Hans O. Lobel

Malaria among United States troops in Somalia

PURPOSE United States military personnel deployed to Somalia were at risk for malaria, including chloroquine-resistant Plasmodium falciparum malaria. This report details laboratory, clinical, preventive, and therapeutic aspects of malaria in this cohort. PATIENTS AND METHODS The study took place in US military field hospitals in Somalia, with US troops deployed to Somalia between December 1992 and May 1993. Centralized clinical care and country-wide disease surveillance facilitated standardized laboratory diagnosis, clinical records, epidemiologic studies, and assessment of chemoprophylactic efficacy. RESULTS Forty-eight cases of malaria occurred among US troops while in Somalia; 41 of these cases were P falciparum. Risk factors associated with malaria included: noncompliance with recommended chemoprophylaxis (odds ratio [OR] 2.4); failure to use bed nets (OR 2.6); and failure to keep sleeves rolled down (OR 2.2). Some patients developed malaria in spite of mefloquine (n = 8) or doxycycline (n = 5) levels of compatible with chemoprophylactic compliance. Five mefloquine failures had both serum levels > or = 650 ng/mL and metabolite:mefloquine ratios over 2, indicating chemoprophylactic failure. All cases were successfully treated, including 1 patient who developed cerebral malaria. CONCLUSIONS P falciparum malaria attack rates were substantial in the first several weeks of Operation Restore Hope. While most cases occurred because of noncompliance with personal protective measures or chemoprophylaxis, both mefloquine and doxycycline chemoprophylactic failures occurred. Military or civilian travelers to East Africa must be scrupulous in their attention to both chemoprophylaxis and personal protection measures.

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.

Malaria chemoprophylaxis and the serologic response to measles and diphtheria-tetanus-whole-cell pertussis vaccines

BackgroundAcute malaria has been associated with a decreased antibody response to tetanus and diphtheria toxoids, meningococcal, salmonella, and Hib vaccines. Interest in giving malaria drug therapy and prevention at the time of childhood immunizations has increased greatly following recent trials of intermittent preventive therapy during infancy (IPTi), stimulating this re-analysis of unpublished data. The effect of malaria chemoprophylaxis on vaccine response was studied following administration of measles vaccines and diphtheria-tetanus-whole cell pertussis (DTP) vaccines.MethodsIn 1975, six villages divided into two groups of children ≤74 months of age from Burkina Faso, were assigned to receive amodiaquine hydrochloride chemoprophylaxis (CH+) every two weeks for seven months or no chemoprophylaxis (CH-). After five months, children in each group received either one dose of measles or two doses of DTP vaccines.ResultsFor recipients of the measles vaccine, the seroconversion rates in CH+ and CH- children, respectively, were 93% and 96% (P > 0.05). The seroresponse rates in CH+ and CH- children respectively, were 73% and 86% for diphtheria (P > 0.05) and 77% and 91% for tetanus toxoid (P > 0.05). In a subset analysis, in which only children who strictly adhered to chemoprophylaxis criteria were included, there were, likewise, no significant differences in seroconversion or seroresponse for measles, diphtheria, or tetanus vaccines (P > 0.05). While analysis for pertussis showed a 43% (CH+) and 67% (CH-) response (P < 0.05), analyses using logistic regression to control for sex, age, chemoprophylaxis, weight-for-height Z-score, and pre-vaccination geometric mean titer (GMT), demonstrated that chemoprophylaxis was not associated with a significantly different conversion rate following DTP and measles vaccines. Seven months of chemoprophylaxis decreased significantly the malaria IFA and ELISA GMTs in the CH+ group.ConclusionMalaria chemoprophylaxis prior to vaccination in malaria endemic settings did not improve or impair immunogenicity of DTP and measles vaccines. This is the first human study to look at the association between malaria chemoprophylaxis and the serologic response to whole-cell pertussis vaccine.

Antimalarial Chemoprophylaxis in Infants and Children

The evolving patterns of drug resistance in malaria parasites and changes in recommendations for malaria prevention present a challenge to physicians who advise travellers on chemoprophylaxis. Because compliance with personal protection measures is usually low, children should receive appropriate chemoprophylaxis, including breast-fed infants who are not protected through maternal chemoprophylaxis. For travel to areas where chloroquine resistance has not yet been reported (i.e. parts of Central America, the Caribbean and parts of the Middle East), chloroquine alone is sufficient for antimalarial prophylaxis. Mefloquine is the drug of choice for chemoprophylaxis in areas with chloroquine-resistant Plasmodium falciparum, and can be given to infants and young children. The combination of chloroquine and proguanil is well tolerated in children but is much less effective against drug-resistant malaria. Further research is needed to determine the best dosage regimen for antimalarial drugs used for chemoprophylaxis in children.