Toxocariasis: seroprevalence in abandoned-institutionalized children and infants

Seroprevalence of human toxocariasis in Latin America and the Caribbean: a systematic review and meta-analysis

Introduction

The current study aimed to quantitatively synthesize available evidence regarding the seroprevalence of human toxocariasis in Latin America and the Caribbean.

Methods

A systematic research involving six electronic databases was conducted using a research strategy that combined MeSH terms with free terms. Article selection and information extraction were performed using a double and independent approach. The Newcastle-Ottawa tool was used to assess the risk of bias in the included articles. The meta-analysis used the random-effects approach, with subgroup analysis and sensitivity analysis for risk of bias also being performed.

Results

We included 101 articles with a total of 31,123 participants. The studies were conducted between 1990 and 2022, with Brazil accounting for the largest number of studies (n = 37). The overall seroprevalence of human toxocariasis was 31.0% (95% CI: 27.0-35.0%, I2 = 99%). The prevalence of the main characteristics observed in seropositive patients were as follows: ocular toxocariasis (30.0%), asymptomatic (26.0%), and presence of dogs at home (68.0%). In addition, the seroprevalence was lower in studies including only adults than in those including children or both. In contrast, no differences in seroprevalences were found between studies conducted in the community and hospital.

Conclusion

The overall seroprevalence of human toxocariasis in Latin America and the Caribbean was high. Notably, our findings showed that the seroprevalence was increased among populations who kept a dog at home but was decreased in populations comprising only adults. Our findings can be used to establish epidemiological surveillance strategies for the prevention and early identification of toxocariasis.

The global prevalence of Toxocara spp. in pediatrics: a systematic review and meta-analysis

BACKGROUND

Toxocariasis is a zoonotic parasitic disease caused by Toxocara canis and Toxocara cati in humans. Various types of T. canis are important.

PURPOSE

The current study aimed to investigate the prevalence of Toxocara spp. in pediatrics in the context of a systematic review and meta-analysis.

METHODS

The MEDLINE (PubMed), Web of Sciences, Embase, Google Scholar, Scopus, and Cumulative Index of Nursing and Allied Health databases were searched to identify peer-reviewed studies published between January 2000 and December 2019 that report the prevalence of Toxocara spp. in pediatrics. The evaluation of articles based on the inclusion and exclusion criteria was performed by 2 researchers individually.

RESULTS

The results of 31 relevant studies indicated that the prevalence of Toxocara spp. was 3%-79% in 10,676 cases. The pooled estimate of global prevalence of Toxocara spp. in pediatrics was 30 (95% confidence interval, 22%-37%; I2=99.11%; P=0.00). The prevalence was higher in Asian populations than in European, American, and African populations.

CONCLUSION

Health policymakers should be more attentive to future research and approaches to Toxocara spp. and other zoonotic diseases to improve culture and identify socioeconomically important factors.

Development of a low-cost copro-LAMP assay for simultaneous copro-detection of Toxocara canis and Toxocara cati

Toxocariasis is a zoonotic disease caused mainly by Toxocara canis and Toxocara cati and diagnosis in dogs and cats is an important tool for its control. For this reason, a new coprological loop-mediated isothermal amplification (LAMP) assay was developed for the simultaneous detection of these species. The primer set was designed on a region of the mitochondrial cox-1 gene. Amplification conditions were evaluated using a temperature gradient (52°C to 68°C), different incubation times (15–120 min), and different concentrations of malachite green dye (0.004–0.4% w/v). The analytical sensitivity was evaluated with serial dilutions of genomic DNA from T. canis and T. cati adult worms, and with serial dilutions of DNA extracted from feces using a low-cost in-house method. The specificity was evaluated using genomic DNA from Canis lupus familiaris, Felis catus, Escherichia coli, Toxascaris leonina, Ancylostoma caninum, Echinococcus granulosus sensu stricto and Taenia hydatigena. The LAMP assay applied to environmental fecal samples from an endemic area showed an analytical sensitivity of 10–100 fg of genomic DNA and 10−5 serial dilutions of DNA extracted from feces using the low-cost in-house method; with a specificity of 100%. Additionally, the total development of the assay was carried out in a basic laboratory and per-reaction reagent cost decreased by ~80%. This new, low-cost tool can help identify the most common agents of toxocariasis in endemic areas in order to manage prevention strategies without having to rely on a laboratory with sophisticated equipment.

High Seroprevalence of Toxocara Infection among Mentally Retarded Patients in Hormozgan Province, Southern Iran

