Estimation Of Parasite Density Research Articles

The effect of paracetamol on the parasitological diagnosis of Plasmodium falciparum malaria

Objectives: Up until the present time, malaria represents an immense public health problem worldwide with a significant morbidity and mortality rate in many developing countries including Sudan. The use of antipyretics and analgesics in the settings of malaria has been a matter of contention over a vast period of time. Now, it is widely believed among the public and some health professionals in Sudan that the antipyretic and analgesic paracetamol disturbs the accuracy of the parasitological diagnosis of malaria. This study investigates the magnitude and effects of that belief through a descriptive study and examines the actual effect of paracetamol on the parasitological diagnosis of falciparum malaria through a clinical trial. Material and Methods: This is a conjoined study that includes a prospective and descriptive study and a randomized, placebo-controlled, double-blind, and parallel-group clinical trial. The descriptive study included 846 participants from various states in Sudan. The targeted study subjects were the public and health professionals and the study was conducted utilizing an online-based questionnaire. The clinical trial included 325 patients with uncomplicated falciparum attending two primary healthcare outpatient clinics in Gezira state, Sudan. The patients were randomly allocated to receive either placebo tablets or 500 mg of oral paracetamol after the first blood smear sample was taken. The second blood smear samples were taken 2 h after taking treatment. Parasite density estimation and other parasitological data were obtained from each sample before and after treatment. Results: The majority of the public thinks that paracetamol affects the parasitological diagnosis of malaria (76.21%, n = 330/433). Personal experience and family and friends were the most dominant information sources for the public (31.20% and 28.01% respectively), while scholarly articles were the most common source of information for the health professional group (45.03%, n = 186/413). No significant differences between the parasitological findings acquired before and after taking the treatments among both the paracetamol group (P = 0.22) and the placebo group (P = 0.12). The parasite density mean for the paracetamol group differed by 16.31 P/μL after taking paracetamol, while the placebo group parasite density mean differed by 15.34 P/μL. The treatments did not inflict impacts on the advanced microscopic features of Plasmodium falciparum blood smears. Conclusion: Paracetamol does not affect the parasitological diagnosis of falciparum malaria.

Inflammatory response in Plasmodium falciparum-infected patients treated using raw liquid extract of Morinda lucida (Oowo) leaf in some traditional homes in Nigeria

Study Background: Morinda lucida is a medicinal plant used in Nigeria for Plasmodium falciparum infection treatment due to its phytochemical constituents and antioxidant activities. Traditional medicine is accepted in Nigeria for its effectiveness. The plant’s various parts treat fever, malaria, diabetes, ulcers, and gonorrhea. It contains alkaloids, anthraquinones, anthraquinols, steroids, terpenoids, tannins, saponins, flavonoids, phenols, and glycosides. Objective: This study aimed to investigate the inflammatory response in P. falciparum-infected patients treated with the raw liquid extract of M. lucida leaves in traditional homes in Nigeria. Materials and Methods: The study was conducted in ten traditional homes in Saki, Nigeria. Fifty P. falciparum-infected participants receiving treatment in traditional homes were recruited, along with 50 participants receiving conventional malaria treatment in hospitals and 50 noninfected participants as controls. Blood samples were collected for the estimation of parasite density by microscopy, plasma interleukin-10 (IL-10), and tumor necrosis factor-alpha (TNF-α) levels by ELISA. The raw liquid extract of M. lucida leaves was prepared and administered to the patients. Statistical analysis was performed to compare the results among the different groups. Results: The results showed a significant difference in plasma IL-10, TNF-α levels, and parasite density across the different groups. Treatment with the raw liquid extract led to a decrease in plasma IL-10 levels and an increase in plasma TNF-α levels and parasite density in the infected patients. No significant difference was observed between traditional home and hospital patients in terms of IL-10 levels and parasite density. Conclusion: The findings suggest that the raw liquid extract of M. lucida leaves may modulate the inflammatory response in P. falciparum-infected patients. Further studies are needed to explore the therapeutic potential of this plant in the treatment of malaria.

