New strategies for the diagnosis and screening of malaria

Evidence of asymptomatic submicroscopic malaria in low transmission areas in Belaga district, Kapit division, Sarawak, Malaysia

BACKGROUND

Malaysia has declared its aim to eliminate malaria with a goal of achieving zero local transmission by the year 2020. However, targeting the human reservoir of infection, including those with asymptomatic infection is required to achieve malaria elimination. Diagnosing asymptomatic malaria is not as straightforward due to the obvious lack of clinical manifestations and often subpatent level of parasites. Accurate diagnosis of malaria is important for providing realistic estimates of malaria burden and preventing misinformed interventions. Low levels of parasitaemia acts as silent reservoir of transmission thus remains infectious to susceptible mosquito vectors. Hence, the aim of this study is to investigate the prevalence of asymptomatic submicroscopic malaria (SMM) in the District of Belaga, Sarawak.

METHODS

In 2013, a total of 1744 dried blood spots (DBS) were obtained from residents of 8 longhouses who appeared healthy. Subsequently, 251 venous blood samples were collected from residents of 2 localities in 2014 based on the highest number of submicroscopic cases from prior findings. Thin and thick blood films were prepared from blood obtained from all participants in this study. Microscopic examination were carried out on all samples and a nested and nested multiplex PCR were performed on samples collected in 2013 and 2014 respectively.

RESULTS

No malaria parasites were detected in all the Giemsa-stained blood films. However, of the 1744 samples, 29 (1.7%) were positive for Plasmodium vivax by PCR. Additionally, of the 251 samples, the most prevalent mono-infection detected by PCR was Plasmodium falciparum 50 (20%), followed by P. vivax 39 (16%), P. knowlesi 9 (4%), and mixed infections 20 (8%).

CONCLUSIONS

This research findings conclude evidence of Plasmodium by PCR, among samples previously undetectable by routine blood film microscopic examination, in local ethnic minority who are clinically healthy. SMM in Belaga district is attributed not only to P. vivax, but also to P. falciparum and P. knowlesi. In complementing efforts of programme managers, there is a need to increase surveillance for SMM nationwide to estimate the degree of SMM that warrant measures to block new transmission of malaria.

A 4-Day Incubation Period of Plasmodium falciparum Infection in a Nonimmune Patient in Ghana: A Case Report

Plasmodium falciparum can cause severe infection and has the shortest incubation period compared with all the other Plasmodium species. Incubation periods of 9–14 days for the immune and 6–14 days for the nonimmune have been reported for P. falciparum. However, an incubation period of less than 5 days has not been reported, as of yet. This report presents a case of a 23-year-old nonimmune female who presented with signs and symptoms 4 days after being bitten by mosquitoes while visiting Ghana. The patient was successfully treated with a 1-day course of parenteral artesunate, followed by a 3-day course of oral artemisinin combination therapy.

Field application of SD bioline malaria Ag Pf/Pan rapid diagnostic test for malaria in Greece

Greece, a malaria-free country since 1974, has experienced re-emergence of Plasmodium vivax autochthonous malaria cases in some agriculture areas over the last three years. In early 2012, an integrated control programme (MALWEST Project) was launched in order to prevent re-establishment of the disease. In the context of this project, the rapid diagnostic tests (RDT) of SD Bioline Malaria Ag Pf/Pan that detects hrp-2 and pan-LDH antigens were used. The aim of this study was to assess the field application of the RDT for the P. vivax diagnosis in comparison to light microscopy and polymerase chain reaction (PCR). A total of 955 samples were tested with all three diagnostic tools. Agreement of RDT against microscopy and PCR for the diagnosis of P. vivax was satisfactory (K value: 0.849 and 0.976, respectively). The sensitivity, specificity and positive predictive value of RDT against PCR was 95.6% (95% C.I.: 84.8-99.3), 100% (95% C.I.: 99.6-100.0) and 100% (95% CI: 91.7-100.0) respectively, while the sensitivity, specificity and positive predictive value of RDT against microscopic examination was 97.4% (95% C.I.: 86.1-99.6), 99.4% (95% C.I.: 98.6-99.8) and 86.1% (95% CI: 72.1-94.7), respectively. Our results indicate that RDT performed satisfactory in a non-endemic country and therefore is recommended for malaria diagnosis, especially in areas where health professionals lack experience on light microscopy.

Quality and reliability of current malaria diagnostic methods

Malaria is a life threatening disease with a major impact on global health. The WHO declared an early diagnosis as one of the most important steps to fight the disease. The quality and the reliability of test results depend on the diagnostic tools used. Not every test meets the needs in every situation. PCR tests have the best sensitivity and specifity but are not as rapid as other tests and also due to the costs not available everywhere. The 'gold standard' method is to check stained blood slides, thick films require experienced persons to obtain correct results. So-called rapid tests are only additional tools no matter whether they are based on the detection of antigens, enzymes or plasmodial DNA by fluorescent staining. Some other blood bound markers may also provide a hint but are no sufficient tool for malaria diagnosis.

