Malaria chemoprophylaxis in the age of drug resistance. I. Currently recommended drug regimens

Occupational exposure to malaria, leishmaniasis and arbovirus vectors in endemic regions: A systematic review

Vector-borne diseases, including dengue, leishmaniasis and malaria, may be more common among individuals whose occupations or behaviours bring them into frequent contact with these disease vectors outside of their homes. A systematic review was conducted to ascertain at-risk occupations and situations that put individuals at increased risk of exposure to these disease vectors in endemic regions and identify the most suitable interventions for each exposure. The review was conducted in accordance with PRISMA guidelines on articles published between 1945 and October 2021, searched in 16 online databases. The primary outcome was incidence or prevalence of dengue, leishmaniasis or malaria. The review excluded ecological and qualitative studies, abstracts only, letters, commentaries, reviews, and studies of laboratory-acquired infections. Studies were appraised, data extracted, and a descriptive analysis conducted. Bite interventions for each risk group were assessed. A total of 1170 articles were screened and 99 included. Malaria, leishmaniasis and dengue were presented in 47, 41 and 24 articles, respectively; some articles presented multiple conditions. The most represented populations were soldiers, 38% (43 of 112 studies); refugees and travellers, 15% (17) each; migrant workers, 12.5% (14); miners, 9% (10); farmers, 5% (6); rubber tappers and missionaries, 1.8% (2) each; and forest workers, 0.9% (1). Risk of exposure was categorised into round-the-clock or specific times of day/night dependent on occupation. Exposure to these vectors presents a critical and understudied concern for outdoor workers and mobile populations. When devising interventions to provide round-the-clock vector bite protection, two populations are considered. First, mobile populations, characterized by their high mobility, may find potential benefits in insecticide-treated clothing, though more research and optimization are essential. Treated clothing offers personal vector protection and holds promise for economically disadvantaged individuals, especially when enabling them to self-treat their clothing to repel vectors. Secondly, semi-permanent and permanent settlement populations can receive a combination of interventions that offer both personal and community protection, including spatial repellents, suitable for extended stays. Existing research is heavily biased towards tourism and the military, diverting attention and resources from vulnerable populations where these interventions are most required like refugee populations as well as those residing in sub-Saharan Africa.

Alkaloids from Plants with Antimalarial Activity: A Review of Recent Studies

Malaria is one of the major health problems in developing countries. The disease kills a large number of people every year and also affects financial status of many countries. Resistance of the plasmodium parasite, the causative agent, to the existing drugs, including chloroquine, mefloquine, and artemisinin based combination therapy (ACT), is a serious global issue in malaria treatment and control. This warrants an urgent quest for novel compounds, particularly from natural sources such as medicinal plants. Alkaloids have over the years been recognized as important phytoconstituents with interesting biological properties. In fact, the first successful antimalarial drug was quinine, an alkaloid, which was extracted from Cinchona tree. In the present review work, the alkaloids isolated and reported recently (2013 till 2019) to possess antimalarial activity are presented. Several classes of alkaloids, including terpenoidal, indole, bisindole, quinolone, and isoquinoline alkaloids, were identified with a promising antimalarial activity. It is hoped that the reports of the review work will spur further research into the structural modification and/or development of the interesting compounds as novel antimalarial drugs.

Safety and effectiveness of antimalarial therapy in sickle cell disease: a systematic review and network meta-analysis

BACKGROUND

About 80% of all reported sickle cell disease (SCD) cases in children anually are recorded in Africa. Although malaria is considered a major cause of death in SCD children, there is limited data on the safety and effectiveness of the available antimalarial drugs used for prophylaxis. Also, previous systematic reviews have not provided quantitative measures of preventive effectiveness. The purpose of this research was to conduct a systematic review and meta-analysis of the available literature to determine the safety and effectiveness of antimalarial chemoprophylaxis used in SCD patients.

METHODS

We searched in PubMed, Medline, CINAHL, POPLine and Cochrane library, for the period spanning January 1990 to April 2018. We considered randomized or quasi-randomized controlled trials comparing any antimalarial chemoprophylaxis to, 1) other antimalarial chemoprophylaxis, 2) placebo or 3) no intervention, in SCD patients. Studies comparing at least two treatment arms, for a minimum duration of three months, with no restriction on the number of patients per arm were reviewed. The data were extracted and expressed as odds ratios. Direct pairwise comparisons were performed using fixed effect models and the heterogeneity assessed using the I-square.

RESULTS

Six qualified studies that highlighted the importance of antimalarial chemoprophylaxis in SCD children were identified. In total, seven different interventions (Chloroquine, Mefloquine, Mefloquine artesunate, Proguanil, Pyrimethamine, Sulfadoxine-pyrimethamine, Sulfadoxine-pyrimethamine amodiaquine) were evaluated in 912 children with SCD. Overall, the meta-analysis showed that antimalarial chemoprophylaxis provided protection against parasitemia and clinical malaria episodes in children with SCD. Nevertheless, the risk of hospitalization (OR = 0.72, 95% CI = 0.267-1.959; I2 = 0.0%), blood transfusion (OR = 0.83, 95% CI = 0.542-1.280; I2 = 29.733%), vaso-occlusive crisis (OR = 19, 95% CI = 1.713-2.792; I2 = 93.637%), and mortality (OR = 0.511, 95% CI = 0.189-1.384; I2 = 0.0%) did not differ between the intervention and placebo groups.

