Rapid diagnosis of malaria by fluorescence microscopy

Quantitative Detection of Plasmodium falciparum Using, LUNA-FL, A Fluorescent Cell Counter

The microscopic examination of Giemsa-stained thin and/or thick blood films (Giemsa microscopy) is the standard method of malaria diagnosis. However, the results of the diagnosis significantly depend on the skills of clinical technicians. Furthermore, sample preparation and analysis are laborious and time-consuming. Therefore, in this study, we investigated if a commercially available fluorescent cell counter, LUNA-FL, was useful for the detection of Plasmodium parasite and the estimation of parasitemia. Whole blood samples from uninfected persons, spiked with P. falciparum-infected erythrocytes, were analysed. Most of the leucocytes and platelets were removed from whole blood samples with SiO₂-nanofiber filters set on spin columns. The filtered samples were stained with acridine orange, and automatic detection, as well as counting of erythrocytes and parasites, were performed using LUNA-FL. Whole blood, with various levels of parasites, was analysed by Giemsa microscopy or with LUNA-FL to estimate parasitemia, and a comparative analysis was performed. The coefficient determination value of the regression line was high (R² = 0.98), indicating that accurate quantitative parasite detection could be performed using LUNA-FL. LUNA-FL has a low running cost; it is compact, fast, and easy to operate, and may therefore be useful for point-of-care testing in the endemic areas.

MTT FORMAZAN REPLACED WST-8 AS A BETTER SIMPLE SCREENING METHOD FOR DETECTION OF GLUCOSE-6-PHOSPHATE DEHYDROGENASE DEFICIENCY

We have previously developed the WST-8 method as a simple and rapid screening test for detection of glucose-6-phosphate dehydrogenase (G6PD) deficiency accomplished by the naked eye. However, it was little difficult to distinguish between faint orange colors developed by heterozygous females and pink colors of normal hemolyzed blood, since both have similar tones. To solve this problem, we established a new and simple screening method that utilizes another formazan substrate, MTT (3-(4,5-dimethyl-2- thiazolyl)-2,5-diphenyl-2H tetrazolium bromide) in combination with a hydrogen carrier, 1-methoxy phenazine methosulfate. MTT formazan exhibits a purple color, thus allowing for the ability to easily distinguish the pink colors of hemolyzed blood. However, MTT has been reported to react with hemoglobin non-specifically and to interfere with the interpretation of the color reaction. In our examinations by mixing MTT with hemolyzed blood, we found that the non-specific reaction was very slow, and that the addition of a small amount of blood (5~10 μl) into a reaction mixture (800 μl) did not interfere with the reaction of G6PD activity. In this new MTT method, a strong purple color was generated in normal blood samples at 20~30 min after incubation, which could be distinguished by the naked eye from G6PD-deficient blood samples with less than 50% residual activity. In addition, quantitative measurement using a spectrophotometer was also possible despite the fact that MTT formazan is water-insoluble.

Improvement of malaria diagnostic system based on acridine orange staining

BACKGROUND

Rapid diagnosis of malaria using acridine orange (AO) staining and a light microscope with a halogen lamp and interference filter was deployed in some malaria-endemic countries. However, it has not been widely adopted because: (1) the lamp was weak as an excitation light and the set-up did not work well under unstable power supply; and, (2) the staining of samples was frequently inconsistent.

METHODS

The halogen lamp was replaced by a low-cost, blue light-emitting diode (LED) lamp. Using a reformulated AO solution, the staining protocol was revised to make use of a concentration gradient instead of uniform staining. To evaluate this new AO diagnostic system, a pilot field study was conducted in the Lake Victoria basin in Kenya.

RESULTS

Without staining failure, malaria infection status of about 100 samples was determined on-site per one microscopist per day, using the improved AO diagnostic system. The improved AO diagnosis had both higher overall sensitivity (46.1 vs 38.9%: p = 0.08) and specificity (99.0 vs 96.3%) than the Giemsa method (N = 1018), using PCR diagnosis as the standard.

CONCLUSIONS

Consistent AO staining of thin blood films and rapid evaluation of malaria parasitaemia with the revised protocol produced superior results relative to the Giemsa method. This AO diagnostic system can be set up easily at low cost using an ordinary light microscope. It may supplement rapid diagnostic tests currently used in clinical settings in malaria-endemic countries, and may be considered as an inexpensive tool for case surveillance in malaria-eliminating countries.

