The laboratory diagnosis of malaria

Antiplasmodial Cyclodecapeptides from Tyrothricin Share a Target with Chloroquine

Previous research found that the six major cyclodecapeptides from the tyrothricin complex, produced by Brevibacillus parabrevis, showed potent activity against chloroquine sensitive (CQS) Plasmodium falciparum. The identity of the aromatic residues in the aromatic dipeptide unit in cyclo-(D-Phe¹-Pro²-(Phe³/Trp³)-D-Phe⁴/D-Trp⁴)-Asn⁵-Gln⁶-(Tyr⁷/Phe⁷/Trp⁷)-Val⁸-(Orn⁹/Lys⁹)-Leu¹⁰ was proposed to have an important role in activity. CQS and resistant (CQR) P. falciparum strains were challenged with three representative cyclodecapeptides. Our results confirmed that cyclodecapeptides from tyrothricin had significantly higher antiplasmodial activity than the analogous gramicidin S, rivaling that of CQ. However, the previously hypothesized size and hydrophobicity dependent activity for these peptides did not hold true for P. falciparum strains, other than for the CQS 3D7 strain. The Tyr⁷ in tyrocidine A (TrcA) with Phe³-D-Phe⁴ seem to be related with loss in activity correlating with CQ antagonism and resistance, indicating a shared target and/or resistance mechanism in which the phenolic groups play a role. Phe⁷ in phenycidine A, the second peptide containing Phe³-D-Phe⁴, also showed CQ antagonism. Conversely, Trp⁷ in tryptocidine C (TpcC) with Trp³-D-Trp⁴ showed improved peptide selectivity and activity towards the more resistant strains, without overt antagonism towards CQ. However, TpcC lead to similar parasite stage inhibition and parasite morphology changes than previously observed for TrcA. The disorganization of chromatin packing and neutral lipid structures, combined with amorphous hemozoin crystals, could account for halted growth in late trophozoite/early schizont stage and the nanomolar non-lytic activity of these peptides. These targets related to CQ antagonism, changes in neural lipid distribution, leading to hemozoin malformation, indicate that the tyrothricin cyclodecapeptides and CQ share a target in the malaria parasite. The differing activities of these cyclic peptides towards CQS and CQR P. falciparum strains could be due to variable target interaction in multiple modes of activity. This indicated that the cyclodecapeptide activity and parasite resistance response depended on the aromatic residues in positions 3, 4 and 7. This new insight on these natural cyclic decapeptides could also benefit the design of unique small peptidomimetics in which activity and resistance can be modulated.

Guideline: the laboratory diagnosis of malaria. General Haematology Task Force of the British Committee for Standards in Haematology

UK National External Quality Assessment Service surveys indicate continuing problems in malaria diagnosis: inaccurate calculation of parasitaemia or failure to estimate it altogether, difficulty distinguishing Plasmodium vivax from P. ovale, reporting malaria parasites when none were present and misidentification of P. falciparum as another species still occur. Therefore, the British Committee for Standards in Haematology Guidelines for the Laboratory Diagnosis of Malaria have been revised. They are intended for use in the UK but may also prove useful in other non-endemic areas. Routine use of thick and thin films is advised for malaria diagnosis. Thick films should be stained using Giemsa or Field stain. Thin films should be stained with Giemsa stain or Leishman stain. Thick films should be examined by two observers, each viewing a minimum of 200 high power fields. If thick films are positive, the species should be determined by examination of a thin film. In the case of P. falciparum or P. knowlesi infection, the percentage of parasitized cells or the number of parasites per microlitre (/μl) should be estimated and reported. Rapid diagnostic tests (RDTs) for malarial antigen cannot replace microscopy but are indicated as a supplementary test when malaria diagnosis is performed by relatively inexperienced staff. Malaria RDTs are negative in babesiosis.

A method for reducing the sloughing of thick blood films for malaria diagnosis

BACKGROUND

The gold standard for malaria diagnosis is the examination of thick and thin blood films. Thick films contain 10 to 20 times more blood than thin films, correspondingly providing increased sensitivity for malaria screening. A potential complication of thick film preparations is sloughing of the blood droplet from the slide during staining or rinsing, resulting in the loss of sample. In this work, two methods for improving thick film slide adherence ('scratch' (SCM) and 'acetone dip' (ADM) methods) were compared to the 'standard method' (SM) of thick film preparation.