CONCLUSION

The data shows that antimalarial prophylaxis reduces the incidence of clinical malaria in children with SCD. However, there was no difference between the occurrence of adverse events in children who received placebo and those who received prophylaxis. This creates an urgent need to assess the efficacy of new antimalarial drug regimens as potential prophylactic agents in SCD patients.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO (CRD42016052514).

Optimal Antimalarial Dose Regimens for Sulfadoxine-Pyrimethamine with or without Azithromycin in Pregnancy Based on Population Pharmacokinetic Modeling

Optimal dosing of sulfadoxine-pyrimethamine (SP) as intermittent preventive treatment in pregnancy remains to be established, particularly when coadministered with azithromycin (AZI). To further characterize SP pharmacokinetics in pregnancy, plasma concentration-time data from 45 nonpregnant and 45 pregnant women treated with SP-AZI (n = 15 in each group) and SP-chloroquine (n = 30 in each group) were analyzed. Population nonlinear mixed-effect pharmacokinetic models were developed for pyrimethamine (PYR), sulfadoxine (SDOX), and N-acetylsulfadoxine (the SDOX metabolite NASDOX), and potential covariates were included. Pregnancy increased the relative clearance (CL/F) of PYR, SDOX, and NASDOX by 48, 29, and 70%, respectively, as well as the relative volumes of distribution (V/F) of PYR (46 and 99%) and NASDOX (46%). Coadministration of AZI resulted in a greater increase in PYR CL/F (80%) and also increased NASDOX V/F by 76%. Apparent differences between these results and those of published studies of SP disposition may reflect key differences in study design, including the use of an early postpartum follow-up study rather than a nonpregnant comparator group. Simulations based on the final population model demonstrated that, compared to conventional single-dose SP in nonpregnant women, two such doses given 24 h apart should ensure that pregnant women have similar drug exposure, while three daily SP doses may be required if SP is given with AZI. The results of past and ongoing trials using recommended adult SP doses with or without AZI in pregnant women may need to be interpreted in light of these findings and consideration given to using increased doses in future trials.

A prospective comparative field study to evaluate the efficacy of a traditional plant-based malaria prophylaxis

Background:

An unceasing threat of resistance of malarial parasites to available antimalarial drugs makes the development of new drugs imperative. Natural plant-based products are an alternative source for discovering new antimalarial drugs.

Aim:

To determine the prophylactic efficacy of a traditionally used plant-based drug on prevention of malaria in endemic villages of Odisha, India.

Methods:

A total of 267 healthy human volunteers of both sexes, aged 18-60 years were enrolled in Odisha, India, to receive either minimum 20 doses of aqueous extract of Traditional Plant-based Malaria Prophylactic drug 74, twice a week (experimental group), or no drug (control group) for 14 weeks. The primary criterion was the occurrence of malaria positive cases confirmed through expert microscopy during the study period. Analyses were by per-protocol (PP) and modified intention-to-treat (mITT).

Results:

A significant (P < 0.01) reduction (64%) of malaria incidence was observed in the experimental group compared to control group, 12.3% and 26.6%, respectively, as PP analysis. However, the reduction was nonsignificant as per mITT analysis (P = 0.22). The experimental group showed a relative risk of 0.36 compared to control group.

Conclusion:

This preliminary study constitutes a potential “proof of concept” for the development of malaria prophylactic drug and provide a scientific basis for the use of traditional remedy as a malaria preventive by tribal populations in India.

Manzamine alkaloids: isolation, cytotoxicity, antimalarial activity and SAR studies

The infectious disease Malaria is caused by different species of the genus Plasmodium. Resistance to quinoline antimalarial drugs and decreased susceptibility to artemisinin-based combination therapy have increased the need for novel antimalarial agents. Historically, natural products have been used for the treatment of infectious diseases. Identification of natural products and their semi-synthetic derivatives with potent antimalarial activity is an important method for developing novel antimalarial agents. Manzamine alkaloids are a unique group of β-carboline alkaloids isolated from various species of marine sponge displaying potent antimalarial activity against drug-sensitive and -resistant strains of Plasmodium. In this review, we demonstrate antimalarial potency, cytotoxicity and antimalarial SAR of manzamine alkaloids.

