Late recrudescence of Plasmodium falciparum malaria in a pregnant woman: a case report

Transcriptional plasticity of virulence genes provides malaria parasites with greater adaptive capacity for avoiding host immunity

Chronic, asymptomatic malaria infections contribute substantially to disease transmission and likely represent the most significant impediment preventing malaria elimination and eradication. Plasmodium falciparum parasites evade antibody recognition through transcriptional switching between members of the var gene family, which encodes the major virulence factor and surface antigen on infected red blood cells. This process can extend infections for up to a year; however, infections have been documented to last for over a decade, constituting an unseen reservoir of parasites that undermine eradication and control efforts. How parasites remain immunologically "invisible" for such lengthy periods is entirely unknown. Here we show that in addition to the accepted paradigm of mono-allelic var gene expression, individual parasites can simultaneously express multiple var genes or enter a state in which little or no var gene expression is detectable. This unappreciated flexibility provides parasites with greater adaptive capacity than previously understood and challenges the dogma of mutually exclusive var gene expression. It also provides an explanation for the antigenically "invisible" parasites observed in chronic asymptomatic infections.

Age-specific patterns of DBLα var diversity can explain why residents of high malaria transmission areas remain susceptible to Plasmodium falciparum blood stage infection throughout life

Immunity to Plasmodium falciparum is non-sterilising, thus individuals residing in malaria-endemic areas are at risk of infection throughout their lifetime. Here we seek to find a genomic epidemiological explanation for why residents of all ages harbour blood stage infections despite lifelong exposure to P. falciparum in areas of high transmission. We do this by exploring, for the first known time, the age-specific patterns of diversity of variant antigen encoding (var) genes in the reservoir of infection. Microscopic and submicroscopic P. falciparum infections were analysed at the end of the wet and dry seasons in 2012-2013 for a cohort of 1541 residents aged from 1 to 91 years in an area characterised by high seasonal malaria transmission in Ghana. By sequencing the near ubiquitous Duffy-binding-like alpha domain (DBLα) that encodes immunogenic domains, we defined var gene diversity in an estimated 1096 genomes detected in sequential wet and dry season sampling of this cohort. Unprecedented var (DBLα) diversity was observed in all ages with 42,399 unique var types detected. There was a high degree of maintenance of types between seasons (>40% seen more than once), with many of the same types, especially upsA, appearing multiple times in isolates from different individuals. Children and adolescents were found to be significant reservoirs of var DBLα diversity compared with adults. Var repertoires within individuals were highly variable, with children having more related var repertoires compared to adolescents and adults. Individuals of all ages harboured multiple genomes with var repertoires unrelated to those infecting other hosts. High turnover of parasites with diverse isolate var repertoires was also observed in all ages. These age-specific patterns are best explained by variant-specific immune selection. The observed level of var diversity for the population was then used to simulate the development of variant-specific immunity to the diverse var types under conservative assumptions. Simulations showed that the extent of observed var diversity with limited repertoire relatedness was sufficient to explain why adolescents and adults in this community remain susceptible to blood stage infection, even with multiple genomes.

Precipitated Malaria: It Never Rains but It Pours

Occasionally, Plasmodium falciparum malaria is apparently precipitated by traumatic events (e.g., a landmine accident) or by noninfectious events (e.g., pregnancy). The authors reporting such cases often seem as baffled as many of their readers probably are. However, the case reports may contain important clues regarding malaria pathogenesis and immunity.

Contribution of Murine Models to the Study of Malaria During Pregnancy

Annually, many pregnancies occur in areas of Plasmodium spp. transmission, particularly in underdeveloped countries with widespread poverty. Estimations have suggested that several million women are at risk of developing malaria during pregnancy. In particular cases, systemic infection caused by Plasmodium spp. may extend to the placenta, dysregulating local homeostasis and promoting the onset of placental malaria; these processes are often associated with increased maternal and fetal mortality, intrauterine growth restriction, preterm delivery, and reduced birth weight. The endeavor to understand and characterize the mechanisms underlying disease onset and placental pathology face several ethical and logistical obstacles due to explicit difficulties in assessing human gestation and biological material. Consequently, the advent of murine experimental models for the study of malaria during pregnancy has substantially contributed to our understanding of this complex pathology. Herein, we summarize research conducted during recent decades using murine models of malaria during pregnancy and highlight the most relevant findings, as well as discuss similarities to humans and the translational capacity of achieved results.

