Real-time PCR versus conventional PCR for malaria parasite detection in low-grade parasitemia

Molecular test for screening malaria-infected blood donors to maximise recipient safety in Acre State, a Brazilian endemic area

BACKGROUND

Although blood transfusion is an essential therapeutic procedure, it can present risks, including transmitting infectious diseases, such as malaria. In Acre, the thick blood smear microscopic examination (TBS) is used to screen infected malaria blood donors. However, TBS has low sensitivity for detecting Plasmodium in situations of low parasitaemia, such as those presented by asymptomatic clinically healthy individuals.

OBJECTIVES

To investigate the pertinence of using polymerase chain reaction (PCR) to detect malarial infection for screening blood donors in Cruzeiro do Sul, Acre, an endemic high-risk malaria area in the Legal Amazon.

METHODS

A cross-sectional study was conducted among individuals eligible and ineligible to be blood donors, according to clinical and epidemiological criteria. Besides the mandatory screening of HCV, HBV, and HIV tests, malaria PCR and TBS were also carried out on all blood donor candidates who attended the Cruzeiro do Sul Blood Centre from July to September 2022.

FINDINGS

Of the 230 participants, 209 (91%) were eligible for blood donation by clinical-epidemiological screening. Surprisingly, no blood donor candidate reported a history of malaria. All TBS microscopic tests were negative at the time of recruitment. However, samples from four blood donor candidates (two eligible by clinical and epidemiological malaria criteria and two ineligible by hypertension and recent tattoo) were positive by Plasmodium and P. vivax molecular tests.

MAIN CONCLUSIONS

Malaria molecular techniques for screening blood donors should be introduced in the Brazilian Blood Centres to maximise recipient safety. Furthermore, selecting zero-risk donors could pave the way to build a transmissible malaria-free environment in the blood bank context in the near future.

Are pvcrt-o and pvmdr1 Gene Mutations Associated with Plasmodium vivax Chloroquine-Resistant Parasites?

(1) Background: Malaria remains a significant global public health issue. Since parasites quickly became resistant to most of the available antimalarial drugs, treatment effectiveness must be constantly monitored. In Brazil, up to 10% of cases of vivax malaria resistant to chloroquine (CQ) have been registered. Unlike P. falciparum, there are no definitive molecular markers for the chemoresistance of P. vivax to CQ. This work aimed to investigate whether polymorphisms in the pvcrt-o and pvmdr1 genes could be used as markers for assessing its resistance to CQ. (2) Methods: A total of 130 samples from P. vivax malaria cases with no clinical and/or parasitological evidence of CQ resistance were studied through polymerase chain reaction for gene amplification followed by target DNA sequencing. (3) Results: In the pvcrt-o exons, the K10 insert was present in 14% of the isolates. Regarding pvmdr1, T958M and F1076L haplotypes showed frequencies of 95% and 3%, respectively, while the SNP Y976F was not detected. (4) Conclusions: Since K10-pvcrt-o and F1076L/T958M-pvmdr1 polymorphisms were detected in samples from patients who responded well to CQ treatment, it can be concluded that mutations in these genes do not seem to have a potential for association with the phenotype of CQ resistance.

Validation of a novel FRET real-time PCR assay for simultaneous quantitative detection and discrimination of human Plasmodium parasites

Increasing numbers of travelers returning from endemic areas, migrants, and refugees have led to a significant rise in the number of imported malaria cases in non-endemic countries. Real- time PCR serves as an excellent diagnostic tool, especially in regions where experience in microscopy is limited. A novel fluorescence resonance energy transfer-based real-time PCR (FRET-qPCR) was developed and evaluated using 56 reference samples of the United Kingdom National External Quality Assessment Service (UK NEQAS) for molecular detection of malaria, including P. falciparum, P. vivax, P. ovale, P. malariae, and P. knowlesi. Species identification is based on single nucleotide polymorphisms (SNPs) within the genome where the MalLC640 probe binds, lowering the melting temperature in the melting curve analysis. The novel FRET-qPCR achieved 100% (n = 56) correct results, compared to 96.43% performing nested PCR. The high sensitivity, with a calculated limit of detection of 199.97 parasites/mL blood for P. falciparum, is a significant advantage, especially if low-level parasitemia has to be ruled out. Even mixed infections of P. falciparum with P. vivax or P. ovale, respectively, were detected. In contrast to many other real-time PCR protocols, this novel FRET-qPCR allows the quantitative and species-specific detection of Plasmodium spp. in one single run. Solely, P. knowlesi was detected but could not be differentiated from P. vivax. The turnaround time of this novel FRET-qPCR including DNA extraction is less than two hours, qualifying it for routine clinical applications, including treatment monitoring.

Howler monkeys are the reservoir of malarial parasites causing zoonotic infections in the Atlantic forest of Rio de Janeiro

BACKGROUND

Although malaria cases have substantially decreased in Southeast Brazil, a significant increase in the number of Plasmodium vivax-like autochthonous human cases has been reported in remote areas of the Atlantic Forest in the past few decades in Rio de Janeiro (RJ) state, including an outbreak during 2015-2016. The singular clinical and epidemiological aspects in several human cases, and collectively with molecular and genetic data, revealed that they were due to the non-human primate (NHP) parasite Plasmodium simium; however, the understanding of the autochthonous malarial epidemiology in Southeast Brazil can only be acquired by assessing the circulation of NHP Plasmodium in the foci and determining its hosts.

METHODOLOGY

A large sampling effort was carried out in the Atlantic forest of RJ and its bordering states (Minas Gerais, São Paulo, Espírito Santo) for collecting and examining free-living NHPs. Blood and/or viscera were analyzed for Plasmodium infections via molecular and microscopic techniques.

PRINCIPAL FINDINGS

In total, 146 NHPs of six species, from 30 counties in four states, were tested, of which majority were collected from RJ. Howler monkeys (Alouatta clamitans) were the only species found infected. In RJ, 26% of these monkeys tested positive, of which 17% were found to be infected with P. simium. Importantly, specific single nucleotide polymorphisms-the only available genetic markers that differentiate P. simium from P. vivax-were detected in all P. simium infected A. clamitans despite their geographical origin of malarial foci. Interestingly, 71% of P. simium infected NHPs were from the coastal slope of a mountain chain (Serra do Mar), where majority of the human cases were found. Plasmodium brasilianum/malariae was initially detected in 14% and 25% free-living howler monkeys in RJ and in the Espírito Santo (ES) state, respectively. Moreover, the malarial pigment was detected in the spleen fragments of 50% of a subsample comprising dead howler monkeys in both RJ and ES. All NHPs were negative for Plasmodium falciparum.

