[Effect of submicroscopic or polyclonal Plasmodium falciparum infection on mother and gestation product: systematic review]

Frequency of placental malaria and its associated factors in northwestern Colombia, pooled analysis 2009–2020

Knowledge about placental malaria (PM) is insufficient in the world, and incipient in Colombia where studies are few and recent. In this country, PM has been reported by Plasmodium vivax, Plasmodium falciparum, and mixed infection. The objective was to determine the frequency of PM and its associated clinical-epidemiological factors in mothers and neonates in northwestern Colombia, 2009–2020. A Retrospective pooled analysis with 602 placentas captured in five investigations. The diagnosis of PM was made with thick blood smear (TBS) and qPCR. The groups with and without PM were compared using the Chi-square test, Mann-Whitney test, and crude and adjusted prevalence ratios in a log-binomial model. The prevalence of PM was 27.7% with 92% (155/167) of submicroscopic cases; 41.3% by P. vivax, 44,3% by P. falciparum, and 14.4% by mixed infections. In the multivariate adjustment, PM was associated with the diagnosis of congenital malaria, low neonatal weight, gestational malaria, maternal anemia, previous malaria during pregnancy, and age between 25–43 years. This research is the investigation with the largest number of subjects for studying PM in Colombia, in the ecoepidemiological zone that produces more cases of malaria per year, finding a high prevalence of submicroscopic PM that caused serious maternal (anemia) and neonatal (congenital malaria and low neonatal weight) effects. The results show limitations in the timely diagnosis and treatment, given that the epidemiological surveillance program in Colombia is based on thick blood smear, which generates a substantial underestimation of the magnitude of PM, with serious effects and clinical risks. It is urgent to demand that the health authorities adopt measures such as prenatal control visits as soon as the pregnancy begins, monthly implementation of TBS, and active search for infected pregnant women in their homes and workplaces.

Placental malaria caused by Plasmodium vivax or P. falciparum in Colombia: Histopathology and mediators in placental processes

Knowledge about the relation of histopathological characteristics and mediators of physiological processes in the placenta malaria (PM) is poor, and that PM caused by Plasmodium vivax is almost null. The objective was to compare histopathological characteristics, cytokines and mediators of physiological processes in PM depending on the parasitic species, through a cross-sectional study in three groups: negative-PM, vivax-PM, falciparum-PM from Northwestern Colombia. The diagnosis of PM was made with thick blood smear, qPCR, and histopathology. Immuno-histochemical was made with EnVision system (Dako) and Zeiss Axio Imager M2 with light microscope. Cells in apoptosis were studied with the TUNEL technique. To measure the expression level of cytokines and mediators qRT-PCR was used. We included 179 placentas without PM and 87 with PM (53% P. vivax and 47% P. falciparum). At delivery, anemia was 25% in negative-PM, 60% in vivax-PM, and 44% in falciparum-PM group. The neonatal weight had an intense difference between groups with 3292±394g in negative-PM, 2,841±239 in vivax-PM, and 2,957±352 in falciparum-PM. The histopathological characteristics and CD+ cells in placenta with statistical differences (Dunn´s test) between negative-PM vs vivax-PM (P. falciparum was similar to P. vivax) were infarction, fibrinoid deposits, calcification, cells in apoptosis, immune infiltrates in decidua and intervillous space, CD4+, CD8+, CD14+, CD56+, CD68+. The expression levels of mediators in the placenta with statistical differences (Dunn´s test) between negative-PM vs vivax-PM (P. falciparum was similar to P. vivax) were Fas, FasL, HIF1α, Cox1, Cox2, VEGF, IL4, IL10, IFNγ, TNF, TGFβ, FOXP3, and CTLA4. PM with P. falciparum and P. vivax, damages this organ and causes significant alteration of various physiological processes, which cause maternal anemia and a reduction in neonatal weight in degrees that are statistically and clinically significant. It is necessary that the search for plasmodial infection in pregnant and placenta goes from passive to active surveillance with adequate diagnostic capacity.