Variability in white blood cell count during uncomplicated malaria and implications for parasite density estimation: a WorldWide Antimalarial Resistance Network individual patient data meta-analysis

BackgroundThe World Health Organization (WHO) recommends that when peripheral malarial parasitaemia is quantified by thick film microscopy, an actual white blood cell (WBC) count from a concurrently collected blood sample is used in calculations. However, in resource-limited settings an assumed WBC count is often used instead. The aim of this study was to describe the variability in WBC count during acute uncomplicated malaria, and estimate the impact of using an assumed value of WBC on estimates of parasite density and clearance.MethodsUncomplicated malaria drug efficacy studies that measured WBC count were selected from the WorldWide Antimalarial Resistance Network data repository for an individual patient data meta-analysis of WBC counts. Regression models with random intercepts for study-site were used to assess WBC count variability at presentation and during follow-up. Inflation factors for parasitaemia density, and clearance estimates were calculated for methods using assumed WBC counts (8000 cells/µL and age-stratified values) using estimates derived from the measured WBC value as reference.ResultsEighty-four studies enrolling 27,656 patients with clinically uncomplicated malaria were included. Geometric mean WBC counts (× 1000 cells/µL) in age groups < 1, 1–4, 5–14 and ≥ 15 years were 10.5, 8.3, 7.1, 5.7 and 7.5, 7.0, 6.5, 6.0 for individuals with falciparum (n = 24,978) and vivax (n = 2678) malaria, respectively. At presentation, higher WBC counts were seen among patients with higher parasitaemia, severe anaemia and, for individuals with vivax malaria, in regions with shorter regional relapse periodicity. Among falciparum malaria patients, using an assumed WBC count of 8000 cells/µL resulted in parasite density underestimation by a median (IQR) of 26% (4–41%) in infants < 1 year old but an overestimation by 50% (16–91%) in adults aged ≥ 15 years. Use of age-stratified assumed WBC values removed systematic bias but did not improve precision of parasitaemia estimation. Imprecision of parasite clearance estimates was only affected by the within-patient WBC variability over time, and remained < 10% for 79% of patients.ConclusionsUsing an assumed WBC value for parasite density estimation from a thick smear may lead to underdiagnosis of hyperparasitaemia and could adversely affect clinical management; but does not result in clinically consequential inaccuracies in the estimation of the prevalence of prolonged parasite clearance and artemisinin resistance.

Field evaluation of the diagnostic performance of EasyScan GO: a digital malaria microscopy device based on machine-learning

BackgroundMicroscopic examination of Giemsa-stained blood films remains the reference standard for malaria parasite detection and quantification, but is undermined by difficulties in ensuring high-quality manual reading and inter-reader reliability. Automated parasite detection and quantification may address this issue.MethodsA multi-centre, observational study was conducted during 2018 and 2019 at 11 sites to assess the performance of the EasyScan Go, a microscopy device employing machine-learning-based image analysis. Sensitivity, specificity, accuracy of species detection and parasite density estimation were assessed with expert microscopy as the reference. Intra- and inter-device reliability of the device was also evaluated by comparing results from repeat reads on the same and two different devices. This study has been reported in accordance with the Standards for Reporting Diagnostic accuracy studies (STARD) checklist.ResultsIn total, 2250 Giemsa-stained blood films were prepared and read independently by expert microscopists and the EasyScan Go device. The diagnostic sensitivity of EasyScan Go was 91.1% (95% CI 88.9–92.7), and specificity 75.6% (95% CI 73.1–78.0). With good quality slides sensitivity was similar (89.1%, 95%CI 86.2–91.5), but specificity increased to 85.1% (95%CI 82.6–87.4). Sensitivity increased with parasitaemia rising from 57% at < 200 parasite/µL, to ≥ 90% at > 200–200,000 parasite/µL. Species were identified accurately in 93% of Plasmodium falciparum samples (kappa = 0.76, 95% CI 0.69–0.83), and in 92% of Plasmodium vivax samples (kappa = 0.73, 95% CI 0.66–0.80). Parasite density estimates by the EasyScan Go were within ± 25% of the microscopic reference counts in 23% of slides.ConclusionsThe performance of the EasyScan Go in parasite detection and species identification accuracy fulfil WHO-TDR Research Malaria Microscopy competence level 2 criteria. In terms of parasite quantification and false positive rate, it meets the level 4 WHO-TDR Research Malaria Microscopy criteria. All performance parameters were significantly affected by slide quality. Further software improvement is required to improve sensitivity at low parasitaemia and parasite density estimations.Trial registration ClinicalTrials.gov number NCT03512678.

