Asymptomatic Plasmodium Infections Research Articles

Recurrence patterns and evolution of submicroscopic and asymptomatic Plasmodium vivax infections in malaria-endemic areas of the Peruvian Amazon.

In the Peruvian Amazon, Plasmodium vivax malaria transmission is maintained due to the high frequency of recurrences. By understanding the recurrence rates of submicroscopic and asymptomatic cases, we can develop informed strategies to prevent transmission more efficiently and disrupt the silent transmission cycle. A three-year, population-based cohort study was conducted in two sites, Cahuide and Lupuna, within the Loreto region in Peru from 2013 to 2015. The study included 385 individuals and aimed to examine the temporal dynamics of malaria recurrences and their impact on transmission and control. Individuals from Lupuna presented a higher risk of P. vivax infections compared to Cahuide, where most recurrences were asymptomatic and submicroscopic. It is estimated that a great proportion of these recurrences were due to relapses in both communities. The application of molecular diagnostic method proved to be significantly more effective, detecting 2.3 times more episodes during the follow-up (PCR, 1068; microscopy, 467). PCR identified recurrences significantly earlier, at 151 days after an initial infection, compared to microscopy, which detected them on average after 365 days. Community, occupation and previous malaria infections were factors associated with recurrences. Finally, potential infection evolution scenarios were described where one frequent scenario involved the transition from symptomatic to asymptomatic infections with a mean evolution time of 240 days. This study explores the contrast in malaria recurrence risk among individuals from two endemic settings, a consequence of prolonged exposure to the parasite. Through the analysis of the evolution scenarios of P. vivax recurrences, it is possible to have a more complete vision of how the transmission pattern changes over time and is conditioned by different factors.

Asymptomatic Malaria Cases and Plasmodium Species among BaAka Pygmies in Central Africa.

Malaria is a significant health problem in Africa, primarily due to the Plasmodium falciparum species, but this is not the only etiological factor responsible for malaria on the continent. The goal of the present research was to describe asymptomatic malaria cases and to identify Plasmodium species responsible for malaria in the BaAka Pygmies, inhabitants of the Central African Republic (CAR). Screening was realised in the period of August-September 2021 among 308 people, including 74 children and 234 adults reporting to a healthcare facility in Monasao (southwest CAR), an area inhabited by a semi-nomadic tribe of BaAka Pygmies. The study consisted of two phases. Phase I, which was conducted in Africa, consisted of performing malaria rapid diagnostic tests (mRDTs), taking haemoglobin measurements and collecting blood samples onto Whatman FTA cards for molecular diagnostics. Phase II, which was conducted in Poland, involved molecular tests (RT-PCR) to confirm or rule out malaria infections and to identify Plasmodium species responsible for the infections. mRDTs detected Plasmodium infections in 50.3% of children and 17.1% of adults participating in the study, whereas RT-PCR assays yielded positive results for 59.5% children and 28.6% adults. Molecular tests detected multiple Plasmodium falciparum infections but also three infections with P. malariae, three with P. ovale and one with P. vivax. The obtained results have confirmed numerous asymptomatic Plasmodium infections among the BaAka Pygmies. The rates of asymptomatic malaria cases in adults were twice as high as those in children, which may be indicative of the gradual acquisition of protective immunity with age. The study findings have also demonstrated that although most cases of malaria in Africa are caused by P. falciparum, three other species are also present in the region.

Comparison of malaria diagnostic methods for detection of asymptomatic Plasmodium infections among pregnant women in northwest Ethiopia

BackgroundMalaria in pregnancy remains a major public health problem in the globe, especially in sub-Saharan Africa. In malaria endemic areas, most pregnant women remain asymptomatic, but malaria could still cause complications on the mother and her offspring; as well as serve as reservoirs to transmit infection. Despite these effects, no attention is given to the diagnosis of asymptomatic Plasmodium infections (APIs) using highly sensitive and specific laboratory diagnostic tools in Ethiopia. Therefore, the goal of this study was to compare the performance of Rapid Diagnostic Test (RDT), microscopy and real-time polymerase chain reaction (RT-PCR) to detect APIs among pregnant women.MethodsA health facility based cross -sectional study was conducted among pregnant women attending antenatal care at Fendeka town health facilities Jawi district, northwest Ethiopia from February to March, 2019. A total of 166 participants were enrolled by using convenient sampling technique. Socio-demographic features were collected using a semi structured questionnaire. Dried blood spot (DBS) samples were collected for molecular analysis. Asymptomatic Plasmodium infection on pregnant women was diagnosed using RDT, microscopy and RT-PCR. Descriptive statistics were used to determine the prevalence of APIs. Method comparison was performed, and Cohen’s kappa coefficient (k) was used to determine the degree of agreement among the diagnostic methods. Parasite densities were also calculated.ResultsThe prevalence of API was 9.6%, 11.4% and 18.7% using RDT, microscopy and RT-PCR, respectively. The overall proportion of API was 19.3%. Sensitivity of the RDT was 83.3% as compared with microscopy. Rapid Diagnostic Test and microscopy also showed sensitivity of 50% and 60%, respectively, as compared with RT-PCR. The mean parasite density was 3213 parasites/µl for P falciparum and 1140 parasites/µl of blood for P. vivax.ConclusionPrevalence of API in the study area was high. Both RDT and microscopy had lower sensitivity when compared with RT-PCR. Therefore, routine laboratory diagnosis of API among pregnant women should be given attention and done with better sensitive and specific laboratory diagnostic tools.

