Diagnosis, treatment, and prevention of malaria

Pharmacodynamics of antimalarial chemotherapy

Malaria chemotherapy is under constant threat from the emergence and spread of multidrug resistance of Plasmodium falciparum. Resistance has been observed to almost all currently used antimalarials. Some drugs are also limited by toxicity. A fundamental component of the strategy for malaria chemotherapy is based on prompt, effective and safe antimalarial drugs. To counter the threat of resistance of P. falciparum to existing monotherapeutic regimens, current malaria treatment is based principally on the artemisinin group of compounds, either as monotherapy or artemisinin-based combination therapies for treatment of both uncomplicated and severe falciparum malaria. Key advantages of artemisinins over the conventional antimalarials include their rapid and potent action, with good tolerability profiles. Their action also covers transmissible gametocytes, resulting in decreased disease transmission. Up to now there has been no prominent report of drug resistance to this group of compounds. Treatment of malaria in pregnant women requires special attention in light of limited treatment options caused by potential teratogenicity coupled with a paucity of safety data for the mother and fetus. Treatment of other malaria species is less problematic and chloroquine is still the drug of choice, although resistance of P. vivax to chloroquine has been reported. Multiple approaches to the identification of new antimalarial targets and promising antimalarial drugs are being pursued in order to cope with drug resistance.

Randomized, double-blind study of the safety, tolerability, and efficacy of tafenoquine versus mefloquine for malaria prophylaxis in nonimmune subjects

This study represents the first phase III trial of the safety, tolerability, and effectiveness of tafenoquine for malaria prophylaxis. In a randomized (3:1), double-blinded study, Australian soldiers received weekly malaria prophylaxis with 200 mg tafenoquine (492 subjects) or 250 mg mefloquine (162 subjects) for 6 months on a peacekeeping deployment to East Timor. After returning to Australia, tafenoquine-receiving subjects received a placebo and mefloquine-receiving subjects received 30 mg primaquine daily for 14 days. There were no clinically significant differences between hematological and biochemical parameters of the treatment groups. Treatment-related adverse events for the two groups were similar (tafenoquine, 13.4%; mefloquine, 11.7%). Three subjects on tafenoquine (0.6%) and none on mefloquine discontinued prophylaxis because of possible drug-related adverse events. No diagnoses of malaria occurred for either group during deployment, but 4 cases (0.9%) and 1 case (0.7%) of Plasmodium vivax infection occurred among the tafenoquine and mefloquine groups, respectively, up to 20 weeks after discontinuation of medication. In a subset of subjects recruited for detailed safety assessments, treatment-related mild vortex keratopathy was detected in 93% (69 of 74) of tafenoquine subjects but none of the 21 mefloquine subjects. The vortex keratopathy was not associated with any effect on visual acuity and was fully resolved in all subjects by 1 year. Tafenoquine appears to be safe and well tolerated as malaria prophylaxis. Although the volunteers' precise exposure to malaria could not be proven in this study, tafenoquine appears to be a highly efficacious drug for malaria prophylaxis.

Drugs for treating uncomplicated malaria in pregnant women

BACKGROUND

Women are more vulnerable to malaria during pregnancy, and malaria infection may have adverse consequences for the fetus. Identifying safe and effective treatments is important.

OBJECTIVES

To compare the effects of drug regimens for treating uncomplicated falciparum malaria in pregnant women.

SEARCH STRATEGY

We searched the Cochrane Infectious Diseases Group Specialized Register (February 2008), CENTRAL (The Cochrane Library 2008, Issue 1), MEDLINE (1966 to February 2008), EMBASE (1974 to February 2008), LILACS (February 2008), mRCT (February 2008), reference lists, and conference abstracts. We also contacted researchers in the field, organizations, and pharmaceutical companies.

SELECTION CRITERIA

Randomized and quasi-randomized controlled trials of antimalarial drugs for treating uncomplicated malaria in pregnant women.