METHODS

Standardized blood droplets from 26 previously examined EDTA whole blood specimens (22 positive and four negative) were concurrently spread on glass slides using the SM, ADM, and SCM. For the SM and ADM prepared slides, the droplet was gently spread to an approximate 22 millimeters in diameter spot on the slide using the edge of a second glass slide. For the SCM, the droplet was spread by carefully grinding (or scratching) it into the slide with the point of a second glass slide. Slides were dried for one hour in a laminar flow hood. For the ADM, slides were dipped once in an acetone filled Coplin jar and allowed to air dry. All slides were then Giemsa-stained and examined in a blinded manner. Adherence was assessed by blinded reviewers.

RESULTS

No significant or severe defects were observed for slides prepared with the SCM. In contrast, 8 slides prepared by the ADM and 3 prepared using the SM displayed significant or severe defects. Thick films prepared by the three methods were microscopically indistinguishable and concordant results (positive or negative) were obtained for the three methods. Estimated parasitaemia of the blood samples ranged from 25 to 429,169 parasites/μL of blood.

CONCLUSIONS

The SCM is an inexpensive, rapid, and simple method that improves the adherence of thick blood films to standard glass slides without altering general slide preparation, microscopic appearance or interpretability. Using the SCM, thick films can be reliably examined less than two hours after sample receipt. This represents a significant diagnostic improvement over protocols requiring extended drying periods.

Is serial testing required to diagnose imported malaria in the era of rapid diagnostic tests?

Exclusion of malaria traditionally requires three negative serial thick and thin blood films. However, many clinical laboratories now routinely perform rapid diagnostic tests (RDTs) in addition to blood films when malaria is suspected. We sought to determine whether serial testing is necessary in this setting. We examined 388 cases of malaria diagnosed during 1999-2010 at three laboratories in Melbourne, Australia. For each case, we ascertained whether the diagnosis was made on initial or follow-up testing. Nine cases (3.5%) were diagnosed after a negative initial blood film and RDT: 7 Plasmodium vivax, 1 P. ovale, and 1 P. falciparum. Of four case-patients with P. vivax in which clinical data were available, all had recent exposure to antimalarial medication. Our data suggest that among patients who have not received recent anti-malarial therapy, and when RDTs are performed and blood films are prepared, most malaria diagnoses are made by using the first set of tests.

Modified Field stain - rapid viability test for Trichomonas vaginalis

AIMS

We previously reported that Modified Field Stain (MF) can be used as a rapid stain for diagnosis. In the present study we extend the observation to include the stain as an alternative method to assess viability of the cells.

METHODS AND RESULTS

Six isolates of Trichomonas vaginalis were used to assess the utility of the Modified Field stain as a rapid viability test for T. vaginalis and to compare with 0·4% Trypan Blue dye exclusion test in three conditions; normal in vitro culture growth using Hollander medium, lysed in distilled water and treated with metronidazole. MF stain showed similar growth profile pattern as Trypan Blue dye exclusion for identifying viable cells of T. vaginalis. Although, Trypan Blue dye exclusion test is ready made, rapid and widely used in laboratory as reliable viability assay, however, the limitation using Trypan Blue is the dye was unable to show internal morphological changes during the parasite's transition from being viable to non-viable. On day 3 where cultures peaked the correlation factor of both assays done to assess the viability of parasites harvested from the controls, metronidazole and distilled water treated parasites were more than 0·9 respectively.

CONCLUSIONS

This confirms that MF staining does not only record permanently the morphological changes and retain internal structural details but also provides a reliable and rapid viability assay for the parasites.

SIGNIFICANCE AND IMPACT OF THE STUDY

Therefore, in our study, Modified Field's stain may offer the researchers and laboratory technologists the opportunity to get the result on the same day and the most important thing is the ability to differentiate between viable and non-viable of T. vaginalis under three different conditions (normal culture, drug and distilled water condition). Modified Field's staining method enhanced the morphological identification of T. vaginalis compared to Trypan Blue dye exclusion.

Modified Field's staining--a rapid stain for Trichomonas vaginalis

Trichomonas vaginalis, a flagellate protozoan parasite commonly found in the human genitourinary tract, is transmitted primarily by sexual intercourse. Diagnosis is usually by in vitro culture method and staining with Giemsa stain. There are laboratories that use Gram stain as well. We compared the use of modified Field's (MF), Giemsa, and Gram stains on 2 axenic and xenic isolates of T. vaginalis, respectively. Three smears from every sediment of spun cultures of all 4 isolates were stained, respectively, with each of the stains. We showed that MF staining, apart from being a rapid stain (20 s), confers sharper staining contrast, which differentiates the nucleus and the cytoplasm of the organism when compared to Giemsa and Gram staining especially on parasites from spiked urine samples. The alternative staining procedure offers in a diagnostic setting a rapid stain that can easily visualize the parasite with sharp contrasting characteristics between organelles especially the nucleus and cytoplasm. Vacuoles are more clearly visible in parasites stained with MF than when stained with Giemsa.