Preservation of wild isolates of human malaria parasites in wet ice and adaptation efficacy to in vitro culture

Wild isolates of malaria parasites were preserved in wet ice for 2–12 days and cultivated by a candle jar method. In four isolates of Plasmodium falciparum collected from Myanmar and preserved for 12 days, all failed to grow. In 31 isolates preserved for 5–10 days, nine were transformed to young gametocytes, but 22 isolates grew well. From Ranong, Thailand, nine isolates preserved for 7 days were examined, and six grew well. On the other hand, all of the 59 isolates collected from eastern Indonesian islands failed to establish as culture-adapted isolates, even most of them were preserved only for 2–3 days: 10 isolates stopped to grow, and 49 isolates were transformed to sexual stages by Day 10. These results indicated that a great difference in adaptation to in vitro culture may exist between wild isolates distributed in continental Southeast Asia and in eastern Indonesia and that gametocytogenesis might be easily switched on in Indonesian isolates. In wild isolates of P. vivax, P. malariae and P. ovale preserved for 2–9 days, ring forms or young trophozoites survived, but adaptation to in vitro culture failed. These results indicate that wild isolates can be preserved in wet ice for 9–10 days.

Optical imaging techniques for the study of malaria

Malarial infection needs to be imaged to reveal the mechanisms behind malaria pathophysiology and to provide insights to aid in the diagnosis of the disease. Recent advances in optical imaging methods are now being transferred from physics laboratories to the biological field, revolutionizing how we study malaria. To provide insight into how these imaging techniques can improve the study and treatment of malaria, we summarize recent progress on optical imaging techniques, ranging from in vitro visualization of the disease progression of malaria infected red blood cells (iRBCs) to in vivo imaging of malaria parasites in the liver.

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.

Determination of red cells, nucleic acid-containing cells and platelets (RNP Determination) by a crossover analysis of emission DNA/RNA light

We developed a new flow cytometry analysis method using a crossover analysis of emission light from intracellular DNA/RNA. Both the RNA and the DNA content in each cell were new parameters obtained by fluorescence analysis using acridine orange supravital stain. With this method, two-dimensional diagrams produced by cellular RNA concentration (CRc) and cellular DNA concentration (CDc) enabled clear separation of red cells and platelets, and the diagram (RNP Diagram) also distinguished fluorescently stained blood cells and small particles derived from background dust of the reagent. This study assessed the capability of RNP Determination concerning reticulocyte count and accurate platelet count obtained by the ratio of red cells and platelets. The distance of each event between red cell distribution and platelet distribution was sufficiently large on the diagram, and the two regions did not overlap. Both reticulocyte count and platelet count showed excellent correlation with those obtained by their respective reference methods. In conclusion, this new assay, using RNP Determination, demonstrated great potential for detecting abnormalities of red cells and platelets.

A survey of malarial infection in endemic areas of Savannakhet province, Lao PDR and comparative diagnostic efficiencies of Giemsa staining, acridine orange staining, and semi-nested multiplex PCR

Malaria remains one of the most important parasitic diseases in Lao PDR, especially in forested rural areas. Knowing the rate of infection using highly sensitive and specific methods, and the factors related to malarial infection, may be helpful in reducing the infection and mortality rates. We aimed to study the malarial infection rate by comparing three detection methods, i.e., Giemsa staining, acridine orange (AO) staining and semi-nested multiplex PCR. The study also included some factors related to malarial infection in the endemic areas of Savannakhet province, Lao PDR. The respective malarial infection rates by Giemsa staining, AO staining and semi-nested multiplex PCR in Houy Jang vs. Keng Thong villages were 13.1 vs. 20.8, 16.2 vs. 25.4 and 20.8 vs. 30.8%. The infection rate among children not over 10 years of age was higher than infection rate among the older ages (p=0.002, Z-test for two proportions). The higher infection rates by semi-nested multiplex PCR over Giemsa and AO staining suggest the existence of many subclinical cases with low level parasitemia, undetected by microscopic techniques. We found no mixed infections using Giemsa or AO staining, but using semi-nested multiplex PCR we found 1.2% (3/260) mixed P. falciparum and P. vivax infections, suggesting that semi-nested multiplex PCR is suitable for detecting malarial infection from endemic areas whose cases may have low parasitemia and/or mixed infection. The factors significantly related to malarial infection from 260 questionnaires were: (1) children and young adults, (2) not having lived in the area more than 5 years, and (3) not using a mosquito net over the bed, indicating an increased risk of new residents of contracting malaria and a need to promote bed nets.