DATA COLLECTION AND ANALYSIS

Two authors assessed trial eligibility and risk of bias, and extracted data. We performed a quantitative analysis only where we could combine the data. We combined dichotomous data using the risk ratio (RR) and presented each result with a 95% confidence interval (CI).

MAIN RESULTS

Ten trials (1805 participants) met the inclusion criteria. Two were quasi-randomized, seven did not describe allocation concealment, and all adjusted treatment failure to exclude new infections. One trial reported fewer treatment failures at day 63 with artesunate plus mefloquine compared with quinine (RR 0.09, 95% CI 0.02 to 0.38; 106 participants). One trial reported fewer treatment failures at day 63 with artesunate plus atovaquone-proguanil compared with quinine (RR 0.14, 95% CI 0.03 to 0.57; 80 participants). One trial reported fewer treatment failures at day 28 when amodiaquine was compared with chloroquine (RR 0.20, 95% CI 0.08 to 0.46; 420 participants) and when amodiaquine plus sulfadoxine-pyrimethamine was compared with chloroquine (RR 0.02, 95% CI 0.00 to 0.26; 418 participants). Compared with sulfadoxine-pyrimethamine given alone, one trial reported fewer treatment failures at delivery (or day 40) with artesunate plus sulfadoxine-pyrimethamine (RR 0.15, 95% CI 0.04 to 0.59; 79 participants) and azithromycin plus sulfadoxine-pyrimethamine (RR 0.27, 95% CI 0.10 to 0.76; 82 participants).

AUTHORS' CONCLUSIONS

Data are scant. Some combination treatments appear to be effective at treating malaria in pregnancy; however, safety data are limited.

An in-depth study of patent medicine sellers' perspectives on malaria in a rural Nigerian community

Background

Malaria remains a major cause of mortality among under five children in Nigeria. Most of the early treatments for fever and malaria occur through self-medication with antimalarial drugs bought from medicine sellers. These have led to increasing calls for interventions to improve treatment obtained in these outlets. However, information about the current practices of these medicine sellers is needed before such interventions. This study aims to determine the medicine sellers' perspectives on malaria and the determinants that underlie their dispensing patterns of antimalarial drugs.

Methods

The study was conducted in Ugwugo-Nike, a rural community in south-east Nigeria. It involved in-depth interviews with 13 patent medicine sellers.

Results

A majority of the medicine sellers were not trained health professionals and malaria is recognized as a major health problem by them. There is poor knowledge and poor dispensing behaviour in relation to childhood malaria episodes. Although referral of severe malaria is common, there are those who will not refer. Verbal advice is rarely given to the care-givers.

Conclusion

More action research and interventions to improve prescription and referral practices and giving verbal advice to care-givers is recommended. Ways to integrate the drug sellers in the health system are also recommended.

Drugs for treating uncomplicated malaria in pregnant women

BACKGROUND

Women are more vulnerable to malaria during pregnancy, and malaria infection may have adverse consequences for the fetus. Identifying safe and effective treatments is important.

OBJECTIVES

To compare the effects of drug regimens for treating uncomplicated falciparum malaria in pregnant women.

SEARCH STRATEGY

We searched the Cochrane Infectious Diseases Group Specialized Register (May 2005), Cochrane Central Register of Controlled Trials (The Cochrane Library Issue 2, 2005), MEDLINE (1966 to May 2005), EMBASE (1974 to May 2005), LILACS (May 2005), reference lists, and conference abstracts. We also contacted researchers in the field, organizations, and pharmaceutical companies.

SELECTION CRITERIA

Randomized and quasi-randomized controlled trials of antimalarial drugs for treating uncomplicated malaria in pregnant women.

DATA COLLECTION AND ANALYSIS

Both authors assessed trial eligibility and methodological quality, and extracted data. We performed a quantitative analysis only where we could combine the data. We combined dichotomous data using relative risk (RR) with 95% confidence intervals (CI).