Meta-analysis of the prevalence of malaria associated with pregnancy in Colombia 2000-2020

Knowledge about malaria associated with pregnancy is scarce in Latin America, and in Colombia, little is known about the magnitude of this infection. A systematic review was conducted to determine the prevalence of malaria associated with pregnancy (MAP) and each of its three forms: gestational (GM), placental (PM), and congenital (CM) tested using thick blood smear (TBS) and PCR. Also to compare the proportion of cases due to Plasmodium falciparum and Plasmodium vivax in Colombia from the year 2000-2020. We searched in Pubmed, Science Direct, EMBASE, EMCare, Cochrane Library, Scielo, Lilacs, Google Scholar, libraries, and repositories of Colombian universities, to obtain data on prevalence of GM, PM and CM with their respective testing method. We performed a meta-analysis with a random-effects model to obtain pooled prevalence of MAP and its three forms categorized by testing methods (TBS and PCR). We used data from 14 studies (out of 258 screened) contributing 7932, 2506 women for GM and PM respectively, also data on 1143 umbilical cord blood samples, and 899 peripheral blood of neonates. We found prevalence by TBS as, MAP 4.5% (95%CI = 2.9-6.9), GM 5.8% (95%CI = 3.8-8.7), PM 3.4% (95%CI = 1.7-6.7) and CM 1.3% (95%CI = 0.6-3.0). With PCR the prevalence was, MAP 14.4% (95%CI = 7.6-25.5), GM 16.7% (95%CI = 9.0-28.8), PM 11.0% (95%CI = 4.1-26.3) and CM 16.2% (95%CI = 8.2-29.5). The prevalence of submicroscopic infection was 8.5% (95%CI = 3.4-19.7) in GM, 10.1% (95%CI = 3.5-25.5) in PM and 22.0% (95%CI = 13.2-34.3) in CM. Infections by P. vivax was dominant over P. falciparum when tested with TBS, the PCR test gave similar proportions of P. falciparum and P. vivax. This meta-analysis has demonstrated high prevalence of MAP in Colombia, and highlights the urgent need to increase attention of researchers, research funding institutions, government agencies, and health authorities to study and intervene MAP, that has currently been under investigated.

Cost-effectiveness of rapid diagnostic tests, compared to microscopic tests, for the diagnosis and treatment of gestational malaria in Colombia from an institutional perspective

BACKGROUND

Gestational malaria is associated with negative outcomes in maternal and gestational health; timely diagnosis is crucial to avoid complications. However, the limited infrastructure, equipment, test reagents, and trained staff make it difficult to use thick blood smear tests in rural areas, where rapid testing could be a viable alternative. The purpose of this study was to estimate the cost-effectiveness of rapid tests type III (Plasmodium falciparum/Plasmodium spp P.f/pan) versus microscopic tests for the diagnosis and treatment of gestational malaria in Colombia.

METHODS

Cost-effectiveness analyses of gestational malaria diagnosis from an institutional perspective using a decision tree. Standard costing was performed for the identification, measurement and assessment phases, with data from Colombian tariff manuals. The data was collected from Health Situation Analysis, SIVIGILA and meta-analysis. Average and incremental cost-effectiveness ratio were estimated. The uncertainty was assessed through probabilistic sensitivity analysis.

RESULTS

The cost of rapid diagnostic tests in 3,000 pregnant women with malaria was US$66,936 and 1,182 disability adjusted life years (DALYs) were estimated. The cost using thick blood smear tests was US$50,838 and 1,023 DALYs, for an incremental cost-effectiveness of US$ 101.2. The probabilistic sensitivity analysis of rapid diagnostic tests determined that they are highly cost-effective in 70% of the cases, even below the US$1,200 threshold; also, they showed an incremental net monetary benefit of $150,000 when payer's willingness is US$1,000.

CONCLUSION

The use of rapid diagnostic tests for timely diagnosis and treatment of gestational malaria is a highly cost-effective strategy in Colombia, with uncertainty analyses supporting the robustness of this conclusion and the increased net monetary benefit that the health system would obtain. This strategy may help in preventing the negative effects on maternal health and the neonate at a low cost.