Malaria transmission heterogeneity in different eco-epidemiological areas of western Kenya: a region-wide observational and risk classification study for adaptive intervention planning

BackgroundUnderstanding of malaria ecology is a prerequisite for designing locally adapted control strategies in resource-limited settings. The aim of this study was to utilize the spatial heterogeneity in malaria transmission for the designing of adaptive interventions.MethodsField collections of clinical malaria incidence, asymptomatic Plasmodium infection, and malaria vector data were conducted from 108 randomly selected clusters which covered different landscape settings including irrigated farming, seasonal flooding area, lowland dryland farming, and highlands in western Kenya. Spatial heterogeneity of malaria was analyzed and classified into different eco-epidemiological zones.ResultsThere was strong heterogeneity and detected hot/cold spots in clinical malaria incidence, Plasmodium prevalence, and vector abundance. The study area was classified into four zones based on clinical malaria incidence, parasite prevalence, vector density, and altitude. The two irrigated zones have either the highest malaria incidence, parasite prevalence, or the highest malaria vector density; the highlands have the lowest vector density and parasite prevalence; and the dryland and flooding area have the average clinical malaria incidence, parasite prevalence and vector density. Different zones have different vector species, species compositions and predominant species. Both indoor and outdoor transmission may have contributed to the malaria transmission in the area. Anopheles gambiae sensu stricto (s.s.), Anopheles arabiensis, Anopheles funestus s.s., and Anopheles leesoni had similar human blood index and malaria parasite sporozoite rate.ConclusionThe multi-transmission-indicator-based eco-epidemiological zone classifications will be helpful for making decisions on locally adapted malaria interventions.

Assessing the daily natural history of asymptomatic Plasmodium infections in adults and older children in Katakwi, Uganda: a longitudinal cohort study

Low-density asymptomatic Plasmodium infections are prevalent in endemic areas, but little is known about their natural history. The trajectories of these infections and their propensity to fluctuate to undetectable densities can affect detection in clinical trials and field studies. We aimed to classify the natural history of these infections in a high transmission area over 29 days. In this longitudinal cohort study, we enrolled healthy, malaria-asymptomatic, afebrile, adults (age 18-59 years) and older children (age 8-17 years) in Katakwi District, Uganda, who were negative for Plasmodium infection on rapid diagnostic tests. Participants were instructed to self-collect one dried blood spot (DBS) per day for a maximum of 29 days. We excluded people if they were pregnant or taking antimalarials. During weekly clinic visits, staff collected a DBS and a 4 mL sample of venous blood. We analysed DBSs by Plasmodium 18S rRNA quantitative RT-PCR (qRT-PCR). We classified DBS by infection type as negative, P falciparum, non-P falciparum, or mixed. We plotted infection type over time for each participant and categorised trajectories as negative, new, cleared, chronic, or indeterminate infections. To estimate the effect of single timepoint sampling, we calculated the daily prevalence for each study day and estimated the number of infections that would have been detected in our population if sampling frequency was reduced. Between April 9 and May 20, 2021, 3577 DBSs were collected by 128 (40 male adults, 60 female adults, 12male children, and 16 female children) study participants. 2287 (64%) DBSs were categorised as negative, 751(21%) as positive for P falciparum, 507 (14%) as positive for non-P falciparum, and 32 (1%) as mixed infections. Daily Plasmodium prevalence in the population ranged from 45·3% (95% CI 36·6-54·1) at baseline to 30·3% (21·9-38·6) on day 24. 37 (95%) of 39 P falciparum and 35 (85%) of 41 non-P falciparum infections would have been detected with every other day sampling, whereas, with weekly sampling, 35 (90%) P falciparum infections and 31 (76%) non-P falciparum infections would have been detected. Parasite dynamics and species are highly variable among low-density asymptomatic Plasmodium infections. Sampling every other day or every 3 days detected a similar proportion of infections as daily sampling, whereas testing once per week or even less frequently could misclassify up to a third of the infections. Even using highly sensitive diagnostics, single timepoint testing might misclassify the true infection status of an individual. US National Institutes of Health and Bill and Melinda Gates Foundation.

