Asymptomatic Plasmodium falciparum Malaria in Pregnant Women in the Chittagong Hill Districts of Bangladesh

Abstract

BackgroundPregnancy is a known risk factor for malaria which is associated with increased maternal and infant mortality and morbidity in areas of moderate-high malaria transmission intensity where Plasmodium falciparum predominates. The nature and impact of malaria, however, is not well understood in pregnant women residing in areas of low, unstable malaria transmission where P. falciparum and P. vivax co-exist.MethodsA large longitudinal active surveillance study of malaria was conducted in the Chittagong Hill Districts of Bangladesh. Over 32 months in 2010–2013, the period prevalence of asymptomatic P. falciparum infections was assessed by rapid diagnostic test and blood smear and compared among men, non-pregnant women and pregnant women. A subset of samples was tested for infection by PCR. Hemoglobin was assessed. Independent risk factors for malaria infection were determined using a multivariate logistic regression model.ResultsTotal of 34 asymptomatic P. falciparum infections were detected by RDT/smear from 3,110 tests. The period prevalence of asymptomatic P. falciparum infection in pregnant women was 2.3%, compared to 0.5% in non-pregnant women and 0.9% in men. All RDT/smear positive samples that were tested by PCR were PCR-positive, and PCR detected additional 35 infections that were RDT/smear negative. In a multivariate logistic regression analysis, pregnant women had 5.4-fold higher odds of infection as compared to non-pregnant women. Malaria-positive pregnant women, though asymptomatic, had statistically lower hemoglobin than those without malaria or pregnancy. Asymptomatic malaria was found to be evenly distributed across space and time, in contrast to symptomatic infections which tend to cluster.ConclusionPregnancy is a risk factor for asymptomatic P. falciparum infection in the Chittagong Hill Districts of Bangladesh, and pregnancy and malaria interact to heighten the effect of each on hemoglobin. The even distribution of asymptomatic malaria, without temporal and spatial clustering, may have critical implications for malaria elimination strategies.

Malaria Parasites in the Asymptomatic: Looking for the Hay in the Haystack

“…Significantly fewer studies have directly addressed the role of host genetic variants in asymptomatic infections, reporting inconclusive results probably due to the low power to detect modest effects [42]. Pregnancy Pregnant women have been identified as a possible large source of chronic asymptomatic carriage of parasites compared with men and non-pregnant women [53]. In areas with stable and intense transmission, malaria in pregnancy has been identified to be commonly asymptomatic [53], even in the presence of infected erythrocytes sequestered in the placenta [54].…”

“…Pregnancy Pregnant women have been identified as a possible large source of chronic asymptomatic carriage of parasites compared with men and non-pregnant women [53]. In areas with stable and intense transmission, malaria in pregnancy has been identified to be commonly asymptomatic [53], even in the presence of infected erythrocytes sequestered in the placenta [54]. Recrudescence of placental parasites can occur up to 187 days after the initial infection [55] and can persist asymptomatically for several months post-delivery [56].…”

Geospatial Technology: A Tool to Aid in the Elimination of Malaria in Bangladesh

“…In another study, in the Bandarban District, a cohort framework of over 4000 households was established and mapped for a longitudinal study [21]. Four studies prepared risk maps in the same district focusing on pregnant women and jhum cultivators-subsistent farmers that use slash and burn methods of farming [18,24]. There were six malaria risk mapping studies conducted in Rajasthali, a sub-district of Rangamati district, which in 2007 had the highest (36%) malaria prevalence rates in the country [23].…”

“…The use of GIS and GPS systems connected to mobile phones [27] can also aid in malaria case detection and delivery of health services particularly in remote areas of CHT where tracking and analyzing malaria prevalence data can often be difficult [28]. With changing malaria epidemiology and reduced burden of malaria throughout the country, Bangladesh needs to focus on CHT region elimination strategies to address malaria hot-spots efficiently and effectively as well as reduce malaria importation, insecticide resistance, drug resistance [29], and the mapping of asymptomatic carrier [24]. Geospatial technology can provide the necessary data to assist in these elimination strategies.…”

“…Based on the findings of these studies, the following are recommendations for the NMCP to implement to further the malaria elimination program in Bangladesh: identify high-risk malaria zones to determine spatial distribution; combine surveillance with GIS and weather pattern database to determine geographic and climate risks [21]; conduct further studies to understand malaria transmission among impacted populations during high transmission season; develop strategies to interrupt transmission in low transmission settings [18]; use mass screening in stable hot-spot areas to identify asymptomatic reservoirs and provide treatment to reduce the malaria burden [16]; promote malaria test and treatment services particularly among vulnerable populations, such as children under five years and jhum cultivators [18]; monitor asymptomatic malaria particularly among pregnant women living in low-intensity malaria transmission areas [24]; target interventions at fine spatial scales for malaria control programs; improve equity of access to interventions [15]; improve collaboration between researchers using geostatistical techniques and malaria control managers; target high malaria transmission areas [8] to provide more GPS, GIS, and RS strategies to characterize spatial heterogeneity with malaria risk at a fine scale and identify high risk areas that have not been studied [19]; and lastly focus on interventions to be targeted and timed according to risk profiles of endemic areas [38].…”