Impact of Submicroscopic Plasmodium falciparum Parasitaemia on Maternal Anaemia and Low Birth Weight in Blue Nile State, Sudan

The aim of the present study was to investigate the prevalence of submicroscopic infections and to assess its impact on maternal anaemia and low birth weight. A cross-sectional study was carried out with 1149 consented pregnant women who delivered at 3 main hospitals in the Blue Nile State, between January 2012 and December 2015. From a matched maternal peripheral, placental maternal side, and cord blood sample, blood films and dried spots were prepared for microscopic examination and nested polymerase chain reaction (n-PCR), respectively. 107 out of 447 negative blood films were found to have submicroscopic infection detected using n-PCR in any of the three compartments. Placental samples had a significantly higher prevalence (142) of submicroscopic infections compared with the peripheral (6.5%) and cord (8.1%) samples. The mean (SD) of the maternal haemoglobin (Hb) was significantly lower in cases with submicroscopic parasitaemia (10.9 (0.8) vs. 12.1 (0.7) g/dl, P < 0.001) compared with those who had no submicroscopic parasitaemia. Submicroscopic malaria infection was associated with anaemia (OR 19.7, (95% CI, 10.3–37.8)). Thirty-eight babies born to women with submicroscopic infections were low birth weight (LBW) and was significantly lower in submicroscopic parasitaemia (2.663 (0.235) vs. 2.926 (0.341) kg, P < 0.001). Submicroscopic malaria infection was associated with LBW (OR = 2.7, (95% CI, 1.2–5.6)). There is a high incidence of submicroscopic infections in any of the three compartments regardless of age or parity. Submicroscopic infection is a risk of maternal anaemia and low birth weight in women in this area of high seasonal malaria transmission.

Submicroscopic Plasmodium infection during pregnancy is associated with reduced antibody levels to tetanus toxoid

Submicroscopic Plasmodium infections in pregnancy are common in endemic areas, and it is important to understand the impact of these low-level infections. Asymptomatic, chronic infections are advantageous for parasite persistence, particularly in areas where the optimal eco-epidemiological conditions for parasite transmission fluctuate. In chronic infections, the persistence of the antigenic stimulus changes the expression of immune mediators and promotes constant immune regulation, including increases in regulatory T cell populations. These alterations of the immune system could compromise the response to routine vaccination. This study aimed to evaluate the effect of submicroscopic plasmodial infection with P. falciparum and P. vivax during pregnancy on the immune response to the tetanus toxoid vaccine in Colombian women. Expression of different cytokines and mediators of immune regulation and levels of anti-tetanus toxoid (TT) immunoglobulin (Ig)G were quantified in pregnant women with and without submicroscopic plasmodial infection. The anti-TT IgG levels were significantly lower in the infected group compared with the uninfected group. The expression of interferon (IFN)-γ, tumour necrosis factor (TNF) and forkhead box protein 3 (FoxP3) was significantly higher in the infected group, while the expression of cytotoxic T lymphocyte antigen 4 (CTLA-4) and transforming growth factor (TGF)-β was lower in the group of infected. In conclusion, submicroscopic Plasmodium infection altered the development of the immune response to the TT vaccine in Colombian pregnant women. The impact of Plasmodium infections on the immune regulatory pathways warrants further exploration.

Low Frequency of Asymptomatic and Submicroscopic Plasmodial Infections in Urabá Region in Colombia

Background

A screening for malaria parasites was conducted with asymptomatic residents in Colombia.

Methods

A descriptive study was carried out in December 2012 in four municipalities of Urabá region in Colombia. A convenience sample of 400 subjects was selected. Participants responded to a survey regarding epidemiological data and blood samples were taken from capillary blood obtained by finger prick for thick smear, rapid diagnostic test (RDT), and polymerase chain reaction (PCR).

Results

399 subjects aged 0.2-98 years were studied (median 22; 221 female (55%)). Episodes of malaria in the last year confirmed by thick film were reported by 47 participants (12%). In 399 samples tested by RDT 4 (1%) were positive (1 with P. falciparum, 3 with P. vivax), and 3 were confirmed by PCR. In 399 thick blood smears examined 5 (1.3%) were positive (2 with P. falciparum, 3 with P. vivax), and 3 were confirmed by PCR. In 227 samples, PCR showed 6 (2.6%) positive samples. The parasitaemia was below 1,440 parasites/μL. The best agreement between diagnoses was found between the RDT and thick blood smears (Kappa = 0.75).

Conclusion

Plasmodial afebrile infection was found in 2% of the studied population, by three diagnostic methods, in residents from a low endemic malaria region in Colombia.

