Development and optimization of polymerase chain reaction-based malaria diagnostic methods and their comparison with quantitative buffy coat assay

How long do rapid diagnostic tests remain positive after anti-malarial treatment?

BACKGROUND

Rapid diagnostic tests (RDTs) are increasingly becoming a paradigm for both clinical diagnosis of malaria infections and for estimating community parasite prevalence in household malaria indicator surveys in malaria-endemic countries. The antigens detected by RDTs are known to persist in the blood after treatment with anti-malarials, but reports on the duration of persistence (and the effect this has on RDT positivity) of these antigens post-treatment have been variable.

METHODS

In this review, published studies on the persistence of positivity of RDTs post-treatment are collated, and a bespoke Bayesian survival model is fit to estimate the number of days RDTs remain positive after treatment.

RESULTS

Half of RDTs that detect the antigen histidine-rich protein II (HRP2) are still positive 15 (5-32) days post-treatment, 13 days longer than RDTs that detect the antigen Plasmodium lactate dehydrogenase, and that 5% of HRP2 RDTs are still positive 36 (21-61) days after treatment. The duration of persistent positivity for combination RDTs that detect both antigens falls between that for HRP2- or pLDH-only RDTs, with half of RDTs remaining positive at 7 (2-20) days post-treatment. This study shows that children display persistent RDT positivity for longer after treatment than adults, and that persistent positivity is more common when an individual is treated with artemisinin combination therapy than when treated with other anti-malarials.

CONCLUSIONS

RDTs remain positive for a highly variable amount of time after treatment with anti-malarials, and the duration of positivity is highly dependent on the type of RDT used for diagnosis. Additionally, age and treatment both impact the duration of persistence of RDT positivity. The results presented here suggest that caution should be taken when using RDT-derived diagnostic outcomes from cross-sectional data where individuals have had a recent history of anti-malarial treatment.

Comparative evaluation of a rapid diagnostic test, an antibody ELISA, and a pLDH ELISA in detecting asymptomatic malaria parasitaemia in blood donors in Buea, Cameroon

BACKGROUND

In malaria endemic areas, infected blood donors serve as a source of infection to blood recipients, which may adversely affect their prognosis. This necessitates the proper screening of blood to be used for transfusion in these areas. The purpose of this study was to determine the prevalence of malaria parasitaemia in blood donors in Buea, Cameroon, and to evaluate the performance of a rapid diagnostic test (RDT), a malaria antibody enzyme-linked immunosorbent assay (ELISA), and a Plasmodium lactate dehydrogenase (pLDH) ELISA in the detection of asymptomatic malaria parasitaemia in the target population.

METHODS

In a prospective study conducted between September 2015 and June 2016, 1 240 potential blood donors were enrolled. The donors were screened for malaria parasites using Giemsa microscopy (GM) and a RDT. A sub-sample of 184 samples, comprising 88 positive and 96 negative samples, were selected for the evaluation of the pLDH ELISA and the antibody ELISA. The chi-square test and correlation analysis were performed as part of the statistical analyses. The statistical significance cut-off was set at P < 0.05.

RESULTS

The prevalence of malaria parasitaemia in this study was found to be 8.1% (95% CI: 6.6 - 9.7). The prevalence was not observed to be dependent on the age or sex of the participants. The RDT had a sensitivity (88.0%), specificity (99.1%), and negative predictive value (99.0%) higher than the ELISAs. The performance of the pLDH ELISA, which demonstrated the highest positive predictive value (91.6%), was generally comparable to the RDT. The sensitivity was lowest with the antibody ELISA (69.9%), which also demonstrated the highest false positive and false negative rates. The detection threshold for the pLDH (three parasites/μl) was lower compared to the RDT (50 - 60 parasites/μl). Non-significant positive correlations were observed between the parasite density and the pLDH titers and malaria antibody titers.

CONCLUSIONS

Overall, the RDT and the pLDH ELISA demonstrated a perfectly correlated agreement with GM, meanwhile the antibody ELISA demonstrated a substantially correlated agreement with GM. The pLDH is therefore recommended for mass screening of blood (to detect malaria parasitaemia) for transfusions in the study area. However, where this is not feasible, an RDT will suffice.

