be seen despite aggressive treatment. Drug resistance has continued to spread and now occurs with P vivax as well as P falciparum.

Comparative test of DNA probes for detection of Plasmodium vivax circumsporozoite protein polymorphs VK 247 and VK 210

Oligonucleotide probes specific to the characteristic repeat sequences of two alleles of the circumsporozoite protein gene of Plasmodium vivax (VK 210 and VK 247) were selected, synthesized, and tested on matched blood and sporozoite DNA amplified by polymerase chain reaction from 182 cases naturally acquired in Thailand. Probe results were compared to those of circumsporozoite phenotype-specific ELISAs used to evaluate sporozoites from the same cases. There was a 96% agreement between probe results for blood and for sporozoites. Although there was also a nearly complete agreement between probe and ELISA results for cases producing only VK 210 or VK 247 sporozoites, the probes detected 45% more mixed infections than did the ELISAs when used to test specimens from western and southern Thailand; there was no discrepancy when mixed cases from Cambodia were tested. Examination of Southern blots from ambiguous mixed cases demonstrated the presence of both genes, suggesting suppression of VK 247 in some mixed cases to numbers below those detectable by the ELISA.

Use of the polymerase chain reaction to directly detect malaria parasites in blood samples from the Venezuelan Amazon

We have examined the reproducibility, sensitivity, and specificity of detecting Plasmodium falciparum using the polymerase chain reaction (PCR) and the species-specific probe pPF14 under field conditions in the Venezuelan Amazon. Up to eight samples were field collected from each of 48 consenting Amerindians presenting with symptoms of malaria. Sample processing and analysis was performed at the Centro Amazonico para la Investigacion y Control de Enfermedades Tropicales Simon Bolivar. A total of 229 samples from 48 patients were analyzed by PCR methods using four different P. falciparum-specific probes. One P. vivax-specific probe and by conventional microscopy. Samples in which results from PCR and microscopy differed were reanalyzed at a higher sensitivity by microscopy. Results suggest that microscopy-negative, PCR-positive samples are true positives, and that microscopy-positive and PCR-negative samples are true negatives. The sensitivity of the DNA probe/PCR method was 78% and its specificity was 97%. The positive predictive value of the PCR method was 88%, and the negative predictive value was 95%. Through the analysis of multiple blood samples from each individual, the DNA probe/PCR methodology was found to have an inherent reproducibility that was highly statistically significant.

Symptomatic identification of malaria in the home and in the primary health care clinic

In endemic areas in the absence of microscopy, the WHO case definition of malaria is the presence or a history of fever without other obvious cause. Yet there is little empirical evidence on the accuracy, predictability and reliability of clinical signs and symptoms for diagnosing malaria within different endemic settings. Studying patients in endemic communities in the Philippines, we found that fever alone did not discriminate well for malaria. In contrast, a sequential occurrence of fever, chills and/or sweating, or a combination of all three symptoms was a good general predictor of the disease. However, the place of diagnosis and observation (home or clinic), age, and season affected the positive predictive values obtained. Specificities and positive predictive values were greatest (over 80%) for those at most risk--children under 9 years of age in highly endemic communities--and were most reliable when the diagnosis was made at home. Predictive values were also greatest during the season when childhood acute lower respiratory infections in the study area increase. The good predictability of clinical signs and symptoms for high-risk groups suggests that simple protocols can be developed for the management of malaria in endemic areas of the Philippines.

Detection of Plasmodium vivax by polymerase chain reaction in a field study

Detection and typing of Plasmodium vivax by the polymerase chain reaction (PCR) was evaluated in a prospective blinded comparative field study in Thailand. PCR amplification of the circumsporozoite (CS) gene was compared with microscopy for the detection of P. vivax in blood samples from 174 Thai Rangers and 50 malaria-free Bangkok residents. For PCR analysis, filter paper specimens collected by finger prick were randomly processed and blindly interpreted for the presence of the CS gene of P. vivax. The VK210 and VK247 CS variants of P. vivax were detected by specific fluorescein or radiolabeled oligoprobes. Autoradiography with 32P-labeled probes and enhanced chemoluminescent detection with fluorescein-labeled probes identified 91% and 96%, respectively, of 119 microscopically confirmed infections; both systems detected < 100 parasites/microL. Compared with microscopy, the specificity of PCR and radiometric or enhanced chemoluminescent detection was 96% and 90%, respectively. The ease of collection and transport of filter-paper specimens combined with the sensitive and specific detection of allelic genes of P. vivax by PCR suggests that this method may prove to be a valuable tool for epidemiologic and heterogeneity studies of P. vivax.

