Problem pathogens: prevention of malaria in travellers

Gametocyte prevalence and risk factors of P. falciparum malaria patients admitted at the Hospital for Tropical Diseases, Thailand: a 20-year retrospective study

BACKGROUND

The incidence of malaria in Thailand has dramatically declined over the past two decades, and the goal is to eliminate malaria by 2025. Despite significant progress, one of the key challenges to malaria elimination are undetected gametocyte carriers. Human migration adds complexity to the malaria situation, as it not only sustains local transmission but also poses the risk of spreading drug-resistant parasites. Currently, no study has assessed the prevalence of gametocytes across multiple years in Plasmodium falciparum malaria patients in Thailand, and the risk factors for gametocyte carriage have not been fully explored.

METHODS

Medical records of all P. falciparum malaria patients admitted from January 1, 2001 to December 31, 2020 at the Hospital for Tropical Diseases, Thailand, were retrospectively examined and a total of 1962 records were included for analysis. Both P. falciparum parasites and gametocytes were diagnosed by microscopy. A regression model was used to evaluate predictors of gametocyte carriage.

RESULTS

The study demonstrated gametocyte prevalence in low malaria transmission areas. Nine risk factors for gametocyte carriage were identified: age between 15 and 24 years [adjusted odds ratio (aOR) = 1.96, 95% confidence interval (CI) 1.18-3.26], Karen ethnicity (aOR = 2.59, 95% CI 1.56-4.29), preadmission duration of fever > 7 days (aOR = 5.40, 95% CI 3.92-7.41), fever on admission (> 37.5 °C) (aOR = 0.61, 95% CI 0.48-0.77), haemoglobin ≤ 8 g/dL (aOR = 3.32, 95% CI 2.06-5.33), asexual parasite density > 5000-25,000/µL (aOR = 0.71, 95% CI 0.52-0.98), asexual parasite density > 25,000-100,000/µL (aOR = 0.74, 95% CI 0.53-1.03), asexual parasite density > 100,000/µL (aOR = 0.51, 95% CI 0.36-0.72), platelet count ≤ 100,000/µL (aOR = 0.65, 95% CI 0.50-0.85, clinical features of severe malaria (aOR = 2.33, 95% CI 1.76-3.10) and dry season (aOR = 1.41, 95% CI 1.10-1.80). An increasing incidence of imported transnational malaria cases was observed over the past two decades.

CONCLUSIONS

This is the first study to determine the prevalence of gametocytes among patients with symptomatic P. falciparum malaria, identify the risk factors for gametocyte carriage, and potential gametocyte carriers in Thailand. Blocking transmission is one of the key strategies for eliminating malaria in these areas. The results might provide important information for targeting gametocyte carriers and improving the allocation of resources for malaria control in Thailand. This study supports the already nationally recommended use of a single dose of primaquine in symptomatic P. falciparum malaria patients to clear gametocytes.

Gaps in knowledge and practices of malaria prevention in Francophone African immigrants in Metropolitan Edmonton

Background

Important knowledge gaps exist in the understanding of the management of the risks of imported malaria in Canada among Francophone immigrants from sub-Saharan Africa (FISSA). The aim of this cross-sectional study was to investigate the malaria related-knowledge, attitude and practices (KAP) of FISSA in Edmonton, where these immigrants are in an official minority language situation and the impact of language barriers on these factors.

Methods

A structured survey was used to examine the KAP of 382 FISSA in the Edmonton area from 2018 to 2019. Fisher’s Exact Test was applied to determine if there were associations between knowledge of malaria and different risk factors.

Results

Almost all FISSA (97%) had an accurate knowledge of fever as the key symptom of malaria. Interestingly, 60% of participants identified bed nets as a preventive method and only 19% of participants had accurate knowledge of malaria transmission. An accurate knowledge of symptoms was significantly associated with a high perceived risk of contracting malaria [odds ratio (OR) 4.33, 95% confidence interval (CI) 1.07–20.62]. Furthermore, even though 70% of FISSA had a high perceived risk of contracting malaria in endemic regions, only 52% of travellers had a pre-travel medical encounter. Importantly, language was not the predominant reason for not seeking pre-travel medical advice, although 84% of respondents chose French as their official language of preference when seeking medical advice. Having a French-speaking physician was correlated with satisfactory prevention knowledge (OR 1.96, 95% CI 1.16–3.35). With respect to health-seeking behaviour, 88% of respondents with a child < 5 years of age would seek medical care for fever in the child after travel to sub-Saharan Africa (SSA).

Conclusion

This study highlights that factors other than knowledge, risk assessment, and language might determine the lack of compliance with pre-travel medical encounters. It underscores the need for effective strategies to improve this adherence in minority settings.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12936-022-04210-w.