Methylene blue vital staining for Trypanosoma cruzi trypomastigotes and epimastigotes

The morphological identification of Trypanosoma cruzi is currently considered to have a high specificity, but its sensitivity, which depends on the volume of the sample examined, is rather low. Trypanosome developmental stages suspended in blood, reduviid feces, and culture media are routinely searched for by means of fresh film examination (about 2 µL). High speed centrifugation of blood samples separates the buffy coat, where most trypomastigotes concentrate. As the parasites are transparent and colorless, their detection is mostly dependent on their motility. The fluorescent vital stain acridine orange has been used to enhance image contrast, as exemplified by the QBC (Quantitative Buffy Coat) technique. Staining blood, buffy coat, reduviid feces, and culture media samples with methylene blue (also a vital dye) is a means of producing sharp, well contrasted images of motile or non-motile T. cruzi developmental stages, only standard laboratory microscopes being required. Slides previously coated with a thin layer of methylene blue are used to stain fresh blood films. Photomicrographs exemplify the results of methylene blue staining applied to living and fixed parasites.

Glucose-6-phosphate dehydrogenase (G6PD) mutations in Cambodia: G6PD Viangchan (871G>A) is the most common variant in the Cambodian population

We conducted a survey of malaria diagnoses and glucose-6-phosphate dehydrogenase (G6PD) testing in remote areas of Cambodia. Blood specimens from 670 people were collected by the finger-prick method. Of these people, 24.9% were found to have malaria, and 7.0% of people were G6PD deficient. In the Khmer, the largest ethnical population in Cambodia, the G6PD deficiency rate of males was 12.6% (25/199) whereas the rates in the minorities of the Tum Pun and the Cha Ray were 1.1% (1/93) and 3.2% (2/63), respectively. Of the G6PD-deficient subjects, 97.9% (46/47) were G6PD Viangchan (871G>A), and only one case (2.1%) was G6PD Union (1360C>T). Since G6PD Mahidol (487G>A) is common in Myanmar according to our previous study, the current finding suggests that the Cambodian population is derived from homogeneous ancestries and is different from the Myanmar population. All G6PD Viangchan cases were linked to two other mutations of 1311C>T and IVS-11 nt93T>C in the G6PD gene.

Glucose-6-phosphate dehydrogenase (G6PD) mutations in Myanmar: G6PD Mahidol (487G>A) is the most common variant in the Myanmar population

We conducted a survey of malaria diagnoses and treatments in remote areas of Myanmar. Blood specimens from more than 1,000 people were collected by the finger-prick method, and 121 (11%) of these people were found to be glucose-6-phosphate dehydrogenase (G6PD) deficient. Of these 121, 50 consented to analysis of the G6PD genome. We read the G6PD sequences of these subjects and found 45 cases of G6PD Mahidol (487G>A), two of G6PD Coimbra (592C>T), two of G6PD Union (1360C>T), and one of G6PD Canton (1376G>T). Taken together with data from our previous report, 91.3% (73/80) of G6PD variants were G6PD Mahidol. This finding suggests that the Myanmar population is derived from homogeneous ancestries and are different from Thai, Malaysian, and Indonesian populations.

Five different glucose-6-phophate [correction phosphate]dehydrogenase (G6PD) variants found among 11 G6PD-deficient persons in Flores Island, Indonesia

We conducted a survey for malaria diagnosis and treatment in four primary schools in Flores Island, one of the Indonesian Islands with an area of 17000 km(2) and a population of 1.8 million. Of those examined, 24.4% were diagnosed as having malaria (90/363) and administered medicine immediately. A glucose-6-phosphate dehydrogenase (G6PD) test was performed at the same time, and 16 persons (4.4%) were diagnosed as G6PD deficient. Eleven persons consented to analysis of the G6PD genome. We analyzed these subjects and found one case of G6PD Vanua Lava (383T>C), five cases of G6PD Coimbra (592C>T), one case of G6PD Viangchan (871G>A), one case of G6PD Chatham (1003G>A), and three cases of G6PD Kaiping (1388G>A). These were unexpected findings because five different G6PD variants were found in such a small population. This suggests that people of Flores Island are derived from various ancestries.