Molecular test for vivax malaria with loop-mediated isothermal amplification method in central China

Vivax malaria has the highest incidence in central China. High-throughput and cost-effective testing methods are essential for vivax malaria diagnosis in this area. Loop-mediated isothermal amplification (LAMP) is an established nucleic acid amplification method, which provides a promising platform for the molecular detection of malaria parasites in development countries. This study was performed to compare the LAMP method, the nested PCR-based method, and microscopic examinations in diagnosing vivax malaria. LAMP detected vivax malaria parasites in 160 of 164 microscopically positive samples (sensitivity, 97.6%), whereas nested PCR detected Plasmodium vivax in 162 of 164 samples (sensitivity, 98.8%). No false-positive results were obtained by LAMP or nested PCR among fever-positive and healthy samples. The sensitivities and specificities of the two molecular tests were consistently high. In addition, the reproducibility of the LAMP assays using water bath, which reduced the cost substantially. LAMP method is an accurate, rapid, simple, and cost-effective method that may be useful for diagnosis in field diagnoses instead of nested PCR. This method is feasible to diagnose vivax malaria parasite in endemic areas of central China.

Monitoring malaria control in Khammouane province, Laos: an active case detection survey of Plasmodium falciparum malaria using the Paracheck rapid diagnostic test

In Khammouane province, Laos, over 5000 slide-positive malaria cases were reported at local health facilities in 1997. To combat the spread of malaria, insecticide-treated nets (ITNs) and community health education were provided to the people in this province by the Lao Ministry of Health and the Japan International Cooperation Agency. In order to document the current malaria situation, an active case detection (ACD) survey using rapid diagnostic tests was conducted at 23 sites from June to July, the rainy season, in 2005. A total of 1711 villagers from 403 households participated in the survey. The proportion of positive cases was 0.7% (12/1711) with a range in each village of 0-8.2%. The low infection rate observed in this ACD survey was consistent with the decrease in the number of slide-positive malaria cases at local health facilities (from over 5000 cases to 536 cases), indicating the substantial progress made in malaria control. Although the reduction of malaria cases can be attributed to multiple factors, continued promotion of the proper use of ITNs as well as community-based testing and treatment services, especially in remote areas, may lead to a further reduction of malaria cases in the province.

Evaluation of a real-time PCR assay for malaria diagnosis in patients from Vietnam and in returned travellers

Real-time PCR diagnosis of malaria has advantages over traditional microscopic methods, especially when parasitaemia is low and when dealing with mixed infections. We have developed a new real-time PCR with specific genes in each Plasmodium species present only in one copy to identify the four pathogenic Plasmodium spp. for humans. The sensitivity was less than 25 parasites/microl. No cross-hybridisation was observed with human DNA or among the four Plasmodium spp. Using LightCycler PCR and conventional microscopy, we compared the diagnosis of malaria in patients from Vietnam and in returned European travellers with suspicion of malaria. In patients from Vietnam with suspicion of malaria, one mixed infection was observed by PCR only; the remaining data (54 of 55 patients) correlated with microscopy. In 79 patients without symptoms, low parasitaemia was detected in 7 samples by microscopy and in 16 samples by PCR. In returned travellers, PCR results were correlated with microscopy for all four species in 48 of 56 samples. The eight discrepant results were resolved in favour of real-time PCR diagnosis. This new real-time PCR is a rapid, accurate and efficient method for malaria diagnosis in returned travellers as well as for epidemiological studies or antimalarial efficiency trials in the field.

[Transfusion-transmitted malaria, preventive measures]

Malaria is a blood parasitic disease in the first place among the most prevalent communicable infectious diseases over the world, which leads to an increased risk of transfusion transmitted malaria. Preventive measures have been undertaken to screen blood donors such as discarding red cell donations according to the medical history, travel history and detection of malarial antibodies. However, these measures may be not sufficient and reliable to avoid the risk of transmission. Preliminary data indicates that combination of travel history, detection of malarial antibodies and antigens by commercialized kits adapted to blood transfusion centres either in endemic or non endemic areas may improve malaria transfusion risk management.