Asymptomatic plasmodial infection in Colombian pregnant women

Information about asymptomatic plasmodial infection is scarce in the world, and the current antimalarial program goals (control, elimination, and eradication) demand this evidence to be well documented in different populations and malaria transmission settings. This study aimed to measure the prevalence of API in Colombian pregnant women at delivery. A retrospective prevalence survey was used. Women were recruited at hospital obstetric facility in each of the municipalities of Turbo, Necoclí in Antioquia department, and Puerto Libertador in Córdoba department. Malaria infection was tested by thick blood smear (TBS) and real-time quantitative PCR (qPCR). Ninety-six pregnant women at delivery were studied: 95% were asymptomatic (91/96), 45% had asymptomatic plasmodial infection (API) by qPCR (41/91), and only 8% (7/91) had API by microscopy. The prevalence of submicroscopic infections (TBS negative and qPCR positive) was very high, 37% (34/91) in asymptomatic women and 41% (39/96) in total women studied (91 asymptomatic and 5 symptomatic). The prevalence of API in Colombian pregnant women is much higher than which is expected for a country that does not have the level of malaria transmission as Sub-Saharan African countries.

Submicroscopic and Asymptomatic Congenital Infection by Plasmodium vivax or P. falciparum in Colombia: 37 Cases with Placental Histopathology and Cytokine Profile in Maternal and Placental Blood

Problem. Congenital plasmodial infection (CPI) is a rare event, which has been little studied in Colombia. Objective. To measure the frequency of CPI and to describe the immune and histological characteristics in maternal blood and placentas when CPI occurs. Methodology. A cross-sectional study was carried out in northwest Colombia. A sample size of 39 unit analysis (a unit of analysis corresponds to the cord, placenta, and peripheral blood of a pregnant woman) was calculated using epidemiological and statistical parameters. Thick blood smear (TBS) and quantitative real-time polymerase chain reaction (qPCR) were used as diagnostic tests. Results and Conclusions. A total of 137 parturient women were studied. All cases of CPI were submicroscopic (TBS negative and qPCR positive) and asymptomatic infections. If the definition of CPI considers only detection of parasites in umbilical cord blood, regardless of what was found in peripheral or placental blood, the frequency of CPI was 27%. However, if that definition is stricter and includes simultaneous detection of parasites in maternal or placental blood with the same species, the frequency of CPI in this study was 13%.

Does Iron Increase the Risk of Malaria in Pregnancy?

Background.  Pregnancy-associated malaria (PAM) remains a significant health concern in sub-Saharan Africa. Cross-sectional studies report that iron might be associated with increased malaria morbidity, raising fears that current iron supplementation policies will cause harm in the present context of increasing resistance against intermittent preventive treatment in pregnancy (IPTp). Therefore, it is necessary to assess the relation of iron levels with malaria risk during the entire pregnancy. Methods.  To investigate the association of maternal iron levels on malaria risk in the context of an IPTp clinical trial, 1005 human immunodeficiency virus-negative, pregnant Beninese women were monitored throughout their pregnancy between January 2010 and May 2011. Multilevel models with random intercept at the individual levels and random slope for gestational age were used to analyze the factors associated with increased risk of a positive blood smear and increased Plasmodium falciparum density. Results.  During the follow-up, 29% of the women had at least 1 episode of malaria. On average, women had 0.52 positive smears (95% confidence interval [CI], 0.44-0.60). High iron levels (measured by the log10 of ferritin corrected on inflammation) were significantly associated with increased risk of a positive blood smear (adjusted odds ratio = 1.75; 95% CI, 1.46-2.11; P < .001) and high P falciparum density (beta estimate = 0.22; 95% CI, 0.18-0.27; P < .001) during the follow-up period adjusted on pregnancy parameters, comorbidities, environmental and socioeconomic indicators, and IPTp regime. Furthermore, iron-deficient women were significantly less likely to have a positive blood smear and high P falciparum density (P < .001 in both cases). Conclusions.  Iron levels were positively associated with increased PAM during pregnancy in the context of IPTp. Supplementary interventional studies are needed to determine the benefits and risks of differently dosed iron and folate supplements in malaria-endemic regions.

Submicroscopic infection of placenta by Plasmodium produces Th1/Th2 cytokine imbalance, inflammation and hypoxia in women from north-west Colombia

BACKGROUND

A large-scale study was set up in order to study the epidemiology, clinical aspects, and immunopathology of gestational and placental malaria in north-west Colombia. In this region, recent reports using a qPCR technique, confirmed frequencies of infection, by Plasmodium falciparum or Plasmodium vivax, up to 45%. Given the high rates of infection observed both in mother and placenta, a first exploratory study was proposed in order to characterize the effect on the inflammation status, tissue damage and hypoxia in Plasmodium spp. infected placentas.