Malaria Surveillance - United States, 2016

PROBLEM/CONDITION

Malaria in humans is caused by intraerythrocytic protozoa of the genus Plasmodium. These parasites are transmitted by the bite of an infective female Anopheles species mosquito. The majority of malaria infections in the United States occur among persons who have traveled to regions with ongoing malaria transmission. However, malaria is occasionally acquired by persons who have not traveled out of the country through exposure to infected blood products, congenital transmission, laboratory exposure, or local mosquitoborne transmission. Malaria surveillance in the United States is conducted to provide information on its occurrence (e.g., temporal, geographic, and demographic), guide prevention and treatment recommendations for travelers and patients, and facilitate transmission control measures if locally acquired cases are identified.

PERIOD COVERED

This report summarizes confirmed malaria cases in persons with onset of illness in 2016 and summarizes trends in previous years.

DESCRIPTION OF SYSTEM

Malaria cases diagnosed by blood film microscopy, polymerase chain reaction, or rapid diagnostic tests are reported to local and state health departments by health care providers or laboratory staff members. Case investigations are conducted by local and state health departments, and reports are transmitted to CDC through the National Malaria Surveillance System (NMSS), the National Notifiable Diseases Surveillance System (NNDSS), or direct CDC consultations. CDC reference laboratories provide diagnostic assistance and conduct antimalarial drug resistance marker testing on blood samples submitted by health care providers or local or state health departments. This report summarizes data from the integration of all NMSS and NNDSS cases, CDC reference laboratory reports, and CDC clinical consultations.

RESULTS

CDC received reports of 2,078 confirmed malaria cases with onset of symptoms in 2016, including two congenital cases, three cryptic cases, and one case acquired through blood transfusion. The number of malaria cases diagnosed in the United States has been increasing since the mid-1970s. However, in 2015 a decrease occurred in the number of cases, specifically from the region of West Africa, likely due to altered travel related to the Ebola virus disease outbreak. The number of confirmed malaria cases in 2016 represents a 36% increase compared with 2015, and the 2016 total is 153 more cases than in 2011, which previously had the highest number of cases (1,925 cases). In 2016, a total of 1,729 cases originated from Africa, and 1,061 (61.4%) of these came from West Africa. P. falciparum accounted for the majority of the infections (1,419 [68.2%]), followed by P. vivax (251 [12.1%]). Fewer than 2% of patients were infected by two species (23 [1.1%]). The infecting species was not reported or was undetermined in 10.8% of cases. CDC provided diagnostic assistance for 12.1% of confirmed cases and tested 10.8% of specimens with P. falciparum infections for antimalarial resistance markers. Of the U.S. resident patients who reported reason for travel, 69.4% were travelers who were visiting friends and relatives. The proportion of U.S. residents with malaria who reported taking any chemoprophylaxis in 2016 (26.3%) was similar to that in 2015 (26.6%), and adherence was poor among those who took chemoprophylaxis. Among the 964 U.S. residents with malaria for whom information on chemoprophylaxis use and travel region were known, 94.0% of patients with malaria did not adhere to or did not take a CDC-recommended chemoprophylaxis regimen. Among 795 women with malaria, 50 were pregnant, and one had adhered to mefloquine chemoprophylaxis. Forty-one (2.0%) malaria cases occurred among U.S. military personnel in 2016, a comparable proportion to that in 2015 (23 cases [1.5%]). Among all reported cases in 2016, a total of 306 (14.7%) were classified as severe illnesses, and seven persons died. In 2016, CDC analyzed 144 P. falciparum-positive and nine P. falciparum mixed species samples for surveillance of antimalarial resistance markers (although certain loci were untestable in some samples); genetic polymorphisms associated with resistance to pyrimethamine were identified in 142 (97.9%), to sulfadoxine in 98 (70.5%), to chloroquine in 67 (44.7%), to mefloquine in six (4.3%), and to atovaquone in one (<1.0%). The completeness of key variables (e.g., species, country of acquisition, and resident status) was 79.4% in 2016 and 75.7% in 2015.

