Extracellular vesicles (EVs) are a heterogeneous group of membrane vesicles secreted by nearly all cell types in normal physiology, and the secretion of their content is influenced by the cells’ current pathophysiological state (Yáñez-Mó et al., 2015). They are classified based on their generation mechanism, including ectosomes, apoptotic bodies and exosomes (Martelli et al., 2018). Ectosomes, known as microvesicles, typically range from 200 to 2,000 nm in size and is generated through outward buddings from the plasma membrane (Wu et al., 2021). Microvesicles mainly contain cytosolic and plasma membrane-associated proteins, such as tetraspanins. They also carry cytoskeletal proteins, heat-shock proteins, integrins and post-translationally modified proteins that have undergone glycosylation and phosphorylation (Doyle and Wang, 2019). The discovery of new proteins in microvesicles have spurred global interest in fully understanding their contents for diagnostic and therapeutic potential. In malaria infection caused by Plasmodium vivax, a rise in the level of plasma-derived microvesicles has been observed in the blood of patients, which potentially allows disease detection at an earlier stage (Campos et al., 2010). Apoptotic bodies, meanwhile, are vesicles with a size ranging from 500 nm to 2 μm, and are discharged by dying cells into the extracellular space. They contain broken down cellular particles, such as intact organelles, chromatin and small amounts of glycosylated proteins (Borges et al., 2013). A recent study has demonstrated that these vesicles may be used as a non-invasive method to track apoptosis in patients with cerebrovascular and neurodegenerative diseases for prognostic purposes (Serrano-Heras et al., 2020).

Exosomes are nanometer-sized (50–150 nm) intraluminal vesicles (ILV) of multivesicular bodies (MVB) secreted by various cells, including the microglia (Mashouri et al., 2019; Fan et al., 2022). They have double membrane structure (Saadatpour et al., 2016) that originates from endocytic compartments and are matured in the MVB of late endosomes (Statello et al., 2018). MVBs can fuse with the plasma membrane, leading to the release of ILVs into the extracellular space as exosomes (Colombo et al., 2014). Exosomes are surrounded by a lipid bilayer, carrying a variety of biomolecules, such as glycans, proteins, metabolites, lipids, DNA, and RNA, including miRNA (Chung et al., 2020). They can potentially serve as an important medium for cell-to-cell or cell-to-internal environment communication (Jeppesen et al., 2019), and the biomolecules may alter physiological responses by mediating short- and long-distance inter-organ communication (Fatima and Nawaz, 2017). Exosomes are less immunogenic, non-cytotoxic and non-mutagenic to their target cells compared with other gene delivery vehicles (O’Loughlin et al., 2012). Depending on the molecules they carry, exosomes can perform a variety of roles, such as encouraging cell proliferation, migration, lowering oxidative stress and preventing apoptosis, besides mediating immune responses like cytokine secretion and inhibition or stimulation of inflammasomes (Noonin and Thongboonkerd, 2021). Emerging findings have suggested that exosomes may play a key role in mediating infection and inflammatory processes (Xie et al., 2022).

Infection by a vector-borne disease will trigger the effects of a host-parasite interaction, which facilitates the parasite’s long-term survival in the host body (Podolska and Nadolna, 2014). The host-parasite interaction can also trigger the host immune response and enhance pathogen diffusion (Cox et al., 2012). As parasites interact with host cells through excretory-secretory channels, the exosomes within excretory-secretory products will naturally serve as a route for successfully mediating the parasite’s contact for host manipulation. It also makes sense that the host would utilize this pathway as a defense mechanism (Nawaz et al., 2019).

Recently, exosomes have gained much research attention in biomarker development as they contain specific proteins, microRNAs (miRNAs) and signaling molecules that are associated with disease progression (Hoshino et al., 2015). Exosome miRNA is highly accessible and stable, thus raising its potential use in precision medicine (Muinelo-Romay et al., 2018). However, studies on the role of exosomes in vector-borne diseases are nonetheless limited by inefficient separation techniques, a lack of distinctive biomarkers, and challenges in obtaining high-resolution imaging methods. Exosomes contain identical protein and RNA profiles to the cells that produce them. However, very few distinct cell-specific proteins and miRNAs exist (Li et al., 2017). Furthermore, exosomes from pathogen-infected cells are heterogeneous, and their concentration exists in a different range than the standard level (Reyes-Ruiz et al., 2019). In this review, we collated and updated the role of exosomal plasma miRNA in various diseases, and then examined the scope of miRNA-derived from plasma exosomes as a reliable diagnostic tool for vector-borne diseases.