The diagnosis and treatment of malaria in Australia

The number of reported malaria cases is increasing each year with several deaths reported recently. This article reviews the types of malarias, including their incidence, prevention, presentation and the standard treatment protocols.

Evaluation of methods for the laboratory diagnosis of malaria in Guyana

When 297 blood samples taken from patients attending a fever clinic in Georgetown Public Hospital were examined microscopically, after thick and thin blood films had been stained with Giemsa, one hundred and forty-two (47.8%) were microscopically positive for malaria. After processing the patient's serum, samples by the Indirect Fluorescent Antibody (IFA) technique, specific IgG and IgM antibodies were detected in 239 (81.3%) and 179 (60.1%), respectively, of the sera. Based on the microscopical findings, the IFAT gave positive predictive and negative values of 54.4% and 81.8% (IgG), and 57.5% and 67.8% (IgM), suggesting that the IgM would be more useful than the IgG in the diagnosis of current malaria. An odds ratio analysis showed that the presence of symptoms, IgG or IgM antibodies, as well as visits to endemic regions, could be good indicators of current malaria. Age and occupation were not. The microscopical method will continue to be the gold standard-the best available criterion for the validation of our tests-for diagnosis of acute malaria.

Efficacy and limitations of QBC acridine orange staining as a routine diagnostic technique for malaria in developing countries

The recently developed QBC technique has been reported to be rapid, sensitive and specific for the detection of malaria infection. We evaluated this technique in comparison with thin and thick Giemsa stained blood films for the diagnosis of malaria in acute fever and PUO cases. The technique was slightly more sensitive than thin blood film but equal to thick blood film examination. Identification of species of malaria posed some difficulties. Due to its high cost and requirement for a fluorescent microscope this technique, in spite of its speed and sensitivity, may not have the potential to be a substitute for the conventional blood film examination for the diagnosis of malaria, especially in developing countries.

Centers for Disease Control and Prevention (CDC). Malaria among U.S. military personnel returning from Somalia, 1993

U.S. military personnel were first deployed to Somalia in late December 1992 as part of Operation Restore Hope. From the time of deployment through April 1993, malaria was diagnosed in 48 personnel who had onset of illness while in Somalia. In addition, through late June, malaria was diagnosed in 83 military personnel following their return from Somalia. This substantial number of cases has reinforced concerns regarding malaria prophylaxis, the estimated risk for infection, and the need for prompt recognition and treatment of malaria in military personnel. This report summarizes the occurrence of malaria in returning personnel and underscores for health-care providers the importance of considering malaria in the diagnostic evaluation of military personnel returning from Somalia and in other persons who have traveled to malarious areas.

[The diagnosis of malaria by the thick film and the QBC: a comparative study of both technics]

BACKGROUND

The diagnosis of paludism is important because of the severity of the clinical picture caused by Plasmodium falciparum, the increasing number of travellers to endemic zones and the emigration from these zones. A comparative study of the QBC techniques (staining with acridin orange and observation with ultraviolet light) and the thick film with Giemsa staining was carried out.

METHODS

The QBC and thick film were performed parallelly for 17 months in a total of 623 samples pertaining to subjects from endemic zones of paludism (emigrants, immigrants and travellers).

RESULTS

Of the 623 samples studied 49 were positive for paludism by both techniques. Ten were positive with only the thick film and six were positive only with QBC. The sensitivity of QBC versus thick film was 83% and specificity 98.9%. The time used to determine diagnosis with the QBC technique ranged from 6 to 12 minutes from withdrawal of the sample, while with the thick film the time spent was more than 2 hours. The cases positive by thick film and negative with QBC corresponded to patients with very low parasitation. The intensity of parasitation was difficult to determine quantitatively by QBC.

CONCLUSIONS

Although the QBC technique has the advantage of speed it is inexact with respect to the quantification of parasitemia. Moreover, it is less sensitive than the thick film in patient with very low parasitations and cannot thus substitute the thick film.