Pharmacokinetic properties of azithromycin in pregnancy

Azithromycin (AZI) is an azalide antibiotic with antimalarial activity that is considered safe in pregnancy. To assess its pharmacokinetic properties when administered as intermittent preventive treatment in pregnancy (IPTp), two 2-g doses were given 24 h apart to 31 pregnant and 29 age-matched nonpregnant Papua New Guinean women. All subjects also received single-dose sulfadoxine-pyrimethamine (SP) (1,500 mg or 75 mg) or chloroquine (450-mg base daily for 3 days). Blood samples were taken at 0, 1, 2, 3, 6, 12, 24, 32, 40, 48, and 72 h and on days 4, 5, 7, 10, and 14 for AZI assay by ultra-high-performance liquid chromatography-tandem mass spectrometry. The treatments were well tolerated. Using population pharmacokinetic modeling, a three-compartment model with zero-order followed by first-order absorption and no lag time provided the best fit. The areas under the plasma concentration-time curve (AUC(0-infinity)) (28.7 and 31.8 mg.h liter(-1) for pregnant and nonpregnant subjects, respectively) were consistent with the results of previous studies, but the estimated terminal elimination half-lives (78 and 77 h, respectively) were generally longer. The only significant relationship for a range of potential covariates, including malarial parasitemia, was with pregnancy, which accounted for an 86% increase in the volume of distribution of the central compartment relative to bioavailability without a significant change in the AUC(0-infinity). These data suggest that AZI can be combined with compounds with longer half-lives, such as SP, in combination IPTp without the need for dose adjustment.

Deficiencia de glucosa 6-fostato deshidrogenasa en hombres sanos y en pacientes maláricos; Turbo (Antioquia, Colombia)

INTRODUCCIÓN: En América Latina la deficiencia de glucosa 6-fosfato deshidrogenasa (d-G6PD) ha sido poco estudiada y en Colombia solo conocemos tres publicaciones antiguas. Urge conocer más la prevalencia de d-G6PD, sobre todo ahora que el tratamiento de la malaria vivax plantea aumentar la dosis diaria o total de primaquina. OBJETIVO: Medir la prevalencia de d-G6PD en poblaciones masculina sana y de enfermos con malaria por Plasmodium vivax, en Turbo (Urabá, departamento de Antioquia, Colombia). METODOLOGÍA: Encuestas de prevalencia, para evaluar la G6PD en dos poblaciones de Turbo (Antioquia): hombres sanos; hombres y mujeres con malaria vivax. Se trabajó con muestras diseñadas con criterios estadístico-epidemiológicos. La actividad enzimática se midió con el método normalizado de Beutler para valorar la G6PD en hemolizados. RESULTADOS: Entre los hombres sanos (n = 508), el intervalo de confianza 95% para el promedio (IC95%) estuvo entre 4,15 y 4,51 UI/g hemoglobina y 14,8% presentaron valores por debajo del "límite normal" de < 2,29 UI/g hemoglobina (prevalencia de d-G6PD). Entre los hombres con malaria (n = 206) el IC95% fue 3,81 a 4,16 UI/g hemoglobina y entre las mujeres palúdicas fue 3,86 a 4,20 UI/g hemoglobina. Los promedios masculinos (sanos vs. maláricos) fueron estadísticamente diferentes (p = 0,028). Únicamente 9,5% (13/137) de los enfermos con paludismo, todos de sexo masculino, presentaron d-G6PD. CONCLUSIONES: la d-G6PD es relativamente alta (14,8%) en la población masculina sana de Turbo y en los enfermos maláricos por P. vivax (9,5%, todos hombres).

Malaria: progress, perils, and prospects for eradication

There are still approximately 500 million cases of malaria and 1 million deaths from malaria each year. Yet recently, malaria incidence has been dramatically reduced in some parts of Africa by increasing deployment of anti-mosquito measures and new artemisinin-containing treatments, prompting renewed calls for global eradication. However, treatment and mosquito control currently depend on too few compounds and thus are vulnerable to the emergence of compound-resistant parasites and mosquitoes. As discussed in this Review, new drugs, vaccines, and insecticides, as well as improved surveillance methods, are research priorities. Insights into parasite biology, human immunity, and vector behavior will guide efforts to translate parasite and mosquito genome sequences into novel interventions.

In search of cyclooxygenase inhibitors, anti-Mycobacterium tuberculosis and anti-malarial drugs from Thai flora and microbes

Malaria continues to be a major infectious disease of the developing world and the problem is compounded not only by the emergence of drug resistant strains but also from a lack of a vaccine. The situation for tuberculosis (TB) infection is equally problematic. Once considered a "treatable" disease for which eradication was predicted, TB has re-emerged as highly lethal, multi-drug resistant strains after the outbreak of AIDS. Worldwide, the disease causes millions of deaths annually. Similarly, treatments for chronic inflammatory diseases such as arthritis have been impeded due to the potentially lethal side effects of the new and widely prescribed non-steroidal anti-inflammatory compounds. Thais have utilized bioresources from plants and some microorganisms for medicine for thousands of years. Because of the need for new drugs to fight malaria and TB, with radically different chemical structures and mode of actions other than existing drugs, efforts have been directed towards searching for new drugs from bioresources. This is also true for anti-inflammatories. Although Thailand is considered species-rich, only a small number of potential bioresources has been investigated. This article briefly describes the pathogenesis of 2 infectious diseases, malaria and TB, and modern medicines employed in chemotherapy. Diversities of Thai flora and fungi and their chemical constituents with antagonistic properties against these 2 diseases are described in detail. Similarly, anti-inflammatory compounds, mostly cyclooxygenase (COX) inhibitors, are also described herein to demonstrate the potential of Thai bioresources to provide a wide array of compounds for treatment of diseases of a different nature.