MAIN RESULTS

Six trials (513 participants) met the inclusion criteria. Two were quasi-randomized, and none described allocation concealment. Data were scarce for the primary outcome, treatment failure. One trial compared artesunate plus mefloquine with quinine and reported fewer treatment failures at day 63 with the combination (RR 0.09, 95% CI 0.02 to 0.38; 106 participants).

AUTHORS' CONCLUSIONS

There is insufficient reliable research on malaria treatment options in pregnancy.

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.

Use of malaria prevention measures by North American and European travelers to East Africa

BACKGROUND

The use of preventive measures, including effective chemoprophylaxis, is essential for protection against malaria among travelers. However, data have shown that travelers and medical advisors are confused by the lack of uniform recommendations and numerous prophylactic regimens of varying effectiveness that are used.

METHODS

To assess the use and type of preventive measures against malaria, we conducted a cross-sectional study in 1997 among travelers departing from the Nairobi and Mombasa airports in Kenya with European destinations.

RESULTS

Seventy-five percent of the travelers studied were residents of Europe and 25% were residents of North America; all stayed less than 1 year, and visited malarious areas. Most travelers, 97.1%, were aware of the risk and 91.3% sought pretravel medical advice. Although 95.4% used chemoprophylaxis and/or antimosquito measures, only 61.7% used both regular chemoprophylaxis and two or more antimosquito measures. Compliance with chemoprophylaxis was lowest amongst those who used a drug with a daily, as opposed to, a weekly dosing schedule, stayed more than 1 month, attributed an adverse health event to the chemoprophylaxis, and were less than 40 years of age. Among US travelers, 94.6% of those taking chemoprophylaxis were taking an effective regimen, that is, mefloquine or doxycycline. Only 1.9% used a suboptimal drug regimen, such as chloroquine/proguanil. Among European travelers, 69% used mefloquine or doxycycline, and 25% used chloroquine/proguanil. Notably, 45.3% of travelers from the UK used chloroquine/proguanil. Adverse events were noted by 19.7% of mefloquine users and 16.4% of travelers taking chloroquine/proguanil. Neuropsychologic adverse events were reported by 7.8% of users of mefloquine and 1.9% of those taking chloroquine/proguanil. The adverse events, however, had a lesser impact on compliance than frequent dosing schedule.

CONCLUSIONS

Health information should be targeted to travelers who are likely to use suboptimal chemoprophylaxis or may be noncompliant with prophylaxis. Uniform recommendations for effective chemoprophylaxis with simple dosing schedules are necessary to reduce rates of malaria among travelers to Africa.

Therapy and drug resistance in malaria

The aim of this study was to highlight the high degree of clinical resistance of P. falciparum and also of P. vivax to chloroquine and also the importance of early diagnosis and prompt treatment. Ninety cases of smear positive malaria aged between 6 months to 14 years were studied with regards to clinical manifestations, management and outcome. Criteria for drug resistance were absence of clearance of parasitemia and/or persistance of fever after 72 hours of therapy. Chloroquin resistance was noted in 15 (62.5%) cases of falciparum malaria and 15 (51.7%) cases of vivax malaria. The resistant and complicated cases were treated with quinine. Four (6.6%) cases were resistant to quinine and responded to artemether. There was no mortality. Early reporting of cases, frequent sampling malarial parasite, prompt diagnosis of falciparum malaria, early institution of appropriate therapy and awareness of choloquine and/or quinine resistance helps in salvaging lives.

Malaria epidemiology and economics in a pharmacist-managed international travel clinic

With high rates of travel and low adherence to malaria prophylaxis, targeting educational efforts to high-risk travelers is vital. We assessed risk factors for acquiring malaria, and resource use and outcomes of these patients in a managed care environment. Patients were identified from January 1, 1994, to December 31, 1997, using microbiology and pharmacy databases, chart reviews, and interviews. Sixteen patients acquired malaria during the study; although only 50% contacted the travel clinic. Only 31% (5) of them had documented adherence. Fifty percent were hospitalized at a cost of $3881/patient. Travelers at greatest risk for nonadherence appear to be expatriates and those visiting Africa. Providers should target these groups with more intensive counseling in an effort to improve therapy adherence and reduce the risk for malaria.