Malaria standby emergency treatment (SBET) for travellers visiting malaria endemic areas: a systematic review and meta-analysis

BACKGROUND

Malaria prevention methods for travellers to low or moderate malaria risk areas vary and remain controversial. Standby emergency treatment (SBET) for malaria is one possible strategy increasingly recommended since 1988 with little evidence on its effectiveness or how it is truly being used.

METHODS

A systematic review and meta-analysis were performed based on a structured search in Embase, Medline, PubMed, Cochrane and Web of Science on 7 September 2018. The primary outcome was the overall prevalence of SBET use in travellers, and secondary outcomes were the proportion carrying SBET, the response to fever [use of SBET, health facility attendance and use of malaria rapid diagnostic test (mRDT)], adverse events to SBET and the proportion using SBET incorrectly (incorrect dosage/duration). The pooled SBET use prevalence was analysed using a random effects model. A descriptive summary was done to present secondary outcomes. The study protocol was registered with PROSPERO CRD42018103703.

RESULTS

A total of 11 studies were eligible for inclusion among the 1027 titles identified by our search. The studies included 7/11 prospective cohort studies that recruited pre-travel clinic attendees in Europe and 4/11 cross-sectional studies, of which 3 recruited travellers at airports before their return home from Southeast Asia and Africa and 1 from an employee registry including long-term travellers. The overall pooled prevalence of SBET use among the 26 403 travellers was 2.5% (95% confidence interval, 1.1-4.3%; range, 0.4-10.8%). There was significant variation in the proportion of travellers carrying SBET medication (40-100%), the proportion of travellers with appropriate response to fever (23-100%), adverse events (0-33%) and incorrect dosage/duration of SBET (0-100%).

CONCLUSION

Adherence to the proposed recommendations for SBET use, notably the response to fever, was poor. If the use of SBET is to be pursued, modifications to the current SBET strategy should be considered, such as better selection of travellers at higher risk for malaria and the potential addition of mRDTs.

Epidemiology of Malaria in the State of Qatar, 2008-2015

Background and Objectives

Imported malaria poses a serious public health problem in Qatar because its population is “naïve” to such infection; where local transmission might lead to serious, life-threatening infection and might even trigger epidemics.

Methods

This study is a retrospective review of the imported malaria cases in Qatar reported by the malaria surveillance program at the Ministry of Public Health (MoPH), during the period between January 2008 and December 2015. All cases were imported and underwent parasitological confirmation through microscopy.

Results

A total of 4092 malaria cases were reported during 2008–2015 in Qatar. The demographic features of the imported cases show that the majority of cases were males (93%), non-Qatari (99.6%), and aged 15 to 44 years (82.1%). Moreover, P. vivax was found to be the main etiologic agent accounting for more than three-quarters (78.7%) of the imported cases. In addition, almost a third (33.1%) of the cases were reported during the months of July, August, and September.

Conclusions

Imported malaria in Qatar has witnessed an increase during the past seven years, despite a long period of constant reduction; where the people most affected were adult male migrants from endemic countries. Many challenges need to be overcome to prevent the reintroduction of malaria into the country.

Resistance screening and trend analysis of imported falciparum malaria in NSW, Australia (2010 to 2016)

Background

The World Health Organization currently recommends artemisinin (along with a partner drug) as the global frontline treatment for Plasmodium falciparum malaria. Artemisinin resistant P. falciparum are now found throughout the greater Mekong subregion of South East Asia. Several polymorphisms in the parasite’s kelch gene have been demonstrated to confer artemisinin resistance. While genotypes within the greater Mekong subregion are thoroughly examined in the literature, P. falciparum populations within several areas that do not (yet) have endemic resistance are underrepresented.

Results

This investigation characterised the Pfkelch13 propeller domains from 153 blood samples of 140 imported cases of P. falciparum malaria in New South Wales from 2010 to 2016. A low level of propeller domain diversity was observed, including the C580Y coding mutation most strongly associated with artemisinin resistance in South East Asia. The resistance genotype was found in a sample originating in Papua New Guinea, where this mutation, or artemisinin treatment failure, have not been previously reported. Sequencing a panel of geographically informative polymorphisms within the organellar genomes identified the C580Y parasite as having Oceanic origins. Patient data analysis revealed that New South Wales, Australia, P. falciparum malaria cases often originated from regions with limited drug resistance screening.

Conclusions

The C580Y finding from outside of the greater Mekong subregion supports the consensus to upscale molecular surveillance of artemisinin resistance outside of South East Asia. The genetic screening results identify a risk of importing resistant falciparum malaria to Australia, supporting an ongoing surveillance protocol to pre-empt treatment failure and contribute to global data gathering.