Plasmodium infections and associated risk factors among parturients in Jawi district, northwest Ethiopia: a cross-sectional study

BackgroundPregnant women have an increased risk of Plasmodium infections and disease. Malaria in pregnancy is a major public health problem in endemic areas. Assessment of the burden and risk factors of malaria in pregnancy across different malaria transmission settings is required to guide control strategies and for malaria elimination. Thus, the current study is generating such evidence from parturient women in northwest Ethiopia.MethodsA cross-sectional study was conducted among 526 pregnant women admitted to the delivery rooms of selected health facilities in Jawi district, northwest Ethiopia, between November 2021 and July 2022. Data on the socio-demographic, clinical, obstetric, and malaria prevention practices of pregnant women were collected using interviewer-administered questionnaires and from women’s treatment cards. Malaria was diagnosed by light microscopy, rapid diagnostic test, and multiplex real-time polymerase chain reaction. Risk factors for malaria were evaluated using bivariable and multivariable logistic regression models. A P-value of < 0.05 was considered statistically significant.ResultsAmong the examined parturient women, 14.3% (95% CI 11.4–17.5%) had Plasmodium infections. The prevalence of peripheral, placental, and congenital malaria was 12.2% (95% CI 9.5–15.3%), 10.9% (95% CI 8.2–14.1%), and 3.7% (95% CI 2.3–6.1%), respectively. About 90.6% of peripheral and 92% of placental Plasmodium infections were asymptomatic. Plasmodium infection at parturiency was independently predicted by maternal illiteracy (AOR = 2.03, 95% CI 1.11–3.74), primigravidity (AOR = 1.88, 95% CI 1.01–3.49), lack of antenatal care follow-up (AOR = 2.28, 95% CI 1.04–5.03), and history of symptomatic malaria during pregnancy (AOR = 4.2, 95% CI 2.32–7.59). Moreover, the blood group O phenotype was significantly associated with placental malaria among the primiparae.ConclusionsOverall, asymptomatic Plasmodium infections were prevalent among parturients in northwest Ethiopia. Maternal illiteracy, primigravidity, lack of antenatal care follow-up, and history of symptomatic malaria during pregnancy were the risk factors for malaria during parturiency. Thus, promotion of a healthy pregnancy through ANC follow-up, strengthening malaria prevention and control practices, and screening of malaria in asymptomatic pregnant women are suggested to reduce its burden in pregnancy.

Asymptomatic Malaria During Pregnancy: Prevalence, Influence on Anemia and Associated Factors in West Guji Zone, Ethiopia - A Community-Based Study.

Pregnant women with asymptomatic malaria parasitemia are at increased risk of anaemia, stillbirth, miscarriage, and preterm delivery. The asymptomatic nature of the population makes diagnosis difficult, and there is generally a lack of urgency to address this specific outcome. This study aimed to determine the prevalence of asymptomatic malaria and associated factors among pregnant women in West Guji Zone, Oromia, Ethiopia. A community-based cross-sectional study was conducted among randomly selected 557 asymptomatic pregnant women in the West Guji Zone from February to March 2022. A standardized questionnaire was used to collect information on socio-demographic and obstetric characteristics. Approximately 2 milliliters of peripheral blood was collected for microscopy to identify species and parasite density. Epi-Data and SPSS were used for data entry and analysis respectively. Binary logistic regression was used to identify risk factors. The prevalence of malaria among asymptomatic pregnant women was 24.10% (95% CI: 20.55%-27.65%). The prevalence of Plasmodium vivax and falciparum prevalence was 73 (54.5%) and 61 (45.5%), respectively. Of the study subjects, 105 (78.4%) had mild parasitemia and 29 (21.6%) had moderate parasitemia. Pregnant women with Plasmodium infection were anaemic in two-thirds (66.5%) of cases. Living near standing water (AOR=2.6, 95% CI: 1.74-3.96), having a history of Plasmodium species infection (AOR=2.12, 95% CI: 1.36-3.31), not using indoor residual spraying (AOR=2.0, 95% CI: 1.32-3.14), and not using insecticide-treated bed nets (AOR=1.62, 95% CI: 1.02-2.55) were all factors that were significantly associated with asymptomatic infection. Pregnant women with Plasmodium infection had a significantly higher rate of anaemia than those who were not infected (OR = 6.31, p = 0.000). Pregnant women had a significant prevalence of asymptomatic Plasmodium infection. Regular screening, appropriate treatment for those who test positive, and health education for pregnant women should be provided by the West Guji Zone Health Bureau.