INTERPRETATION

The number of reported malaria cases in 2016 continued a decades-long increasing trend and is the highest since 1972. The importation of malaria reflects the overall increase in global travel trends to and from areas where malaria is endemic; a transient decrease in the acquisition of cases, predominantly from West Africa, occurred in 2015. In 2016, more cases (absolute number) originated from regions of the world with widespread malaria transmission. Since the early 2000s, worldwide interventions to reduce malaria have been successful; however, progress has plateaued in recent years, the disease remains endemic in many regions, and the use of appropriate prevention measures by travelers remains inadequate.

PUBLIC HEALTH ACTIONS

The best way to prevent malaria is to take chemoprophylaxis medication during travel to a country where malaria is endemic. Malaria infections can be fatal if not diagnosed and treated promptly with antimalarial medications appropriate for the patient's age and medical history, the likely country of malaria acquisition, and previous use of antimalarial chemoprophylaxis. In 2018, two tafenoquine-based antimalarials were approved by the Food and Drug Administration (FDA) for use in the United States. Arakoda was approved for use by adults for chemoprophylaxis and is available as a weekly dosage that is convenient during travel, which might improve adherence and also can prevent relapses from P. vivax and P. ovale infections. Krintafel was approved for radical cure of P. vivax infections in those >16 years old. In April 2019, intravenous artesunate became the first-line medication for treatment of severe malaria in the United States. Because intravenous artesunate is not FDA approved, it is available from CDC under an investigational new drug protocol. Detailed recommendations for preventing malaria are available to the general public at the CDC website (https://www.cdc.gov/malaria/travelers/drugs.html). Health care providers should consult the CDC Guidelines for Treatment of Malaria in the United States and contact the CDC's Malaria Hotline for case management advice when needed. Malaria treatment recommendations are available online (https://www.cdc.gov/malaria/diagnosis_treatment) and from the Malaria Hotline (770-488-7788 or toll-free at 855-856-4713). Persons submitting malaria case reports (care providers, laboratories, and state and local public health officials) should provide complete information because incomplete reporting compromises case investigations and efforts to prevent infections and examine trends in malaria cases. Adherence to recommended malaria prevention strategies is low among U.S. travelers; reasons for nonadherence include prematurely stopping after leaving the area where malaria was endemic, forgetting to take the medication, and experiencing a side effect. Molecular surveillance of antimalarial drug resistance markers (https://www.cdc.gov/malaria/features/ars.html) enables CDC to track, guide treatment, and manage drug resistance in malaria parasites both domestically and internationally. More samples are needed to improve the completeness of antimalarial drug resistance analysis; therefore, CDC requests that blood specimens be submitted for all cases of malaria diagnosed in the United States.

Etiology of Placental Plasmodium falciparum Malaria in African Women

Plasmodium falciparum parasites causing placental malaria express the VAR2CSA type of the clonally variant antigen family erythrocyte membrane protein 1 (PfEMP1). This enables evasion of preexisting immunity and results in placental accumulation of infected erythrocytes. We present data on seasonal variation in levels of VAR2CSA-specific immunoglobulin G (IgG) and IgG specific for a placental malaria-unrelated PfEMP1 protein among Ghanaian women at their first antenatal visit. Our results indicate that placental malaria does not require recent exposure to infected mosquitoes, in contrast to malaria in general. This has implications for the impact of insecticide-treated bed nets on placental malaria incidence and for antenatal care in woman with preexisting immunity.