CONCLUSIONS/SIGNIFICANCE

Our data indicate that howler monkeys act as the main reservoir for the Atlantic forest human malarial parasites in RJ and other sites in Southeast Brazil and reinforce its zoonotic characteristics.

Evaluation on the presence of Anaplasma, Ehrlichia, and Babesia spp. in goats (Capra hircus) in Cebu, the Philippines

BACKGROUND

Tick-borne diseases are caused by a wide variety of viruses, pathogens, and diseases. Anaplasma, Ehrlichia, and Babesia spp. are among the most known tick-borne pathogens in Asia. In the Philippines, these pathogens were already reportedly present in dogs and large ruminants, but no study has been reported yet evaluating their presence in goats.

AIM

The present study aimed to evaluate the presence of Anaplasma, Ehrlichia, and Babesia spp. in goats in Cebu, the Philippines.

MATERIALS AND METHODS

A total of 100 blood samples from goats were collected in Cebu, the Philippines. Profile of sampled goats including age, body score, and sex was obtained. Peripheral blood smear examination and DNA extraction were performed. Nested polymerase chain reaction assay was used to evaluate the presence of Anaplasma, Ehrlichia, and Babesia spp.

RESULTS

None of the samples were found positive with Anaplasma, Ehrlichia, and Babesia spp. infection.

CONCLUSION

Tested goats were negative with Anaplasma, Ehrlichia, and Babesia spp. and calls for continuous surveillance of these pathogens due to the reported detection of these pathogens in other livestock animals in the area.

Considerations on PCR-based methods for malaria diagnosis in China malaria diagnosis reference laboratory network

Precise diagnosis is a key measurement for malaria control and elimination, traditional microscopy and rapid diagnostic tests cannot satisfy the requirements especially in the low transmission endemic areas or in the malaria elimination phase. Polymerase chain reaction (PCR) with high sensitivity and specificity can be considered as a diagnostic standard while no uniform PCR assay was established due to variations in their performance and lack of formal external quality assurance programs for validation for PCR assays in use. Here, 24 articles including 43 paired comparative evaluations limited to paired comparison of diagnostic performance between real-time PCR and conventional PCR to detect plasmodium in blood samples of human subjects from clinics or the field are systematically summarized. And according to the Landis and Koch classification, nineteen pairs showed almost perfect agreement, followed by 8 pairs of moderate agreement and 4 pairs of good agreement, while the kappa values of 12 pairs couldn't be examined. Moreover, the performance of 14 pairs were completely the same and 8 pairs had no differences, but 14 pairs were significant different including 8 pairs of real-time PCR with better performance than conventional PCR. Therefore, it is still an outstanding issue to choose PCR methods, and more work such as the standardization of materials and methods in use and their availability are needed to settle priority to better promote the role of malaria diagnosis reference laboratories.

Strategy to improve malaria surveillance system preventing transfusion-transmitted malaria in blood banks using molecular diagnostic

Background

Malaria can be transmitted by blood transfusion through donations collected from asymptomatic or parasitic donors. The parasites are released into the bloodstream during its life cycle and will therefore be present in donated blood by infected individuals. All cases of transfusion-transmitted malaria (TTM) notified since 2005 in Brazil were fatal. A good screening tool for Plasmodium spp. detection in blood units must have a high detection threshold, and the prevention of TTM relies entirely on the exclusion of potentially infected donors. However, in Brazilian blood banks, the screening test relies on blood thick smears examination.

Methods

The molecular diagnostic based on mitochondrial DNA (mtDNA) using real time PCR (mt-qPCR) was improved to detect Plasmodium falciparum, Plasmodium vivax, and standardized for use in Plasmodium malariae. The analytic sensitivity of this mt-qPCR methodology was performed using a sample of P. vivax.

Results

The mt-qPCR was highly efficient, and the analytic sensitivity for P. vivax was determined (0.000006 parasites/µL). This method was tested to detect P. vivax and P. falciparum in individuals from two malaria-endemic areas in Brazil, Amazon region (Pará and Rondônia states), the samples were collected in 10 reference units of two blood banks (Pará/nine cities and Rondônia/Porto Velho), and parasites mtDNA were detected in 10 of 2224 potential blood donors (0.45%). In all 10 positive samples, only P. vivax was detected.

Conclusion

Molecular diagnostic using mt-qPCR was effective in revealing infected potential donors with good perspectives to be applied as screening routine of asymptomatic carriers for preventing transfusion-transmitted malaria in blood banks.

Frozen blood clots can be used for the diagnosis of distinct Plasmodium species in man and non-human primates from the Brazilian Atlantic Forest

BACKGROUND

Zoonotic infections with epidemic potential, as non-human primate malaria and yellow fever (YF), can overlap geographically. Optimizing a small blood sample for diagnosis and surveillance is of great importance. Blood are routinely collected for YF diagnosis and blood clots usually discarded after serum obtention. Aiming to take sample advantage, the sensitivity of a PCR using extracted DNA from long-term frozen clots from human and non-human primates for detection of Plasmodium spp. in low parasitaemia conditions was assayed.

RESULTS

Malaria diagnosis with DNA extracted from blood clots generated results in agreement with samples obtained with whole blood, including mixed Plasmodium vivax/simium and Plasmodium malariae/brasilianum infections.

CONCLUSION

Blood clots from human and non-human primates may be an important and low cost source of DNA for malaria surveillance in the Atlantic Forest.

Serological and molecular techniques applied for identification of Plasmodium spp. in blood samples from nonhuman primates

The aim of this study was to identify Plasmodium spp. in blood samples from nonhuman primates (NHPs) in the state of Maranhão, using classical and alternative techniques for examination of human malaria. A total of 161 blood samples from NHPs were analyzed: 141 from captive animals at a Wildlife Screening Center (CETAS) and 20 from free-living animals in a private reserve. The techniques used were microscopy, rapid diagnostic test (RDT), Indirect fluorescent antibody test (IFAT) and molecular techniques (semi-nested PCR, quantitative real-time PCR and LAMP). Two serological methods (dot-ELISA and indirect ELISA) were also standardized with rhoptry protein-soluble antigen of P. falciparum and P. berghei. Trophozoite forms of Plasmodium sp. were identified on slides from five different animals. No samples were positive through RDT and LAMP. Four samples were seropositive for P. malariae through IFAT. The samples showed low reactivity to ELISA. Plasmodium sp. was detected in 34.16% (55/161) of the samples using qPCR based on the 18S rRNA gene. After sequencing, two samples showed 100% identityl to P. malariae, one showed 97% identity to Plasmodium sp. ZOOBH and one showed 99% identity to P. falciparum . PCR was shown to be the most sensitive technique for diagnosing Plasmodium in NHP samples.