Persistence of mRNA indicative of Plasmodium falciparum ring-stage parasites 42\xa0days after artemisinin and non-artemisinin combination therapy in naturally infected Malians

BackgroundMalaria control in sub-Saharan Africa relies upon prompt case management with artemisinin-based combination therapy (ACT). Ring-stage parasite mRNA, measured by sbp1 quantitative reverse-transcriptase PCR (qRT-PCR), was previously reported to persist after ACT treatment and hypothesized to reflect temporary arrest of the growth of ring-stage parasites (dormancy) following exposure to artemisinins. Here, the persistence of ring-stage parasitaemia following ACT and non-ACT treatment was examined.MethodsSamples were used from naturally infected Malian gametocyte carriers who received dihydroartemisinin–piperaquine (DP) or sulfadoxine–pyrimethamine (SP–AQ) with or without gametocytocidal drugs. Gametocytes and ring-stage parasites were quantified by qRT-PCR during 42 days of follow-up.ResultsAt baseline, 89% (64/73) of participants had measurable ring-stage parasite mRNA. Following treatment, the proportion of ring-stage parasite-positive individuals and estimated densities declined for all four treatment groups. Ring-stage parasite prevalence and density was generally lower in arms that received DP compared to SP–AQ. This finding was most apparent days 1, 2, and 42 of follow-up (p < 0.01). Gametocytocidal drugs did not influence ring-stage parasite persistence. Ring-stage parasite density estimates on days 14 and 28 after initiation of treatment were higher among individuals who subsequently experienced recurrent parasitaemia compared to those who remained free of parasites until day 42 after initiation of treatment (pday 14 = 0.011 and pday 28 = 0.068). No association of ring-stage persistence with gametocyte carriage was observed.ConclusionsThe current findings of lower ring-stage persistence after ACT without an effect of gametocytocidal partner drugs affirms the use of sbp1 as ring-stage marker. Lower persistence of ring-stage mRNA after ACT treatment suggests the marker may not reflect dormant parasites whilst it was predictive of re-appearance of parasitaemia.

A Systematic Literature Review of Microscopy Methods Reported in Malaria Clinical Trials.

ABSTRACTMicroscopy of stained blood films is essential for the diagnosis of malaria, differentiation of parasite species, and estimation of parasite density performed for assessments of antimalarial drug efficacy. The accuracy and comparability of these measures over time and space are vital to discern the emergence or spread of antimalarial drug resistance. Although evidence-based guidelines for malaria microscopy methods exist, the age-old microscopy techniques for parasitological assessments are subject to considerable methodological variations. The purpose of this review was to explore critically how microscopy methods were reported in published malarial studies between 2013 and 2017 with the focus on outlining the methodological differences and improving reporting standards in practice.