METHODS

A descriptive, prospective, cross-sectional design was applied to pregnant women with (PM+) and without (PM-) placental malaria. Messenger RNA expression of Fas, FasL; COX-1, COX-2, HIF, VEGF, and the cytokines IL-2, IL-4, IL-10, IFN-γ and TNF, were measured in peripheral and placental blood using a quantitative PCR. The percentage of apoptotic cells was determined with a TUNEL assay.

RESULTS

In total 50 placentas were studied: 25 were positive for submicroscopic infection and 25 were negative for Plasmodium infection. Expression of IL-4 and IL-10 was observed high in placental tissue of PM+, while IL-2 was high in peripheral blood of the same group. Expression of TNF and IFNγ in peripheral blood of the PM + group was high. Similarly, the apoptotic index and Fas expression were significantly high in PM+. However, FasL expression was observed low in PM + compared to PM-. Inflammation markers (HIF, VEGF) and hypoxia markers (COX-1, COX-2) were high in the PM + group.

CONCLUSION

During placental malaria expression of some pro-inflammatory cytokines is up-regulated and markers of hypoxia and tissue damage are increased in cases of submicroscopic infection.

Prevalence of gestational, placental and congenital malaria in north-west Colombia

BACKGROUND

The frequency of pregnancy-associated malaria is increasingly being documented in American countries. In Colombia, with higher frequency of Plasmodium vivax over Plasmodium falciparum infection, recent reports confirmed gestational malaria as a serious public health problem. Thick smear examination is the gold standard to diagnose malaria in endemic settings, but in recent years, molecular diagnostic methods have contributed to elucidate the dimension of the problem of gestational malaria. The study was aimed at exploring the prevalence of gestational, placental and congenital malaria in women who delivered at the local hospitals of north-west Colombia, between June 2008 and April 2011.

METHODS

A group of 129 parturient women was selected to explore the prevalence of gestational, placental and congenital malaria in a descriptive, prospective and transversal (prevalence) design. Diagnosis was based on the simultaneous application of two independent diagnostic tests: microscopy of thick blood smears and a polymerase chain reaction assay (PCR).

RESULTS

The prevalence of gestational malaria (thick smear /PCR) was 9.1%/14.0%; placental malaria was 3.3%/16.5% and congenital malaria was absent. A history of gestational malaria during the current pregnancy was significantly associated with gestational malaria at delivery. Plasmodium vivax caused 65% of cases of gestational malaria, whereas P. falciparum caused most cases of placental malaria.

CONCLUSIONS

Gestational and placental malaria are a serious problem in the region, but the risk of congenital malaria is low. A history of malaria during pregnancy may be a practical indicator of infection at delivery.

Malaria in pregnancy: diagnosing infection and identifying fetal risk

Despite increased malaria control efforts, recent reports indicate that over 1.2 million deaths due to malaria occurred in 2010. Pregnant women represent a particularly vulnerable risk group as malaria infection can lead to life-threatening disease for the mother and fetus. With 125 million women at risk of malaria in pregnancy every year, better diagnostic tools are needed for timely identification and treatment of malaria infection. Diagnostic surveillance tools are also needed to estimate disease burden and inform public health policies. In this review, the authors focus on malaria diagnostics in pregnancy and discuss considerations for different Plasmodium species and geographic regions. The authors also look at promising diagnostic modalities to monitor fetal and maternal health in pregnancy and discuss implementation barriers for low resource settings.

Factors determining the occurrence of submicroscopic malaria infections and their relevance for control

Malaria parasite prevalence in endemic populations is an essential indicator for monitoring the progress of malaria control, and has traditionally been assessed by microscopy. However, surveys increasingly use sensitive molecular methods that detect higher numbers of infected individuals, questioning our understanding of the true infection burden and resources required to reduce it. Here we analyse a series of data sets to characterize the distribution and epidemiological factors associated with low-density, submicroscopic infections. We show that submicroscopic parasite carriage is common in adults, in low-endemic settings and in chronic infections. We find a strong, non-linear relationship between microscopy and PCR prevalence in population surveys (n=106), and provide a tool to relate these measures. When transmission reaches very low levels, submicroscopic carriers are estimated to be the source of 20–50% of all human-to-mosquito transmissions. Our findings challenge the idea that individuals with little previous malaria exposure have insufficient immunity to control parasitaemia and suggest a role for molecular screening.

