Prevalence Of Asymptomatic Malaria Infections Research Articles

Asymptomatic Malaria among Pregnant Women Attending Ante-Natal Clinic in Osogbo, Nigeria

Background: Pregnant women are in danger from malaria infection during pregnancy, which is a serious public health issue. A key obstacle to eradicating malaria is the reservoir host for the parasite, and is also regarded as one of the main obstacles to eliminating malaria. This study assessed the prevalence of asymptomatic malaria and associated factors among pregnant women attending antenatal clinics in Osogbo, Southwestern Nigeria. Methods: A hospital-based cross-sectional study was conducted between July and October 2020 to assess the prevalence and predictors of asymptomatic malaria among 294 consenting pregnant women. Socio-demographic data, Intermittent Preventive Treatment in pregnancy with SP (IPTp-SP), and information on insecticide-treated nets use were collected using a structured questionnaire. SD BIOLINE Malaria rapid diagnostic test kits and Giemsa-stained blood smear microscopy were used to diagnose Plasmodium infections. Anaemia status was determined using microhematocrit centrifugation. Data were analysed using SPSS version 20.0 statistical software. In all comparisons, p-values ≤ 0.05 were considered statistically significant. Results: The prevalence of asymptomatic malaria infection was 20.4% (60/294) and 23.5% (69/ 294) using microscopy and RDT, respectively. Among those infected, 76.7% were anaemic (p=0.001). Asymptomatic malaria was significantly associated with not using insecticide-treated bed nets (ITN). Secundigravida women and being in third-trimester pregnancy were significant determinants of pregnancy-associated malaria. Conclusion: This study showed that malaria and anaemia are still prevalent among pregnant women in Southern Nigeria, and it is a significant concern for public health. Improved access to intermittent preventive treatment with sulphadoxine-pyrimethamine and the use of long-lasting insecticidal nets should be encouraged to help further diminish the risk of malaria infection amongst pregnant women in the region.

Schoolchildren with asymptomatic malaria are potential hotspot for malaria reservoir in Ethiopia: implications for malaria control and elimination efforts

BackgroundSchoolchildren with asymptomatic malaria infections often go undiagnosed and untreated, serving as reservoirs for infection that hamper malaria control and elimination efforts. In this context, little is known about the magnitude of asymptomatic malaria infections in apparently healthy schoolchildren in Ethiopia. This study was aimed at determining the prevalence of asymptomatic malaria infection and its associated factors in apparently healthy schoolchildren in Ethiopia.MethodsFrom September 2021 to January 2022, a school-based cross-sectional study was conducted on 994 apparently healthy schoolchildren (aged 6–15 years) selected from 21 primary schools in the Gomma district, of Jimma zone, southwestern Oromia, Ethiopia. A multi-stage sampling technique was used to select schools and participants. After allocating the total sample proportionally to each school and then to each grade, participants were selected using the lottery method from a list of student records (rosters). Finger-pricked blood samples were collected for microscopy blood film preparation and malaria rapid diagnostic test (RDT) (SD Bioline Malaria Ag Pf/Pv). Moreover, dry blood spots (DBSs) were prepared onto filter papers for quantitative real time polymerase chain reaction (qPCR) analysis.ResultsAs determined by RDT and microscopy, the prevalence of asymptomatic malaria was 2.20% and 1.51%, respectively. Using qPCR, the overall prevalence was 5.03% (50/994). Of this, Plasmodium falciparum, Plasmodium vivax and mixed infections accounted for 90%, 6% and 4%, respectively. Submicroscopic asymptomatic malaria infection was also accounted for 70% (35/50) of the overall prevalence. Household head age, nighttime outdoor activities of household heads, family history of malaria, absence of insecticide-treated nets (ITN), and presence of stagnant water around the houses are all significantly associated with asymptomatic malaria infections among schoolchildren.ConclusionsThis study found that both RDT and microscopy underestimated the prevalence of asymptomatic malaria in schoolchildren. However, qPCR was able to detect even low levels of parasitaemia and revealed a higher prevalence of asymptomatic submicroscopic malaria infections. The findings imply that schoolchildren with asymptomatic malaria infection are potential hotspot for malaria reservoir that fuels ongoing transmission. Therefore, it is imperative to include schoolchildren and schools in malaria intervention package and equally important is the adoption of more advanced and sensitive diagnostic tools, which would be crucial for successful malaria control and elimination efforts. Targeted interventions for asymptomatic malaria-infected schoolchildren can provide invaluable support to the National Malaria Control Programme in controlling and eventually eliminating the disease.

