Direct acridine orange staining is not a 'miracle' solution to the problem of malaria diagnosis in the field

Assessment of LED fluorescence microscopy for the diagnosis of Plasmodium falciparum infections in Gabon

Background

Rapid and accurate diagnosis of malaria is central to clinical management and the prevention of drug-overuse, which may lead to resistance development, toxicity and economic losses. So far, light microscopy (LM) of Giemsa-stained thick blood smears is the gold standard. Under optimal conditions the procedure is fast and reliable; nevertheless a gain in speed would be a great advantage. Rapid diagnosis tests are an alternative, although they cost more and give qualitative instead of quantitative results. Light-emitting diode (LED) fluorescence microscopy (ledFM 400 ×, 1000 ×) may offer a reliable and cheap alternative, which can be used at the point of care.

Methods

LedFM and conventional fluorescence microscopy (uvFM) were compared to LM in 210 samples from patients with history of fever in the last 24 hours admitted to the Albert Schweitzer Hospital in Lambaréné, Gabon.

Results

Sensitivities were 99.1% for ledFM and 97.0% for uvFM, specificities 90.7% for ledFM 400 × and 92.6% for ledFM 1000 × and uvFM. High agreement was found in Bland-Altman-plot and Kappa coefficient (ledFM 1000 ×: 0.914, ledFM 400 × and uvFM: 0.895). The time to diagnosis for both FM methods was shorter compared to LM (LM: 43 min, uvFM: 16 min, ledFM 1000 ×: 14 min, ledFM 400 ×: 10 min).

Conclusion

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.

Laboratory diagnosis of malaria in nonhuman primates

Nonhuman primates (NHPs) are commonly used for biomedical research because of the high level of gene homology that underlies physiologic similarity to human beings. Malaria parasites of the genus Plasmodium cause one of the most frequent parasitic diseases of NHPs originating from tropical and subtropical areas and as such represent a significant research confounder. Malaria in NHPs presents a diagnostic challenge especially to those laboratories that see no more than a few malaria cases per year in NHPs. The accurate and timely diagnosis of malaria infection in NHPs facilitates the appropriate treatment of individuals infected with the malaria parasites. Conventional microscopy based on the examination of Giemsa-stained thick and thin blood films remains the mainstay of laboratory diagnosis of malaria infection because of the high diagnostic sensitivity and specificity and also the capability for Plasmodium species identification and parasite counts. This procedure is recognized as technically difficult and time-consuming, requiring considerable training to obtain the necessary skills. In the past few years, efforts to replace the traditional but tedious reading of blood films have led to different techniques for the detection of malaria parasites, including fluorescence microscopy, detection of intraleukocytic hemozoin or malaria pigment using automated blood cell analyzers, immunochromatographic rapid diagnostic tests based on malaria antigen detection, and PCR assays. These techniques offer new approaches for diagnosing malaria in NHPs. This review focuses on the available laboratory diagnostic tools for malaria in NHPs.

Acridine Orange for malaria diagnosis: its diagnostic performance, its promotion and implementation in Tanzania, and the implications for malaria control

One hundred years ago, Giemsa's stain was employed for the first time for malaria diagnosis. Giemsa staining continues to be the method of choice in most malarious countries, although, in the recent past, several alternatives have been developed that exhibit some advantages. Considerable progress has been made with fluorescent dyes, particularly with Acridine Orange (AO). The literature on the discovery, development and validation of the AO method for malaria diagnosis is reviewed here. Compared with conventional Giemsa staining, AO shows a good diagnostic performance, with sensitivities of 81.3%-100% and specificities of 86.4%-100%. However, sensitivities decrease with lower parasite densities, and species differentiation may occasionally be difficult. The most notable advantage of the AO method over Giemsa staining is its promptness; results are readily available within 3-10 min, whereas Giemsa staining may take 45 min or even longer. This is an important advantage for the organization of health services and the provision of effective treatment of malaria cases. The national malaria control programme of Tanzania, together with the Japan International Co-operation Agency, began to introduce the AO method in Tanzania in 1994. So far, AO staining has been introduced in 70 regional and district hospitals, and 400 laboratory technicians have been trained to use the method. The results of this introduction, which are reviewed here and have several important implications, indicate that AO is a viable alternative technique for the laboratory diagnosis of malaria in highly endemic countries.