Imported tertian malaria resistant to primaquine

In Plasmodium vivax and Plasmodium ovale malaria, some of the liver stage parasites remain dormant. The activation of these dormant forms (called hypnozoite) can give rise to relapse weeks, months or years after the initial infection. To prevent relapses, a course of primaquine may be given as terminal prophylaxis to patients. Different strains of Plasmodium vivax vary in their sensitivity to primaquine and, recently, cases of relapse of Plasmodium vivax after this standard primaquine therapy were reported from various countries. We reported a case of primaquine resistant malaria which initially was thought to be relapsed caused by loss of terminal prophylaxis.

Safety and efficacy of atovaquone and proguanil hydrochloride for the prophylaxis of Plasmodium falciparum malaria in South Africa

The objective of this study was to determine the safety and efficacy of atovaquone and proguanil hydrochloride combination therapy for the prophylaxis of Plasmodium falciparum malaria in at-risk nonimmune subjects in South Africa. This open-label trial was conducted at research sites in South Africa during the main malaria transmission season, February through July. The study volunteers were temporarily living in, or traveling to, a malaria-endemic area. They received I tablet of 250 mg atovaquone and 100 mg proguanil hydrochloride once daily for up to 10 weeks. Subjects were monitored using sequential clinical and laboratory assessments. Thick blood smears were stained and evaluated by a central laboratory. An immunochromatographic test for P. falciparum was also used for on-site patient management. Prophylactic success was summarized using a 95% confidence interval for the proportion of subjects who did not develop parasitemia or who withdrew due to a treatment-related adverse event. A total of 175 subjects (15% women) were enrolled in the trial. The mean duration of drug exposure was 8.9 weeks. The combination of atovaquone and proguanil hydrochloride was well tolerated. The most frequently reported adverse events considered possibly related to study treatment were headache (7%), abdominal pain (2%), increased cough (2%), and skin disorder (2%). No serious adverse events were reported, and no treatment-emergent effects were noted for any laboratory variables. One subject who was noncompliant with therapy developed parasitemia, and 3 subjects withdrew due to a treatment-related adverse event (2 subjects with headache and 1 with nausea and dizziness). The prophylaxis success rate was 97%. In this study, atovaquone and proguanil hydrochloride combination therapy had an excellent safety and efficacy profile for prophylaxis of P. falciparum malaria in nonimmune subjects.

Retrospective study of malaria cases treated in Newcastle General Hospital between 1990 and 1996

BACKGROUND

Malaria, in particular Falciparum malaria, continues to pose a substantial risk to travelers to endemic areas.

METHODS

In this study we examined 93 case notes of patients with malaria treated in our department between 1990 and 1996.

RESULTS

Forty-seven (50.5%) patients had infection with Plasmodium falciparum, 41 (44.1%) had Plasmodium vivax and 5 (5.4%) had Plasmodium ovale. One of these patients had a dual infection with P. falciparum and P. vivax. None of our patients had Plasmodium malariae. Forty-four of the P. falciparum cases (93.6%) were imported from sub-Saharan Africa, 33 of the P. vivax cases (78.5%) were imported from the Indian subcontinent. All the P. ovale cases were imported from sub-Saharan Africa. Fifty-four of our patients (58.1%) did not take any form of chemoprophylaxis. Forty-two out of 93 (45.2%) of the "travelers" were settled immigrants in the UK. Seventy-eight percent of travelers of British caucasian origin took prophylaxis whereas only 13.5% of travelers of ethnic minorities origin took prophylaxis.

CONCLUSIONS

Greater awareness of the risk of malaria by travelers and medical practitioners in UK must be encouraged and in particular appropriate chemoprophylaxis instituted for travelers to chloroquine-resistant areas.

