Evaluation of blood preservation methods in the performance of the WHO in vitro micro-test for Plasmodium falciparum in the field

In vitro drug susceptibility testing of <I>Plasmodium falciparum</I> must be conducted immediately after collecting a sample of the patient‘s blood; otherwise the parasites may weaken and the culture fail. Collecting blood samples from individuals in areas far from the field station or clinic where in vitro testing is conducted requires a reliable method of sample preservation during transportation. We examined and compared three different methods used to preserve blood samples in endemic areas in the Philippines. The three methods are as follows: the on-site method (test is conducted soon after blood sampling), flask culture method (sample is taken to the laboratory in a culture flask with medium) and EDTA tube method (sample is taken to the laboratory in a blood collection tube). The WHO <I>in vitro</I> micro-test for susceptibility of <I>P. falciparum</I> to chloroquine was performed using an AnaeroPack® system and a portable thermostat incubator. Evaluation of the three methods was based on schizont maturation, ease of handling, and risk of contamination during the test. The on-site and flask culture methods, but not the EDTA tube method, were effective for keeping the parasites viable. Furthermore, schizont maturation appeared better with the flask method than with the on-site method, especially in the control wells (drug-free wells). In addition, it was easier to perform the flask method than the on-site method. No contamination was observed using any of the methods. The results of the study suggest that the flask culture method is the most effective and useful way to preserve blood samples for the in vitro test and, moreover, that it aids in providing detailed field evidence of drug-resistant malaria.

A PILOT FIELD TRIAL OF AN IN VITRO DRUG SUSCEPTIBILITY TEST USING THE ANAEROPACK MALARIA CULTURE SYSTEM ON THE THAI-MYANMAR BORDER

The AnaeroPack<SUP>®</SUP> malaria culture system with a portable thermostat incubator was evaluated in a field laboratory on the Thai-Myanmar border conducting <I>in vitro</I> drug susceptibility tests on blood samples from 5 Karen children infected with <I>P. falciparum</I>. Only one isolate was susceptible to chloroquine; the others were highly resistant. The IC<SUB>50</SUB> value of an isolate was only resistant to mefloquine, whereas the values of the 3 patients who presumably showed recrudescence were slightly elevated in the susceptible ranges. These results suggested that chloroquine should no longer be used for <I>P. falciparum</I> malaria in this geographic area, and that mefloquine should be carefully monitored for its <I>in vivo</I> effectiveness. In this study, the AnaeroPack<SUP>®</SUP> malaria culture system with portable thermostatic incubator is a powerful and useful mobile tool, which aids in providing detailed evidence-based distribution data concerning of drug resistant malaria in the field.