Prevalence and predictors of asymptomatic malaria infection in Boricha District, Sidama Region, Ethiopia: implications for elimination strategies

BackgroundMalaria remains a major public health threat in Ethiopia despite the tremendous progress made towards the 2030 elimination targets. The silent transmission of asymptomatic infection is one of the factors that enhance the persistence of the disease as a public health issue and impedes efforts to eliminate malaria. Thus, this study aimed at investigating the prevalence and risk factors of asymptomatic malaria infection in Boricha district, Sidama region of Ethiopia.MethodsA community-based cross-sectional study was conducted in eight selected kebeles (smallest administrative unit) in Boricha district. Representative households were chosen using a multi-stage sampling technique. A total of 573 participants were included in the study. Malaria diagnosis was performed using rapid diagnostic test (RDT) and microscopy. A structured questionnaire was administered to collect socio-demographic information. Epi data 3.1 was employed for data entry, and SPSS version 25 was used for analysis.ResultsOf the 573 asymptomatic participants tested, 6.1% were found to be positive by RDT and 4.0% by microscopy. Participants aged under 5 years (AOR = 1.57, 95% CI 0.46–5.39) and 5–14 years old (AOR = 2.42, 95% CI 1.08–5.40), Insecticide-treated net utilization (AOR = 8.41; 95% CI 1.09–65.08), travel history (AOR = 6.85, 95% CI 2.32–20.26) and living in a house with windows (AOR = 2.11, 95% CI 1.02–4.36) were significantly associated with the asymptomatic malaria infection.ConclusionThe findings of this study revealed that prevalence of asymptomatic malaria infection was higher in the study area. As a result, rigorous implementation of existing interventions, such as vector control and anti-malaria drugs, is strongly recommended. In addition, devising new ones that are suited to the contextual situations is highly suggested.

Prevalence of asymptomatic malaria infection by microscopy and its determinants among residents of Ido-Ekiti, Southwestern Nigeria.

Asymptomatic malaria infections have received less attention than symptomatic malaria infections in major studies. Few epidemiological studies on asymptomatic malaria infections have often focused on pregnant women and children under-five years of age as the most vulnerable groups. However, there is limitation on data regarding asymptomatic infections among the old adult populations, particularly in the study area. Therefore, this study determined the prevalence of asymptomatic malaria infection by microscopy and its determinants among residents of Ido- Ekiti, Southwestern Nigeria. A hospital-based cross-sectional study was conducted between July and September 2021 among 232 consenting apparently healthy individuals aged 40 years and above who were recruited during a free health screening program using a standardised interviewer-administered questionnaire. The questionnaire sought information on respondents' socio-demographics, presence and types of co-morbidity, and the prevention methods being adopted against malaria infection. Venous blood samples were collected and processed for asymptomatic infections using Giemsa-stained blood smear microscopy. Data were analysed using SPSS version 21. Multivariate logistic regression was used to identify factors associated with asymptomatic infections. Of the total 232 respondents, 19.0% (48/232) were confirmed to be infected with Plasmodium falciparum (95% confidence interval (CI): 14.1% - 24.6%). Lack of formal education (Adjusted odds ratio (AOR): 5.298, 95% (CI): 2.184-13.997), being diabetic (AOR: 4.681, 95% CI: 1.669-16.105), and not sleeping under Long Lasting Insecticide Net (LLINs) (AOR: 4.594, 95% CI: 1.194-14.091), were the determinants of asymptomatic Plasmodium falciparum infection. The prevalence of asymptomatic Plasmodium falciparum was 19%. Lack of formal education, being diabetic, and not sleeping under LLINs were the determinants of asymptomatic infections.

