Molecular-based assay for simultaneous detection of four Plasmodium spp. and Wuchereria bancrofti infections

Diagnostic Methods for Non-Falciparum Malaria

Malaria is a serious public health problem that affects mostly the poorest countries in the world, killing more than 400,000 people per year, mainly children under 5 years old. Among the control and prevention strategies, the differential diagnosis of the Plasmodium-infecting species is an important factor for selecting a treatment and, consequently, for preventing the spread of the disease. One of the main difficulties for the detection of a specific Plasmodium sp is that most of the existing methods for malaria diagnosis focus on detecting P. falciparum. Thus, in many cases, the diagnostic methods neglect the other non-falciparum species and underestimate their prevalence and severity. Traditional methods for diagnosing malaria may present low specificity or sensitivity to non-falciparum spp. Therefore, there is high demand for new alternative methods able to differentiate Plasmodium species in a faster, cheaper and easier manner to execute. This review details the classical procedures and new perspectives of diagnostic methods for malaria non-falciparum differential detection and the possibilities of their application in different circumstances.

Rapid diagnosis of parasitic diseases: current scenario and future needs

BACKGROUND

Parasitic diseases are one of the world's most devastating and prevalent infections, causing millions of morbidities and mortalities annually. In the past, many of these infections have been linked predominantly to tropical or subtropical areas. Nowadays, however, climatic and vector ecology changes, a significant increase in international travel, armed conflicts, and migration of humans and animals have influenced the transmission of some parasitic diseases from 'book pages' to reality in developed countries. It has also been noted that many patients who have never travelled to endemic areas suffer from blood-borne infections caused by protozoa. In the light of existing knowledge, this new trend can be explained by the fact that in the process of migration a large number of asymptomatic carriers become a part of the blood bank donor and transplant donor populations. Accurate and rapid diagnosis represents the crucial weapon in the fight against parasitic infections.

AIMS

To review old and new approaches for rapid diagnosis of parasitic infections.

SOURCES

Data for this review were obtained through searches of PubMed using combinations of the following terms: parasitological diagnostics, microscopy, lateral flow assays, immunochromatographic assays, multiplex-PCR, and transplantation.

CONTENT

In this review, we provide a brief account of the advantages and limitations of rapid methods for diagnosis of parasitic diseases and focus our attention on current and future research in this area. The approximate costs associated with the use of different techniques and their applicability in endemic and non-endemic areas are also discussed.

IMPLICATIONS

Microscopy remains the cornerstone of parasitological diagnostics, especially in the field and low-resource settings, and provides epidemiological assessment of parasite burden. However, increased use and availability of point-of-care tests and molecular assays in modern era allow more rapid and accurate diagnoses and increased sensitivity in the identification of parasitic infections.

Malaria transmission dynamics surrounding the first nationwide long-lasting insecticidal net distribution in Papua New Guinea

BACKGROUND

The major malaria vectors of Papua New Guinea exhibit heterogeneities in distribution, biting behaviour and malaria infection levels. Long-lasting, insecticide-treated nets (LLINs), distributed as part of the National Malaria Control Programme, are the primary intervention targeting malaria transmission. This study evaluated the impact of LLINs on anopheline density, species composition, feeding behaviour, and malaria transmission.

METHODS

Mosquitoes were collected by human landing catch in 11 villages from East Sepik Province and Madang Province. Mosquitoes were collected for 3 years (1 year before distribution and 2 years after), and assayed to determine mosquito species and Plasmodium spp. infection prevalence. The influence of weather conditions and the presence of people and animals on biting density was determined. Determinants of biting density and sporozoite prevalence were analysed by generalized estimating equations (GEE).

RESULTS

Mosquito biting rates and entomological inoculation rates decreased significantly after the distribution. Plasmodium falciparum and P. vivax sporozoite prevalence decreased in year 2, but increased in year 3, suggesting the likelihood of resurgence in transmission if low biting rates are not maintained. An earlier shift in the median biting time of Anopheles punctulatus and An. farauti s.s. was observed. However, this was not accompanied by an increase in the proportion of infective bites occurring before 2200 hours. A change in species composition was observed, which resulted in dominance of An. punctulatus in Dreikikir region, but a decrease in An. punctulatus in the Madang region. When controlling for village and study year, An. farauti s.s., An. koliensis and An. punctulatus were equally likely to carry P. vivax sporozoites. However, An. punctulatus was significantly more likely than An. farauti s.s. (OR 0.14; p = 0.007) or An. koliensis (OR 0.27; p < 0.001) to carry P. falciparum sporozoites.

