Toxocara canis is a widespread parasitic nematode predominantly affecting dogs, especially puppies, and is recognised as a major causative agent of visceral larva migrans in humans. Traditional diagnostic methods, including morphological examination of eggs or larvae and serological tests, often lack the required specificity to reliably distinguish T. canis from other Toxocara species or related nematodes. Morphological similarities between species, particularly at larval stages, frequently lead to misidentification, while serological cross‑reactivity complicates the interpretation of results. In this context, molecular genetic markers offer a more precise and reliable approach for species identification and phylogenetic studies, enabling researchers to overcome the limitations of conventional methods.
The present work aims to achieve several key objectives. Firstly, it reviews the principal molecular genetic markers employed for the identification of T. canis. Secondly, it evaluates the effectiveness of these markers in differential diagnosis, considering both sensitivity and specificity. Thirdly, it discusses the role of molecular markers in phylogenetic analysis, highlighting their contribution to understanding evolutionary relationships among nematode species. Finally, the study outlines future perspectives in the field, emphasising emerging technologies and their potential applications.
Several genetic regions have been utilised as molecular markers for T. canis, each offering distinct advantages depending on the specific research objective. The internal transcribed spacer (ITS) regions of ribosomal DNA (rDNA), comprising ITS‑1 and ITS‑2, are characterised by high inter‑species variability coupled with intra‑species conservation. These features make ITS sequences particularly suitable for differentiating T. canis from T. cati and other nematodes. Polymerase chain reaction (PCR) amplification of ITS regions, followed by sequencing, allows for precise species identification, providing a reliable tool for diagnostic purposes.
Mitochondrial DNA (mtDNA) genes, such as cox1 (cytochrome c oxidase subunit 1) and cytb (cytochrome b), exhibit relatively high mutation rates, rendering them valuable for intraspecific variation studies. These markers are particularly useful in population genetics and phylogeographic analysis of T. canis, offering higher resolution for distinguishing closely related isolates compared to nuclear markers. The analysis of mitochondrial genes enables researchers to trace geographic distribution patterns and migration routes of parasite populations, contributing to a better understanding of transmission dynamics.
Ribosomal RNA genes, including 18S and 28S rRNA, are more conserved and are primarily employed in higher‑level phylogenetic studies, such as those addressing relationships at the family or genus level. Although these genes display lower variability compared to ITS regions, they play a crucial role in establishing evolutionary relationships among nematode genera. Their conserved nature allows for the alignment of sequences across distantly related taxa, facilitating the reconstruction of deep phylogenetic branches.
Single nucleotide polymorphisms (SNPs), representing single‑base variations in the genome, serve as high‑resolution markers for population studies. The advent of next‑generation sequencing (NGS) technologies has significantly enhanced the identification of numerous SNPs across the T. canis genome. SNP analysis enables the detection of fine‑scale genetic structure and transmission patterns, providing insights into the epidemiology of toxocariasis. This approach is particularly valuable for tracking the spread of specific parasite strains and identifying potential sources of infection.
The implementation of molecular markers has significantly improved the accuracy of T. canis diagnosis, addressing several limitations of traditional methods. PCR assays targeting species‑specific sequences in ITS or mtDNA regions minimise cross‑reactivity with other parasites, ensuring high specificity. Furthermore, molecular methods demonstrate remarkable sensitivity, capable of detecting low levels of parasite DNA in clinical samples, such as faeces or tissues, as well as in environmental samples, including soil. This sensitivity is critical for early detection and monitoring of infection prevalence.
Real‑time PCR and loop‑mediated isothermal amplification (LAMP) offer rapid results compared to conventional diagnostic techniques, facilitating timely intervention and control measures. These methods are especially valuable in epidemiological surveys and outbreak investigations, where quick identification is paramount. Moreover, molecular markers effectively differentiate T. canis from T. cati, two species that are morphologically similar but differ in host preference and zoonotic potential. Accurate differentiation prevents misdiagnosis and ensures appropriate public health responses.
Molecular genetic markers are indispensable for elucidating the evolutionary history and relationships of T. canis. Sequences of ITS, cox1, or 18S rRNA are routinely used to construct phylogenetic trees, revealing the evolutionary relationships among Toxocara species and other ascarid nematodes. These analyses contribute to a comprehensive understanding of parasite diversification and adaptation strategies.
Mitochondrial markers, in particular, aid in tracing the geographic distribution and migration patterns of T. canispopulations, shedding light on historical dispersal events and contemporary transmission routes. Phylogenetic analysis can also identify strains with higher zoonotic risk, thereby informing public health interventions and risk mitigation strategies. Comparative studies of genetic markers across species provide insights into the evolution of host specificity and pathogenicity, helping to unravel the mechanisms underlying parasite‑host interactions.
Despite their undeniable advantages, molecular markers are not without limitations. PCR‑based methods are susceptible to DNA contamination, which may lead to false‑positive results, necessitating stringent laboratory protocols and controls. The implementation of advanced molecular techniques requires specialised equipment and trained personnel, posing challenges in resource‑poor settings where toxocariasis is often endemic.
Intraspecific variation in marker regions may complicate species identification if reference sequences are incomplete or poorly curated. Additionally, gaps in sequence databases can result in misidentification, highlighting the need for continuous updating and expansion of genetic repositories. Standardisation of protocols and quality control measures is essential to ensure the reliability and reproducibility of molecular diagnostics.
Advances in molecular biology present promising avenues for improving T. canis diagnostics and phylogenetics. Whole‑genome sequencing (WGS) offers comprehensive genetic data, enabling the discovery of novel markers and a deeper understanding of parasite biology, including virulence factors and drug resistance mechanisms. Environmental metagenomics holds potential for detecting T. canis DNA in soil and water, aiding surveillance and risk assessment in endemic areas.
Emerging CRISPR‑based diagnostic technologies promise rapid, field‑deployable tools with high specificity, potentially revolutionising point‑of‑care testing. Improved bioinformatics tools and algorithms for sequence analysis and phylogenetic reconstruction will further enhance data interpretation, facilitating large‑scale studies and global collaborations.
Molecular genetic markers have fundamentally transformed the differential diagnosis and phylogenetic analysis of Toxocara canis. Markers such as ITS regions, mitochondrial genes, and SNPs provide high specificity and sensitivity, overcoming the limitations of traditional methods. These tools not only facilitate accurate species identification but also offer valuable insights into the evolutionary relationships and population dynamics of T. canis. Continued advancements in molecular techniques and bioinformatics will further enhance our ability to control and prevent toxocariasis, ultimately protecting both animal and human health.
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