Case Report: Delayed or Recurrent Plasmodium falciparum Malaria in Migrants: A Report of Three Cases with a Literature Review

Emerging evidence indicates that migrants from Plasmodium falciparum endemic regions are at risk of delayed presentation of P. falciparum malaria. We report three cases of P. falciparum malaria occurring years after arrival in Europe. All patients were originally from Sub-Saharan Africa. Two subjects had controlled human immunodeficiency virus infection and one was a pregnant woman. We performed a literature review of all published cases of delayed presentation of P. falciparum in migrants and identified 32 additional cases. All cases but one originate from sub-Saharan Africa. There was a median time of 36 months between the last visit to a malaria-endemic country and clinical malaria (range: 3 months to 10 years). Pregnancy was the most frequently reported risk factor (11/35 or 31.4%). Parasitemia was ≤ 0.1% in 38% of cases (11/29 reported), and no death was reported. The underlying possible mechanisms for this delayed presentation in migrants from an endemic area probably include the persistence of submicroscopic parasitemia combined with decaying P. falciparum-specific immunity. Suspicion of P. falciparum delayed malaria should remain high in migrants, mainly from sub-Saharan Africa, even without a recent travel history, especially in those presenting risk factors for impaired parasite clearance or distinct immune responses such as pregnancy and HIV infection. In these patients, new prevention and screening strategies should be studied and blood safety policies adapted.

Plasmodium falciparum Recrudescence Two Years after Treatment of an Uncomplicated Infection without Return to an Area Where Malaria Is Endemic

We report evidence, confirmed by the lack of travel activity outside of France and genetic diversity analysis using polymorphic microsatellite markers, that Plasmodium falciparum malaria infection effectively treated with an artemisinin-based combination can remain dormant and relapse during pregnancy at least 2 years after treatment.

Symptomatic Falciparum Malaria After Living in a Nonendemic Area for 10 Years: Recrudescence or Indigenous Transmission?

AbstractWe report the case of a patient from Mali who, after 10 years of living in Spain, presented with symptomatic Plasmodium falciparum malaria without having visited an endemic area during that time. We cannot completely rule out the possibility of indigenous transmission, but this case most likely represents recrudescence of an infection acquired over 10 years earlier.

Recrudescence of Plasmodium falciparum in a Primigravida After Nearly 3 Years of Latency

We present a case of a primigravid woman who presented with Plasmodium falciparum nearly 3 years after she last visited a malaria-endemic region. We review the literature to identify case reports of recrudescent P. falciparum malaria during pregnancy, including those with prolonged latency. Reports of recrudescence of P. falciparum during pregnancy are limited. Plasmodium falciparum infection can persist for years. Recrudescence can occur with waning of immunity following departure from endemic areas. Pregnancy, particularly the primigravid state, is a risk factor for severe infection.

Clinical implications of a gradual dormancy concept in malaria

Malaria recurrences after an initially successful therapy and malarial fever occurring a long time after infection are well-known problems in malariology. Currently, two distinct types of malaria recurrences are defined: recrudescence and relapse. A recrudescence is thought to originate from circulating Plasmodium blood stages which do not cause fever before a certain level of a microscopically detectable parasitemia is reached. Contrary, a relapse is thought to originate from quiescent intracellular hepatic parasite stages called hypnozoites. Recrudescences would typically occur in infections due to Plasmodium falciparum. Plasmodium knowlesi, and Plasmodium malariae, whereas relapses would be caused exclusively by Plasmodium vivax and Plasmodium ovale. This schematic view is, however, insufficiently supported by experimental evidence. For instance, hypnozoites of P. ovale have never been experimentally documented. On the other hand, the nonfinding of P. malariae hypnozoites turned into the proof for the nonexistence of P. malariae hypnozoites. Clinical relapse-type recurrences have been observed in both P. ovale and P. malariae infections, and decade-long incubation times have also been reported in P. falciparum infections. We propose a gradual hypothesis in accordance with the continuity concept of biological evolution: both, relapse and recrudescence may be potentially caused by all Plasmodium spp. We hypothesize that the difference between the various Plasmodium spp. is quantitative rather than qualitative: there are Plasmodium spp. which frequently cause relapses such as P. vivax, particularly the P.v. Chesson strain, species which cause relapses less frequently, such as P. ovale and sometimes P. malariae, and species which may exceptionally cause relapses such as P. falciparum. All species may cause recrudescences. As clinical consequences, we propose that 8-aminquinolines may be considered in a relapse-type recrudescence regardless of the causal Plasmodium sp., whereas primaquine relapse prevention might not be routinely indicated in malaria due to P. ovale.