Malaria

The preeminent infectious threat to unwary tropical travelers, malaria is a preventable, mosquito-borne protozoan infection of red blood cells, which causes fever, anemia, respiratory failure, coma, and death. Malaria is a true medical emergency that requires rapid diagnosis and treatment. Unfortunately, in two thirds of tropical travelers who die of malaria, either treatment is delayed or the diagnosis is simply missed. Every tropical traveler with fever or unexplained, flu-like illness must be assumed to have life-threatening malaria and must have thick and thin blood smears immediately examined to confirm the diagnosis.

Information about antimalarial chemoprophylaxis in hospitalised patients--is it adequate?

Malaria remains a huge public health problem worldwide, with over 100 million new cases annually, causing one to two million deaths. This global problem spills over into the UK, with around 2000 cases of reported annually. The proportion of infections due to Plasmodium falciparum (PF) continues to increase and worse still accounts for five to 12 deaths per year. In 1992, Nathwani et al reported the 10 year experience of malaria cases admitted to the Regional Infection Unit, in Aberdeen, Scotland--the "Oil Capital". This study was of interest in that 46% of those British residents who acquired infection had travelled to West or Central Africa on oil related business. The Oil boom of the 1980's appeared to very much centred around Aberdeen and the neighbouring hinterland but did not appear to extend to Dundee which was only 60 miles further down the North-East coast. We, therefore, carried out a retrospective study of patients with malaria admitted to the Regional Infectious Diseases Unit in Dundee over a fifteen year period between 1980 and 1994.

Pregnancy and travel

Travel is not generally contraindicated during pregnancy, but there are some risks. The pregnant traveler needs a careful predeparture evaluation, and her itinerary should not take her far from available medical and obstetric care. The pregnant traveler must avoid diseases (such as malaria and hepatitis E) that can have devastating effects. Travel must be curtailed when there would be potential exposure to certain infectious diseases or extreme environmental conditions.

Falciparum malaria

Falciparum malaria is one of the most common infectious illnesses in the world and can progress rapidly to coma and death in the nonimmune patient. The presentation is nonspecific, so blood smears must be made and read quickly. Proper therapy requires taking into account drug resistance, recognizing the signs of severe malaria, and proper treatment for complications. Long-sleeved clothing, bed nets, insecticides, and chemoprophylaxis can help prevent malaria, but the infection must be suspected in any traveler returning from an endemic area. This article reviews epidemiology, diagnosis, treatment, and prevention of falciparum malaria in the temperate zone.

Chemotherapy of drug-resistant malaria

OBJECTIVE

To review the impact of drug-resistant malaria on current management of plasmodial infections.

DATA SOURCES

A MEDLINE search of the English-language medical literature from 1985 to 1995; bibliographies of selected papers; international malaria advisory experts.

DATA SYNTHESIS

Combinations of artemisinin derivatives and mefloquine or atovaquone plus proguanil appear to be the most active drug regimens against multidrug-resistant falciparum malaria from Southeast Asia. The optimal therapy for chloroquine-resistant Plasmodium vivax is unknown, but recent data indicate that halofantrine or chloroquine plus high doses of primaquine are efficacious.

CONCLUSIONS

The incidence of drug-resistant malaria continues to increase at a rate that exceeds new drug development. Ultimately the control of malaria will require more creative approaches than just the development of additional inhibitory drugs. These might include the identification of biochemical pathways unique to the parasite (such as drug efflux and heme polymerization), making it possible to design new classes of antimalarial agents that are selectively toxic to the parasite; methods to block parasite development in the mosquito vector; and multistage vaccines against asexual and sexual stages to block both the pathophysiology and the transmission of disease.