Prevalence and proportion estimate of asymptomatic Plasmodium infection in Asia: a systematic review and meta-analysis

Asymptomatic Plasmodium infection raises a problem for the persistent transmission of malaria in low-endemic areas such as Asia. This systematic review was undertaken to estimate the prevalence and proportion of asymptomatic Plasmodium infection in Asia. The systematic review was registered at PROSPERO (ID: CRD42022373664). The research followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses. A comprehensive search of five databases, Ovid, Scopus, MEDLINE, PubMed, and Embase, was conducted to identify studies of asymptomatic Plasmodium infection in Asian countries. The pooled prevalence of asymptomatic Plasmodium infection, the pooled proportion of asymptomatic Plasmodium infection among all parasitised individuals, and the associated 95% confidence intervals were estimated using a random-effects model. A total of 916 articles were retrieved, and 87 articles that met the criteria were included in the systematic review. The pooled prevalence of asymptomatic Plasmodium infection among enrolled participants in Southeast Asia, South Asia, and Western Asia was 5.8%, 9.4%, and 8.4%, respectively. The pooled proportion of asymptomatic Plasmodium infection among all parasitised individuals in Southeast Asia, South Asia, and Western Asia was 89.3%, 87.2%, and 64.8%, respectively. There was a low prevalence of asymptomatic Plasmodium infection, but there was a high proportion of asymptomatic Plasmodium infection per all parasitised individuals in different parts of Asia. These results may support and facilitate elimination and control programs for asymptomatic Plasmodium infection in Asia.

The prevalence and density of asymptomatic plasmodium infections among children in a rural community of South- Western Nigeria.

Asymptomatic malaria is highly prevalent in endem ic areas of Africa and it is a new challenge for the malaria elimination agenda. In recent years, the number of hospitalizations due to malaria cases in sub-Saharan Africa has steadily decreased. However, there are indications that this positive trend could suffer a setback due to asymptomatic malaria cases, which may serve as reservoir of infections for vulnerable populations. This cross-sectional study examined the prevalence of asymptomatic malaria in school-aged children living in a rural community in South- West, Nigeria. The study was conducted from August to September 2020, involving 300 randomly selected school children. Histidine rich protein II rapid diagnostic test kits (HRP2) were used to screen participants for malaria. All blood samples were further examined microscopically using 3% Giemsa-stained blood smears for confirmation, speciation, and parasites. The anaemia status of the children was quantification of malaria determined by measuring the haematocrit. Statistical analysis of the data was done using the chi-square test, student t-test, Mann Whitney U test and Kruskal-Wallis rank sum tests to determine the association between variables and the difference in mean/median with a significance level p≤ 0.05. The results showed a high prevalence of asymptomatic malaria of 41% by microscopy. The prevalence of asymptomatic malaria was statistically significantly higher among children aged 6 to 11 years (52%), compared to children &gt;12years (37%), and &lt; 5years old (13%), (p=0.00001). Plasmodium falciparum was responsible for 96% of the infection while the remaining 4% had multiple infections with Plasmodium falciparum and Plasmodium ovale. This study confirms that the prevalence of asymptomatic cases of malaria among children in malaria endemic areas is high and they will benefit from malaria chemoprophylaxis.

Asymptomatic Plasmodium Infection and Associated Factors in Selected Districts of the Kaffa Zone, Southwest Ethiopia: A Cross-Sectional Study.

Malaria remains a serious public health problem, particularly in resource scarce areas of the world. The number of malaria cases has dropped remarkably in Ethiopia over the last decade, and efforts to eliminate the disease are underway. Asymptomatic infections may pose significant challenges to the elimination program. The essence of this study was to assess the prevalence of asymptomatic Plasmodium infection and the associated factors among communities of the selected districts in the Kaffa zone. April to May and September to October 2021, were the two seasons in which the community-based cross-sectional survey was conducted. Capillary blood from a finger prick was examined by light microscopy (LM) and screened using rapid diagnostic tests (RDTs). The participants' sociodemographic characteristics and malaria prevention measures were collected using a pretested semistructured questionnaire. Data entry and analyses were carried out using EpiData and SPSS version 25.0. Logistic regression (bivariate and multivariable) analyses were carried out to assess the possible associations between the dependent variable and the associated factors. 566 study participants were involved in the two cross-sectional surveys, including 234 male and 332 female subjects with a mean age of 18.486 (SD ± 15.167). Thirty-eight blood samples (6.7%) were found to be positive for Plasmodium species tested by both LM and RDT. Last night's use of long-lasting insecticidal net (LLIN) (AOR = 2.448, 95% CI: 1.009 5.938, p=0.048), presence of eave (AOR = 4.144, 95% CI: 1.049-16.363, p=0.043), and house sprayed in the last year (AOR = 5.206, 95% CI: 2.176-12.455, p < 0.001) were among factors that showed significant association with asymptomatic Plasmodium infection. The asymptomatic Plasmodium infection prevalence recorded in the study area was low. Last night's LLIN usage, the presence of an eave, a house sprayed in the last year, and the presence of stagnant water near the home of the study participants were among the factors associated with an increased risk of catching the disease.