Detection of Plasmodium species and parasite density among patients attending some selected hospitals in Skoto Metropolis

Malaria remains a major cause of mortality in developing countries; it is endemic throughout Nigeria with seasonal variation in different geographic zones of the country. More than 120 Plasmodium Species are known, but only six infect humans: P. falciparum, P. vivax P. ovale; Curtisi and willikeri, P. malariae, P. knowlesi. The aim of this study was to detect the Plasmodium species and parasite density among patient attending some selected hospitals in Sokoto metropolis. A total of 297 samples were collected and analyzed using thick and thin blood films. An overall prevalence of 28% was obtained and Plasmodium falciparum was responsible for all the cases of infection. Based on gender, prevalence rates of 57% and 43% were obtained for male and female patients respectively. The mean parasite density of 690 µ/l and 450 µ/l were obtained for male and female subjects respectively. Based on age groups, the prevalence rates of 43%, 29%, 17%, 6% and 5% were recorded for ≤14 years, 15-24 years, 25-34 year, 35-44 years and 45-54 years respectively. Statistical analysis using Pearson’s correlation showed a significant r value of 0.020 while p value was insignificant (0.731). Based on gender, a significant correlation coefficient value of 0.103 was obtained and the p value (0.76) was insignificant. This study revealed that parasite density decreases with increase in age. Females had higher parasite density than males and Plasmodium falciparum was the only specie identified. Parasite density estimation using assumed WBC count in the diagnosis of malaria is recommended.

The National External Quality Assessment Scheme for Diagnostic Medical Parasitology in the Philippines, 2009–2015

OBJECTIVE The Research Institute for Tropical Medicine (RITM)–National Reference Laboratory (NRL) for Malaria and Other Parasites, mandated by the Department of Health–Philippines (DOH), administers an annual Proficiency Test (PT) in diagnostic medical parasitology to clinical laboratories throughout the Philippines through the National External Quality Assessment Scheme (NEQAS). The PT in Parasitology aims to monitor and evaluate the capability of Philippine laboratories in the identification of blood and intestinal parasites, and the estimation of malaria parasite density in malaria-infected blood films. As of 2018, participation in the NEQAS is an annual requirement by the Department of Health–Health Facilities and Services Regulatory Bureau (DOH-HFSRB) for each clinical laboratory to obtain a license to operate. This report aims to summarize the results of the PT for Parasitology and assess the performance of participating laboratories in malaria and fecal parasite microscopy from 2009 to 2015. METHODOLOGY RITM–NRL oriented clinical laboratories in the NEQAS in 2008. Laboratories submitted their accomplished enrolment forms to RITM–NRL and paid fees to enroll in the PT in 2009 to 2015. Participating laboratories identified the species of malaria in blood films and the parasite/s in formalin-preserved fecal specimens. Estimation of parasite density in malaria blood films was performed as well. RESULTS One thousand five hundred forty laboratories participated in 2009 to 2015. Mean and median scores in all seven years were below the cut-off score of 80. Schistosoma japonicum was the most difficult to identify with only 7.7% of laboratories having correct identification result. Majority of participants in 2010 to 2014 gave malaria parasite density estimates outside the acceptable range. CONCLUSION Microscopy requires skill that is honed through training and refresher courses in order to enhance and maintain the quality of performance of laboratorians in diagnostic parasitology.

Sensitive and accurate quantification of human malaria parasites using droplet digital PCR (ddPCR)

Accurate quantification of parasite density in the human host is essential for understanding the biology and pathology of malaria. Semi-quantitative molecular methods are widely applied, but the need for an external standard curve makes it difficult to compare parasite density estimates across studies. Droplet digital PCR (ddPCR) allows direct quantification without the need for a standard curve. ddPCR was used to diagnose and quantify P. falciparum and P. vivax in clinical patients as well as in asymptomatic samples. ddPCR yielded highly reproducible measurements across the range of parasite densities observed in humans, and showed higher sensitivity than qPCR to diagnose P. falciparum, and equal sensitivity for P. vivax. Correspondence in quantification was very high (>0.95) between qPCR and ddPCR. Quantification between technical replicates by ddPCR differed 1.5–1.7-fold, compared to 2.4–6.2-fold by qPCR. ddPCR facilitates parasite quantification for studies where absolute densities are required, and will increase comparability of results reported from different laboratories.