Anesthetic management of urgent cesarean delivery in a parturient with acute malaria infection: a case report

Malaria is associated with high rates of morbidity and mortality worldwide, particularly in Africa, Southeast Asia and South America. Nonetheless, several cases of malaria have been reported in Western countries involving travelers from endemic areas, though very few involve pregnant women. In this article, we report a case of a young woman born in Sierra Leone who had been living in Italy for two years. She was admitted to our hospital with malaise; worsening of her condition led to Plasmodium falciparum infection diagnosis early during her hospital stay, as well as an urgent cesarean delivery. We briefly discuss the features of malaria in pregnancy, the difficulties associated with early diagnosis, and the possible fetal and maternal implications, and also consider how the disease may affect anesthetic management.

The duration of Plasmodium falciparum infections

Plasmodium vivax and Plasmodium ovale are often considered the malaria parasites best adapted to long-term survival in the human host because of their latent exo-erythrocytic forms. The prevailing opinion until the middle of the last century was that the maximum duration of Plasmodium falciparum infections was less than two years. Case reports and series investigating blood donors following accidental malaria infection of blood transfusion recipients and other sporadic malaria cases in non-endemic countries have shown clearly that asymptomatic P. falciparum infections may persist for up to a decade or longer (maximum confirmed 13 years). Current policies in malaria-free countries of excluding blood donors who have lived in malarious areas are justified. Vigilance for longer than three years after declaring elimination in an area may be needed.

Two cases of Plasmodium falciparum malaria in the Netherlands without recent travel to a malaria-endemic country

Recently, two patients of African origin were given a diagnosis of Plasmodium falciparum malaria without recent travel to a malaria-endemic country. This observation highlights the importance for clinicians to consider tropical malaria in patients with fever. Possible transmission routes of P. falciparum to these patients will be discussed. From a public health perspective, international collaboration is crucial when potential cases of European autochthonous P. falciparum malaria in Europe re considered.

The case for PfEMP1-based vaccines to protect pregnant women against Plasmodium falciparum malaria

Vaccines are very cost-effective tools in combating infectious disease mortality and morbidity. Unfortunately, vaccines efficiently protecting against infection with malaria parasites are not available and are not likely to appear in the near future. An alternative strategy would be vaccines protecting against the disease and its consequences rather than against infection per se, by accelerating the development of the protective immunity that is normally acquired after years of exposure to malaria parasites in areas of stable transmission. This latter strategy is being energetically pursued to develop a vaccine protecting pregnant women and their offspring against mortality and morbidity caused by the accumulation of Plasmodium falciparum-infected erythrocytes in the placenta. It is based on a detailed understanding of the parasite antigen and the host receptor involved in this accumulation, as well as knowledge regarding the protective immune response that is acquired in response to placental P. falciparum infection. Nevertheless, it remains controversial in some quarters whether such a vaccine would have the desired impact, or indeed whether the strategy is meaningful. This article critically examines the relevance of several perceived obstacles to development of a vaccine against placental malaria.