CONCLUSIONS

LLINs had a significant impact on malaria transmission, despite exophagic and crepuscular feeding behaviours of dominant vectors. Changes in species composition and feeding behaviour were observed, but their epidemiological significance will depend on their durability over time.

Molecular diagnosis in clinical parasitology: When and why?

Microscopic detection and morphological identification of parasites from clinical specimens are the gold standards for the laboratory diagnosis of parasitic infections. The limitations of such diagnostic assays include insufficient sensitivity and operator dependence. Immunoassays for parasitic antigens are not available for most parasitic infections and have not significantly improved the sensitivity of laboratory detection. Advances in molecular detection by nucleic acid amplification may improve the detection in asymptomatic infections with low parasitic burden. Rapidly accumulating genomic data on parasites allow the design of polymerase chain reaction (PCR) primers directed towards multi-copy gene targets, such as the ribosomal and mitochondrial genes, which further improve the sensitivity. Parasitic cell or its free circulating parasitic DNA can be shed from parasites into blood and excreta which may allow its detection without the whole parasite being present within the portion of clinical sample used for DNA extraction. Multiplex nucleic acid amplification technology allows the simultaneous detection of many parasitic species within a single clinical specimen. In addition to improved sensitivity, nucleic acid amplification with sequencing can help to differentiate different parasitic species at different stages with similar morphology, detect and speciate parasites from fixed histopathological sections and identify anti-parasitic drug resistance. The use of consensus primer and PCR sequencing may even help to identify novel parasitic species. The key limitation of molecular detection is the technological expertise and expense which are usually lacking in the field setting at highly endemic areas. However, such tests can be useful for screening important parasitic infections in asymptomatic patients, donors or recipients coming from endemic areas in the settings of transfusion service or tertiary institutions with transplantation service. Such tests can also be used for monitoring these recipients or highly immunosuppressed patients, so that early preemptive treatment can be given for reactivated parasitic infections while the parasitic burden is still low.

Population genetics of the filarial worm wuchereria bancrofti in a post-treatment region of Papua New Guinea: insights into diversity and life history

BACKGROUND

Wuchereria bancrofti (Wb) is the primary causative agent of lymphatic filariasis (LF). Our studies of LF in Papua New Guinea (PNG) have shown that it is possible to reduce the prevalence of Wb in humans and mosquitoes through mass drug administration (MDA; diethylcarbamazine with/without ivermectin). While MDAs in the Dreikikir region through 1998 significantly reduced prevalence of Wb infection, parasites continue to be transmitted in the area.

METHODS

We sequenced the Wb mitochondrial Cytochrome Oxidase 1 (CO1) gene from 16 people infected with Wb. Patients were selected from 7 villages encompassing both high and moderate annual transmission potentials (ATP). We collected genetic data with the objectives to (i) document contemporary levels of genetic diversity and (ii) distinguish between populations of parasites and hosts across the study area.

PRINCIPLE FINDINGS

We discovered 109 unique haplotypes currently segregating in the Wb parasite population, with one common haplotype present in 15 out of 16 infections. We found that parasite diversity was similar among people residing within the same village and clustered within transmission zones. For example, in the high transmission area, diversity tended to be more similar between neighboring villages, while in the moderate transmission area, diversity tended to be less similar.

CONCLUSIONS

In the Dreikikir region of PNG there are currently high levels of genetic diversity in populations of Wb. High levels of genetic diversity may complicate future MDAs in this region and the presence of dominant haplotypes will require adjustments to current elimination strategies.