Asymptomatic Plasmodium infection among primary schoolchildren and Anopheles-mediated malaria transmission: A cross-sectional study in Ouidah; south-western Benin

Understanding the contribution of asymptomatic Plasmodium carriers in malaria transmission might be helpful to design and implement new control measures. The present study explored the prevalence of asymptomatic and symptomatic Plasmodium infections (asexual and sexual stages) and the contribution of asymptomatic P. falciparum carriers to Anopheles-mediated malaria transmission in Ouidah (Benin). Thick and thin blood smears were examined from finger-prick blood specimens using light microscopy, and the density of both asexual and sexual stages of Plasmodium species was calculated. Infectivity of gametocyte-infected blood samples to Anopheles gambiae was assessed through direct membrane feeding assays. The prevalence of asymptomatic Plasmodium infections was 28.73% (289/1006). All the asymptomatic gametocyte-carriers (19/19), with gametocytaemia ranging from 10 ̶ 1200 gametocytes/μL of blood, were infectious to An. gambiae mosquitoes. The mean oocyst prevalences varied significantly (χ2 = 16.42, df = 7, p = 0.02) among laboratory mosquito strains (6.9 ̶ 39.4%) and near-field mosquitoes (4.9 ̶ 27.2%). Likewise, significant variation (χ2 = 56.85, df = 7, p = 6.39 × 10−10) was observed in oocyst intensity. Our findings indicate that asymptomatic Plasmodium carriers could significantly contribute to malaria transmission. Overall, this study highlights the importance of diagnosing and treating asymptomatic and symptomatic infection carriers during malaria control programmes.

Evidence-Based Malaria Control and Elimination in the Amazon: Input from the International Center of Excellence in Malaria Research Network in Peru and Brazil.

Malaria remains endemic in 17 countries in the Americas, where 723,000 cases were reported in 2019. The majority (> 90%) of the regional malaria burden is found within the Amazon Basin, which includes nine countries and territories in South America. Locally generated evidence is critical to provide information to public health decision makers upon which the design of efficient and regionally directed malaria control and elimination programs can be built. Plasmodium vivax is the predominant malaria parasite in the Amazon Basin. This parasite species appears to be more resilient to malaria control strategies worldwide. Asymptomatic Plasmodium infections constitute a potentially infectious reservoir that is typically missed by routine microscopy-based surveillance and often remains untreated. The primary Amazonian malaria vector, Nyssorhynchus (formerly Anopheles) darlingi, has changed its behavior to feed and rest predominantly outdoors, reducing the efficiency of core vector control measures such as indoor residual spraying and distribution of long-lasting insecticide-treated bed nets. We review public health implications of recent field-based research carried out by the Amazonia International Center of Excellence in Malaria Research in Peru and Brazil. We discuss the relative role of traditional and novel tools and strategies for better malaria control and elimination across the Amazon, including improved diagnostic methods, new anti-relapse medicines, and biological larvicides, and emphasize the need to integrate research and public health policymaking.

Asymptomatic and submicroscopic Plasmodium infections in an area before and during integrated vector control in Homa Bay, western Kenya

BackgroundLong-lasting insecticidal nets (LLINs) have been the primary vector control strategy until indoor residual spraying (IRS) was added in Homa Bay and Migori Counties in western Kenya. The objective of this study was to evaluate the impact of LLINs integrated with IRS on the prevalence of asymptomatic and submicroscopic Plasmodium infections in Homa Bay County.MethodsA two-stage cluster sampling procedure was employed to enroll study participants aged ≥ 6 months old. Four consecutive community cross-sectional surveys for Plasmodium infection were conducted in residents of Homa Bay county, Kenya. Prior to the start of the study, all study households received LLINs, which were distributed between June 2017 and March 2018. The first (February 2018) and second (June 2018) surveys were conducted before and after the first round of IRS (Feb–Mar 2018), while the third (February 2019) and fourth (June 2019) surveys were conducted before and after the second application of IRS (February–March 2019). Finger-prick blood samples were obtained to prepare thick and thin smears for microscopic determination and qPCR diagnosis of Plasmodium genus.ResultsPlasmodium spp. infection prevalence by microscopy was 18.5% (113/610) before IRS, 14.2% (105/737) and 3.3% (24/720) after the first round of IRS and 1.3% (11/849) after the second round of IRS (p < 0.0001). Submicroscopic (blood smear negative, qPCR positive) parasitaemia reduced from 18.9% (115/610) before IRS to 5.4% (46/849) after IRS (p < 0.0001). However, the proportion of PCR positive infections that were submicroscopic increased from 50.4% (115/228) to 80.7% (46/57) over the study period (p < 0.0001). Similarly, while the absolute number and proportions of microscopy positives which were asymptomatic decreased from 12% (73/610) to 1.2% (9/849) (p < 0.0001), the relative proportion increased. Geometric mean density of P. falciparum parasitaemia decreased over the 2-year study period (p < 0.0001).ConclusionsThese data suggest that two annual rounds of IRS integrated with LLINs significantly reduced the prevalence of Plasmodium parasitaemia, while the proportion of asymptomatic and submicroscopic infections increased. To reduce cryptic P. falciparum transmission and improve malaria control, strategies aimed at reducing the number of asymptomatic and submicroscopic infections should be considered.

