Malaria imported to the United States from Vietnam. Chemoprophylaxis evaluated in returning soldiers

8-Aminoquinoline Therapy for Latent Malaria

The technical genesis and practice of 8-aminoquinoline therapy of latent malaria offer singular scientific, clinical, and public health insights. The 8-aminoquinolines brought revolutionary scientific discoveries, dogmatic practices, benign neglect, and, finally, enduring promise against endemic malaria. The clinical use of plasmochin-the first rationally synthesized blood schizontocide and the first gametocytocide, tissue schizontocide, and hypnozoitocide of any kind-commenced in 1926. Plasmochin became known to sometimes provoke fatal hemolytic crises. World War II delivered a newer 8-aminoquinoline, primaquine, and the discovery of glucose-6-phosphate dehydrogenase (G6PD) deficiency as the basis of its hemolytic toxicity came in 1956. Primaquine nonetheless became the sole therapeutic option against latent malaria. After 40 years of fitful development, in 2018 the U.S. Food and Drug Administration registered the 8-aminoquinoline called tafenoquine for the prevention of all malarias and the treatment of those that relapse. Tafenoquine also cannot be used in G6PD-unknown or -deficient patients. The hemolytic toxicity of the 8-aminoquinolines impedes their great potential, but this problem has not been a research priority. This review explores the complex technical dimensions of the history of 8-aminoquinolines. The therapeutic principles thus examined may be leveraged in improved practice and in understanding the bright prospect of discovery of newer drugs that cannot harm G6PD-deficient patients.

Primaquine: the risks and the benefits

Primaquine is the only generally available anti-malarial that prevents relapse in vivax and ovale malaria, and the only potent gametocytocide in falciparum malaria. Primaquine becomes increasingly important as malaria-endemic countries move towards elimination, and although it is widely recommended, it is commonly not given to malaria patients because of haemolytic toxicity in subjects who are glucose-6-phosphate dehydrogenase (G6PD) deficient (gene frequency typically 3-30% in malaria endemic areas; >180 different genetic variants). In six decades of primaquine use in approximately 200 million people, 14 deaths have been reported. Confining the estimate to reports with known denominators gives an estimated mortality of one in 621,428 (upper 95% CI: one in 407,807). All but one death followed multiple dosing to prevent vivax malaria relapse. Review of dose-response relationships and clinical trials of primaquine in G6PD deficiency suggests that the currently recommended WHO single low dose (0.25 mg base/kg) to block falciparum malaria transmission confers a very low risk of haemolytic toxicity.

Reinventing primaquine for endemic malaria

After sixty years of continuous use, primaquine remains the only therapy licensed for arresting transmission and relapse of malaria. The US Army developed primaquine for soldiers in a wartime crisis setting. Dosing strategies suited to that narrow population were adopted without modification or validation for the broader population of humans exposed to risk of malaria. The poor suitability of these strategies in populations exhibiting greater vulnerability to hemolytic toxicity among glucose-6-phosphate dehydrogenase deficient patients has not been addressed. Primaquine requires chemotherapeutic reinvention delivering less threatening doses by leveraging unexplored co-drug synergies.

Primaquine toxicity forestalls effective therapeutic management of the endemic malarias

Treatment of acutely ill patients, informed by a diagnosis of the species of Plasmodium involved, has long dominated strategic thinking in malaria chemotherapeutics. This bias for both acute illness and access to diagnosis resulted in therapeutic strategies poorly suited to malaria as it occurs in endemic zones. Most of those malarias do not provoke illness and occur beyond diagnostic reach for technical or practical reasons. Therapies effective against all species and stages would likely prove more practical in endemic zones, especially if safely administered without laboratory screening for contraindications. The primary impediment to such therapies is the mild to severe hemolytic toxicity of primaquine in patients with glucose-6-phosphate dehydrogenase deficiency. Primaquine is the only treatment licensed for therapy against relapse caused by dormant liver stages occurring in some species, and against the sexual blood stages responsible for transmission to mosquitoes in all species. Despite being licensed over 50 years ago, no alternative drugs have been developed, and safer dosing regimens of primaquine have not been explored. These failures forestalled the emergence of therapies practical for use in endemic zones, especially in the context of eliminating transmission.

Compliance with antimalaria chemoprophylaxis in a combat zone

Compliance with malaria chemoprophylaxis by military service members (MSMs) is notoriously low, ranging from 30% to 56%. Our objective was to determine the rate of compliance and reasons for non-compliance with malaria chemoprophylaxis among healthy US MSMs in Afghanistan. An eight-question, anonymous online survey was used to collect data regarding the compliance of healthy MSMs with malaria chemoprophylaxis. E-mail surveys were sent to 1,200 MSMs; 528 (44%) MSMs completed the survey. One-time daily doxycycline was the most commonly prescribed chemoprophylaxis (90%); 60% (N = 318) responded that they were compliant with their chemoprophylaxis as prescribed, whereas 40% (N = 221) indicated that they were not compliant. Compliance with daily dosing was 61% and weekly dosing was 38%. The most common reasons for non-compliance were gastrointestinal effects (39%), forgetfulness (31%), and low perception of risk (24%). Malaria chemoprophylaxis compliance by healthy MSMs in Afghanistan is poor. Side effects, forgetfulness, and lack of education are contributing factors. Commanders bear the primary responsibility for the health of their soldiers, and the individual MSM bears personal responsibility; however, additional public health interventions could possibly have a positive impact on prevention.