Risk factors for imported fatal Plasmodium falciparum malaria, France, 1996-2003

Plasmodium falciparum malaria is a serious health hazard for travelers to malaria-endemic areas and is often diagnosed on return to the country of residence. We conducted a retrospective study of imported falciparum malaria among travelers returning to France from malaria-endemic areas from 1996 through 2003. Epidemiologic, clinical, and parasitologic data were collected by a network of 120 laboratories. Factors associated with fatal malaria were identified by logistic regression analysis. During the study period, 21,888 falciparum malaria cases were reported. There were 96 deaths, for a case-fatality rate of 4.4 per 1,000 cases of falciparum malaria. In multivariate analysis, risk factors independently associated with death from imported malaria were older age, European origin, travel to East Africa, and absence of chemoprophylaxis. Fatal imported malaria remains rare and preventable. Pretravel advice and malaria management should take into account these risk factors, particularly for senior travelers.

In vitro efficacy, resistance selection, and structural modeling studies implicate the malarial parasite apicoplast as the target of azithromycin

Azithromycin (AZ), a broad-spectrum antibacterial macrolide that inhibits protein synthesis, also manifests reasonable efficacy as an antimalarial. Its mode of action against malarial parasites, however, has remained undefined. Our in vitro investigations with the human malarial parasite Plasmodium falciparum document a remarkable increase in AZ potency when exposure is prolonged from one to two generations of intraerythrocytic growth, with AZ producing 50% inhibition of parasite growth at concentrations in the mid to low nanomolar range. In our culture-adapted lines, AZ displayed no synergy with chloroquine (CQ), amodiaquine, or artesunate. AZ activity was also unaffected by mutations in the pfcrt (P. falciparum chloroquine resistance transporter) or pfmdr1 (P. falciparum multidrug resistance-1) drug resistance loci, as determined using transgenic lines. We have selected mutant, AZ-resistant 7G8 and Dd2 parasite lines. In the AZ-resistant 7G8 line, the bacterial-like apicoplast large subunit ribosomal RNA harbored a U438C mutation in domain I. Both AZ-resistant lines revealed a G76V mutation in a conserved region of the apicoplast-encoded P. falciparum ribosomal protein L4 (PfRpl4). This protein is predicted to associate with the nuclear genome-encoded P. falciparum ribosomal protein L22 (PfRpl22) and the large subunit rRNA to form the 50 S ribosome polypeptide exit tunnel that can be occupied by AZ. The PfRpl22 sequence remained unchanged. Molecular modeling of mutant PfRpl4 with AZ suggests an altered orientation of the L75 side chain that could preclude AZ binding. These data imply that AZ acts on the apicoplast bacterial-like translation machinery and identify Pfrpl4 as a potential marker of resistance.

Atovaquone/proguanil for the prophylaxis and treatment of malaria

Increases in international travel and escalating drug resistance have resulted in a growing number of travelers at risk of contracting malaria. Drug resistance and intolerance to standard agents such as chloroquine, sulfadoxine/pyrimethamine and mefloquine has highlighted the need for new antimalarials. The recently licensed fixed combination of atovaquone and proguanil hydrochloride (Malarone) is a promising new agent to prevent and treat Plasmodium falciparum malaria. Randomized controlled trials have shown that atovaquone/proguanil is well tolerated and efficacious for the prevention and treatment of drug-resistant P. falciparum malaria. Atovaquone/proguanil is active against the liver stage of P. falciparum malaria parasites and when used as a prophylactic agent it can be discontinued shortly after leaving malaria-endemic areas, offering a clear advantage for drug adherence.

Problem pathogens: prevention of malaria in travellers

Human infection with Plasmodium spp leading to clinical episodes of malaria probably began very early in the history of humankind and has persistently inflicted disease among human populations. Malaria is currently considered the world's most important parasitic infection. The global impact of malaria is incalculable and appears to be worsening over the past decades. Although most of this burden of disease is carried by developing tropical countries, cases of imported malaria acquired by international travel are increasingly reported. These numbers are growing because of increased travel to malaria-endemic areas and also due to increased risk of transmission in these areas. Indeed, travel has contributed to the global spread of malaria during the history of humankind. Travellers visiting malaria risk areas should use both personal protective measures and chemoprophylaxis. Non-adherence to chemoprophylactic regimens is frequently secondary to drug side-effects. Therefore, a careful risk-benefit analysis on the use of antimalarial prophylaxis should be carried out in every individual travelling to malaria risk areas. Standby malaria self-treatment represents an alternative in some travellers. However, carefully selected and geographically specific antimalarial drug regimens should be recommended to non-immune people travelling to high-risk areas.

Malaria Primer for Clinicians in the United States

Though low, the incidence of malaria in the United States is not insignificant and can be the source of infection in febrile travelers returning from endemic areas. Clinicians practicing in the United States must have a basic understanding of the malaria life cycle and its treatments to properly diagnose and treat this potentially fatal disease. Malaria chemotherapy can be broken into clinical classes for easier understanding, and any traveler to a malaria-endemic region should be placed on prophylactic medications. Mosquito bite prevention should be undertaken by all travelers, and methods of deterring mosquito bites should be understood.

