Experimental toxocariasis in BALB/c mice: relationship between parasite inoculum and the IgG immune response

An evaluation of techniques to diagnose Dioctophyme renale in dogs

Dioctophyme renale is a nematode with zoonotic potential that affects the kidneys of carnivorous, wild, and domestic mammals. In this study, we sought to evaluate the indirect ELISA method against routine methods used to diagnose dioctophimosis. Hence, 38 dogs parasitized by D. renale, as confirmed by surgery, were selected. The dogs were evaluated by abdominal ultrasound and urinalysis, and their sera were tested by indirect ELISA using D. renale adult secretion and excretion antigen (DES). Five dogs were followed up with serum collections on day 0 (day of surgery) and 30, 60, and 90 days after surgery to evaluate antibody kinetics. Abdominal ultrasound and indirect ELISA successfully diagnosed 37 dogs parasitized by D. renale, while urinalysis diagnosed 29 animals. The positive animals were parasitized with 1-7 parasites; 17 dogs were infected by male and female parasites, 15 only by female parasites, and six were parasitized only by male parasites. When assessing specificity and sensitivity, all techniques showed 100% specificity and 81.6%, 97.4%, and 97.4% sensitivity for urinalysis, ultrasound, and ELISA, respectively (p < 0.001). The five positive dogs that were followed up after surgery showed a progressive decrease in mean absorbances in indirect ELISA (0.644, 0.516, 0.511, and 0.440, respectively). This study demonstrated that the indirect ELISA using the DE antigen could diagnose dioctophimosis regardless of the number, sex, and location of the parasites, with the potential to be used in epidemiological research and implementing immunological and molecular studies, opening new lines of research on D. renale.

Toward anthelmintic drug candidates for toxocariasis: Challenges and recent developments

Infections caused by parasitic helminths rank among the most prevalent infections of humans and animals. Toxocariasis, caused by nematodes of the genus Toxocara, is one of the most widespread and economically important zoonotic parasitic infections that humans share with dogs and cats. Despite the completion of the Toxocara canis draft genome project, which has been an important step towards advancing the understanding of this parasite and the search for drug targets, the treatment of toxocariasis has been dependent on a limited set of drugs, necessitating the search for novel anthelmintic agents, specially against Toxocara larvae in tissues. Given that research, development, and innovation are crucial to finding appropriate solutions in the fight against helminthiasis, this paper reviews the progress made in the discovery of anthelmintic drug candidates for toxocariasis. The main compounds reported in the recent years regards on analogues of albendazole, reactive quinone derivatives and natural produts and its analogues. Nanoparticles and formulations were also reviewed. The in vitro and/or in vivo anthelmintic properties of such alternatives are herein discussed as well as the opportunities and challenges for treatment of human toxocariasis. The performed review clarify that the scarcity of validated molecular targets and limited chemical space explored are the main bottlenecks for advancing in the field of anti-Toxocara agents.

Toxocara canis infection worsens the course of experimental autoimmune encephalomyelitis in mice

Toxocara canis, a gastrointestinal parasite of canids, is also highly prevalent in many paratenic hosts, such as mice and humans. As with many other helminths, the infection is associated with immunomodulatory effects, which could affect other inflammatory conditions including autoimmune and allergic diseases. Here, we investigated the effect of T. canis infection on the course of experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis. Mice infected with 2 doses of 100 T. canis L3 larvae 5 weeks prior to EAE induction (the Tc+EAE group) showed higher EAE clinical scores and greater weight loss compared to the non-infected group with induced EAE (the EAE group). Elevated concentrations of all measured serum cytokines (IL-1α, IL-2, IL-4, IL-6, IL-10, IL-17A, IFN-γ and TNF-α) were observed in the Tc+EAE group compared to the EAE group. In the CNS, the similar number of regulatory T cells (Tregs; CD4+FoxP3+Helios+) but their decreased proportion from total CD4+ cells was found in the Tc+EAE group compared to the EAE group. This could indicate that the group Tc+EAE harboured significantly more CD4+ T cells of non-Treg phenotype within the affected CNS. Altogether, our results demonstrate that infection of mice with T. canis worsens the course of subsequently induced EAE. Further studies are, therefore, urgently needed to reveal the underlying pathological mechanisms and to investigate possible risks for the human population, in which exposure to T. canis is frequent.