Therapeutic enhancement of newly derived bacteriocins against Giardia lamblia

Trials for identifying efficient anti-giardial agents are still ongoing. Nowadays, bacteriocins have attracted the attention as potential antimicrobial compounds. For the first time, the current study evaluated the therapeutic efficacy of bacteriocins derived from newly isolated Egyptian strains of probiotics Lactobacilli; L. acidophilus (P106) and L. plantarum (P164) against Giardia lamblia. Bacteriocins' efficacy was evaluated both in vitro; by growth inhibition and adherence assays, and in vivo; through estimation of parasite density, intestinal histopathological examination and ultrastructural analysis of Giardia trophozoites. In vivo bacteriocins' clinical safety was assessed. In vitro results proved that 50 µg of L. acidophilus bacteriocin induced reduction of the mean Giardia lamblia trophozoites by 58.3 ± 4.04%, while at lower concentrations of 10 and 20 µg of both L. acidophilus and L. plantarum, non significant reduction of the mean parasite density was achieved. In vitro trophozoites adherence was susceptible to the tested bacteriocins at all studied concentrations with variable degrees, while the highest adherence reduction was demonstrated using 50 µg of L acidophilus bacteriocin. In vivo, oral inoculation of 50 µg/mouse L. acidophilus bacteriocin for 5 successive days resulted in a noteworthy decline of the intestinal parasite density, along with amelioration of intestinal pathology of infected mice. Ultrastructural examination proved thatfive doses of L. acidophilus bacteriocin showed marked changes in cellular architecture of the trophozoites with evident disorganization of the cell membrane, adhesive disc and cytoplasmic components. This is the first reported study of the safe anti-giardial efficacy of L. acidophilus (P106) derived bacteriocin, hence highlighting its great promise as a potential therapeutic safe alternative to existing commercial drugs.

Clinical malaria among pregnant women on combined insecticide treated nets (ITNs) and intermittent preventive treatment (IPTp) with sulphadoxine-pyrimethamine in Yaounde, Cameroon.

BackgroundMalaria remains a burden for pregnant women and the under 5. Intermittent preventive treatment of pregnant women (IPTp) for malaria with sulfadoxine – pyrimethamine (SP) has since replaced prophylaxis and legislation has been reinforced in the area of insecticide treated mosquito nets (ITNs) in Cameroon. Clinical malaria despite all these measures remains a problem. We compared the socio-obstetrical characteristics of women who developed clinical malaria and those who did not though in the same regimen.MethodsA 5 – year nested cohort study (2007 – 2011 inclusive) at the tertiary level hospitals in Yaounde. Pregnant women who willingly accepted to participate in the study were enrolled at booking and three doses of SP were administered between 18 – 20 weeks of gestation, between 26–28 weeks and between 32 – 34 weeks. Those who developed clinical malaria were considered as cases and were compared for socio – obstetrical characteristics with those who did not. Venous blood was drawn from the women in both arms for parasite density estimation and identification and all the clinical cases were treated conventionally.ResultsEach arm had 166 cases and many women who developed clinical malaria were between 15 and 19 years (OR 5.5, 95% CI 3.9 – 5.3, p < 0.001). They were of low gravidity (OR 6.5, 95% CI 3.8 – 11.3, p < 0.001) as well as low parity (OR 4.6, 95% CI 2.7 – 7.9, p < 0.001). The cases were single women (OR 4.58, 95% CI 2.54 – 8.26, p < 0.001) and had attained only primary level of education (OR 4.6, 95% CI 2.8 – 7.9, p < 0.001). Gestational ages were between 20 to 30 weeks during clinical malaria (OR 6.8, 95% CI 4.1 – 11.7, p < 0.001). The time between the first and second dose of SP was longer than ten weeks in the cases (OR 5.5, 95% CI 3.2 – 9.3, p < 0.001) and parasite density was higher also among the cases (OR 6.9, 95% CI 5.9 – 12.1, p < 0.001).ConclusionLong spacing between the first and second dose of SP seemed to be responsible for clinical malaria in the cases.