Tentative checklist of the mosquitoes of Vietnam employing new classification for tribe Aedini (Diptera, Culicidae)

The new classification of tribe Aedini is used in a tentative checklist of the mosquitoes found in Vietnam, which contains 34 genera, 28 subgenera, and 191 species and subspecies. Mosquito-borne diseases in Vietnam are mentioned. Mosquito records from U.S. military sources during the Vietnam War are also considered.

Risk assessments for exposure of deployed military personnel to insecticides and personal protective measures used for disease-vector management

Infectious diseases are problematic for deployed military forces throughout the world, and, historically, more military service days have been lost to insect-vectored diseases than to combat. Because of the limitations in efficacy and availability of both vaccines and therapeutic drugs, vector management often is the best tool that military personnel have against most vector-borne pathogens. However, the use of insecticides may raise concerns about the safety of their effects on the health of the military personnel exposed to them. Therefore, our objective was to use risk assessment methodologies to evaluate health risks to deployed U.S. military personnel from vector management tactics. Our conservative tier-1, quantitative risk assessment focused on acute, subchronic, and chronic exposures and cancer risks to military personnel after insecticide application and use of personal protective measures in different scenarios. Exposures were estimated for every scenario, chemical, and pathway. Acute, subchronic, and chronic risks were assessed using a margin of exposure (MOE) approach. Our MOE was the ratio of a no-observed-adverse-effect level (NOAEL) to an estimated exposure. MOEs were greater than the levels of concern (LOCs) for all surface residual and indoor space spraying exposures, except acute dermal exposure to lambda-cyhalothrin. MOEs were greater than the LOCs for all chemicals in the truck-mounted ultra-low-volume (ULV) exposure scenario. The aggregate cancer risk for permethrin exceeded 1 x 10(-6), but more realistic exposure refinements would reduce the cancer risk below that value. Overall, results indicate that health risks from exposures to insecticides and personal protective measures used by military personnel are low.

Endemic infectious diseases of Afghanistan

The current crisis in Afghanistan has resulted in an influx of Western military personnel, peacekeepers, humanitarian workers, and journalists. At the same time, unprecedented numbers of internally displaced persons and refugees have overwhelmed much of the already fragile infrastructure, setting the stage for outbreaks of infectious diseases among both foreigners and local populations. This review surveys the literature concerning the infectious diseases of Afghanistan and south-central Asia, with particular emphasis on diseases not typically seen in the Western world.

Enhancement of the curative activity of primaquine by concomitant administration of mirincamycin

Mirincamycin, a lincomycin derivative with unequivocal but limited activity against the pre-erythrocytic and persisting exoerythrocytic stages of Plasmodium cynomolgi, has been evaluated for capacity to enhance the radical curative potential of the conventional primaquine-chloroquine combination. Established infections with sporozoites of the above plasmodium in rhesus monkeys served this evaluation. The results showed that the dose of primaquine required for cure of 50% of active infections was reduced by one-half to two-thirds by coadministration with 2.5 mg of mirincamycin per kg, 1/16 the 50% curative dose of this lincomycin derivative when used in a mono-drug regimen. The dimensions of the enhancement of the curative activity of primaquine were inversely related to the size of the sporozoite inoculum. The smallest dose of mirincamycin productive of enhancement was 2.5 mg/kg; whether doses larger than 2.5 mg/kg would have been more effective was not determined. There is much to be done before it is known whether a mirincamycin-primaquine combination is useful for suppressive cure or radical cure of the human malarias. Irrespective of that result, the current study serves to focus attention on a somewhat novel approach to the development of more effective and better-tolerated regimens for radical cure, an alternative to the empirical chemical synthesis and screening approach that has dominated searches heretofore.

Relationships between chemical structures of 8-aminoquinolines and their capacities for radical cure of infections with Plasmodium cynomolgi in rhesus monkeys

Evaluation of 200 8-aminoquinolines for the capacities to effect radical cure of infections with sporozoites of Plasmodium cynomolgi in rhesus monkeys led to identification of 34 derivatives with activity equal or superior to that of primaquine and to characterization of substituents on the quinoline nucleus and side chain that favored or prejudiced curative activity. Of the 34 derivatives, 19 were as active as primaquine, 9 were twice as active, and 6 were four times as active. With respect to nuclear substituents, all were methoxy substituted at position 6; 24 had one and 10 had two additional substituents. The additions with most favorable impact on activity included methyl substituents at positions 4 and 2 and alkoxy, fluoro, and a group of 3- or 4-substituted phenoxy substituents at position 5. With respect to 8-amino substituents, 14 of the 15 derivatives more active than primaquine, and 13 of the 19 as active as primaquine, carried a branched alkyl chain, four to five carbons in length, between the 8- and terminal amino groups. Proximity of branching to the 8-amino group could be an important determinant of curative activity; however, the effect of such branching was not predictable. All 15 derivatives more active than primaquine and a substantial fraction of those comparable to primaquine in activity have sufficient structural novelty to merit evaluation for tolerability and radical curative activity in humans, with reasonable prospects that one or more would be better tolerated than primaquine and superior to this drug for cure of Plasmodium vivax infections.