Analytical Performance of Four Polymerase Chain Reaction (PCR) and Real Time PCR (qPCR) Assays for the Detection of Six Leishmania Species DNA in Colombia

Leishmaniasis comprises a spectrum of parasitic diseases caused by protozoans of the genus Leishmania. Molecular tools have been widely employed for the detection of Leishmania due to its high sensitivity and specificity. However, the analytical performance of molecular platforms as PCR and real time PCR (qPCR) including a wide variety of molecular markers has never been evaluated. Herein, the aim was to evaluate the analytical performance of 4 PCR-based assays (designed on four different targets) and applied on conventional and real-time PCR platforms. We evaluated the analytical performance of conventional PCR and real time PCR, determining exclusivity and inclusivity, Anticipated Reportable Range (ARR), limit of detection (LoD) and accuracy using primers directed to kDNA, HSP70, 18S and ITS-1 targets. We observed that the kDNA was the most sensitive but does not meet the criterion of exclusivity. The HSP70 presented a higher LoD in conventional PCR and qPCR in comparison with the other markers (1 × 10¹ and 1 × 10^-1 equivalent parasites/mL respectively) and had a higher coefficient of variation in qPCR. No statistically significant differences were found between the days of the test with the four molecular markers. The present study revealed that the 18S marker presented the best performance in terms of analytical sensitivity and specificity for the qPCR in the species tested (species circulating in Colombia). Therefore, we recommend to explore the analytical and diagnostic performance in future studies using a broader number of species across America.

Identification of Plasmodium spp. in Neotropical primates of Maranhense Amazon in Northeast Brazil

In the Brazilian Amazon region, malaria caused by Plasmodium malariae is considered to be a zoonosis because of cross-transfer of the parasite between humans and Neotropical primates. To contribute information on this issue, we investigated occurrences of natural infection with Plasmodium sp. among Neotropical primates in the Maranhense Amazon (Amazon region of the state of Maranhão), in the northeastern region of Brazil. Blood samples were collected from 161 Neotropical primates of six species that were caught in an environmental reserve (Sítio Aguahy) and from captive primates (CETAS-Wildlife Screening Center, municipality of São Luís), in Maranhão. Plasmodium sp. was diagnosed based on light microscopy, PCR, qPCR and LAMP for amplification of the 18S rRNA gene. Serum samples were also assayed by means of indirect immunofluorescence for IgG antibodies against P. malariae/P. brasilianum, P. falciparum and P. berghei. Parasites were detected through light microscopy on five slides from captive primates (four Sapajus spp. and one Callithrix jacchus). In the molecular tests, 34.16% (55/161) and 29.81% (48/161) of the animals sampled were positive in the qPCR and PCR assays, respectively. In the PCR, 47/48 animals were positive for P. malariae/P. brasilianum; of these, eight were free-living primates and 39 from CETAS, São Luís. One sample showed a band in the genus-specific reaction, but not in the second PCR reaction. Anti-P. malariae/P. brasilianum IgG antibodies were detected in four serum samples from Sapajus spp. in captivity. In this study, circulation of P. malariae/P. brasilianum in Neotropical primates was confirmed, with low levels of parasitemia and low levels of antibodies. The importance of these animals as reservoirs of human malaria in the region studied is still unknown. This scenario has an impact on control and elimination of malaria in this region.

New molecular detection methods of malaria parasites with multiple genes from genomes

For the effective control of malaria, development of sensitive, accurate and rapid tool to diagnose and manage the disease is essential. In humans subjects, the severe form of malaria is caused by Plasmodium falciparum (Pf) and Plasmodium vivax (Pv) and there is need to identify these parasites in acute, chronic and latent (during and post-infection) stages of the disease. In this study, we report a species specific and sensitive diagnostic method for the detection of Pf and Pv in humans. First, we identified intra and intergenic multiloci short stretch of 152 (PfMLS152) and 110 (PvMLS110) nucleotides which is present up to 44 and 34 times in the genomes of Pf and Pv respectively. We developed the single-step amplification-based method using isolated DNA or from lysed red blood cells for the detection of the two malaria parasites. The limit of detection of real-time polymerase chain reaction based assays were 0.1copyof parasite/μl for PfMLS152 and PvMLS110 target sequences. Next, we have tested 250 clinically suspected cases of malaria to validate the method. Sensitivity and specificity for both targets were 100% compared to the quantitative buffy coat microscopy analysis and real-time PCR (Pf-chloroquine resistance transporter (PfCRT) and Pv-lactate dehydrogenase (PvLDH)) based assays. The sensitivity of microscopy and real-time PCR (PfCRT and PvLDH primers) assays were 80.63%; 95%CI 75.22%-85.31%; p<0.05 and 97.61%; 95%CI 94.50%-99.21%; p<0.05 in detecting malaria infection respectively when compared to PfMLS152 and PvMLS110 targets to identify malaria infection in patients. These improved assays may have potential applications in evaluating malaria in asymptomatic patients, treatment, blood donors and in vaccine studies.

Application of a cell microarray chip system for accurate, highly sensitive, and rapid diagnosis for malaria in Uganda

Accurate, sensitive, rapid, and easy operative diagnosis is necessary to prevent the spread of malaria. A cell microarray chip system including a push column for the recovery of erythrocytes and a fluorescence detector was employed for malaria diagnosis in Uganda. The chip with 20,944 microchambers (105 μm width and 50 μm depth) was made of polystyrene. For the analysis, 6 μl of whole blood was employed, and leukocytes were practically removed by filtration through SiO2-nano-fibers in a column. Regular formation of an erythrocyte monolayer in each microchamber was observed following dispersion of an erythrocyte suspension in a nuclear staining dye, SYTO 21, onto the chip surface and washing. About 500,000 erythrocytes were analyzed in a total of 4675 microchambers, and malaria parasite-infected erythrocytes could be detected in 5 min by using the fluorescence detector. The percentage of infected erythrocytes in each of 41 patients was determined. Accurate and quantitative detection of the parasites could be performed. A good correlation between examinations via optical microscopy and by our chip system was demonstrated over the parasitemia range of 0.0039-2.3438% by linear regression analysis (R(2) = 0.9945). Thus, we showed the potential of this chip system for the diagnosis of malaria.

Still Searching for a Suitable Molecular Test to Detect Hidden Plasmodium Infection: A Proposal for Blood Donor Screening in Brazil

Background

Efforts have been made to establish sensitive diagnostic tools for malaria screening in blood banks in order to detect malaria asymptomatic carriers. Microscopy, the malaria reference test in Brazil, is time consuming and its sensitivity depends on microscopist experience. Although molecular tools are available, some aspects need to be considered for large-scale screening: accuracy and robustness for detecting low parasitemia, affordability for application to large number of samples and flexibility to perform on individual or pooled samples.