Article search and data collection were performed on PubMed, Google Scholar, and World Health Organization (WHO) databases. It included peer-reviewed articles with original data from 2010 to 2022. Non-peer-reviewed articles, conference abstracts, letters, articles without full-text were excluded. All articles were collected and compiled using the Mendeley application to eliminate duplicates. A PubMed database search using the keywords “extracellular vesicles and vector bore diseases” resulted in a total of 225 articles. After subsequently applying the keywords “exosomes and vector-borne disease,” a total of 115 articles were produced. As the search was narrowed down with the keywords “miRNA biomarker and vector bore diseases,” the articles were further reduced to 79. Finally, 31 articles remained when the second parameter “plasma miRNA and vector-borne diseases” was added. The articles were manually divided into two groups: “original articles” and “others” (not related to topic, reviews, reports, editorials, commentaries, etc.). The original articles addressing plasma exosome miRNA and vector-borne diseases became the focus of the study and were used as material in this review.

Exosomes are critical paracrine mediators that may be detected in bodily fluids, including plasma (Carrozzo et al., 2021). The content of human plasma exosomes have been linked to a variety of physiological and pathological conditions (Yáñez-Mó et al., 2015). Such exosomes may be isolated using ultracentrifugation, polymer-based precipitation kits, size exclusion chromatography, immunoaffinity, and ultrafiltration (Kalra et al., 2013). Ultracentrifugation and polymer-based precipitation kits are the most popular methods, but the former has several limitations, including low exosome concentration and considerable albumin contamination (Baranyai et al., 2015). These may be resolved by changing the isolation parameters, such as viscosity, sedimentation distance and temperature, or by prolonging the ultracentrifugation time to increase yield (Koh et al., 2018). The presence of exosomes may be characterized using complex methods, such as nanoparticle tracking analysis, electrophoretic light scattering, transmission electron microscopy and EXOCET colorimetric assay, or simple protein quantification like Western blotting (Martins et al., 2018). In blood samples, plasma exosomes have a higher concentration of miRNA compared with serum, and this may serve as a better sample for blood-based proteomics research of exosomes (Cao et al., 2019). Plasma cells may be more protected from degradation and this enables more accurate distribution of target cells, providing a distinctive perspective into pertinent diseases, or defining novel diagnostic and prognostic potential for different disorders (Ludwig et al., 2017). Hence, plasma-derived exosomes are a clinically valuable biomarker to assess the immune system of patients because its molecular profiling and protein monitoring may show the degree of immunological suppression before and during treatment (Ludwig et al., 2017).

MiRNA are naturally occurring short non-coding RNA molecules with a length of about 21–25 nucleotides (Ha and Kim, 2014). MiRNA from exosomes may affect the body’s physiological modulation and disease progression (Liu et al., 2020). Depending on disease condition, the level of miRNA in bodily fluids will be up- or down-regulated (Abdellatif, 2012). The miRNA level in blood, for example, is affected by various factors and will differ from sample to sample (e.g., plasma, serum, and other fluids) (Blondal et al., 2013). Hemolysis can influence the expression of miRNA in serum, but plasma-derived miRNA is unaffected (Foye et al., 2017). MiRNA in the exosomal plasma are in more stable form than any other bodily fluids because they are protected from endogenous RNase degradation (Köberle et al., 2013). This makes them useful in the diagnosis of infectious diseases, besides diseases of the central nervous system and respiratory systems, including malignancy (Alipoor et al., 2016).

During the early stage of human immunodeficiency virus-1 (HIV-1) infection, changes in exosomal miR-155 expression play a role in the development of an effective antiviral effector response by CD8 T cells and at the same time increase the number of regulatory T cells (Lind et al., 2013). Thus, exosomal miRNA involved in the regulation of immune and inflammatory responses, and also serve as an excellent companion in the diagnosis of HIV infection (Hubert et al., 2015). Tuberculosis is another infectious disease that is currently screened by microscopic examination and confirmed using genotypic assays (line probe assay, cartridge-based nucleic acid amplification test, or loop-mediated isothermal amplification), besides the gold standard culture methods (liquid culture media) (Chopra and Singh, 2020). Still, there is research on finding a reproducible, efficient, cost-effective tool with minimal infrastructure requirements for this infectious disease. Recently, upregulated miRNA-185-5p expression in exosome plasma has been identified in tuberculosis (Kaushik et al., 2021). In hepatitis C (HCV), immunomodulatory miRNA enrichment exosomes are found to be associated with their inhibitory activity on innate immune cell function. This may provide valuable biomarkers to monitor immune response recovery (Santangelo et al., 2018).