Prevalence and diversity of Plasmodium species in pregnant women attending antenatal clinics in selected health centers of Kakamega County, Western Kenya

Malaria remains a major public health concern around the world with tropical and sub-tropical regions bearing the greatest brunt despite up-scaling of control strategies. Despite the provisioning of insecticidal nets to expectant women attending antenatal care facilities, Plasmodium infections was a recurrent problem in Kakamega County. We hypothesized that socioeconomic factors were risk factors for the high prevalence levels of asymptomatic Plasmodium infections (API) among pregnant women in the County. A prospective cohort of 304 asymptomatic pregnant women aged 18 years and older was identified to assess the association between patient characteristics and risk of API using a cross-sectional study design. The study was conducted across four representative antenatal clinics (ANC) in the region. A pre-structured and pre-tested questionnaire was used to obtain the socio-demographic characteristics, residence, and knowledge of malaria. The questionnaire was followed by a face-to-face interview. Each participant provided a fingerprick blood sample for a thick and thion blood smear for parasite studies at Masinde Muliro University Science and Technology. The slides were examined at ×100 oil immersion. Plasmodium and the developmental stages were checked, quantified, and recorded. The data were analyzed using SPSS ver 16. Differences in parasite densities for various parameters was assessed using Mann Whitney U and Kruskal Wallis non-parametric tests. Ordinary linear squares (OLS) regression was used to uncover any significant associations at 95% CI and p-value ≤ 0.05. The majority of the women had a post-primary education (75%), were married (60.9%), multigravidae (50%), in their second trimester (41.4%), residing in rural areas (62.2%), used ITNs (77%), and did not practice IRS (67.8%) as a malaria prevention method. Plasmodium species infection prevalence was (24.34%; 95% CI, 19.52–29.16) P. falciparum (82.4%; 95% CI 73.72–91.08) accounting for the majority of infections. The parity and gestation status of the pregnant women were found to have a significant association with API. This study showed that a significant number of women in Kakamega County attending ANCs were asymptomatic for Plasmodium malaria. We propose that malaria screening through microscopy and treatment should be incorporated into maternal health within the county.

Low Prevalence of Deletions of the pfhrp2 and pfhrp3 Genes in Plasmodium falciparum Parasites in Freetown, Sierra Leone in 2015.

Sierra Leone relies heavily on histidine-rich protein 2-based diagnostics for malaria because of the high transmission of Plasmodium falciparum. During the 2015 recombinant vesicular stomatitis virus (VSV)-Zaire Ebola virus envelope glycoprotein (GP) vaccine trial, 77 participants with asymptomatic Plasmodium infection were enrolled, with all but four having P. falciparum malaria. Of the 73 participants with P. falciparum malaria, one infection (1 of 73, 1.4%; 95% CI, 0.03-7.4) showed P. falciparum with a pfhrp3 single deletion, and two P. falciparum infections (2 of 73, 2.7%; 95% CI, 0.03-9.6) showed pfhrp2/pfhrp3 dual deletions. This study shows evidence of pfhrp2- and pfhrp3-deleted parasites in Freetown, Sierra Leone. Additional studies for more precise estimates of prevalence are warranted.

Prevalence of malaria and associated factors among symptomatic pregnant women attending antenatal care at three health centers in north-west Ethiopia.

