Craig, M. H. & Sharp, B. L. Comparative evaluation of four techniques for the diagnosis of Plasmodium falciparum infections. Trans. R. Soc. Trop. Med. Hyg. 91, 279-282
Four diagnostic techniques for Plasmodium falciparum infection were evaluated against serial parasite dilutions and on identical field samples. These were (i) Giemsa-stained
thick blood films (GTF), (ii) acridine orange-stained thick (AOTF) and thin (AOTnF) blood films, (iii) the quantitative buffy
coat technique (QBC®); and (iv) the ParaSight TM-F dipstick test (PS). PS had a consistently higher sensitivity and speed, was easiest to learn, and required no laboratory
facility. The 100% sensitivity cut-off points against known parasite densities (per mm3) were: PS, 30; GTF, 84; QBC®, 84; AOTnF, 84; AOTF, 149. In the field study, test sensitivities compared with examination of 800 microscope fields of a
Giemsa-stained thin blood film were PS, 96·6%; AOTF, 93·1%; GTF, 91·4%; QBC®, 89·7%; AOTnF, 82·8%. In the dilution study, one false positive result was recorded with QBC®; in the field study there was one false positive each with PS, AOTnF and AOTF. When a newly trained microscopist examined
samples of the parasite dilutions, the 100% sensitivity cut-off points were AOTF, 84; GTF, 140; QBC®, 390. Total handling time was shortest with PS regardless of whether samples were processed individually or in batches of
10 or 100. The ParaSightTM-F test is recommended as the diagnostic tool for the future.
Available from: Christine Manyando
- "The over-prescription pattern found in Chibombo and the RDT compared to microscopy discrepancies reported in Chipata (based on microscopy and RDT performance as validated by other studies [9,26,27]) may indicate a need for further orientation of the clinicians and laboratory technicians in Chibombo and Chipata, respectively. "
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In Zambia, there has been a large scaling up of interventions to control malaria in recent years including the deployment of rapid diagnostic tests (RDTs) to improve malaria surveillance data as well as guide malaria treatment in health facilities. The practical challenge is the impact of RDT results on subsequent management of patients. This study explored the role of RDTs in malaria diagnosis and the health workers’ adherence to test results.
An observational prospective study was carried out at health centres in four districts, namely Chibombo, Chingola, Chipata, and Choma. Children under the age of five years with history of fever were recruited and the clinicians’ use of RDT results was observed to establish whether prescriptions were issued prior to the availability of parasitological results or after, and whether RDT results influenced their prescriptions.
Of the 2, 393 recruited children, 2, 264 had both RDT and microscopic results. Two in three (68.6%) children were treated with anti-malarials despite negative RDT results and almost half (46.2%) of these were prescribed Coartem®. Only 465 (19.4%) of the 2,393 children were prescribed drugs before receiving laboratory results. A total of 76.5% children were prescribed drugs after laboratory results. Children with RDT positive results were 2.66 (95% CI (2.00, 3.55)) times more likely to be prescribed anti-malarial drugs. Children who presented with fever at admission (although history of fever or presence of fever at admission was an entry criterion) were 42% less likely to be prescribed an anti-malarial drug compared to children who had no fever (AOR = 0.58; 95% CI (0.52, 0.65)). It was noted that proportions of children who were RDT- and microscopy-positive significantly declined over the years from 2005 to 2008.
RDTs may contribute to treatment of febrile illness by confirming malaria cases from non-malaria cases in children under the age of five. However, the adherence of the health workers to prescribing anti-malarials to only RDT-positive cases at health facility level will still require to be explored further as their role is crucial in more precise reporting of malaria cases in this era towards malaria elimination as the target.