Life-Threatening Plasmodium Falciparum Malaria in Patient after Visiting Angola-Case Report

Malaria is a potentially life-threatening disease, especially when complicated by a septic shock. It is caused by infection of erythrocytes with protozoan parasites of the genus Plasmodium that are inoculated into the humans by a feeding female anopheline mosquito. Of the four Plasmodia species, infection with Plasmodium (P.) falciparum is often associated with different types of complications and significant mortality. Most imported cases of malaria are not in tourists but in immigrants and their children who have returned to the country of their family’s origin to visit friends and relatives (so-called VFR travelers) and have forgone chemoprophylaxis.

We described a case of a 52 year old patient who came from Angola, an African country with endemic malaria before the occurrence of the first symptoms of the disease. The first symptoms were not recognized by the presence of nonspecific symptoms. Very soon the patient was gone under the hemodynamic unstability that eas followed by shock and high percentage parasitemia of 25%. A global health disorder was developed accompanied with hemodynamic instability and cerebral dysfunction. He performs pulmonary ventilation disorder and renal failure. Only data from social epidemiological survey of travel to the African country, was sufficient to cast doubt on malaria. The diagnosis was conducted using the standard method - peripheral blood smear. After turning antimalarial drugs, improvement of health status with complete recovery within 10 days was noticed. The only consequence of the disease is persistent hypertension that is sensitive to standard antihypertensive therapy.

Natural Mosquito-Pathogen Hybrid IgG4 Antibodies in Vector-Borne Diseases: A Hypothesis

Chronic exposure to antigens may favor the production of IgG4 antibodies over other antibody types. Recent studies have shown that up to a 30% of normal human IgG4 is bi-specific and is able to recognize two antigens of different nature. A requirement for this specificity is the presence of both eliciting antigens in the same time and at the same place where the immune response is induced. During transmission of most vector-borne diseases, the pathogen is delivered to the vertebrate host along with the arthropod saliva during blood feeding and previous studies have shown the existence of IgG4 antibodies against mosquito salivary allergens. However, there is very little ongoing research or information available regarding IgG4 bi-specificity with regard to infectious disease, particularly during immune responses to vector-borne diseases, such as malaria, filariasis, or dengue virus infection. Here, we provide background information and present our hypothesis that IgG4 may not only be a useful tool to measure exposure to infected mosquito bites, but that these bi-specific antibodies may also play an important role in modulation of the immune response against malaria and other vector-borne diseases in endemic settings.

Antimalarials in the treatment of systemic lupus erythematosus: a registry-based cohort study in Denmark

BACKGROUND

Evidence-based international guidelines for the treatment of systemic lupus erythematosus (SLE) recommend treatment with antimalarials (AMs) for all patients with SLE irrespective of disease activity. Only a few studies have investigated the use of AMs among newly diagnosed patients with SLE.

OBJECTIVES

The objective of this paper is to analyze prescription patterns of AMs in newly diagnosed SLE patients in Denmark from 2000 to 2011.

METHODS

Using the Danish Prescription Register (DNPR), we conducted a nationwide cohort study including all patients with a first-time diagnosis of SLE (the Danish National Registry of Patients (NPR)). We used Kaplan-Meier estimates to compute the cumulative probability of starting AM treatment within a year and Cox regression analysis to compare time to treatment between patient groups.

RESULTS

AMs were prescribed to 37.7% of the newly diagnosed SLE patients within the first year of follow-up. Approximately 20% did not receive any medical treatment. Women were more likely than men to start AM (adjusted HR of 1.28 (95% CI 1.08-1.52)). Patients diagnosed with SLE between 2005 and 2011 were more likely to start treatment than patients diagnosed between 2000 and 2004 (HR of 1.21 (95% CI 1.07-1.36)). Patients with renal disease were less likely to start AM treatment than patients without this condition (adjusted HR of 0.50 (95% CI 0.36-0.68)). Current users of corticosteroids were more likely to start AM treatment than non-users (adjusted HR 1.81 (95% CI 1.59-2.06)).

CONCLUSION

Time to start of AM treatment following SLE diagnosis could be further reduced, especially among patients with renal disease. However, our results showed that treatment practice in recent years has changed toward initiating AM treatment earlier.

Men traveling away from home are more likely to bring malaria into high altitude villages, northwest Ethiopia

BACKGROUND

Information about malaria risk factors at high altitudes is scanty. Understanding the risk factors that determine the risk of malaria transmission at high altitude villages is important to facilitate implementing sustainable malaria control and prevention programs.