Advances in malaria diagnosis

Malaria is a leading cause of mortality worldwide and accurate diagnostic testing for malaria can potentially save an estimated 100,000 lives annually. New technologies have the potential to circumvent limitations of the traditional diagnostic method, light microscopy, which is labor intensive and requires considerable technician expertise. Immunochromatographic tests, which are easy to use in field conditions and relatively inexpensive, offer a potential solution to the problem of malaria overtreatment in resource-poor endemic countries. Assays based on the PCR are highly sensitive, can be used for unambiguous species identification and, thus, may increasingly complement or even replace light microscopy in developed countries. Experimental diagnostics using flow cytometry and mass spectrometry are currently under investigation for high-throughput screening.

Is a Plasmodium lactate dehydrogenase (pLDH) enzyme-linked immunosorbent (ELISA)-based assay a valid tool for detecting risky malaria blood donations in Africa?

Background

Malaria is a leading cause of mortality in southern Benin. The main causative agent, Plasmodium falciparum, poses a threat on critical transfusions in pregnant women and children. This study’s objective was to compare the performance of different malaria screening methods in blood donors in southern Benin, a malaria-endemic country.

Methods

Blood from 2,515 voluntary blood donors in Benin was collected over a period of 10 months in ethylenediaminetetraacetic acid (EDTA) tubes, which were then classified according to extraction time: long rainy season, short dry season, short rainy season, and long dry season. Microscopic examination was used to count parasites. Parasite density (PD) was expressed as the number of parasites per μL of blood. Pan Plasmodium pLDH detection was assessed by an ELISA-malaria antigen test. Using crude soluble P. falciparum antigens, an ELISA-malaria antibody test detected anti-Plasmodium antibodies.

Results

Among the 2,515 blood donors (2,025 males and 488 females) screened, the rate of asymptomatic Plasmodium carriage was 295/2,515 (11.72%, 95% CI: 10.5-13.1%). Males had a higher infection rate (12.4%) than did females (8.8%). Parasite density was very low: between seven and100 parasites per μL of blood was reported in 80% of donors with parasitaemia. Three Plasmodium species were diagnosed: P. falciparum in 280/295 patients (95.0%), Plasmodium malariae in 14/295 (5.0%), and Plasmodium ovale in 1/295 (0.34%). Malaria prevalence in donors was higher during the rainy seasons (13.7%) compared with the dry seasons (9.9%). The use of a highly sensitive assay enabled pan Plasmodium pLDH detection in 966/2,515 (38.4%, 95% CI: 36.5%-40.3%). Malaria antibody prevalence was 1,859/2,515 (73.9%, 95% CI: 72.16-75.6%). Donors’ antigenaemia and antibody levels varied significantly (P <0.05) over the course of the four seasons. The highest antigenaemia rate 323/630 (51.3%), was observed during the short rainy season, while the highest antibody prevalence, 751/886 (84.7%), was recorded during the long dry season.

Conclusion

Blood donations infected with Plasmodium can transmit malaria to donation recipients. Malaria diagnostic methods are currently available, but the feasibility criteria for mass screening in endemic areas become preponderant. Detection of the pLDH antigen seems to be an adequate screening tool in endemic areas, for this antigen indicates parasite presence. Routine screening of all donated blood would prevent infected blood donations and reduce P. falciparum transmission in critical patients, such as children and pregnant women. This tool would also decrease medical prophylaxis in donation recipients and contribute to lower Plasmodium resistance.

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.

Malaria seroprevalence in blood bank donors from endemic and non-endemic areas of Venezuela