Methodology

In this retrospective study, we evaluated four molecular assays for detection of malaria parasites in a set of 56 samples previously evaluated by expert microscopy. In addition, we evaluated the effect of pooling samples on the sensitivity and specificity of the molecular assays. A well-characterized cultured sample with 1 parasite/μL was included in all the tests evaluated. DNA was extracted with QIAamp DNA Blood Mini Kit and eluted in 50 μL to concentrate the DNA. Pools were assembled with 10 samples each. Molecular protocols targeting 18S rRNA, included one qPCR genus specific (Lima-genus), one duplex qPCR genus/Pf (PET-genus, PET-Pf) and one duplex qPCR specie-specific (Rougemont: Roug-Pf/Pv and Roug-Pm/Po). Additionally a nested PCR protocol specie-specific was used (Snou-Pf, Snou-Pv, Snou-Pm and Snou-Po).

Results

The limit of detection was 3.5 p/μL and 0.35p/μl for the PET-genus and Lima-genus assays, respectively. Considering the positive (n = 13) and negative (n = 39) unpooled individual samples according to microscopy, the sensitivity of the two genus qPCR assays was 76.9% (Lima-genus) and 72.7% (PET-genus). The Lima-genus and PET-genus showed both sensitivity of 86.7% in the pooled samples. The genus protocols yielded similar results (Kappa value of 1.000) in both individual and pooled samples.

Conclusions

Efforts should be made to improve performance of molecular tests to enable the detection of low-density parasitemia if these tests are to be utilized for blood transfusion screening.

Dengue infection as a potential trigger of an imported Plasmodium ovale malaria relapse or a long incubation period in a non-endemic malaria region

OBJECTIVES

To report that dengue fever (DF) could have triggered Plasmodium ovale wallikeri malaria.

METHODS

A retrospective case report of P. ovale malaria and DF in a single patient in Rio de Janeiro, Brazil, who had lived in Angola, is presented.

RESULTS

On the second week of illness, the patient was referred to our research service. As symptoms had persisted up to day 14, malaria was also considered, based on the patient's long-standing epidemiological history. On day 16 of illness, a thick blood smear was positive for P. ovale (3480 parasites/mm(3)), PCR for malaria was positive for P. ovale wallikeri, and the kinetics of dengue virus (DENV) antibodies suggested a recent primary dengue infection.

CONCLUSIONS

Concurrent infections of DENV and malaria have rarely been reported; the actual impact of these sequential or simultaneous infections remains unknown. Therefore, DF must be considered as a potential co-morbidity for malaria, because of its influence on fluid electrolyte management. The case presented showed consistent temporal, clinical, and laboratory evidence that the relapse or the long incubation period of P. ovale malaria may have been triggered by a recent DF episode. To the authors' knowledge, this is the first report of DENV and P. ovale co-infection.

Development of High Resolution Melting Analysis for the Diagnosis of Human Malaria

Molecular detection has overcome limitations of microscopic examination by providing greater sensitivity and specificity in Plasmodium species detection. The objective of the present study was to develop a quantitative real-time polymerase chain reaction coupled with high-resolution melting (qRT-PCR-HRM) assay for rapid, accurate and simultaneous detection of all five human Plasmodium spp. A pair of primers targeted the 18S SSU rRNA gene of the Plasmodium spp. was designed for qRT-PCR-HRM assay development. Analytical sensitivity and specificity of the assay were evaluated. Samples collected from 229 malaria suspected patients recruited from Sabah, Malaysia were screened using the assay and results were compared with data obtained using PlasmoNex(TM), a hexaplex PCR system. The qRT-PCR-HRM assay was able to detect and discriminate the five Plasmodium spp. with lowest detection limits of 1-100 copy numbers without nonspecific amplifications. The detection of Plasmodium spp. in clinical samples using this assay also achieved 100% concordance with that obtained using PlasmoNex(TM). This indicated that the diagnostic sensitivity and specificity of this assay in Plasmodium spp. detection is comparable with those of PlasmoNex(TM). The qRT-PCR-HRM assay is simple, produces results in two hours and enables high-throughput screening. Thus, it is an alternative method for rapid and accurate malaria diagnosis.

A multi-detection assay for malaria transmitting mosquitoes

The Anopheles gambiae species complex includes the major malaria transmitting mosquitoes in Africa. Because these species are of such medical importance, several traits are typically characterized using molecular assays to aid in epidemiological studies. These traits include species identification, insecticide resistance, parasite infection status, and host preference. Since populations of the Anopheles gambiae complex are morphologically indistinguishable, a polymerase chain reaction (PCR) is traditionally used to identify species. Once the species is known, several downstream assays are routinely performed to elucidate further characteristics. For instance, mutations known as KDR in a para gene confer resistance against DDT and pyrethroid insecticides. Additionally, enzyme-linked immunosorbent assays (ELISAs) or Plasmodium parasite DNA detection PCR assays are used to detect parasites present in mosquito tissues. Lastly, a combination of PCR and restriction enzyme digests can be used to elucidate host preference (e.g., human vs. animal blood) by screening the mosquito bloodmeal for host-specific DNA. We have developed a multi-detection assay (MDA) that combines all of the aforementioned assays into a single multiplex reaction genotyping 33SNPs for 96 or 384 samples at a time. Because the MDA includes multiple markers for species, Plasmodium detection, and host blood identification, the likelihood of generating false positives or negatives is greatly reduced from previous assays that include only one marker per trait. This robust and simple assay can detect these key mosquito traits cost-effectively and in a fraction of the time of existing assays.

Severe Plasmodium falciparum infection mimicking acute myocardial infarction

This case report describes a case of presumed acute myocardial infarction in a returned traveler who was later diagnosed to have severe malaria. Emergency coronary angiography was normal and subsequent peripheral blood film was positive for Plasmodium falciparum.

Unexpected detection of Plasmodium vivax and Plasmodium falciparum DNA in asymptomatic blood donors: fact or artifact?

A study searching for Plasmodium vivax and Plasmodium falciparum DNA among blood donors from the non-endemic area in Brazil reported a rate of 7.41%. This number is at least three times higher than what has been observed in blood donors from the Amazon, an endemic area concentrating >99% of all malaria cases in Brazil. Moreover, the majority of the donors were supposedly infected by P. falciparum, a rare finding both in men and anophelines from the Atlantic forest. These findings shall be taken with caution since they disagree with several publications in the literature and possibly overestimate the actual risk of malaria transmission by blood transfusion in São Paulo city.