METHODS

An unmatched case control study was conducted among patients seeking treatment at health centers in high altitude areas. Either microscopy or rapid diagnostic tests were used to confirm the presence of plasmodium species. A generalized linear model was used to identify the predictors of malaria transmission in high altitude villages.

RESULTS

Males (AOR = 3.11, 95%CI: 2.28, 4.23), and those who traveled away from the home in the previous month (AOR = 2.01, 95% CI: 1.56, 2.58) were strongly associated with presence of malaria in high altitude villages. Other significant factors, including agriculture in occupation (AOR = 1.41, 95% CI: 1.05, 1.93), plants used for fencing (AOR = 1.70, 95% CI: 1.18, 2.52) and forests near the house (AOR = 1.60, 95% CI: 1.15, 2.47), were found predictors for malaria in high altitude villages.

CONCLUSION

Travel outside of their home was an important risk of malaria infections acquisition. Targeting males who frequently travel to malarious areas can reduce malaria transmission risks in high altitude areas.

Using mitochondrial genome sequences to track the origin of imported Plasmodium vivax infections diagnosed in the United States

Although the geographic origin of malaria cases imported into the United States can often be inferred from travel histories, these histories may be lacking or incomplete. We hypothesized that mitochondrial haplotypes could provide region-specific molecular barcodes for tracing the origin of imported Plasmodium vivax infections. An analysis of 348 mitochondrial genomes from worldwide parasites and new sequences from 69 imported malaria cases diagnosed across the United States allowed for a geographic assignment of most infections originating from the Americas, southeast Asia, east Asia, and Melanesia. However, mitochondrial lineages from Africa, south Asia, central Asia, and the Middle East, which altogether contribute the vast majority of imported malaria cases in the United States, were closely related to each other and could not be reliably assigned to their geographic origins. More mitochondrial genomes are required to characterize molecular barcodes of P. vivax from these regions.

Training programs within global networks: lessons learned in the Fogarty International Clinical Research Scholars and Fellows Program

The Fogarty International Clinical Research Scholars and Fellows Support Center at Vanderbilt describes administrative lessons learned from the management of 436 scholars (American students or host country junior trainees) and 122 post-doctoral fellows (Americans or host country nationals). Trainees spent 10-11 months working on mentored research projects at 61 well-vetted sites in 27 low- or middle-income host countries (LMICs) with strong US partners. Economies of scale, strong centralized information exchange, and effective standardized operations linking US institutions with LMIC field sites were achieved in a program that minimized administrative overhead. Advantages and drawbacks of this approach are presented and discussed. Training of a new generation of global research leaders is greatly facilitated by an overseas mentored research experience that is administratively streamlined to optimize the use of resources for training, research, and capacity building.

Impact of routine real-time PCR testing of imported malaria over 4 years of implementation in a clinical laboratory

In clinical laboratories, diagnosis of imported malaria is commonly performed by microscopy. However, the volume of specimens is generally low and maintaining proficiency in reading blood smears, particularly at the species level, is challenging in this setting. To address this problem, the Provincial Laboratory for Public Health (ProvLab) in Alberta, Canada, implemented real-time PCR for routine confirmation of all smear-positive samples in the province. Here we report our experience over a 4-year period (2008 to 2012) with this new diagnostic algorithm. While detection of Plasmodium falciparum by microscopy alone was accurate, real-time PCR served as an important adjunct to microscopy for the identification of non-falciparum species. In 18% of cases, the result was reported as non-falciparum or the species could not be identified by microscopy alone, and in all cases, the species was resolved by real-time PCR. In another 4% of cases, the species was misidentified by microscopy. To enhance surveillance for malaria, we integrated our demographic, clinical, and laboratory data into a new system developed by the Canadian Network for Public Health Intelligence, called the Malaria System for Online Surveillance (SOS). Using this application, we characterized our patient populations and travel history to identify risk factors associated with malaria infection abroad.

Self-boosting vaccines and their implications for herd immunity

Advances in vaccine technology over the past two centuries have facilitated far-reaching impact in the control of many infections, and today's emerging vaccines could likewise open new opportunities in the control of several diseases. Here we consider the potential, population-level effects of a particular class of emerging vaccines that use specific viral vectors to establish long-term, intermittent antigen presentation within a vaccinated host: in essence, "self-boosting" vaccines. In particular, we use mathematical models to explore the potential role of such vaccines in situations where current immunization raises only relatively short-lived protection. Vaccination programs in such cases are generally limited in their ability to raise lasting herd immunity. Moreover, in certain cases mass vaccination can have the counterproductive effect of allowing an increase in severe disease, through reducing opportunities for immunity to be boosted through natural exposure to infection. Such dynamics have been proposed, for example, in relation to pertussis and varicella-zoster virus. In this context we show how self-boosting vaccines could open qualitatively new opportunities, for example by broadening the effective duration of herd immunity that can be achieved with currently used immunogens. At intermediate rates of self-boosting, these vaccines also alleviate the potential counterproductive effects of mass vaccination, through compensating for losses in natural boosting. Importantly, however, we also show how sufficiently high boosting rates may introduce a new regime of unintended consequences, wherein the unvaccinated bear an increased disease burden. Finally, we discuss important caveats and data needs arising from this work.