Assumed white blood cell count of 8,000 cells/μL overestimates malaria parasite density in the Brazilian Amazon.

Quantification of parasite density is an important component in the diagnosis of malaria infection. The accuracy of this estimation varies according to the method used. The aim of this study was to assess the agreement between the parasite density values obtained with the assumed value of 8,000 cells/μL and the automated WBC count. Moreover, the same comparative analysis was carried out for other assumed values of WBCs. The study was carried out in Brazil with 403 malaria patients who were infected in different endemic areas of the Brazilian Amazon. The use of a fixed WBC count of 8,000 cells/μL to quantify parasite density in malaria patients led to overestimated parasitemia and resulted in low reliability when compared to the automated WBC count. Assumed values ranging between 5,000 and 6,000 cells/μL, and 5,500 cells/μL in particular, showed higher reliability and more similar values of parasite density when compared between the 2 methods. The findings show that assumed WBC count of 5,500 cells/μL could lead to a more accurate estimation of parasite density for malaria patients in this endemic region.

Statistical properties of parasite density estimators in malaria.

Malaria is a global health problem responsible for nearly one million deaths every year around 85% of which concern children younger than five years old in Sub-Saharan Africa. In addition, around million clinical cases are declared every year. The level of infection, expressed as parasite density, is classically defined as the number of asexual parasites relative to a microliter of blood. Microscopy of Giemsa-stained thick blood films is the gold standard for parasite enumeration. Parasite density estimation methods usually involve threshold values; either the number of white blood cells counted or the number of high power fields read. However, the statistical properties of parasite density estimators generated by these methods have largely been overlooked. Here, we studied the statistical properties (mean error, coefficient of variation, false negative rates) of parasite density estimators of commonly used threshold-based counting techniques depending on variable threshold values. We also assessed the influence of the thresholds on the cost-effectiveness of parasite density estimation methods. In addition, we gave more insights on the behavior of measurement errors according to varying threshold values, and on what should be the optimal threshold values that minimize this variability.

Measuring the efficacy of anti-malarial drugs in vivo: quantitative PCR measurement of parasite clearance

BackgroundArtemisinin-based combination therapy, currently considered the therapy of choice for uncomplicated Plasmodium falciparum malaria in endemic countries, may be under threat from newly emerging parasite resistance to the artemisinin family of drugs. Studies in Southeast Asia suggest some patients exhibit an extended parasite clearance time in the three days immediately following treatment with artesunate monotherapy. This phenotype is likely to become a more important trial endpoint in studies of anti-malarial drug efficacy, but currently requires frequent, closely spaced blood sampling in hospitalized study participants, followed by quantitation of parasite density by microscopy.MethodsA simple duplex quantitative PCR method was developed in which distinct fluorescent signals are generated from the human and parasite DNA components in each blood sample. The human amplification target in this assay is the β tubulin gene, and the parasite target is the unique methionine tRNA gene (pgmet), which exhibits perfect sequence identity in all six Plasmodium species that naturally infect humans. In a small series of malaria cases treated as hospital in-patients, the abundance of pgmet DNA was estimated relative to the human DNA target in daily peripheral blood samples, and parasite clearance times calculated.ResultsThe qPCR assay was reproducibly able to replicate parasite density estimates derived from microscopy, but provided additional data by quantification of parasite density 24 hours after the last positive blood film. Robust estimates of parasite clearance times were produced for a series of patients with clinical malaria.ConclusionsLarge studies, particularly in Africa where children represent a major proportion of treated cases, will require a simpler blood sample collection regime, and a method capable of high throughput. The duplex qPCR method tested may fulfil these criteria, and should now be evaluated in such field studies.