Finding connections in the unexpected detection of Plasmodium vivax and Plasmodium falciparum DNA in asymptomatic blood donors: a fact in the Atlantic Forest

A recent paper in Malaria Journal reported the observation of unexpected prevalence rates of healthy individuals carrying Plasmodium falciparum (5.14%) or Plasmodium vivax (2.26%) DNA among blood donors from the main transfusion centre in the metropolitan São Paulo, a non-endemic area for malaria. The article has been challenged by a group of authors who argued that the percentages reported were higher than those found in blood banks of the endemic Amazon Region and also that that paper had not considered the literature on the classical dynamics of malaria transmission in the Atlantic Forest, which involves Anopheles (Kerteszia) cruzii and bromeliad malaria, due to P. vivax and Plasmodium malariae parasites, but not P. falciparum. The present commentary paper responds to this challenge and brings evidence and literature data supporting that the observed prevalence ratios may indicate a proportion of individuals that are exposed to Plasmodium transmission in permissive environments; that blood carrying parasite DNA may not be necessarily infective if used in transfusion; and that in the literature, there are examples supporting the circulation of P. falciparum in the area.

Development and efficacy of real-time PCR in the diagnosis of vivax malaria using field samples in the Republic of Korea

The development of sensitive, rapid, and accurate diagnostic methods for vivax malaria is essential for the effective control of malaria in the Republic of Korea, where vivax malaria patients usually show low parasitemia. In this study, a TaqMan-based real-time polymerase chain reaction (PCR) method was established and compared with other PCR-based assays, including nested PCR, loop-mediated isothermal amplification, and multiplex PCR, using samples from febrile patients with suspected vivax malaria. The established real-time PCR had a high sensitivity (99.6%) and specificity (100%). Therefore, this sensitive, specific, rapid, and quantitative real-time PCR method could be used for the routine diagnosis of vivax malaria in the laboratory of the Korea National Institute of Health.

Detection of Plasmodium falciparum and Plasmodium vivax subclinical infection in non-endemic region: implications for blood transfusion and malaria epidemiology

Background

In Brazil, malaria is endemic in the Amazon River basin and non-endemic in the extra-Amazon region, which includes areas of São Paulo state. In this state, a number of autochthonous cases of malaria occur annually, and the prevalence of subclinical infection is unknown. Asymptomatic infections may remain undetected, maintaining transmission of the pathogen, including by blood transfusion. In these report it has been described subclinical Plasmodium infection in blood donors from a blood transfusion centre in São Paulo, Brazil.

Methods

In this cross-sectional study, representative samples of blood were obtained from 1,108 healthy blood donors at the Fundação Pró-Sangue Hemocentro de São Paulo, the main blood transfusion centre in São Paulo. Malaria exposure was defined by the home region (exposed: forest region; non-exposed: non-forest region). Real-time PCR was used to detect Plasmodium falciparum and Plasmodium vivax. Subclinical malaria cases were geo-referenced.

Results

Eighty-four (7.41%) blood donors tested positive for Plasmodium; 57 of these were infected by P. falciparum, 25 by P. vivax, and 2 by both. The prevalence of P. falciparum and P. vivax was 5.14 and 2.26, respectively. The overall prevalence ratio (PR) was 3.23 (95% confidence interval (CI) 2.03, 5.13); P. falciparum PR was 16.11 (95% CI 5.87, 44.21) and P. vivax PR was 0.47 (95% CI 0.2, 1.12). Plasmodium falciparum subclinical malaria infection in the Atlantic Forest domain was present in the mountain regions while P. vivax infection was observed in cities from forest-surrounded areas.

Conclusions

The presence of Plasmodium in healthy blood donors from a region known as non-endemic, which is important in the context of transfusion biosafety, was described. Infected recipients may become asymptomatic carriers and a reservoir for parasites, maintaining their transmission. Furthermore, P. falciparum PR was positively associated with the forest environment, and P. vivax was associated with forest fragmentation.

Malaria, a difficult diagnosis in a febrile patient with sub-microscopic parasitaemia and polyclonal lymphocyte activation outside the endemic region, in Brazil

A case of autochthonous Plasmodium vivax malaria with sub-microscopic parasitaemia and polyclonal B-cell activation (PBA) (as reflected by positive IgM and IgG serology for toxoplasmosis, cytomegalovirus, and antinuclear and rheumatoid factors) was diagnosed by polymerase chain reaction (PCR) after consecutive negative rapid diagnostic test results and blood films. The patient, a 44-year-old man from Rio de Janeiro state, Brazil, had visited the Atlantic Forest, a tourist, non-malaria-endemic area where no autochthonous cases of ’bromeliad malaria‘ has ever been described. The characteristic pattern of fever, associated with PBA, was the clue to malaria diagnosis, despite consecutive negative thick blood smears. The study highlights a need for changes in clinical and laboratory diagnostic approaches, namely the incorporation of PCR as part of the current routine malaria diagnostic methods in non-endemic areas.

Improved assay to detect Plasmodium falciparum using an uninterrupted, semi-nested PCR and quantitative lateral flow analysis

BACKGROUND

A rapid, non-invasive, and inexpensive point-of-care (POC) diagnostic for malaria followed by therapeutic intervention would improve the ability to control infection in endemic areas.

METHODS

A semi-nested PCR amplification protocol is described for quantitative detection of Plasmodium falciparum and is compared to a traditional nested PCR. The approach uses primers that target the P. falciparum dihydrofolate reductase gene.

RESULTS

This study demonstrates that it is possible to perform an uninterrupted, asymmetric, semi-nested PCR assay with reduced assay time to detect P. falciparum without compromising the sensitivity and specificity of the assay using saliva as a testing matrix.

CONCLUSIONS

The development of this PCR allows nucleic acid amplification without the need to transfer amplicon from the first PCR step to a second reaction tube with nested primers, thus reducing both the chance of contamination and the time for analysis to < two hours. Analysis of the PCR amplicon yield was adapted to lateral flow detection using the quantitative up-converting phosphor (UCP) reporter technology. This approach provides a basis for migration of the assay to a POC microfluidic format. In addition the assay was successfully evaluated with oral samples. Oral fluid collection provides a simple non-invasive method to collect clinical samples.