Web-based GIS: the vector-borne disease airline importation risk (VBD-AIR) tool

Background

Over the past century, the size and complexity of the air travel network has increased dramatically. Nowadays, there are 29.6 million scheduled flights per year and around 2.7 billion passengers are transported annually. The rapid expansion of the network increasingly connects regions of endemic vector-borne disease with the rest of the world, resulting in challenges to health systems worldwide in terms of vector-borne pathogen importation and disease vector invasion events. Here we describe the development of a user-friendly Web-based GIS tool: the Vector-Borne Disease Airline Importation Risk Tool (VBD-AIR), to help better define the roles of airports and airlines in the transmission and spread of vector-borne diseases.

Methods

Spatial datasets on modeled global disease and vector distributions, as well as climatic and air network traffic data were assembled. These were combined to derive relative risk metrics via air travel for imported infections, imported vectors and onward transmission, and incorporated into a three-tier server architecture in a Model-View-Controller framework with distributed GIS components. A user-friendly web-portal was built that enables dynamic querying of the spatial databases to provide relevant information.

Results

The VBD-AIR tool constructed enables the user to explore the interrelationships among modeled global distributions of vector-borne infectious diseases (malaria. dengue, yellow fever and chikungunya) and international air service routes to quantify seasonally changing risks of vector and vector-borne disease importation and spread by air travel, forming an evidence base to help plan mitigation strategies. The VBD-AIR tool is available at http://www.vbd-air.com.

Conclusions

VBD-AIR supports a data flow that generates analytical results from disparate but complementary datasets into an organized cartographical presentation on a web map for the assessment of vector-borne disease movements on the air travel network. The framework built provides a flexible and robust informatics infrastructure by separating the modules of functionality through an ontological model for vector-borne disease. The VBD‒AIR tool is designed as an evidence base for visualizing the risks of vector-borne disease by air travel for a wide range of users, including planners and decisions makers based in state and local government, and in particular, those at international and domestic airports tasked with planning for health risks and allocating limited resources.

Air travel and vector-borne disease movement

Recent decades have seen substantial expansions in the global air travel network and rapid increases in traffic volumes. The effects of this are well studied in terms of the spread of directly transmitted infections, but the role of air travel in the movement of vector-borne diseases is less well understood. Increasingly however, wider reaching surveillance for vector-borne diseases and our improving abilities to map the distributions of vectors and the diseases they carry, are providing opportunities to better our understanding of the impact of increasing air travel. Here we examine global trends in the continued expansion of air transport and its impact upon epidemiology. Novel malaria and chikungunya examples are presented, detailing how geospatial data in combination with information on air traffic can be used to predict the risks of vector-borne disease importation and establishment. Finally, we describe the development of an online tool, the Vector-Borne Disease Airline Importation Risk (VBD-Air) tool, which brings together spatial data on air traffic and vector-borne disease distributions to quantify the seasonally changing risks for importation to non-endemic regions. Such a framework provides the first steps towards an ultimate goal of adaptive management based on near real time flight data and vector-borne disease surveillance.

Knowledge, attitudes, and practices toward malaria risk and prevention among frequent business travelers of a major oil and gas company

BACKGROUND

Despite significant morbidity and mortality among business travelers due to malaria, very little has been published on knowledge, attitudes, and practices (KAP) toward malaria risk. The aim of this study was to assess KAP among frequent international business travelers (FBT) and to identify recommendations for improving malaria prevention that could be applied to the wider FBT community in occupational health.

METHODS

A retrospective web-based survey was conducted in 2005 among self-registered FBT of an oil and gas company based in the Netherlands.

RESULTS

The survey was completed by 328 of the 608 self-registered FBT (54%). Fifty-four percent of respondents had visited a high-risk area for malaria. Most respondents (96%) were experienced travelers; the majority (71%) sought health advice before their trip and made use of a company health resource. Fever was recognized as a malaria symptom by all FBT; travel to high-risk malaria areas was correctly identified by 96%, and 99% of these travelers adhered to use of adequate personal protective measures. The proportion of travelers carrying appropriate anti-malaria drug regimen was positively associated with receiving company advice among FBT traveling to high-risk destinations (RR = 2.10, 95% CI: 1.21-3.67), but not for those traveling to low- or no-risk destinations. Only 8% (14) of those going to a high-risk area were not carrying malaria prophylaxis. One in five of FBT traveling to no-risk areas were unnecessarily carrying malaria prophylaxis.