Reliable enumeration of malaria parasites in thick blood films using digital image analysis

BackgroundQuantitation of malaria parasite density is an important component of laboratory diagnosis of malaria. Microscopy of Giemsa-stained thick blood films is the conventional method for parasite enumeration. Accurate and reproducible parasite counts are difficult to achieve, because of inherent technical limitations and human inconsistency. Inaccurate parasite density estimation may have adverse clinical and therapeutic implications for patients, and for endpoints of clinical trials of anti-malarial vaccines or drugs. Digital image analysis provides an opportunity to improve performance of parasite density quantitation.MethodsAccurate manual parasite counts were done on 497 images of a range of thick blood films with varying densities of malaria parasites, to establish a uniformly reliable standard against which to assess the digital technique. By utilizing descriptive statistical parameters of parasite size frequency distributions, particle counting algorithms of the digital image analysis programme were semi-automatically adapted to variations in parasite size, shape and staining characteristics, to produce optimum signal/noise ratios.ResultsA reliable counting process was developed that requires no operator decisions that might bias the outcome. Digital counts were highly correlated with manual counts for medium to high parasite densities, and slightly less well correlated with conventional counts. At low densities (fewer than 6 parasites per analysed image) signal/noise ratios were compromised and correlation between digital and manual counts was poor. Conventional counts were consistently lower than both digital and manual counts.ConclusionUsing open-access software and avoiding custom programming or any special operator intervention, accurate digital counts were obtained, particularly at high parasite densities that are difficult to count conventionally. The technique is potentially useful for laboratories that routinely perform malaria parasite enumeration. The requirements of a digital microscope camera, personal computer and good quality staining of slides are potentially reasonably easy to meet.

Test characteristics of two rapid antigen detection tests (SD FK50 and SD FK60) for the diagnosis of malaria in returned travellers

BackgroundTwo malaria rapid diagnostic tests were evaluated in a travel clinic setting: the SD FK50 Malaria Ag Plasmodium falciparum test (a two-band test) and the SD FK60 Malaria Ag P. falciparum/Pan test (a three-band test).MethodsA panel of stored whole blood samples (n = 452 and n = 614 for FK50 and FK60, respectively) from returned travellers was used. The reference method was microscopy with PCR in case of discordant results.ResultsFor both tests, overall sensitivity for the detection of P. falciparum was 93.5%, reaching 97.6% and 100% at parasite densities above 100 and 1,000/μl respectively. Overall sensitivities for Plasmodium vivax, Plasmodium ovale and Plasmodium malariae for the FK60 test were 87.5%, 76.3% and 45.2%, but they reached 92.6% and 90.5% for P. vivax and P. ovale at parasite densities above 500/μl. Specificities were above 95% for all species and both tests when corrected by PCR, with visible histidine-rich protein-2 lines for P. malariae (n = 3) and P. vivax and P. ovale (1 sample each). Line intensities were reproducible and correlated to parasite densities. The FK60 tests provided clues to estimate parasite densities for P. falciparum below or above 1,000/μl.ConclusionBoth the FK50 and FK60 performed well for the diagnosis of P. falciparum in the present setting, and the FK60 for the diagnosis of P. vivax and P. ovale at parasite densities > 500/μl. The potential use of the FK60 as a semi-quantitative estimation of parasite density needs to be further explored.

Evaluating parasite densities and estimation of parameters in transmission systems

Mathematical modelling of parasite transmission systems can provide useful information about host parasite interactions and biology and parasite population dynamics. In addition good predictive models may assist in designing control programmes to reduce the burden of human and animal disease. Model building is only the first part of the process. These models then need to be confronted with data to obtain parameter estimates and the accuracy of these estimates has to be evaluated. Estimation of parasite densities is central to this. Parasite density estimates can include the proportion of hosts infected with parasites (prevalence) or estimates of the parasite biomass within the host population (abundance or intensity estimates). Parasite density estimation is often complicated by highly aggregated distributions of parasites within the hosts. This causes additional challenges when calculating transmission parameters. Using Echinococcus spp. as a model organism, this manuscript gives a brief overview of the types of descriptors of parasite densities, how to estimate them and on the use of these estimates in a transmission model.