Occurrence of asymptomatic malaria infection and living conditions in the lowlands of Ethiopia: a community-based cross-sectional study

BackgroundA significant decline in malaria burden was documented in previously high burden African countries. Even though the global decline in malaria burden is significant, about 95% of it was typically found in 29 African countries and the decline was affected by COVID-19 in 2020. The considerable reduction in malaria incidence was noted due to effective prevention and treatment efforts, and rapid changes in living conditions. The relationship between the occurrence of asymptomatic malaria infection and household living conditions is well unstudied. This study aimed to determine the association between household living conditions and the occurrence of asymptomatic malaria in the lowlands of Ethiopia.MethodsA community-based cross-sectional study was conducted from January to March 2021 in twelve villages of Gambella, Southern Nation Nationalities and People Region and Afar in Ethiopia. A total of 1366 households were randomly selected, interviewed, and tested for malaria by rapid diagnostic test and blood film microscopic examination. Multiple logistic regression model was used to determine the independent association between living conditions and asymptomatic malaria infection.ResultsThe prevalence of asymptomatic malaria infection among individuals living in dwellings built with traditional floor/wall/roof ranges from 8.1% to 8.4% while it ranges from 2.0% to 4.6% among those living in modern floor/wall/roof houses. Dwellings built with traditional wall materials (P = 0.050), spending nights with cattle in the same house (P < 0.001), and availability of kitchen in the main house with no partition (P = 0.004) were significantly associated with asymptomatic malaria infection.ConclusionsAsymptomatic malaria infection was 4.3 times higher among occupants residing in dwellings built with traditional wall materials; 5.6 times higher among households spending nights with cattle in the same house, and 2.3 times higher among households with kitchen in the main house with no partition. Therefore, policies and strategies on malaria elimination need to address or target improvements of the above listed living conditions for the community. A multi sectoral action is required to use these social determinants as a vector control strategic addition; and malaria elimination programs are expected to coordinate the implementation.

Asymptomatic malaria and nurturing factors in lowlands of Ethiopia: A community based cross-sectional study.

Although asymptomatic malaria cases are reservoirs of malaria parasites, there is limited evidence on the burden and nurturing factors in malaria endemic areas during dry season. Thus, this study aims to determine the prevalence of asymptomatic malaria infection and nurturing factors in endemic areas of Ethiopia during dry season.A community based cross-sectional study was conducted in malaria endemic areas in Ethiopia. Six villages with a total of 1,366 households from three malaria endemic regions of Ethiopia were selected by stratified random sampling method. One asymptomatic member of the household was randomly selected from each household. A structured questionnaire was used to collect data on socio-demographic and other factors. Finger prick blood samples for malaria rapid diagnostic test (RDT) and blood film were collected and examined. Multivariable logistic regression model was used to determine the nurturing factors with asymptomatic malaria infection. The prevalence of asymptomatic malaria infection was 7.7% with both blood film microscopic examination and malaria RDT. Plasmodium falciparum was the predominantly observed type of malaria species (48.0%). The presence of bodies of water around the households (adjusted odds ratio (AOR = 5.4; 95% CI (2.7 ─ 9.7); p < 0.000), infrequent indoor residual spray (IRS) applied four to six months ago (AOR = 3.5; 95% CI (1.0─11.6); p = 0.045) and more than six months (AOR = 5.2; 95% CI (1.3─20.5); p = 0.019) and personal protection measure for malaria prevention (LLIN, repellent and clothing) (AOR = 0.41; 95% CI (0.2 ─ 0.9); p = 0.028) were associated significantly with asymptomatic malaria infection. The prevalence of asymptomatic malaria infection during dry season was considerable. Strong interventions that target stagnant bodies of water, infrequent household IRS spray and personal protection measure for malaria prevention is required to decrease asymptomatic malaria infection during dry season.

Asymptomatic Malaria Infections in the Time of COVID-19 Pandemic: Experience from the Central African Republic.