Available from: Seyed Mahmoud Sadjjadi
- "Gold standard diagnostic method of malaria is based on microscopic examination. Since the microscopic observation of malaria parasites is difficult in low parasitemia blood smears   and it leads to some problems in the output of epidemiological studies; using molecular techniques such as PCR, which has proved more sensitive and specific than microscopic evaluation, can help to detect infection in patients with low level of parasites and mixed infections [7– 11]. Furthermore, molecular characterization of parasites can be used for any survey on drug resistance, pathogenicity, and molecular epidemiology. "
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ABSTRACT: Despite malaria control programs in recent years, malaria transmission has not been eliminated in Iran. Molecular techniques including PCR, which has proved more sensitive and specific than microscopic examination methods, help to detect infection in low levels of parasitemia and mixed infections. Main our objectives were setting up nested PCR for detection of malaria and evaluating PCR based on plasmodia DNA from blood smears in Fars province, the comparison of this method with traditional microscopy and also evaluate the data in comparison with its neighboring province, Hormozgan. A total of 149 malaria positive samples including 116, 19, and 14 samples from Shiraz, Jask, and Lengeh ports were utilized in this study, respectively. Blood slides were prepared for microscopic observation. DNA from thin smears was extracted and nested PCR was analyzed using rPLU5 and rPLU6 for genus specification, rFAL1, rFAL2, and rVIV1, rVIV2 for P. falciparum and P. vivax detection, respectively. The results showed that 126 (84.6%), 16 (10.7%), and 7 (4.7%) out of 149 cases were positive for P. vivax, P. falciparum, and mixed infections, respectively, by microscopy. The PCR indicated that 95 (63.7%), 15 (10.1%), and 22 (14.8%) cases were infected with P. vivax, P. falciparum, and mixed mentioned species, respectively, and 17 (11.4%) cases were uninfected. Our results confirmed the considerable sensitivity of nested PCR for detection of the mixed infections. Simultaneous application of PCR even based on microscopy slides can facilitate access to the highest level of confidence in malaria researches.
Available from: Mahamadou Diakite
- "Parasite density estimation is highly valuable for the clinician, as it is an important determinant of treatment schedules for P. falciparum. If parasite density exceeds 10% in P. falciparum, exchange transfusion may be indicated [14,15]. A variety of studies have clearly demonstrated that microscopic diagnosis of malaria can vary greatly in its accuracy, particularly at low parasitaemia rates [12,16,17]. "
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ABSTRACT: Recent developments in diagnostic techniques for malaria, particularly DNA probes and sero-immunology, have raised questions as to how these techniques might be used to facilitate malaria diagnosis at the most peripheral levels of the primary health care system. At present, malaria diagnosis is based on the standard microscopic examination of blood films in most field epidemiologic studies and is likely to remain so in the immediate future in Africa. The objective of this study was to assess inter-observer agreement for the examination of Giemsa-stained slides for Plasmodium falciparum parasites.
Children aged 0 to 10 years were enrolled yearly in Bancoumana village (West Africa), mainly during the transmission season (June to October). The blood smears obtained from the persistently negative children in June 1996, August 1996, October 1996 and March 1997 were systematically re-examined. A stratified random sample (10%) proportional to the following parasite density classes 1--100, 101--5000, and 5001 and over was taken from the slides collected. The kappa statistics and the intra-class correlation were used as measures of agreement the first and the second slide examinations.
The weighted kappa statistic, widely used as a chance-corrected measure for nominal agreement, showed excellent inter-observer agreement (kappaw=0.7926; 95% CI [0.7588, 0.8263]; p=0.01). The intra-class correlation co-efficient had the same value of 0.7926 confirming the appropriateness of the weighted kappa statistic. Inter-observer agreement for slides read as negative by one observer, or as containing more than 100 parasites per mul, was excellent: 97% (493/506) and 92% (145/158), respectively. In contrast, the inter-observer agreement for slides read by one observer as containing 1--100 parasites/mul was poor, 36% (96/268).
In field conditions in Mali, there was a high reproducibility for slides reported as negative or as having more than 100 parasites per mul. However, smears with readings of 1--100 parasites per mul were less reproducible and should be re-examined carefully.
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