The complete mitochondrial genome sequence of the filarial nematode Wuchereria bancrofti from three geographic isolates provides evidence of complex demographic history

Mitochondrial (mt) genome sequences have enabled comparison of population genetics and evolution for numerous free-living and parasitic nematodes. Here we define the complete mt genome of Wuchereria bancrofti through analysis of isolates from Papua New Guinea, India and West Africa. Sequences were assembled for each isolate and annotated with reference to the mt genome sequence for Brugia malayi. The length of the W. bancrofti mt genome is approximately 13,637 nucleotides, contains 2 ribosomal RNAs (rrns), 22 transfer RNAs (trns), 12 protein-coding genes, and is characterized by a 74.6% AT content. The W. bancrofti mt gene order is identical to that reported for Onchocerca volvulus, Dirofilaria immitis, Setaria digitata and B. malayi. In addition to using translational start codons identified previously in the mt protein-coding genes of other filarial nematodes, W. bancrofti appears to be unique in using TGT as a translational start codon. Similarly, use of incomplete stop codons in mt protein-coding genes appears to be more common in W. bancrofti than in other human filarial parasites. The complete mt genome sequence reported here provides new genetic markers for investigating phylogenetic and geographic relationships between isolates, and assessing population diversity within endemic regions. The sequence polymorphism enables new strategies to monitor the progress of public health interventions to control and eliminate this important human parasite. We illustrate the utility of this sequence and single nucleotide polymorphisms by inferring the divergence times between the three W. bancrofti isolates, suggesting predictions into their origin and migration.

Development of a highly sensitive genus-specific quantitative reverse transcriptase real-time PCR assay for detection and quantitation of plasmodium by amplifying RNA and DNA of the 18S rRNA genes

A highly sensitive genus-specific quantitative reverse transcriptase real-time PCR (qRT-PCR) assay for detection of Plasmodium has been developed. The assay amplifies total nucleic acids (RNA and DNA) of the 18S rRNA genes with a limit of detection of 0.002 parasite/μl using cultured synchronized ring stage 3D7 parasites. Parasite densities as low as 0.000362 parasite/μl were detected when analyzing clinical samples. Analysis of clinical samples showed that detection of 18S rRNA genes from total nucleic acids increased the analytical sensitivity of the assay by more than 1 log unit compared to DNA only. When clinical samples with no parasites present by microscopy were analyzed by qRT-PCR, 90% (117 of 130) were positive for the presence of Plasmodium nucleic acids. Quantification of clinical samples by qRT-PCR using total nucleic acid versus DNA was compared to microscopy. There was a significantly greater correlation of parasite density to microscopy when DNA alone was used than with total nucleic acid. We conclude that analysis of total nucleic acids by qRT-PCR is a suitable assay for detection of low parasite levels in patients with early-stage malaria and/or submicroscopic infections and could greatly benefit malaria diagnosis, intervention trials, and malaria control and elimination efforts.

Molecular diagnosis of infections and resistance in veterinary and human parasites

Since 1977, >2000 research papers described attempts to detect, identify and/or quantify parasites, or disease organisms carried by ecto-parasites, using DNA-based tests and 148 reviews of the topic were published. Despite this, only a few DNA-based tests for parasitic diseases are routinely available, and most of these are optional tests used occasionally in disease diagnosis. Malaria, trypanosomiasis, toxoplasmosis, leishmaniasis and cryptosporidiosis diagnosis may be assisted by DNA-based testing in some countries, but there are very few cases where the detection of veterinary parasites is assisted by DNA-based tests. The diagnoses of some bacterial (e.g. lyme disease) and viral diseases (e.g. tick borne encephalitis) which are transmitted by ecto-parasites more commonly use DNA-based tests, and research developing tests for these species makes up almost 20% of the literature. Other important uses of DNA-based tests are for epidemiological and risk assessment, quality control for food and water, forensic diagnosis and in parasite biology research. Some DNA-based tests for water-borne parasites, including Cryptosporidium and Giardia, are used in routine checks of water treatment, but forensic and food-testing applications have not been adopted in routine practice. Biological research, including epidemiological research, makes the widest use of DNA-based diagnostics, delivering enhanced understanding of parasites and guidelines for managing parasitic diseases. Despite the limited uptake of DNA-based tests to date, there is little doubt that they offer great potential to not only detect, identify and quantify parasites, but also to provide further information important for the implementation of parasite control strategies. For example, variant sequences within species of parasites and other organisms can be differentiated by tests in a manner similar to genetic testing in medicine or livestock breeding. If an association between DNA sequence and phenotype has been demonstrated, then qualities such as drug resistance, strain divergence, virulence, and origin of isolates could be inferred by DNA-based tests. No such tests are in clinical or commercial use in parasitology and few tests are available for other organisms. Why have DNA-based tests not had a bigger impact in veterinary and human medicine? To explore this question, technological, biological, economic and sociological factors must be considered. Additionally, a realistic expectation of research progress is needed. DNA-based tests could enhance parasite management in many ways, but patience, persistence and dedication will be needed to achieve this goal.