According to the latest World Health Organization malaria report, 95% of 241 million global malaria cases and 96% of 627,000 malaria deaths that were recorded in 2020 occurred in Africa. Compared to 2019, 14 million more cases and 69,000 more malaria deaths were recorded, mainly because of disruptions to medical services during the COVID-19 pandemic. The aim of this study was to assess the prevalence of asymptomatic malaria cases in children and adults living in the Dzanga Sangha region in the Central African Republic (CAR) during the COVID-19 pandemic. Rapid immunochromatographic assays for the qualitative detection of Plasmodium species (P. falciparum, P. vivax, P. ovale/P. malariae) circulating in whole blood samples were used. A screening was performed in the group of 515 patients, 162 seemingly healthy children (aged 1–15) and 353 adults, all inhabiting the villages in the Dzanga Sangha region (southwest CAR) between August and September 2021. As much as 51.2% of asymptomatic children and 12.2% of adults had a positive result in malaria rapid diagnostic tests (mRDTs). Our findings demonstrated a very high prevalence of asymptomatic malaria infections in the child population. Limited access to diagnostics, treatment and prevention of malaria during the global COVID-19 pandemic and less medical assistance from developed countries may be one of the factors contributing to the increase in the prevalence of disease in Africa.

Prevalence of Asymptomatic Malaria Infections in Seemingly Healthy Children, the Rural Dzanga Sangha Region, Central African Republic.

According to the World Health Organization 94% of global malaria cases and 94% of global malaria deaths have been reported from Africa. Unfortunately, it is difficult to determine the exact prevalence of disease in some African countries due to a large number of asymptomatic cases. The aim of this study was to assess the prevalence of malaria infections in seemingly healthy children living in the Central African Republic (CAR). CareStartTM Malaria HRP2 rapid diagnostic test (RDT) targeting Plasmodium falciparum was used to test a group of 500 asymptomatic children aged 1-15 years old (330 settled Bantu and 170 semi-nomadic BaAka Pygmies) inhabiting the villages in the Dzanga Sangha region (south-west CAR) in March 2020. In total, 32.4% of asymptomatic Bantu and 40.6% of asymptomatic Pygmy children had a positive result of malaria RDT. Our findings allowed us to demonstrate the high prevalence of asymptomatic malaria infections in south-west CAR. RDTs seem to be a useful tool for the detection of Plasmodium falciparum in areas with limited possibilities of using other diagnostic methods, such as light microscopy and molecular biology.

High prevalence of asymptomatic malaria infections in adults, Ashanti Region, Ghana, 2018

BackgroundGhana is among the high-burden countries for malaria infections and recently reported a notable increase in malaria cases. While asymptomatic parasitaemia is increasingly recognized as a hurdle for malaria elimination, studies on asymptomatic malaria are scarce, and usually focus on children and on non-falciparum species. The present study aims to assess the prevalence of asymptomatic Plasmodium falciparum and non-falciparum infections in Ghanaian adults in the Ashanti region during the high transmission season.MethodsAsymptomatic adult residents from five villages in the Ashanti Region, Ghana, were screened for Plasmodium species by rapid diagnostic test (RDT) and polymerase chain reaction (PCR) during the rainy season. Samples tested positive were subtyped using species-specific real-time PCR. For all Plasmodium ovale infections additional sub-species identification was performed.ResultsMolecular prevalence of asymptomatic Plasmodium infection was 284/391 (73%); only 126 (32%) infections were detected by RDT. While 266 (68%) participants were infected with Plasmodium falciparum, 33 (8%) were infected with Plasmodium malariae and 34 (9%) with P. ovale. The sub-species P. ovale curtisi and P. ovale wallikeri were identified to similar proportions. Non-falciparum infections usually presented as mixed infections with P. falciparum.ConclusionsMost adult residents in the Ghanaian forest zone are asymptomatic Plasmodium carriers. The high Plasmodium prevalence not detected by RDT in adults highlights that malaria eradication efforts must target all members of the population. Beneath Plasmodium falciparum, screening and treatment must also include infections with P. malariae, P. o. curtisi and P. o. wallikeri.

Prevalence of asymptomatic malaria infections in selected military camps in Tanzania