Shortcomings of some currently available DNA probes for malaria detection

A non-radioactive DNA probe based-method for detecting malaria will greatly aid epidemiological studies. Using putative Plasmodium falciparum and P. vivax-specific 18S ribosomal RNA directed oligonucleotides, different enzymatic and chemiluminescent detection methods were attempted without success. The sensitivity of the corresponding 32P-labelled probes was found to be inadequate. A published procedure based on chemiluminescent detection of repetitive DNA sequences of P. falciparum was found to be adequately sensitive but lacking in specificity.

Detection of antigens in the urine of patients with acute Plasmodium vivax malaria

Plasmodium antigens were detected by dot-blot assay in the urine of 50 patients infected with Plasmodium vivax. Antigens also were detected in 12/15 patients who no longer had detectable parasitemia, 3 weeks after chemotherapy. Antigenuria was negative 6 weeks after treatment. By Western blotting, four predominant protein antigens were identified in the urine of patients infected with P. vivax: 200, 180, 150, and 110 kDa. The dot-blot technique may prove to be a rapid and inexpensive method for diagnosing malaria in field studies and for clinical evaluation during chemotherapy.

Rhabdomyolysis associated with malaria tertiana in a patient with myoadenylate deaminase deficiency

A male patient presented with malaria tertiana due to Plasmodium vivax. He developed a severe attack of rhabdomyolysis with acute renal failure. The patient was treated successfully with chloroquine medication. After complete recovery further muscle study revealed a deficiency of myoadenyl deaminase (MAD). The infection with P. vivax probably has been the triggering factor in the process of muscle necrosis, because the patient also had MAD deficiency.

On-site diagnosis of Plasmodium falciparum, P. vivax, and P. malariae by using the Quantitative Buffy Coat system

The Quantitative Buffy Coat (QBC) system was used for the detection and identification of malaria parasites in blood specimens from 570 residents of Oksibil, an isolated highland valley in the eastern Jayawijaya Mountains of Irian Jaya (Indonesian New Guinea). The availability of a battery-powered centrifuge and a fiberoptic Paralens enabled us to complete and interpret the assay in this remote environment. Of 322 QBC tubes examined for 2-4 min each, results of 295 (92%) concurred with findings on the matched Giemsa-stained thick smear (GTS). The 27 discrepant results included 13 QBC+/GTS- that, upon reexamination, were found to be GTS+. When using the corrected GTS results as the standard, the sensitivity and specificity of the QBC were 94% and 96%, respectively. Because electricity was available only 3 hr per day, it was decided to decrease the examination for an additional 248 QBC to a maximum of 90 sec per tube. This shortened inspection time resulted in a reduction of sensitivity to 53% but specificity was preserved at 89%. Forty-two of 45 conflicting results, QBC-/GTS+ from cases of light Plasmodium falciparum infections with < 1 trophozoite or gametocyte per field, were resolved by reexamination of the QBC in the laboratory. Tubes held at 4 C could be reexamined, without noticeable loss of fluorescence, for at least 6 wk after collection. Despite some difficulty in the identification of Plasmodium species, it was concluded that the QBC is an easy, sensitive method for the rapid diagnosis of malaria in the field and that it provides the inexperienced microscopist with an additional means for on-site identification of individuals needing treatment.

Detection of circulating plasmodial antigens in human sera by sandwich ELISA with monoclonal antibodies

Two monoclonal antibodies (MAbs), one produced against Plasmodium falciparum (PF-IG8) and the other against P. cynomolgi (PC-IE12) schizont antigens were used in a sandwich ELISA for the detection of circulating plasmodial antigens in sera of patients infected with either P. falciparum, P. vivax or P. malariae. The mean +/- SD optical density (OD) values for the normal control group using PF-108 and PC-1E12 were 0.351 +/- 0.036 and 0.205 +/- 0.044, respectively. Mean OD values for the three infected groups were found to be significantly higher than those of the normal control group for both MAbs. However, ELISA values for individual serum specimens did not correlate with the level of parasitemia in the infected blood. Using a cut-off point of mean OD +/- 3 SD of the normal control group as indicating a positive reading, the specificity of this assay with both MAbs was 100%. The sensitivity of the assay using PF-1G8 was 95% while that obtained with PC-1E12 was 98%.