CONCLUSIONS

The majority of KAP results were excellent. We postulate that a company culture with a strong focus on health, safety, security, and environment can positively contribute to high KAP scores. Notwithstanding the excellent findings, this study also provides a cautionary tale for company health functions against overprescribing of malaria prophylaxis. It demonstrates the need for constant review and audit of adherence to quality criteria.

Malaria Prophylaxis: A Comprehensive Review

The flow of international travellers to and from malaria-endemic areas, especially Africa, has increased in recent years. Apart from the very high morbidity and mortality burden imposed on malaria-endemic areas, imported malaria is the main cause of fever possibly causing severe disease and death in travellers coming from tropical and subtropical areas, particularly Sub-Saharan Africa. The importance of behavioural preventive measures (bed nets, repellents, etc.), adequate chemoprophylaxis and, in selected circumstances, stand-by emergency treatment may not be overemphasized. However, no prophylactic regimen may offer complete protection. Expert advice is needed to tailor prophylactic advice according to traveller (age, baseline clinical conditions, etc.) and travel (destination, season, etc.) characteristics in order to reduce malaria risk.

Inhibiting Plasmodium falciparum growth and heme detoxification pathway using heme-binding DNA aptamers

The human parasite Plasmodium falciparum enzymatically digests hemoglobin during its intra-erythrocytic developmental stages in acidic food vacuole compartments. The released heme is rapidly detoxified by polymerization into the chemically inert pigment, hemozoin. Several heme-binding anti-malarial compounds, such as chloroquine, efficiently inhibit this process, and this is believed to be the predominant mechanism by which these drugs induce parasite toxicity. In an effort to expand the biochemical tools available for exploration of this pathogen's basic biology, we chose this heme-detoxification pathway as a model system for exploring the suitability of DNA aptamers for modulating this essential parasite biochemical pathway. In this report, we demonstrate that heme-binding DNA aptamers efficiently inhibit in vitro hemozoin formation catalyzed by either a model lipid system or parasite-derived extracts just as or more potently than chloroquine. Furthermore, when parasites are grown in red cells loaded with heme-binding aptamers, their growth is significantly inhibited relative to parasites exposed to non-heme-binding DNA oligonucleotides. Both the timing of parasite-induced toxicity and the concentration of heme-binding aptamer required for inducing toxicity correlate well with the uptake of red cell cytosolic components by the parasite, and the requirement for compounds with similar in vitro hemozoin inhibitory potency to preconcentrate within the parasite before observing toxicity. Thus, these heme-binding aptamers recapitulate the in vitro hemozoin inhibition activity and induce parasite toxicity in a manner consistent with inhibition of this pathway. Altogether, these data demonstrate that aptamers can be versatile tools with applicability in functionally dissecting important P. falciparum-specific pathways both in vitro and in vivo.

Epidemiology of imported malaria in Qatar

OBJECTIVE

This study estimated the annual incidence of imported malaria in Qatar from 1997 to 2006 and described the epidemiological features of malaria from 2004 to 2006.

METHODS

A retrospective review was conducted of the imported malaria cases in Qatar reported by the malaria surveillance program during the period 1997 to 2006 to estimate annual incidence. Data on 438 malaria cases reported during 2004 to 2006 were analyzed to describe the epidemiological features of imported malaria in Qatar.

RESULTS

The incidence of malaria in 1997 was 58.6/100,000, and since then, it has shown a consistent decline to reach the lowest rate of 9.5/100,000 in 2004. After that the incidence of malaria has increased by more than two times in 2005 and 2006. All 438 malaria cases were contracted as a result of travel to endemic countries, namely India, Pakistan, and Sudan. The majority of cases were male, non-Qatari, and aged 15 years and older. Plasmodium vivax was the main etiologic agent in 40% of cases and most occurred between August and October.

CONCLUSIONS

Imported malaria reported in Qatar has shown an increase in the past 2 years after a long period of constant reduction, and the people most affected were adult male migrants from endemic countries. This group should be targeted by malaria prevention programs.

Imported cases of malaria admitted to two hospitals of Margarita Island, Venezuela, 1998-2005

BACKGROUND

Imported cases of malaria constitute an important public health problem in many countries, even in those with autochthonous cases, where disease could be acquired in these areas and then seen in non-endemic regions. Non-immune populations are susceptible to complications due to malaria infection, particularly in malaria caused by Plasmodium falciparum. However, Plasmodium vivax the predominant Plasmodium spp. in Venezuela can also lead to severe malaria.