Background: Despite a decrease in malaria burden reported between 2000 and 2015, an increasing trend of malaria transmission has been recently reported in some endemic countries including Tanzania. Periodic monitoring to identify pocket areas for asymptomatic Plasmodium falciparum infection is vital for malaria elimination efforts. The objective of this study was to determine prevalence of asymptomatic malaria infections among military recruits in selected camps in Tanzania.&#x0D; Methods: A cross-sectional study was conducted in 2015 at four military camps (Bulombora, Mgambo, Ruvu, and Rwamkoma) of National Service located in regions with varying malaria endemicity in Tanzania. Finger prick blood samples collected from asymptomatic military recruits who had been at the camps for over two months were simultaneously tested using microscopy and malaria rapid diagnostic tests (mRDTs) to detect malaria parasite infections.&#x0D; Results: Malaria parasite prevalence among asymptomatic recruits was 20.3% and 19.4% by microscopy and mRDT respectively. There was moderate agreement (Kappa=0.724) between microscopy and mRDT test results. A significant difference (p&lt;0.001) of malaria parasite prevalence among the four study camps was observed; ranging from 1.9% in Bulombora to 39.4% in Rwamkoma. The geometric mean parasite density was 11,053 asexual parasites/µl and most recruits (56.8%) had 200 to 1999 asexual parasites/µl. P. falciparum was the predominant (99.2%) malaria parasite species.&#x0D; Conclusion: Our study found high prevalence of asymptomatic malaria infections among military recruits in the selected camps, and this varied from one camp to another. The study has highlighted that public residence institutions such as military camps can be potential hotspots for malaria infection and therefore should not be skipped in routine national malaria surveillance system for monitoring trends of infections

Asymptomatic malaria infection among pregnant women attending antenatal care in malaria endemic areas of North-Shoa, Ethiopia: a cross-sectional study

BackgroundThe effort to reduce the burden of malaria should target transmission in the community by accurate identification of asymptomatic infections. In malaria-endemic areas, asymptomatic malaria infection is still associated with complications. Malaria during pregnancy is characterized by anaemia and placental malaria, leading to low birth weight and perinatal morbidity and mortality. This study aimed to provide reliable data on the burden of asymptomatic malaria among pregnant women in malaria endemic areas of North-Shoa, Ethiopia.MethodsCross-sectional study was carried out to assess the prevalence and predictors of asymptomatic malaria in pregnant women from November 2018 to January 2019. Multistage sampling technique was employed to include 263 study participants. Data were analysed using SPSS version 20.0 statistical software. In all comparisons, p-values ≤ 0.05 was considered as statistically significant.ResultsThe prevalence of asymptomatic malaria infection was 5.7% (15/263) and 3.4% (9/263) by using microscopy and RDTs, respectively. Plasmodium falciparum was a dominant species 9 (3.4%) and Plasmodium vivax accounted for 6 (2.3%) of Plasmodium infections as detected by microscopy. Multivariate analysis showed that ITN usage and haemoglobin level had a statistically significant association with Plasmodium infection after adjusting other possible factors. Compared to those who were using ITN always, the odds of Plasmodium infection was 18.16 times higher (95% CI 1.84–179.07) in pregnant women who were not using ITN, and 5.19 times higher (95% CI 0.55–49.21) in pregnant women who were using ITN sometimes. Asymptomatic malaria infected pregnant women were 3.78 times (95% CI 0.98–14.58) more likely to be anaemic compared to non-infected pregnant women.ConclusionThe present study showed asymptomatic malaria is prevalent in pregnant women and it has statistically significance association with the haemoglobin level of pregnant women. This indicates pregnant women have to be screened for asymptomatic malaria to avoid health consequences of malaria infection during pregnancy for the mother and fetus.

Spatial distribution and determinants of asymptomatic malaria risk among children under 5\xa0years in 24 districts in Burkina Faso