An adequacy evaluation of a 10-year, four-country nutrition and health programme

BACKGROUND

Evaluations of large-scale health and nutrition programmes in developing countries are needed for determining the effectiveness of interventions. This article critically analyses a non-governmental organization (NGO)-led large-scale, multi-country, 10-year micronutrient and health (MICAH) programme with an 'adequacy evaluation', that is, a documentation of time trends in the expected direction.

METHODS

MICAH was implemented from 1996 to 2005 in selected areas of Ethiopia, Ghana, Malawi and Tanzania, reaching >6 million people with numerous health and nutrition interventions. Coverage and impact were monitored through surveys at baseline, midpoint and end of funding. The data were subjected to post-hoc methods of quality determination, and, if of suitable quality, included in the adequacy evaluation.

RESULTS

Most collected data were of moderate or high quality and therefore included in the adequacy evaluation. There were moderate to large improvements in vitamin A status in Ethiopian school-age children, children <5 years of age in Tanzania and Ghana and mothers in Ghana. Iodine status improved in Malawi and Tanzania. Anaemia rates and malaria prevalence decreased in women, pregnant women and pre-school children in Ghana, Malawi and Tanzania, but anaemia increased in Ethiopian women. Large increases were reported for rates of exclusive breastfeeding and immunization. Child growth improved to the maximum that would be predicted with the given interventions.

CONCLUSIONS

Numerous nutrition and health impacts were observed in the intervention areas, often of a magnitude equal to or larger than observed in controlled interventions or trials. These results show the value of integrated long-term interventions.

The impact of an integrated community-based micronutrient and health programme on anaemia in non-pregnant Malawian women

OBJECTIVE

To assess the impact of an integrated community-based micronutrient and health (MICAH) programme on anaemia (Hb < 120 g/l) among non-pregnant rural Malawian women aged 15-49 years from communities that participated in the 1996-2005 MICAH programme.

DESIGN

Prospective study of two large-scale cross-sectional surveys conducted in 2000 and 2004 as part of programme evaluation in MICAH and Comparison areas.

SETTING

Rural areas across Malawi. The MICAH programme implemented a comprehensive package of interventions to reduce anaemia, based on a broad range on direct and indirect causes in Malawi. The project approaches included: Fe supplementation; dietary diversification and modification; food fortification; and strengthening primary health care.

PARTICIPANTS

Non-pregnant women of childbearing age (15-49 years old, n 5422), from randomly selected households that responded to a household questionnaire, had their Hb measured from finger-prick blood samples using the HemoCue.

RESULTS

In 2000, there was no significant difference in Hb concentration between MICAH and Comparison areas (mean (SE): 117.4 (0.4) v. 116.8 (0.5) g/l, P > 0.05) and the corresponding prevalence of anaemia (53.5 % v. 52.9 %, P > 0.05). By 2004, Hb concentration had increased significantly in MICAH but not in Comparison areas (mean (SE): 121.0 (0.4) v. 115.7 (0.6) g/l, P < 0.001), and the prevalence of anaemia had declined significantly in MICAH areas (53.5 % to 44.1 %, chi2 = 28.2, P < 0.0001) but not in Comparison areas (52.8 % to 54.0 %, chi2 = 0.3, P = 0.6).

CONCLUSIONS

The MICAH programme was an effective public health nutrition programme that was associated with significant reductions in the prevalence of anaemia among non-pregnant rural Malawian women.

Update on rapid diagnostic testing for malaria

To help mitigate the expanding global impact of malaria, with its associated increasing drug resistance, implementation of prompt and accurate diagnosis is needed. Malaria is diagnosed predominantly by using clinical criteria, with microscopy as the current gold standard for detecting parasitemia, even though it is clearly inadequate in many health care settings. Rapid diagnostic tests (RDTs) have been recognized as an ideal method for diagnosing infectious diseases, including malaria, in recent years. There have been a number of RDTs developed and evaluated widely for malaria diagnosis, but a number of issues related to these products have arisen. This review highlights RDTs, including challenges in assessing their performance, internationally available RDTs, their effectiveness in various health care settings, and the selection of RDTs for different health care systems.