In Venezuela, a total of 363,466 malaria cases were reported between 1999-2009. Several states are experiencing malaria epidemics, increasing the risk of vector and possibly transfusion transmission. We investigated the risk of transfusion transmission in blood banks from endemic and non-endemic areas of Venezuela by examining blood donations for evidence of malaria infection. For this, commercial kits were used to detect both malaria-specific antibodies (all species) and malaria antigen (Plasmodium falciparum only) in samples from Venezuelan blood donors (n = 762). All samples were further studied by microscopy and polymerase chain reaction (PCR). The antibody results showed that P. falciparum-infected patients had a lower sample/cut-off ratio than Plasmodium vivax-infected patients. Conversely, a higher ratio for antigen was observed among all P. falciparum-infected individuals. Sensitivity and specificity were higher for malarial antigens (100 and 99.8%) than for antibodies (82.2 and 97.4%). Antibody-positive donors were observed in Caracas, Ciudad Bolívar, Puerto Ayacucho and Cumaná, with prevalences of 1.02, 1.60, 3.23 and 3.63%, respectively. No PCR-positive samples were observed among the donors. However, our results show significant levels of seropositivity in blood donors, suggesting that more effective measures are required to ensure that transfusion transmission does not occur.

Newer versus Conventional Methods in the Diagnosis of Malaria: A Comparison

BACKGROUND

This study attempts to evaluate and compare the efficacy of polymerase chain reaction (PCR) and quantitative buffy coat (QBC) assay with conventional Giemsa stained peripheral blood smear (PBS) examination in the diagnosis of malaria.

METHODS

The study was conducted on 50 cases of smear positive malaria (group 1), 50 cases of clinically suspected malaria (group 2) and 15 healthy controls. All were subjected to Giemsa stain slide examination both thick and thin smear, QBC assay and PCR. PBS examination by Giemsa stain was taken as gold standard.

RESULT

In this study the overall sensitivity and positive predictive value (PPV) of QBC assay in group 1 was 100% and that of PCR was 60% and 100% respectively. In group 2 the sensitivity, specificity, PPV and NPV of QBC assay was 100% and that of PCR was 71%, 100%, 100% and 73% respectively as compared to the gold standard. All the 15 healthy controls were negative by all the three assays showing 100% specificity.

CONCLUSION

QBC assay was an excellent alternative to the conventional method as it is rapid and less time consuming and can directly demonstrate the parasite. Utility of PCR lies in species-specific diagnosis of falciparum malaria especially when there is a high degree of clinical suspicion and the report is negative by the other two methods.

Molecular approaches for the detection of Schistosoma mansoni: possible applications in the detection of snail infection, monitoring of transmission sites, and diagnosis of human infection

The detection of specific DNA sequences by polymerase chain reaction (PCR) has proved extremely valuable for the analysis of genetic disorders and the diagnosis of a variety of infectious disease pathogens. However, the application to the detection of Schistosoma mansoni is rare, despite a recommendation of the World Health Organization that a major focus of research on schistosomiasis should be on the development and evaluation of new strategies and tools for control of the disease. In this context, a few studies were published for the detection of the parasite in snails, monitoring of cercariae in water bodies, and diagnosis of human infection. The present minireview describes sensitive and specific PCR based systems to detect S. mansoni, indicating possible applications in the detection of snail infection, monitoring of transmission sites, and diagnosis of human infection.

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

We have optimized a faster and cheaper real-time PCR and developed a conventional genus specific PCR based on 18S rRNA gene to detect malaria parasites in low-grade parasitemias. Additionally, we compared these PCRs to the OptiMAL-IT test. Since there is no consensus on choice of standard quantitative curve in real-time assays, we decided to investigate the performance of parasite DNA from three different sources: "genome", amplicon and plasmid. The amplicon curve showed the best efficiency in quantifying parasites. Both PCR assays detected 100% of the clinical samples tested; the sensitivity threshold was 0.5 parasite/mul and no PCR positive reaction occurred when malaria parasites were not present. Conversely, if OptiMAL-IT were employed for malaria diagnosis, 30% of false-negative results could be expected. We conclude that PCR assays have potential for detecting malaria parasites in asymptomatic infections, in evaluation of malaria vaccine molecule candidates, for screening blood donors, especially in endemic areas, or even in monitoring malaria therapy.

[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.