BackgroundIn malaria endemic countries, asymptomatic cases constitute an important reservoir of infections sustaining transmission. Estimating the burden of the asymptomatic population and identifying areas with elevated risk is important for malaria control in Burkina Faso. This study analysed the spatial distribution of asymptomatic malaria infection among children under 5 in 24 health districts in Burkina Faso and identified the determinants of this distribution.MethodsThe data used in this study were collected in a baseline survey on “evaluation of the impact of pay for performance on the quality of care” conducted in 24 health districts in Burkina Faso, between October 2013 and March 2014. This survey involved 7844 households and 1387 community health workers. A Bayesian hierarchical logistic model that included spatial dependence and covariates was implemented to identify the determinants of asymptomatic malaria infection. The posterior probability distribution of a parameter from the model was summarized using odds ratio (OR) and 95% credible interval (95% CI).ResultsThe overall prevalence of asymptomatic malaria infection in children under 5 years of age was estimated at 38.2%. However, significant variation was observed between districts ranging from 11.1% in the district of Barsalgho to 77.8% in the district of Gaoua. Older children (48–59 vs < 6 months: OR: 6.79 [5.62, 8.22]), children from very poor households (Richest vs poorest: OR: 0.85 [0.74–0.96]), households located more than 5 km from a health facility (< 5 km vs ≥ 5 km: OR: 1.14 [1.04–1.25]), in localities with inadequate number of nurses (< 3 vs ≥ 3: 0.72 [0.62, 0.82], from rural areas (OR: 1.67 [1.39–2.01]) and those surveyed in high transmission period of asymptomatic malaria (OR: 1.27 [1.10–1.46]) were most at risk for asymptomatic malaria infection. In addition, the spatial analysis identified the following nine districts that reported significantly higher risks: Batié, Boromo, Dano, Diébougou, Gaoua, Ouahigouya, Ouargaye, Sapouy and Toma. The district of Zabré reported the lowest risk.ConclusionThe analysis of spatial distribution of infectious reservoir allowed the identification of risk areas as well as the identification of individual and contextual factors. Such national spatial analysis should help to prioritize areas for increased malaria control activities.

Studies on asymptomatic malaria, prevention and treatment seeking behaviours in Abeokuta, south-west Nigeria

Recurrent cycles of fevers and chills are obvious symptoms for malaria disease usually necessitating treatment. However, some Plasmodium infections could be without symptoms, leading to late diagnosis and delayed treatment- seeking behaviours. The objective of this study was to determine the prevalence of asymptomatic malaria infections, and document associated prevention and treatment-seeking behaviours among literates in Abeokuta. A cross-sectional study design involving 309 attendees at the 2016 World Malaria Day Celebration event held at the Federal University of Agriculture, Abeokuta was conducted. Finger-prick blood samples were collected for Plasmodium parasite detection by malaria rapid diagnostic test (mRDT) and anthropometric indices such as weight, height and age were also collected to estimate Body-Mass-Index. An already pre-tested questionnaire was also used to collect information on malaria prevention and treatment-seeking behaviours. Data were analysed in SPSS 20.0 software. Results revealed that the prevalence of asymptomatic malaria was 7.4% (23/309), with no significant association between sex, febrile illness and Body Mass Index ( p >0.05). Participants aged 15-25 years were more infected with malaria than other age groups. Only 58.3% of the participants have heard of Long Lasting Insecticidal Nets (LLINs) and about 78% do not have mosquito bed-net. Self-diagnosis for the disease was more common (60.8%) among the participants, compared to other measures; seeking laboratory test (26.5%) and clinical diagnosis (9.1%). A good proportion of the participants (73.1%) rely on Artemisinin-based Combination Therapy (ACT) drugs for treating malaria, although few others still rely on non-ACT drugs (17.8%), chloroquine (1.9%) and herbs (1.6%). Findings show existence of asymptomatic malaria. Also, access to and utilization of malaria prevention and control commodities is poor among the literates. There is thus a need to intensify efforts in addressing these concerns as we move towards eliminating the disease. Keywords: Asymptomatic malaria; World Malaria Day; prevalence; Abeokuta; Nigeria

Burden of asymptomatic malaria among a tribal population in a forested village of central India: a hidden challenge for malaria control in India

ObjectiveChhattisgarh in India is a malaria-endemic state with seven southern districts that contributes approximately 50–60% of the reported malaria cases in the state every year. The problem is further complicated due to asymptomatic malaria cases which are largely responsible for persistent transmission. This study was undertaken in one of the forested villages of the Keshkal subdistrict in Kondagaon district to ascertain the proportion of the population harbouring subclinical malarial infections. Study designCommunity-based cross-sectional study. MethodsMass blood surveys were undertaken of the entire population of the village in the post-monsoon seasons of 2013 and 2014. Fingerprick blood smears were prepared from individuals of all ages to detect malaria infections in their blood. Individuals with fever at the time of the survey were tested with rapid diagnostic tests, and parasitaemia in thick blood smears was confirmed by microscopy. Malaria-positive cases were treated with anti-malarials in accordance with the national drug policy. ResultsPeripheral blood smears of 134 and 159 individuals, including children, were screened for malaria infection in 2013 and 2014, respectively. Overall, the malaria slide positivity rates were 27.6% and 27.7% in 2013 and 2014, respectively, and the prevalence rates of asymptomatic malaria were 20% and 22.8%. This study showed that, for two consecutive years, the prevalence of asymptomatic malaria infection was significantly higher among children aged ≤14 years (34.4% and 34.1% for 2013 and 2014, respectively) compared with adults (15.2% and 18.2% for 2013 and 2014, respectively; P = 0.023 and 0.04, respectively). ConclusionThe number of asymptomatic malaria cases, especially Plasmodium falciparum, is significant, reinforcing the underlying challenge facing the malaria elimination programme in India.