Alternative polymerase chain reaction method to identify Plasmodium species in human blood samples: the semi-nested multiplex malaria PCR (SnM-PCR)

A simplified protocol for the identification of Plasmodium species by semi-nested multiplex polymerase chain reaction (SnM-PCR) in human blood samples is compared with microscopical examination of thin and thick blood films in 2 field trials in Côte d'Ivoire and Cameroon. Also, dried blood spots or liquid blood collected from Dutch soldiers returning from Goma, Zaire (n = 141), Angola (n = 40), and from Marechaussee (Dutch border police) returning from various parts of the world (n = 161) were examined, together with miscellaneous other material obtained from laboratories and hospitals. The method is based on features of the small subunit nuclear ribosomal ribonucleic acid (RNA) gene (ssrDNA), a multicopy gene which possesses both highly conserved domains and domains characteristic for each of the 4 human malaria parasites. The first reaction of the SnM-PCR includes a universal reverse primer with 2 forward primers specific for Plasmodium and mammals, respectively. The mammalian-specific primer was included as a positive control to distinguish uninfected cases from simple PCR failures. The second PCR reaction includes a Plasmodium-specific forward primer plus species-specific reverse primers for P. vivax, P. ovale, P. falciparum and P. malariae. The technique worked better with samples collected in the field as dried blood spots on filter paper and heparinized blood rather than with frozen pelleted blood; it was more sensitive and more specific than the standard microscopical examination.

Unusual plasmodium malariae-like parasites in southeast Asia

During malaria surveys in Myanmar, 2 peculiar forms of Plasmodium malariae-like parasites were found. The morphologies of their early trophozoite stages were distinct from that of the typical P. malariae, resembling instead that of Plasmodium vivax, var. minuta, reported by Emin, and Plasmodium tenue, reported by Stephens, both in 1914. Two polymerase chain reaction (PCR)-based diagnoses, which target the same regions in the small subunit ribosomal RNA (SSUrRNA) genes, indicated that these parasites were new variant forms of P. malariae and that they could be separated into 2 genetic types that correlated with the 2 morphological types. Sequence analysis of the SSUrRNA and the circumsporozoite protein genes revealed that they were distinct both from each other and from other known P. malariae isolates and that the P. tenue-like type was closer to a monkey quartan malaria parasite, Plasmodium brasilianum. These results illustrate that the microscopic appearance of human P. malariae parasites may be more varied than previously assumed and suggest the value of molecular tools in the evaluation of malaria morphological variants.

Wide distribution of Plasmodium ovale in Myanmar

The presence of Plasmodium ovale has never been previously reported in Myanmar. Using blood samples obtained in many villages across the country between 1996 and 2000, molecular diagnosis of Plasmodium species was made with semi- or full-nested polymerase chain reaction (PCR) with species-specific primers, followed by agarose gel electrophoresis to detect amplification products. The presence of P. ovale was also confirmed with the another PCR-based diagnosis, the microtiterplate hybridization (MPH) method using species-specific probes. Both methods target the A type of the small subunit ribosomal RNA gene of the four human malaria parasites. Plasmodium ovale DNA was amplified in samples from 65 (4.9%) of 1323 PCR-positive patients, with perfect agreement between results obtained by nested PCR and MPH. Only four P. ovale-infected patients had single-species infection; all others were coinfected with P. falciparum, P. vivax and/or P. malariae. Quadruple infections were observed in six subjects. Parasites with typical P. ovale morphology were found in only 19 patients by conventional microscopy of Giemsa-stained thin smears or fluorescence microscopy of acridine orange-stained thin smears. Plasmodium ovale infections were found in villages situated in the southern, central and western regions of Myanmar, suggesting that P. ovale may be widely distributed in this country.

How prevalent are Plasmodium ovale and P. malariae in East Asia?

Plasmodium ovale and Plasmodium malariae, two of the four human malaria parasites, are usually found at very low prevalence in East Asia, even in areas with intense malaria transmission. In this article, Fumihiko Kawamoto, Qing Liu, Marcelo Ferreira and Indah Tantular review data obtained in recent field surveys, using alternative diagnostic methods such as acridine orange staining and PCR-based methods, to evaluate the prevalence of these two malaria species in East Asia. They argue that these species might be much more prevalent in East Asia than reported previously. In addition, they discuss the implications of sequence variations found in the small subunit ribosomal RNA genes of the two species targeted by diagnostic PCR and compare morphological criteria for speciation of malaria parasites stained with Giemsa and acridine orange.

