Diagnosis Of Plasmodium Falciparum Malaria Research Articles

Investigation of the kinetics of histidine-rich protein 2 and of the antibody responses to this antigen, in a group of malaria patients from India

Although immunological tests based on the detection of histidine-rich protein 2 (HRP2) from the parasites permit the rapid diagnosis of Plasmodium falciparum malaria, such tests are not yet sufficiently sensitive to detect every bloodsmear-positive case. Some individuals infected with P. falciparum may appear test-negative because of the presence of anti-HRP2 antibodies in their sera. A longitudinal follow-up of HRP2 antigenaemia and antibody responses to this antigen has now been conducted in a group of 45, bloodsmear-positive malaria cases of various ages, both during acute infection with P. falciparum and after antimalarial treatment. Pre-treatment, 'day-0' samples of fingerprick blood were tested for HRP2 (in antigen-capture ELISA) and for antigen-specific IgM and IgG (in indirect ELISA). The patients were then treated, with standard doses of chloroquine, before being retested, for HRP2 and anti-HRP2 antibodies, on days 7, 15 and 28. The level of antigenaemia, which on day 0 was found to be positively correlated with parasitaemia (r = 0.741; P < 0.001), had only fallen by an insignificant amount by day 7 but showed further, significant falls between days 7 and 15 (P < 0.001) and between days 15 and 28 (P < 0.01). Although no significant relationship was observed between the blood concentrations of HRP2 and anti-HRP2 IgM or IgG on days 0 or 7, the level of HRP2 antigenaemia was found to be positively correlated with the concurrent titre of anti-HRP2 IgM on day 15 (r = 0.612; P < 0.001) and day 28 (r = 0.501; P < 0.001). The titres of HRP2-specific IgG gradually increased over the 28 days of follow-up but were not found to be significantly correlated with the decreasing levels of HRP2 antigenaemia. When the 45 day-0 samples of blood were tested for HRP2 in a rapid diagnostic test (RDT), three appeared negative, probably because of interference from the circulating, free, anti-HRP2 antibodies in the plasma. The three RDT-negative samples were significantly different from the 42 RDT-positive, having relatively low HRP2 antigenaemias (P < 0.001) and relatively high titres of anti-HRP2 IgM (P < 0.05) and IgG (P < 0.001). Control samples of blood, from four patients infected with P. vivax and five healthy, normal individuals, were considered ELISA-negative for HRP2 and anti-HRP2 IgM or IgG. It appears that, during human infection with P. falciparum, serum levels of HRP2 antigen remain elevated for at least 7 days post-treatment, despite the host's development of antigen-specific immune responses both before and after treatment.

USEFULNESS OF A RAPID ON-SITE PLASMODIUM FALCIPARUM DIAGNOSIS (PARACHECK® PF) IN FOREST MIGRANTS AND AMONG THE INDIGENOUS POPULATION AT THE SITE OF THEIR OCCUPATIONAL ACTIVITIES IN CENTRAL INDIA

Logistic, economic, and technical factors limit rapid access to microscopic confirmation of malaria in many tropical countries, including India. The occurrence of high-grade fever and three deaths during the hot summer months in some forest migrants created an emergency situation in Jabalpur in central India. A cheap and rapid malaria test, Paracheck Pf, was tested in this group of migrants in parallel with microscopy. The indigenous population at the site of occupational activities of these migrants approximately 250 km from Jabalpur was also screened by both methods. The results of this field investigation are very encouraging. Among migrants, the test had a sensitivity of 100% and a specificity of 67%. The positive and negative predictive values were 94% and 100%, respectively. Among indigenous population, the corresponding values were 100%, 97.3%, 98.4%, and 100%, respectively, indicating the usefulness of test as a diagnostic tool for providing on-site confirmation of symptomatic diagnosis of Plasmodium falciparum malaria.

Malaria Screening of Blood Donors in Saudi Arabia

Transfusion-associated malaria is a potentially serious complication that continues to pose risks in blood bank settings. There is a need for effective malaria screening of blood donations to improve on the current exclusion policies of potentially infected carriers on the basis of clinical and travel history. We evaluated the potential usefulness of ELISA screening for malaria antibody and P. falciparum antigen among Saudi blood donors. A total of 1756 donors were studied, 1100 from the malaria endemic Southern Region and 656 donors from the known malaria-free Riyadh area. The overall antibody prevalence for the antibody was 7.6%, in comparison to only 0.17% for the antigen. In the endemic region, the antibody positivity rate of 9.1% was almost double the rate in the non-endemic area (4.8%). There was no difference in the antigen prevalence rates; 0.18% in endemic and 0.15% in nonendemic areas. In malaria endemic countries like Saudi Arabia, excluding antibody-positive donations would result in too much wastage of blood units. However, antigen malaria testing appears to offer a potential utility, as only few donations would be rejected.