Falciparum Malaria

Malaria is one of the most common infectious diseases in the world today, being the most important parasitic infection, and Plasmodium falciparum is the organism responsible for most of the mortality [1]. It has been estimated that approximately 300–500 million people contract malaria every year, with approximately 1–2 million deaths, most of these occurring in children [1–5]. Plasmodium falciparum, Mycobacterium tuberculosis and measles currently compete for the title of the single most important pathogen causing human morbidity and mortality [2, 3]. Infection with Plasmodium falciparum has a wide variety of potential clinical consequences [4, 6, 7].

Rapid diagnostic testing for malaria

Malaria rapid diagnostic devices (MRDD) have been developed with the hope that they would offer accurate, reliable, rapid, cheap and easily available alternatives to traditional methods of malaria diagnosis. The results from early malaria rapid diagnostic studies were quite promising, especially for detecting Plasmodium falciparum at densities of more than 100-500 parasites/microl. Despite the introduction of these devices over a decade ago, only a few target antigens have been introduced. Of greater concern, these devices have shown limitations in sensitivity, ability to differentiate species and robustness under field conditions in the tropics. Recent trials have revealed wide variability in sensitivity both within and between products. We review the recent trials assessing MRDD use for the diagnosis of P. falciparum and non-P. falciparum infections in endemic and non-endemic countries and describe the various aspects of these devices which need further improvement. High quality, accurate, rapid and affordable diagnostic tools are urgently needed now that new antimalarial regimens, characterized by higher cost and increased toxicity, have been introduced more widely in response to emerging multi-drug resistance.

Sensitivity of hemozoin detection by automated flow cytometry in non- and semi-immune malaria patients

BACKGROUND

Cell-Dyn automated blood cell analyzers use laser flow cytometry technology, allowing detection of malaria pigment (hemozoin) in monocytes. We evaluated the value of such an instrument to diagnose malaria in febrile travelers returning to Berlin, Germany, the relation between the instrument's performance and the patients' immune status, and the capacity to increase its sensitivity.

METHODS

Malaria diagnosis was routinely established by thick-film microscopy. The patients' immune status was determined by an indirect fluorescent antibody test. Hemozoin detection was performed with a Cell-Dyn 3000. To assess the capacity for sensitivity increase, the relative frequencies of pigment-containing monocytes were determined for a subgroup of patients with the Cell-Dyn 3000 in comparison with a flow cytometer specifically adapted to rare-event analysis.

RESULTS

Of 403 patients screened microscopically, 107 had malaria. Overall sensitivity with the Cell-Dyn 3000 reached 48.6% (73.7% in semi-immune and 28.6% in nonimmune individuals; P < 0.0001). Specificity was 96.2%. The detection limit was at a relative concentration of 2 x 10(-4) pigment-containing monocytes (PCMs). By employing rare-event flow cytometry, the detection limit decreased to 3.25 x 10(-5), thus yielding a considerably increased sensitivity for the subgroup studied.

CONCLUSIONS

The correlation between immune status and relative concentration of PCMs explains the failure of the routine instrument for nonimmune patients and its significantly higher sensitivity for semi-immune individuals. The technique can be significantly improved by rare-event flow cytometry.

Current strategies to avoid misdiagnosis of malaria

Malaria remains the most important parasitic disease, and tens of thousands of cases are imported into non-endemic countries annually. However, any single institution may see only a very few cases-this is probably the reason why laboratory and clinical misdiagnosis may not be uncommon. In the laboratory, unfamiliarity with microscopic diagnosis may be the main reason, considering the large number of laboratory staff who provide on-call services, often without expert help at hand, as well as the difficulty in detecting cases with low-level parasitemia. Staff should therefore be provided with continuing microscopic training to maintain proficiency. The complementary use of immunochromatographic rapid detection tests (RDTs) may be useful, especially during on-call hours, although, in order to ensure correct interpretation, their inherent limitations have to be well known. Diagnosis based on the polymerase chain reaction is still unsuitable for routine use, due to its long turnaround time, its cost, and its unavailability outside regular hours, although it may be helpful in selected cases. Once the alert clinician has considered the possibility of malaria, and suspicion continues to be high, malaria can be excluded by repeat smears or RDTs. However, the absence of clinical suspicion may not be infrequent, and may have more serious consequences. Depending on the local number of malaria cases seen, laboratory staff should have a low threshold for the decision to perform unsolicited malaria diagnostic tests on suspicious samples, especially if other laboratory tests are abnormal (e.g. thrombocytopenia, presence of atypical lymphocytes, or raised lactate dehydrogenase). The detection of intraleukocytic hemozoin during automated full blood counts is a promising new way to avoid misdiagnosis of clinically unsuspected malaria.