METHODS

We reviewed retrospectively cases of malaria to identify the clinical features of those imported cases diagnosed at two institutions in Margarita Island (a non-endemic area), Venezuela, in an 8-year period. We conducted a retrospective observational study to identify the clinical and epidemiological features among hospitalized patients at Hospital Central and Hospital Agustin Hernández with malaria acquired at malaria-endemic locations.

RESULTS

We identified eighteen imported cases of malaria confirmed by thin and thick peripheral blood smears at these two institutions over an 8-year period. The mean age of diagnosis was 27 years. P. vivax was responsible for the majority of cases. All patients presented with fever, 89% with malaise, 78% with chills, and 67% with myalgia, among others symptoms. Mean haemoglobin levels on admission were 8.1g/dL (100% <12g/dL); platelets: 79,283cells/mm(3) (89% had platelets below 150,000); and a mean total leukocyte count: 3.4x10(3)cells/mm(3) (78% had leukopenia). Thirty nine percent of patients required blood transfusions. Two fatalities were identified (CFR=11%), one associated to severe malaria due to P. falciparum and the other due to a complicated case of P. vivax malaria.

DISCUSSION

Imported cases of malaria due to P. vivax and P. falciparum in the studied population are associated with significant hematological complications. These findings illustrate the importance of educating non-immune populations about the malaria risk and prevention strategies; and from a pubic health perspective, the need to develop further malaria prevention strategies at a national level.

Performance of self-diagnosis and standby treatment of malaria in international oilfield service employees in the field

Background

Falciparum malaria remains a major occupational illness that accounts for several deaths per year and numerous lost working days among the expatriate population, working or living in high-risk malarious areas. Compliance to preventive strategies is poor in travellers, especially business travellers, expatriates and long-term travellers.

Methods

In this cross-sectional, web-based study the adherence to and outcome of a preventive malaria programme on knowledge, attitudes and practices, including the practice of self-diagnosis and standby treatment (curative malaria kit, CMK) was evaluated in 2,350 non-immune expatriates, who had been working in highly malaria endemic areas.

Results

One-third (N = 648) of these expatriates visited a doctor for malaria symptoms and almost half (29 of 68) of all hospitalizations were due to malaria. The mandatory malaria training for non-immunes was completed by 92% of those who visited or worked in a high risk malaria country; 70% of the respondents at risk also received the CMK. The malaria awareness training and CMK significantly increased malaria knowledge [relative risk (RR) of 1.5, 95%CI 1.2–2.1], attitudes and practices, including compliance to chemoprophylaxis [RR = 2.2, 95%CI 1.6–3.2]. Hospitalization for malaria tended to be reduced by the programme [RR = 0.4, 95%CI 0.1–1.1], albeit not significantly. Respondents who did not receive instructions on the rapid diagnostic test were two times [RR = 2.3, 95%CI 1.6–3.3] more likely to have difficulties. Those who did receive instructions adhered poorly to the timing of repeating the test. Moreover, 6% (31 of 513) of those with a negative test result were diagnosed with malaria by a local doctor. 77% (N = 393) of the respondents with a negative test result did not take curative medication. 57% (252 of 441) of the respondents who took the curative medication that was included in the kit did not have a positive self-test or clinical malaria diagnosis made by a doctor.

Conclusion

This survey demonstrated that a comprehensive programme targeting malaria prevention in expatriates can be effectively implemented and that it significantly increased malaria awareness.

Treatment and prevention of malaria in pregnancy and newborn

Pregnant women are at increased risk for malaria infection. Although important advances have been made in the last years, the mechanisms that explain the increased susceptibility are not yet fully understood. Malaria infection in pregnancy is associated with maternal and fetal morbidity and mortality. The severity of the disease depends on the level of pre-pregnancy acquired immunity against malaria, and the consequences of infection are more severe in non-immune women. In highly endemic areas, the frequency and severity of the infection is higher in primigravida and decreases with increasing parity. In non-immune women, the risk is similar across the parity and malaria may be an important direct cause of maternal mortality. Malaria infection during pregnancy has important negative effects on infant's health, causing intrauterine growth retardation and prematurity or directly through congenital infection. In this paper, we review the pathology, diagnosis, and current recommendations for treatment and prevention of malaria in the pregnant woman and her infant.