Most recently, reverse-transcription polymerase chain reaction (RT-PCR) has been mainly used to confirm COVID-19 infection. However, false-negatives may occur in a small percentage of tests due to a low viral load in patient samples (Anand et al., 2021). The use of exosomes as a diagnostic tool for COVID-19 has yet to be widely studied. Therefore, there is an immediate need to study and develop an alternative method that is more sensitive, specific and easy to apply. The study of the exosomal cargo may provide key information with respect to differential secretion of miRNA in SARS-CoV 2 infected cells compared with uninfected cells. Table 1 summarizes the exosomal plasma-derived miRNA biomarkers for diagnostic applications in various diseases. The preceding studies support the notion that plasma-derived exosomal miRNAs play important roles in diseases as a promising biomarker and provide knowledge for developing a new diagnostic tool for the diseases.

From DNA sequences, miRNAs are translated into precursor miRNAs (pre-miRNAs), mature miRNAs and primary miRNAs (pri-miRNAs). MiRNAs regulate protein translation by binding to the 3’ untranslated regions of mRNA template (MacFarlane and Murphy, 2010). However, it has been reported that they can also interact with other regions, including the 5’ UTR coding sequence and gene promoters (Broughton et al., 2016). These miRNAs play a crucial role in influencing molecular and cellular processes in cancer and inflammation (O’Connell et al., 2012).

Enterotoxigenic Bacteroides Fragilis (ETBF) is an enterotoxin-producing bacterium that is strongly associated with inflammatory bowel disease (IBD), colitis-associated colorectal cancer and colorectal cancer (CRC) as it has been observed to change the mucosal immune response and induce epithelial cell changes (Zamani et al., 2020). A recent study on ETBF shows that the exosomal down- regulated miR-149-3p derived from ETBF-treated cells facilitated T-helper type 17 cell differentiation and promoted the PHF5A (Plant homeodomain finger protein 5A) mediated RNA alternative splicing of the KAT2A gene in CRC cells. Thus, the ETBF/miR-149-3p pathway showed a potential solution for treatment of patients with intestinal inflammation and CRC with a high amount of ETBF (Cao et al., 2021). Plasma-derived exosomal miR-216a-5p may also inhibit rTp17-induced inflammatory cytokine production and the TLR4-MYD88 signaling pathway in syphilis infection, suggesting a possible therapeutic target for inflammation caused by the sexually transmitted disease (Peng et al., 2019).

Medulloblastoma (MB) is a malignant brain tumor that commonly affects children. Exosomal miR-101-3p and miR-423-5p from plasma of MB patients have been identified to act as tumor suppressors by directly targeting FOXP4 and EZH2 oncogenes (Xue et al., 2022). This shows that plasma-derived exosomal miRNA can control the expression of oncogenes, making them a potential therapeutic agent. An interesting study on long-term exercise-derived plasma exosome found that miR-342-5p may prevent ischemic heart disease by suppressing the level of Caspase 9 and JNK2, thus reducing hypoxia/reoxygenation-induced cardiomyocyte apoptosis; moreover, it increased survival signaling (p-Akt) by targeting the phosphatase gene Ppm1f (Hou et al., 2019). These studies provided the information needed to understand the role plasma-derived exosomal miRNA as a therapeutic agent by controlling the expression of genes that cause various diseases.

Vector-borne diseases are infections caused by pathogens that are usually transmitted by arthropods, such as mosquitoes, triatomine bugs, black flies, tsetse flies, sand flies, lice and ticks (Golding et al., 2015). However, they may also include other carriers such water snails, which serve as a reservoir for Schistosomiasis. In the case of insects, they include dengue, Chagas disease, Japanese encephalitis, leishmaniasis, lymphatic filariasis, malaria, and yellow fever, which all together threaten more than 80% of the world’s population. They are inordinately distributed in the tropics and subtropics (Chala and Hamde, 2021), and the World Health Organization (WHO) estimated that they account for more than 700,000 deaths annually (World Health Organization, 2022a). Figure 1 shows the number of vector-borne cases reported worldwide from 2011 to 2020. Table 2 summarizes the laboratory method for vector-borne disease detection in the host and its vectors.