Prevalence of asymptomatic malaria infection and use of different malaria control measures among primary school children in Morogoro Municipality, Tanzania.

BackgroundMalaria is a public health problem in Tanzania affecting all age groups. It is known that school children are the age group most commonly infected with malaria parasites. Their infections are usually asymptomatic, go unnoticed and thus never get treated, result in anaemia, reduced ability to concentrate and learn in school and if fallen sick may lead to school absenteeism. Effective malaria control requires frequent evaluation of effectiveness of different malaria interventions.MethodsA cross-sectional study design involving 317 out of 350 school children aged 6–13 years from five primary schools within municipality was conducted. Multistage cluster sampling and simple random sampling methods were used to obtain primary school and study participants, respectively. Finger-prick blood samples were collected for Plasmodium parasite detection by malaria rapid diagnostic test (mRDT) and haemoglobin level assessment by Easy Touch® GHb system machine. A questionnaire was administered to assess use of insecticide-treated nets (ITNs) and anti-malarial drugs.ResultsThe prevalence of asymptomatic malaria was 5.4 % (95 % CI 3.3–8.6 %) and anaemia was 10.1 % (95 % CI 7.2–13.9 %). School children aged 6–9 years were more affected by malaria than those aged 10–13 years. The proportion of ITNs used was 90.6 % (95 % CI 86.3–93.9 %) while that of artemisinin combination therapy (ACT) was 71.9 % (95 % CI 66.2–77.1 %).ConclusionFindings show existence of asymptomatic malaria and walking anaemia among primary school children in Morogoro municipality. The majority of school children reported use of ITNs and ACT for malaria control. These findings provide a rationale for using schools and school children to assess effectiveness of malaria interventions.

Asymptomatic Malaria in Refugees Living in a Non-Endemic South African City

BackgroundAsymptomatic malaria infection in refugees is both a threat to the lives of the individuals and the public in the host country. Although South Africa has been experiencing an unprecedented influx of refugees since 1994, data on malaria infection among refugees is lacking. Such information is critical since South Africa is among the countries that have planned to eliminate malaria. The objective of this study was to determine prevalence of asymptomatic malaria infection among a refugee population living in a city of KwaZulu-Natal province, South Africa.Methods and FindingsA survey was conducted on adult refugee participants who attended a faith-based facility offering social services in a city of KwaZulu-Natal province, South Africa. The participants were screened for the presence of malaria using rapid diagnostic tests and microscopy. Demographic data for the participants were obtained using a closed ended questionnaire. Data was obtained for 303 participants consisting of 51.5% females and 47.5% males, ranging from 19 to 64 years old. More than 95% of them originated from sub-Saharan African countries. Two hundred and ninety participants provided a blood sample for screening of malaria. Of these, 3.8% tested positive for rapid diagnostic test and 5.9% for microscopy. The majority of malaria infections were due to Plasmodium falciparum.ConclusionsThe study confirms the presence of asymptomatic malaria infections among a refugee population residing in a city of KwaZulu-Natal province that is not endemic for malaria. The results have important implications for both public health and malaria control in South Africa, particularly since the country has decided to eliminate malaria by 2018. To achieve this goal, South Africa needs to expand research, surveillance and elimination activities to include non-endemic areas, particularly with high refugee populations. We further recommend use of powerful diagnostic tests such as PCR for these interventions.