Malaria is the disease caused by Plasmodium species and primarily transmitted by the bite of female Anopheles mosquitoes. During pregnancy, malaria causes life threatening outcomes to the mother, the fetus and the new born. Even though, malaria symptomatic pregnant women highly attract mosquitoes and have higher potential of transmitting the disease in communities, most of the previous studies focused on pregnant women with asymptomatic Plasmodium infections. Therefore, the aim of this study was to assess the prevalence of malaria and associated factors among symptomatic pregnant women attending antenatal care at three health centers in northwest Ethiopia. A health facility based cross-sectional study was conducted from February to April, 2021. A total of 312 malaria symptomatic pregnant women were involved from three health centers and enrolled by convenient sampling technique. A questionnaire was used to collect socio demographic and clinical data through face to face interview. Capillary blood samples were collected and used to prepare thin and thick blood smears, which were then stained using 10% Giemsa and examined under light microscope. Logistic regression was used to assess factors associated with malaria. Adjusted odds ratio with 95% confidence interval was calculated and P-value < 0.05 was considered statistically significant. The prevalence of malaria among symptomatic pregnant women was 20.8% (65/312) of which 12.2% (38/312), 4.8% (15/312) and 3.8% (12/312) were P. falciparum, P. vivax and mixed infections, respectively. Being illiterate (p< 0.001), first trimester (p = 0.036), primigravidae (p<0.001), living far from health center (p<0.001), not sleeping under long lasting insecticide treated nets (p<0.001) and living near irrigation areas (p = 0.006) were significantly associated with prevalence of malaria in malaria symptomatic pregnant women. Even though prevalence of malaria is decreasing in the country because of scale-up of intervention and prevention measures, this study showed that, malaria is still the major public health problem among pregnant women. Being illiterate, first trimester, primigravidae, living far from health centers, not sleeping under long lasting insecticide treated nets and living near irrigation areas were factors that increased the prevalence of malaria in malaria symptomatic pregnant women. Therefore, special attention should be given to pregnant women prone to these factors.

Accuracy of a rapid diagnosis test, microscopy and loop-mediated isothermal amplification in the detection of asymptomatic Plasmodium infections in Korhogo, Northern C\xf4te d\u2019Ivoire

BackgroundHighly sensitive and accurate malaria diagnostic tools are essential to identify asymptomatic low parasitaemia infections. This study evaluated the performance of histidine-rich protein 2 (HRP-2) based rapid diagnostic tests (RDTs), microscopy and loop-mediated isothermal amplification (LAMP) for the detection of asymptomatic Plasmodium spp. infections in Northern Côte d’Ivoire, using nested polymerase chain reaction (nPCR) as reference.MethodsA household-based survey was carried out in July 2016, in the health district of Korhogo, involving 1011 adults without malaria symptom nor history of fever during the week before recruitment. The fresh capillary blood samples were collected to detect Plasmodium infections using on HRP-2-based RDTs, microscopy and LAMP and stored as dried blood spots (DBS). A subset of the DBS (247/1011, 24.4%) was randomly selected for nPCR analyses. Additionally, venous blood samples, according to LAMP result (45 LAMP positive and 65 LAMP negative) were collected among the included participants to perform the nested PCR used as the reference.ResultsThe prevalence of asymptomatic Plasmodium spp. infections determined by RDT, microscopy, and LAMP were 4% (95% confidence interval (CI) 2.8–5.3), 5.2% (95% CI 3.9–6.6) and 18.8% (95% CI 16.4–21.2), respectively. Considering PCR on venous blood as reference, performed on 110 samples, the sensibility and specificity were, respectively, 17.8% (95% CI 6.1–29.4) and 100% for RDT, 20.0% (95% CI 7.8–32) and 100% for microscopy, and 93.3% (95% CI 85.7–100) and 95.4% (95% CI 92.2–100) for LAMP.ConclusionIn Northern Côte d’Ivoire, asymptomatic Plasmodium infection was found to be widely distributed as approximately one out of five study participants was found to be Plasmodium infected. LAMP appears currently to be the only available diagnostic method that can identify in the field this reservoir of infections and should be the method to consider for potential future active case detection interventions targeting elimination of these infections.

Detection of asymptomatic malaria in Asian countries: a meta-analysis of diagnostic accuracy

