Field evaluation of DNA detection of human filarial and malaria parasites using mosquito excreta/feces

Assessment of the capacity of Whatman filter papers as support to store stools for the molecular diagnostic testing of soil-transmitted helminthiasis

Storage of stools for the detection of soil-transmitted helminths (STH) remains challenging for the molecular diagnostic testing of STH infections. This study aimed to overcome this challenge by assessing the capacity of Whatman filter papers to store stools for the molecular detection of STHs. Stool samples were collected from school-aged children of soil-transmitted helminthiasis endemic areas of Cameroon and then, analysed using Kato Katz technique. For this study, 128 and 40 stool samples respectively with and without STH eggs were analysed. From each sample, 10, 20, 40 and 80 mg of stool were weighted and spread on 6 grades of Whatman filter papers that were stored at room temperature from one to ten weeks. DNA was extracted from spread stool using CTAB based-method. The amount of stool to spread on filter papers and the grade of filter paper offering good storage were determined by amplifying specific DNA fragments of Ascaris lumbricoides. The capacity of filter papers to store stool samples for several weeks before the molecular detection of STH species was assessed by amplifying specific DNA fragments of different STHs. The amplification rates of A. lumbricoides were significantly higher (P < 0.0001) for 10 and 20 mg of stored stools. Stools spread on Whatman paper grade 2 yielded the highest amplification rate of 100% for A. lumbricoides, T. trichiura and hookworm. PCR revealed STH infections in all the 128 spread stools carrying STH eggs. It also revealed Necator americanus and Ancylostoma duodenale respectively in 10 and 13 of 15 spread stools contained hookworm eggs. PCR confirmed the co-infections of these hookworm species as well as that of A. lumbricoides and Trichuris trichiura in 7 spread stools. Out of 40 stools without STH eggs, PCR revealed that 5 (12.5%) and 9 (22.5%) had respectively A. lumbricoides and T. trichiura infections. The amplification rate of each STH species was 100% from one to 8 weeks and decreased to 86.7% after 10 weeks of storage. This study highlighted the capacity of filter papers to store stools for the molecular detection of STHs. Storing stools on these papers will enable to monitor and evaluate control programs and ensure post-elimination surveillance.

Excretion Dynamics of Arboviruses in Mosquitoes and the Potential Use in Vector Competence Studies and Arbovirus Surveillance

The increasing threat of arboviruses such as West Nile virus (WNV) and Usutu virus (USUV) requires the fast and efficient surveillance of these viruses. The examination of mosquitoes takes up an important part; however, these investigations are usually very time-consuming. An alternative sample type for arbovirus surveillance might be mosquito excreta. In order to determine the excretion dynamics under laboratory conditions, laboratory colonies of Aedes vexans and Culex pipiens biotype molestus were infected with WNV, USUV or tick-borne encephalitis virus (TBEV). After infection, the excreta were sampled and investigated for viral RNA. Excretion of viral RNA together with infectious blood meal could be detected up to five days after infection. Further excretion seemed to correlate with a disseminated infection in mosquitoes, at least after USUV infection. In addition, it could be determined that the amount of viral RNA in the excretions correlated positively with the viral load in the mosquito bodies. Overall, this study shows that the usage of mosquito excreta as a sample type for surveillance enables the detection of endemic viruses (WNV, USUV) as well as non-mosquito-borne viruses (TBEV). In addition, examination of viral shedding during vector competence studies can provide insights into the course of infection without sacrificing animals.

Nondestructive Methods of Pathogen Detection: Importance of Mosquito Integrity in Studies of Disease Transmission and Control

Mosquitoes are vectors of many pathogens, including viruses, protozoans, and helminths, spreading these pathogens to humans as well as to wild and domestic animals. As the identification of species and the biological characterization of mosquito vectors are cornerstones for understanding patterns of disease transmission, and the design of control strategies, we conducted a literature review on the current use of noninvasive and nondestructive techniques for pathogen detection in mosquitoes, highlighting the importance of their taxonomic status and systematics, and some gaps in the knowledge of their vectorial capacity. Here, we summarized the alternative techniques for pathogen detection in mosquitoes based on both laboratory and field studies. Parasite infection and dissemination by mosquitoes can also be obtained via analyses of saliva- and excreta-based techniques or of the whole mosquito body, using a near-infrared spectrometry (NIRS) approach. Further research should be encouraged to seek strategies for detecting target pathogens while preserving mosquito morphology, especially in biodiversity hotspot regions, thus enabling the discovery of cryptic or new species, and the determination of more accurate taxonomic, parasitological, and epidemiological patterns.