Evaluation of anti-malarial effects of mass chemoprophylaxis in the Republic of Korea army

Vivax malaria was endemic on the Korean peninsula for many centuries until the late 1970's when the Republic of Korea (ROK) was declared "malaria free". Since its re-emergence in 1993, the number of malaria cases in the military increased exponentially through 2000 near the demilitarized zone. Chemoprophylaxis with chloroquine and primaquine has been used in the ROK Army since 1997 in an attempt to reduce the number of the malaria cases throughout the ROK. Data show that chemoprophylaxis contributed, in part, to the decrease in the number of malaria cases among military personnel. However, mass chemoprophylaxis on a large scale in the ROK Army is unprecedented and extensive supervision and monitoring is warranted to determine its effectiveness and to monitor the appearance of chloroquine tolerant/resistant strains of Plasmodium vivax.

Prevention of travel-related infectious diseases in families of internationally adopted children

Pretravel consultation before international adoption must encompass standard advice for those who travel, advice for those who are exposed to the newly adopted child, and information about caring for a new child during travel. Children who travel to meet siblings may need special accommodations before and during travel. Data on the health of internationally adopted children illustrate the risk of exposing family members and close contacts to some infectious diseases during or after international adoption. Parents, family members, and close contacts of the newly adopted child should be given advice to reduce their own and their child's risk. Targeted preadoption counseling, close attention to hygiene and safety advice, and prompt identification and treatment of infections lead to the safest and most trouble-free adoption travel experience.

Efficacy of antimalarial chemoprophylaxis among French residents travelling to Africa

Controversy exists about which antimalarial chemoprophylaxis regimen should be used among travellers to Africa: the WHO and other experts recommend the use of mefloquine throughout sub-Saharan Africa, whereas French experts still support the combination of chloroquine and proguanil in most of West Africa (the so-called zone 2 countries). In this case-control study based at a travel clinic, we examined the compliance with antimalarial chemoprophylaxis and its efficacy among travellers to tropical areas. Cases were patients with Plasmodium falciparum malaria (n = 131). Controls were patients who had a negative malaria film (n = 158). Of all controls, only 36 (22.8%) were adequately protected (i.e. compliant with an adapted regimen of chemoprophylaxis). In zone 2 countries, the efficacy of the combined chloroquine and proguanil was 58% (95% CI 22-78%) for all users, but increased to 100% (95% CI 89-100%) for compliant users. In zone 3 countries, the efficacy of mefloquine was 90% (95% CI 51-98%) and 100% (95% CI 58-100%) for all users and compliant users, respectively.

New strategies for the prevention of malaria in travelers

Malaria prevention has benefited from many diverse disciplines of research, including epidemiologic monitoring, development of laboratory techniques, assessment of insect repellents, or pharmaceutical innovations. Strategies in all these sectors have been explored in recent years, resulting in improved options to prevent travelers' malaria. The addition of atovaquone-proguanil for malaria chemoprophylaxis and the recommendation of primaquine as primary prophylaxis have been significant advances. Tafenoquine seems promising. Standby treatment recommendations have been refined. Many areas still need better strategies. Problematic areas include chemoprophylaxis for long-term travelers, expatriates, and pregnant women; optimal criteria for terminal prophylaxis; and the prevention of malaria in populations that are least likely to seek pretravel evaluations, such as those visiting friends and relatives in their home countries (VFRs). Finally, research in travel and tropical medicine should continue to focus on additional strategies to confront the ever-widening challenge of drug-resistant malaria.

Prevention of infectious diseases among international pediatric travelers: considerations for clinicians

An estimated 1.9 million children travel overseas annually. Infectious disease risks associated with international travel are diverse and depend on the destination, planned activities, and baseline medical history. Children have special needs and vulnerabilities that should be addressed when preparing for travel abroad. Children should have a pretravel health assessment that includes recommendations for both routine and special travel-related vaccination; malaria chemoprophylaxis, if indicated; and prevention counseling regarding insect and animal exposures, food and water safety, and avoiding injuries. Special consideration should be given to children with chronic diseases. Families should be given anticipatory guidance for management of potential illnesses and information about the location of medical resources overseas.

Atovaquone-proguanil versus chloroquine-proguanil for malaria prophylaxis in nonimmune pediatric travelers: results of an international, randomized, open-label study

Atovaquone-proguanil has been shown to be effective and well tolerated for malaria prophylaxis in residents of countries of endemicity and in nonimmune adult travelers, but data about traveling children are limited. In a randomized, open-label, multicenter prophylaxis trial, 221 nonimmune pediatric travelers (age, 2-17 years) received either atovaquone-proguanil or chloroquine-proguanil. Safety and clinical outcome were evaluated 7, 28, and 60 days after travel. By posttravel day 7, a total of 39 (35%) of 110 atovaquone-proguanil and 41 (37%) of 111 chloroquine-proguanil recipients reported > or =1 adverse event. The data indicate that, over the course of treatment, fewer atovaquone-proguanil recipients had treatment-related adverse events (8% vs. 14%), including gastrointestinal complaints (5% vs. 10%). Two subjects discontinued prophylaxis because of drug-related adverse events; both had received chloroquine-proguanil. Observed compliance with prophylaxis was similar before and during travel, but it was higher for atovaquone-proguanil in the posttravel period. No study participant developed malaria. Atovaquone-proguanil was well tolerated and is an important addition to the limited arsenal of prophylactic agents available to children.