Performance evaluation of automated depolarization analysis for detecting clinically unsuspected malaria in endemic countries

This prospective study evaluated the efficiency of automated depolarization analysis for recognition of unsuspected malaria by haemozoin detection during routine full blood count (FBC) screening of 676 randomly selected out-patients in a malaria hypoendemic area of Senegal. An additional 123 patients with clinically suspected malaria were studied for comparison. Of the 799 samples, 648 (81.1%) were categorized as malaria-negative, 83 (10.4%) as malaria-positive, and 68 as treated (early convalescence) or subclinical malaria (indirect evidence of infection). At a discrimination level of one or more atypical pigment-containing monocytes (PCM), negative and positive agreement was found to be 95.6% and 91.6% respectively for all malaria-negative and parasite-positive samples combined. Increasing the discriminator to two or more PCM events improved the overall agreement to 97.5%. Multivariate analysis showed that the only significant risk factor for the presence of PCM (odds ratio>200) was malaria infection. In the randomly selected group of 676 patients, 41 unsuspected cases of malaria infection were detected using the panel of reference diagnostic tests, and 37 (90.2%) of these had atypical PCM. The detection of clinically unrecognized malaria infection as part of a routine FBC procedure is a potentially useful extended application for laboratories in countries with endemic malaria.

Espondilite tuberculosa em adolescente

Relata-se o caso de uma adolescente com tuberculose osteoarticular em coluna lombossacral, uma localização incomum. O seu diagnóstico permanece um desafio por apresentar sintomas gerais inespecíficos e lesões ósseas que podem ser confundidas com outras afecções. A doença é degenerativa e de prognóstico reservado. São discutidos aspectos clínicos, laboratoriais e de imagem, incluindo tomografia computadorizada e ressonância magnética. A reação em cadeia da polimerase, usando o marcador IS 6110 para M. tuberculosis, foi positiva, sugerindo fortemente a presença do patógeno. Este ensaio é particularmente indicado quando se exige um diagnóstico de tuberculose rápido e sensível.

Identification and characterization of an interspersed repetitive DNA fragment in Plasmodium vivax with potential use for specific parasite detection

We cloned and characterized a Plasmodium vivax repeat element of 7872bp named PvRE7.8. Several internal tandem repeats were found along the sequence. The repetitive nature of the PvRE7.8 element was confirmed by hybridization of a P. vivax YAC library. Based on the data bank analysis and the presence of two contiguous putative genes that may encode proteins related to DNA metabolism, PvRE7.8 could be considered an inactivated transposon-LINE element. By using Pv79 as probe or primers derived from Pv79-flanking sequences, P. vivax DNA Could be detected from whole blood and mosquito samples. We consider that the repeat element described here has potential for P. vivax malaria diagnosis and for epidemiological analysis of P. vivax transmission areas.

Development of a single tube hemi-nested PCR for genus-specific detection of Plasmodium in oligoparasitemic patients

Primers targeting the Plasmodium small-subunit (SSU) rDNA were designed to amplify DNA from P. vivax, P. falciparum, P. malariae, and P. ovale, using conventional PCR, two-step nested PCR (HNPCR), and single tube hemi-nested PCR (STHNPCR). The limit of detection of parasite DNA for the conventional PCR, HNPCR, and STHNPCR were 10 pg, 0.01 pg, and 0.1 pg, respectively, indicating that the STHNPCR is 100-fold more sensitive than conventional PCR, and only 10 times less sensitive than HNPCR. In addition, the detection limit was also defined using blood from a patient infected with P. falciparum. Using the saponin method, the detection limit of the conventional PCR, HNPCR, and STHNPCR were 70, 0.7, and 0.07 parasites/microl, respectively. Finally, the three techniques were evaluated using blood from 30 patients receiving antimalarial treatment, and negative by microscopy and conventional PCR. The HNPCR could still detect specific DNA in 16/30 patients, whereas STHNPCR detected parasite DNA in 10/30 patients, but the difference was not statistically significant. No significant correlation was found between presence of clinical manifestations and presence of parasite DNA, detected by either HNPCR or STHNPCR. We conclude that these sensitive molecular diagnostic systems can be used for the diagnosis of asymptomatic oligoparasitemic patients.

Use of a rapid, single-round, multiplex PCR to detect malarial parasites and identify the species present

A new, rapid assay, based on a single-round, multiplex PCR, can be used to detect Plasmodium falciparum, P. vivax, P. malariae or P. ovale in human blood. The PCR, which targets the conserved 18S small-subunit RNA genes of the parasites, not only permits a malarial infection to be detected but also allows each Plasmodium species present to be identified, even in cases of mixed infection.