Standard white blood cell count for malaria density estimation: A need for review?

To compare the actual white blood cell (WBC) counts, used to calculate malaria parasite densities against the standard WBC counts of 8000/µl. The WBC counts of 111 Plasmodium falciparum -infected children in north central Nigeria, Aged 1-4 ( 5) years were estimated in a cross-sectional study. These gave average values of 7487/µl and 5985/µl against the assumed standard count of 8000/µl. A comparison of blood samples grouped into those with WBC counts of 8000/µl (3.95% and 8.57%), those below (57.89% and 82.86%) and above (38.16% and 8.57%) showed a significantly higher number in the group below the standard value for the two age groups (X2, df = 3, P > 0.05). This paper draws attention to the disparity between the assumed standard WBC counts and the real values encountered among Nigerian children and proposes a review for achieving more accurate malaria parasite density estimation among other reasons. To best of our knowledge, the present study is the first such report from north central Nigeria.

Comparative analysis of malaria parasite density using actual and assumed white blood cell counts

To compare malaria parasite densities, calculated using the white cell counts (WBC) of individual children with a standard WBC count of 8.0 x 10(9)/L. In a cross-sectional study, the prevalence of malaria WBCs and malaria parasite densities were estimated in 240 healthy Nigerian children aged 1-8 years. Of 240 children, 75 (31.25%) were infected with malaria, 69 (28.75%) with P. falciparum and 9 (3.75%) with other species. The mean (SD) WBC count was 5.1 (2.0) x 10(9)/L. There was an age-related significant difference in the mean WBC counts (t=2.000, p<0.05), with values higher in the under-5s [5.6 (2.0) x 10(9)/L] than in the > or =5-years group [5.0 (1.8) x 10(9)/L]. No significant difference was observed with regard to gender and malaria infection. The mean (SD) parasite densities of P. falciparum obtained using the assumed value of 8.0 x 10(9)/L [1936 (1119.5)] was significantly higher than the parasite densities estimated using the individual WBC counts [1140 (862.8) for P. falciparum] (p<0.0001). Parasite density estimation using the assumed count of 8.0 x 10(9)/L might result in over-estimation of the parasite burden. The WBCs of individual patients should always be estimated when parasite density is required.

Estimation of malaria parasite density using leukocyte counts as an index in adults volenteers of southwestern Nigeria

Leukocyte counts and screening for malaria parasites were carried out on 252 apparently healthy blood donors attending a transfusion centre in Ibadan. The leukocyte count range for the donors was 2.5-9.6 x 109 /l; the mean leukocyte count being 4.98 x 109 /l. 193 (76.6%) had leukocyte count less than 6.0 x 109 /l. Eighty-one (32.1%) of the 252 blood donors had malaria parasitaemia. There was no significant difference between the mean leukocyte count for Aparasitaemic donors (5.04 x 109 /l) and that for Parasitaemic donors (4.87 x 109 /l). Three methods (A, B and C) (A, based on true leukocyte count, B and C, based on assumed leukocyte counts of 8,000/ul and 6,000/ul respectively) were used to estimate malaria parasite density. The result of the ANOVA showed that there was no significant difference among the means of the three methods. The test for homogeneity showed a significant heterogeneity between methods A and B but homogeneity between methods A and C. Method C is a better substitute for method A than method B in the estimation of parasite density. Keywords: Adults; Asymptomatic Malaria; Parasite Density; Leukocyte counts.Ife Journal of Science Vol. 8 (2) 2006: pp. 137-139