Cyclosporine A increases the intensity of Toxocara canis infection in swiss mice

Toxocariasis is a zoonotic disease of worldwide distribution. The connection between parasitic diseases and conditions that depress the immune system, such as the use of immunosuppressive drugs, has been studied. The purpose of this study was to evaluate the effect of Cyclosporine A (CsA) on the intensity of infection, humoral response and gene transcription of interleukins IL-4, IL-10 and IL-12 in mice experimentally infected with Toxocara canis. To this end, mice were divided into two groups treated with CsA (G1: 10 mg/Kg and G2: 50 mg/kg), the G3 and G4 group received PBS. After the last administration of the drug or PBS (orally every 48 hours for 15 days), groups G1, G2 and G3 were inoculated with 1200 eggs of T. canis. Was collected blood samples on days zero, 15 and 30 days post-inoculation (PI), for ELISA test and the mice were euthanized 30 days PI. The organs and striated muscle tissue were collected for the recovery of larvae. The splenocytes were analyzed by RT-PCR. The intensity of infection in the mice treated with 50 mg/kg of CsA was 65.5% higher than in the control group (p=0.001). An analysis of the kinetics of anti-Toxocara antibody revealed that the groups treated with CsA showed significantly higher mean levels of antibodies on day 15 PI. The transcription of the three tested interleukins showed no statistical difference between G2 and G3 (control). It was concluded that the immunosuppression triggered by CsA (50 mg/Kg) favored the establishment of a larger number of T. canis larvae without, however, altering immunoglobulin production and IL-4, IL-10 and IL-12 transcription on day 30 PI.

Larva migrans in BALB/c mice experimentally infected with Toxocara cati ensured by PCR assay

BACKGROUND

Toxocara cati, the cat roundworm, is a parasitic nematode that known to cause toxocariasis in intermediate hosts and humans. In this study, we characterized the dynamics of T. cati larvae migration in BALB/c mice after inoculation with eggs and ensured the migration detecting the larval DNA by a PCR. To evaluate the dynamics of larval migration and distribution, twenty-four BALB/c mice were orally inoculated with 2500 T. cati infective eggs and the visceral organs of the infected animals were examined by pepsin digestion and microscopic parasite counts, followed by PCR at day 1 to 28 post-inoculation.

RESULTS

The PCR assays were successfully used for detection of T. cati larvae in tissue samples and T. cati larvae and the DNAs were found in the liver, lungs, heart, kidneys and the brain. We detected T. cati in 92.2% of tissue samples by PCR, 30% higher than the conventional pepsin digestion technique.

CONCLUSION

Our findings demonstrated that the PCR assay is a sensitive and specific for the detection of T. cati larvae. Therefore, it could become a useful tool for the investigation of the dynamics of larval migration and Toxocara infection in murine model.

Toxocara canis 30-35 kDa excretory-secretory antigen is an important marker in mice challenged by inocula containing different parasite load levels

The Western-blotting technique was applied to identify antigenic fractions of excretory-secretory Toxocara canis antigen recognized by IgG antibodies throughout an experimental infection in mice challenged by different inocula. Mice were inoculated with 5, 50 and 500 embryonated eggs and serum samples were collected 15, 30, 60, 90 and 120 days post-infection. Serum samples were analyzed using an excretory-secretory Toxocara antigen. Antibodies recognized antigenic fractions from 30 to 90 kDa. The protein fraction of 30-35 kDa was the most frequently recognized regardless of the size of inoculum and the stage of infection represented by the different collection times, but the antigenic recognition was more evident in groups infected with 50 and 500 eggs. This study presents an antigenic panel of the excretory-secretory antigen of T. canis and suggests that the 30-35 kDa antigenic fraction is a promising marker of the infection and should be further explored in future studies on experimental toxocariasis.