Antibody detection ELISAS for malaria diagnosis

Parasite extracts of Plasmodium falciparum and P. chabaudi and three synthetic peptides from the P. falciparum MSA2 merozoite antigen were tested for suitability as antigens in an antibody detection ELISA using sera from malaria patients in Brisbane. The P. chabaudi extract was superior to P. falciparum extract for detecting P. vivax cases, while for P. falciparum cases the two parasite extracts were equivalent. Single peptide antigens were generally less sensitive than parasite extracts; however, peptides G3 and G7 were more sensitive than parasite extracts in detecting first attacks of P. vivax. Examination of isotype specific responses demonstrated that this may be explained by higher IgG responses to these peptides in first than in subsequent P. vivax attacks. Because of the differing antibody specificities in primary and secondary P. falciparum and P. vivax cases, the best sensitivity was achieved by using the combined results of assays with three antigens: P. chabaudi, peptide G3 and peptide G7. The combined sensitivity was 77.1% for P. falciparum and 88.6% for P. vivax acute cases with 91.1% specificity.

Two-site sandwich ELISA for detection of Plasmodium vivax blood stage antigens using monoclonal and polyclonal antibodies

Two systems of sandwich enzyme-linked immunosorbent assay (ELISA), a two-site monoclonal antibody sandwich ELISA MAb-MAb sandwich ELISA) and a two site polyclonal-monoclonal antibody sandwich ELISA (PAb-MAb sandwich ELISA) for the detection of Plasmodium vivax antigens were developed. The assays showed good correlation with the level of parasitemia when tested against serially diluted P. vivax parasites (r = 0.937, and 0.997 for MAb-MAb and PAb-MAb sandwich ELISA, respectively), with the ability to detect as few as 6.68 parasites/10(6) erythrocytes and 2.69 parasites/10(3) erythrocytes, respectively. The MAb-MAb sandwich ELISA was specific, since it was positive only with P. vivax-infected erythrocytes from vivax malaria patients and negative when erythrocytes from 34 healthy individuals and 30 falciparum malaria cases were tested. In contrast, cross-reaction was found in the PAb-MAb sandwich ELISA when the plates were coated with polyclonal IgG and tested against the serially diluted P. falciparum SO strain antigen prepared from in vitro cultures. Comparison between the two systems of two-site sandwich ELISA showed that the MAb-MAb sandwich ELISA was superior to the PAb-MAb sandwich ELISA: (1) it gave a higher sensitivity when tested with serially diluted P. vivax antigen preparations from vivax malaria patients; (2) it gave a higher specificity when tested with the SO strain of P. falciparum from in vitro cultures, (3) it gave a lower absorbance value when tested with erythrocytes from healthy individuals. All 281 cases of vivax malaria already proven by microscopic examination were positive by MAb-MAb sandwich ELISA.(ABSTRACT TRUNCATED AT 250 WORDS)

Two-site pan-species monoclonal antibody ELISA for detection of blood stage malaria antigen

A two-site pan-species monoclonal antibody sandwich ELISA (MAb-MAb ELISA) was developed to detect both Plasmodium vivax and P. falciparum antigens in whole blood impregnated on filter paper. In this assay, the plates were coated with pan-species MAb 3F9 and another pan-species MAb M26-32 conjugated with alkaline phosphatase was used for detection of bound antigen. The sensitivity of this assay was 5, 10 and 10 parasites per 10(6) erythrocytes for cultured P. falciparum, patient-derived P. vivax and P. falciparum, respectively. The coincidence rates for this assay were 93% (92/99) with healthy individuals and 93% (42/45) with microscopically confirmed vivax malaria cases. After two weeks treatment, 77.7% (14/18) of vivax malaria were still positive by this assay but with diminished level of reactivities [corrected].

Demonstration by the polymerase chain reaction of mixed Plasmodium falciparum and P. vivax infections undetected by conventional microscopy

Mixed malaria infections (Plasmodium falciparum and P. vivax) are suspected to occur at a greater frequency than is detected by conventional light microscopy. To determine this frequency we carried out a prospective 'blinded' comparison of diagnosis by conventional light microscopy and enzymatic amplification of the circumsporozoite gene extracted from dried spotted blood samples. Patients were previously healthy, active duty Thai soldiers assigned to a malaria risk area presenting with malaria. Microscopy (oil immersion objective at 1000 x magnification) involved examination of Giemsa-stained thick and thin blood films by an experienced microscopist. Whole blood samples (25 microliters) dried on filter paper were used for species-specific parasite deoxyribonucleic acid (DNA) amplification by the polymerase chain reaction (PCR) and hybridization with radiolabelled P. falciparum and P. vivax probes. Of 137 consecutive cases of malaria studied, 9% (3/32) of microscopically diagnosed P. falciparum infections and 5% (5/104) of microscopically diagnosed P. vivax infections were found to be mixed by the PCR/DNA probe systems, while 1 case was diagnosed as mixed by both microscopy and PCR. The possibility that malaria patients may have undetected mixed infections should be kept in mind because of the specific therapy required both for P. falciparum and for radical cure of P. vivax.