Validity, reliability and ease of use in the field of five rapid tests for the diagnosis of Plasmodium falciparum malaria in Uganda

A study was conducted to measure the overall performance of several rapid diagnostic tests for Plasmodium falciparum infection, in order to select the most appropriate test to be used in the field. A total of 742 patients attending the out-patient department of Mbarara Hospital with a clinical suspicion of malaria were included in the study. For each patient, a thick/thin film and 5 rapid tests based on the detection of histidine-rich protein II (HRP-II) (Paracheck Pf dipstick and device, ParaHIT f, Malaria Rapid and BIO P.F.) were performed. Outcomes were validity, inter-reader reliability and ‘ease of use in the field’, measured by both the general characteristics of the test and by the opinion of the readers. About half (57%) of the patients were positive for P. falciparum. The Paracheck Pf (dipstick and device) was considered as the most appropriate for the use in the field, being sensitive (97%), moderately specific (88%), reliable (kappa coefficient = 0·97), easy to use and cheap (about US$ 0.5/test). The ParaHIT f represented a good alternative.

Field evaluation of a rapid immunochromatographic test 'Parachek-F' in a post-monsoon Plasmodium falciparum malaria outbreak in villages of South India.

An indigenous rapid immunochromatographic test Parachek-F for diagnosis of Plasmodium falciparum malaria was evaluated by the field staff in a post-monsoon P. falciparum malaria outbreak in villages of district Raichur, Karnataka, South India in November 1999. The test functions based on dipstick P. falciparum histidine rich protein-2 (PfHRP-2) antigen capture assay. Of the 232 uncomplicated clinically diagnosed malaria cases, 158 (68.1%) were positive for malaria by microscopy of JSB-stained thick blood smears. Of these, 13 were infected with P. vivax, 140 with P. falciparum and 5 had mixed infections of P. vivax and P. falciparum. Malaria patients were treated with age-specific oral doses of quinine followed by primaquine. Taking microscopy as gold standard, Parachek-F detected PfHRP-2 antigen in 136 samples (ratio 0.93) and was 93.1% sensitive and 98.8% specific. Positive predictive value, negative predictive value and efficacy were 99.2%, 89.6% and 95.2% respectively. No cross reactivity was observed with P. vivax infection. False negative interpretation was associated in 40% (10/25) lower-grade parasitaemias (parasitaemia <100/p/ blood) where sensitivity was only 60%. False positive result was associated in 1 case (1/74). Cases showing false negative results had taken presumptive treatment with chloroquine prior to the test. Careful microscopical examination on thin smears of such cases demonstrated that the morphology of the parasites was abnormal and distorted indicating the parasites were affected by chloroquine. The possible role of chloroquine resulting false negative results is suggested in this communication. Positive correlation between test bands intensity and parasite density was observed (r=0.137; P<0.05). The test is indigenously developed, rapid, simple in its application and was found suitable for field condition. Parameters like patients' conditions, history of drug intake, morphology of parasites at different developmental stages are to be considered for evaluation of such tests.

Evaluation of a colorimetric PCR-based assay to diagnose Plasmodium falciparum malaria in travelers.

New diagnostic tests are needed to facilitate the diagnosis of Plasmodium falciparum malaria in the returned traveler. We performed a blinded evaluation of a nonisotopic colorimetric PCR-based assay (Digene SHARP Signal System) and compared the results with those obtained by microscopy and nested PCR for the detection of P. falciparum malaria in 150 febrile travelers. By using nested PCR as the reference standard, the colorimetric assay had a sensitivity of 100% and a specificity of 95.4% for the detection of P. falciparum. This PCR-based nonisotopic assay is a rapid, sensitive, and specific method for the detection of falciparum malaria in returned travelers.

Comparison of the ParaSight ™-F test and the ICT Malaria Pf ™ test with the polymerase chain reaction for the diagnosis of Plasmodium falciparum malaria in travellers

Rapid and accurate methods are needed for the diagnosis of imported malaria. The ParaSight ™-F test and the ICT Malaria Pf ™ test are commercially available kits marketed for the diagnosis of Plasmodium falciparum malaria. Both tests are antigen-capture assays based on the detection of P. falciparum histidinerich protein 2 in peripheral blood. Using microscopy and a polymerase chain reaction (PCR)-based method as reference standards, we performed a ‘blinded’ comparison of these assays for the detection of P. falciparum infection in 200 febrile travellers returning from malaria-endemic areas. As determined by PCR and microscopy, 148 travellers had malaria and, of these patients, 54·7% ( 81 148 ) were infected with P. vivax only, 31·1% ( 46 148 ) with P. falciparum only, 9·5% ( 14 148 ) with P. ovale, 0·7% ( 1 148 ) with P.malariae, and 4·1% ( 6 148 ) had mixed infections. Compared to PCR, the ParaSight ™-F and ICT Malaria Pf ™ tests had initial sensitivities of 94% and 90% and specificities of 95% and 97%, respectively, for the detection of P. falciparum malaria. When discrepant samples were retested with day 0 and day 1 bloods, the sensitivities improved to 96% and 94%, respectively. The 2 remaining false negative results with the Para-Sight ™-F test and 2 of the 3 false negative results with the ICT Malaria Pf ™ test occurred in samples with <100 parasites/μL. The performance of these kits was not significantly different ( P = 0.75) and both are simple, rapid, and accurate tests for the detection of P. falciparum infection in the returned traveller.