Analysis of trapped mosquito excreta as a noninvasive method to reveal biodiversity and arbovirus circulation

Emerging and endemic mosquito-borne viruses can be difficult to detect and monitor because they often cause asymptomatic infections in human or vertebrate animals or cause nonspecific febrile illness with a short recovery waiting period. Some of these pathogens circulate into complex cryptic cycles involving several animal species as reservoir or amplifying hosts. Detection of cases in vertebrate hosts can be complemented by entomological surveillance, but this method is not adapted to low infection rates in mosquito populations that typically occur in low or nonendemic areas. We identified West Nile virus circulation in Camargue, a wetland area in South of France, using a cost-effective xenomonitoring method based on the molecular detection of virus in excreta from trapped mosquitoes. We also succeeded at identifying the mosquito species community on several sampling sites, together with the vertebrate hosts on which they fed prior to being captured using amplicon-based metabarcoding on mosquito excreta without processing any mosquitoes. Mosquito excreta-based virus surveillance can complement standard surveillance methods because it is cost-effective and does not require personnel with a strong background in entomology. This strategy can also be used to noninvasively explore the ecological network underlying arbovirus circulation.

Targeting a highly repetitive genomic sequence for sensitive and specific molecular detection of the filarial parasite Mansonella perstans from human blood and mosquitoes

BACKGROUND

Mansonella perstans is among the most neglected of the neglected tropical diseases and is believed to cause more human infections than any other filarial pathogen in Africa. Based largely upon assumptions of limited infection-associated morbidity, this pathogen remains understudied, and many basic questions pertaining to its pathogenicity, distribution, prevalence, and vector-host relationships remain unanswered. However, in recent years, mounting evidence of the potential for increased Mansonella infection-associated disease has sparked a renewal in research interest. This, in turn, has produced a need for improved diagnostics, capable of providing more accurate pictures of infection prevalence, pathogen distribution, and vector-host interactions.

METHODOLOGY/PRINCIPAL FINDINGS

Utilizing a previously described pipeline for the discovery of optimal molecular diagnostic targets, we identified a repetitive DNA sequence, and developed a corresponding assay, which allows for the sensitive and species-specific identification of M. perstans in human blood samples. Testing also demonstrated the ability to utilize this assay for the detection of M. perstans in field-collected mosquito samples. When testing both sample types, our repeat-targeting index assay outperformed a ribosomal sequence-targeting reference assay, facilitating the identification of additional M. perstans-positive samples falsely characterized as "negative" using the less sensitive detection method.

CONCLUSIONS/SIGNIFICANCE

Through the development of an assay based upon the systematic identification of an optimal DNA target sequence, our novel diagnostic assay will provide programmatic efforts with a sensitive and specific testing platform that is capable of accurately mapping M. perstans infection and determining prevalence. Furthermore, with the added ability to identify the presence of M. perstans in mosquito samples, this assay will help to define our knowledge of the relationships that exist between this pathogen and the various geographically relevant mosquito species, which have been surmised to represent potential secondary vectors under certain conditions. Detection of M. perstans in mosquitoes will also demonstrate proof-of-concept for the mosquito-based monitoring of filarial pathogens not vectored primarily by mosquitoes, an approach expanding opportunities for integrated surveillance.

Integrated xenosurveillance of Loa loa, Wuchereria bancrofti, Mansonella perstans and Plasmodium falciparum using mosquito carcasses and faeces: A pilot study in Cameroon

BACKGROUND

Community presence of loiasis must be determined before mass drug administration programmes for lymphatic filariasis and onchocerciasis can be implemented. However, taking human blood samples for loiasis surveillance is invasive and operationally challenging. A xenosurveillance approach based on the molecular screening of mosquitoes and their excreta/feces (E/F) for Loa loa DNA may provide a non-invasive method for detecting the community presence of loiasis.

METHODS

We collected 770 wild mosquitoes during a pilot study in a known loiasis transmission area in Mbalmayo, Cameroon. Of these, 376 were preserved immediately while 394 were kept in pools to collect 36-hour E/F samples before processing. Carcasses and E/F were screened for L. loa DNA. To demonstrate this method's potential for integrated disease surveillance, the samples were further tested for Wuchereria bancrofti, Mansonella perstans, and Plasmodium falciparum.

RESULTS

Despite limited sample numbers, L. loa DNA was detected in eight immediately-stored mosquitoes (2.13%; 95% CI 1.08 to 4.14), one carcass stored after providing E/F (0.25%; 95% CI 0.04 to 1.42), and three E/F samples (estimated prevalence 0.77%; 95% CI 0.15 to 2.23%). M. perstans and P. falciparum DNA were also detected in carcasses and E/F samples, while W. bancrofti DNA was detected in E/F. None of the carcasses positive for filarial worm DNA came from pools that provided a positive E/F sample, supporting the theory that, in incompetent vectors, ingested parasites undergo a rapid, complete expulsion in E/F.