High throughput multiplex assay for species identification of Papua New Guinea malaria vectors: members of the Anopheles punctulatus (Diptera: Culicidae) species group

Malaria and filariasis are transmitted in the Southwest Pacific region by Anopheles punctulatus sibling species including An. punctulatus, An. koliensis, the An. farauti complex 1-8 (includes An. hinesorum [An. farauti 2], An. torresiensis [An. farauti 3]). Distinguishing these species from each other requires molecular diagnostic methods. We developed a multiplex polymerase chain reaction (PCR)-based assay specific for known species-specific nucleotide differences in the internal transcribed spacer 2 region and identified the five species most frequently implicated in transmitting disease (An. punctulatus, An. koliensis, An. farauti 1, An. hinesorum, and An. farauti 4). A set of 340 individual mosquitoes obtained from seven Papua New Guinea provinces representing a variety of habitats were analyzed by using this multiplex assay. Concordance between molecular and morphological diagnosis was 56.4% for An. punctulatus, 85.3% for An. koliensis, and 88.9% for An. farauti. Among 158 mosquitoes morphologically designated as An. farauti, 33 were re-classified by PCR as An. punctulatus, 4 as An. koliensis, 26 as An. farauti 1, 49 as An. hinesorum, and 46 as An. farauti 4. Misclassification results from variable coloration of the proboscis and overlap of An. punctulatus, An. koliensis, the An. farauti 4. This multiplex technology enables further mosquito strain identification and simultaneous detection of microbial pathogens.

Filarial worms reduce Plasmodium infectivity in mosquitoes

BACKGROUND

Co-occurrence of malaria and filarial worm parasites has been reported, but little is known about the interaction between filarial worm and malaria parasites with the same Anopheles vector. Herein, we present data evaluating the interaction between Wuchereria bancrofti and Anopheles punctulatus in Papua New Guinea (PNG). Our field studies in PNG demonstrated that An. punctulatus utilizes the melanization immune response as a natural mechanism of filarial worm resistance against invading W. bancrofti microfilariae. We then conducted laboratory studies utilizing the mosquitoes Armigeres subalbatus and Aedes aegypti and the parasites Brugia malayi, Brugia pahangi, Dirofilaria immitis, and Plasmodium gallinaceum to evaluate the hypothesis that immune activation and/or development by filarial worms negatively impact Plasmodium development in co-infected mosquitoes. Ar. subalbatus used in this study are natural vectors of P. gallinaceum and B. pahangi and they are naturally refractory to B. malayi (melanization-based refractoriness).

METHODOLOGY/PRINCIPAL FINDINGS

Mosquitoes were dissected and Plasmodium development was analyzed six days after blood feeding on either P. gallinaceum alone or after taking a bloodmeal containing both P. gallinaceum and B. malayi or a bloodmeal containing both P. gallinaceum and B. pahangi. There was a significant reduction in the prevalence and mean intensity of Plasmodium infections in two species of mosquito that had dual infections as compared to those mosquitoes that were infected with Plasmodium alone, and was independent of whether the mosquito had a melanization immune response to the filarial worm or not. However, there was no reduction in Plasmodium development when filarial worms were present in the bloodmeal (D. immitis) but midgut penetration was absent, suggesting that factors associated with penetration of the midgut by filarial worms likely are responsible for the observed reduction in malaria parasite infections.

CONCLUSIONS/SIGNIFICANCE

These results could have an impact on vector infection and transmission dynamics in areas where Anopheles transmit both parasites, i.e., the elimination of filarial worms in a co-endemic locale could enhance malaria transmission.