BackgroundAchieving malaria elimination requires the targeting of the human reservoir of infection, including those patients with asymptomatic infection. The objective was to synthesise evidence on the accuracy of the rapid-onsite diagnostic tests (RDTs) and microscopy for the detection of asymptomatic malaria as part of the surveillance activities in Asian countries.MethodsThis was a meta-analysis of diagnostic test accuracy. Relevant studies that evaluated the diagnostic performance of RDTs and microscopy for detection of asymptomatic malaria were searched in health-related electronic databases. The methodological quality of the studies included was assessed using the QUADAS-2 tool.ResultsTen studies assessing RDT and/or microscopy were identified. The diagnostic accuracies in all these studies were verified by PCR. Overall, the pooled sensitivities of RDT, as well as microscopy for detection of any malaria parasites in asymptomatic participants, were low, while their pooled specificities were almost ideal. For the detection of Plasmodium falciparum, pooled sensitivity by RDT (59%, 95%CI:16–91%) or microscopy (55%, 95%CI: 25–82%) were almost comparable. For detection of Plasmodium vivax, pooled sensitivity of RDT (51%, 95% CI:7–94%) had also the comparable accuracy of microscopy (54%, 95%CI,11–92%). Of note are the wide range of sensitivity and specificity.ConclusionThe findings of this meta-analysis suggest that RDTs and microscopy have limited sensitivity and are inappropriate for the detection of asymptomatic Plasmodium infections. Other methods including a combination of PCR-based strategies, Loop-Mediated Isothermal Amplification (LAMP) technique must be considered to target these infections, in order to achieve malaria elimination. However, more data is needed for the wide acceptance and feasibility of these approaches. Studies to explore the role of asymptomatic and sub-patent infections in the transmission of malaria are of critical importance and are recommended.

Relative contribution of low-density and asymptomatic infections to Plasmodium vivax transmission in the Amazon: pooled analysis of individual participant data from population-based cross-sectional surveys

SummaryBackgroundLow-density and asymptomatic Plasmodium vivax infections remain largely undetected and untreated and may contribute significantly to malaria transmission in the Amazon.MethodsWe analysed individual participant data from population-based surveys that measured P vivax prevalence by microscopy and polymerase chain reaction (PCR) between 2002 and 2015 and modelled the relationship between parasite density and infectiousness to vectors using membrane feeding assay data. We estimated the proportion of sub-patent (i.e., missed by microscopy) and asymptomatic P vivax infections and examined how parasite density relates to clinical manifestations and mosquito infection in Amazonian settings.FindingsWe pooled 24,986 observations from six sites in Brazil and Peru. P vivax was detected in 6·8% and 2·1% of them by PCR and microscopy, respectively. 58·5% to 92·6% of P vivax infections were asymptomatic and 61·2% to 96·3% were sub-patent across study sites. P vivax density thresholds associated with clinical symptoms were one order of magnitude higher in children than in adults. We estimate that sub-patent parasite carriers are minimally infectious and contribute 12·7% to 24·9% of the community-wide P vivax transmission, while asymptomatic carriers are the source of 28·2% to 79·2% of mosquito infections.InterpretationAsymptomatic P vivax carriers constitute a vast infectious reservoir that, if targeted by malaria elimination strategies, could substantially reduce malaria transmission in the Amazon. Infected children may remain asymptomatic despite high parasite densities that elicit clinical manifestations in adults.FundingUS National Institutes of Health, Fundação de Amparo à Pesquisa do Estado de São Paulo, and Belgium Development Cooperation.

Antiplasmodial Activities of Some Locally Prepared Herbs Against Plasmodium falciparum Obtained from Asymptomatic School Children in Zaria, Kaduna State, Nigeria

The efficacy of current or any intended antimalarial can only be resolute by cultivation and susceptibility studies. The aim of this research was to cultivate Plasmodium falciparum in vitro and comparing the antiplasmodial effects of standard antimalarial medications including herbaceous preparation. Asymptomatic pupils attending some schools in Zaria, Kaduna state, Nigeria were recruited into this research and blood samples were collected from them. Microscopy was done after thin and thick blood films were prepared and stained. The antiplasmodial activities of antimalarial drugs as well as herbal preparation were determined after the successful culturing of red blood cells in the Jatropha curcas medium.The phytochemical constituents of the herbs that made up the concoction were determined. The incidence of asymptomatic Plasmodium infection amongst school kids was 17.5%. There was no statistical association of location, gender and age with the obtained prevalence. Presence of alkaloids was observed in every plant screened while the same was also observed for tannins except in Enantia chloranta.Steroids and phlobatanins were observed in Citrus aurantifolia while there was presence of saponins in all the plant extracts except Cymbopogbon citratus. All the plants except Enantia chloranta contained flavonoids. There was presence of terpenoids in all screened plants except Azadirachta indica and Cymbopogbon citratus while cardiac glycosides were found in every plant except Magnifera indica and Enantia chloranta. Results obtained from the in vitro cultivation of the Plasmodium falciparum with Athemether/lumefanthrine, amodiaquine and herbal concoction showed average percentage parasite inhibition of 80%, 37.8% and 38.6% respectively. This implies that Arthemether/lumefanthrine was capable of inhibiting the growth of the parasite best. The herbal concoction also inhibited growth (38.6% inhibition). There is need for additional investigation on a wider variety of plants to explore their antiplasmodial activities since there is evidence that it works, and it is quite available and affordable.