The role of reactive oxygen species in Anopheles aquasalis response to Plasmodium vivax infection

Malaria affects millions of people worldwide and hundreds of thousands of people each year in Brazil. The mosquito Anopheles aquasalis is an important vector of Plasmodium vivax, the main human malaria parasite in the Americas. Reactive oxygen species (ROS) have been shown to have a role in insect innate immune responses as a potent pathogen-killing agent. We investigated the mechanisms of free radicals modulation after A. aquasalis infection with P. vivax. ROS metabolism was evaluated in the vector by studying expression and activity of three key detoxification enzymes, one catalase and two superoxide dismutases (SOD3A and SOD3B). Also, the involvement of free radicals in the mosquito immunity was measured by silencing the catalase gene followed by infection of A. aquasalis with P. vivax. Catalase, SOD3A and SOD3B expression in whole A. aquasalis were at the same levels of controls at 24 h and upregulated 36 h after ingestion of blood containing P. vivax. However, in the insect isolated midgut, the mRNA for these enzymes was not regulated by P. vivax infection, while catalase activity was reduced 24 h after the infectious meal. RNAi-mediated silencing of catalase reduced enzyme activity in the midgut, resulted in increased P. vivax infection and prevalence, and decreased bacterial load in the mosquito midgut. Our findings suggest that the interactions between A. aquasalis and P. vivax do not follow the model of ROS-induced parasite killing. It appears that P. vivax manipulates the mosquito detoxification system in order to allow its own development. This can be an indirect effect of fewer competitive bacteria present in the mosquito midgut caused by the increase of ROS after catalase silencing. These findings provide novel information on unique aspects of the main malaria parasite in the Americas interaction with one of its natural vectors.

Prevalence of Plasmodium falciparum and P. vivax in an area of transmission located in Pará State, Brazil, determined by amplification of mtDNA using a real-time PCR assay

The need for a more sensitive and time-efficient assay for malaria has led to the development of molecular assays involving real-time PCR (qPCR), a procedure that has the potential to detect low levels of parasitemia, identify mixed infections, and allow for precise differentiation of species via melting curve analysis or TaqMan fluorescence-labeled probes. Since the first study published in 2001 at least 17 assays have been developed, most of them using SSUrRNA as the target gene. We used qPCR to detect Plasmodium falciparum and P. vivax by amplification of mtDNA; this technique was evaluated on whole-blood samples from people living in areas of malaria transmission in the Brazilian Amazon region located in the area of inclusion of highway BR-163 (Cuiabá-Santarém) in Pará State: São Luiz do Tapajós, a municipal district of Itaituba (N = 74); Três Boeiras, a municipal district of Trairão (N = 134), and São Raimundo, a municipal district of Aveiro (N = 62). The results from the real-time PCR-based method were compared to conventional microscopy and to an established mtDNA-PCR assay. The qPCR (mtDNA) method was 16-19 times more efficient than the conventional PCR (mtDNA) and microscopy for detecting plasmodial infections.

Correlates of HIV and malaria co-infection in Southern India

Background

Malaria and HIV co-infection adversely impact the outcome of both diseases and previous studies have mostly focused on falciparum malaria. Plasmodium vivax contributes to almost half of the malaria cases in India, but the disease burden of HIV and P. vivax co-infection is unclear.

Methods

HIV-infected subjects (n=460) were randomly selected from the 4,611 individuals seen at a Voluntary Counseling and Testing Center in Chennai, India between Jan 2 to Dec 31 2008. Malaria testing was performed on stored plasma samples by nested PCR using both genus-specific and species-specific primers and immunochromatography-based rapid diagnostic test for detecting antibodies against Plasmodium falciparum and P. vivax.

Results

Recent malaria co-infection, defined by the presence of antibodies, was detected in 9.8% (45/460) participants. Plasmodium vivax accounted for majority of the infections (60%) followed by P. falciparum (27%) and mixed infections (13%). Individuals with HIV and malaria co-infection were more likely to be men (p=0.01). Between those with and without malaria, there was no difference in age (p=0.14), CD4+ T-cell counts (p=0.19) or proportion CD4+ T-cell below 200/mL (p=0.51).

Conclusions

Retrospective testing of stored plasma samples for malaria antibodies can facilitate identification of populations with high rates of co-infection, and in this southern India HIV-infected cohort there was a considerable burden of malaria co-infection, predominantly due to P. vivax. However, the rate of P. falciparum infection was more than 6-fold higher among HIV-infected individuals than what would be expected in the general population in the region. Interestingly, individuals co-infected with malaria and HIV were not more likely to be immunosuppressed than individuals with HIV infection alone.

Microscopy and molecular biology for the diagnosis and evaluation of malaria in a hospital in a rural area of Ethiopia

BACKGROUND

Malaria is a leading public health problem in Ethiopia. Accurate diagnosis of Plasmodium infections is crucial for the reduction of malaria in tropical areas and for epidemiological studies. The role of light microscopy (LM) as gold standard has been questioned and, therefore, new molecular methods have been developed for the detection of Plasmodium species. The aim of the present work was to compare different malaria diagnostic methods in order to detect the most common species of Plasmodium and to broaden the knowledge of malaria prevalence in a hospital in a rural area in Ethiopia.

METHODS

A cross-sectional survey of 471 individuals was carried out in a hospital in the rural area of Gambo (Ethiopia). Blood samples were prepared for microscopic observation and collected in filter paper for Seminested-Multiplex PCR (SnM-PCR) and real time PCR (qPCR) testing. The SnM-PCR was considered as the gold standard technique and compared with the rest. Thus, agreement between SnM-PCR and LM was determined by calculating Kappa Statistics and correlation between LM and qPCR quantification was calculated by pair-wise correlation co-efficient.

RESULTS

Samples analysed by LM and SnM-PCR were positive for Plasmodium sp. 5.5% and 10.5%, respectively. Sensitivity was 52.2% by LM and 70% by qPCR. Correlation co-efficient between microscopy counts and qPCR densities for Plasmodium vivax was R2 = 0.586. Prevalence was estimated at 7% (95% CI: 4.7-9.3). Plasmodium vivax was the dominant species detected and the difference was statistically significant (χ2 = 5.121 p < 0.05). The highest prevalence of the parasite (10.9%) was observed in age groups under 15 years old.

CONCLUSION

Accurate malaria diagnostic methods have a great effect in the reduction of the number of malaria-infected individuals. SnM-PCR detection of malaria parasites may be a very useful complement to microscopic examination in order to obtain the real prevalence of each Plasmodium species. Although SnM-PCR shows that it is a good tool for the determination of Plasmodium species, today light microscopy remains the only viabletool for malaria diagnosis in developing countries. Therefore, re-inforcement in the training of microscopists is essential for making the correct diagnosis of malaria. Plasmodium vivax was the predominant species in Gambo, a meso-endemic area for this species.