Field trials of a rapid test for G6PD deficiency in combination with a rapid diagnosis of malaria

A rapid single-step screening method for detection of glucose-6-phosphate dehydrogenase (G6 PD) deficiency was evaluated on Halmahera Island, Maluku Province, Indonesia, and in Shan and Mon States, Myanmar, in combination with a rapid diagnosis of malaria by an acridine orange staining method. Severe deficiency was detected by the rapid test in 45 of 1126 volunteers in Indonesia and 54 of 1079 in Myanmar, but it was difficult to distinguish blood samples with mild deficiency from those with normal activity. 89 of 99 severely deficient cases were later confirmed by formazan ring method in the laboratory, but 5 with mild and 5 with no deficiency were misdiagnosed as severe. Of the samples diagnosed as mild and no deficiency on-site, none was found to be severely deficient by the formazan method. Malaria patients were simultaenously++ detected on-site in 273 samples on Halmahera island and 277 samples from Shan and Mon States. In Mon State, primaquine was prescribed safely to G6 PD-normal malaria patients infected with Plasmodium vivax and/or gametocytes of P. falciparum. The new rapid test for G6 PD deficiency may be useful for detecting severe cases under field conditions, and both rapid tests combined are can be useful in malaria-endemic areas, facilitating early diagnosis, prompt and radical treatment of malaria and suppression of malaria transmission.

Sequence variation in the small-subunit rRNA gene of Plasmodium malariae and prevalence of isolates with the variant sequence in Sichuan, China

By two PCR-based diagnostic methods, Plasmodium malariae infections have been rediscovered at two foci in the Sichuan province of China, a region where no cases of P. malariae have been officially reported for the last 2 decades. In addition, a variant form of P. malariae which has a deletion of 19 bp and seven substitutions of base pairs in the target sequence of the small-subunit (SSU) rRNA gene was detected with high frequency. Alignment analysis of Plasmodium sp. SSU rRNA gene sequences revealed that the 5' region of the variant sequence is identical to that of P. vivax or P. knowlesi and its 3' region is identical to that of P. malariae. The same sequence variations were also found in P. malariae isolates collected along the Thai-Myanmar border, suggesting a wide distribution of this variant form from southern China to Southeast Asia.

High prevalence of Plasmodium malariae and Plasmodium ovale in malaria patients along the Thai-Myanmar border, as revealed by acridine orange staining and PCR-based diagnoses

The prevalence of the four human malaria parasites was investigated among malaria patients at northern, central and southern towns in Thailand along the border with Myanmar between September 1995 and May 1996. Thin smears obtained from 548 Thai and Burmese patients were reviewed by an acridine orange staining method, and many mixed infections with two to four species, including P. malariae and P. ovale, were detected. These diagnostic results were compared with those by two PCR-based diagnoses, microtitre plate hybridization (MPH) and a nested PCR method, both of which targets the same, species-specific regions in the 18S rRNA genes. In both PCR diagnoses, many P. malariae and P. ovale infections were also detected. Detection sensitivity of P. malariae infection was higher in nested PCR than MPH, and a total prevalence of P. malariae infection estimated by nested PCR reached 24.3% (133/548). In 16 of them, the size of PCR products amplified by the P. malariae-specific primer was about 20-bp shorter than the expected size of 115-bp. Four of 16 possessed two different bands with normal and shorter sizes, suggesting that P. malariae isolates may be separated into two types, and that those with shorter products may be new variant form (s) with a nucleotide deletion in the target region. On the other hand, 21 P. ovale infections (3.8%) were detected by nested PCR, but four of them were MPH-negative because of the sequence variation at the probe region. These results indicated that the prevalence of P. malariae and P. ovale along the Thai-Myanmar border may be substantially higher than previously reported.

Sequence variation in the 18S rRNA gene, a target for PCR-based malaria diagnosis, in Plasmodium ovale from southern Vietnam

Field surveys of malaria were performed in southern Vietnam by using an acridine orange staining method for rapid diagnosis and a PCR-based, microtiter plate hybridization method for accurate diagnosis. A total of three patients of Plasmodium ovale infection were detected, but PCR-amplified DNA of the P. ovale isolates from two of the patients did not hybridize with the P. ovale-specific probe. Analysis of the target sequence in the 18S rRNA gene indicated that in the DNA of isolates from both patients three nucleotides in the probe region from the typical P. ovale sequence were different, with deletions of two nucleotides and the substitution of one nucleotide. These results may suggest that in addition to molecular biological methods, careful microscopic examination of stained thin blood films is still required in studies of the prevalence of different malaria species.