Epidemiology and clinical features of vivax malaria imported to Europe: sentinel surveillance data from TropNetEurop

BACKGROUND

Plasmodium vivax is the second most common species among malaria patients diagnosed in Europe, but epidemiological and clinical data on imported P. vivax malaria are limited. The TropNetEurop surveillance network has monitored the importation of vivax malaria into Europe since 1999.

OBJECTIVES

To present epidemiological and clinical data on imported P. vivax malaria collected at European level.

MATERIAL AND METHODS

Data of primary cases of P. vivax malaria reported between January 1999 and September 2003 were analysed, focusing on disease frequency, patient characteristics, place of infection, course of disease, treatment and differences between network-member countries.

RESULTS

Within the surveillance period 4,801 cases of imported malaria were reported. 618 (12.9%) were attributed to P. vivax. European travellers and immigrants were the largest patient groups, but their proportion varied among the reporting countries. The main regions of infection in descending order were the Indian subcontinent, Indonesia, South America and Western and Eastern Africa, as a group accounting for more than 60% of the cases. Regular use of malaria chemoprophylaxis was reported by 118 patients. With 86 (inter-quartile range 41-158) versus 31 days (inter-quartile range 4-133) the median symptom onset was significantly delayed in patients with chemoprophylaxis (p < 0.0001). Common complaints were fever, headache, fatigue, and musculo-skeletal symptoms. All patients survived and severe clinical complications were rare. Hospitalization was provided for 60% and primaquine treatment administered to 83.8% of the patients, but frequencies varied strongly among reporting countries.

CONCLUSIONS

TropNetEurop data can contribute to the harmonization of European treatment policies.

Current status and replies to frequently posed questions on atovaquone plus proguanil (Malarone) for the prevention of malaria

Each year at least 30 000 Western travellers acquire malaria and approximately 1-4% of those who acquire Plasmodium falciparum malaria will die as a result of infection. Almost all cases and fatalities are preventable with the use of measures to reduce mosquito bites and appropriate chemoprophylaxis for those at high risk of infection. There are currently a limited number of licensed drugs available to prevent malaria in travellers. New effective and well tolerated agents are urgently needed because of increasing resistance to antimalarials such as chloroquine and proguanil, and real and perceived intolerance to standard drugs such as mefloquine. A newly licensed antimalarial (atovaquone plus proguanil; Malarone) compares favourably with other drug options, although some prescribers may be unfamiliar with the specific advantages and disadvantages of this antimalarial. This article reviews recent clinical experience and randomised controlled trial data in order to address frequently asked questions about this new combination drug.

Antimosquito precautions and medical chemoprophylaxis in French children with malaria

BACKGROUND

France is the European country with the highest number of imported malaria cases (7,500 in 2000). The aim of this prospective study was to evaluate the nature and efficacy of prophylactic measures in children under 15 years of age referred for malaria.

METHODS

Post travel questionnaires were given to the parents of malarial children in the emergency room. The study took place in two university hospitals in Marseilles, southern France, from August to October 2001.

RESULTS

Eighty-eight children under 15 years of age were included in this 3-month period. Most of them had been infected in Comoro archipelago. Almost two-thirds used bed nets, but only 47% did so every night. Sprayed bed nets were used by 23%. Average compliances with cutaneous repellents, bedroom repellents and long-sleeved clothing were 32%, 24% and 26%, respectively. Air conditioners were uncommon. Only 22% of the children used chemoprophylaxis correctly, according to French recommendations. Five percent did not use any chemoprophylaxis, and 61% reported non recommended drug use. Although all the children traveled to chloroquine-resistant areas, chemoprophylaxis with mefloquine was less common than that with chloroquine + proguanil. No child fully complied with French recommendations concerning both anti mosquito measures and chemoprophylaxis.

CONCLUSIONS

Insufficient use of antimalaria precautions by traveling families is associated with the high incidence of pediatric imported malaria in southern France. Travelers' education should be increased to allow the optimization of malaria prophylaxis.

Genetic confirmation of atovaquone-proguanil-resistant Plasmodium falciparum malaria acquired by a nonimmune traveler to East Africa

We report a case of atovaquone-proguanil-resistant Plasmodium falciparum malaria acquired by a nonimmune traveler to Kenya. Recurrent parasitemia occurred 30 days after directly observed therapy with a combination of atovaquone and proguanil. Treatment failure was confirmed by genetic fingerprinting and sequencing. The primary isolate had wild-type sequence of cytochrome b; however, the recrudescent isolate had a single mutation at position 268 (Tyr268Ser).