When feeding on their hosts, arthropods release exosomes into the host blood through their saliva (Figure 2; Oliva Chávez et al., 2021). In response, the host cells will also release their own exosomes to inhibit the transmission of pathogens (Alenquer and Amorim, 2015). This increases exosome concentrations in the plasma and other body fluids (Opadokun and Rohrbach, 2021). As a result, exosomes from the host and pathogen will play distinct roles in the survival and suppression of vector-borne diseases.

The exosomes in the arthropod’s saliva can be considered a carrier for various biological processes in vector-borne diseases. They transfer antigens, proteins and RNA into the host cell to influence metabolic processes, gene expression and immunological responses (Figure 2; Yuan et al., 2021). Through this process, these exosomes may facilitate the transmission of arboviruses that cause dengue and encephalitis to mammals (Zhou et al., 2019). The discovery of exosomes produced by arthropods has spurred the development of new methods to prevent the spread of vector-borne diseases through the understanding of molecular determinants in the mode of pathogen transmission. A Malaysian study has found that the EV secreted by Aedes albopictus and Aedes aegypti contains a tetraspanin domain-containing glycoprotein known as Tsp29Fb that could facilitate the transmission of Dengue Virus 2 (DENV2) in host cells (Vora et al., 2018). This study has led to a novel proposal to restrict the transmission of DENV2 and other mosquito-borne flaviviruses to mammalian cells by inhibiting the effects of Tsp29Fb in mosquitoes using the GW4869 inhibitor. A proteomic study on exosomes of Drosophila cells infected by the cricket paralysis virus (CrPV) also revealed that they contained viral RNA to facilitate the spread of the pathogen’s genetic material in the host (Kerr et al., 2018).

Pathogen surveillance in arthropods may provide essential details for disease control. A central American study tried to discover the best method to survey the prevalence of Trypanosoma cruzi that causes Chagas disease in the vector Triatoma dimidiata (blood-sucking bug) (Stevens et al., 2021). The researchers concluded that using genotype-by-sequencing (GBS) was twice superior in detecting the pathogen in its vector compared with PCR assay (based on a test with the significant agreement; 53% vs. 19%) However, the difficulty of pathogen detection in insects may be caused by genetic variations in the parasite itself, and this can affect the disease surveillance and control process. Meanwhile, detection of the EV secreted by pathogens may also assist in the development of new clinical biomarkers and therapeutic agents. The study of exosomes in Brugia malayi has found that miRNA let-7 (lethal 7) could function as a biomarker for lymphatic filariasis disease (Zamanian et al., 2015). Table 3 summarizes the potential miRNA biomarkers for vector-borne diseases. Table 4 summarizes the exosomal miRNA biomarkers for diagnostic applications in vector-borne diseases.

The currently available diagnostic methods for many vector-borne diseases are insufficient and have many limitations. Most of the detection is dependent on the existence of signs and symptoms, or antibodies of particular pathogen. Therefore, there is an urgent need to support the development of new biomarker techniques in diagnostic platforms. Plasma-derived exosome miRNAs are more stable, reliable and highly concentrated than any other bodily fluids. Recent studies have indicated that exosomal miRNA within excretory-secretory products may serve as a route for successfully mediating parasite-host contacts for host manipulation. Interestingly, previous studies discovered certain differentially expressed host plasma-derived exosome miRNAs that may be potential diagnostic and prognostic biomarker of vector-borne diseases. However, there is still limited research of plasma exosome in vector-borne diseases as compared with other diseases such as malignancy. The lack of consistent definitions and a standard method causes considerable confusion in the laboratory study of exosomes. We believe that further research in this area will solve the problem, and provide the new ideas and approaches for the application of plasma-derived exosome miRNA in clinical practice.

GV conducted the literature search and drafted the manuscript. WS conceived the idea of this review and gathered the data. WNS, SI, and AM gave critical ideas in drafting the manuscript. All authors approved the final submission of this manuscript.