Trial of the ParaSight-F test for malaria diagnosis in the primary health care system, Zimbabwe.

Rapid diagnosis of Plasmodium falciparum malaria remains one of the main limitations to prompt treatment. Diagnosis based on clinical symptoms is decidedly unreliable, especially in areas of seasonal transmission like Zimbabwe. In view of this, the Plasmodium falciparum histidine rich protein (HRP-II) antigen detection assay (ParaSight-F test) was tried at 10 health centres in 3 malaria endemicity zones of Zimbabwe, as a malaria diagnostic tool for primary health care. Parasitological evaluations were conducted using thick and thin film microscopy as gold standard, and ease of test operation and practicability to nurses were ascertained by questionnaire. The sensitivity of the test did not vary substantially by endemicity zone and was approximately 93%. Specificities were 85, 72 and 92% in the hyperendemic, mesoendemic and hypoendemic zones, respectively. Positive predictive values varied considerably with endemicity, the lowest being in the hypoendemic zone (56%). However, negative predictive values did not change significantly, with a mean of 94%. It was found that the ParaSight-F test reduced mistreatment for malaria, relative to clinical diagnosis, by up to 81%, especially in the hypoendemic region. Test acceptability evaluations were good.

Malaria diagnosis: standardization of a polymerase chain reaction for the detection of Plasmodium falciparum parasites in individuals with low-grade parasitemia.

In Brazil, no study has been done concerning the detection of malaria parasites by polymerase chain reaction (PCR) related to the diagnosis of Plasmodium falciparum malaria. In the present report we describe a highly sensitive methodology for malaria diagnosis using a nested PCR method based on amplification of the p126 P. falciparum gene detected by simple ethidium bromide staining. The P. falciparum Palo Alto strain (culture samples) was serially diluted in blood from an uninfected donor to a final level of parasitemia corresponding to 10(-8)% and was processed for PCR amplification. In each of these dilutions a parasitological examination was performed to compare the sensitivity with that of PCR amplification. Blood samples (field samples) were obtained from 51 malarious patients with positive thick blood smears (TBS) who were living in endemic regions of the Brazilian Amazon. They corresponded to 42 P. falciparum and 9 P. vivax cases, with parasitemia levels ranging from only 16 to 20,200 parasites/microliter for P. falciparum disease and from 114 to 11,000 parasites/microliter for P. vivax malaria. We demonstrate that the use of nested PCR allows the detection of 0.005 parasites/microliter without the use of radioactive material. The use of a 1-ml sample volume and the organic DNA extraction method should be suitable in blood banks and for the evaluation of patients during and after drug treatment.

Simple method for diagnosis of Plasmodium falciparum malaria by polymerase chain reaction from dried blood spot samples

Simple method for diagnosis of Plasmodium falciparum malaria by polymerase chain reaction from dried blood spot samples

Malaria: overview and update.

Each year 1,000 imported cases of malaria are reported in the United States, and several thousand such cases are reported in Europe. Delays in the diagnosis of Plasmodium falciparum malaria have resulted in death in some of the cases. Unfortunately, many travelers to malarious regions either are provided with inadequate or incorrect advice on measures for preventing malaria or fail to follow correct advice, which puts them at risk for acquiring malaria. These facts underscore the need to periodically review some of the salient points about the diagnosis, treatment, and prevention of this disease.

Choice of therapy for imported cases of falciparum malaria in children: a retrospective study of 100 cases seen in Marseilles, France

We have carried out a retrospective study on 100 children in hospital in Marseilles, France with a diagnosis of Plasmodium falciparum malaria. On admission, the main clinical features were anaemia (90 cases), fever (83 cases, >40 °C in 22 cases), hepatomegaly (44 cases), vomiting (29 cases), neurological signs (22 cases), thrombocytopenia (13 cases), hyperparasitaemia (6 cases), jaundice (4 cases), shock (1 case) and hypoglycaemia (1 case). Severe malaria, as defined by the World Health Organization Malaria Action Programme, was rare in our study (only 2 cases) and the prognosis was good (no death, no sequela). The search for neurological signs such as impaired consciousness, prostration or convulsions is an effective and simple way to diagnose potentially severe cases. In the presence of these signs, intravenous quinine treatment resulted in a shortened duration of fever (30 h instead of 63 h) and thereby avoided patients becoming worse. In children without neurological signs or persistent vomiting, oral therapy may be used even if there is high fever or hyperparasitaemia, but close surveillance is required. Patients treated with halofantrine or mefloquine had a shorter stay in hospital than those treated with chloroquine (mean = 4 d instead of 5·7 d). The resistance of some strains to chloroquine may explain this difference.