Randomised placebo-controlled trial of primaquine for prophylaxis of falciparum and vivax malaria

Drug resistance has made malaria prevention difficult and the new agents are too expensive for widespread use. Primaquine, an established drug for treatment, is potentially useful for prevention. Malaria prophylaxis with primaquine was evaluated in Irian Jaya during one year in Javanese men who were not deficient in glucose-6-phosphate dehydrogenase (G-6-PD). 126 volunteers were randomised to receive 0.5 mg/kg primaquine base or placebo daily (double-blinded), or 300 mg chloroquine base weekly (open). The protective efficacy of primaquine relative to placebo was 94.5% (95% confidence interval 57-99) for Plasmodium falciparum and 90.4% (95% CI 58-98) for P vivax. Attack rates for either parasite did not differ significantly between the chloroquine and placebo groups. Incidence density of physical complaints not associated with parasitaemia was low (17-18 complaints/person-year) and was about the same in all groups except for cough, which was increased in the primaquine group. Complete blood counts were normal and no evidence of hepatic or renal dysfunction was found with primaquine. However, at 50 weeks the primaquine group had a mean methaemoglobin of 5.8% (range 1.4-13%), which declined by half within 7 days of ending prophylaxis. When used daily for one year by men with normal G-6-PD activity, primaquine was well tolerated and effective for prevention of malaria.

Chemotherapy and prevention of drug-resistant malaria

Drug-resistant falciparum and vivax malaria will continue to be an increasing problem. The incidence of drug-resistant malaria has been increasing at a rate that exceeds new drug development. Plasmodium falciparum has rapidly developed resistance to new synthetic antimalarials, including mefloquine and halofantrine. P. vivax malaria resistant to chloroquine and primaquine is now widespread in parts of Oceania; the optimal therapy for this infection is unknown. At present, a combination of qinghaosu derivatives and mefloquine appears to be the most active drug regimen against multidrug-resistant falciparum malaria from Southeast Asia. However, qinghaosu compounds are not yet licensed and widely available. The capacity of P. falciparum to rapidly develop drug resistance and the growing evidence that other plasmodia can evolve resistance suggests that within the next 10 years, we face the real prospect of untreatable malaria. Ultimately, control of malaria may require more creative approaches than additional inhibitory drugs. These might include: the identification of biochemical pathways unique to the parasite (such as drug efflux and heme polymerase), making it possible to design new classes of antimalarial agents that are selectively toxic to the parasite; methods to block parasite development in the mosquito vector; and multistage vaccines against both asexual and sexual stages in order to block both the pathophysiology and transmission of disease.

Interleukin 12 induction of interferon gamma-dependent protection against malaria

Intraperitoneal injection of recombinant Interleukin 12 (rIL-12) at 30 ng/day for 5 days beginning 1 to 2 days before sporozoite challenge or administration of a single dose of 150 ng of rIL-122 days before challenge protected 100% of BALB/c mice against challenge with 10(2) Plasmodium yoelii sporozoites. rIL-12-induced protection was eliminated in all mice by administration of a monoclonal antibody against interferon gamma and in 50% of mice by administration of NG-monomethyl-L-arginine, a competitive inhibitor of nitric oxide synthase. rIL-12 protected BALB/c mice treated with cytotoxic anti-CD4 and anti-CD8 monoclonal antibodies, as well as T-cell- and B-cell-deficient severe combined immunodeficiency mice. These data suggest that rIL-12 stimulates non-B, non-T cells to produce interferon gamma that kills intrahepatic parasites by stimulating nitric oxide production. If rIL-12 proves to be well tolerated by humans, our findings support consideration of rIL-12 as an immunoprophylactic against malaria.

Fever in the returned traveler

Febrile infections can be fatal in travelers to tropical countries unless the patient seeks medical care in a timely manner and the physician takes the time and has the skill to make a rapid diagnosis and prescribe appropriate therapy. In addition to the usual febrile illnesses present in temperate climates, the patient may have an "exotic" infection, e.g., malaria, infectious hepatitis, enteric fever, or dengue fever. The potential causes of fever in travelers are extensive. This article provides practical clues to assist the physician in making the correct diagnosis--by using exposure information, symptoms and signs, and concomitant symptom complexes.