[The phenomenon of the delayed initial attack of tertian malaria]

From 1986 to 1990 we have treated 215 patients with falciparum malaria. In 8 patients (4%) who had not returned to any malarial area, malaria attacks recurred after 6-20 weeks. Curiously these were now caused by different species: Plasmodium vivax (4 patients) and P. ovale (4 patients). After proper management of malignant tertian malaria caused by P. falciparum, patients are considered cured, provided the treatment has been in accordance with the resistance pattern of the parasite in the country of origin. Yet, in a small number of patients attacks of malaria recur after different time intervals. The explanation of this seemingly paradoxical phenomenon is that these were delayed primary attacks of benign tertian malaria rather than recrudescences of malignant tertian malaria. Consequently the patients must have been infected by two different species of malaria at a time. In P. vivax and P. ovale hypnozoites occur (notably absent in P. falciparum), dormant stages in the liver that are not susceptible to the antimalarials in use for the eradication or prophylaxis of the blood stages which cause the acute attacks of malaria. After a variable amount of time the blood is then (re)invaded and the patient suffers a delayed primary attack or a relapse. Physicians should be aware that definite cure of malignant tertian malaria does not prevent future attacks of benign tertian malaria. They should inform their patients accordingly.

Detection of malaria antigen in blood by inhibition ELISA

Demonstration of parasite associated antigen in blood by inhibition ELISA in malaria patients and controls is described. The test was negative in all the healthy controls and positive in 90 per cent of the Plasmodium vivax malaria cases. The test was found to be quite sensitive, being able to detect 5 parasites/10(6) RBC in a case of natural P. falciparum infection. There was 95.3 per cent agreement between the results of this test and IgM-IIF test.

Practical uses of acridine orange fluorescence microscopy of centrifuged blood (QBC Malaria Test) and the QBCII Hematology System in patients attending malaria clinics in Thailand

We evaluated the detection of malaria parasites using acridine orange fluorescence microscopy of centrifuged blood (AOFM/CB or "QBC Malaria Test") at two government malaria clinics in rural Thailand. In a subgroup of the patients, a QBC Hematology System for the determination of complete blood counts was also utilized. A Giemsa-stained thick smear (GTS) reading of 100 (1,000x) microscopic fields was used as standard. The AOFM/CB sensitivities were 97% overall and 95% for P. falciparum (Pf). Sensitivity was lower for P. vivax (Pv) (76%). Pv sensitivity depended largely on ameboid form density. A threshold for AOFM/CB to consistently detect Pv ameboid forms was estimated to be 10/100 WBC (700/microliters blood). AOFM/CB was capable of detecting Pf gametocytes and schizonts more frequently than GTS. The total Pf rings per microliter blood estimated from GTS was highly correlated with the number of Pf rings per Paralens microscopic field (PMF) suggesting that AOFM/CB could be used quantitatively. From a technical standpoint, the rural tropical settings of Thailand in this study were not an obstacle to the use of QBC Hematology. The system was found to be useful in conjunction with AOFM/CB. However, in patients heavily infected with Pf gametocytes of Pv ameboid forms, their total WBC and lymphocyte counts needed to be appropriately corrected. Overall, AOFM/CB appears to be a promising tool for field diagnosis of malaria if it is affordable to developing countries.

An immunocytochemical test for the diagnosis of antibodies to Plasmodium vivax

An immunocytochemical peroxidase test (ICPT) has been developed to allow serological measurement of the antibody response to Plasmodium vivax by light microscopy. Acetone fixed P. vivax erythrocyte stages were used as source of antigen. The immunofluorescent antibody test (IFAT) was used as reference test. In testing sera from individuals infected with P. vivax in southeastern Venezuela a high correlation (100%) was obtained between the ICPT and the IFAT. There were cross reactions with sera from patients with malaria by P. falciparum but not with those from patients with other parasitic diseases. Antibody titres as measured by the ICPT showed a positive correlation with past P. vivax malarial experiences.