CONCLUSIONS

Mosquito xenosurveillance may provide a useful tool for the surveillance of loiasis alongside other parasitic diseases.

Molecular Survey of Vector-Borne Pathogens in Ticks, Sheep Keds, and Domestic Animals from Ngawa, Southwest China

Vector-borne pathogens are mainly transmitted by blood-feeding arthropods such as ticks, mosquitoes, fleas, lice, mites, etc. They pose a significant threat to animal and human health due to their worldwide distribution. Although much work has been performed on these pathogens, some neglected areas and undiscovered pathogens are still to be further researched. In this study, ticks (Haemaphysalis qinghaiensis), sheep keds (Melophagus ovinus), and blood samples from yaks and goats were collected in Ngawa Tibetan and Qiang Autonomous Prefecture located on the eastern edge of the Qinghai–Tibet Plateau, Southwest China. Several vector-borne bacterial pathogens were screened and studied. Anaplasma bovis strains representing novel genotypes were detected in ticks (8.83%, 37/419), yak blood samples (45.71%, 64/140), and goat blood samples (58.93%, 33/56). Two spotted fever group (SFG) Rickettsiae, Candidatus Rickettsia jingxinensis, and a novel Rickettsia species named Candidatus Rickettsia hongyuanensis were identified in ticks. Another Rickettsia species closely related to the Rickettsia endosymbiont of Polydesmus complanatus was also detected in ticks. Furthermore, a Coxiella species was detected in ticks (3.34%, 14/419), keds (1.89%, 2/106), and yak blood (0.71%, 1/140). Interestingly, another Coxiella species and a Coxiella-like bacterium were detected in a tick and a goat blood sample, respectively. These results indicate the remarkable diversity of vector-borne pathogens circulating in this area. Further investigations on their pathogenicity to humans and domestic animals are still needed.

Liquid Biopsy for Promising Non-invasive Diagnostic Biomarkers in Parasitic Infections

BACKGROUND

Liquid biopsy refers to the sampling and molecular analysis of body fluids such as blood, saliva, and urine in contrast to conventional tissue biopsies. Liquid biopsy approach can offer powerful non-invasive biomarkers (circulating markers) for diagnosis and monitoring treatment response of a variety of diseases, including parasitic infections.

METHODS

In this review, we concentrate on cell-free DNA (cfDNA), microRNA (miRNA), and exosomes in the published literature.

RESULTS

Considering the high prevalence and severity of parasitic infections worldwide, circulating biomarkers can provide a new insight into the diagnosis and prognosis of parasites in the near future. Moreover, identifying and characterizing parasite- or host-derived circulating markers are important for a better understanding of the pathogenesis of parasite infection and host-parasite relationship at the molecular level. Profiling of biomarkers for parasitic diseases is a promising potential field, though further studies and optimization strategies are required, both in vitro and in vivo.

CONCLUSION

In this review, we discuss three approaches in the liquid biopsy including circulating cfDNA, miRNAs, and exosomes for diagnosis and evaluation of parasites and summarize circulating biomarkers in non-invasive samples during parasitic infections.

Evaluating the Diagnostic Test Accuracy of Molecular Xenomonitoring Methods for Characterizing Community Burden of Lymphatic Filariasis

Background

Molecular xenomonitoring (MX), the detection of pathogen DNA in mosquitoes, is a recommended approach to support lymphatic filariasis (LF) elimination efforts. Potential roles of MX include detecting presence of LF in communities and quantifying progress towards elimination of the disease. However, the relationship between MX results and human prevalence is poorly understood.

Methods

We conducted a systematic review and meta-analysis from all previously conducted studies that reported the prevalence of filarial DNA in wild-caught mosquitoes (MX rate) and the corresponding prevalence of microfilaria (mf) in humans. We calculated a pooled estimate of MX sensitivity for detecting positive communities at a range of mf prevalence values and mosquito sample sizes. We conducted a linear regression to evaluate the relationship between mf prevalence and MX rate.

Results

We identified 24 studies comprising 144 study communities. MX had an overall sensitivity of 98.3% (95% confidence interval, 41.5–99.9%) and identified 28 positive communities that were negative in the mf survey. Low sensitivity in some studies was attributed to small mosquito sample sizes (<1000) and very low mf prevalence (<0.25%). Human mf prevalence and mass drug administration status accounted for approximately half of the variation in MX rate (R² = 0.49, P < .001). Data from longitudinal studies showed that, within a given study area, there is a strong linear relationship between MX rate and mf prevalence (R² = 0.78, P < .001).

Conclusions

MX shows clear potential as tool for detecting communities where LF is present and as a predictor of human mf prevalence.