Malaria can persist at levels that escape detection by standard microscopy, but can be detected by PCR. Okell et al. now show that rates of submicroscopic infection can be predicted using more widely available microscopy data, and are most epidemiologically significant in areas with low malaria transmission.

Molecular detection of malaria at delivery reveals a high frequency of submicroscopic infections and associated placental damage in pregnant women from northwest Colombia

Plasmodium infection in pregnancy causes substantial maternal and infant morbidity and mortality. In Colombia, both P. falciparum and P. vivax are endemic, but the impact of either species on pregnancy is largely unknown in this country. A cross-sectional study was carried out with 96 pregnant women who delivered at their local hospital. Maternal, placental, and cord blood were tested for malaria infection by microscopy and real-time quantitative polymerase chain reaction (qPCR). A high frequency of infection was detected by qPCR (45%). These infections had low concentrations of parasite DNA, and 79% were submicroscopic. Submicroscopic infections were associated with placental villitis and intervillitis. In conclusion, the overall frequency of Plasmodium infection at delivery in Colombia is much higher than previously reported. These data prompt a re-examination of the local epidemiology of malaria using molecular diagnostics to establish the clinical relevance of submicroscopic infections during pregnancy as well as their consequences for mothers and newborns.

Placental malaria in Colombia: histopathologic findings in Plasmodium vivax and P. falciparum infections

Studies on gestational malaria and placental malaria have been scarce in malaria-endemic areas of the Western Hemisphere. To describe the histopathology of placental malaria in Colombia, a longitudinal descriptive study was conducted. In this study, 179 placentas were studied by histologic analysis (112 with gestational malaria and 67 negative for malaria). Placental malaria was confirmed in 22.35%, 50.0% had previous infections, and 47.5% had acute infections. Typical malaria-associated changes were observed in 37%. The most common changes were villitis, intervillitis, deciduitis, increased fibrin deposition, increased syncytial knots, mononuclear (monocytes/macrophages and lymphocytes), polymorphonuclear cell infiltration, and trophozoites in fetal erythrocytes. No association was found between type of placental changes observed and histopathologic classification of placental malaria. The findings are consistent with those reported for placental malaria in other regions. Plasmodium vivax was the main parasite responsible for placental and gestational malaria, but its role in the pathogenesis of placental malaria was not conclusive.

Evaluation of antigen detection tests, microscopy, and polymerase chain reaction for diagnosis of malaria in peripheral blood in asymptomatic pregnant women in Nanoro, Burkina Faso

Rapid diagnostics tests (RDTs) detect malaria specific antigen(s) in the circulation, even when parasites are sequestered in the placenta and not visible by microscopy. However, research on their diagnostic accuracy during pregnancy is limited. Pregnant women (n = 418) were screened for malaria during routine antenatal care by using two RDTs that detect histidine-rich protein 2 (HRP2) or Plasmodium lactate dehydrogenase, and enzyme-linked immunosorbent assays with antibodies that detect dihydrofolate reductase-thymidylate synthase or heme-detoxification protein, and compared with real-time polymerase chain reaction (RT-PCR) and microscopy for evaluation of their diagnostic accuracy. Prevalence of malaria infection was high (53% by PCR). The RT-PCR and the HRP2 RDT detected most cases of malaria during pregnancy, whereas microscopy, the Plasmodium lactate dehydrogenase RDT, and enzyme-linked immunosorbent assays for dihydrofolate reductase-thymidylate synthase and heme-detoxification protein antibodies did not detect several low-density infections. Therefore, the HRP2 RDT could be a useful tool in high-transmission areas for diagnosis of malaria in asymptomatic pregnant women.

Genotype comparison of Plasmodium vivax and Plasmodium falciparum clones from pregnant and non-pregnant populations in North-west Colombia

BACKGROUND

Placental malaria is the predominant pathology secondary to malaria in pregnancy, causing substantial maternal and infant morbidity and mortality in tropical areas. While it is clear that placental parasites are phenotypically different from those in the peripheral circulation, it is not known whether unique genotypes are associated specifically with placental infection or perhaps more generally with pregnancy. In this study, genetic analysis was performed on Plasmodium vivax and Plasmodium falciparum parasites isolated from peripheral and placental blood in pregnant women living in North-west Colombia, and compared with parasites causing acute malaria in non-pregnant populations.

