Malaria diagnosis by dipstick assay in a honduran population with coendemic Plasmodium falciparum and Plasmodium vivax

A Plasmodium lactate dehydrogenase dipstick designed to separately detect P. falciparum and P. vivax malaria was evaluated in two Honduran populations where both species are endemic. The dipstick was compared to thick film microscopy; the polymerase chain reaction (PCR) was used to analyze discordant results. The dipstick had a sensitivity of 100% and a specificity of 95% compared with microscopy in the diagnosis ofPlasmodium infections in a hospital population; the mean parasite density was approximately 590/mm 3 . In a field sample of mostly asymp- tomatic volunteers, the sensitivity of the dipstick for Plasmodium infection varied with parasite density. Additionally, the sensitivity and specificity of the dipstick was similar to thick film microscopy in the diagnosis of vivax malaria compared with the PCR. The dipstick was unable to detect P. vivax in the presence of P. falciparum because of cross-reactivity in the pan-specific band. Accurate species identification in mixed infections remains a problem in malaria diagnosis. 1-4 However, for dipsticks to effectively replace microscopy, they must pro- vide reliable species diagnosis. Of the four Plasmodiumspe- cies that naturally infect humans, P. falciparum causes the most severe disease. Despite its obligate requirement for re- ticulocytes, 5 P. vivax, does not always cause benign infec- tions. Reports of significant morbidity, mortality and drug resistance in P. vivax infections are generating new interest in this Plasmodium. 6,7 The need to clear the hepatic hypno- zoite stage of patients with P. vivax infections is another reason to document vivax infections. Most routinely admin- istered antimalarials are ineffective against the exo-erythro- cytic stages of Plasmodia. Thus, a tissue schizontocidal drug must be added to the treatment regimen for vivax malaria to preclude an unpredictable relapse of the disease. 8