Current state and future trends in the diagnosis of babesiosis

An overview is given of the currently available methods to diagnose babesiosis in livestock. Microscopic techniques are still the only appropriate techniques to diagnose acute disease. Thin or thick blood films stained with Giemsa's stain are sufficient. The sensitivity ranges from 10(-5) to 10(-6), i.e. one parasite per 10(5)-10(6) erythrocytes can be detected. Thick films stained with acridine orange (sensitivity approximately 10(-7)) and the Quantitative Buffy Coat (QBC) analysis tube system (sensitivity approximately 10(-7)-10(-8)) are applicable for diagnosis in the laboratory. DNA probes are very specific tools to identify haemoparasites in organs post mortem and in ticks. For the identification of carrier animals the sensitivity (approximately 10(-5)-10(-6)) is generally not sufficient. For the latter the polymerase chain reaction (PCR) technique is a very powerful tool (sensitivity approximately 10(-9)). Many different serodiagnostic tests have been described; however, the immunofluorescence antibody test is the most widely used, while the enzyme-linked immunosorbent assay (ELISA) is the test system which holds the greatest promise for the future. Thus far, improvements to the ELISA have been limited as the quality of antigen preparations made from infected blood is generally poor with a few exceptions (Babesia bovis, Babesia caballi). Potentially, most of the problems associated with crude antigens can be overcome by the production of recombinant antigens. Several ELISAs based on highly defined recombinant antigens have been described and show promise. None of these tests has been validated to the extent that it could be applied globally. Future research requirements as well as the need for coordination of the research effort and collaboration between institutions involved in the diagnosis of babesiosis are discussed.

Prevalence of malaria and its relationship to anemia, blood glucose levels, and serum somatomedin c (IGF-1) levels in the Solomon Islands

As part of establishing effective methods for malaria control, the malaria-associated nutritional status was surveyed on Guadalcanal Island in the Solomon Islands in 1993. A total of 506 residents participated in this study. The slide positive rate for malaria was 54% (275/506) in all ages, with a high of 79% for children aged 4-6 years. Plasmodium falciparum was the most common species (52%), followed by P. vivax (29%). Splenomegaly in children from infants to age 15 was detected at the rate of 30% (104/343) by the palpation method. Body mass index was lower in Solomon Islanders than for the Japanese population up to 15 years old in both genders. Mean values for serum insulin-like growth factor-1 (IGF-1) were also lower in Solomon Islanders in children under 18 years old. The hemoglobin distribution curves were almost identical in the malaria-positive (P(+)) and -negative (P(-)) groups. The percentage of cases with less than 80 mg/dl of blood glucose and those with less than 50 ng/ml of IGF-1 were higher in the P(+) group than for the anti-malaria drug-untreated malaria-negative (P(-)D(-)) group. It is suggested that low blood glucose and low IGF-1 levels may have some relationship with the malaria infection.

Rapid diagnosis of malaria by use of fluorescent probes

Malaria diagnosis relies on observation of parasites in blood smears and the Giemsa-stained thick blood smear (G-TS) is the reference test. Diagnosis by G-TS in low-density infections requires long periods of observation and experienced microscopists. Examination of Giemsa-stained thin smears enables more reliable differentiation of species but may miss low-grade infections. Fluorescent stains may offer an alternative technique. We compared the Giemsa technique with 4,6-diamidine-2-phenilindolo-propidium iodide (DAPI-PI) stainings in order to evaluate the time required for diagnosis. A Plasmodium falciparum-infected blood specimen was diluted to obtain concentrations ranging from 6192 to 24 parasites/microliters (p/microliter), and thin and thick smears were stained with the two methods. The DAPI-PI proved useful: parasites were easily recognized and their morphology was preserved in thin and thick smears. The method allowed more rapid evaluation of thin smears as compared with Giemsa staining and enabled recognition of parasites in case of low-level parasitemias. The DAPI-PI staining technique may acquire an important role in malaria diagnosis, especially in nonendemic countries where technicians are not experienced with G-TS; in developing countries, it could be used in epidemiologic surveys of populations with low-density parasitemias, for which it enables a fast examination of smears and possibly the identification of parasite species.