METHODS

A total of 57 pregnant women at delivery with malaria infection confirmed by real-time PCR in peripheral or placental blood were included, as well as 50 pregnant women in antenatal care and 80 men or non-pregnant women with acute malaria confirmed by a positive thick smear for P. vivax or P. falciparum. Five molecular markers per species were genotyped by nested PCR and capillary electrophoresis. Genetic diversity and the fixation index FST per species and study group were calculated and compared.

RESULTS

Almost all infections at delivery were asymptomatic with significantly lower levels of infection compared with the groups with acute malaria. Expected heterozygosity for P. vivax molecular markers ranged from 0.765 to 0.928 and for P. falciparum markers ranged from 0.331 to 0.604. For P. vivax infections, the genetic diversity was similar amongst the four study groups and the fixation index from each pairwise comparison failed to show significant genetic differentiation. For P. falciparum, no genetic differentiation was observed between placental and peripheral parasites from the same woman at delivery, but the parasites isolated at delivery showed significant genetic differentiation compared with parasites isolated from subjects with acute malaria.

CONCLUSIONS

In North-west Colombia, P. vivax parasites have high genetic diversity that is equivalent in pregnant and non-pregnant populations as well as in symptomatic and asymptomatic infections. For P. falciparum, the overall genetic diversity is lower, with specific genotypes associated with asymptomatic infections at delivery.

Imported submicroscopic malaria in Madrid

Background

Submicroscopic malaria (SMM) can be defined as low-density infections of Plasmodium that are unlikely to be detected by conventional microscopy. Such submicroscopic infections only occasionally cause acute disease, but they are capable of infecting mosquitoes and contributing to transmission. This entity is frequent in endemic countries; however, little is known about imported SMM.

The goals of this study were two-fold: a) to know the frequency of imported SMM, and b) to describe epidemiological, laboratorial and clinical features of imported SMM.

Methods

A retrospective study based on review of medical records was performed. The study population consisted of patients older than 15 years attended at the Tropical Medicine Unit of Hospital Carlos III, between January 1, 2002 and December 31, 2007. Routinely detection techniques for Plasmodium included Field staining and microscopic examination through thick and thin blood smear. A semi-nested multiplex malaria PCR was used to diagnose or to confirm cases with low parasitaemia.

Results

SMM was diagnosed in 104 cases, representing 35.5% of all malaria cases. Mean age (IC95%) was 40.38 years (37.41-43.34), and sex distribution was similar. Most cases were in immigrants, but some cases were found in travellers. Equatorial Guinea was the main country where infection was acquired (81.7%). Symptoms were present only in 28.8% of all SMM cases, mainly asthenia (73.3% of symptomatic patients), fever (60%) and arthromialgias (53.3%). The associated laboratory abnormalities were anaemia (27.9%), leukopaenia (15.4%) and thrombopaenia (15.4%). Co-morbidity was described in 75 cases (72.1%).

Conclusions

Results from this study suggest that imported SMM should be considered in some patients attended at Tropical Medicine Units. Although it is usually asymptomatic, it may be responsible of fever, or laboratory abnormalities in patients coming from endemic areas. The possibility of transmission in SMM has been previously described in endemic zones, and presence of vector in Europe has also been reported. Implementation of molecular tests in all asymptomatic individuals coming from endemic area is not economically feasible. So re-emergence of malaria (Plasmodium vivax) in Europe may be speculated.

How hidden can malaria be in pregnant women? Diagnosis by microscopy, placental histology, polymerase chain reaction and detection of histidine-rich protein 2 in plasma

BACKGROUND

Accurate diagnosis of malaria infection during pregnancy remains challenging because of low parasite densities and placental sequestration of Plasmodium falciparum. The performance of different methods to detect P. falciparum in pregnancy and the clinical relevance of undetected infections were evaluated.

METHODS

P. falciparum infections were assessed in 272 Mozambican women at delivery by microscopy, placental histology, quantitative polymerase chain reaction (qPCR) and detection of histidine-rich protein 2 (HRP2) in plasma by enzyme-linked immunosorbent assay (ELISA) and a rapid diagnostic test (RDT). Association between infection and delivery outcomes was determined.