Avoiding misdiagnosis of imported malaria: screening of emergency department samples with thrombocytopenia detects clinically unsuspected cases

BACKGROUND

Misdiagnosis of imported malaria is not uncommon and even abnormal routine laboratory tests may not trigger malaria smears. However, blind screening of all thrombocytopenic samples might be a possible way to detect clinically unsuspected malaria cases in the accident and emergency department (AED).

METHODS

The frequency and degree of thrombocytopenia was determined in two cohorts of malaria patients (Lisbon, Portugal and Berlin, Germany). The frequency of thrombocytopenia in full blood count (FBC) samples from patients presenting at the ED at a large teaching hospital in Lisbon, Portugal, was determined and compared with urgent samples from in-patients, both determined at a dedicated emergency laboratory. A cut-off value was established for screening of all FBC samples from the ED with Giemsa-stained thick-blood films.

RESULTS

In 4,362 unselected samples from the ED in Lisbon a thrombocytopenia of <150,000/microL was found in 7% and of <100,000/microL in 2.2% of cases (2.5 samples/day with <100.000/microL). In patients with malaria, a thrombocytopenia was found in 75% and 77% (<150,000/microL) or 53% and 45% (<100,000/microL) in Lisbon, (n=60) and Berlin (n=170), respectively. Blind screening of all samples with <100,000 thrombocytes/microL by thick-blood film microscopy led to the diagnosis of 5 unsuspected malaria cases (3 Plasmodium falciparum, 1 Plasmodium vivax and 1 Plasmodium ovale), during the study. The diagnosis of each unsuspected malaria case would have cost 21 hours of dedicated technician's time.

CONCLUSIONS

The problem of clinically unsuspected malaria seems to be more common than generally expected and is dependent on the local incidence of malaria as well as clinical and laboratory expertise. The blind screening of all thrombocytopenic samples with <100,000/microL may be a cost-effective way to reduce the misdiagnosis of imported malaria.

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.

Artefactually-normal automated platelet counts due to malaria-infected RBC

Protein aggregates, red cell or white cell fragments are known to interfere with platelet counts in automated blood analysers, both by aperture impedance and optical technologies. When a falsely high value is suspected, interference by pseudo-platelet particles can be confirmed by systematic examination of stained blood films. The method that best avoids these sources of interference is the reference, immunological platelet count. We describe a case of treated malaria with a false normal platelet count. The blood smear revealed small red cells, infected by trophozoites of Plasmodium falciparum, that interfered with the platelet count. The Cell Dyn 4000 shows different patterns of interference by infected red cells in its impedance and optical counts, and thrombocytopenia was suspected immediately. This was confirmed by a phase-contrast microscopic platelet count.

Malaria diagnosis with the haematology analyser Cell-Dyn 3500: What does the instrument detect?

The Cell-Dyn 3500 instrument could become a sensitive and specific tool in the diagnosis of malaria. The instrument appears to detect malaria-pigment within monocytes and granulocytes. A case of P. vivax malaria in a patient with increased osmotically resistant erythrocytes illustrates the potential of the instrument to detect intraerythrocytic parasites with pigment. However, in most malaria-patients with normal red cell osmotic resistance the observed phenomena seem rather to represent intraleukocytic pigment. This can remain in the circulation of clinically and parasitologically cured individuals and thus may not indicate acute infection. While the instrument can indicate those patients who have been infected a diagnosis of acute malaria must be established independently.

External quality assessment in the examination of blood films for malarial parasites within Ontario, Canada

OBJECTIVE

To assess laboratory practice in the examination of blood films for malarial parasites.

METHOD

Ontario medical laboratories, licensed by the Ministry of Health, are required to participate in external quality assessment by the Laboratory Proficiency Testing Program, which assesses performance of laboratory assays and also examines the total testing process. Educational strategies are used to improve performance.

RESULTS

A 1995 survey indicated shortcomings in detection and identification of malarial parasites in blood films. Consequently, recommendations for the investigation of malarial parasites in blood were issued. In 1996 and 1997, 16 workshops were conducted. A 1997 follow-up external quality assessment survey indicated that problems persist as 27% of laboratories failed to correctly speciate Plasmodium falciparum. Good Practice Guidelines were issued in 1998.

CONCLUSION

Further education and assessment are required. Laboratories lacking expertise must establish referral arrangements with more proficient laboratories.

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.