Management of admitted malaria cases in four major hospitals of Delhi: a case study

A hospital-based retrospective case study of admitted patients was undertaken in four major hospitals of Delhi during 1991, with a view to assessing (i) recording and reporting system of malaria cases, (ii) diagnostic criteria being followed, (iii) management of complicated and severe malaria cases, and (iv) availability of life-saving antimalarials. The study showed that none of the hospitals either followed the international coding system for recording or adopted the National Malaria Eradication Programme guidelines for diagnostic criteria malaria, i.e. by blood smear examination. Diagnosis of malaria in three out of four hospitals was not preceded by blood examination in all cases. Only 55% of the 283 clinically suspected malaria cases were screened for malaria parasite with overall positivity of 20.14 per cent and of 38.25 per cent in examined cases. Age and sex break-up indicated that males suffered more and 65 per cent of the patients belonged to 16-40 years' age groups as compared to 38.4 per cent population falling in this age group according to 1981 census. Out of 263 recovered study cases, 13 per cent came from adjoining states while this percentage went up to 35 per cent (7 out of 20 cases) in the case of malaria deaths. Over 80 per cent of the clinically suspected cases presented with signs and symptoms of fever or fever with rigour, chills or vomiting. In 38 per cent of the cases there was a definite time lag in reporting of the cases to hospitals but most of the cases (91 per cent) were administered antimalarials within 24 h of admission.(ABSTRACT TRUNCATED AT 250 WORDS)

Malaria seroepidemiology: comparison between indirect fluorescent antibody test and enzyme immunoassay using bloodspot eluates

Blood sampling on filter paper is a current practice in malaria seroepidemiological studies by indirect fluorescent antibody test (IFAT). There is, however, scant comparative information about the use of bloodspot eluates for detection of malarial IgG antibodies simultaneously by IFAT and enzyme immunoassay (ELISA). Here we report data obtained by both serological methods done on 219 bloodspot eluate samples collected in a rural community in Brazilian Amazon Basin (Alto Paraíso, Ariquemes municipality) where malaria is endemic. Plasmodium falciparum and P. vivax thick smear antigens were used in the IFAT; a detergent-soluble P. falciparum antigen was prepared for ELISA. Substantial agreement of results (Kappa coefficient k = 0.686) was observed when P. falciparum antigen was used in both tests, and IFAT titers were found to be strongly correlated to ELISA antibody units (Spearman correlation coefficient rs = 0.818, p < 0.001). Only moderate agreement (k = 0.467) between IFAT with P. vivax antigen and ELISA with P. falciparum antigen was observed. Spearman correlation coefficient value between quantitative results (IFAT titers and ELISA antibody units) in this case was numerically lower (rs = 0.540, p < 0.0001). Our results suggest that, with P. falciparum antigen, both IFAT and ELISA performed on bloodspot eluates are equivalent for seroepidemiological purposes.

Post-operative transfusion malaria

Two Saudi patients who underwent cardiac surgery, developed fever after being discharged from hospital. Both received blood transfusion during operation. The cause of fever was found to be due to malaria acquired from the transfused blood. As no single measure could prevent transfusion malaria, clinical awareness of the condition should lead to early diagnosis and management of such cases.

Modern immunological approaches to assess malaria transmission and immunity and to diagnose plasmodial infection

The present paper reviews our recent data concerning the use of immunological methods employing monoclonal antibodies and synthetic peptides to study malaria transmission and immunity and to diagnose plasmodial infection. As concerns malaria transmission, we studied the main vectors of human malaria and the plasmodial species transmitted in endemic areas of Rondônia state, Brazil. The natural infection of anopheline was evaluated by immunoradiometric assay (IRMA) using monoclonal antibodies to an immunodominant sporozoite surface antigen (CS protein) demonstrated to be species specific. Our results showed that among six species of Anopheles found infected, An. darlingi was the main vector transmitting Plasmodium falciparum and P. vivax malaria in the immediate vicinity of houses. In order to assess the level of anti-CS antibodies we studied, by IRMA using the synthetic peptide corresponding to the repetitive epitope of the sporozoite CS protein, sera of individuals living in the same areas where the entomological survey has been performed. In this assay the prevalence of anti-CS antibodies was very low and did not reflect the malaria transmission rate in the studied areas. In relation to malaria diagnosis, a monoclonal antibody specific to an epitope of a 50 kDa exoantigen, the major component of supernatant collected at the time of schizont rupture, was used as a probe for the detection of P. falciparum antigens. This assay seemed to be more sensitive than parasitological examination for malaria diagnosis since it was able to detect plasmodial antigens in both symptomatic and asymptomatic individuals with negative thick blood smear at different intervals after a last parasitologically confirmed attack of malaria.