A novel real-time PCR assay for the detection of Plasmodium falciparum and Plasmodium vivax malaria in low parasitized individuals

The rapid, accurate diagnosis of Plasmodium spp. is essential for the effective control of malaria, especially in asymptomatic infections. In this study, we developed a sensitive, genus-specific, real-time quantitative PCR assay. It was compared with the microscopic examination of Giemsa-stained blood smears and two different molecular diagnostic techniques: nested PCR and multiplex PCR. For the effective quantitative detection of malaria parasites, all reagents were designed with a lyophilized format in one tube. Plasmodium was detected successfully in all 112 clinically suspected malaria patients, including 32 individuals with low parasitemia (1-100 parasites/μl). The sensitivity threshold was 0.2 parasites/μl and no PCR-positive reaction occurred when malaria parasites were not present. This may be a useful method for detecting malaria parasites in endemic areas.

Usefulness of polymerase chain reaction to supplement field microscopy in a pre-selected population with a high probability of malaria infections

This study determines the use of nested PCR as a diagnostic tool to supplement field microscopy in symptomatic individuals suspected of being positive for malaria, and it explores its role in active case detection to identify asymptomatic parasite carriers. In symptomatic individuals, compared with PCR, microscopy had a sensitivity of 86.6% (95% confidence interval [CI] = 77.8-92.4) and specificity of 100% (95% CI = 96.9-100). During active case detection, two asymptomatic persons were diagnosed as having vivax malaria by polymerase chain reaction (PCR) but not microscopy. Currently, PCR is being carried out in Sri Lanka only for population surveys to estimate the hidden reservoir of malaria. Based on the results of this study and because of cost considerations, pooled PCR will be used in the future to screen samples from clinically suspected foci to increase the proportion of malaria cases detected. This strategy will assist the success of the malaria elimination program in Sri Lanka.

High specificity of semi-nested multiplex PCR using dried blood spots on DNA Banking Card in comparison with frozen liquid blood for detection of Plasmodium falciparum and Plasmodium vivax

BACKGROUND

Venipuncture sampling in test tubes for detecting malaria parasites using PCR assays possesses a number of limitations such as reluctance of patients, some difficulties in transportation of blood samples and freezing them for long time. To overcome the mentioned limitations, some approaches have been employed by a number of authors. This study was proposed to compare between DNA Banking Card (DBC) filter papers containing dried finger-prick blood and venipunctured frozen liquid blood.

METHODS

A total of 75 specimens was prepared from the equal enrolled individuals using three blood storage approaches; making Geimsa-stained thin and thick smears from each individual to determine the malaria-positive or -negative specimens, spotting two to three drops of finger-prick blood onto the DBC filter paper, and collecting a 2-ml venous blood sample into EDTA-contained test tube from each individual. A semi-nested Multiplex PCR technique with DNA extracted from the two latter sets of specimens was used for plasmodia diagnosis.

RESULTS

DNA samples isolated from dried blood spotted on the DBC filter papers resulted in 32 (42.7%) positive and 43 (57.3%) negative cases comparable with the results outcome of frozen liquid blood with 35 (46.7%) positive and 40 (53.3%) negative cases. Statistical analysis revealed higher sensitivity for SnM-PCR using DNA from liquid blood with 100% vs. dried blood spotted on DBC with 97% but higher specificity for the DBC with 100% vs. liquid blood with 95.2%.

CONCLUSIONS

Based on the results obtained from this study to overcome the problems of venipuncture frozen liquid blood sampling, replacement of a reliable filter paper for preserving finger-prick blood samples is a trustable and useful facilitator particularly in remote malaria-endemic areas.

Mapping hypoendemic, seasonal malaria in rural Bandarban, Bangladesh: a prospective surveillance

Background

Until recently the Chittagong Hill tracts have been hyperendemic for malaria. A past cross-sectional RDT based survey in 2007 recorded rates of approximately 15%. This study was designed to understand the present epidemiology of malaria in this region, to monitor and facilitate the uptake of malaria intervention activities of the national malaria programme and to serve as an area for developing new and innovative control strategies for malaria.

Methods

This research field area was established in two rural unions of Bandarban District of Bangladesh north of Bandarban city, which are known to be endemic for malaria due to Plasmodium falciparum. The project included the following elements: a) a demographic surveillance system including an initial census with updates every four months, b) periodic surveys of knowledge attitude and practice, c) a geographic information system, d) weekly active and continuous passive surveillance for malaria infections using smears, rapid tests and PCR, f) monthly mosquito surveillance, and e) daily weather measures. The programme included both traditional and molecular methods for detecting malaria as well as lab methods for speciating mosquitoes and detecting mosquitoes infected with sporozoites.

Results

The demographic surveillance enumerated and mapped 20,563 people, 75% of which were tribal non-Bengali. The monthly mosquito surveys identified 22 Anopheles species, eight of which were positive by circumsporozoite ELISA. The annual rate of malaria was close to 1% with 85% of cases in the rainy months of May-October. Definitive clustering identified in the low transmission season persisted during the high transmission season.

Conclusion

This demographically and geographically defined area, near to the Myanmar border, which is also hypoendemic for malaria, will be useful for future studies of the epidemiology of malaria and for evaluation of strategies for malaria control including new drugs and vaccines.

Detection and species identification of microsporidial infections using SYBR Green real-time PCR

Diagnosis of microsporidial infections is routinely performed by light microscopy, with unequivocal non-molecular species identification achievable only through electron microscopy. This study describes a single SYBR Green real-time PCR assay for the simultaneous detection and species identification of such infections. This assay was highly sensitive, routinely detecting infections containing 400 parasites (g stool sample)(-1), whilst species identification was achieved by differential melt curves on a Corbett Life Science Rotor-Gene 3000. A modification of the QIAamp DNA tissue extraction protocol allowed the semi-automated extraction of DNA from stools for the routine diagnosis of microsporidial infection by real-time PCR. Of 168 stool samples routinely analysed for microsporidian spores, only five were positive by microscopy. By comparison, 17 were positive for microsporidial DNA by real-time analysis, comprising 14 Enterocytozoon bieneusi, one Encephalitozoon cuniculi and two separate Pleistophora species infections.

Rapid and highly sensitive detection of malaria-infected erythrocytes using a cell microarray chip

Background

Malaria is one of the major human infectious diseases in many endemic countries. For prevention of the spread of malaria, it is necessary to develop an early, sensitive, accurate and conventional diagnosis system.