[Malaria prevention in international travel]

For travelers malaria represents the principal infectious risk of severe complications and death. Infection during traveling depends on the geographical area visited, the predominant species of parasite, the frequency of resistance to antimalarial agents, and whether preventive measures have been taken. Until a vaccine has been developed, prevention strategies consist of providing travelers with information, the use of barrier methods against vector bites, the correct use of chemoprophylaxis, and the possibility of self-diagnosis and treatment. The choice of chemoprophylaxis regimen should be individualized since no regimen guarantees 100% protection or is free of adverse effects or contraindications. The most effective drugs are doxycycline, atovaquone-proguanil and mefloquine while those producing severe adverse effects with the least frequency are atovaquone-proguanil and doxycycline.

Atovaquone/proguanil: the need for family protection

An increasing number of families, including children and the elderly, are seeking more adventurous travel in exotic parts of the world. Holiday destinations now include once-remote regions such as subSaharan Africa and New Guinea. This increase in visits to tropical and subtropical regions, combined with widespread chloroquine-resistant malaria, now places millions of Western travelers at risk of infection annually. At least 30,000 travelers from industrialized countries are reported to contract malaria each year and approximately 1 in 100 travelers who acquire Plasmodium falciparum malaria will die.

Problems in prescribing malaria chemoprophylaxis for travelers

To offer effective malaria chemoprophylaxis for travelers in a country, the physician must know the precise status of malaria there (frequency, resistance), determine the degree of exposure to mosquito bites, evaluate the precise clinical condition of the traveler, and improve the traveler's compliance with treatment by providing good information on potential side-effects. These side-effects, sometimes overemphasized in the media, lead to poor compliance, particularly after returning home, and, consequently, increase the risk of acquiring malaria. The recently approved Malarone could overcome these drawbacks. But its cost is high and its wide use could also lead to the emergence of resistant strains. Therefore, training professionals in travel medicine is important in malaria prevention and decrease the prescription of abusive or inaccurate prophylaxis (e.g., most tourists traveling in organized tours in Asia, with no stay in remote malaria endemic areas, do not need any prophylaxis). In addition, prevention of mosquito bites with repellents, impregnated bed nets, and indoor insecticide-dispensing devices is still an important tool for controlling malaria in travelers.

The clinical spectrum of severe imported falciparum malaria in the intensive care unit: report of 188 cases in adults

Little is known about severe imported malaria in nonendemic industrialized countries. The purpose of this retrospective study was to describe the clinical spectrum of severe imported malaria in adults and to determine factors that were present at admission and were associated with in-intensive care unit mortality. This retrospective study evaluated the 188 patients who were admitted to our intensive care unit in 1988-1999 with severe and/or complicated imported malaria. Among them, 93 had strictly defined severe malaria, and 95 had less severe malaria. The mean age was 38 years, 51% of patients were nonimmune whites, 94% acquired Plasmodium falciparum in sub-Saharan Africa, and 96% had taken inadequate antimalarial chemoprophylaxis. Mortality was 11% (10 patients) in the severe malaria group, whereas no patients died in the less severe malaria group (p = 0.002). In the bivariable analysis, the main factors associated with death in the severe malaria group were the Simplified Acute Physiology Score, shock, acidosis, coma, pulmonary edema (p < 0.001 for each), and coagulation disorders (p = 0.002). Bacterial coinfection is not infrequent and may contribute to death. Severe imported malaria remains a major threat to travelers. In our population, the most relevant World Health Organization major defining criteria were coma, shock, pulmonary edema, and acidosis.

The prevention of malaria

Long before the advent of modern chemoprophylaxis drugs, many practitioners successfully prevented the debilitating and fatal outcomes associated with infection by the Plasmodium parasites that cause malaria. Today, with effective insect repellents and several excellent medications available for chemoprophylaxis, there has never been a better array of quality products to prevent mosquito bites and infection and to suppress parasites once in the blood stream; however, there are thousands of imported cases into nonendemic countries and scores of deaths and near-fatal outcomes every year in returning travelers, soldiers, immigrants, and refugees. In this article, the author focuses on practical uses of currently available prevention tools.

Evaluation of the Makromed dipstick assay versus PCR for diagnosis of Plasmodium falciparum malaria in returned travelers

Microscopy has been the traditional reference standard for malaria diagnosis. However, difficulty in maintaining the required technical skills, particularly in areas where malaria is not endemic, has prompted the development of rapid nonmicroscopic diagnostic assays based on the detection of malaria parasite antigen in whole blood. In this study, we evaluated the performance of one such device, the Makromed dipstick test, blindly compared to PCR and microscopy for the diagnosis of Plasmodium falciparum malaria in 200 febrile returned travelers. The Makromed assay detects the presence of P. falciparum-specific histidine-rich protein II with an antigen capture immunochromatographic strip format. Compared to PCR as the reference standard, the dipstick assay had a sensitivity of 97.0% and a specificity of 96.0%. The positive and negative predictive values were 81.2% and 99.5%, respectively. Rapid malaria diagnostic devices may provide a useful diagnostic adjunct in a clinical setting.