RESULTS

Among the 122 women qPCR-positive for P. falciparum in peripheral and/or placental blood samples, 87 (71.3%) did not receive a positive diagnosis by peripheral microscopy, 75 (61.5%) by HRP2 ELISA, and 74 (60.7%) by HRP2 RDT in plasma. Fifty-seven of the 98 qPCR-positive placental infections (58.2%) were not detected by histology. Women who were qPCR-positive but negative in their peripheral blood by microscopy or HRP2 RDT in plasma (n = 62) were at increased risk of anemia, compared with negative women (n = 141; odds ratio, 2.03; 95% confidence interval, 1.07-3.83; P = .029).

CONCLUSIONS

Microscopy, placental histology and HRP2-based plasma diagnostic methods fail to identify the majority of the P. falciparum infections detected by qPCR in peripheral and placental blood. Undetected infections were associated with maternal anemia, highlighting the urgent need for more accurate malaria diagnostic tools for pregnant women to avoid the negative clinical impact that hidden infections can have during pregnancy.

CLINICAL TRIALS REGISTRATION

NCT00209781.

Systematic review and meta-analysis: rapid diagnostic tests versus placental histology, microscopy and PCR for malaria in pregnant women

BACKGROUND

During pregnancy, malaria infection with Plasmodium falciparum or Plasmodium vivax is related to adverse maternal health and poor birth outcomes. Diagnosis of malaria, during pregnancy, is complicated by the absence or low parasite densities in peripheral blood. Diagnostic methods, other than microscopy, are needed for detection of placental malaria. Therefore, the diagnostic accuracy of rapid diagnostic tests (RDTs), detecting antigen, and molecular techniques (PCR), detecting DNA, for the diagnosis of Plasmodium infections in pregnancy was systematically reviewed.

METHODS

MEDLINE, EMBASE and Web of Science were searched for studies assessing the diagnostic accuracy of RDTs, PCR, microscopy of peripheral and placental blood and placental histology for the detection of malaria infection (all species) in pregnant women.

RESULTS

The results of 49 studies were analysed in metandi (Stata), of which the majority described P. falciparum infections. Although both placental and peripheral blood microscopy cannot reliably replace histology as a reference standard for placental P. falciparum infection, many studies compared RDTs and PCR to these tests. The proportion of microscopy positives in placental blood (sensitivity) detected by peripheral blood microscopy, RDTs and PCR are respectively 72% [95% CI 62-80], 81% [95% CI 55-93] and 94% [95% CI 86-98]. The proportion of placental blood microscopy negative women that were negative in peripheral blood microscopy, RDTs and PCR (specificity) are 98% [95% CI 95-99], 94% [95% CI 76-99] and 77% [95% CI 71-82]. Based on the current data, it was not possible to determine if the false positives in RDTs and PCR are caused by sequestered parasites in the placenta that are not detected by placental microscopy.

CONCLUSION

The findings suggest that RDTs and PCR may have good performance characteristics to serve as alternatives for the diagnosis of malaria in pregnancy, besides any other limitations and practical considerations concerning the use of these tests. Nevertheless, more studies with placental histology as reference test are urgently required to reliably determine the accuracy of RDTs and PCR for the diagnosis of placental malaria. P. vivax-infections have been neglected in diagnostic test accuracy studies of malaria in pregnancy.

Diagnosis of gestational, congenital, and placental malaria in Colombia: comparison of the efficacy of microscopy, nested polymerase chain reaction, and histopathology

The technical capability of different methods to diagnose Plasmodium in maternal peripheral blood, placenta, and umbilical cord blood has not been assessed in Colombia and seldom explored in other malaria-endemic regions. We designed a study to compare the technical and the operational-economical performances of light microscopy (LM), nested polymerase chain reaction (nPCR), and histopathology (HP). In maternal blood, LM had 41% sensitivity and 100% specificity and in placental blood, 35% and 100%, respectively, compared with nPCR. In placental tissue, LM had 33% sensitivity and 95% specificity; and nPCR 47% and 77%, respectively; compared with HP. Light microscopy had the best operational-economical qualification. We concluded that nPCR and HP performed better compared with LM, but field implementation of these two techniques remains a problem. Therefore, LM is recommended as the gold standard for diagnosis of gestational malaria and placental blood infection in the field.