Methods and Findings

A cell microarray chip was used to detect for malaria-infected erythrocytes. The chip, with 20,944 microchambers (105 µm width and 50 µm depth), was made from polystyrene, and the formation of monolayers of erythrocytes in the microchambers was observed. Cultured Plasmodium falciparum strain 3D7 was used to examine the potential of the cell microarray chip for malaria diagnosis. An erythrocyte suspension in a nuclear staining dye, SYTO 59, was dispersed on the chip surface, followed by 10 min standing to allow the erythrocytes to settle down into the microchambers. About 130 erythrocytes were accommodated in each microchamber, there being over 2,700,000 erythrocytes in total on a chip. A microarray scanner was employed to detect any fluorescence-positive erythrocytes within 5 min, and 0.0001% parasitemia could be detected. To examine the contamination by leukocytes of purified erythrocytes from human blood, 20 µl of whole blood was mixed with 10 ml of RPMI 1640, and the mixture was passed through a leukocyte isolation filter. The eluted portion was centrifuged at 1,000×g for 2 min, and the pellet was dispersed in 1.0 ml of medium. SYTO 59 was added to the erythrocyte suspension, followed by analysis on a cell microarray chip. Similar accommodation of cells in the microchambers was observed. The number of contaminating leukocytes was less than 1 on a cell microarray chip.

Conclusion

The potential of the cell microarray chip for the detection of malaria-infected erythrocytes was shown, it offering 10–100 times higher sensitivity than that of conventional light microscopy and easy operation in 15 min with purified erythrocytes.

Detection of Plasmodium vivax by nested PCR and real-time PCR

Malaria is endemic in the Cukurova region while it is sporadic in other regions of Turkey. Therefore, the laboratory and clinical diagnosis of malaria is important for the treatment of malaria. In this study, 92 blood samples that were taken from the suspected malaria patients for routine diagnosis in a period of 10 years between 1999 and 2009 were analyzed. All of these blood samples were examined by microscopic examinations using Giemsa-stained thick blood films, nested PCR, and real-time PCR. The sensitivity-specificity and positive-negative predictive values for these diagnostic tests were then calculated. It was found that the positive predictive values of microscopic examination of thick blood films, nested PCR, and real-time PCR were 47.8%, 56.5%, and 60.9% for malaria, respectively. The real-time PCR was found to have a specificity of 75% and sensitivity of 100%, while specificity and sensitivity of nested PCR was found 81.2% and 97.7% according to the microscopic examination of thick blood films, respectively.

Anopheles aquasalis Infected by Plasmodium vivax displays unique gene expression profiles when compared to other malaria vectors and plasmodia

Malaria affects 300 million people worldwide every year and is endemic in 22 countries in the Americas where transmission occurs mainly in the Amazon Region. Most malaria cases in the Americas are caused by Plasmodium vivax, a parasite that is almost impossible to cultivate in vitro, and Anopheles aquasalis is an important malaria vector. Understanding the interactions between this vector and its parasite will provide important information for development of disease control strategies. To this end, we performed mRNA subtraction experiments using A. aquasalis 2 and 24 hours after feeding on blood and blood from malaria patients infected with P. vivax to identify changes in the mosquito vector gene induction that could be important during the initial steps of infection. A total of 2,138 clones of differentially expressed genes were sequenced and 496 high quality unique sequences were obtained. Annotation revealed 36% of sequences unrelated to genes in any database, suggesting that they were specific to A. aquasalis. A high number of sequences (59%) with no matches in any databases were found 24 h after infection. Genes related to embryogenesis were down-regulated in insects infected by P. vivax. Only a handful of genes related to immune responses were detected in our subtraction experiment. This apparent weak immune response of A. aquasalis to P. vivax infection could be related to the susceptibility of this vector to this important human malaria parasite. Analysis of some genes by real time PCR corroborated and expanded the subtraction results. Taken together, these data provide important new information about this poorly studied American malaria vector by revealing differences between the responses of A. aquasalis to P. vivax infection, in relation to better studied mosquito-Plasmodium pairs. These differences may be important for the development of malaria transmission-blocking strategies in the Americas.

Comparison of three real-time PCR methods with blood smears and rapid diagnostic test in Plasmodium sp. infection

In cases of malaria, rapid and accurate diagnosis of Plasmodium sp. is essential. In this study three different quantitative, real-time PCR methods were compared with routine methods used for malaria diagnosis. A comparative study was conducted prospectively in the laboratories of Montpellier and Nîmes University Hospitals. The methods used for routine diagnostic malaria testing consisted of microscopic examination of Giemsa-stained blood smears and rapid diagnostic tests. Three quantitative real-time PCR methods (qRT-PCR) were tested: qRT-PCR1 amplified a specific sequence on the P. falciparum Cox1 gene, qRT-PCR2 amplified a species-specific region of the multicopy 18S rDNA, and qRT-PCR3 amplified a mitochondrial DNA sequence. Among the 196 blood samples collected, 73 samples were positive in at least one of the five tests. Compared with the routine method, there were no false negatives for P. falciparum diagnosis in either qRT-PCR1 or qRT-PCR3. In all P. ovale, P. vivax and P. malariae infections diagnosed from blood smears, qRT-PCR1 was negative, as expected, whereas qRT-PCR2 and qRT-PCR3 were positive and concordant (simple kappa coefficient = 1). One negative sample from microscopy was positive with both qRT-PCR2 and qRT-PCR3. Together, qRT-PCR3 and the combined qRT-PCR1 and qRT-PCR2 were concordant with routine methods for malaria diagnosis (99% and 99.5%, respectively). These three rapid, molecular qRT-PCR methods, used alone or in association, showed excellent results, with high concordance, accuracy and reliability in malaria diagnosis.

Diagnóstico molecular da malária em uma unidade de atenção terciária na Amazônia Brasileira

O exame de rotina para o diagnóstico da malária continua sendo a gota espessa, apesar da comprovada diminuição da sensibilidade e especificidade em situações de densidade parasitária baixa e infecções mistas. A reação em cadeia da polimerase vem sendo cada vez mais utilizada para a detecção molecular e identificação das espécies de plasmódio, por apresentar maior sensibilidade e especificidade. Foi realizada a nested-PCR em amostras de sangue total de 344 pacientes com síndrome febril aguda que se apresentaram para o diagnóstico de malária, em uma unidade terciária de saúde, em Manaus (Amazonas). Nenhum caso de malária por Plasmodium malariae foi diagnosticado à gota espessa ou PCR. Observou-se co-positividade de 96,7%, co-negatividade de 62,2% e coeficiente kappa de 0,44 entre PCR e gota espessa para Plasmodium falciparum. Para Plasmodium vivax, co-positividade de 100%, co-negatividade de 78,1% e coeficiente kappa de 0,56. Na detecção da malária mista, co-positividade de 100%, co-negatividade de 84,9% e coeficiente kappa de 0,26. A reação em cadeia da polimerase detectou alto número de infecções mistas nas amostras analisadas, mas seu uso rotineiro no diagnóstico da malária merece ainda ampla discussão.