Prospects and Pitfalls of Pregnancy-Associated Malaria Vaccination Based on the Natural Immune Response to Plasmodium falciparum VAR2CSA-Expressing Parasites

Pregnancy-associated malaria, a manifestation of severe malaria, is the cause of up to 200,000 infant deaths a year, through the effects of placental insufficiency leading to growth restriction and preterm delivery. Development of a vaccine is one strategy for control. Plasmodium falciparum-infected red blood cells accumulate in the placenta through specific binding of pregnancy-associated parasite variants that express the VAR2CSA antigen to chondroitin sulphate A on the surface of syncytiotrophoblast cells. Parasite accumulation, accompanied by an inflammatory infiltrate, disrupts the cytokine balance of pregnancy with the potential to cause placental damage and compromise foetal growth. Multigravid women develop immunity towards VAR2CSA-expressing parasites in a gravidity-dependent manner which prevents unfavourable pregnancy outcomes. Although current vaccine design, targeting VAR2CSA antigens, has succeeded in inducing antibodies artificially, this candidate may not provide protection during the first trimester and may only protect those women living in areas endemic for malaria. It is concluded that while insufficient information about placental-parasite interactions is presently available to produce an effective vaccine, incremental progress is being made towards achieving this goal.

Malaria hidden in a patient with diffuse large-B-cell lymphoma and sickle-cell trait

We report a case of an African patient with sickle cell trait who was diagnosed in Spain with B-cell lymphoma. Blood smears were negative for malaria, and no plasmodium antigens were detected in the blood. To treat his lymphoma, the patient underwent chemotherapy and autologous stem cell transplantation. Following a splenectomy due to a worsening condition, he developed clinical malaria with detectable parasitemia. This case suggests that the humoral response and parasite removal by the spleen may afford protection from overt disease and may even help maintain subclinical human reservoirs of the disease.

Clinical practice: the diagnosis of imported malaria in children

The present paper reviews the diagnosis of imported malaria in children. Malaria is caused by a parasite called Plasmodium and occurs in over 100 countries worldwide. Children account for 10-15% of all patients with imported malaria and are at risk to develop severe and life-threatening complications especially when infected with Plasmodium falciparum. Case-fatality ratios vary between 0.2% and 0.4%. Children visiting friends and relatives in malaria endemic areas and immigrants and refugees account for the vast majority of cases. Symptoms are non-specific and delayed infections (more than 3 months after return from an endemic country) may occur. Microscopic analysis of the thick blood film is the cornerstone of laboratory diagnosis. For pragmatic reasons, EDTA-anticoagulated blood is accepted, provided that slides are prepared within 1 h after collection. Information about the Plasmodium species (in particular P. falciparum versus the non-falciparum species) and the parasite density is essential for patient management. Molecular methods in reference settings are an adjunct for species differentiation. Signals generated by automated hematology analyzers may trigger the diagnosis of malaria in non-suspected cases. Malaria rapid diagnostic tests are reliable in the diagnosis of P. falciparum but not for the detection of the non-falciparum species. They do not provide information about parasite density and should be used as an adjunct (and not a substitute) to microscopy. In case of persistent suspicion and negative microscopy results, repeat testing every 8-12 h for at least three consecutive samplings is recommended. A high index of suspicion and a close interaction with the laboratory may assure timely diagnosis of imported malaria.

Of mice and women: rodent models of placental malaria

Pregnant women are at increased malaria risk. The infections are characterized by placental accumulation of infected erythrocytes (IEs) with adverse consequences for mother and baby. Placental IE sequestration in the intervillous space is mediated by variant surface antigens (VSAs) selectively expressed in placental malaria (PM) and specific for chondroitin sulfate A (CSA). In Plasmodium falciparum, these VSA(PM) appear largely synonymous with the P. falciparum erythrocyte membrane protein 1 (PfEMP1) family variant VAR2CSA. As rodent malaria parasites do not possess PfEMP1 homologs, the usefulness of experimental mouse PM models remains controversial. However, many features of murine and human PM are similar, including involvement of VSAs analogous to PfEMP1. It thus appears that rodent model studies can further the understanding of VSA-dependent malaria pathogenesis and immunity.

Prolonged Plasmodium falciparum infection in immigrants, Paris

Few immigrant travelers have Plasmodium falciparum infections >2 months after leaving malaria-endemic areas. We conducted a case-control study to identify factors associated with prolonged P. falciparum infection in immigrant travelers. Results suggest that P. falciparum infection should be systematically suspected, even months after travel, especially in pregnant women and first-arrival immigrants.