with malarial countermeasures. Retrospective analysis led the authors to conclude that the 38 rangers became infected while working at two specific forward-operating bases during summer 2002 (Kotwal et al. 2005).
The antimalarial chemoprophylaxis prescribed for this Army Ranger task force consisted of 250-mg mefloquine tablets ingested weekly beginning 2 weeks before deployment and ending 4 weeks after deployment. To prevent the late onset of malaria, the troops also were instructed to ingest one 15-mg primaquine tablet daily for 2 weeks after deployment. In addition, it is expected that all US soldiers at risk of malaria are trained and supplied to minimize their exposure to mosquitoes by impregnating their uniforms and bed nets with permethrin, wearing the uniforms properly, using the bed nets, and frequently coating exposed skin with insect repellent that contains 33% DEET (Johnson 2004; Kotwal et al. 2005).
The first three rangers to become symptomatic had vivax malaria diagnosed in March and April 2003. Fifteen more rangers fell ill and had diagnoses in May; the remaining 20 cases came to light in June-November 2003 (Lay 2005). The attack rate for the 725-person task force was 52.4 cases per 1,000 soldiers.
P. vivax infection causes flu-like symptoms that are often severe and debilitating (Boecken and Bronnert 2005; Spudick et al. 2005). Most of the infected rangers presented with fever; many also complained of chills, headache, muscle aches, or nausea. A complete blood-cell count obtained for 31 of the patients demonstrated that most had mild to moderate anemia and thrombocytopenia. The attending physicians based their initial diagnoses on those clinical signs and symptoms. Each case was confirmed with microscopic visualization of malaria parasitemia in the patient’s red blood cells on laboratory-prepared blood smears. A median of 233 days (range, 1-399 days) elapsed between these soldiers’ return from the theater of war and confirmation of their diagnoses.
Two rangers relapsed after completing their first treatment regimen. One of those cases was complicated by life-threatening acute respiratory distress syndrome (ARDS) during the primary attack; the patient relapsed three times from June to December 2003. The multiple relapses indicated infection with primaquine-tolerant P. vivax (Spudick et al. 2005). Pulmonary complications, such as ARDS, might occur with vivax malaria more frequently than is generally recognized.
The results of the anonymous postdeployment survey reported by Kotwal and colleagues indicate that at least 72% of the 725-member task force complied poorly with most of the malarial countermeasures described above (Kotwal et al. 2005). Some 52% followed the US Army guidelines for mefloquine, 41% for primaquine, and 31% for both; 82% reportedly treated their uniforms with permethrin, but only 29% routinely applied DEET to exposed skin. Delayed presentation of vivax malaria is well described, primarily in people who fail to take primaquine as terminal prophylaxis after returning from malaria-endemic areas of the Middle East (Gasser et al. 1991).
Only 14 cases of malaria were reported in US troops in 2004, a 63% decrease from the year before (Lay 2005). All the cases were caused by P. vivax infection and were contracted in Afghanistan (Kilpatrick 2005), and they presented sporadically from February to November.
Kotwal and colleagues suggest that continuously educating field troops about the importance of countermeasures and having leaders monitor and enforce the use of chemoprophylaxis and personal protective measures might further reduce the occurrence of malaria among US forces (Kotwal et al. 2005). At the same time, they and others note several shortcomings of the countermeasures themselves (Boecken and Bronnert 2005; Kotwal et al.