Absence of Asymptomatic Malaria Infections in Previously High Endemic Areas of Sri Lanka

As the goal of malaria elimination from Sri Lanka is currently being pursued, this study was planned to determine the prevalence of asymptomatic malaria infections. Five health areas in Trincomalee and Kurunegala districts that reported high prevalence in the recent past were purposively selected. The smallest administrative units (GN divisions) having high malaria risk within each area were identified. From these divisions, 20% of the population was randomly selected for blood smear examination and in a 50% sub-sample polymerase chain reaction (PCR) assay was performed. A population of 3,730 from 13 GN divisions was sampled. Thick and thin Giemsa-stained blood smears were negative for malaria parasites. The PCR carried out in 50% of the study sample was also negative for malaria parasites. The findings illustrate the absence of asymptomatic carriers in previously high transmission areas and it appears that achieving malaria elimination in Sri Lanka by 2015 is feasible.

PROTECTIVE EFFICACY OF LAMBDA-CYHALOTHRIN TREATED NETS IN ANOPHELES GAMBIAE PYRETHROID RESISTANCE AREAS OF CÔTE D’IVOIRE

The efficacy of nets treated with lambda-cyhalothrin, a pyrethroid insecticide, on malaria infection and disease was assessed for the first time at the community level in Anopheles gambiae pyrethroid resistance areas. The study was carried out in northern Côte d'Ivoire, which is an area of kdr resistance. Four pairs of villages were selected and matched according to demographic, sociological, and ecological criteria. Among each pair, a village was randomly allocated to receive mosquito nets. More than 80% of beds were covered with nets treated with lambda-cyhalothrin and retreated after 6 months. In each village, 54 children aged 0-59 months were randomly selected and clinically monitored for 8 periods of 7 days throughout the year. Results showed that the efficacy of treated nets was maintained with a reduction of the prevalence of asymptomatic malaria infection by 12% and an estimated protective efficacy against malaria disease of 56%.

Glucose-6-phosphate dehydrogenase deficiency and Southeast Asian ovalocytosis in asymptomatic Plasmodium carriers in Sumba island, Indonesia

Glucose-6-phosphate dehydrogenase (G6PD) deficiency and Southeast Asian ovalocytosis (SAO) caused by a 27-bp deletion in the band 3 gene (Band3Delta 27) are well-documented genetic traits resistant to malarial diseases; however, relationships between these traits and asymptomatic malaria infection hitherto had not been investigated. Filter-blotted blood samples were collected from a total of 210 healthy individuals, 100 males and 110 females, aged 6-17 years, in Sumba island, Indonesia, to survey for the presence of Plasmodium parasites, G6PD activity and the Band3Delta 27 mutation. Presence of P. falciparum and/or P. vivax was identified in 25 subjects (11.9%). In all, 24 subjects (11.4%) showed Band3Delta 27 heterozygously. In males and females, eight and nine subjects, respectively, showed G6PD deficiency. There was no significant difference in the prevalence of asymptomatic malaria infection between individuals with or without these traits (P>0.05). No alterations in the prevalence of asymptomatic malaria infection suggest that parasite invasion into erythrocytes is unlikely to be a target phase in which the two polymorphisms demonstrate possible protective effects against malaria.

Evidence for an Age-Dependent Pyrogenic Threshold of Plasmodium falciparum Parasitemia in Highly Endemic Populations

The high prevalence of asymptomatic malaria infections and the nonspecific signs and symptoms of the disease make the individual diagnosis of clinical malaria uncertain in highly endemic areas. Longitudinal data obtained during a four-month period from a daily survey of 200 permanent inhabitants (one month-83 years old) living in a holoendemic area were analyzed in a random-effects logistic regression model to investigate the relationship between the level of Plasmodium falciparum parasitemia and risk of fever. It was not possible to build a model that described/summarized correctly this relationship by a continuous function. Findings provide evidence for an age-dependent threshold effect of parasitemia on the occurrence of fever. The level of this threshold varied by 2.45 trophozoites per leukocyte, maximum at one year of age, to 0.5 trophozoites per leukocyte, minimum at 60 years of age. When the parasite density of a person crossed the threshold level corresponding to his or her age, the individual's risk of fever was multiplied by 44 (95% confidence interval = 13.6-144.8). The existence of this threshold effect allows parasite density to be used to distinguish malaria attacks from other causes of fever within an individual and should facilitate the accurate evaluation of the incidence of clinical malaria in highly endemic areas.