Fluorescence Microscopy Assessed for Malaria Diagnosis

The laboratory diagnosis of Plasmodium infections is either by light microscopy (LM) of Giemsa-stained thick blood smears or by rapid diagnosis tests as an alternative, although they cost more and give qualitative instead of quantitative results.

Scientists from the University of Tuebingen (Germany) working in Lambaréné (Gabon), took blood samples from 210 anonymous patients between September and November in 2009. The patients had attended the outpatient department of the local Albert Schweitzer Hospital with a history of fever within the last 24 hours and suspected diagnosis of malaria. The investigators compared LM with LED fluorescence microscopy (ledFM) at two different magnifications, and conventional fluorescence microscopy (uvFM) for the diagnosis of malaria.

Analysis of sensitivity and specificity showed sensitivities between 97% and 99 %, with best values of 99% for both magnifications of ledFM. Specificity of the methods ranged from 91% using the × 400 ledFM magnification and up to 93% for the two other methods. The results demonstrate a high sensitivity and acceptable specificity for the fluorescent techniques. The lower specificity may be at least partially due to missed positive samples in the Giemsa gold standard compared to the acridine orange technique. In this study, the Optiphot-2 mercury lamp epifluorescence microscope (Nikon; Tokyo, Japan) and the Primo Star iLED epifluorescence microscope equipped with a 455 nm LED (Carl Zeiss; Oberkochen, Germany) were used.

Fluorescence microscopy based on light-emitting diodes (LED) of one wavelength using acridine orange as a nucleic acid fluorescent dye, which stains DNA and ribonucleic acid (RNA) instantly. This is a very useful tool in field-settings as the LED consume less energy, are long-lasting and brighter, as a result of which they do not require darkrooms which has been a major drawback of conventional fluorescence microscopy. Additionally, they offer battery operation during power shutdowns or in areas where no electricity is available allowing fast and accurate diagnosis even under these circumstances. The authors concluded that ledFM is a reliable, accurate, fast, and inexpensive tool for daily routine malaria diagnosis and may be used as a point of care diagnostic tool. The study was published on July 18, 2011, in the Malaria Journal.

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