Toxocara DNA amplification in serum and tissue samples in BALB/c mice

Toxocariasis is still a neglected parasitic disease worldwide and much about its biology and diagnosis has yet to be understood. The migration of third stage larvae via bloodstream suggests a potential use of molecular tools in diagnosis as well to deepen the knowledge about its migration behaviors. Conventional PCR was applied in serum and tissue samples from BALB/c mice infected with 5 and 500 embryonated eggs. Blood samples were collected at 15, 30, 60, 90 and 120 days post-infection. Organs were excised at 170 days post infection. There was no DNA amplification in serum samples in any group or day post-infection; contrarily, tissue samples showed DNA amplification. These results also support a continuous larval migration after and/or simultaneously with the neurotropic-myotropic phase. Thus, molecular tools might be useful as a differential diagnosis method, but do not replace immunodiagnostics techniques.

Human Toxocariasis: 2010 to 2020 Contributions from Brazilian Researchers

This is a review of the published contributions made by Brazilian researchers between 2010 and 2020 on the natural history of human toxocariasis and the effects of human toxocariasis on nonhuman paratenic hosts.

"Begging the Question"-Does Toxocara Infection/Exposure Associate with Multiple Sclerosis-Risk?

Although the cause of multiple sclerosis (MS) is unclear, infectious agents, including some parasitic roundworms (nematodes), have been proposed as possible risk factors or contributors. Here, we conducted a systematic review and meta-analysis of published observational studies to evaluate whether there is a possible association between infection with, or exposure to, one or more members of the genus Toxocara (phylum Nematoda; superfamily Ascaridoidea) and MS. We undertook a search of public literature databases to identify relevant studies and then used a random-effects meta-analysis model to generate the pooled odds ratio (OR) and 95% confidence intervals (CIs). This search identified six of a total of 1371 articles that were relevant to the topic; these published studies involved totals of 473 MS patients and 647 control subjects. Anti-Toxocara IgG serum antibodies were detected in 62 MS patients and 37 controls, resulting in respective seroprevalences of 13.1% (95% CI: 8.2-20.3) and 4.8% (95% CI: 2.5-9.2), indicating an association (pooled OR, 3.01; 95% CI: 1.46-6.21). Because of the publication bias identified (six eligible studies), well-designed and -controlled studies are required in the future to rigorously test the hypothesis that Toxocara infection/exposure has an association with MS.

Toxocara-induced neural larva migrans (neurotoxocarosis) in rodent model hosts

Neural larva migrans (NLM), or neurotoxocarosis, induced by Toxocara canis or Toxocara cati results from migrating and persisting larvae in the central nervous system of paratenic hosts, including humans. As the diagnosis of NLM in humans is not straightforward, most knowledge on the disease is derived from only a few published clinical cases. To improve our understanding of human NLM, studies on the pathogenesis and clinical symptoms in laboratory animal model systems are indispensable, and rodents have been accepted as the most appropriate model organisms for NLM. As research has mostly focused on neuroinvasive T. canis-larvae, information regarding the pathogenesis of T. cati-induced NLM remains scarce. This review summarises the current state of knowledge on neuroinvasion by both T. canis and T. cati in different rodent model hosts, the resulting behavioural changes, and histopathological alterations during the course of NLM as well as the potential molecular pathogenic mechanisms.

Reactivity of recombinant Toxocara canis TES-30/120 in experimentally infected mice

AIM

While the use of recombinant antigens is being widely investigated in the diagnosis of human toxocariasis, relatively little attention has been given to animal diagnostic models. For this reason, this study aimed to investigate the diagnosis potential of Toxocara canis TES-30 and TES-120 recombinant antigens in mice, the animal model for toxocariasis studies.