Rapid diagnostic tests for malaria parasites

Malaria presents a diagnostic challenge to laboratories in most countries. Endemic malaria, population movements, and travelers all contribute to presenting the laboratory with diagnostic problems for which it may have little expertise available. Drug resistance and genetic variation has altered many accepted morphological appearances of malaria species, and new technology has given an opportunity to review available procedures. Concurrently the World Health Organization has opened a dialogue with scientists, clinicians, and manufacturers on the realistic possibilities for developing accurate, sensitive, and cost-effective rapid diagnostic tests for malaria, capable of detecting 100 parasites/microl from all species and with a semiquantitative measurement for monitoring successful drug treatment. New technology has to be compared with an accepted "gold standard" that makes comparisons of sensitivity and specificity between different methods. The majority of malaria is found in countries where cost-effectiveness is an important factor and ease of performance and training is a major consideration. Most new technology for malaria diagnosis incorporates immunochromatographic capture procedures, with conjugated monoclonal antibodies providing the indicator of infection. Preferred targeted antigens are those which are abundant in all asexual and sexual stages of the parasite and are currently centered on detection of HRP-2 from Plasmodium falciparum and parasite-specific lactate dehydrogenase or Plasmodium aldolase from the parasite glycolytic pathway found in all species. Clinical studies allow effective comparisons between different formats, and the reality of nonmicroscopic diagnoses of malaria is considered.

Diagnosis of malaria: a review of alternatives to conventional microscopy

Malaria causes significant morbidity and mortality worldwide, including countries with mainly imported malaria. In developing nations, scarce resources lead to inadequate diagnostic procedures. In affluent countries, poor familiarity with malaria may cause clinical and laboratory misdiagnosis. Microscopy of Giemsa-stained thick and thin films remains the current standard for diagnosis. Although it has good sensitivity and allows species identification and parasite counts, it is time consuming, requires microscopical expertise and maintenance of equipment. Microscopy with fluorescent stains (QBC), dipstick antigen detection of HRP2 and pLDH (Parasight-F, ICT Malaria Pf, OptiMAL), polymerase chain reaction assays and some automated blood cell analysers offer new approaches and are reviewed here, with emphasis on clinical relevance and their potential to complement conventional microscopy, especially in countries with imported malaria.

Comparison of a rapid dipstick test and thick blood films for detecting parasites of plasmodium falciparum used under typical conditions at a semi-rural hospital in Cote d'Ivoire

This prospective study compares a rapid dipstick test (ParaSight-F) with thick blood films for the detection of parasites of P falciparum, under 'typical' conditions and constraints to be found in a semi-rural hospital in a tropical developing country in Africa. Eighty-two samples were tested using the two techniques and found to concur in 95.1% of cases. However, in four of the samples the results differed. The thick blood films of 60 samples were later re-read by a local reference laboratory. Of these 98.3% were in agreement with the reading performed at the hospital. Only one of the 60 slides differed. The rapid dipstick test proved to be both easy to use and free from many of the usual constraints such as a need for formally trained or experienced laboratory staff, laboratory equipment, and reliable water and electricity supplies. In an holoendemic area for P falciparum transmission, it would appear to be eminently suitable, in technical terms and ease of handling as well as on the basis of rapid results, for wider distribution within this region. Its main drawback remains financial.

Acridine orange fluorescence techniques as alternatives to traditional Giemsa staining for the diagnosis of malaria in developing countries

Traditional Giemsa-stained thick blood films were compared with 2 fluorescence microscopy techniques, acridine orange (AO) staining of thin blood films and the quantitative buffy coat (QBC) method, for the microscopical diagnosis of malaria. Of 200 samples examined, 141 were positive by Giemsa staining, 146 by AO and 137 by QBC. Overall sensitivities for the 2 fluorescence techniques compared to Giemsa staining were good: AO 97.9% and QBC 93.6%. However, with parasitaemias < 100/microL the QBC sensitivity fell to 41.7% whereas that of AO was 83.3%. Both AO and QBC were unable to differentiate accurately between individual malaria species. We conclude that the QBC technique alone cannot replace Giemsa-stained thick blood films for most purposes in an African setting. However, apart from species differentiation, the AO method is an appropriate technique for the laboratory diagnosis of malaria in developing countries.