Rapid test for malaria diagnosis [letter]

In early 1992 researchers at the Armed Forces Research Institute of Medical Sciences (AFRIMS) in Bangkok Thailand and at the Regional Malaria Centre No. 5 in Nonthaburi compared 2 tests which detect malaria parasites at 2 rural malaria in clinics in Thailand. They obtained blood samples from 236 patients and prepared a thin smear and on the same slide a thick and thin smear. The researchers stained the thin smear with acridine-orange according to the technique of Kawamoto and Billingsley. They looked at the acridine-orange stained thin smear samples through a microscope with an interference filter and a barrier film. They examined the samples with the assistance of an external halogen light and a mirror. This interference filter system (IFS) for detecting malaria parasites was 98% sensitive for Plasmodium falciparum and 89% for P. vivax when compared with the malaria clinic findings (Giemsa technique). In addition IFS found 8 more P. falciparum and 2 more P. vivax cases. AFRIMS researchers identified 41% of patients who were positive for malaria parasites using the Giemsa technique. IFS found 88% of the Giemsa positive cases to be positive. Moreover it detected all cases with densities >8/100 white blood cells (WBC) for P. falciparum and >14/100 WBC for P. vivax. This study found IFS required only half the time of the Giemsa technique to stain and examine smears. In fact if a thin smear had been well stained with acridine-orange health workers could recognize with more confidence 1 parasite than they could with Giesma. Further since IFS allows examiners to expand the number of microscopic fields and the reading time it is probably as sensitive as extensive reading of Giemsa slides by experienced examiners. In conclusion health workers need to properly prepare thin smears for an accurate diagnosis by IFS.