Diagnosis of malaria in the field by fluorescence microscopy of QBC capillary tubes

The diagnostic performance of commercial capillary tubes containing acridine orange dye (QBC) was compared with the standard diagnosis of malaria by microscopical examination of Giemsa-stained thick blood films (GTS) in remote field conditions. The comparison was conducted among 165 volunteers living in northeastern Irian Jaya, Indonesia, an area having hyperendemic malaria transmission. By GTS, 65 volunteers were positive for malaria, but only 49 were judged positive by QBC. Among the 100 blood films found negative by GTS, 5 were considered positive by QBC. Thus, relative to a GTS standard, the sensitivity and specificity of the QBC was 75% and 95%, respectively. The mean limit of detection for the QBC was approximately 60 parasites per microliter blood, whereas the limit of detection for GTS was 20 parasites per microliter blood. Also, a number of practical difficulties were encountered using the QBC at the field site. The QBC approach to diagnosis of malaria was less sensitive and more inconvenient than GTS under the conditions in remote Irian Jaya.

Development of an immunoenzymatic assay using a monoclonal antibody against a 50-kDa catabolite from the P126 Plasmodium falciparum protein to the diagnosis of malaria infection

The WHO criterion of defering any donation of blood by a confirmed case of malaria for three years after cessation of therapy can not be applied in areas where malaria is endemic. For this reason we developed an immunoenzymatic assay for the detection of plasmodial antigens for blood screening in malarial endemic areas. So, we tested sera from 191 individuals. Among patients with active disease 100% of the cases of Plasmodium falciparum or mixed infections and 91.7% of those with P. vivax were positive for the presence of plasmodial antigens. The lower parasitaemia detected was 0.0003% for P. falciparum and 0.001% for P. vivax malária. When the frequency of positive circulating malarial antigens was evaluated among asymptomatic and symptomatic individuals with negative TBS, positive results were found in respectively 38.7% and 17.7% of the individuals studied in the 30 days after confirmed malaria attack. Data provide by these assays have shown that ELISA seemed to be more sensitive than parasitological examination for malaria diagnosis. This test by virtue of its high sensitivity and the facilities in processing a large number of specimens, can prove to be useful in endemic areas for the recognition of asymptomatic malaria and screening of blood donors.

Laboratory diagnosis of malaria

Diagnostic procedures for the detection of malaria differ considerably depending on the aims of evaluation. The current requirements of any laboratory procedure for general application to the detection and diagnosis of malaria include: sensitivity, specificity, simplicity in application, unambiguous interpretation, and rapid turn-around time. Presently the differential stained thick and thin blood smear, examined under the microscope, remains the most reliable and definitive test for diagnosis of malaria.

[The results of serological studies in different foci of tropical and tertiary malaria]

Attempt was made to determine the value of serologic indices of malaria surveys. Following uniformed methodological and technical approaches 3 foci of P. vivax and 6 foci of P. falciparum malaria were surveyed in different endemic zones of Vietnam and the USSR. It was shown that the most objective criteria for a foci classification is its serologic mean geometric titre. The latter in its turn directly depends of transmission longevity in a foci.

Malaria and Widal reaction

Widal reaction was studied in 52 patients having malaria parasites in the peripheral blood smear. Twenty had Plasmodium vivax, 26 had Plasmodium falciparum and the rest had mixed (both vivax and falciparum) infections. Widal test for both O and H antigens of Salmonella typhi was positive in high titres in 3 falciparum, 3 vivax and 2 cases of mixed infection. Of these 8 cases, one had been treated for typhoid fever 3 months back and again one month back for relapse. Blood culture for Salmonella typhi was negative in all. All were cured after antimalarial therapy. The positive Widal reaction may be false.