Inhibition of endosomal/lysosomal degradation increases the infectivity of human immunodeficiency virus

Productive entry of human immunodeficiency virus type 1 (HIV-1) into a host cell is believed to proceed via fusion of the viral envelope with the host cell's plasma membrane. Interestingly, the majority of HIV-1 particles that bind to the cell surface are taken up by the host cell via endocytosis; however, this mode of internalization generally does not result in infection. Presumably, virus particles remain trapped in the endocytic pathway and are eventually degraded. Here, we demonstrate that treatment of cells with various pharmacological agents known to elevate the pH of endosomes and lysosomes allows HIV-1 to efficiently enter and infect the host cell. Pretreatment of cells with bafilomycin A1 results in up to a 50-fold increase in the infectivity of HIV-1(SF2). Similarly, pretreatment of target cells with amantadine, concanamycin A, concanamycin B, chloroquine, and ammonium chloride resulted in increases in HIV-1 infectivity ranging between 2- and 15-fold. Analysis of receptor and coreceptor expression, HIV-long terminal repeat (LTR) transactivation, and transduction with amphotropic-pseudotyped murine leukemia virus (MLV)-based vectors suggests that the increase in infectivity is not artifactual. The increased infectivity under these conditions appears to be due to the ability of HIV-1 and MLV particles to enter via the endocytic pathway when spared from degradation in the late endosomes and lysosomes. These results could have significant implications for the administration of current and future lysosmotropic agents to patients with HIV disease.

Pyrimethamine and WR99210 exert opposing selection on dihydrofolate reductase from Plasmodium vivax

Plasmodium vivax is a major public health problem in Asia and South and Central America where it is most prevalent. Until very recently, the parasite has been effectively treated with chloroquine, but resistance to this drug has now been reported in several areas. Affordable alternative treatments for vivax malaria are urgently needed. Pyrimethamine-sulfadoxine is an inhibitor of dihydrofolate reductase (DHFR) that has been widely used to treat chloroquine-resistant Plasmodium falciparum malaria. DHFR inhibitors have not been considered for treatment of vivax malaria, because initial trials showed poor efficacy against P. vivax. P. vivax cannot be grown in culture; the reason for its resistance to DHFR inhibitors is unknown. We show that, like P. falciparum, point mutations in the dhfr gene can cause resistance to pyrimethamine in P. vivax. WR99210 is a novel inhibitor of DHFR, effective even against the most pyrimethamine-resistant P. falciparum strains. We have found that it is also an extremely effective inhibitor of the P. vivax DHFR, and mutations that confer high-level resistance to pyrimethamine render the P. vivax enzyme exquisitely sensitive to WR99210. These data suggest that pyrimethamine and WR99210 would exert opposing selective forces on the P. vivax population. If used in combination, these two drugs could greatly slow the selection of parasites resistant to both drugs. If that is the case, this novel class of DHFR inhibitors could provide effective and affordable treatment for chloroquine- and pyrimethamine-resistant vivax and falciparum malaria for many years to come.

Prevention of malaria in children

Although malaria kills approximately 1 million children each year, preventive measures can be effective in limiting the mortality and morbidity associated with malaria. Mosquito bites can be avoided by use of appropriate environmental control and use of protective clothing, bed nets, repellents, and insecticide. Chemoprophylaxis is a mainstay of malaria prevention, and new, effective agents are increasingly available. Rapid, accurate diagnosis and effective medical treatment can help people who become ill with malaria despite their preventive efforts. With careful attention to preventive efforts, malaria should be extremely rare in travelers; similarly, broader implementation of preventive measures could decrease the burden of malaria on residents in areas where it is endemic.

Malaria chemoprophylaxis in the age of drug resistance. II. Drugs that may be available in the future

All current regimens of malaria chemoprophylaxis have serious drawbacks as a result of either suboptimal efficacy, difficulty with medication compliance, or adverse events. Two 8-aminoquinolines may be approaching registration, with primaquine having completed its prophylactic field testing and tafenoquine having begun advanced field testing at the end of 2000. Primaquine has long been used for management of relapses of malaria, but in the past decade, it has been reexamined for use in malaria prevention in order to stop infection in the liver. In field trials performed in Indonesia and Colombia, the efficacy of primaquine for malaria prevention was approximately 90%, compared with that of placebo. Because of its short half-life, primaquine requires daily administration. For adults, the prevention regimen is 30 mg base daily (0.5 mg base/kg/day), and it can probably be discontinued soon after departure from an area where malaria is endemic. To kill parasites that already exist in the liver, terminal prophylaxis is given after exposure to relapses of malaria infection; for adults, such prophylaxis usually consists of 15 mg base (0.3 mg base/kg/day) given daily for 2 weeks. Primaquine-induced gastrointestinal disturbances can be minimized if the drug is taken with food. Neither primaquine nor tafenoquine should be given to persons with glucose-6-phosphate dehydrogenase deficiency, to avoid the development of potentially severe drug-induced hemolysis. Tafenoquine is an analogue of primaquine that is more potent than the parent drug. Field trials in Kenya, Ghana, Gabon, and Southeast Asia have demonstrated an efficacy rate of approximately 90% for tafenoquine. Its long half-life allows for infrequent dosing (currently tested at 200 mg base/week), and its effect on parasites at the liver stage may allow for drug discontinuation at the time of departure from the area of endemicity.