METHODS AND RESULTS

Serum samples obtained from mice infected with T. canis or Toxocara cati were tested by indirect ELISA using T. canis TES-30 and TES-120 recombinant antigens produced in Escherichia coli. 90% of the samples reacted with rTES-30, whereas there was almost no reactivity with rTES-120.

CONCLUSION

Despite rTES-120 being a good antigen for diagnosis in humans, it could not reproduce its reactivity in this animal model. As rTES-30 has good reactivity in mice, it is a valuable tool for diagnosis.

Detection and Evaluation of Antibody Response to a Baylisascaris-Specific Antigen in Rodent Hosts with the Use of Western Blotting and Elisa

Diagnosis of parasitic diseases that involve tissue-stage larvae is challenging, and serology remains the most effective antemortem test for detecting these infections. Baylisascaris procyonis, the raccoon roundworm, is a zoonotic ascarid. Raccoons are the usual definitive host, and humans may be infected as accidental hosts. More than 150 species of birds and mammals may act as paratenic hosts, and rodents play an important role in the transmission and maintenance of this parasite in nature. Migratory larvae in paratenic host tissues can produce ocular disease and severe to fatal neurologic disease, but not all infected hosts develop signs. A sensitive and specific Western blot (WB) assay based on a recombinant Baylisascaris-specific antigen (rBpRAG-1) has been developed for use in humans. We evaluated the use of this antigen to detect Baylisascaris spp. infections in rodent paratenic hosts. With the use of 4 species of Peromyscus mice ( Peromyscus californicus, Peromyscus leucopus, Peromyscus maniculatus, Peromyscus polionotus) from a previous infection trial, we developed species-adapted WB and ELISA assays and evaluated performance compared to detection of larvae in tissue samples. These assays revealed species-level differences in seroconversion and terminal antibody concentrations, with P. leucopus developing significantly greater antibody concentrations than P. californicus and P. polionotus at all dose levels, and P. maniculatus at the low dose. Some P. californicus and P. polionotus failed to seroconvert despite the recovery of larvae from their tissues. WB and ELISA results were correlated; however, the WB demonstrated higher sensitivity than the ELISA overall (72.2% versus 63.9%, respectively). With the use of experimental samples, specificity was 100% for WB and 94.1% for ELISA. A WB was also used to test Mus and Rattus samples, and although numbers were too limited to evaluate sensitivity and specificity, all animals known to be infected by tissue digestion were WB positive, and all uninfected animals were negative. Finally, the Peromyscus-adapted WB and ELISA were used to test a set of serum samples from wild-trapped P. maniculatus and Rattus rattus. Both assays were generally sensitive, but specificity was equivocal. This emphasizes the challenge of using serology for investigation of wildlife diseases, in which hosts have unknown exposure histories. Nevertheless, serologic methods have utility in the study of Baylisascaris spp. in paratenic hosts, either wild or captive, and have advantageous attributes (non-lethal, high-throughput), but results should be interpreted carefully.

Humoral response of mice infected with Toxocara canis following different infection schemes

The study was focused on the dynamics of humoral response to Toxocara canis excretory-secretory antigens (TES antigens) in mice experimentally infected by T. canis L3 larvae in different ways. In particular, we compared the effect of infection with two doses of 1000 larvae vs. repeated infections with a low number of larvae (daily infection with 10 larvae and weekly infection with 100 larvae in the course of 22 weeks). In ELISA, all infections, including both schemes with lower larval doses, elicited significant antibody response. Elevated levels of total IgE and TES-antigen-specific IgM were detected on day 12 after the first infection, followed by IgG and IgG1, and later by IgG3, IgG2a and IgG2b; specific IgE response was not detected. It seems that the high levels of IgM and IgG1 represent the best markers of infection. In addition, gradual increase of IgG2a and IgG2b could help in determination of the infection course. As a byproduct of our work, a new method of infection by repeated drinking of larvae was introduced; it minimizes the pain and discomfort for the experimental mice.