Real-time PCR for detection and identification of Plasmodium spp

Rapid and accurate detection of malaria parasites in blood is needed to institute proper therapy. We developed and used a real-time PCR assay to detect and distinguish four Plasmodium spp. that cause human disease by using a single amplification reaction and melting curve analysis. Consensus primers were used to amplify a species-specific region of the multicopy 18S rRNA gene, and SYBR Green was used for detection in a LightCycler instrument. Patient specimens infected at 0.01 to 0.02% parasitemia densities were detected, and analytical sensitivity was estimated to be 0.2 genome equivalent per reaction. Melting curve analysis based on nucleotide variations within the amplicons provided a basis for accurate differentiation of Plasmodium falciparum, P. vivax, P. ovale, and P. malariae. For assay validation, 358 patient blood samples from the National University Hospital in Singapore and Evanston Northwestern Healthcare in Illinois were analyzed. Of 76 blinded patient samples with a microscopic diagnosis of P. falciparum, P. vivax, or P. ovale infection, 74 (97.4%) were detected by real-time PCR, including three specimens containing mixed P. falciparum-P. vivax infections. No Plasmodium DNA was amplified in any of the 82 specimens sent for malaria testing but that were microscopically negative for Plasmodium infection. In addition, 200 blood samples from patients whose blood was collected for reasons other than malaria testing were also determined to be negative by real-time PCR. Real-time PCR with melting curve analysis could be a rapid and objective supplement to the examination of Giemsa-stained blood smears and may replace microscopy following further validation.

Comparison of blood smear, antigen detection, and nested-PCR methods for screening refugees from regions where malaria is endemic after a malaria outbreak in Quebec, Canada

The importation of malaria into a region where it is not endemic raises many concerns, including the timely delivery of appropriate care, safety of the blood supply, and the risk of autochthonous transmission. There is presently no consensus on the best way to screen mobile populations for malaria. Between August 2000 and March 2001, 535 refugees arrived in Quebec, Canada, from Tanzanian camps. Within 4 weeks of resettlement of the first group of 224, the McGill University Centre for Tropical Diseases noted an outbreak of malaria across the province (15 cases over a 3-week period). This group (group 1) was traced and screened for malaria between 3 and 4 months after arrival in Canada. Subsequent groups of 106 and 205 refugees were screened immediately upon arrival in Canada (group 2) and immediately prior to their departure from refugee camps (group 3), respectively. A single EDTA-blood sample was obtained from 521 refugees for testing by thick and thin blood smears (groups 1 and 2), antigen detection (ICT Malaria Pf and OptiMAL; group 1 only), and nested PCR (all groups). Overall, 98 of 521 refugees were found to be infected (18.8%). The vast majority of infections (81 of 98) were caused by Plasmodium falciparum alone. Using PCR as the "gold standard," both microscopy (sensitivity, 50%; specificity, 100%) and antigen detection (ICT sensitivity, 37.5%; ICT specificity, 100%; OptiMAL sensitivity, 29.1%; OptiMAL specificity, 95.6%) performed poorly. None of the PCR-positive subjects were symptomatic at the time of testing, and only two had recently had symptoms compatible with malaria (with or without diagnosis and treatment). Active surveillance of migrants from regions of intense malaria transmission can reduce the risk of morbidity in the migrant population and mitigate against transmission to the host population. Our data demonstrate that PCR is, by far, the most powerful tool for such surveillance.

Evaluation of the RealArt Malaria LC real-time PCR assay for malaria diagnosis

PCR-based methods have advantages over traditional microscopic methods for the diagnosis of malaria, especially in cases of low parasitemia and mixed infections. However, current PCR-based assays are often labor-intensive and not readily quantifiable and have the potential for contamination due to a requirement for postamplification sample handling. Real-time PCR can address these limitations. This study evaluated the performance characteristics of a commercial malaria real-time PCR assay (RealArt Malaria LC Assay; Artus GmbH, Hamburg, Germany) on the LightCycler platform for the detection of malaria parasites in 259 febrile returned travelers. Compared to nested PCR as the reference standard, the real-time assay had a sensitivity of 99.5%, specificity of 100%, positive predictive value of 100%, and negative predictive value of 99.6% for the detection of malaria. Our results indicate that the RealArt assay is a rapid (<45 min), sensitive, and specific method for the detection of malaria in returned travelers.

Clinical review: Severe malaria

Malaria represents a medical emergency because it may rapidly progress to complications and death without prompt and appropriate treatment. Severe malaria is almost exclusively caused by Plasmodium falciparum. The incidence of imported malaria is increasing and the case fatality rate remains high despite progress in intensive care and antimalarial treatment. Clinical deterioration usually appears 3-7 days after onset of fever. Complications involve the nervous, respiratory, renal, and/or hematopoietic systems. Metabolic acidosis and hypoglycemia are common systemic complications. Intravenous quinine and quinidine are the most widely used drugs in the initial treatment of severe falciparum malaria, whereas artemisinin derivatives are currently recommended for quinine-resistant cases. As soon as the patient is clinically stable and able to swallow, oral treatment should be given. The intravascular volume should be maintained at the lowest level sufficient for adequate systemic perfusion to prevent development of acute respiratory distress syndrome. Renal replacement therapy should be initiated early. Exchange blood transfusion has been suggested for the treatment of patients with severe malaria and high parasitemia. For early diagnosis, it is paramount to consider malaria in every febrile patient with a history of travel in an area endemic for malaria.