Fever of unknown origin in the returning traveler

The returning traveler with fever presents a diagnostic challenge for the health care provider. When evaluating such a patient, the highest priority should be given to diseases that are potentially fatal or may represent public health threats. A good history is paramount and needs to include destination, time and duration of travel, type of activity, onset of fever in relation to travel, associated comorbidities, and any associated symptoms. Pretravel immunizations and chemoprophylaxis may alter the natural course of disease and should be inquired about specifically. The fever pattern, presence of a rash or eschar, organomegaly, or neurologic findings are helpful physical findings. Laboratory abnormalities are nonspecific but when corroborated with clinical and epidemiologic data may offer a clue to diagnosis.

A comparison of three diagnostic techniques for malaria: a rapid diagnostic test (NOW Malaria), PCR and microscopy

Malaria is a common, life-threatening infection in endemic tropical areas and one that presents a diagnostic challenge to laboratories in most non-endemic countries. A rapid and accurate diagnosis is a prerequisite for effective treatment, especially for the potentially fatal cases of Plasmodium falciparum infection. In the present, multi-centre study, the performances of a rapid diagnostic test (NOW) Malaria) and several, commercial, PCR-based assays (AMS61, AMS42, AMS43, AMS4 and AMS45) were compared against the results of microscopical examination of bloodsmears (the current 'gold standard'). The subjects were either non-European immigrants (N=135) or international travellers (N=171). There was good concordance between the results of all the detection methods, with kappa values of >0.8. Although the NOW Malaria rapid test was both sensitive (100%) and specific (100%) in detecting P. falciparum infections, it was less specific (93.1%) and sensitive (90.7%) in identifying the other Plasmodium species. The results from the AMS61 assay, designed to detect any malarial infection, generally parallelled those of the microscopy (kappa = 0.89), giving a specificity of 98.2% and a sensitivity of 91.0%. Although the use of species-specific molecular primers to identify pure infections with P. falciparum and P. vivax gave results that were in good agreement with those of the microscopy, the subjects who had apparently pure infections with P. ovale or P. malariae were always found PCR-negative. Compared with the standard microscopy, both the NOW Malaria test and the PCR-based assays were therefore poor at identifying mixed infections. The NOW Malaria test and the PCR-based assays clearly need to be improved, particularly for the correct identification of infections with Plasmodium spp. other than P. falciparum, including mixed infections. For now, expert microscopy must remain the mainstay of the laboratory diagnosis of malaria.

Malaria Chemotherapeutics Part I: History of Antimalarial Drug Development, Currently Used Therapeutics, and Drugs in Clinical Development

Since ancient times, humankind has had to struggle against the persistent onslaught of pathogenic microorganisms. Nowadays, malaria is still the most important infectious disease worldwide. Considerable success in gaining control over malaria was achieved in the 1950s and 60s through landscaping measures, vector control with the insecticide DDT, and the widespread administration of chloroquine, the most important antimalarial agent ever. In the late 1960s, the final victory over malaria was believed to be within reach. However, the parasites could not be eradicated because they developed resistance against the most widely used and affordable drugs of that time. Today, cases of malaria infections are on the rise and have reached record numbers. This review gives a short description of the malaria disease, briefly addresses the history of antimalarial drug development, and focuses on drugs currently available for malaria therapy. The present knowledge regarding their mode of action and the mechanisms of resistance are explained, as are the attempts made by numerous research groups to overcome the resistance problem within classes of existing drugs and in some novel classes. Finally, this review covers all classes of antimalarials for which at least one drug candidate is in clinical development. Antimalarial agents that are solely in early development stages will be addressed in a separate review.

Estimating the malaria risk of African mosquito movement by air travel

Background

The expansion of global travel has resulted in the importation of African Anopheles mosquitoes, giving rise to cases of local malaria transmission. Here, cases of 'airport malaria' are used to quantify, using a combination of global climate and air traffic volume, where and when are the greatest risks of a Plasmodium falciparum-carrying mosquito being importated by air. This prioritises areas at risk of further airport malaria and possible importation or reemergence of the disease.

Methods

Monthly data on climate at the World's major airports were combined with air traffic information and African malaria seasonality maps to identify, month-by-month, those existing and future air routes at greatest risk of African malaria-carrying mosquito importation and temporary establishment.

Results

The location and timing of recorded airport malaria cases proved predictable using a combination of climate and air traffic data. Extending the analysis beyond the current air network architecture enabled identification of the airports and months with greatest climatic similarity to P. falciparum endemic regions of Africa within their principal transmission seasons, and therefore at risk should new aviation routes become operational.

Conclusion

With the growth of long haul air travel from Africa, the identification of the seasonality and routes of mosquito importation is important in guiding effective aircraft disinsection and vector control. The recent and continued addition of air routes from Africa to more climatically similar regions than Europe will increase movement risks. The approach outlined here is capable of identifying when and where these risks are greatest.