Mentally retarded individuals are more likely to become infected with soil-transmitted infections including toxocariasis. The current study aimed to determine the serostatus of toxocariasis among institutionalized mentally retarded individuals in Hormozgan Province, in the south of Iran. Subjects of the study were 117 mentally disabled individuals, including children and adults, maintained in a charity-based institution. Three millilitres of venous blood was taken from each subject. While sampling, demographic features of the subject were documented in a questionnaire. An ELISA system based on Toxocara larvae excretory-secretory antigens (TES) was utilized to detect anti-Toxocara IgG antibodies in the sera of the patients. The mean age of the subject was 27.6 (±12.31) years and consisted of 55 (47%) males and 62 (53%) females. Out of 117 cases, 33 (28.2%) were seropositive for toxocariasis. The seroprevalence was higher in females (37.1%) than males (18.2%), and the difference was statistically significant (p < 0.05). Out of 117 subjects, 76 (64.9%) had severe and 41 (35.1%) had profound mental retardation. Anti-Toxocara antibodies were detected in 18 (23.7%) patients with severe and 15 (35.6%) patients with profound mental retardation. The highest seroprevalence rate of toxocariasis (44.4%) was observed in the age group of ≤10 years followed by 21–30 years old (36.7%). No statistically significant association was seen between the age and also the duration of residency in the care center and seropositivity of toxocariasis (p > 0.05). The current study represents the high prevalence of toxocariasis in mentally retarded patients in Hormozgan Province, southern Iran. The elevated seroprevalence rate of toxocariasis in the current study indicates that these subjects constitute a high-risk group for Toxocara infection, which may be attributed to their behavioral patterns.

Visceral larva migrans detection using PCR-RFLP in BALB/c mice infected with Toxocara canis

Toxocara canis is an important zoonotic roundworm distributed worldwide. The infective larvae of T. canis are one of the causes of visceral larva migrans (VLM), a clinical syndrome in humans. Diagnosing VLM is difficult, and the differential diagnosis of the larval development stage is limited. Therefore, this experimental research aimed to diagnose T. canis larvae using a molecular method, not only in liver tissue, which is the most commonly affected tissue, but also in the limb muscles, lungs and brain tissues. For this purpose, 24 BALB/c mice were infected with 1000 embryonated T. canis eggs. Necropsies were performed on the second, fourth, seventh and 14th days post-infection. While a part of the samples were digested with pepsin-HCl, the molecular method was used for the remainder of the samples to replicate the mitochondrial DNA adenosine triphosphate (ATP) synthase subunit-6 gene region of T. canis. BbsI, a restriction endonuclease, was used to determine the specificity of the amplicons obtained from Polymerase chain reaction (PCR). The detection limit for embryonated eggs was recorded. The PCR results showed that the sensitivity of the PCR analysis was 83.3% in the liver (with 88.8% accuracy), 87.5% in the lungs (with 91.6% accuracy) and 75.0% in the brain, forelimb and hindlimb muscles (with 83.3% accuracy). In all tissues, the test specificity was determined to be 100%. In this study, the molecular method was applied to only experimentally infected BALB/c mice tissues; thus, it is suggested that it can be also employed in different paratenic hosts and materials possibly infected with T. canis.

Tissue expression pattern of ABCG transporter indicates functional roles in reproduction of Toxocara canis

Toxocara canis is a zoonotic parasite with worldwide distribution. ATP-binding cassette (ABC) transporters are integral membrane proteins which involve in a range of biological processes in various organisms. In present study, the full-length coding sequence of abcg-5 gene of T. canis (Tc-abcg-5) was cloned and characterized. A 633 aa polypeptide containing two conserved Walker A and Walker B motifs was predicted from a continuous 1902 nt open reading frame. Quantitative real-time PCR was employed to determine the transcriptional levels of Tc-abcg-5 gene in adult male and female worms, which indicated high mRNA level of Tc-abcg-5 in the reproductive tract of adult female T. canis. Tc-abcg-5 was expressed to produce rabbit polyclonal antiserum against recombinant TcABCG5. Indirect-fluorescence immunohistochemical assays were carried out to detect the tissue distribution of TcABCG5, which showed predominant distribution of TcABCG5 in the uterus (especially in the germ cells) of adult female T. canis. Tissue transcription and expression pattern of Tc-abcg-5 indicated that Tc-abcg-5 might play essential roles in the reproduction of this parasitic nematode.

Molecular characterization and transcriptional analysis of the female-enriched chondroitin proteoglycan 2 of Toxocara canis

Toxocara canis is an important but neglected zoonotic parasite, and is the causative agent of human toxocariasis. Chondroitin proteoglycans are biological macromolecules, widely distributed in extracellular matrices, with a great diversity of functions in mammals. However, there is limited information regarding chondroitin proteoglycans in nematode parasites. In the present study, a female-enriched chondroitin proteoglycan 2 gene of T. canis (Tc-cpg-2) was cloned and characterized. Quantitative real-time polymerase chain reaction (qRT-PCR) was employed to measure the transcription levels of Tc-cpg-2 among tissues of male and female adult worms. A 485-amino-acid (aa) polypeptide was predicted from a continuous 1458-nuleotide open reading frame and designated as TcCPG2, which contains a 21-aa signal peptide. Conserved domain searching indicated three chitin-binding peritrophin-A (CBM_14) domains in the amino acid sequence of TcCPG2. Multiple alignment with the inferred amino acid sequences of Caenorhabditis elegans and Ascaris suum showed that CBM_14 domains were well conserved among these species. Phylogenetic analysis suggested that TcCPG2 was closely related to the sequence of chondroitin proteoglycan 2 of A. suum. Interestingly, a high level of Tc-cpg-2 was detected in female germline tissues, particularly in the oviduct, suggesting potential roles of this gene in reproduction (e.g. oogenesis and embryogenesis) of adult T. canis. The functional roles of Tc-cpg-2 in reproduction and development in this parasite and related parasitic nematodes warrant further functional studies.